AU2023251557A1 - Method for fracturing rock formation through fracture network based on variable-frequency pulse and device thereof - Google Patents
Method for fracturing rock formation through fracture network based on variable-frequency pulse and device thereof Download PDFInfo
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Classifications
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B19/00—Handling rods, casings, tubes or the like outside the borehole, e.g. in the derrick; Apparatus for feeding the rods or cables
- E21B19/14—Racks, ramps, troughs or bins, for holding the lengths of rod singly or connected; Handling between storage place and borehole
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B21/00—Methods or apparatus for flushing boreholes, e.g. by use of exhaust air from motor
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B33/00—Sealing or packing boreholes or wells
- E21B33/10—Sealing or packing boreholes or wells in the borehole
- E21B33/12—Packers; Plugs
- E21B33/122—Multiple string packers
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B47/00—Survey of boreholes or wells
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B7/00—Special methods or apparatus for drilling
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B7/00—Special methods or apparatus for drilling
- E21B7/04—Directional drilling
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D9/00—Tunnels or galleries, with or without linings; Methods or apparatus for making thereof; Layout of tunnels or galleries
- E21D9/10—Making by using boring or cutting machines
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21F—SAFETY DEVICES, TRANSPORT, FILLING-UP, RESCUE, VENTILATION, OR DRAINING IN OR OF MINES OR TUNNELS
- E21F17/00—Methods or devices for use in mines or tunnels, not covered elsewhere
- E21F17/18—Special adaptations of signalling or alarm devices
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
- F04B17/00—Pumps characterised by combination with, or adaptation to, specific driving engines or motors
- F04B17/03—Pumps characterised by combination with, or adaptation to, specific driving engines or motors driven by electric motors
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/10—Geothermal energy
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- General Life Sciences & Earth Sciences (AREA)
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- Environmental & Geological Engineering (AREA)
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- Fluid Mechanics (AREA)
- Mechanical Engineering (AREA)
- Geophysics (AREA)
- General Engineering & Computer Science (AREA)
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- Drilling And Exploitation, And Mining Machines And Methods (AREA)
Abstract
TEXT OF THE ABSTRACT
The present disclosure discloses a method for fracturing a rock formation through a
fracture network base on a variable-frequency pulse and a device thereof. In the method
for fracturing the rock formation through the fracture network base on the variable
frequency pulse, an initial pulse pressure peak value for each layer of the rock formation
is determined according to physical and mechanical properties and a confining pressure of
each layer of the rock formation, subsequently a pumping scheme on fracturing through
the fracture network based on the variable-frequency pulse is designed, and eventually a
borehole arrangement scheme on fracturing the rock formation through the fracture
network based on the variable-frequency pulse is designed according to different operating
conditions. The device for fracturing the rock formation through the fracture network based
on the variable-frequency pulse includes a fracturing pump with variable pumping mode
and frequency, a hydraulic fracturing measuring and controlling instrument, an automatic
packer, a mechanical rod feeder and a Double-way water-injection steel pipe. The method
for fracturing the rock formation through the fracture network based on the variable
frequency pulse and the device thereof can forms a plurality of annular fracture network
structures in grading around the borehole from near to far, and eventually the annular
fracture network structures are superimposed into a large-scale fracture network in
sequence, thus sufficiently breaking a larger-scale rock formation.
FIGURE ACCOMPANYING THE ABSTRACT
3-1
- 1 1
3-3
Small scale of the
fracture network based
on conventional pulse
fracturing
Large scale of the fracture
network based on gradually
pressurized pulse fracturing
Description
3-1
- 11 3-3
Small scale of the fracture network based on conventional pulse fracturing
Large scale of the fracture network based on gradually pressurized pulse fracturing
[0001] The present disclosure relates to a method for breaking a rock formation and a device thereof, and in particular to a method for fracturing a rock formation through a fracture network based on a variable-frequency pulse and a device thereof.
[0002] In the engineering such as the roadway (tunnel) tunneling and the mining, the complete rock formation plays an active role in maintaining the stability of the roadway (tunnel) and the stope. However, the speed of tunneling in hard rock roadway (tunnel) is slow, the hard roof is difficult to cave during the stoping of the coal mining working face, and the problem such as the hard ore that is difficult to fall during the mining process of the natural caving method at the metal ore stage is the difficult technical problem restricting the rapid tunnelling of the roadway (tunnel) and the safety and high efficient production of the coal mine. A common core problem involved in solving these difficult problems is the reconstruction of the rock formation structure, which involves artificially adding fractures in the rock formation to weaken the strength of the rock formation.
[0003] The methods for forming fractures in the rock formations mainly include a explosive blasting, CO2phase change fracturing and hydraulic fracturing. The explosive blasting is widely used in mine production. However, the security management of the rock formation weakened by the explosive blasting is complicated, which involves the management and transportation of the explosive and the detonator, and the "one blasting, three inspection system" and "three-person chain blasting system" must be strictly followed during blasting. A large quantity of harmful gas such as CO generated by a large
scale blasting have a huge impact on the mine ventilation security management. For high gas coal mines, the explosive blasting is not suitable for use due to the hidden danger of gas explosion induced by blasting sparks, the single-hole blasting has a small range of action, so a large quantity of pyrotechnics such as the gunpowder and the detonators are required and the economic costs for the blasting is high, and during the deep hole blasting, due to the influence of the confining pressure, the range of the fractures generated by the blasting is relatively small, and the effect of the blasting is limited.
[0004] C02 phase change fracturing uses the energy difference between supercritical C02 and gaseous C02 as the power for rock breaking. During fracturing, liquid C02firstly absorbs heat and transforms into a supercritical state, and subsequently transforms into high-pressure gas after depressurization and expansion to break the rock formation. The entire rock formation fracturing process not only has no sparks, but also absorbs heat and suppresses combustion, which is a typical physical explosion and is suitable for high-gas coal mines. However, compared with the explosive blasting, the power of C02 phase change fracturing is lower and the blasting cost is higher.
[0005] Hydraulic fracturing is a fracturing technology that uses clean water as the fracturing fluid. Hydraulic fracturing technology is first applied in the fields such as oilfield stimulation, shale gas exploitation, geothermal exploitation, in-situ stress measurement, and rockburst control. In recent years, the hydraulic fracturing technology is also widely applied in the mining industry. Hydraulic fracturing is process of acting on the rock mass continuously. Therefore, compared with the explosive blasting and C02 phase change fracturing, the hydraulic fracturing has the characteristics of longer fracture length and wider control range; however, the fractures formed inside the rock formation by the conventional hydraulic fracturing controlled by the in-situ stress is relatively single, the effect on breaking the rock formation is limited.
[0006] In view of the above-mentioned technical problems, provided in the present disclosure are a method for fracturing a rock formation through a fracture network based
on variable-frequency pulse and a device thereof. The provided method for fracturing the rock formation through the fracture network based on the variable-frequency pulse modifies a pressure peak value and a pulse frequency for an initial pulse to adapt to the rock formations of different strengths, during the fracturing of each layer of the rock formation, the pressure peak value raised gradually can forms a plurality of annular fracture network structures around a borehole from near to far, and eventually the plurality of annular fracture network structures are superimposed into a large-scale fracture network in sequence, thus sufficiently breaking a larger-scale rock formation.
[0007] In order to achieve the above-mentioned technical objectives, the technical solutions adopted in the present disclosure are as follows.
[0008] Provided is a method for fracturing a rock formation through a fracture network based on a variable-frequency pulse. The method comprise the following steps.
[0009] In Sl, an initial pulse pressure peak value and a pulse frequency are modified to adapt to rock formations of different strengths. The initial pulse pressure peak value for each layer of the rock formation is determined according to physical and mechanical properties and a confining pressure of each layer of the rock formation. The initial pulse pressure peak value is less than a breaking pressure of the rock formation in a constant displacement fracturing, and the pulse frequency of each layer of the rock formation is determined according to a collision force measurement experiment of each layer of the rock formation.
[0010] In S2, a pumping scheme on fracturing through the fracture network based on the variable-frequency pulse is designed. The first layer of the rock formation is fractured with an initial pulse pressure peak value and a pulse frequency corresponding to the first layer of the rock formation for 5 to 10 minutes. Subsequently, the pulse pressure peak value is increased by 2 to 5 Mpa to fracture for 5 to 10 minutes. Subsequently, the pulse pressure peak value is increased by 2 to 5 MPa again, and so on until a fracturing of thefirst layer of the rock formation is completed. Subsequently, the second layer of the rock formation is fractured with an initial pulse pressure peak value and a pulse frequency corresponding to the second layer of the rock formation for 5 to 10 minutes. Subsequently, the pulse pressure peak value is increased by 2 to 5 MPa to fracture for 5 to 10 minutes. Subsequently,
the pulse pressure value is increased by 2 to 5 MPa again, and so on until a fracturing of the second layer of the rock formation is completed, and a same method is adopted, until the fracturing of all layers of the rock formation is completed. The pulse pressure peak value is gradually increased during the fracturing process of each layer of the rock formation to form a plurality of annular fracture network structures in grading around a borehole from near to far, and eventually superimposed into a large-scale fracture network in turn, so that a larger-scale rock mass is broken sufficiently.
[0011] In S3, a borehole arrangement scheme on fracturing the rock formation through the fracture network based on the variable-frequency pulse is designed according to different operating conditions.
[0012] In S4, fracturing holes are drilled in the rock formation to be fractured, and observation holes are drilled at an edge of an expansion area of a designed fracture network, according to the borehole arrangement scheme on fracturing the rock formation through the fracture network based on the variable-frequency pulse.
[0013] In S5, the fracturing is implemented according to the pumping scheme on fracturing the rock formation through the fracture network based on the variable-frequency pulse. A pumping displacement is controlled to fluctuate periodically with high-frequency in a form of a pulse-wave, resulting in periodic changes in a water pressure. A quantity of micro fractures are randomly distributed in the rock formation around the borehole, causing random fatigue damages under an action of a lower pulse cyclic loading, eliminating an influence of a principal stress difference in a surrounding rock, and forming a dense fracture network around the borehole.
[0014] In S6, the fracturing is terminated after fracturing fluid flows out of the observation hole. A method for determining the initial pulse pressure peak value is as follows. The physical
and mechanical parameters for the rock formation are tested to obtain a triaxial tensile yield
strength of the rock formation through taking a rock sample on site and testing a confining
pressure. The initial pulse pressure peak value is the triaxial tensile yield strength of the
rock formation.
A method for determining the pulse frequency is as follows. In a laboratory, different
collision forces generated by collisions between a certain quality of water pumped by a
fracturing pump in one cycle and the rock sample on site at different frequencies are
measured, and a frequency corresponding to the collision force that is the tensile yield
strength is selected as the pulse frequency.
[0015] A method for fracturing through the fracture network based on the variable frequency pulse and the constant displacement is adopted in Step S2. A pulse fracturing fracture network is formed through fracturing with the initial pulse pressure and the pulse frequency for a certain time. Subsequently, the fracturing is continued by using a constant displacement pumping mode instead, causing tips of the dense pulse fracture network to be re-opened to form a dense multi-fractures expansion. And at the same time, the fracture network formed by the pulse fracturing changes a local stress field, slowing down a direction change of an inter-fracture interference, reducing a direction change of the fractures controlled by a far-field stress, and forming a fracture network with a larger range.
[0016] The rock formation to be fractured in Step S4 is a hard rock formation to be exposed in front of a tunneling head. During a tunneling process in a hard rock roadway, central long boreholes are constructed at a central position of the tunneling head along a tunneling direction and are fractured by the pulse to pre-form a dense fracture network in the hard rock formation to be exposed in front of the tunneling head, the rock formation is sufficiently broken, so that the rock formation is capable of falling off smoothly under a subsequent cutting or blasting action of a tunneling machine, thereby improving a tunneling velocity. Before a formal fracturing construction, firstly, the central long boreholes are drilled at the central of the tunneling heading along the tunneling direction, the observation holes that are parallel to the central long boreholes and equal in length of the central long boreholes are respectively drilled at a roof, both sides and a floor of the roadway and humidity sensors are arranged in the observation holes, the central long boreholes are fractured and a variation of a humidity of each observation borehole with the fracturing time is recorded, to deduce time that the fracture expands to the surrounding rock in a pre-tunnelled roadway, and the time is taken as a time for the subsequent pulse fracturing.
[0017] The rock formation to be fractured in Step S4 is a hard roof above a coal seam
during an initial caving of the coal mining working face. During an initial caving of the coal mining working face, boreholes are drilled in the hard roof above an open-off cut and two crossheadings and are fractured by the pulse to perform a dense fracture network in the roof, and an opened position of the open-off cut borehole is located approximate to a rear coal wall, and an opened position of a transporting crossheading borehole and an opened position of a return air crossheading borehole are located at a centerline of the roof of the crossheading.
[0018] The rock formation to be fractured in Step S4 is a hard roof above both ends of the coal mining working face during processing a hanging roof at ends of the coal mining working face. During processing the hanging roof at ends of the coal mining working face, boreholes are drilled at ends of the coal mining working face and are fractured by the pulse to form a dense fracture network in the hard roof above the ends of the coal mining working face, and the rock formation in this area is sufficiently broken. An opened position of the borehole drilled at ends of the coal mining working face is located at a centerline of a roof of a crossheading, an inclination angle of the borehole is 70, and a direction of the borehole is inclined to a goaf.
[0019] The rock formation to be fractured in Step S4 is a thick-hard dirt band and a thick hard floor within a mining height range during a period when the coal mining working face passes through the thick-hard dirt band and an under cutting. During the period when coal mining working face passes through the thick-hard dirt band and the undercutting, long boreholes are drilled in crossheading and are fractured by the pulse to form a dense fracture network in the dirt band or the floor. A gangue or the floor is sufficiently broken, so that the gangue and the floor is capable of falling off smoothly under a subsequent cutting of a shearer. An opened position of the long borehole constructed in the crossheading is located at a centerline position of the dirt band in a side wall of a crossheading working face or a pre-cut floor, and the borehole is constructed along the dirt band or a inclined direction of the floor, a mechanized hole position of the borehole is located in a side wall of another crossheading working face of the working face, and a spacing between the boreholes is controlled within a range from 4 m to 5 m.
