CN111366472A - True triaxial hydraulic fracturing physical simulation equipment and method for variable core size - Google Patents
True triaxial hydraulic fracturing physical simulation equipment and method for variable core size Download PDFInfo
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
- G01N3/10—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces generated by pneumatic or hydraulic pressure
- G01N3/12—Pressure testing
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- G01N2203/0019—Compressive
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
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- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
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- G01N2203/006—Crack, flaws, fracture or rupture
- G01N2203/0062—Crack or flaws
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- G01N2203/02—Details not specific for a particular testing method
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- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
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- G01N2203/0658—Indicating or recording means; Sensing means using acoustic or ultrasonic detectors
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Abstract
The invention provides true triaxial hydraulic fracturing physical simulation equipment applied to variable core size, which comprises a hydraulic pressure stabilizing source, a true triaxial simulation test stand and a fracturing fluid comprehensive injection control device, wherein the true triaxial simulation test stand is connected with the hydraulic pressure stabilizing source to provide hydraulic pressure for a fracturing experiment, the true triaxial simulation test stand is connected with the fracturing fluid comprehensive injection control device to control the injection of the fracturing fluid in the experiment process, and the true triaxial simulation test stand is respectively provided with confining pressure applying devices which apply pressure in a layered manner and have adjustable height in the direction of X, Y, Z so as to be suitable for simulating the conditions of different stress pressures on the surface of a tightly-adhered acting sample. The invention has the beneficial effects that: the method can be used for developing a true triaxial hydraulic fracturing experiment aiming at the underground core subjected to field coring, and researching the fracture initiation and expansion rules of the true underground stratum.
Description
Technical Field
The invention relates to the technical field of oil and gas drilling rock physical engineering, in particular to true triaxial hydraulic fracturing physical simulation equipment and method for variable core size.
Background
In recent years, along with the continuous deepening of oil gas exploration and development, unconventional oil gas resources such as shale gas, compact oil, compact gas, coal bed gas and the like have great development potential under the existing economic and technical conditions. The hydraulic fracturing technology is one of core technologies of unconventional oil and gas resource development, is widely applied to the transformation of reservoirs, and can greatly improve the productivity of unconventional oil and gas wells.
The hydraulic fracturing technology is developed for more than 50 years, and remarkable development is achieved from theoretical research to field practice, wherein true triaxial hydraulic fracturing physical simulation experiments are the most intuitive method for researching hydraulic fracturing fracture initiation and fracture propagation, but the existing true triaxial hydraulic fracturing devices generally have a series of problems that (1) most samples of the true triaxial hydraulic fracturing devices are cubic rock samples with fixed sizes, such as 100mm × 100mm × 100mm, 300mm × 300mm × 300mm, 400mm × 400mm × 400mm and the like, (2) samples used by the true triaxial hydraulic fracturing devices are generally manual sample samples (such as cement mixed sand) or natural outcrop rock samples, the two samples and underground real stratum rock physical properties and mechanical properties have a plurality of differences, the obtained experiment results cannot accurately reflect real conditions, and (3) the existing true triaxial hydraulic fracturing devices generally do not have horizontal stress loading function, so that the three-axis hydraulic fracturing devices cannot simulate the actual stress distribution and the stress distribution of underground real stratum rock, and the problem that a plurality of stress components are excessively and are subjected to complex loading is caused.
Disclosure of Invention
The invention overcomes the defects in the prior art, provides the true triaxial hydraulic fracturing physical simulation equipment and method for the variable core size, and can be used for developing a true triaxial hydraulic fracturing experiment aiming at an underground core subjected to field coring and researching the fracture initiation and expansion rules of a true underground stratum.
The purpose of the invention is realized by the following technical scheme.
Be applied to true triaxial hydraulic fracturing physical simulation equipment that is used for variable rock core size, including hydraulic pressure steady voltage source, true triaxial analogue test frame and fracturing fluid integrated injection controlling means, true triaxial analogue test frame with hydraulic pressure steady voltage source is connected and is provided hydraulic pressure for the fracturing experiment, true triaxial analogue test frame with fracturing fluid integrated injection controlling means is connected, and the injection of control experiment in-process fracturing fluid, its characterized in that: true triaxial simulation experiment frame is equipped with layering respectively in the X, Y, Z direction and exerts device and height-adjustable's confined pressure to be applicable to the condition that different stresses of the close laminating effect sample surface simulation exerted pressure.
