CN112160792B - Staged hydraulic fracturing working method for underground hard top plate - Google Patents
Staged hydraulic fracturing working method for underground hard top plate Download PDFInfo
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Abstract
The invention discloses a segmented hydraulic fracturing method for an underground hard roof, belonging to the technical field of segmented hydraulic fracturing methods for underground hard roofs; the technical problem to be solved is as follows: an improvement of a method for staged hydraulic fracturing of a hard roof downhole is provided; the technical scheme for solving the technical problems is as follows: the method comprises the following steps: collecting a hard thick rock sample on the upper part of a working face, and testing the physical and mechanical properties and the ground stress state of a fractured target rock stratum to obtain the tensile strength, the plumb stress, the maximum horizontal stress and the minimum horizontal stress of the target rock stratum; designing an embodiment of a fracture borehole; determining a construction position and a drilling implementation process according to the arrangement form and the drilling direction of the fracturing drill holes of the designed fracturing drill hole implementation scheme; determining a fracturing pipe staged hydraulic fracturing construction process to complete the integral fracturing of a hard target rock stratum according to the construction position and the drilling process; the invention is applied to the exploitation of hard roofs of mines.
Description
Technical Field
The invention discloses a staged hydraulic fracturing working method for an underground hard roof, and belongs to the technical field of staged hydraulic fracturing working methods for underground hard roofs.
Background
During the primary mining period of the working face with the hard top plate, large-area suspended roofs in the goaf can not be collapsed in time along with the mining of the working face, and therefore the roofs can not collapse in time to suddenly collapse to form hurricanes, and great safety threats are brought to personnel and equipment in the working face. At present, the forced caving means during the primary mining period of the working face mainly comprises two methods: forced roof caving by deep hole blasting and forced roof caving by hydraulic fracturing. The former is limited by application conditions and cannot be used in high gas mines; compared with the former, the hard top plate can be fractured and softened, the strength of the coal bed can be reduced to a certain extent through water permeation, consumption of cutting teeth and other materials and consumption of a coal mining machine can be reduced, water in the coal rock layer is increased, coal rock dust is reduced, and spontaneous combustion of the coal bed is prevented.
There are generally two ways to perform hydraulic fracturing on hard roof currently: firstly, constructing an L-shaped or vertical long drilled hole on the ground to a hard target rock stratum before coal seam mining, and fracturing by using a hydraulic jet staged fracturing method; and the other method is that inclined short drill holes are constructed in two underground roadways or working face top plates in the working face mining process to reach a target rock stratum with a hard top plate, and if the target rock stratum is a thick coal seam, the fracturing drill holes are even arranged along a coal seam top plate construction process roadway.
The construction of ground L-shaped long drilling holes or vertical drilling holes needs to drill the whole overlying strata from a hard top plate to the ground surface, the drilling work amount is large, the time and labor are wasted, the cost is high, and the method is only suitable for mines with shallow coal seam burial depth and simple geological conditions; the underground inclined short drill hole construction needs different quantities of fracturing drill holes at certain intervals, even additional construction process lanes are needed, the number of the drill holes is large, the workload is high, and the production is delayed when the drill holes are actually drilled on the working face. Therefore, it is necessary to provide a method for performing hard roof hydraulic fracturing by performing horizontal drilling of upper-layer branches underground, which can overcome the defects of large construction amount of long drilling on the ground, high cost, large number of short drilling holes in underground construction and production delay.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to solve the technical problems that: an improvement is provided for a staged hydraulic fracturing operation method for a downhole hard roof.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows: a segmental hydraulic fracturing working method of a downhole hard roof comprises the following steps:
the method comprises the following steps: collecting hard and thick rock sample samples of the upper part of the working face and testingPhysical and mechanical properties and ground stress state of the fractured target rock stratum: testing physical and mechanical parameters of a target rock mass through an experimental method to obtain the tensile strength sigma of the rock sample t ；
Meanwhile, the ground stress state of the rock stratum to be fractured is tested through an experimental method to obtain the plumb stress sigma of the target rock stratum z And maximum horizontal stress sigma hmax And minimum horizontal stress σ hmin ；
Step two: designing an implementation scheme of fracturing a borehole according to the plumb stress, the maximum horizontal stress and the minimum horizontal stress of the target rock stratum obtained in the first step and the arrangement mode of a stoping roadway system;
step three: determining a construction position and a drilling implementation process according to the fracturing drilling arrangement form and the drilling direction of the embodiment of the fracturing drilling designed in the step two;
step four: and determining the fracturing pipe staged hydraulic fracturing construction process to complete the integral fracturing of the hard target rock stratum according to the construction position and the drilling process in the third step.