[0020] The rock formation to be fractured in Step S4 is a hard rock formation around a
fault during a period when the coal mining working face passes through the fault. During the period when the coal mining working face passes through the fault, long boreholes are constructed in a crossheading and are fractured by the pulse to form a dense fracture network in the fault, and the rock formation of the fault is sufficiently broken, so that the rock formation of the fault is capable of falling off smoothly under the subsequent cutting of a shearer. An opened position of the long borehole constructed in the crossheading is located at a middle position of a side wall of the crossheading working face, and the borehole is constructed along an inclined direction of an open-off cut, a mechanized hole position of the borehole passes through a meeting coal position of the fault, and a spacing between the boreholes is controlled within a range from 4 m to 5 m.
[0021] The rock formation to be fracture in Step S4 is a hard rock formation above a coal seam mined in the coal mining working face during a period of preventing a rock burst in the coal mining face. Long boreholes are constructed in roofs and slope walls of two crossheadings and are fractured by the pulse. A peripheral surrounding rock of a crossheading supporting structure is sufficiently broken. The broken surrounding rock is used to prevent a dynamic mining pressure of the working face from transmitting to the crossheading of the working face, so that an impact risk of an advanced support section of the crossheading of the working face is reduced. A length of the borehole constructed in the roofs and the slope walls of the two crossheadings of the coal mining working face is m, a range from 20 m to 40 m is defined as a fracturing section.
[0022] The rock formation to be fractured in Step S4 is a hard rock formation above a roadway during a period of a double-roadway tunnelling. In a crossheading of the double roadway tunnelling, firstly, multi-holes in a main roof above a coal pillar are fractured by the pulse simultaneously, generating a resonance effect in a surrounding rock around the hole, the rock formation between the holes are broken preferentially, and eventually a fracture zone is formed along a connecting direction of the boreholes to prevent the dynamic mining pressure from transmitting to an adjacent crossheading. subsequently a hanging roof at an end of the working face is processed to accelerate an rotation and sinking of a roof of a goaf, thus avoiding a formation of a hanging roof, and reducing a stress of the goaf transmitting to the adjacent crossheading. An opened position of the
borehole in the main roof above the coal pillar is located at the roof 0.2 m away from the side wall of the crossheading, a mechanized hole position of the borehole is located at an upper surface of the main roof directly above 1/3 of a width of the coal pillar, and a spacing between the boreholes is controlled within a range from 4 m to 5 m.
[0023] The rock formation to be fractured in Step S4 is a hard rock formation above a protective coal pillar of a main roadway at a final stage of a stoping in a coal mining working face. At the last stage of the stoping in the coal mining working face, firstly, before the working face is advanced to a stop line, a resonance effect is generated in a surrounding rock around the hole through simultaneously fracturing multi-holes by pulse in a main roadway of a mining area, the rock formation between the holes is broken preferentially, and eventually a fracture zone is formed along a connection direction of the boreholes, so that the propagation path of the mining stress to the main roadway in a panel is blocked. Subsequently, when the working face is stoped to the stop line, a hard roof above a coal seam is fractured at the stop line of the working face, thus avoiding forming a cantilever beam structure on a goaf side of the stop line, and blocking a high stress of the goaf from propagating to a system main roadway, and further reducing a degree of a deformation and a damage of the main roadway in the mining area. A mechanized hole position of the borehole cutting off the dynamic pressure is more than 30 m away from each main roadway in a horizontal direction but not beyond the stop line.
[0024] The rock formation to be fractured in Step S4 is metal ores stoped by a stage natural caving method. In an engineering of stoping metal ores by adopting the stage natural caving method, long boreholes are constructed in a weakened roadway and are fractured by the pulse to form a dense fracture network in the ores. The ores are sufficiently broken, so that the ores are capable of falling off smoothly during a subsequent ore drawing process, and a spacing between the boreholes is controlled within a range from 4 m to 8 m.
[0025] The rock formation to be fractured in Step S4 is metal ores stoped by a single-layer caving method. In an engineering of stoping the metal ores by adopting the single-layer caving method, fan-shaped boreholes are drilled in a transmitting roadway along a vein at a stage of open-off cutting an area directly below a district rise in a working face and are fractured by the pulse to weaken a hard main roof above a stoping face. A spacing between
the fan-shaped final hole is 5 m, and a roof above an entire working face is covered with the fan-shaped boreholes sufficiently.
[0026] The rock formation to be fractured in Step S4 is an ore-bearing aquifer of low permeability uranium ore. When the low-permeability of the ore-bearing aquifer leads to a high cost and a low efficiency of mining the uranium, a pulse fracturing is performed in a liquid injection hole to form a dense fracture network around the liquid injection hole, so that the permeability of the uranium ore-bearing aquifer is increased, and an efficiency of the uranium mining is further improved. When the fracturing boreholes are designed, a hole spacing of the fracturing holes is equal to twice a spacing from a sealing section to an upper roof and an lower floor, so that when the fractures in the two boreholes are connected, the fractures have not expanded to the floor. In addition, a fracturing time is required to be controlled accurately, the fracturing time is determined by a field test. Before a formal fracturing construction, an observation borehole that is parallel to the fracturing borehole and equal in length of the fracturing borehole is drilled at a middle position of two fracturing holes and a humidity sensor is arranged in the observation borehole. One of the fracturing holes on both sides of the observation hole is fractured and a variation of a borehole humidity with fracturing time is observed and recorded, so that time of the fracture expanding to the observation hole is deduced, and the time is taken as the subsequent pulse fracturing time.
[0027] Provided is a device for fracturing a rock formation through a fracture network based on a variable-frequency pulse. The device comprises as followings.
[0028] The device comprises a fracturing pump with variable pumping mode and frequency. The fracturing pump is configured to output pulse water to fracture the rock formation, and supply constant displacement water for an automatic packer to seal holes. A motor that is connected to a power end of the fracturing pump with variable pumping mode and frequency is a variable frequency motor. A hydraulic end of the fracturing pumping with variable pumping mode and frequency includes three plungers. One of the three plungers corresponds to a liquid outlet cut-off valve arranged on a liquid outlet channel and a liquid inlet cut-off valve arranged on a liquid inlet channel at a pump head, and an operating chamber corresponding to the plunger is provided with a channel in
communication with an exterior. The channel is provided with a water supply cut-off valve, and the water supply cut-off valve is in communication with a water tank through a water supply rubber hose.
[0029] High-pressure rubber hoses output by the fracturing pump with variable pumping mode and frequency are divided into two ways by a tee. One way called as a fracturing rubber hose is configured to input the pulse water into the borehole to fracture the rock formation, another way called as a sealing hole rubber hose is configured to supply the constant displacement water for the automatic packer to seal the hole.
[0030] A fracturing cut-off valve, a fracturing drain valve, a pressure sensor and a flow sensor are sequentially arranged on the fracturing rubber hose along a water flow direction, and a one-way valve, a pressure gauge and a sealing hole drain vale are sequentially arranged on the sealing hole rubber hose along the water flow direction.
[0031] The device further comprises a hydraulic fracturing measuring and controlling instrument that is in signal connection with the pressure sensor and the flow sensor, and that is configured to monitor and record a pressure and a flow of the pulse water during a fracturing process.
[0032] The device further comprises an automatic packer including two expansion capsule hole packers. The two expansion capsule hole packers are connected to each other through a first double-way water-injection steel pipe of an outer pipe with a channel, and an interior of the expansion capsule hole packer is a second double-way water-injection steel pipe of an inner pipe with a channel, a steel wire rubber sleeve is wrapped on an exterior of the second double-way water-injection steel pipe of the inner pipe with a channel, one end of the steel wire rubber sleeve is fixed at one end of the second double-way water-injection steel pipe of the inner pipe with a channel, another end of the steel wire rubber sleeve is slidable on the second double-way water-injection steel pipe of the inner pipe with a channel, and connections are sealed under high pressure.
[0033] The device further comprises a mechanical rod feeder that is configured to send the automatic packer to the borehole fracturing zone. The mechanical rod feeder includes a cylinder, a pallet, an outrigger connector, a connecting rod, and a third double-way water injection steel pipe.
[0034] The pallet is sleeved on an cylinder wall and slidable on the cylinder wall.
[0035] The outrigger connector is fixedly connected at a top end of a cylinder wall of the cylinder, the outrigger connector is connected to an outrigger through a bolt, and the outrigger is rotatable around the bolt on a side face of the outrigger connector.
[0036] One end of the connecting rod is connected to the pallet, and another end of the connecting rod passes through the outrigger connector to connect to a connecting disk, and the connecting disk is fixedly connected at an end of a piston rod of the cylinder.
[0037] One end of the third double-way water-injection steel pipe is fixedly connected to the outrigger connector, and another end of the third double-way water-injection steel pipe is provided with a connection that is connected to the second double-way water-injection steel pipe on the automatic packer.
[0038] The third double-way water-injection steel pipe is fixedly connected to the outrigger connector through a limiting clamp, the double-way water-injection steel pipe includes an external pulse steel pipe and an internal high-pressure steel pipe that are equal in length and are coaxially sleeved with each other, the external pulse steel pipe and the internal high-pressure steel pipe are connected with each other by a connecting rod, both sides of the external pulse steel pipes are respectively provided with internal and external threads, and both sides of the internal high-pressure steel pipes are respectively provided with hermaphrodite quick plugs.
[0039] A sealing ring is placed in the internal thread of the external pulse steel pipe, and is configured to high-pressure seal a connection between two double-way water-injection steel pipes.
[0040] One side of the external pulse steel pipe approximate to the internal thread is provided with a limiting ring that is configured to cooperate with the limiting clamp to fix the double-way water-injection steel pipe.
[0041] A double-way conversion joint is externally connected to one end of the external pulse steel pipe through a thread, and internally connected to one end of the internal high pressure steel pipe through a quick plug.
[0042] The outrigger is an retractable outrigger.
[0043] Provided is a method for operating the device for fracturing the rock formation
through the fracture network based on variable-frequency pulse. The method comprises following steps.
[00441 In Step_1, the mechanical rod feeder is installed directly below the borehole to be fractured. An angle of the mechanical rod feeder is adjusted to align with the borehole through adjusting the outriggers, and the two expansion capsule hole packers of the automatic hole packer are connected to each other through the double-way water-injection steel pipe of the outer pipe with a channel, and are sent into an orifice position.
[0045] Firstly, one end of a first one of third double-way water-injection steel pipes is installed on the outrigger connector of the mechanical rod feeder, and another end of the first one of the third double-way water-injection steel pipes is connected to a lower end of the second double-way water-injection steel pipe on the automatic packer. The pallet is driven to slide upwards on an outer wall of the cylinder through injecting high-pressure gas into the cylinder of the mechanical rod feeder, subsequently the gas injection is terminated after the automatic packer and the first one of the third double-way water injection steel pipes are lifted upwards for a distance S1. The automatic packer and the first one of the third double-way water-injection steel pipes are fixed on the outrigger connector of the mechanical rod feeder through the limiting clamp to prevent the automatic packer and the first one of third double-way water-injection steel pipes from falling under an action of self-weight. The gas is discharged from the cylinder to return the pallet to a bottom end of the cylinder under an action of gravity. Subsequently a second one of the third double-way water-injection steel pipes is taken and is connected to the third double way water-injection steel pipe located at the limiting clamp. The gas is injected into the cylinder again. When the pallet is in contact with a lower end of the second one of the third double-way water-injection steel pipes, the limiting clamp is opened. The second one of the third double-way water-injection steel pipes, the first one of the third double-way water-injection steel pipes and the automatic packer are lifted for a distance S Iagain, and so on until the automatic packer is sent to a borehole fracturing area, eventually, the limiting clamp is closed to fix a last one of the third double-channel water-injection steel pipes on the outrigger connecter of the mechanical rod feeder. The gas in the cylinder is discharged to return the pallet to the bottom end of the cylinder, and the double-way
conversion joint is connected with an end of the third double-way water-injection steel pipe located at the limiting clamp.
[0046] In Step 2, the fracturing pump with variable pumping mode and frequency, a supporting water tank, a hydraulic fracturing monitoring and controlling instrument are installed in sequence and are connected to each other. The third double-way water-injection steel pipe located at the limiting clamp is connected to an end of the fracturing rubber hose and an end of the hole sealing rubber hose through the double-way conversion joint.
[0047] In Step 3, the fracturing cut-off valve is closed, and the hydraulic fracturing monitoring and control instrument is opened. The liquid inlet cut-off valve and the liquid outlet cut-off valve of the fracturing pump with variable pumping mode and frequency are opened, and the water supply cut-off valve of the fracturing pump with variable pumping mode and frequency is closed. The fracturing pump with variable pumping mode and frequency is opened to enable three pistons of the fracturing pump with variable pumping mode and frequency to operate normally. The constant discharge water is inputted into the automatic packer to seal the hole. When a water pressure of the pressure gage on the rubber hose rises to 35 Mpa, the fracturing pump with variable pumping mode and frequency is closed. Since a one-way valve is installed on the hole sealing rubber hose, the water in the automatic packer is not flown back after the fracturing pump with variable pumping mode and frequency is closed, and the hole sealing is completed.
[0048] In Step 4, the water supply cut-off valve of the fracturing pump with variable pumping mode and frequency is opened, and the liquid inlet cut-off valve and the liquid outlet cut-off valve of the fracturing pump with variable pumping mode and frequency are closed. The fracturing cut-off valve is opened, and the fracturing pump with variable pumping mode and frequency is opened to enable two pistons of the fracturing pump with variable pumping mode and frequency to operate normally and one piston of the fracturing pump with variable pumping mode and frequency to idle. The liquid inlet channel and the liquid outlet channel of the operating chamber corresponding to the idling piston is closed, so that the operating chamber corresponding to the idling piston is not capable of supplying liquid to the fracturing rubber hose, the operating chamber corresponding to the idling piston is connected to the water tank through the water supply rubber hose directly, thus
ensuring a normal water absorption and discharge when the piston is idling, and ensuring a lubrication; and inputting the pulse water into the borehole in this mode.
[0049] Compared with the existing methods for forming fractures in rock formations, the present disclosure has the following beneficial effects.
