True triaxial hydraulic fracturing experimental device for low-permeability medium

Abstract

The invention is suitable for the technical field of petroleum engineering, and provides a true triaxial hydraulic fracturing experimental device for a low-permeability medium. Comprising a fracturing chamber; a square simulation medium is arranged in the fracturing chamber, three faces of the simulation medium are attached to three faces in the fracturing chamber, the other three faces of the simulation medium are attached to three pressing plates respectively, each pressing plate is connected to the output end of an oil cylinder, the oil cylinders are installed on the fracturing chamber, and a fracturing pipe is further arranged in the center of the simulation medium. Drainage filter plates are arranged on the side, close to the simulation medium, of the pressing plate, and drainage filter plates are arranged at the positions, attached to the simulation medium, in the fracturing chamber; the fracturing pump injection device is used for injecting fracturing fluid into the fracturing pipe in the fracturing chamber; and a true triaxial loading device. The drainage filter plates are arranged on all the faces of the simulation medium, all the faces can drain water in the fracturing process when the real pressure environment is simulated, and simulation is more real.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum engineering, in particular to a true triaxial hydraulic fracturing experimental device for low permeability media. Background Art

[0002] Fracturing technology was first used to increase oil production and exploit shale gas. It forms artificial cracks by pressurizing the rock and soil layers, and injects viscosity agents and proppants to prevent the cracks from closing. Proppants generally use coarser particles than the original medium, filling the crack grid formed by fracturing to increase the permeability of the medium; at the same time, the extension of the cracks may change the original structure of the medium, so that the heterogeneity can be improved. Research by foreign scholars shows that fractures expand preferentially in the original fractures. The main factors affecting the morphology and range of the fracturing grid in the medium include fracturing pressure, fracturing form, fracturing fluid properties, and physical and chemical indicators of the rock and soil medium. Research on the mechanism of fracturing is mostly concentrated in the field of oil and gas field exploitation.

[0003] In terms of contaminated site remediation, research has mostly focused on using hydraulic fracturing as a pretreatment method for low-permeability formation site remediation in combination with other technologies to achieve remediation goals.

[0004] The name of the prior art patent is low-permeability medium hydraulic fracturing experimental device (CN202021583145.6), which includes a transparent tank body, in which a geotextile layer, a filter layer and a simulated medium layer are arranged from bottom to top; a cover plate is arranged on the top of the transparent tank body and is equipped with a first pressure gauge, and a drain pipe connected to the interior of the transparent tank body is installed on the cover plate, and is equipped with a first valve and a first flow meter; an aeration device is provided at the bottom of the transparent tank body; a measuring part is provided on the side of the transparent tank body, and it simply sets a water filtration structure at the bottom of the simulated medium, which cannot fully simulate the fracturing state. In order to solve this technical problem, a low-permeability medium true triaxial hydraulic fracturing experimental device is proposed. Summary of the invention

[0005] The object of the present invention is to provide a true triaxial hydraulic fracturing experimental device for low permeability media to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions: A low permeability medium true triaxial hydraulic fracturing experimental device, comprising: a fracturing chamber; a block-shaped simulated medium is arranged inside the fracturing chamber, three surfaces of the simulated medium are attached to three surfaces inside the fracturing chamber, and the other three surfaces of the simulated medium are attached to three pressing plates, each pressing plate is connected to the output end of an oil cylinder, the oil cylinder is installed on the fracturing chamber, and a fracturing pipe is also arranged at the center of the simulated medium; a drainage filter plate is arranged on one side of the pressing plate close to the simulated medium, and drainage filter plates are arranged at the positions of the simulated medium attached inside the fracturing chamber; A fracturing pumping device, which is used to inject fracturing fluid into the fracturing pipe inside the fracturing chamber; and a true three-axis loading device, which provides high-pressure hydraulic oil to three cylinders.

[0007] As a further solution of the present invention: the drainage filter plate includes a frame, a geotextile layer and a pebble cushion layer, the geotextile layer and the pebble cushion layer are both arranged inside the frame, the pebble cushion layer is close to the simulated medium, and the geotextile layer is attached to the pebble cushion layer.

[0008] As a further solution of the present invention: a drainage cavity is arranged at the position of the pressure plate close to the frame, and a drainage cavity is also arranged at the position of the fracturing chamber close to the adjacent frame, and all the drainage cavities are provided with drainage pipes.

[0009] As a further solution of the present invention: a heating device is also provided on the fracturing chamber, and the heating device is used to heat both sides of the simulated medium.

[0010] As a further solution of the present invention: the fracturing chamber is also provided with a CT scanning device, which includes a CT radiation source and a CT detector arranged at the front and rear sides of the fracturing chamber, and all accessories located in the scanning area are made of carbon fiber.