In the first step, the physical and mechanical parameters of the target rock mass are tested by an experimental method, and the specific steps are as follows:
step 1.1: hard thick rock stratum rock samples at the upper part of a mining working face are mined on site;
step 1.2: the method comprises the following steps of testing the tensile strength of a target rock body through an experimental method, wherein the experimental method comprises a direct stretching method or a splitting method, the direct stretching method specifically comprises the steps of adopting a cylindrical sample, connecting two ends of the sample into a tensile testing machine in a bonding or clamping mode, and then applying tensile load to the two ends of the sample to enable the sample to generate tensile failure, so that the tensile strength of the sample is obtained; the splitting method applies a load in the diameter direction of a test sample by adopting a disc-shaped test piece, so that the test sample is damaged in the diameter direction, and the tensile strength of the test sample is obtained;
the height-diameter ratio of the cylindrical test piece is more than 2:1, and the height-diameter ratio of the disc-shaped test piece is 1:2.
The concrete steps for designing the implementation scheme of the fracturing drilling hole in the second step are as follows:
step 2.1: setting a drilling arrangement form of a fracturing drilling main hole;
step 2.1.1: the main hole of the fracturing drilling hole penetrates through a hard top plate above the whole extraction area along the trend of the working surface;
step 2.1.2: the main fracturing hole is obliquely positioned in the middle of the stope face, and the distance d from the fracturing hole to the bottom plate of the hard target rock stratum is measured in the vertical direction 0 Less than the hydrajetting fracturing radius d, i.e. d 0 ＜d；
Step 2.1.3: when the integral thickness of the rock stratum is less than or equal to 2 times of the hydraulic jet fracturing radius d, the position of a main hole of a fractured drilling hole is positioned in the middle of the fractured rock stratum;
step 2.2: setting a drilling arrangement form of fracture drilling branch holes: the distance between the branch holes of the fracturing drill hole is determined according to the period collapse step L designed by the top plate, and the distance L between the branch drill holes is ensured because the fracturing is carried out on the main hole and the branch holes 0 ＜2L；
Step 2.3: setting the arrangement form of the fracturing fractures: the extending direction of the fracturing crack is vertical to the trend of the drilling hole, and the water pressure P of the required annular pipe meets the condition that P is more than or equal to sigma t +σ l In the above formula: sigma t Is tensile strength, σ l Positive stress in the drilling direction;
when the drilling hole is designed to be in the horizontal direction, the normal stress is applied in the drilling direction
In the above formula: theta is an included angle between the drill hole and the maximum principal stress;
when the drilling direction is within the included angle of the two horizontal main stresses, the calculation formula of the positive stress of the drilling direction is as follows:
when the drilling direction is taken outside the included angle of the two horizontal main stresses, the calculation formula of the positive stress of the drilling direction is as follows:
the construction position and drilling implementation process in the third step comprises the following specific steps:
step 3.1: preparing a roadway layout construction site in the lowest coal mining area of the coal seam or the close-distance coal seam through a kilometer directional drilling machine;
step 3.2: according to the natural bending rule of the drill rod, designing an opening position by adopting a screw motor with a bend angle to carry out directional drilling construction;
step 3.3: adjusting the tool face angle of the screw drill in real time by a field technician according to the design track and the concrete condition of the rock stratum, realizing the controlled and accurate orientation of the drilling track, extending the drilling track to a preset target stratum horizontal section according to the design requirement, and then keeping the horizontal position at the fracturing position of the hard rock stratum;
step 3.4: after the main fracturing drilling construction is completed, a retreating type branch drilling construction process is adopted, branch drilling construction is carried out at a specified design position, namely the drilling arrangement form of the branch holes in the step 2.2, and the work of punching, deslagging and the like is completed.