Further, confining pressure is applyed the device and is included layering pressure plate, pressure plate connecting block, hydraulic jack, liftable spiral support and spiral support sleeve, there is the sample laminating in one side of layering pressure plate, the opposite side of layering pressure plate with the pressure plate connecting block is connected, hydraulic jack does the pressure plate connecting block with layering pressure plate provides pressure, liftable spiral support's lower part is equipped with the spiral support sleeve, the spiral support sleeve passes through slide slidable and sets up on the true triaxial simulation test frame.
Further, the layered pressure plate is composed of an arrangement of metal plates of different materials and equal thickness.
Furthermore, the material of each metal plate can be any combination of two of cast iron, carbon steel, cast steel and aluminum.
Further, an acoustic emission probe is mounted on the layering pressure plate and attached to the surface of the sample.
Further, an electric heating rod is arranged on the layered pressure plate to heat the sample.
Furthermore, the comprehensive injection control device for the fracturing fluid comprises a fracturing fluid tank, a sand-carrying fluid tank and a backflow fluid tank, wherein the fracturing fluid tank, the sand-carrying fluid tank and the backflow fluid tank are respectively connected with a fluid injection pipeline through valves, and a fluid injection hole of the fluid injection pipeline is connected with a shaft in a sample.
Further, the frame of true triaxial simulation test frame includes from last roof-rack, grudging post, platform and the support that connects gradually extremely down, and sets up the roof-rack the grudging post with seal box between the platform, inject silicone oil in the seal box.
Further, the liquid pressure in the seal box is the same as the applied pore pressure of the sample, and the fluid injected into the sample is prevented from leaking out due to the pressure difference.
A method for simulating a hydraulic fracture physical experiment using the hydraulic fracture physical simulation experiment apparatus of claim 1, comprising the steps of:
the method comprises the following steps: placing a sample on a true triaxial test stand, adjusting the vertical position of a confining pressure applying device relative to the sample through a liftable spiral support, adjusting the horizontal position of the confining pressure applying device relative to the sample through a sliding spiral support sleeve, enabling a pressure plate to be attached to the side face of the sample, and enabling an acoustic emission probe to be in contact with the surface of the sample;
step two: injecting silicone oil into the sealing box to fill the sealing box with the silicone oil;
step three: opening a hydraulic pressure stabilizing source, respectively setting the magnitude of the confining pressure in X, Y, Z three directions according to an experimental scheme, and after the three-direction confining pressure reaches a specified value, placing the sample for 15 minutes to enable the interior of the sample to reach a stress balance state;
step six: opening the fracturing fluid comprehensive injection control device, injecting the sample, starting the fracturing process, wherein the process is as follows:
the method comprises the following steps that firstly, the fracturing fluid is injected into a control device in a comprehensive mode, and the fracturing fluid is pumped into a sample to enable the sample to generate cracks;
secondly, injecting sand-carrying liquid of the mixed sand by utilizing the comprehensive fracturing liquid injection control device;
opening a valve to enable the fluid in the sample to enter a backflow liquid tank under the action of negative pressure, and simulating a backflow condition;
step seven: and the comprehensive injection control device of the fracturing fluid closes the hydraulic pressure stabilizing source to enable the three-way confining pressure to be unloaded to zero, and then the sample is taken out.
The invention has the beneficial effects that:
the size of the layered pressure plate of the true triaxial equipment is adjustable, so that the true triaxial experimental device can be used for carrying out experiments on samples with different sizes, and particularly can be used for carrying out experiments on cores with the diameters ranging from 100mm to 200mm underground.
By changing the material of which the pressure plate is made, the layered pressurization of horizontal stresses can be conveniently realized. The equipment can realize a small-sized hydraulic fracturing experiment of the underground real core, and the pressed rock sample can meet the size requirement of most CT equipment; therefore, the fracture initiation and expansion properties of the actual reservoir rock are researched on the premise of not damaging the rock sample.