[0011] As a further solution of the present invention: the true three-axis loading device includes a first base and an oil tank and an oil supply pump installed on the first base, the output end of the oil supply pump is connected to the input end of the three pressure plates, the oil supply pump is used to provide high-pressure hydraulic oil to the three pressure plates, the input end of the oil supply pump is connected to the bottom of the oil tank, and the output end of the oil cylinder is connected to the top of the oil tank.

[0012] As a further solution of the present invention: the bottom of the oil tank is installed on the first base through a plurality of shock-absorbing legs.

[0013] As a further solution of the present invention: the shock-absorbing leg includes a base plate, a first cylinder body, a second cylinder body, a piston rod, an energy storage member, a piston and a dividing block, the first cylinder body and the second cylinder body are fixedly mounted on the base plate, the second cylinder body is sleeved on the outside of the first cylinder body, the second cylinder body and the outside of the first cylinder body and the base plate are enclosed to form a third chamber, the piston is slidably arranged in the first cylinder body, the bottom of the piston rod is fixedly mounted on the piston, the top of the piston rod is fixedly mounted on the oil tank, and the base plate is fixedly mounted on the first base; the two ends of the energy storage member are respectively fixedly connected to the first cylinder body and the piston rod; a dividing block is fixedly mounted inside the first cylinder body, the dividing block is arranged below the piston, the dividing block divides the position below the piston inside the first cylinder body into a first chamber and a second chamber, the second chamber is below the dividing block, the second chamber is connected to the third chamber through the second connecting hole at the bottom of the first cylinder body, the first chamber and the second chamber are filled with liquid medium, and the third chamber is also provided with liquid medium; the dividing block is provided with no less than two throttling holes, and the throttling holes are used to connect the first chamber with the second chamber.

[0014] As a further solution of the present invention: an opening self-adjusting mechanism is provided on the segmentation block, and the opening self-adjusting mechanism is used to adjust the throttle hole opening.

[0015] As a further solution of the present invention: the opening self-adjusting mechanism includes a first mounting groove arranged on the dividing block and a second mounting groove arranged at the center position of the first mounting groove, an adjusting disk is fixedly installed on the outside of an up and down sliding adjusting member inside the second mounting groove, the first outlet of the throttle hole is arranged on the side wall of the first mounting groove, and the outer ring of the adjusting disk abuts against the side wall of the first mounting groove; the second outlet of the throttle hole is arranged below the dividing block; the adjusting member is elastically mounted on the dividing block; the upper edge of the adjusting disk is higher than the first outlet of the throttle hole, and the lower edge of the adjusting disk is arranged below the upper end of the first outlet of the throttle hole.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: by arranging drainage filter plates on each surface of the simulated medium, each surface can drain water during the fracturing process when simulating a real pressure environment, and the simulation is more realistic; and by arranging a fracturing pumping device and three pressure plates to squeeze each surface of the simulated medium, the pressure of the real situation is simulated, and the experiment is more realistic. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic diagram of a true triaxial hydraulic fracturing test device for low permeability media according to an embodiment of the present invention Figure 1 .

[0018] Figure 2 A schematic diagram of a true triaxial hydraulic fracturing test device for low permeability media according to an embodiment of the present invention Figure 2 .

[0019] Figure 3 A schematic diagram of a true triaxial hydraulic fracturing test device for low permeability media according to an embodiment of the present invention Figure 3 .

[0020] Figure 4 It is a schematic structural diagram of a shock-absorbing leg in a true triaxial hydraulic fracturing experimental device for low permeability media according to an embodiment of the present invention.

[0021] Figure 5 The figure is a schematic diagram of the internal structure of a shock-absorbing leg in a true triaxial hydraulic fracturing experimental device for low permeability media according to an embodiment of the present invention.

[0022] Figure 6 for Figure 5 Enlarged view of point A in the middle.

[0023] Figure 7 This is a schematic structural diagram of a segmentation block in a true triaxial hydraulic fracturing experimental device for low permeability media according to an embodiment of the present invention.