The fracturing pipe staged hydraulic fracturing construction process in the fourth step comprises the following specific steps:
step 4.1: the construction process of staged fracturing adopts a mode of branching holes and then main holes, the implementation direction adopts a retreating mode, and the hydraulic jet fracturing process technology is adopted to jointly complete hydraulic jet and annular extrusion;
step 4.2: by means of hydraulic jet fracturing, the wall of a rock stratum drilling hole is subjected to microcrack generation, and then the annular water injection pressure is increased to the design water pressure through a high-pressure water injection pump;
step 4.3: the automatic telescopic hole packer temporarily seals the front and rear parts of the fractured drilling section in the drilling hole, so that the generated micro-cracks can be expanded.
Compared with the prior art, the invention has the following beneficial effects:
(1) For the hard top plate of the coal bed with larger mine burial depth, the project of arranging the whole long overlying strata rock layer drilled through the hard top plate to the ground surface on the ground is saved, the construction is directly performed nearby the underground adjacent coal rock layer, the drilling length is greatly reduced, and the construction cost is reduced.
(2) The defects that a large number of construction drill holes are needed and the workload is large when the hard roof is fractured by adopting the inclined short drill holes underground are overcome, the fracturing work on the hard roof can be completed at one time before mining, the mining along with a working face is not needed to be carried out all the time, the production is not influenced, the process is simplified, and the cost is saved.
Drawings
The invention is further described below with reference to the accompanying drawings:
FIG. 1 is a schematic diagram of staged hydraulic fracturing of a hard roof of a horizontal borehole of an underground uphole branch of the present invention;
FIG. 2 is a schematic diagram of the calculation of the normal stress in the drilling direction according to the present invention.
Detailed Description
As shown in fig. 1 and 2, the invention relates to a segmental hydraulic fracturing working method of a downhole hard roof, which comprises the following steps:
the method comprises the following steps: collecting a hard thick rock sample on the upper part of a working face, and testing the physical and mechanical properties and the ground stress state of a fractured target rock: testing physical and mechanical parameters of a target rock mass through an experimental method to obtain the tensile strength sigma of the rock sample t ；
Meanwhile, the ground stress state of the rock stratum to be fractured is tested through an experimental method, and the plumb stress sigma of the target rock stratum is obtained z And maximum horizontal stress sigma hmax And minimum horizontal stress σ hmin ；
Step two: designing an implementation scheme of fracturing a borehole according to the plumb stress, the maximum horizontal stress and the minimum horizontal stress of the target rock stratum obtained in the step one and the arrangement mode of a stoping roadway system;
step three: determining a construction position and a drilling implementation process according to the fracturing drilling arrangement form and the drilling direction of the embodiment of the fracturing drilling designed in the step two;
step four: and determining a fracturing pipe staged hydraulic fracturing construction process to complete the integral fracturing of the hard target rock stratum according to the construction position and the drilling process in the third step.
In the first step, the physical and mechanical parameters of the target rock mass are tested by an experimental method, and the specific steps are as follows:
step 1.1: hard thick rock stratum rock samples at the upper part of a mining working face are mined on site;
step 1.2: the method comprises the steps of testing the tensile strength of a target rock body through an experimental method, wherein the experimental method comprises a direct tensile method or a splitting method, the direct tensile method specifically comprises the steps of adopting a cylindrical sample, connecting two ends of the sample into a tensile testing machine in a bonding or clamping mode, and then applying tensile loads to the two ends of the sample to enable the sample to generate tensile damage, so that the tensile strength of the sample is obtained; the splitting method applies a load to a test sample in the diameter direction by adopting a disc-shaped test piece, so that the test sample is damaged in the diameter direction, and the tensile strength of the test sample is obtained;
the height-diameter ratio of the cylindrical test piece is more than 2:1, and the height-diameter ratio of the disc-shaped test piece is 1:2.