Drawings
FIG. 1 is a schematic structural view of the present invention;
FIG. 2 is a schematic structural diagram of a true triaxial simulation test stand;
FIG. 3 is a schematic structural diagram of a sample confining pressure applying device for installing an acoustic emission device;
FIG. 4-1 is a front view of a layered pressure plate;
FIG. 4-2 is a side view of a layered pressure plate;
4-3 are top views of layered pressure plates;
FIG. 5 is a schematic diagram of a sample placement configuration;
in the figure:
1. a top frame; 2. an upper cover plate; 3. erecting a frame; 4. a platform; 5. a support; 6. an O-shaped sealing ring; 7. a liquid injection cover plate;
8. a sample; 9. an oil jack; 10. a pressure plate connecting block; 11. a layered pressure plate; 12. a lifting spiral support; 13. a helical support sleeve; 15. a wellbore; 16. a liquid injection line; 17. a hydraulic jack priming line; 18. a rubber pad; 19. A true triaxial simulation test stand; 20. a hydraulic pressure stabilizing source; 21. a fracturing fluid comprehensive injection control device;
22. an acoustic emission probe fixing plate; 23; a liquid injection inlet end pressure gauge; 24. and a pressure electronic recorder;
26. a fracturing fluid tank; 27. a sand carrying liquid tank; 28. a back-drain liquid tank; 29. a pressure gauge; 30. a sealing box;
31-1, 31-2, 31-3, 31-4, 31-5 and a valve; 32. a latex film; 33. heat shrink tubing;
34. an acoustic emission probe fixing hole; 35. an upper pressure plate; 36. a lower pressure plate; 37. a medium pressure plate;
38. a cylindrical bore.
Detailed Description
The technical solution of the present invention is further illustrated by the following specific examples.
As shown in fig. 1 and 2, the true triaxial hydraulic fracturing physical simulation equipment for variable core size mainly comprises a hydraulic pressure stabilizing source 20, a true triaxial simulation test stand 19 and a fracturing fluid comprehensive injection control device 21, wherein the true triaxial simulation test stand 19 is connected with the hydraulic pressure stabilizing source 20, the true triaxial simulation test stand 19 is connected with the fracturing fluid comprehensive injection control device 21, and the injection process of the fracturing fluid in the experiment process is controlled.
The hydraulic pressure stabilizing source 20 is provided with a pressure gauge 29 for displaying a pressure value, which is expressed as a pressure value of oil pressure in the oil jack 9, so that the confining pressure value of the three-way stress can be reflected. And the confining pressure can be accurately loaded by computer servo control.
The fracturing fluid comprehensive injection control device 21 is provided with a liquid injection inlet end pressure gauge 23 and a pressure electronic recorder 24, and can record and display the change of the pressure of the liquid injection end along with the time in real time. The fracture curve obtained by the pressure electronic recorder 24 can be used for judging the fracture initiation and extension process of the fracture in the fracturing process.