[0050] First, the method for fracturing the rock formation through the fracture network based on the variable-frequency pulse is provided in the present disclosure. During the process of fracturing by constant displacement pumping, when the water pressure reaches the critical value for the water pressure of the formation of the dominant fracture surface, a single main fracture is generated inside the rock formation under the control of the in situ stress, and since the direction of the single main fracture is controlled by the in-situ stress, it is difficult for the single main fracture to penetrate the layers and the dirt bands, the mechanical properties between the layers are significantly different, and the reconstruction volume is limited. During the process of fracturing through the pulse hydraulic pressure, the pumping displacement fluctuates periodically with high frequency in the form of pulse waves, which results in periodic changes in water pressure. A large quantity of micro-fractures randomly distributed in the rock formation around the bore do not form a main fracture under the action of a lower cyclic loading, but generate random fatigue damages. In addition, compared with the slow quasi-static cyclic loading, the cyclic loading period of the pulse fracturing is shorter (higher frequency), and the pulse fracturing is the dynamic loading with the impact energy input, which results in aggravating the random fatigue damage of the rock formation around the borehole by the collision force during the collision between the fracturing liquid and the rock formation around the borehole again. In comprehensive consideration of the above two factors, when the fracturing pressure of the traditional constant displacement fracturing is far from being reached, the micro-fractures and micro-cavities inside the rock formation are gradually stimulated to expand forwards to connect with each other under the action of the fatigue impact of the pulse fracturing. And the fracture network formed by the pulse fracturing changes the local stress field, and the direction change of the interference between the fractures is slow, which slows down the direction change of the fractures controlled by the far field and forms the fracture network with a larger scale, so that the dense fracture
network around the borehole is formed, which eliminates the influence of the principal stress difference of the surrounding rock. Furthermore, the pulse pumping produces the transpression fatigue, the tension fatigue and the impact effect on the layer, which fractures the layers and the dirt bands and enables the fracture network to penetrate the layers, and solves the problem that "gangue fracturing is much higher than the layer" to inhibit the fractures from penetrating the layers in another way. Based on the characteristics of the above-mentioned pulse fracturing, the method for fracturing the rock formation through the fracture network based on the variable-frequency pulse provided by the present disclosure modifies the initial pulse pressure peak value and the pulse frequency to adapt to the rock formations with different strengths. During the fracturing of each layer of the rock formation, the pulse pressure peak value is gradually increased, which can form a plurality of the annular fracture network structures around the borehole from near to far in grading, and eventually, the plurality of the annular fracture network structures are superimposed into a large-scale fracture network in sequence, so that a large-scale rock mass is broken sufficiently.
[0051] In addition to fracturing coal seam rocks by adopting gradual pressurization, constant displacement fracturing can also be performed on the basis of the pulse fracturing fracture networks, which enables the tips of the dense fracture network to re-open to form the dense multi-fractures expansion. The characteristic of pulse fracturing is that the fractures are multiple but not long, and the characteristic of the constant displacement fracturing is that the fractures are long but not multiple. The fracture network fracturing method "variable-frequency pulse and constant displacement" is provided in combination of the advantages of the pulse fracturing and the constant displacement fracturing, which solves the problems of the influences of the poor principal stress, poor performances of the layers and between the layers, and generates the fracture network with long distance.
[0052] Second, a complete set of device for fracturing the rock formation through the fracture network based on the variable-frequency pulse provided in the present disclosure includes a fracturing pump with variable pumping mode and frequency and a supporting water tank, a hydraulic fracturing measurement and control instrument, a mechanical rod feeder and a supporting double-way water-injection steel pipe, and an automatic packer.
The fracturing pump with variable pumping mode and frequency is configured to output pulse water to fracture the rock formation, and supply constant displacement water for the packer to seal the hole. The hydraulic fracturing monitoring and control instrument is configured to monitor and record the pressure and the flow rate of the pulse water during the fracturing process. The mechanical rod feeder is configured to send the automatic packer to the borehole fracturing area, and the automatic packer is configured to seal the hole.
[0053] A motor that is connected to a power end of the fracturing pump with variable pumping mode and frequency is a variable-frequency motor. The variable-frequency pulse adapts to the difference in mechanical properties between the layers. A hydraulic end of the fracturing pump with variable pumping mode and frequency includes three plungers. One of the three plungers corresponds to a liquid outlet cut-off valve arranged on a liquid outlet channel and a liquid inlet cut-off valve arranged on a liquid inlet channel at a pump head, and an operating chamber corresponding to the plunger is provided with a channel communicating with an exterior, the channel is provided with a water supply cut-off valve, and the water supply cut-off valve is in communication with a water tank through a water supply rubber hose. One of the pistons is capable of operating normally or idling through opening and closing the liquid outlet cut-off valve, the liquid inlet cut-off valve and the water supply cut-off valve, so as to implement the free switching between the three-piston pump and the two-piston pump, and eventually output constant displacement water to seal the hole and output the pulse water to fracture the rock formation. Furthermore, a one-way valve is arranged on the sealing hole rubber hose. After the hole sealing is completed, when the fracturing pump with variable pumping mode and frequency is turned off to switch between the constant displacement and the pulse, the one-way valve enables the water in the automatic hole packer not to flow back, which ensures the stability of hole sealing at the beginning of the fracturing. During the normal fracturing stage, due to the rock formation on the hole sealing section is compressed for a long time, which may lead to generate the situations of enlarging the aperture and reducing the water pressure in the automatic packer. Once the water pressure in the automatic packer is less than that in the hole, the one-way valve on the hole sealing rubber hose is opened immediately, which
enables the water pressure in the automatic packer is permanently greater than or equal to that in the hole, and ensures the stability of the hole sealing in the normal stage of the fracturing. Compared with sealing the hole by adopting the pulse water, the initial hole sealing by adopting the constant displacement water enables the automatic packer under the constant water pressure for most of the time, which reduces the fatigue damage of the automatic packer and prolongs the service life of the automatic packer.
[0054] The mechanical rod feeder includes a cylinder, a pallet, outrigger connectors, outriggers, and limiting clamps. The pallet is sleeved on the cylinder wall and is slidable on the cylinder wall, and is connected with the piston rod of the cylinder through the connecting rod and the connecting plate. The connecting rod is slidable inside the outrigger connector. The outrigger connectors are connected with four outriggers through bolts, and the outriggers are rotatable around the bolts on the sides of the outrigger connectors. Four outrigger are retractable outriggers. The limiting clamp is located on the front of the outrigger connector and is configured to fix the double-way water-injection steel pipe. The mechanical rod feeder is compact, lightweight, easy to carry, and can implement multi angle mechanical rod feeding at the same time, which solves the problem of difficult manual rod feeding in traditional fracturing process, and significantly saves the man power.
[0055] The double-way water-injection steel pipe includes an external pulse steel pipe and an internal high-pressure steel pipe that are equal in length and are coaxially sleeved with each other. The external pulse steel pipe and the internal high pressure steel pipe are connected with each other by a connecting rod. Both sides of the external pulse steel pipes are respectively provided with internal and external threads, and both sides of the internal high-pressure steel pipes are respectively provided with hermaphrodite quick plugs. A sealing ring is placed in the internal thread of the external pulse steel pipe, and is configured to high-pressure seal a connection between two double-way water-injection steel pipes. One side of the external pulse steel pipe approximate to the internal thread is provided with a limiting ring that is configured to cooperate with the limiting clamp to fix the double-way water-injection steel pipe. Comparing with the conventional double-way hole packer that requires to use the water injection steel pipe and the thin hole sealing hose, the double-way water-injection steel pipe that combines the pulse fracturing liquid channel
and the high-pressure water channel of the automatic packer into one saves the space in the hole and saves the installation time. And during the dismantling of the water injection steel pipe and the thin hole sealing hose used in the conventional double-way hole sealer after completing the fracturing, the thin hole sealing hose is currently entangled with the water injection steel pipe, which results in failure in dismantling, thus losing a large quantity of conventional double-way hole packers, water injection steel pipes and thin hole sealing hoses, but the double-way water-injection steel pipe avoids such problems.
[0056] The automatic packer includes two expansion capsule hole packers. The two expansion capsule hole packers are connected with each other through different sections of the double-way water-injection steel pipe of the outer pipe with a channel. An interior of the expansion capsule hole packer is a double-way water-injection of an inner pipe with a channel. A steel wire rubber sleeve is wrapped on an exterior of the double-way water injection steel pipe of the inner pipe with a channel, one end of the steel wire rubber sleeve is fixed at one end of the double-way water-injection steel pipe, the other end of the steel wire rubber sleeve is slidable on the double-way water-injection steel pipe (the connection is high pressure sealed), and the automatic hole packer eliminates the disadvantages that the conventional single-way hole packer is unstable in hole sealing and the hole is prone to be punched.
[0057] Third, the beneficial effects in terms of technology application lie in the following.
[0058] 1Rock breaking assisted by the pulse fracturing in the hard rock roadway (tunnel) tunneling: during the hard rock roadway (tunnel) tunneling, the rock formations to be exposed are relatively hard, which seriously affects the velocity of the roadway (tunnel) tunneling. Long boreholes are construed in the tunneling head and are fractured by the pulse to pre-form a dense fracture network in the hard rock to be exposed at the front of the tunneling head, the rock formations are sufficiently broken, so that the rock formations can be fallen off smoothly under a subsequent cutting or blasting action of the tunneling machine, thereby improving the tunneling velocity.
[0059] 1Pulse fracturing controlling for the initial roof caving in the coal mining face: during the periodical weighting of the coal mining face, the roof can be simplified as a cantilever beam, and during the initial weighting, the roof can be simplified as a beam with
fixed supports at both ends, which causes that the step distance of the initial weighting is greater than that of the periodical weighting. The step distance of the initial caving of the coal mining working face is excessive large, and a hurricane is prone to form due to a sudden caving of the roof, which pushes a large quantity of gas and other toxic gases from the goaf into the working face, and has a serious safety hazard. A dense fracture network formed in the hard roof above the open-off cut and two crossheadings eliminates the disadvantages that the fractures of the conventional fracturing are single, and the expansion of the fractures is controlled by the in-situ stress. The rock formations in this area are sufficiently broken, so that the roof is changed from the state of fixed support at both ends to the state of the cantilever beam when the working face stopes to the initial weighting, which can significantly shorten the step distance of the initial roof caving.
[0060] 1Pulse fracturing controlling for the hanging roof at the end of the coal mining face: during normal mining, the roof in the intermediate part of the working face is generally prone to cave, but due to the supporting of the coal pillar, the roof at the end is hard to cave. A dense fracture network is formed in the hard roof above the end of the crossheading by the pulse fracturing technology, which eliminates the disadvantages that the fractures of the conventional fracturing are single, and the expansion of the fractures is controlled by the in-situ stress. The rock formations in this area are sufficiently broken. And as the working face advances, the fractured roof above the end is entered the goaf, and the roof at the end can be caved in time under the action of mine pressure.
[0061] 1Rock breaking assisted by the pulse fracturing during a period when the coal mining working face passes through the thick-hard dirt band and an undercutting of the coal mining working face: one or more beds of the dirt bands currently exist in the coal seam, when the thickness of the dirt band is excessively thick, the shearer drum cannot cut the dirt band off, the drilling and blasting are generally performed in the working face to loosen the gangue, which seriously affects the efficiency of the coal cutting. When the coal seam suddenly becomes thinner, and the thickness of the coal seam is less than the minimum mining height of the shearer, the undercutting is currently adopted to continue advancing, that is the drilling and the blasting is performed in the working face to pre fracture the floor. Long boreholes are constructed and fractured in the crossheading by the
pulse fracturing technology to form a dense fracture network in the dirt band or the floor. The gangue or the floor is sufficiently broken, so that the gangue or the floor can be smoothly fallen off under the subsequent cutting of the shearer, which eliminates the disadvantages that the explosive blasting requires to drill and blast in the working face and affects the normal stoping.
[0062] @Rock breaking assisted by the pulse fracturing during the coal mining face passes through the fault: when encountering the fault during the stoping of the coal mining working face, the fault is currently treated by the blasting in the working face, which seriously affects the efficiency of the coal cutting. Long boreholes are constructed and fractured in the crossheading by the pulse fracturing technology to form a dense fracture network in the fault. The rock formations in the fault are sufficiently broken, so that the rock formations can be smoothly fallen off under the subsequent cutting of the shearer, which eliminates the disadvantages that the explosive blasting requires to drill and blast in the working face and affects the normal stoping.
[0063] 1Pulse fracturing preventing the rock burst for the crossheading surrounding rocks in the coal mining working face: during the stoping of the coal mining face, the mining dynamic pressure is delivered to the advanced supporting sections of the two crossheadings, which is prone to form the rock burst. The peripheral surrounding rock of the supporting structure of the crossheading can be sufficiently broken by adopting the pulse fracturing technology, and the broken surrounding rock can prevent the dynamic mining pressure of the working face from transmitting to the crossheading of the working face, which reduces the impact tendency of the advanced supporting of the crossheading in the working face.
[0064] 1!Pulse fracturing controlling a large deformation of the adjacent crossheading at the roof in the coal mining working face: when the design strike length of the working face is longer, it is currently difficult to ventilate during the crossheading tunneling. Therefore, many mines adopt double-roadway tunneling, which causes that one crossheading is affected by the mining dynamic pressure of the working face for twice. However, by adopting the pulse fracturing technology, firstly, multi-holes in the main roof above the coal pillar are fractured by the pulse simultaneously, the resonance effect is generated in the surrounding rock around the holes, the rock formation between the holes are broken
preferentially, and eventually a fracture zone is formed along the connecting direction of the boreholes, which prevents the dynamic mining pressure from transmitting to the adjacent crossheading; subsequently a hanging roof at an end of the working face is processed to accelerate an rotation and sinking of a goaf roof, thus avoiding a formation of a hanging roof, and reducing a stress of the goaf transmitting to the adjacent crossheading. From the above two aspects, the influences of the dynamic pressure and the static pressure on adjacent crossheading can be weakened, and the deformation of the adjacent crossheading can be effectively controlled.
[0065] @Pulse fracturing transferring the stress to protect the mining main roadway for the roof of the coal mining working face: at a final stage of the stoping of the coal mining face, the main roadway in the mining area is currently affected by the mining and causes deformation. When the deformation of the roadway is relative large, the later use of the roadway is seriously affected. By adopting the pulse fracturing technology, firstly, before the working face advances to the stop line, a resonance effect is generated in the surrounding rock around the holes through pulse-fracturing multi-holes in the main roadway of the mining area simultaneously, the rock formation between the holes is fractured preferentially, and eventually a fracture zone is formed along a connection direction of the boreholes, so that the propagation path of the mining stress to the main roadway in a panel is blocked. Subsequently, when the working face is stoped to the stop line, the hard roof above the coal seam is fractured at the stop line of the working face, thus avoiding forming a cantilever beam structure on a goaf side of the stop line, blocking a high stress of the goaf from propagating to a system main roadway, and further reducing the degree of a deformation and damage of the main roadway in the mining area.