The concrete steps for designing the implementation scheme of the fracturing drilling hole in the second step are as follows:
step 2.1: setting a drilling arrangement form of a fracturing drilling main hole;
step 2.1.1: the main hole of the fracturing drilling hole penetrates through a hard top plate above the whole extraction area along the trend of the working surface;
step 2.1.2: the main fracturing hole is obliquely positioned in the middle of the stope face, and the distance d from the fracturing hole to the bottom plate of the hard target rock stratum is measured in the vertical direction 0 Less than the hydraulic jet fracturing radius d, i.e. d 0 ＜d；
Step 2.1.3: when the integral thickness of the rock stratum is less than or equal to 2 times of the hydraulic jet fracturing radius d, the position of a main hole of a fractured drilling hole is positioned in the middle of the fractured rock stratum;
step 2.2: setting a drilling arrangement form of fracture drilling branch holes: the distance between the branch holes of the fracturing drill hole is determined according to the period collapse step L designed by the top plate, and the distance L between the branch drill holes is ensured because the fracturing is carried out on the main hole and the branch holes 0 ＜2L；
Step 2.3: setting a fractureArrangement of the cracks: the extending direction of the fracturing crack is vertical to the trend of the drilling hole, and the water pressure P of the required annular pipe meets the condition that P is more than or equal to sigma t +σ l In the above formula: sigma t For tensile strength, σ l Positive stress in the drilling direction;
when the drilling hole is designed to be in the horizontal direction, the normal stress is applied in the drilling direction
In the above formula: theta is an included angle between the drill hole and the maximum main stress;
when the drilling direction is within the included angle of the two horizontal main stresses, the calculation formula of the positive stress of the drilling direction is as follows:
when the drilling direction is taken outside the included angle of the two horizontal main stresses, the calculation formula of the normal stress of the drilling direction is as follows:
the construction position and drilling implementation process in the third step comprises the following specific steps:
step 3.1: preparing a roadway layout construction site in the lowest coal mining area of the coal seam or the close-distance coal seam through a kilometer directional drilling machine;
step 3.2: according to the natural bending rule of the drill rod, adopting a screw motor with a bending angle to design an opening position for directional drilling construction;
step 3.3: adjusting the tool face angle of the screw drill in real time by a field technician according to the design track and the concrete condition of the rock stratum, realizing the controlled and accurate orientation of the drilling track, extending the drilling track to a preset target stratum horizontal section according to the design requirement, and then keeping the horizontal position at the fracturing position of the hard rock stratum;
step 3.4: after the main fracturing drilling construction is completed, a retreating type branch drilling construction process is adopted, branch drilling construction is carried out at a specified design position, namely the drilling arrangement form of the branch holes in the step 2.2, and the work of punching, deslagging and the like is completed.
The fracturing pipe staged hydraulic fracturing construction process in the fourth step comprises the following specific steps:
step 4.1: the construction process of staged fracturing adopts a mode of branching holes and then main holes, the implementation direction adopts a retreating mode, and the hydraulic jet fracturing process technology is adopted to jointly complete hydraulic jet and annular extrusion;
step 4.2: by means of hydraulic jet fracturing, the wall of a rock stratum drilling hole is subjected to microcrack generation, and then the annular water injection pressure is increased to the design water pressure through a high-pressure water injection pump;
step 4.3: the front and rear parts of the fractured drill hole section in the drill hole are temporarily sealed by the automatic telescopic hole packer, so that the generated micro-cracks can be expanded.
The staged hydraulic fracturing working method of the underground hard roof plate solves the problems of large construction amount, high cost, complex extraction process and the like of the fracturing construction of the ground long drilled hole and the underground short drilled Kong Jianying roof plate.