The true triaxial simulation test stand 19 includes: the device comprises a top frame 1, an upper cover plate 2, a vertical frame 3, a platform 4, a support 5, an O-shaped sealing ring 6, a liquid injection cover plate 7, a rubber pad 8 with a hole in the middle, an oil jack 9, a pressure plate connecting block 10, a layered pressure plate 11, a liftable spiral support 12, a spiral support sleeve 13, a slide way 14, a shaft 15, a liquid injection pipeline 16, an oil jack liquid injection pipeline 17 and a sample 18;
the whole frame of the true triaxial simulation test frame 19 consists of a top frame 1, a vertical frame 3, a platform 4 and a support 5, other devices and parts are all arranged on the frame, a sealing box 30 is arranged on the frame, silicone oil is injected into the sealing box 30, the liquid pressure in the sealing box 30 is the same as the applied pore pressure of the sample 8, and the fluid injected into the sample 8 is prevented from leaking out due to the action of pressure difference; wherein, the layered pressure plate 11 and the pressure plate connecting block 10 are connected by hexagon socket head cap screws to jointly form a confining pressure applying device. Wherein the pressure plate connecting block 10 is arranged on the liftable spiral support 12, and the liftable spiral support 12 is arranged on the pressure plate connecting block; the lower part is a spiral support sleeve 13, the height of the pressure plate connecting block 10 is adjusted by rotating the liftable spiral support 12, and then the height of the upper surface of the pressure plate 10 is adjusted to be consistent with that of the upper surface of the sample 18. In addition, the spiral support sleeve 13 can slide on the slide way 14, and the adaptability to samples with different sizes is realized by adjusting the front-back distance between the pressure plate and the samples. The confining pressure is applied by providing pressure through an oil jack 9, and the oil jack 9 is connected with a hydraulic pressure stabilizing source 21 through an oil jack liquid injection pipeline 17. The hydraulic pressure is provided by a hydraulic pressure stabilizing source 20 to drive the oil jack 9 to move, so that a confining pressure applying device consisting of a layered pressure plate 11 and a pressure plate connecting block 10 is pushed to provide confining pressure for the sample. The upper part of the sample 18 is provided with a rubber pad 9 with a hole in the middle, so as to ensure the sealing property of the injected liquid. The upper part of the middle perforated rubber pad 9 is provided with an injection cover plate 7, the middle of the cover plate is provided with a protruding injection hole, the injection hole is connected with a shaft 15 in a sample and is connected with an external injection pipeline 16, and an O-shaped sealing ring is arranged around the injection hole to ensure the sealing performance in the injection process. The upper cover plate 2 is arranged above the liquid injection cover plate 7 and is connected with the top frame 1 through screws.
In order to carry out true triaxial experiments on underground rock core samples with different sizes, the invention provides a confining pressure applying device which mainly comprises a pressure plate connecting block and a pressure plate, wherein the samples with different sizes are subjected to true triaxial fracturing experiments by changing the size of the pressure plate, and the pressure plate connecting block is connected with the pressure plate through an inner hexagonal screw, so that the experiments on the rock cores with the diameters from 100mm to 200mm underground can be realized;
the present invention also provides a sample confining pressure applying apparatus for installing an acoustic emission device, as shown in fig. 3, comprising: the acoustic emission probe comprises a pressure plate connecting block 10, a pressure plate for mounting an acoustic emission probe, an acoustic emission probe fixing plate 22 and an acoustic emission probe fixing hole 34. The pressure plate connecting block 10 is connected with a pressure plate for mounting the acoustic emission probe through an inner hexagonal screw, the acoustic emission probe fixing plate 22 is connected with the pressure plate for mounting the acoustic emission probe through an inner hexagonal screw, and the acoustic emission probe penetrates through the pressure plate through an acoustic emission probe fixing hole 34 and is attached to the surface of a sample; the pressure plate is made of metal plates with different materials and equal thicknesses, the pressure plate and the pressure plate connecting block 10 are fixedly connected through hexagon socket screws, two cylindrical through holes are formed in the pressure plate, and an electric heating rod is placed in the through holes; the pressure plates referred to above may be either layered pressure plates 11 or non-layered pressure plates;
the principle that the layered pressure plate 11 can realize layered pressing as shown in fig. 4-1, 4-2 and 4-3 is as follows: the pressure plate only deforms elastically during the pressure application process, and when the right end of the combined layered pressure plate 11 applies the same acting force through the pressure plate connecting block 10, the Young modulus and the Poisson ratio of different materials are different, so that the acting force of the contact end surfaces of the different materials and the sample is different, namely the stress is different in magnitude. Therefore, by adjusting the material composition of the combined layered pressure plate 11, calculation and application of different stresses in the horizontal direction can be realized; two cylindrical perforations 38 are made in the laminating pressure plate 11 and an electrical heating rod is placed to heat the sample 8 as the laminating pressure plate 11 is in direct contact with the sample 8.