[0066] @Pulse fracturing weakening the hard ores in the working face mined by the metal ore stage natural caving method: during the mining of the metal ores, when the metal ores are recovered by the stage natural caving method, the ores are required to be prone to cave naturally. When the ores are relatively hard and difficult to cave, long boreholes can be constructed in the weakened roadway and fractured by the pulse to form a dense fracture network in the ores. The ores are sufficiently broken, so that the ores can be fallen smoothly in a subsequent ore drawing, which improves the efficiency of ore drawing.
[0067] @Pulse fracturing controlling the initial weighting and the periodic weighting of the working face stoped by the single-layer caving method: during the mining of the metal ores, when the metal ore body is a gently inclined ore bed less than 3 m, the single-layer caving method is currently adopted to stope. When the main roof is relatively hard, the excessively large caving step distance of the main roof not only threatens the safe production, but also affects such as the labor productivity, the pillar consumption, and the mining cost to a large extent. Fan-shaped boreholes are drilled in a transmitting roadway along a vein at a stage of open-off cutting an area directly below a district rise in a working face and are fractured by the pulse to weaken a hard main roof above a stoping face, thereby effectively shortening the caving step distance of the main roof and reducing the impact hazard caused by the caving of the main roof.
[0068] 1Pulse fracturing enhancing the permeability for the low-permeability sandstone uranium deposits: in-situ leaching uranium mining is an advanced technology for the high efficiency mining of the sandstone-type uranium mines. The basic principle of the in-situ leaching uranium mining is that the in-situ leaching liquid is injected through the drilling hole (well) from the liquid inlet hole to sufficiently react with the uranium, and subsequently pumped out to the ground through the liquid pumping hole, and is extracted on the surface to implement the uranium mining. Based on the technical characteristics of the in-situ leaching uranium mining, the permeability of the uranium ore-bearing aquifer is a key factor that affects the in-situ leaching uranium mining. When the low permeability of the ore-bearing aquifer is low, a small liquid injection volume of the single well, a low production capacity, and a little ore control area of a single well are caused in the in-situ leaching developing of the ore deposit. Under the prior art, the infilled well pattern is required to mine, which leads to the high costs and the lower efficiency of the uranium mining. In order to solve this problem, the pulse fracturing can be performed in the liquid injection hole, and a dense fracture network is formed around the liquid injection hole, thereby increasing the permeability of the uranium ore-bearing aquifer, and further improving the mining efficiency of the uranium ore.
[0069] FIG. 1 illustrates a mechanism for forming a fracture fractured by a constant displacement in the present disclosure.
[0070] FIG. 2 illustrates a mechanism for forming a fracture network of a rock formation fractured by a variable-frequency pulse fracture network in the present disclosure.
[0071] FIG. 3 illustrates a method for fracturing a rock formation through a fracture network based on a variable-frequency pulse in the present disclosure.
[0072] FIG. 4 illustrates a method for fracturing a rock formation through a fracture network based on "variable-frequency pulse and constant displacement" in the present disclosure.
[0073] FIG. 5 illustrates a schematic diagram of an overall structure of a device for fracturing a rock formation through a fracture network based on a pulse in the present disclosure.
[0074] FIG. 6 illustrates a schematic structural diagram of a fracturing pump with variable pumping mode and frequency in the present disclosure.
[0075] FIG. 7(a) illustrates a schematic structural diagram of a mechanical rod feeder in the present disclosure.
[0076] FIG. 7(b) illustrates a structural schematic diagram of a double-way conversion joint and the third double-way water-injection steel pipe in the present disclosure.
[0077] FIG. 7(c) illustrates a A-A sectional view of FIG. 7(b).
[0078] FIG. 8 illustrates a schematic structural diagram of an automatic packer.
[0079] FIG. 9 illustrates a stereogram of a rock breaking assisted by a pulse fracturing in a tunneling of a hard rock roadway (tunnel).
[0080] FIG. 10 illustrates a cross-sectional view of the rock breaking assisted by the pulse fracturing in a tunneling of the hard rock roadway (tunnel).
[0081] FIG. 11 illustrates a plan view of a pulse fracturing controlling for an initial roof caving in a coal mining face.
[0082] FIG. 12 illustrates a sectional view of FIG. 11A-A.
[0083] FIG. 13 illustrates a sectional view of FIG. 11B-B.
[0084] FIG. 14 illustrates a plan view of a pulse fracturing controlling for a hanging roof
at an end in the coal mining face.
[0085] FIG. 15 illustrates a A-A sectional view of FIG. 14.
[0086] FIG. 16 illustrates a plan view of the rock breaking assisted by the pulse fracturing during a period when the coal mining working face passes through a thick-hard dirt band and an undercutting of the coal mining working face.
[0087] FIG. 17 illustrates a A-A sectional view of FIG. 16.
[0088] FIG. 18 illustrates a B-B sectional view of FIG. 16.
[0089] FIG. 19 illustrates a plan view of the rock breaking assisted by the pulse fracturing during a period when the coal mining working face passes through the fault.
[0090] FIG. 20 illustrates a A-A sectional view of FIG. 19.
[0091] FIG. 21 illustrates a plan view of the pulse fracturing preventing the rock burst for the crossheading surrounding rocks in the coal mining working face.
[0092] FIG. 22 illustrates a A-A sectional view of FIG. 21.
[0093] FIG. 23 illustrates a plan view of the pulse fracturing controlling the large deformation of the adjacent crossheading at the roof in the coal mining working face.
[0094] FIG. 24 illustrates a A-A sectional view of FIG. 23.
[0095] FIG. 25 illustrates a B-B sectional view of FIG. 23.
[0096] FIG. 26 illustrates a plan view of the pulse fracturing transferring the stress to protect the mining main roadway for the roof of the coal mining working face.
[0097] FIG. 27 illustrates a A-A sectional view of FIG. 26.
[0098] FIG. 28 illustrates a schematic diagram of the pulse fracturing weakening the hard ores in the working face mined by the metal ore stage natural caving method.
[0099] FIG. 29 illustrates a plan view of the pulse fracturing controlling the initial weighting and the periodic weighting of the working face stoped by the single-layer caving method.
[00100] FIG. 30 illustrates a A-A sectional view of FIG. 29.
[00101] FIG. 31 illustrates a schematic diagram of the pulse fracturing enhancing the permeability for the low-permeability sandstone uranium deposits.
[00102] In the drawings, 1-1. Fracturing borehole; 1-2. Observation borehole; 2. Constant displacement hydraulic fracture; 3. Pulse hydraulic fracture network; 3-1. First
stage pulse fracturing network; 3-2. Second-stage pulse fracturing network; 3-3. Third stage pulse fracturing network; 4. Fracturing pump with variable pumping mode and frequency; 4-1. Crankshaft; 4-2. Crosshead, 4-3. Connecting rod; 4-4. Plunger; 4-5. Pump head; 4-5-1. Liquid output valve cover; 4-5-2. Liquid inlet valve cover; 4-5-3. Operating chamber. 4-5-4. Liquid output cut-off valve; 4-5-5. Liquid inlet cut-off valve; 4-5-6. Water supply cut-off valve. 5. Liquid inlet rubber hose; 6. Water supply rubber hose; 7. Counter flow rubber hose; 8. Water tank; 9. Tee; 10. Fracturing cut-off valve; 11. Fracturing outlet valve; 12. Sensor; 13. Hydraulic fracturing measurement and control instrument; 14. One way valve; 14-1. Water flow; 14-2. Iron ball; 14-3. Spring; 15. Pressure gauge; 16. Hole sealing drain valve; 17. Hole sealing rubber hose; 18. Fracturing rubber hose; 19. Mechanical rod feeder; 19-1. Cylinder; 19-2. Outrigger; 19-3. Connecting rod; 19-4. Pallet; 19-5. Slideway; 19-6. Piston rod; 19-7. Connecting plate; 19-8. Limiting clamp; 20. Double-way water-injection steel pipe; 20-1. External pulse steel pipe; 20-2, Internal high pressure steel pipe; 20-3. Internal thread; 20-4. Limiting ring; 20-5. Sealing ring; 20-6. Connecting rod I ; 20-7. Male head I of quick plug; 20-8. External thread I , 20-9. Quick plug female I; 21. Automatic packer; 21-1. Expansion capsule hole sealer; 21-1-1. Fixed end; 21-1-2. Sliding end; 21-1-3. Steel wire rubber sleeve; 21-1-4. Double-way water injection steel pipe of the inner pipe with channels; 21-1-4-1. Channel I; 21-2. Double-way water-injection steel pipe of the outer pipe with channels; 21-2-1. Channel II; 21-3. Nut; 22. Double-way conversion joint; 22-1. Quick plug female II; 22-2. Quick plug male II; 22-3. External thread II; 22-4. Connecting rod II; 23. Roadway; 23-1. Crossheading; 23 1-1. Transporting crossheading; 23-1-2. Return air crossheading; 23-2. Main road; 23-3. Weakened roadway; 23-4. Transporting roadway along the vein; 24. Roof; 25. Floor; 26. Working face; 27. Coal seam; 28. Hard dirt band; 29. Fault; 30. Dynamic pressure caused by roof fracture; 31. Coal pillar, 32. Stop line; 33. Ore drawing funnel; 34. Ground surface; 35. Water-resisting layer; 36. Ore-bearing aquifer; 37. Sealing section.
[00103] In order to make the objectives, technical solutions and advantages in the
embodiments of the present disclosure more clearer, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present disclosure. It will be apparent that the described embodiments are merely a part of embodiments of the present disclosure rather than all the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those of ordinary skill in the art without any creative efforts shall fall within the protection scope of the present disclosure.
[00104] During the process of fracturing by constant displacement pumping fracturing, when the water pressure reaches the critical value for the water pressure of the formation of the dominant fracture surface, a single main fracture is generated inside the rock formation under the control of the in-situ stress, and since the direction of the single main fracture is controlled by the in-situ stress, it is difficult for the single main fracture to penetrate the layers and the dirt bands, the mechanical properties between the layers are significantly different, and the reconstruction volume is limited. During the process of fracturing through the pulse hydraulic pressure, the pumping displacement fluctuates periodically with high frequency in the form of pulse waves, which results in periodic changes in water pressure. A large quantity of micro-fractures randomly distributed in the rock formation around the bore do not formed a main fracture under the action of a lower cyclic loading, but generate random fatigue damages. In addition, compared with the slow quasi-static cyclic loading, the cyclic loading period of the pulse fracturing is shorter (higher frequency), and the pulse fracturing is the dynamic loading with the impact energy input, which results in aggravating the random fatigue damage of the rock formation around the borehole by the collision force during the collision between the fracturing liquid and the rock formation around the borehole again. In comprehensive consideration of the above two factors, when the static fracturing pressure of the traditional constant displacement fracturing is far from being reached, the micro-fractures and micro-cavities inside the rock formation are gradually stimulated to expand forwards to connect with each other under the action of the fatigue impact of the pulse fracturing. And the fracture network formed by the pulse fracturing changes the local stress field, and the direction change of the interference between the fractures is slow, which slows down the direction
change of the fractures controlled by the far field and forms the fracture network with a larger scale, so that the dense fracture network around the borehole is formed, which eliminates the influence of the principal stress difference of the surrounding rock. Furthermore, the pulse pumping produces the transpression fatigue, the tension fatigue and the impact effect on the layer, which fractures the layers and the dirt bands and enables the fracture network to penetrate the layers, and solves the problem that "gangue fracturing is much higher than the layer" to inhibit the fractures from penetrating the layers in another way. Based on the characteristics of the above-mentioned pulse fracturing, the method for fracturing the rock formation through the fracture network based on the variable-frequency pulse provided by the present disclosure modifies the initial pulse pressure peak value and the pulse frequency to adapt to the rock formations with different strengths. During the fracturing of each layer of the rock formation, the pulse pressure peak value is gradually increased, which can form a plurality of the annular fracture network structures around the borehole from near to far in grading, and eventually, the plurality of the annular fracture network structures are superimposed into a large-scale fracture network in sequence, so that a large-scale rock mass is broken sufficiently.
[00105] As illustrated in FIG. 1, the rock formation is a heterogeneous anisotropic material, and a large quantity of micro-fractures, micro-holes and layers are randomly distributed inside the rock formation. During the process of drilling into the rock formation, a large quantity of micro-fractures are also formed on the hole wall.
[00106] During the process of fracturing by constant displacement pumping, when the water pressure reaches the critical value for the water pressure of the formation of the dominant fracture surface, one single main fracture is generated inside the rock formation under the control of the in-situ stress, and since the direction of the single main fracture is controlled by the in-situ stress, it is difficult for the single main fracture to penetrate the layers and the dirt bands, and the mechanical properties between the layers are significantly different, and the reconstructed volume is limited.
[00107] As illustrated in FIG. 2, during the process of fracturing through the pulse hydraulic process, the pumping displacement fluctuates periodically at a high frequency in the form of pulse waves, which results in periodic changes in water pressure, and a large
quantity of micro-fractures randomly distributed in the rock formations around the borehole do not form a main fracture under an action of a lower cyclic loading, but generate random fatigue damages. In addition, compared with the slow quasi-static cyclic loading, the cyclic loading period of the pulse fracturing is shorter (higher frequency), and the pulse fracturing is the dynamic loading with the collision energy input, which results in aggravating the random fatigue damages of the rock formations around the borehole by the collision force during the collision between the fracturing liquid and the rock formation around the borehole again. In comprehensive consideration of the above two factors, when the static fracturing pressure of the traditional constant displacement fracturing is far from being reached, the micro-fractures and micro-cavities inside the rock formations are gradually stimulated to expand forwards to connect with each other under an action of the fatigue impact of the pulse fracturing. And the fracture network formed by the pulse fracturing changes the local stress field, the direction change of the interference between the fractures is slow, which slows down the direction change of the fractures controlled by the far field and forms a fracture network with a larger scale, so that a dense fracture network around the borehole is formed, which eliminates the influence of the principal stress difference of the surrounding rock. Furthermore, the pulse pumping produces the transpression fatigue, the tension fatigue and the impact effects on the layers, which fracture the layers and the dirt bands, and enables the fracture network to penetrate the layers, and solves the problem that "gangue fracturing is much higher than the layer" to inhibit the fractures from penetrating the layer in another way.