The method comprises the following specific working steps:
(1) Testing the physical and mechanical properties and the ground stress state of the fractured target rock stratum;
the maximum tensile stress that can be sustained when failure is reached under the action of uniaxial tensile load is called uniaxial tensile strength (tenslestrength) of the rock, which is called tensile strength for short. The experimental method for measuring the tensile strength of the rock mainly comprises an indirect stretching method and a direct stretching method, wherein the indirect stretching method mainly adopts a Brazilian splitting method, and a disc-shaped test piece (the height-diameter ratio is 1:2) is adopted, and a load is applied in the diameter direction of the test piece, so that the test piece is damaged in the diameter direction of the test piece.
The direct tensile method is to use a cylindrical sample (the height-diameter ratio is more than 2:1), connect the two ends of the sample into a tensile testing machine by means of bonding or clamping, and then apply tensile load to the two ends of the sample to generate tensile failure. Hard and thick rock sample on the upper part of the mining working face is mined on site, and the target rock mass is subjected to laboratory experimentThe physical mechanical parameters are tested, and the tensile strength sigma of the rock sample is obtained by using a direct stretching method or a splitting method t (ii) a Testing the ground stress state of the rock stratum to be fractured to obtain the plumb stress sigma of the target rock stratum z And maximum horizontal stress σ hmax Minimum horizontal stress σ hmin 。
(2) Designing a fracture drilling embodiment;
and designing a fracturing drilling arrangement mode according to the arrangement mode of the stoping roadway system. The main hole of the fracturing drilling hole penetrates through a hard top plate above the whole stoping area along the working face trend, the main hole is positioned in the middle of the stoping working face in the inclined direction, and the distance from the fracturing drilling hole to a hard target rock stratum bottom plate in the vertical direction is smaller than the hydraulic jet fracturing radius, namely d 0 If the integral thickness of the rock stratum is less than or equal to 2 times of the fracturing radius d, the drilling position is located in the middle of the fractured rock stratum. The distance between the branch holes of the fracturing drill hole can be determined according to the period collapse step L designed by the top plate, and the distance L between the branch drill holes is ensured due to the fracturing of the main hole and the branch holes 0 ＜2L。
In addition, the extending direction of the fracturing fracture needs to be perpendicular to the trend of the drilled hole, so that the top plate is convenient to break, the water pressure of the required annular pipe is not less than the sum of the tensile strength of the rock stratum and the normal stress in the drilling direction of the drilled hole, namely P is not less than sigma t +σ l Since the bore hole is designed in the horizontal direction, the bore hole direction positive stress σ l From maximum horizontal principal stress σ hmax Minimum horizontal principal stress σ hmax It is decided that,
when the drilling direction is within the included angle of the two horizontal main stresses, the plus sign is taken, and the minus sign is taken outside the included angle.
(3) Determining a construction position and a drilling implementation process;
preparing a roadway layout construction site in the coal mining area of the coal seam or the lowest layer of the close-distance coal seam by using a kilometer directional drilling machine, and designing the position of an opening by using a screw motor with a bending angle according to the natural bending rule of a drill rod to carry out directional drilling construction. And adjusting the tool facing angle of the screw drilling tool in real time by field technicians according to the design track and the concrete condition of the rock stratum to realize the controlled and accurate orientation of the drilling track, so that the drilling track extends to a preset target stratum horizontal section according to the design requirement and then keeps horizontal at the fracturing part of the hard rock stratum. And after the main fracturing drilling construction is finished, adopting a retreating type branch drilling construction process to perform branch drilling construction at a specified design position, and finishing the work of punching, deslagging and the like.