Preferably, the layered pressure plate 11 is divided into three layers, wherein the upper and lower pressure plates 35, 36 are made of cast iron and have an elastic modulus of 100GPa, and the middle pressure plate 37 is made of steel and has an elastic modulus of 200 GPa. After completion of the installation of sample 8 and the apparatus, the strain corresponding to the three pressure plates was dl/l of 0.00005 assuming that a displacement of 0.002mm dl was applied by the oil jack. The stress applied to the surfaces of different materials can be calculated according to linear elasticity mechanics as follows: sigmaCast iron＝50MPa；σSteel100 MPa. The stress applied to the steel surface is 2 times that of the cast iron material, i.e. sigma is the same displacementCast iron/σSteel＝ECast iron/ESteel。
Given the same displacement of 0.002mm, the stress exerted by the layered pressure plate 11 of different materials on the sample 8 is shown in table 1:
TABLE 1 stress applied to samples by pressure plates of different materials
In summary, the laminated pressure plate 11 is divided into three layers, wherein the upper and lower pressure plates 35, 36 are made of different materials, and the material of the pressure plate is different from that of the middle pressure plate 37;
or the upper and lower pressure plates 35, 36 are made of the same material, but different from the pressure plate 37;
the upper and lower pressure plates 35, 36 are made of any one or two of cast iron, carbon steel, cast steel and aluminum, and the middle pressure plate 37 is made of any one of cast iron, carbon steel, cast steel and aluminum.
The invention also provides a sample preparation method for the true triaxial test of the soft rock sample. Due to the high permeability of soft rock, the low strength of the sample, the transport and loading process may cause damage to the sample. Therefore, for soft rock, a layer of impermeable membrane is added around the sample, and the impermeable membrane has certain strength and can prevent the sample from being damaged in the process of transporting and preventing the sample.
A method for simulating a hydraulic fracturing physical experiment by using true triaxial hydraulic fracturing physical simulation equipment for underground cores with different sizes comprises the following steps:
the method comprises the following steps: placing the sample 8 on a true triaxial test stand 19, wrapping the sample 8 with a latex film 32 and a heat shrinkable tube 33 before the experiment as shown in fig. 5, ensuring the sealing property of the sample 8, adjusting the vertical position of the confining pressure applying device relative to the sample 8 through a liftable spiral support 13, adjusting the horizontal position of the confining pressure applying device relative to the sample 8 through a sliding spiral support sleeve 13, attaching a layered pressure plate 11 to the side surface of the sample 8, and contacting an acoustic emission probe with the surface of the sample 8;
step two: injecting silicone oil into the seal box 30 to fill the seal box 30 with the silicone oil;
step three: opening a hydraulic pressure stabilizing source 20, respectively setting the confining pressure in X, Y, Z three directions according to an experimental scheme, and placing the sample 8 for 15 minutes after the three-direction confining pressure reaches a specified value, so that the interior of the sample 8 reaches a stress balance state;
step six: open fracturing fluid and synthesize injection control device 21, annotate the liquid to sample 8, begin the fracturing process, the process is as follows:
firstly, injecting liquid by utilizing a fracturing fluid comprehensive injection control device 21, and pumping the fracturing fluid into the sample to generate cracks in the sample 8;
secondly, injecting the sand-carrying fluid mixed with the sand into a fracturing fluid comprehensive injection control device 21;
thirdly, opening a valve 31-5, closing valves 31-1, 31-2, 31-3 and 31-4 to enable the fluid in the sample 8 to enter the backflow liquid tank 28 under the action of negative pressure, and simulating the backflow condition;
step seven: and (3) comprehensively injecting the fracturing fluid into the control device 21, closing the hydraulic pressure stabilizing source 20 to enable the three-way confining pressure to be unloaded to be zero, and then taking out the sample 8.