[00108] As illustrated in FIG. 3, under the condition that the pulse pressure is constant, after the pulse fracture network expands to a certain scale, due to the friction loss of the pressure inside the fracture, such that the stress at the fracture tip at the front of the fracture network cannot satisfy the damage conditions of the rock formation, and the expansion of the fracture network is stopped. When the pulse pressure remains unchanged after the fracture network stops expanding, a plurality of new fractures is initially fractured and expanded form the hole wall again due to the maximum pressure at the hole wall, and repeating in this way, so that the density of the fracture network is increased. In order to expand the radius of the fracture network, when the expansion of the fracture network is
stopped, the peak value for the pulse pressure can be increased step by step, so that the stress at the fracture tip at the front of the fracture network can gradually satisfy the damage conditions of the rock formation, which can gradually expand the radius of the fracture network until the radius satisfies the design requirements.
[00109] As illustrated in FIG. 4, in addition to pulse-fracturing coal seam rocks by adopting gradual pressurization, constant displacement fracturing can also be performed on the basis of the pulse fracturing fracture networks, which enables the tips of the dense fracture network to re-open to form the dense multi-fractures expansion. The characteristic of pulse fracturing is that the fractures are multiple but not long, and the characteristic of the constant displacement fracturing is that the fractures are long but not multiple. The fracture network fracturing method "variable-frequency pulse and constant displacement" is provided in Combination of the advantages of the pulse fracturing and the constant displacement fracturing, which solves the problems of the influences of the poor principal stress, poor performances of the layers and between the layers, and generates the fracture network with long distance.
[00110] In order to solve the problems the problem of single fractures and difficulty in penetrating layers caused by conventional fracturing, based on the above-mentioned principle for breaking rock formations by pulse fracturing, a method for fracturing the rock formation through the fracture network based on the variable-frequency pulse is specifically provided in the present disclosure. Firstly, an initial pulse pressure of each layer of the rock formation is determined according to the physical and mechanical properties of each layer of the rock formation, and a pulse frequency of each layer of the rock formation is determined according to an experiment for measuring a collision force. Subsequently, a borehole is drilled in the rock formation to be fractured, and an observation hole is drilled at an edge of an expansion area of the designed fracture network. Eventually, the rock formation is fractured with the pressure and the pulse frequency of the initial pulse of each layer of the rock formation for 5 minutes, subsequently the pulse pressure is increased by 2 Mpa to fracture for 5 minutes, subsequently the pulse pressure is increased by 2 Mpa and so on until the fracturing liquid is flown out from the observation hole, the fracturing is stopped. Subsequently, a second layer of the rock formation is fracture with
the initial pulse pressure peak value and pulse frequency corresponding to the second layer of the rock formation for 5 to 10 minutes, subsequently the initial pulse pressure peak value for the pulse is increased by 2 to 5 MPa to fracture for 5 to 10 minutes. Subsequently the pressure value for the pulse frequency is increased by 2 to 5 MPa again, and so on until a fracturing of the second layer of the rock formation is completed, and the same method is adopted until the fracturing of all layers of the rock formation is completed.
[00111] The methods for determining the pulse pressure and the pulse amplitude are as follows. When the pulse pressure is less than the fatigue damage condition (tensile yield limit) of the rock formation, the rock formation merely generates the elastic deformation. When the pulse pressure is slightly greater than the fatigue damage condition of the rock formation, the rock formation generates less plastic deformation, which generates a plurality of random damages, and is benefit to form the fracture network in the later stage. When the pulse pressure is much greater than the fatigue damage condition of the rock formation, the rock formation generates larger plastic deformation and forms main fractures, which is not benefit to form the fracture network in the later stage. Therefore, before determining the initial pulse pressure, the physical and mechanical parameters for the rock formation should be tested by taking rock samples on site, so as to obtain the tensile yield strength of the rock formation, so that the initial pulse pressure is slightly greater than the tensile yield strength. A small stress amplitude represents the development of the micro-fracture, and a large stress amplitude represents the development of the main fracture. Therefore, the initial pulse pressure is controlled to be slightly greater than the tensile yield strength, and the obtained stress amplitude is smaller.
[00112] The method for determining the pulse frequency is as follows. Different pulse frequencies represent that the speed at which a certain mass of water is injected into the rock formation in the sealing section is different in each cycle, and the resulting collision forces are different. In order to generate more fractures, the collision force should be slightly greater than the tensile yield strength of the rock formation. The different collision forces generated by the collision between a certain quantity of water pumped by the fracturing pump in one cycle and the on-site rock samples at different frequencies are measured in the laboratory, a frequency corresponding to the collision force that is slightly
greater than the tensile yield strength is selected as the pulse frequency.
[00113] As illustrated in FIGS. 5 to 8, in order to implement the method for fracturing the rock formation through the fracture network based on the pulse on site, a complete set of device for fracturing the rock formation through the fracture network based on the frequency is provided in the present disclosure. In which, the device includes a fracturing pump with variable pumping mode and frequency and a supporting water tank, a hydraulic fracturing measurement and control instrument, a mechanical rod feeder and a supporting double-way water-injection steel pipe, and an automatic packer. The fracturing pump with variable pumping mode and frequency is configured to output the pulse water to fracture the rock formation, and supply the constant displacement water for the automatic packer to seal the hole. The hydraulic fracturing monitoring and control instrument is configured to monitor and record the pressure and the flow rate of the pulse water during the fracturing process. The mechanical rod feeder is configured to send the automatic packer to the borehole fracturing area, and the automatic packer is configured to seal the hole.
[00114] (1) Fracturing pump with variable-frequency pumping mode and frequency and supporting water tank.
[00115] The device includes the fracturing pump with variable-frequency pumping mode and frequency and the supporting water tank. A motor that is connected to a power end of the fracturing pump with variable pumping mode and frequency is a variable frequency motor. A hydraulic end of the fracturing pumping with variable pumping mode and frequency includes three plungers. One of the three plungers corresponds to a liquid outlet cut-off valve arranged on a liquid outlet channel and a liquid inlet cut-off valve arranged on a liquid inlet channel at a pump head, and an operating chamber corresponding to the plunger is provided with a channel communicating with an exterior. The channel is provided with a water supply cut-off valve, and the water supply cut-off valve is in communication with a water tank through a water supply rubber hose. The high-pressure rubber hoses output by the fracturing pump with variable pumping mode and frequency are divided into two ways by a tee. One way called as a fracturing rubber hose is configured to input the pulse water into the borehole to fracture the rock formation, the other way called as a sealing hole rubber hose is configured to supply the constant displacement water
for the automatic packer to seal the hole. A fracturing cut-off valve, a fracturing drain valve, sensors of the measuring and controlling instrument (pressure sensor and flow sensor) are sequentially arranged on the fracturing rubber hose, and a one-way valve, a pressure gauge and a sealing hole drain vale are sequentially arranged on the sealing hole rubber hose.
[00116] (2) Hydraulic fracturing measuring and controlling instrument
[00117] The hydraulic fracturing measuring and controlling instrument includes a host of the measuring and controlling instrument, and sensors (pressure sensor and flow sensor).
[00118] (3) Mechanical rod feeder and supporting double-way water-injection steel pipe
[00119] The mechanical rod feeder and the supporting double-way water-injection steel pipe includes the mechanical rod feeder, the supporting double-way water-injection steel pipe and the double-way conversion joint. The mechanical rod feeder includes a cylinder, a pallet, outrigger connectors, outriggers, and limiting clamps. The pallet is sleeved on the cylinder wall and is slidable on the cylinder wall, and is connected with the piston rod of the cylinder through the connecting rod and the connecting plate. The connecting rod is slidable inside the outrigger connector. The outrigger connectors are connected with four outriggers through bolts, and the outriggers are rotatable around the bolts on the sides of the outrigger connectors. Four outriggers are retractable outriggers. The limiting clamp is located on the front of the outrigger connector and is configured to fix the double-way water-injection steel pipe. The ouble-way water-injection steel pipe includes an external pulse steel pipe and an internal high-pressure steel pipe that are equal in length and are coaxially sleeved with each other. The external pulse steel pipe and the internal high pressure steel pipe are connected with each other by a connecting rod. Both sides of the external pulse steel pipes are respectively provided with internal and external threads, and both sides of the internal high-pressure steel pipes are respectively provided with hermaphrodite quick plugs. A sealing ring is placed in the internal thread of the external pulse steel pipe, and is configured to high-pressure seal a connection between two double way water-injection steel pipes. One side of the external pulse steel pipe approximate to the internal thread is provided with a limiting ring that is configured to cooperate with the limiting clamp to fix the double-way water-injection steel pipe.
[00120] (4) Automatic packer
[00121] The automatic packer includes two expansion capsule hole packers. The two expansion capsule hole packers are connected with each other through the double-way water-injection steel pipes of the outer pipe with a channel. An interior of the expansion capsule hole packer is a double-way water-injection of an inner pipe with a channel. A steel wire rubber sleeve is wrapped on an exterior of the double-way water-injection steel pipe of the inner pipe with a channel, one end of the steel wire rubber sleeve is fixed at one end of the double-way water-injection steel pipe, the other end of the steel wire rubber sleeve is slidable on the double-way water-injection steel pipe (the connection is high pressure sealed).
[00122] The method for operating the device for fracturing the rock formation through the fracture network based on the variable-frequency pulse is as follows.
[00123] In Step 1, the mechanical rod feeder is installed directly below the borehole to be fractured. An angle of the mechanical rod feeder is adjusted to align with the borehole through adjusting the outriggers, and the two expansion capsule hole packers of the automatic hole packer are connected to each other through different sections of the double way water-injection steel pipe of the outer pipe with a channel, and are sent into an orifice position. A lower end of the automatic packer is connected with the double-way water injection steel pipe. The pallet is driven to slide upwards on an outer wall of the cylinder through injecting high-pressure gas into the cylinder of the mechanical rod feeder, subsequently the gas injection is terminated after the automatic packer and the double-way water-injection steel pipe are lifted upwards for a distance for 1 m. The automatic packer and the double-way water-injection steel pipe are fixed on the outrigger connector of the mechanical rod feeder through the limiting clip and the limiting ring on the double-way water-injection steel pipe. The cylinder gas is discharged from the cylinder to return the pallet to a bottom end of the cylinder under an action of gravity. Subsequently another double-way water-injection steel pipe is taken and is connected with the double-way water injection steel pipe located at the limiting clip. The gas is inflated into the cylinder again, when the pallet is in contact with a lower end of the double-way water-injection steel pipe, the limiting clip is opened, subsequently the automatic packer and the double-way water
injection steel pipe are lifted for 1 m again, and so on until the automatic packer is sent into the borehole fracturing area. Eventually, the limiting clip is closed to fix the double way water-injection steel pipes on the outrigger connector of the mechanical rod feeder. The gas in the cylinder is discharged to return the pallet to the bottom end of the cylinder, and the double-way conversion joint is connected with an end of the double-way water injection steel pipe located at the limiting clip.
[00124] In Step 2, the fracturing pump with variable pumping mode and frequency, a supporting water tank, a hydraulic fracturing monitoring and controlling instrument are sequentially installed and are connected to each other. The fracturing rubber hose and the hole sealing rubber hose are connected with the double-way water-injection steel pipe through the double-way conversion joint.
[00125] In Step 3, the fracturing cut-off valve is closed, and the hydraulic fracturing monitoring and control instrument is opened. The liquid inlet cut-off valve and liquid outlet cut-off valve of the fracturing pump with variable pumping mode and frequency are opened, and the water supply cut-off valve of the fracturing pump with variable pumping mode and frequency is closed. The fracturing pump with variable pumping mode and frequency is opened to enable three pistons of the fracturing pump with variable pumping mode and frequency operate normally to input constant discharge water into the automatic packer to seal the hole. When a water pressure of the pressure gage on the rubber hose rises to 35 Mpa, the fracturing pump with variable pumping mode and frequency is closed. Since a one-way valve is installed on the hole sealing rubber hose, the water in the automatic packer is not flown back after the fracturing pump with variable pumping mode and frequency is closed, and the hole sealing is completed.
[00126] In Step 4, the water supply cut-off valve of the fracturing pump with variable pumping mode and frequency is opened, and the liquid inlet cut-off valve and the liquid outlet cut-off valve of the fracturing pump with variable pumping mode and frequency are closed. The fracturing cut-off valve is opened, and the frequency of the variable-frequency motor is adjusted. The fracturing pump with variable pumping mode and frequency is opened to enable two pistons of the fracturing pump with variable pumping mode and frequency to operate normally and one piston of the fracturing pump with variable
pumping mode and frequency to operate idle (The liquid inlet channel and the liquid outlet channel of the operating chamber corresponding to the idling piston is closed, so that the operating chamber corresponding to the idling piston is not capable of supplying liquid to the fracturing rubber hose, the operating chamber corresponding to the idling piston is connected to the water tank through the water supply rubber hose directly, thus ensuring a normal water absorption and discharge when the piston is idling, and ensuring a lubrication), and inputting the pulse water into the borehole in this mode.
[00127] The specific applications of the present disclosure are as follows.
[00128] Embodiment 1: rock breaking assisted by the pulse fracturing in the hard rock roadway (tunnel) tunneling.
[00129] As illustrated in FIG. 9 and FIG. 10, a whole-rock roadway with a length of 1373.437 m is designed for a return air uphill roadway in a certain coal mine. A cross section of the whole-rock roadway is shaped as a straight wall semicircular arch, and the combined support form is bolt wire cable and shotcrete. The fine sandstone layer exists in the roadway, and the texture is hard, which seriously affects the tunneling velocity of the roadway.