(4) A fracturing pipe staged hydraulic fracturing construction process;
and hydraulic jet fracturing technology is adopted to jointly complete hydraulic jet and annular extrusion. The method comprises the steps of utilizing hydraulic jet fracturing to enable a rock stratum drilling wall to generate micro cracks, then increasing the pressure of annular water injection to the designed water pressure through a high-pressure water injection pump, and temporarily sealing the front part and the rear part of a fractured drilling section in a drilling hole by utilizing an automatic telescopic hole packer to enable the generated micro cracks to be expanded. Meanwhile, in order to avoid the collapse of the branch holes caused by the fracturing of the main hole, the construction process of staged fracturing can adopt a mode of firstly branching the hole and then main hole, and the implementation direction adopts a retreating mode.
In the implementation of the invention, the following implementation procedures of the embodiment are given, as shown in fig. 1, a schematic diagram of mining of coal seams 8# and 9# is given in fig. 1, and the implementation procedures are as follows:
in the figure 1, a certain coal seam 8# and a short-distance coal seam 9# are mined, the burial depth of two coal layers is about 600m, and the coal mining method of top coal caving combined mining is planned to be adopted for mining, wherein the coal seam 8# is partially damaged by a room and pillar type mining method, but the top plate is completely stored without caving. A limestone hard top plate with the thickness of about 10m is arranged on the upper portion of the 8# coal bed directly jacking the mud rock layer. If the roof is not broken, the recovery rate of the combined mining and top coal caving mining method is influenced, and even if the roof collapses in a large area to form a hurricane disaster, the hard roof needs to be subjected to hydraulic fracturing damage. Because of the great depth of coal seam, it is too costly to carry out fracturing drilling from the surface, and in addition, the short drilling which is carried out along with face mining affects production, and part of the drilling can pass through the mined area of the upper 8# coal seam and cannot be carried out. Therefore, the underground upper crossing branch horizontal drilling hard roof staged hydraulic fracturing working method is adopted.
(1) Testing the physical and mechanical properties and the ground stress state of the fractured target rock stratum;
on-site mining of a hard and thick rock sample of a rock stratum on the upper part of a mining working face, testing of physical and mechanical parameters of a target rock mass by a laboratory experiment method, and measurement of tensile strength sigma of the rock sample t =15MPa; testing the ground stress state of the rock stratum to be fractured to obtain the plumb stress sigma of the target rock stratum z =16MPa and maximum horizontal stress, minimum horizontal stress sigma kmax =24MPa and sigma hmin =10MPa. As shown in fig. 2, the bore hole is at an angle θ =45 ° to the maximum principal stress and outside of both principal stresses.
(2) Designing fracturing bore embodiments
And designing a fracturing drilling arrangement mode according to the arrangement mode of the stoping roadway system. Since the fracture radius is d =5m and the hard formation thickness is 10m, just equal to 2 times the fracture radius, the drilling location is placed in the middle of the fractured formation. The designed roof period collapse step is L0=30m, the design branches are alternately arranged and all fractured, and the branch distance L is 0 =60m, the extension direction of the fracture is perpendicular to the borehole direction. The drilling direction takes a sign outside the included angle of the two horizontal main stresses. The positive stress with the drilling direction is calculated by a calculation formula to obtain sigma l =9.9MPa, the water pressure of the required annular tube is not less than the sum of the tensile strength of a rock stratum and the ground stress of the drilling direction of the drill hole, namely P is more than or equal to sigma t +σ l ＝15+9.9＝24.9MPa。
(3) Construction position determination and drilling implementation process
Preparing a roadway layout construction site in the lowest coal mining area of the coal seam or the close-range coal seam by utilizing a kilometer directional drilling machine, and arranging the drilling hole at the middle part of two roadways of the roadway working face of the mining area of the 9# coal seam. According to the natural bending rule of the drill rod, the hole opening position is designed by adopting a screw motor with a bending angle to carry out directional drilling construction. And the field technician adjusts the tool face angle of the screw drill in real time according to the design track and the concrete condition of the rock stratum, realizes the controlled and accurate orientation of the drilling track, extends the drilling track to a preset target stratum horizontal section according to the design requirement, and then keeps the horizontal position at the fracturing position of the hard rock stratum. And after the main fracturing drilling construction is finished, adopting a retreating type branch drilling construction process to perform branch drilling construction at a specified design position, and finishing the work of punching, deslagging and the like.