Example 1
As shown in fig. 1, according to the true triaxial hydraulic fracturing physical simulation experiment equipment applied to cores with different sizes in a well, a true triaxial hydraulic fracturing experiment is carried out on a cubic core sample 8 with the thickness of 100mm × 100mm × 100mm, and the true triaxial hydraulic fracturing experiment equipment sequentially comprises the following steps:
selecting a pressure plate 11 with the thickness of 100mm × 100mm and provided with an acoustic emission probe, and mounting an acoustic emission probe fixing plate 22 on the pressure plate according to the figure 3, and then connecting the pressure plate to a pressure plate connecting block (10) to obtain a confining pressure loading device for a cubic core sample experiment with the thickness of 100mm × 100mm × 100 mm;
step two: the sample 8 is placed on a true triaxial test stand 19, and a confining pressure loading device is placed above the liftable spiral support 12 around the sample according to the diagram. The horizontal position of the support relative to the sample is adjusted by sliding the spiral support sleeve 13, and the vertical position of the liftable spiral support 12 relative to the sample is adjusted by rotating the liftable spiral support, so that the layered pressure plate 11 is attached to the side surface of the sample 8. Then, the acoustic emission probe penetrates through an acoustic emission probe fixing hole in the pressure plate, the probe is made to contact with the surface of the sample 8, and finally the probe is fixed to complete the installation of the acoustic emission device;
placing a 100mm × 100mm square rubber pad with a hole in the middle on the upper surface of the sample, then placing a 100mm × 100mm square liquid injection cover plate 7 above the rubber pad 18, and finally fixing the upper cover plate 2 on the top frame 1 through screws to complete the installation of the true triaxial test frame 19;
step four: connecting a true triaxial test stand 19, a comprehensive fracturing fluid injection control device 21 and a hydraulic pressure stabilizing source 20 according to the mode shown in the figure 1;
step five: and (4) opening the hydraulic pressure stabilizing source 20, and respectively setting X, Y, Z confining pressure in three directions according to an experimental scheme. After the three-dimensional confining pressure reaches a specified value, placing the sample for 15 minutes to enable the interior of the sample to reach a stress balance state, and preparing to carry out the next experiment;
step six: open fracturing fluid and synthesize injection control device 21, annotate liquid to sample 8, annotate the liquid simultaneously, can observe notes liquid end pressure through annotating liquid entry end pressure gauge 23 and pressure electronic record appearance 24, the fracturing process as follows:
firstly, injecting liquid by utilizing a fracturing fluid comprehensive injection control device 21, and pumping the fracturing fluid into the sample to generate cracks in the sample 8;
secondly, injecting the sand-carrying fluid mixed with the sand into a fracturing fluid comprehensive injection control device 21;
thirdly, opening a valve 31-5, closing valves 31-1, 31-2, 31-3 and 31-4 to enable the fluid in the sample 8 to enter the backflow liquid tank 28 under the action of negative pressure, and simulating the backflow condition;
step seven: after the experiment is finished, the comprehensive fracturing fluid injection control device 21 is closed, the hydraulic pressure stabilizing source 20 is closed, the three-way confining pressure is unloaded to zero, and then the sample is taken out.
While one embodiment of the present invention has been described in detail, the present invention is only a preferred embodiment of the present invention and should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made within the scope of the present invention shall fall within the scope of the present invention.
Claims (10)
1. A real triaxial hydraulic fracturing physical simulation equipment for variable rock core size, including hydraulic pressure steady voltage source (20), real triaxial simulation test frame (19) and fracturing fluid integrated injection controlling means (21), real triaxial simulation test frame (19) with hydraulic pressure steady voltage source (20) are connected and are provided hydraulic pressure for the fracturing experiment, real triaxial simulation test frame (19) with fracturing fluid integrated injection controlling means (21) are connected, control the injection of fracturing fluid in the experimentation, its characterized in that: the true triaxial simulation experiment rack (19) is respectively provided with a confining pressure applying device with layered pressure application and adjustable height in the direction of X, Y, Z so as to be suitable for the situation that the surface of a sample is tightly attached to simulate different stress pressure applications.
2. The true triaxial hydraulic fracturing physical simulation equipment for variable core size of claim 1, wherein: confining pressure applying device includes layering pressure plate (11), pressure plate connecting block (10), hydraulic jack (9), liftable spiral support (12) and spiral support sleeve (13), there is the sample laminating one side of layering pressure plate (11), the opposite side of layering pressure plate with pressure plate connecting block (10) are connected, hydraulic jack (9) do pressure plate connecting block (10) with layering pressure plate (11) provide pressure, the lower part of liftable spiral support (12) is equipped with spiral support sleeve (13), spiral support sleeve (13) are in through slide slidable setting on true triaxial simulation test frame (19).