[00130] As illustrated in FIG. 9 and FIG. 10, in order to solve this problem, long boreholes are constructed at a central position of the tunneling head along a tunneling direction and are fractured by the pulse to pre-form a dense fracture network in the hard rock formation to be exposed at the front of the tunneling head, and the rock formation is sufficiently broken, so that the rock formation is capable of pulling off smoothly under a subsequent cutting or blasting action of a tunneling machine, thereby improving the tunneling velocity. In order to ensure that the pulse fractures can not damage the roof of the pre-drilling roadway, it is necessary to strictly control the expansion range of the pulse fracture network. The expansion range of the pulse fracture network can be controlled by controlling the fracturing time. The fracturing time can be determined by the field test. Before the formal fracturing construction, a borehole is firstly drilled at the center of the tunneling head along the tunneling direction, and an observation borehole that is parallel to the central borehole and equal in length of the central borehole is respectively drilled at the roof, both sides, and a floor of the roadway and a humidity sensor is arranged in the
observation borehole. The central borehole is fractured and a variation of a humidity of each observation borehole with the fracturing time is recorded, to deduce time that the fracture expands to the surrounding rock in a pre-tunnelled roadway, and the time is taken as a time for the subsequent pulse fracturing.
[00131] Embodiment 2: pulse fracturing controlling for the initial roof caving in the coal mining face.
[00132] As illustrated in FIGS. 11 to 13, the average thickness of the coal seam mined in a certain coal mine is 10.5 m. The mudstone layer with the thickness of 4.6 m, the siltstone layer with the thickness of 8 m and the fine sandstone layer with the thickness of 21 m are existed above the coal seam in sequence. The cross-sections of the two crossheadings in the working face are both rectangular sections, and the combined support form is a supporting combing the anchor rod, the anchor cable and the metal mesh. The two crossheading roadways are tunnelled along the floor. The specification of the air inlet roadway is: widthxheight=5.6x4.2 m 2, and the specification of the air return roadway is: widthxheight =5.6x4.2 m 2 . The roof of the wall coal mining face can be simplified as a cantilever beam during the periodic weighting, and the roof of the wall coal mining face can be simplified as a beam with fixed supports at both ends during the initial weighting, which causes the step distance of the initial weighting is greater than that of the periodical weighting. In addition, the thicker siltstone layer and the fine sandstone layer are existed above the coal seam, the sudden caving of the roof is prone to form a hurricane, which leads that the step distance of the initial caving in the coal mining working face is excessive large, and pushes a large quantity of gas and other toxic gases in the goaf into the working face, and a serious safety hazard is occurred.
[00133] As illustrated in FIGS. 11 to 13, in order to solve this problem, boreholes can be drilled in the hard roof above the open-off cut and the two crossheadings and are fractured by the pulse to form a dense fracture network in the roof, which eliminates the disadvantages that the fractures of the conventional fracturing are single, and the expansion of the fractures controlled by the in-situ stress are not insufficient. The rock formations in this area are sufficiently broken, so that the roof is changed from the state of fixed support at both ends to the state of the cantilever beam when the working face stopes to the initial
weighting, which can significantly shorten the step distance of the initial roof caving. Since the density of the fracture network required for the control of the pulse fracturing for the initial roof caving in the coal mining working face is low, in addition to the pulse fracturing method in the whole process, the method that performs fracturing with the pressure and the pulse frequency of the initial pulse for 5 minutes, and subsequently changes into the constant displacement pumping to continue fracture can be adopted. In order to minimize the step distance of the initial roof caving, the hole position of the open-off cut borehole should be as close as possible to the rear coal wall. In order to sufficiently weaken the end roof and the anchorage, the opened position of the transporting crossheading borehole and the opened position of the return air crossheading borehole are located at a centerline of the roof of the crossheading.
[00134] Embodiment 3: pulse fracturing controlling for the hanging roof at the end of the coal mining face.
[00135] As illustrated in FIG. 14 and FIG. 15, the average thickness of the coal seam mined in a certain coal mine is 10.5 m. The mudstone layer with the thickness of 4.6, the siltstone layer with the thickness of 8 m and the fine sandstone layer with the thickness of 21 m are existed above the coal seam in sequence. The cross-sections of the two crossheadings in the working face are both rectangular sections, and the combined support form is a supporting combing the anchor rod, the anchor cable and the metal mesh. The two crossheading roadways are tunnelled along the floor. The specification of the air inlet roadway is: width X height=5.6 X 4.2 m2 , and the specification of the air return roadway is: width X height=5.6 X 4.2 m 2 . During the stoping of the working face, a suspended roof with a strike of 15 m and a dip of7 m appears at the end of the transporting crossheading. During normal mining, the roof in the intermediate part of the working face is generally prone to cave, but due to the supporting of the coal pillar, the roof at the end is hard to cave.
[00136] As illustrated in FIG. 14 and FIG. 15, in order to solve this problem, boreholes can be drilled at the end of the working face and are fractured by the pulse to form a dense fracture network in the hard roof above the end of the coal mining working face, which eliminates the disadvantages that the fractures of the conventional fracturing are single and the expansion of the fractures is controlled by the in-situ stress. As the working
face advances, the fractured roof above the end is entered the goaf, and under the action of the pressure of the mine, the roof at the end can be caved in time. In order to sufficiently weaken the roof at the end and the anchorage, the opened position of the borehole is located at a centerline of the roof of the crossheading, and in order to enable the hanging roof of the end cave to be caved as soon as possible, the borehole is inclined towards the goaf with a 700 angle for construction.
[00137] Embodiment 4: Rocking breaking assisted by the pulse fracturing during a period when the coal mining working face passes through the thick-hard dirt band and an undercutting of the coal mining working face.
[00138] As illustrated in FIG. 16 to 18, the average thickness of the coal seam mined in a coal mine is 3.5 m. The sandstone layer with the thickness of 1.2 m is existed in the lower part of the coal seam, and the texture of the sandstone layer is relatively hard. At the end of stoping, the coal seam below the dirt band is gradually thinned and disappeared, merely the coal seam above the dirt band can be mined. The cross-sections of the two crossheadings in the working face are both rectangular sections, and the combined support form is a supporting combing the anchor rod, the anchor cable, and the metal mesh. The two crossheading roadways are tunnelled along the floor. The specification of the air inlet roadway is: widthxheight=5.6x4.2 m2 , the specification of the air return roadway is: widthxheight =5.6x4.2 m 2. One or more beds of the dirt bands currently exist in the coal seam, when the thickness of the dirt band is excessively large, the shearer drum cannot cut the dirt band off, the drilling and blasting are generally performed in the working face to loosen the gangue, which seriously affects the efficiency of the coal cutting. When the coal seam suddenly becomes thinner, and the thickness of the coal seam is less than the minimum mining height of the shearer, the undercutting is currently adopted to continue advancing that is the drilling and the blasting is performed in the working face to pre fracture the floor.
[00139] As illustrated in FIG. 16 to 18, in order to solve this problem, long boreholes are constructed in the crossheading and are fractured by the pulse to form a dense fracture network in the dirt band or the floor. The gangue and the floor are sufficiently broken, so that the gangue and the floor can be fallen off smoothly under the subsequent cutting of
the shearer, which eliminates the deficiency that the explosive blasting requires to drill and shoot in the working face and affects the normal stoping. In order to enable the dirt band and the floor to be broken as much as possible, the opened position of the borehole is located at the centerline of the dirt band of the side wall of the crossheading working face or the pre-cut floor, and is constructed along the dirt band or the inclined direction of the floor, and a mechanized hole position of the borehole is located in a side wall of another crossheading working face, and a spacing between the boreholes is controlled at approximately 5 m.
[00140] Embodiment 5: Rock breaking assisted by the pulse fracturing during a period when the coal mining working face passes through the fault.
[00141] As illustrated in FIG.19 and FIG. 20, the average thickness of the coal seam mined in a certain coal mine is 3.5 m. The immediate floor of the coal seam is the siltstone layer with the thickness of 7 m, and the texture of the siltstone layer is relatively hard. The normal fault exists 115 m away from the open-off cut, with a drop ranging from 3 m to 5 m. The cross-sections of the two crossheadings in the working face are both rectangular sections, and the combined support form is a supporting combing the anchor rod, the anchor cable, and the metal mesh. The two crossheading roadways are tunnelled along the floor, the specification of the air inlet lane is: widthxheight=5.6x4.2 m2 , and the specification of the air return roadway is: widthxheight =5.6x4.2 m2 . When encountering the fault during the stoping of the coal mining working face, the fault is currently treated by the blasting in the working face, which seriously affects the efficiency of the coal cutting.
[00142] As illustrated in FIG. 19 and FIG. 20, in order to solve this problem, long boreholes are constructed in the crossheading and are fractured by the pulse to form a dense fracture network in the fault. The rock formation in the fault is sufficiently broken, so that the rock formation can be fallen off smoothly under the subsequent cutting of the shearer, which eliminates the deficiency that the explosive blasting requires to drill and shoot in the working face and affects the normal stoping. In order to enable the rock formation around the fault to be broken as much as possible, the opened position of the borehole is located at the middle position of the side-slope wall of the crossheading working face, and is constructed along the inclined direction of the open-off cut, and a mechanized hole
position of the borehole is located at a meeting coal positing passing through the fault, and the spacing between the boreholes is controlled at approximately 5 m.
[00143] Embodiment 6: Pulse fracturing preventing the rock burst for the crossheading surrounding rocks in the coal mining working face.
[00144] As illustrated in FIG. 21 and FIG. 22, the average thickness of the coal seam mined in a certain mine is 6.5 m, the average buried depth is 810 m, and the hard siltstone layer with the thickness of 30.2 m is existed at 56.2 m above the coal seam, and the hard siltstone layer with the thickness of 25.2m is existed below the coal seam. The cross sections of the two crossheadings in the working face are both rectangular sections, and the combined support form is a supporting combining the anchor rod, the anchor cable, and the metal mesh. The two crossheading roadways are tunnelled along the floor. The specification of the air inlet roadway is: widthxheight=5.6x4.2 m2 , and the specification of the air return roadway is: widthxheight=5.6x4.2 m 2 . During the stoping of the coal mining working face, due to the larger buried depth of the coal seam and the thick and hard rock formation existed in the roof and the floor of the coal seam, the mining dynamic pressure is delivered to the advanced supporting sections of the two crossheadings, which is prone to form the rock burst.
[00145] As illustrated in FIG 21 and 22, in order to solve this problem, long boreholes are constructed in roofs and slope walls of two crossheadings and are fractured by the pulse. The peripheral surrounding rock of the supporting structure of the crossheading can be sufficiently broken. The broken surrounding rock can prevent the dynamic mining pressure of the working face from transmitting to the crossheading of this working face, which reduces the impact risk for the advanced support section of the crossheading of this working face. In order to ensure the stability of the roadway surrounding rock and the support body inside the weak structure, the length of the borehole is determined to be 40 m, of which the range from 20 m to 40 m is designated as the fracturing section.
[00146] Embodiment 7: pulse fracturing controlling the large deformation of the adjacent crossheading at the roof in the coal mining working face.
[00147] As illustrated in FIGS. 23 to 25, the average thickness of the coal seam in a certain mine is 2.7 m. The fine sandstone layer with the thickness of 14 m exists at 10 m
above the coal seam, and is relatively hard. The design strike length of the working face is 3200 m, it is currently difficult to ventilate during the crossheading tunneling. Therefore, double-roadway tunneling is adopted, which causes that one crossheading is affected by the mining dynamic pressure of the working face twice.
[00148] As illustrated in FIGS. 23 to 25, in order to solve this problem, firstly, multi holes in the main roof above the coal pillar are fractured by the pulse simultaneously, the resonance effect is generated in the surrounding rock around the holes, the rock formation between the holes are broken preferentially, and eventually a fracture zone is formed along the connecting direction of the boreholes, which prevents the dynamic mining pressure from transmitting to the adjacent crossheading; subsequently a hanging roof at an end of the working face is processed to accelerate an rotation and sinking of a goaf roof, thus avoiding a formation of a hanging roof, and reducing a stress of the goaf transmitting to the adjacent crossheading. From the above two aspects, the influences of the dynamic pressure and the static pressure on adjacent crossheading can be weakened, the deformation of the adjacent crossheading can be effectively controlled. In order to ensure the stability of the surrounding rock of the crossheading of the working face and the surrounding rock of the crossheading of the adjacent working face, the opened position of the borehole is located at the roof of the crossheading 0.2 m close to the side wall of the coal pillar, a mechanized hole position of the borehole is at an upper surface of the main roof directly above 1/3 of a width of the coal pillar, and a spacing between the boreholes is controlled at approximately 5 m.
[00149] Embodiment 8: pulse fracturing transferring the stress to protect the mining main roadway for the roof of the coal mining working face.
[00150] As illustrated in FIG. 26 and FIG. 27, the average thickness of the coal seam mined in a working face of a coal mine is 7.9 m. The fine sandstone layer with the thickness of 13.5 m, the mudstone layer with the thickness of 2.8 m, the mudstone layer with the thickness of 3.5 m, and the fine sandstone layer with the thickness of 10.2 m exist above the coal seam in sequence. The immediate floor of the coal seam is the siltstone layer with the thickness of 25 m, the working face is 1388 m in strike length and 207 m in inclination width. At the end of the mining face, the roadway in the mining area is affected by the
mining and has a large deformation, which seriously affects the later use of the roadway.
[00151] As illustrated in FIG. 26 and FIG. 27, in order to solve this problem, firstly, before the working face advances to the stop line, a resonance effect is generated between the hole and the surrounding rock around the hole through pulse-fracturing multiple holes in the main roadway of the mining area simultaneously. The rock formation between the holes is fractured preferentially, and eventually a fracture zone is formed along the connection direction of the boreholes, so that the transmission path of the mining stress to the panel main roadway is blocked. Subsequently when the working face is stoped to the stop line, a hard roof above a coal seam is fractured at the stop line of the working face, thus avoiding forming a cantilever beam structure on a goaf side of the stop line, blocking a high stress in the goaf from propagating to a system main roadway, and further reducing a degree of a deformation and damage of the main roadway in the mining area. In order to ensure that the pulse fracture network can not damage the stability of the surrounding rock of the main roadway after fracturing, a mechanized hole position of the borehole cutting off the dynamic pressure is more than 30m away from each main roadway in the horizontal direction but not beyond the stop line.
[00152] Embodiment 9: pulse fracturing weakening the hard ores in the working face mined by the metal ore stage natural caving method.
[00153] As illustrated in FIG. 28, a copper mine adopts the stage natural caving method to mine ore, the stage height is 70 m, and the thickness of the ore body is 30 m. The ore is relatively hard and not prone to break, which seriously affects the velocity of the ore stoping.