(4) Staged hydraulic fracturing construction process for fracturing pipe
By means of the hydraulic jet fracturing technology, a plurality of jet pore canals are formed in the drilling subsection part of a hard target rock stratum, the wall of a rock stratum drilling hole is enabled to generate micro cracks through the water attack effect, meanwhile, the annular water injection pressure is increased to the designed water pressure through an annular pipe through a high-pressure water injection pump, and the front part and the rear part of the drilled hole section to be fractured in the drilling hole are temporarily sealed through an automatic telescopic hole packer, so that the generated micro cracks can be expanded. In order to avoid the collapse of the branch holes caused by the fracturing of the main hole, the construction process of staged fracturing can adopt a mode of firstly branching the hole and then main hole, and the implementation direction is a retreating mode. The branch holes on one side can be sequentially fractured from inside to outside in sequence, then the branch drill holes on the other side are sequentially fractured from inside to outside in sequence, finally the main holes are sequentially fractured from inside to outside in sequence, and the fracturing pipes and the tools are guided to enter the branch drill holes by utilizing the bent guide shoes.
The method can effectively overcome the defects of large drilling amount, large drilling quantity, high cost and the like of the water injection fracturing of the hard top plate, realize the integral fracturing of a low-cost area and do not influence normal production.
It should be noted that, regarding the specific structure of the present invention, the connection relationship between the modules adopted in the present invention is determined and can be realized, except for the specific description in the embodiment, the specific connection relationship can bring the corresponding technical effect, and the technical problem proposed by the present invention is solved on the premise of not depending on the execution of the corresponding software program.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (4)
1. A segmental hydraulic fracturing working method of a downhole hard roof is characterized by comprising the following steps: the method comprises the following steps:
the method comprises the following steps: collecting a hard thick rock sample on the upper part of a working face, and testing the physical and mechanical properties and the ground stress state of a fractured target rock: testing physical and mechanical parameters of the target rock mass through an experimental method to obtain the tensile strength of the rock sample
；
Meanwhile, the ground stress state of the rock stratum to be fractured is tested through an experimental method to obtain the plumb stress of the target rock stratum
And maximum horizontal stress
And minimum horizontal stress
；
Step two: designing an implementation scheme of fracturing a borehole according to the plumb stress, the maximum horizontal stress and the minimum horizontal stress of the target rock stratum obtained in the step one and the arrangement mode of a stoping roadway system;
the specific steps for designing the implementation scheme of the fracturing and drilling in the second step are as follows:
step 2.1: setting a drilling arrangement form of a fracturing drilling main hole;
step 2.1.1: the main hole of the fracturing drilling hole penetrates through a hard top plate above the whole extraction area along the trend of the working surface;
step 2.1.2: the main fracturing hole is obliquely positioned in the middle of the stope face, and the distance from the fracturing hole to the bottom plate of the hard target rock stratum in the vertical direction
Less than the hydraulic jet fracture radius
I.e. by
；
Step 2.1.3: when the integral thickness of the rock stratum is less than or equal to the hydraulic jet fracturing radius
2 times of the fracturing drilling hole, the position of the main hole of the fractured drilling hole is positioned in the middle of the fractured rock stratum;
step 2.2: setting a drilling arrangement form of fracture drilling branch holes: the distance between the branch holes of the fracturing drill hole is determined according to the designed period collapse step L of the top plate, and the distance between the branch drill holes is ensured because fracturing is carried out on the main hole and the branch holes
；
Step 2.3: setting the arrangement form of the fracturing fractures: the extending direction of the fracturing crack is vertical to the trend of the drilling hole, and the water pressure P of the required annular tube meets the requirement
In the above formula:
for the purpose of the tensile strength,
positive stress in the drilling direction;
when the drilling hole is designed to be in the horizontal direction, the normal stress is applied in the drilling direction
；
In the above formula: theta is an included angle between the drill hole and the maximum main stress;
when the drilling direction is within the included angle of the two horizontal main stresses, the calculation formula of the positive stress of the drilling direction is as follows:
；
when the drilling direction is taken outside the included angle of the two horizontal main stresses, the calculation formula of the positive stress of the drilling direction is as follows:
；
step three: determining a construction position and a drilling implementation process according to the fracturing drilling arrangement form and the drilling direction of the embodiment of the fracturing drilling designed in the step two;
step four: and determining the fracturing pipe staged hydraulic fracturing construction process to complete the integral fracturing of the hard target rock stratum according to the construction position and the drilling process in the third step.