3. The true triaxial hydraulic fracturing physical simulation equipment for variable core size of claim 2, wherein: the layered pressure plate (11) is formed by arranging metal plates of different materials and equal thickness.
4. The true triaxial hydraulic fracturing physical simulation equipment for variable core size of claim 2, wherein: the material of each metal plate can be any combination of two of cast iron, carbon steel, cast steel and aluminum.
5. The true triaxial hydraulic fracturing physical simulation experiment equipment applied to cores of different sizes in a well according to claim 4, wherein the true triaxial hydraulic fracturing physical simulation experiment equipment comprises: and an acoustic emission probe is mounted on the layered pressure plate (11) and is attached to the surface of the sample.
6. The true triaxial hydraulic fracturing physical simulation equipment for variable core size of claim 5, wherein: and an electric heating rod is arranged on the layered pressure plate (11) to heat the sample (8).
7. The true triaxial hydraulic fracturing physical simulation equipment for variable core size of claim 1, wherein: the comprehensive injection control device for the fracturing fluid comprises a fracturing fluid tank (26), a sand-carrying fluid tank (27) and a backflow fluid tank (28), wherein the fracturing fluid tank (26), the sand-carrying fluid tank (27) and the backflow fluid tank (28) are respectively connected with a fluid injection pipeline (16) through valves, and a fluid injection hole of the fluid injection pipeline (16) is connected with a shaft (15) in a sample (8).
8. The true triaxial hydraulic fracturing physical simulation equipment for variable core size according to any one of claims 1 to 7, wherein: the frame of true triaxial simulation test frame (19) includes from last roof-rack (1), grudging post (3), platform (4) and support (5) that connect gradually extremely down, and sets up roof-rack (1) grudging post (3) with seal box between platform (4), inject silicone oil in seal box (30).
9. The true triaxial hydraulic fracturing physical simulation equipment for variable core size of claim 8, wherein: the liquid pressure in the sealed box (30) is the same as the applied pore pressure of the sample (8), and the fluid injected into the sample (8) is prevented from leaking out due to the pressure difference.
10. A method for simulating a hydraulic fracture physical experiment using the hydraulic fracture physical simulation experiment apparatus of claim 9, wherein: the method comprises the following steps:
the method comprises the following steps: placing a sample (8) on a true triaxial test stand (19), adjusting the vertical position of a confining pressure applying device relative to the sample (8) through a liftable spiral support (12), adjusting the horizontal position of the confining pressure applying device relative to the sample (8) through a sliding spiral support sleeve (13), enabling a pressure plate (11) to be attached to the side surface of the sample (18), and enabling an acoustic emission probe to be in contact with the surface of the sample (8);
step two: injecting silicone oil into the sealing box (30) to fill the sealing box (30) with the silicone oil;
step three: opening a hydraulic pressure stabilizing source (20), respectively setting X, Y, Z confining pressure in three directions according to an experimental scheme, and after the three-dimensional confining pressure reaches a specified value, placing the sample (8) for 15 minutes to enable the interior of the sample (8) to reach a stress balance state;
step six: opening a fracturing fluid comprehensive injection control device (21), injecting the sample (8) and starting a fracturing process, wherein the process comprises the following steps:
the method comprises the following steps that firstly, the fracturing fluid is injected by utilizing a comprehensive injection control device (21), and the fracturing fluid is pumped into a sample (8), so that cracks are generated in the sample (8);
secondly, injecting sand-carrying liquid of the mixed sand by utilizing the comprehensive fracturing liquid injection control device (21);
thirdly, opening a valve to enable the fluid in the sample (8) to enter a backflow liquid tank (28) under the action of negative pressure, and simulating the backflow condition;
step seven: and the comprehensive injection control device (21) of the fracturing fluid closes the hydraulic pressure stabilizing source (20), so that the three-way confining pressure is unloaded to zero, and then the sample (8) is taken out.
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