[00154] As illustrated in FIG. 28, in order to solve this problem, long boreholes can be constructed in a weakened roadway and are fractured by the pulse to form a dense fracture network in the ores. The ores are sufficiently broken, so that the ores can be fallen smoothly in a subsequent ore drawing, which improves the efficiency of the ore drawing. The spacing between the boreholes is controlled within the range from 4 m to 8 m.
[00155] Embodiment 10: pulse fracturing controlling the initial weighting and the periodic weighting of the working face stoped by the single-layer caving method.
[00156] As illustrated in FIG. 29 and FIG. 30, the strike length of the ore bed of a certain
iron is 1388 m, the thickness is 1.5 m and the inclined angle is in the range from 250 to 350. The ore is mined by the long-arm caving method. The relatively hard main roof of the ore bed causes that the step distance of the main roof caving is excessive large, which not only threatens safe production, but also greatly affects such as labor productivity, pillar consumption and mining costs to a large extent.
[00157] As illustrated in FIG. 29 and FIG. 30, in order to solve this problem, fan-shaped boreholes are drilled in a transmitting roadway along a vein at a stage of open-off cutting an area directly below a district rise in a working face and are fractured by the pulse to weaken a hard main roof above a stoping face, thereby effectively shortening the caving step distance of the main roof and reducing the impact hazard caused by the caving of the main roof. In order to sufficiently break the main roof, a spacing between each two fan shaped final hole is 5 m, and an upper roof of the entire working face is covered with the fan-shaped borehole finished sufficiently.
[00158] Embodiment 11: pulse fracturing enhancing the permeability for the low permeability sandstone uranium deposits.
[00159] As illustrated in FIG. 31, an ore bed of the uranium deposit is 6 m in thickness and has an inclination angle in the range from 1 to 5°, and is mined by in-situ leaching uranium mining technology. In-situ leaching uranium mining is an advanced technology for the high-efficiency mining of the sandstone-type uranium mines. The basic principle of the in-situ leaching uranium mining is that the in-situ leaching liquid is injected through the drilling hole (well) from the liquid inlet hole to sufficiently react with the uranium, and subsequently pumped out to the ground through the liquid pumping hole, and is extracted on the surface to implement the uranium mining. Based on the technical characteristics of the in-situ leaching uranium mining, the permeability of the uranium ore-bearing aquifer is a key factor that affects the in-situ leaching uranium mining. When the low permeability of the ore-bearing aquifer is low, a small liquid injection volume of the single well, a low production capacity, and a little the ore control area of a single well are caused in the in situ leaching developing of the ore deposit. Under the prior art, the infilled well pattern is required to mine, which leads to the high costs and the lower efficiency of the uranium mining.
[00160] As illustrated in FIG. 31, in order to solve this problem, pulse fracturing can be performed inside the liquid injection hole to form a dense fracture network around the liquid injection hole, thus increasing the permeability of the uranium ore-bearing aquifer, and improving the efficiency of the uranium mining. It is necessary for the in situ leaching mining of the uranium ore to ensure the integrity of the upper roof and the lower floor of the ore-bearing aquifer, otherwise the water level of the ore-bearing aquifer is continued to decline, which results in the inability to mine uranium ore. In order to ensure that the pulse fractures can not damage the roof and floor of the ore-bearing aquifer, it is necessary to strictly control the expansion range of the pulse fracture network. For this reason, when the fracturing boreholes are designed, a hole spacing between the fracturing holes is slightly less than twice a spacing from a sealing section to an upper roof and an lower floor, so that when the fractures in the two boreholes are connected, the fractures have not yet expanded to the floor. In addition, a fracturing time is required to be controlled accurately, the fracturing time is determined by a field test. Before a formal fracturing construction, an observation borehole that is parallel to the fracturing borehole and equal in length of the fracturing borehole is drilled at a middle position of two fracturing holes and a humidity sensor is arranged in the observation borehole. One of the fracturing holes on both sides of the observation hole is fractured and a variation of a borehole humidity with fracturing time is observed and recorded, so that time of the fracture expanding to the observation hole is deduced, and the time is taken as the subsequent pulse fracturing time.
Claims (17)
- What is claimed is: 1. A method for fracturing a rock formation through a fracture network based on a variable frequency pulse, comprising following steps: Si, modifying an initial pulse pressure peak value and a pulse frequency to adapt to rock formations of different strengths; determining, according to physical and mechanical properties and a confining pressure of each layer of the rock formation, the initial pulse pressure peak value for each layer of the rock formation, wherein the initial pulse pressure peak value is less than a breaking pressure of the rock formation in a constant displacement fracturing; and determining, according to a collision force measurement experiment of each layer of the rock formation, the pulse frequency of each layer of the rock formation; S2, designing a pumping scheme on fracturing through the fracture network based on the variable-frequency pulse, fracturing, with an initial pulse pressure peak and a pulse frequency corresponding to a first layer of the rock formation, the first layer of the rock formation for 5 to 10 minutes; subsequently increasing the pulse pressure peak value by 2 to 5 MPa to fracture for 5 to 10 minutes; subsequently increasing the pulse pressure peak value by 2 to 5 MPa again, and so on until completing fracturing the first layer of the rock formation; subsequently fracturing, with an initial pulse pressure peak value and a pulse frequency corresponding to a second layer of the rock formation, the second layer of the rock formation for 5 to 10 minutes; subsequently increasing the pulse pressure value by 2 to 5 MPa to fracture for 5 to 10minitues; subsequently increasing the pulse pressure value by 2 to 5 MPa again, and so on until completing fracturing the second layer of the rock formation; adopting a same method until completing fracturing all layers of the rock formation; wherein the pulse pressure peak value is gradually increased during the fracturing process of each layer of the rock formation, a plurality of annular fracture network structures are formed in grading around a borehole from near to far, and eventually superimposed into a large-scale fracture network in sequence, so that a larger-scale rock mass is broken sufficiently;S3, designing, according to different operating conditions, a borehole arrangement schemeon fracturing the rock formation through the fracture network based on the variablefrequency pulse;S4, drilling, according to the borehole arrangement scheme on fracturing the rockformation through the fracture network based on the variable-frequency pulse, fracturingholes in the rock formation to be fractured, and observation holes at an edge of anexpansion area of a designed fracture network;S5, fracturing according to the pumping scheme on fracturing the rock formation throughthe fracture network based on the variable-frequency pulse; controlling a pumpingdisplacement to fluctuate periodically with high frequency in a form of pulse waves,resulting in periodic changes in a water pressure, wherein a quantity of micro-fractures arerandomly distributed in the rock formation around the borehole, causing random fatiguedamages under an action of a lower pulse cyclic loading, eliminating an influence of aprincipal stress difference in a surrounding rock, and forming a dense fracture networkaround the borehole; andS6, terminating fracturing after fracturing fluid flows out of the observation holes;wherein a method for determining the initial pulse pressure peak value is: testing, throughtaking a rock sample on site and testing the confining pressure, the physical and mechanicalparameters for the rock formation to obtain a triaxial tensile yield strength of the rockformation, wherein the initial pulse pressure peak value is the triaxial tensile yield strengthof the rock formation; anda method for determining the pulse frequency is: in a laboratory, measuring differentcollision forces generated by collisions between a certain quality of water pumped by afracturing pump in one cycle and the rock sample on site at different frequencies, andselecting a frequency corresponding to the collision force that is the tensile yield strengthas the pulse frequency.
- 2. The method for fracturing the rock formation through the fracture network based on thevariable-frequency pulse according to claim 1, wherein a method for fracturing through thefracture network based on the variable-frequency pulse and the constant displacement isadopted in Step S2, a pulse fracturing fracture network is formed through fracturing withthe initial pulse pressure and the pulse frequency for a certain time, subsequently thefracturing is continued by using a constant displacement pumping mode instead, causingtips of the dense pulse fracture network to be re-opened to form a dense multi-fracturesexpansion, and at the same time, the fracture network formed by the pulse fracturingchanges a local stress field, slowing down a direction change of an inter-fractureinterference, reducing a direction change of the fractures controlled by a far-field stress,forming a fracture network with a larger scale.
- 3. The method for fracturing the rock formation through the fracture network based on thevariable-frequency pulse according to claim 1, wherein the rock formation to be fracturedin Step S4 is a hard rock formation to be exposed in front of a tunneling head, during atunneling process in a hard rock roadway, central long boreholes are constructed at a centralposition of the tunneling head along a tunneling direction and are fractured by the pulse topre-form a dense fracture network in the hard rock formation to be exposed in front of thetunneling head, the rock formation is sufficiently broken, so that the rock formation iscapable of falling off smoothly under a subsequent cutting or blasting action of a tunnelingmachine, thereby improving a tunneling velocity; before a formal fracturing construction,firstly, the central long boreholes are drilled at the central of the tunneling heading alongthe tunneling direction, the observation holes that are parallel to the central long boreholesand equal in length of the central long boreholes are respectively drilled at a roof, bothsides and a floor of the roadway and humidity sensors are arranged in the observation holes,the central long boreholes are fractured and a variation of a humidity of each observationborehole with the fracturing time is recorded, to deduce time when the fracture expands tothe surrounding rock in a pre-tunnelled roadway, and the time is taken as a fracturing timeof a subsequent pulse.
- 4. The method for fracturing the rock formation through the fracture network based on thevariable-frequency pulse according to claim 1, wherein the rock formation to be fracturedin Step S4 is a hard roof above a coal seam during an initial caving of the coal miningworking face, during the initial caving of the coal mining working face, boreholes aredrilled in the hard roof above an open-off cut and two crossheadings and are fractured bythe pulse to perform a dense fracture network in the roof, and an opened position of anopen-off cut borehole is located approximate to a rear coal wall, and an opened position ofa transporting crossheading borehole and an opened position of a return air crossheadingborehole are located at a centerline of the roof of the crossheading.
- 5. The method for fracturing the rock formation through the fracture network based on thevariable-frequency pulse according to claim 1, wherein the rock formation to be fracturedin Step S4 is a hard roof above both ends of the coal mining working face during processinga hanging roof at ends of the coal mining working face, during processing the hanging roofat ends of the coal mining working face, boreholes are drilled at ends of the coal miningworking face and are fractured by the pulse to form a dense fracture network in the hardroof above the ends of the coal mining working face, the rock formation in this area issufficiently broken, an opened position of the borehole drilled at ends of the coal miningworking face is located at a centerline of a roof of a crossheading, an inclination angle ofthe borehole is 70, and a direction of the borehole is inclined to a goaf.
- 6. The method for fracturing the rock formation through the fracture network based on thevariable-frequency pulse according to claim 1, wherein the rock formation to be fracturedin Step S4 is a thick-hard dirt band and a thick-hard floor within a mining height rangeduring a period when the coal mining working face passes through the thick-hard dirt band and an undercutting, during the period when the coal mining working face passes through the thick-hard dirt band and the undercutting, long boreholes are drilled in the crossheading and are fractured by the pulse to form a dense fracture network in the dirt band or the floor, a gangue or the floor is sufficiently broken, so that the gangue and the floor is capable of falling off smoothly under a subsequent cutting of a shearer, an opened position of the long borehole constructed in the crossheading is located at a centerline position of the dirt band in a side wall of a crossheading working face or a pre-cut floor, and the borehole is constructed along the dirt band or a inclined direction of the floor, a mechanized hole position of the borehole is located in a side wall of another crossheading working face of the working face, and a spacing between the boreholes is controlled within a range from 4 m to 5 m.
- 7. The method for fracturing the rock formation through the fracture network based on the variable-frequency pulse according to claim 1, wherein the rock formation to be fractured in Step S4 is a hard rock formation around a fault during a period when the coal mining working face passes through the fault, during the period when the coal mining working face passes through the fault, long boreholes are constructed in a crossheading and are fractured by the pulse to a dense fracture network in the fault, the rock formation of the fault is sufficiently broken, so that the rock formation of the fault is capable of falling off smoothly under a subsequent cutting of a shearer, an opened position of the long borehole constructed in the crossheading is located at a middle position of a side wall of the crossheading working face, and the long borehole is constructed along an inclined direction of an open-off cut, a mechanized hole position of the borehole passes through a meeting coal position of the fault, and a spacing between the boreholes is controlled within a range from 4 m to 5 m.
- 8. The method for fracturing the rock formation through the fracture network based on thevariable-frequency pulse according to claim 1, wherein the rock formation to be fracturein Step S4 is a hard rock formation above a coal seam mined in the coal mining workingface during a period of preventing a rock burst in the coal mining face, long boreholes areconstructed in roofs and slope walls of two crossheadings and are fractured by the pulse, aperipheral surrounding rock of a crossheading supporting structure is sufficiently broken,the broken surrounding rock is used to prevent a dynamic mining pressure of the workingface from transmitting to the crossheading of the working face, so that an impact risk of anadvanced supporting section of the crossheading of the working face is reduced, a lengthof the borehole constructed in the roofs and the slope walls of the two crossheadings in thecoal mining working face is 40 m, a range from 20 m to 40 m is defined as a fracturingsection.
- 9. The method for fracturing the rock formation through the fracture network based on thevariable-frequency pulse according to claim 1, wherein the rock formation to be fracturedin Step S4 is a hard rock formation above a roadway during a period of a double-roadwaytunnelling, in a crossheading of the double-roadway tunneling, firstly, multi-holes in a mainroof above a coal pillar are fractured by the pulse simultaneously, generating a resonanceeffect in a surrounding rock around the hole, the rock formation between the holes arebroken preferentially, and eventually a fracture zone is formed along a connecting directionof the boreholes to prevent the dynamic mining pressure from transmitting to an adjacentcrossheading; subsequently a hanging roof at an end of the working face is processed toaccelerate an rotation and sinking of a goaf roof, thus avoiding a formation of a hangingroof, and reducing a stress of the goaf transmitting to the adjacent crossheading, an openedposition of the borehole in the main roof above the coal pillar is located at the roof 0.2 maway from the side wall of the crossheading, a mechanized hole position of the borehole islocated at an upper surface of the main roof directly above 1/3 of a width of the coal pillar,and a spacing between the boreholes is controlled within a range from 4 m to 5 m.