2. The segmented hydraulic fracturing working method of the underground hard roof plate as claimed in claim 1, wherein: in the first step, the physical and mechanical parameters of the target rock mass are tested by an experimental method, and the specific steps are as follows:
step 1.1: hard thick rock stratum rock samples at the upper part of a mining working face are mined on site;
step 1.2: the method comprises the following steps of testing the tensile strength of a target rock body through an experimental method, wherein the experimental method comprises a direct stretching method or a splitting method, the direct stretching method specifically comprises the steps of adopting a cylindrical sample, connecting two ends of the sample into a tensile testing machine in a bonding or clamping mode, and then applying tensile load to the two ends of the sample to enable the sample to generate tensile failure, so that the tensile strength of the sample is obtained; the splitting method applies a load in the diameter direction of a test sample by adopting a disc-shaped test piece, so that the test sample is damaged in the diameter direction, and the tensile strength of the test sample is obtained;
the height-diameter ratio of the cylindrical test piece is more than 2:1, and the height-diameter ratio of the disc-shaped test piece is 1:2.
3. The segmented hydraulic fracturing working method of the underground hard roof plate as claimed in claim 2, wherein: the construction position and drilling implementation process in the third step comprises the following specific steps:
step 3.1: preparing a roadway layout construction site in the lowest coal mining area of the coal seam or the close-distance coal seam through a kilometer directional drilling machine;
step 3.2: according to the natural bending rule of the drill rod, adopting a screw motor with a bending angle to design an opening position for directional drilling construction;
step 3.3: adjusting the tool face angle of the screw drill in real time by a field technician according to the design track and the concrete condition of the rock stratum, realizing the controlled and accurate orientation of the drilling track, extending the drilling track to a preset target stratum horizontal section according to the design requirement, and then keeping the horizontal position at the fracturing position of the hard rock stratum;
step 3.4: after the main fracturing drilling construction is completed, a retreating type branch drilling construction process is adopted, branch drilling construction is carried out at a specified design position, namely the drilling arrangement form of the branch holes in the step 2.2, and punching and deslagging are completed.
4. The segmented hydraulic fracturing working method of the underground hard roof plate as claimed in claim 3, wherein: the fracturing pipe staged hydraulic fracturing construction process in the fourth step comprises the following specific steps:
step 4.1: the construction process of staged fracturing adopts a mode of branching holes and then main holes, the implementation direction adopts a retreating mode, and the hydraulic jet fracturing process technology is adopted to jointly complete hydraulic jet and annular extrusion;
step 4.2: by means of hydraulic jet fracturing, the wall of a rock stratum drilling hole is subjected to microcrack generation, and then the annular water injection pressure is increased to the design water pressure through a high-pressure water injection pump;
step 4.3: the automatic telescopic hole packer temporarily seals the front and rear parts of the fractured drilling section in the drilling hole, so that the generated micro-cracks can be expanded.
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| CN114294059B (en) * | 2021-12-29 | 2024-05-07 | 中煤科工开采研究院有限公司 | High-precision control method for hydraulic fracturing layer of hard rock stratum |
| CN114776272B (en) * | 2022-05-25 | 2022-11-22 | 中国矿业大学(北京) | Pressure-relief permeability-increasing method for overlying key layer of hydraulic fracturing |
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