- 10. The method for fracturing the rock formation through the fracture network based onthe variable-frequency pulse according to claim 1, wherein the rock formation to befractured in Step S4 is a hard rock formation above a protective coal pillar of a mainroadway at a final stage of a stoping in a coal mining working face, at the last stage of thestoping in the coal mining working face, firstly, before the working face is advanced to astop line, a resonance effect is generated in a surrounding rock around the hole throughsimultaneously fracturing multi-holes by pulse in a main roadway of a mining area, therock formation between the holes is broken preferentially, and eventually a fracture zoneis formed along a connection direction of the boreholes, so that the propagation path of themining stress to the main roadway in a panel is blocked; subsequently, when the workingface is stoped to the stop line, a hard roof above a coal seam is fractured at the stop line ofthe working face, thus avoiding forming a cantilever beam structure on a goaf side of thestop line, and blocking a high stress of the goaf from propagating to a system main roadway,and further reducing a degree of deforming and damaging the main roadway in the miningarea; and a mechanized hole position of the borehole cutting off the dynamic pressure ismore than 30 m away from each main roadway in a horizontal direction but not beyond thestop line.
- 11. The method for fracturing the rock formation through the fracture network based onthe variable-frequency pulse according to claim 1, wherein the rock formation to befractured in Step S4 is metal ores stoped by a stage natural caving method, in anengineering of stoping metal ores by adopting the stage natural caving method, longboreholes are constructed in a weakened roadway and are fractured by the pulse to form adense fracture network in the ores, the ores are sufficiently broken, so that the ores arecapable of falling off smoothly during a subsequent ore drawing process, and a spacingbetween the boreholes is controlled within a range from 4 m to 8 m.
- 12. The method for fracturing the rock formation through the fracture network based on the variable-frequency pulse according to claim 1, wherein the rock formation to be fractured in Step S4 is metal ores stoped by a single-layer caving method, and in an engineering of stoping the metal ores by adopting the single-layer caving method, fan shaped boreholes are drilled in a transmitting roadway along a vein at a stage of open-off cutting an area directly below a district rise in a working face and are fractured by the pulse to weaken a hard main roof above a stoping face, and a spacing between the fan-shaped final hole is 5 m, and a roof above an entire working face is covered with the fan-shaped boreholes sufficiently.
- 13. The method for fracturing the rock formation through the fracture network based on the variable-frequency pulse according to claim 1, wherein the rock formation to be fractured in Step S4 is an ore-bearing aquifer of low-permeability uranium ore, when the low-permeability of the ore-bearing aquifer leads to a high cost and a low efficiency of mining the uranium, a pulse fracturing is performed in a liquid injection hole to form a dense fracture network around the liquid injection hole, so that the permeability of the uranium ore-bearing aquifer is increased, and an efficiency of the uranium mining is further improved; when the fracturing boreholes are designed, a hole spacing of the fractured holes is equal to twice a spacing from a sealing section to an upper roof and an lower floor, so that when the fractures in two boreholes are connected, the fractures have not expanded to the roof; in addition, a fracturing time is required to be controlled accurately, the fracturing time is determined by a field test; before a formal fracturing construction, an observation borehole that is parallel to the fracturing borehole and equal in length of the fracturing borehole is drilled at a middle position of two fracturing holes and a humidity sensor is arranged in the observation borehole, one of the fracturing holes on both sides of theobservation hole is fractured and a variation of a borehole humidity with fracturing time is observed and recorded, so that time of the fracture expanding to the observation hole is deduced, and the time is taken as subsequent pulse fracturing time.
- 14. A device for fracturing a rock formation through a fracture network based on a variable frequency pulse, comprising: a fracturing pump with variable pumping mode and frequency, wherein the fracturing pump is configured to output pulse water to fracture the rock formation, and supply constant displacement water for an automatic packer to seal holes, a motor that is connected to a power end of the fracturing pump with variable pumping mode and frequency is a variable frequency motor, a hydraulic end of the fracturing pumping with variable pumping mode and frequency includes three plungers, one of the three plungers corresponds to a liquid outlet cut-off valve arranged on a liquid outlet channel and a liquid inlet cut-off valve arranged on a liquid inlet channel at a pump head, and an operating chamber corresponding to the plunger is provided with a channel in communication with an exterior, the channel is provided with a water supply cut-off valve, and the water supply cut-off valve is in communication with a water tank through a water supply rubber hose; high-pressure rubber hoses output by the fracturing pump with variable pumping mode and frequency is divided into two ways by a tee, one way called as a fracturing rubber hose is configured to input the pulse water into the borehole to fracture the rock formation, another way called as a sealing hole rubber hose is configured to supply the constant displacement water for the automatic packer to seal the hole; a fracturing cut-off valve, a fracturing drain valve, a pressure sensor and a flow sensor are sequentially arranged on the fracturing rubber hose along a water flow direction; and a one way valve, a pressure gauge and a sealing hole drain vale are sequentially arranged on the sealing hole rubber hose along the water flow direction; comprising a hydraulic fracturing measuring and controlling instrument, in signal connection with thepressure sensor and the flow sensor, and configured to monitor and record a pressure and a flow of the pulse water during a fracturing process; an automatic packer, including two expansion capsule hole packers, wherein the two expansion capsule hole packers are connected to each other through afirst double-way water-injection steel pipe of an outer pipe with a channel, and an interior of the expansion capsule hole packer is a second double-way water-injection steel pipe of an inner pipe with a channel, a steel wire rubber sleeve is wrapped on an exterior of the second double-way water-injection steel pipe of the inner pipe with a channel, one end of the steel wire rubber sleeve is fixed at one end of the second double-way water-injection steel pipe of the inner pipe with a channel, another end of the steel wire rubber sleeve is slidable on the second double-way water-injection steel pipe of the inner pipe with a channel, and connections are sealed under high pressure; and a mechanical rod feeder, configured to send the automatic packer to the borehole fracturing zone, wherein the mechanical rod feeder includes: a cylinder; a pallet, sleeved on an cylinder wall and slidable on the cylinder wall; an outrigger connector, fixedly connected at a top end of a cylinder wall of the cylinder, wherein the outrigger connector is connected to an outrigger through a bolt, and the outrigger is rotatable around the bolt on a side face of the outrigger connector; a connecting rod, wherein one end of the connecting rod is connected to the pallet, and another end of the connecting rod passes through the outrigger connector to connect to a connecting disk, and the connecting disk is fixedly connected at an end of a piston rod of the cylinder; and a third double-way water-injection steel pipe, wherein one end of the third double-way water-injection steel pipe is fixedly connected to the outrigger connector, and another end of the third double-way water-injection steel pipe is provided with a connection that is connected to the second double-way water-injection steel pipe on the automatic packer.
- 15. The device for fracturing the rock formation through the fracture network based on thevariable-frequency pulse according to claim 14, whereinthe third double-way water-injection steel pipe is fixedly connected to the outriggerconnector through a limiting clamp, the double-way water-injection steel pipe includes anexternal pulse steel pipe and an internal high-pressure steel pipe that are equal in lengthand are coaxially sleeved with each other, the external pulse steel pipe and the internalhigh-pressure steel pipe are connected with each other by a connecting rod, both sides ofthe external pulse steel pipes are respectively provided with internal and external threads,and both sides of the internal high-pressure steel pipes are respectively provided withhermaphrodite quick plugs;a sealing ring is placed in the internal thread of the external pulse steel pipe, and configuredto high-pressure seal a connection between two double-way water-injection steel pipes;one side of the external pulse steel pipe approximate to the internal thread is provided witha limiting ring that is configured to cooperate with the limiting clamp to fix the doubleway water-injection steel pipe; anda double-way conversion joint is externally connected to one end of the external pulse steelpipe through a thread, and internally connected to one end of the internal high-pressuresteel pipe through a quick plug.
- 16. The device for fracturing the rock formation through the fracture network based on thevariable-frequency pulse according to claim 14, wherein the outrigger is an retractableoutrigger.
- 17. A method for operating the device for fracturing the rock formation through the fracturenetwork based on the variable-frequency pulse according to claims 14 to 16, comprisingfollowing steps:Step 1, installing the mechanical rod feeder directly below the borehole to be fractured; adjusting, through adjusting the outriggers, an angle of the mechanical rod feeder to align with the borehole; and connecting, through the double-way water-injection steel pipe of the outer pipe with a channel, two expansion capsule hole packers of the automatic hole packer and sending the two expansion capsule hole packers into an orifice position; firstly, installing one end of a first one of third double-way water-injection steel pipes on the outrigger connector of the mechanical rod feeder; connecting another end of the first one of the third double-way water-injection steel pipes to a lower end of the second double way water-injection steel pipe on the automatic packer; driving, through injecting high pressure gas into the cylinder of the mechanical rod feeder, the pallet to slide upwards on an outer wall of the cylinder, and subsequently terminating, after lifting the automatic packer and the first one of the third double-way water-injection steel pipes upwards for a distance Sl, the gas injection; fixing, through the limiting clamp, the automatic packer and the first one of the third double-way water-injection steel pipes on the outrigger connector of the mechanical rod feeder to prevent the automatic packer and the first one of third double-way water-injection steel pipes from falling under an action of self-weight; discharging the gas from the cylinder to return the pallet to a bottom end of the cylinder under an action of gravity; subsequently taking a second one of the third double-way water injection steel pipes, and connecting the second one of the third double-way water-injection steel pipes to the third double-way water-injection steel pipe located at the limiting clamp; injecting the gas into the cylinder again; opening, when the pallet is in contact with a lower end of the second one of the third double-way water-injection steel pipes, the limiting clamp; lifting the second one of the third double-way water-injection steel pipes, the first one of the third double-way water-injection steel pipes and the automatic packer for a distance S1 again, repeating in this way until the automatic packer is sent to a borehole fracturing area; eventually, closing the limiting clamp to fix a last one of the third double way water-injection steel pipes on the outrigger connecter of the mechanical rod feeder;discharging gas in the cylinder to return the pallet to the bottom end of the cylinder; andconnecting the double-way conversion joint with an end of the third double-way waterinjection steel pipe located at the limiting clamp;Step 2, installing the fracturing pump with variable pumping mode and frequency, asupporting water tank, a hydraulic fracturing monitoring and controlling instrument insequence, and connecting the fracturing pump with variable pumping mode and frequency,the supporting water tank, as well as the hydraulic fracturing monitoring and controllinginstrument to each other; connecting, through the double-way conversion joint, ends of thefracturing rubber hose and hole sealing rubber hose to the third double-way water-injectionsteel pipe located at the limiting clamp;Step 3, closing the fracturing cut-off valve; opening the hydraulic fracturing monitoringand control instrument; opening the liquid inlet cut-off valve and the liquid outlet cut-offvalve of the fracturing pump with variable pumping mode and frequency; closing the watersupply cut-off valve of the fracturing pump with variable pumping mode and frequency;opening the fracturing pump with variable pumping mode and frequency to enable threepistons of the fracturing pump with variable pumping mode and frequency to operatenormally; inputting constant discharge water into the automatic packer to seal the hole;closing, when a water pressure of the pressure gage on the rubber hose rises to 35 Mpa, thefracturing pump with variable pumping mode and frequency; wherein since a one-wayvalve is installed on the hole sealing rubber hose, the water in the automatic packer is notflown back after closing the fracturing pump with variable pumping mode and frequency;and completing the hole sealing; and Step 4, opening the water supply cut-off valve of the fracturing pump with variable pumping mode and frequency; closing the liquid inlet cut-off valve and the liquid outlet cut-off valve of the fracturing pump with variable pumping mode and frequency; opening the fracturing cut-off valve; opening the fracturing pump with variable pumping mode and frequency to enable two pistons of the fracturing pump with variable pumping mode and frequency to operate normally and one piston of the fracturing pump with variablepumping mode and frequency to idle; wherein the liquid inlet channel and the liquid outlet channel of the operating chamber corresponding to the idling piston is closed, so that the operating chamber corresponding to the idling piston is not capable of supplying liquid to the fracturing rubber hose, the operating chamber corresponding to the idling piston is connected to the water tank through the water supply rubber hose directly, thus ensuring a normal water absorption and discharge when the piston is idling, and ensuring a lubrication; and inputting the pulse water into the borehole in this mode.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202211261651.7A CN115749713B (en) | 2022-10-14 | 2022-10-14 | Rock stratum variable frequency pulse seam net fracturing method and equipment |
| CN202211261651.7 | 2022-10-14 | ||
| PCT/CN2023/078951 WO2024077842A1 (en) | 2022-10-14 | 2023-03-01 | Rock stratum fracturing method and equipment using variable-frequency pulse fracture network |
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| AU2023251557A1 true AU2023251557A1 (en) | 2024-05-02 |
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| AU2023251557A Pending AU2023251557A1 (en) | 2022-10-14 | 2023-03-01 | Method for fracturing rock formation through fracture network based on variable-frequency pulse and device thereof |
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| CN (1) | CN115749713B (en) |
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| CN115749713B (en) * | 2022-10-14 | 2023-06-16 | 中国矿业大学 | Rock stratum variable frequency pulse seam net fracturing method and equipment |
| CN116658143B (en) * | 2023-07-17 | 2023-10-27 | 延长油田股份有限公司七里村采油厂 | Open hole fracturing crack directional opening tool and construction method |
| CN116988792B (en) * | 2023-09-25 | 2023-12-15 | 太原理工大学 | Comprehensive mechanized mining process for subcoal hard gibbsite |
| CN117684937B (en) * | 2024-01-04 | 2024-06-14 | 中国矿业大学 | Cracking and staged fracturing method based on aerodynamic force impact fluid cracking and staged fracturing integrated device |
| CN117605413B (en) * | 2024-01-24 | 2024-04-26 | 中国石油大学(华东) | Oil well high-energy gas fracturing yield and injection increasing equipment and method |
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| CN102803650B (en) * | 2010-03-19 | 2015-11-25 | 埃克森美孚上游研究公司 | The system and method for rock in fracturing tight reservoir |
| RU2467171C1 (en) * | 2011-06-01 | 2012-11-20 | Федеральное государственное бюджетное образовательное учреждение высшего профессионального образования "Новосибирский национальный исследовательский государственный университет" (Новосибирский государственный университет, НГУ) | Method of diagnosing dangerous situations in deep mining and forecasting parameters of fissuring zones formed by fracturing |
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-
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- 2023-03-01 AU AU2023251557A patent/AU2023251557A1/en active Pending
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| WO2024077842A1 (en) | 2024-04-18 |
| CN115749713A (en) | 2023-03-07 |
| CN115749713B (en) | 2023-06-16 |
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