[0024] In the figure: 1-fracturing chamber, 2-fracturing pumping device, 3-CT scanning device, 4-true triaxial loading device, 5-first base, 6-oil tank, 7-oil supply pump, 8-oil cylinder, 9-pressing plate, 10-drainage filter plate, 11-frame, 12-geotextile layer, 13-pebble cushion layer, 14-drainage cavity, 15-drainage pipe, 16-shock-absorbing legs, 17-bottom plate, 18-first cylinder body, 19-second cylinder body, 20-piston rod, 21-energy storage member, 22-piston, 23-dividing block, 24-adjusting member, 25-adjusting disk, 26-throttle hole, 27-first elastic member, 28-first connecting hole, 29-first mounting groove, 30-second mounting groove, 31-second connecting hole, 32-first cavity, 33-camera, 34-second cavity, 35-third cavity, 36-simulation medium, 37-heating device, 38-control device. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Example 1

[0027] See also Figure 1 to Figure 3, a structural diagram of a true triaxial hydraulic fracturing experimental device for low permeability media provided in Example 1 of the present invention, the true triaxial hydraulic fracturing experimental device for low permeability media comprises: a fracturing chamber 1, a fracturing pumping device 2 and a true triaxial loading device 4; a block-shaped simulated medium 36 is arranged inside the fracturing chamber 1, three surfaces of the simulated medium 36 are attached to three surfaces inside the fracturing chamber 1, and the other three surfaces of the simulated medium 36 are attached to three pressure plates 9 respectively, each of which is connected to the output end of an oil cylinder 8 respectively, and the oil cylinder 8 is installed on the fracturing chamber 1; the true triaxial loading device 4 provides high-pressure hydraulic oil for the three oil cylinders 8; a fracturing pipe is also arranged at the center of the simulated medium 36; a drainage filter plate 10 is arranged on the side of the pressure plate 9 close to the simulated medium 36, and a drainage filter plate 10 is arranged at the position of the simulated medium 36 inside the fracturing chamber 1; the fracturing pumping device 2 is used to add fracturing fluid to the fracturing pipe inside the fracturing chamber 1.

[0028] Specifically, three surfaces of the simulation medium 36 are attached to three adjacent surfaces inside the fracturing chamber 1 .

[0029] The present invention is provided with drainage filter plates 10 on each surface of the simulated medium 36, which can simulate the real pressure environment so that each surface can drain water during the fracturing process, making the simulation more realistic. In addition, by setting the fracturing pumping device 2 and three pressure plates 9, each surface of the simulated medium 36 is squeezed to simulate the pressure of the real situation, making the experiment more realistic.

[0030] like Figure 2 As shown, in some embodiments, the drainage filter plate 10 includes a frame 11, a geotextile layer 12 and a pebble cushion layer 13, the geotextile layer 12 and the pebble cushion layer 13 are both arranged inside the frame 11, the pebble cushion layer 13 is close to the simulation medium 36, and the geotextile layer 12 is attached to the pebble cushion layer 13, so that the water generated by the pressure can be simulated and discharged in real conditions. The frame 11 can be a metal frame to support the geotextile layer 12 and the pebble cushion layer 13.

[0031] In some embodiments, a drainage cavity 14 is provided at the pressure plate 9 near the frame 11, and a drainage cavity 14 is also provided at the fracturing chamber 1 near the adjacent frame 11. All drainage cavities 14 are provided with drainage pipes 15 for draining water.

[0032] In some embodiments, a heating device 37 is further provided on the fracturing chamber 1 , and the heating device 37 is used to heat both sides of the simulation medium 36 to simulate the real temperature.

[0033] like Figure 3As shown, in some embodiments, the fracturing chamber 1 is further provided with a CT scanning device 3, the CT scanning device 3 includes a CT radiation source and a CT detector arranged at the front and rear sides of the fracturing chamber 1, and all accessories located in the scanning area are made of carbon fiber. The CT scanning device 3 can be provided to observe the real state of the simulated medium 36 during the pressure process.

[0034] like Figure 3 As shown, the present invention also includes a control device 38, and the fracturing chamber 1, the fracturing pumping device 2, the CT scanning device 3 and the true triaxial loading device 4 are all connected to the control device 38 so as to collect data during the experiment of the fracturing chamber 1, the fracturing pumping device 2, the CT scanning device 3 and the true triaxial loading device 4.

[0035] Example 2

[0036] See also Figure 1 to Figure 7 The main difference between this embodiment 2 and embodiment 1 is that the true triaxial loading device 4 includes a first base 5 and an oil tank 6 and an oil supply pump 7 installed on the first base 5, the output end of the oil supply pump 7 is connected to the input end of the three pressure plates 9, the oil supply pump 7 is used to provide high-pressure hydraulic oil to the three pressure plates 9, the input end of the oil supply pump 7 is connected to the bottom of the oil tank 6, and the output end of the oil cylinder 8 is connected to the top of the oil tank 6.

[0037] In some embodiments of the present invention, a camera 33 is installed on the top of the fuel tank 6. An observation window is also provided on the top of the fuel tank 6. The observation window is made of transparent material. The camera 33 is used to obtain the internal image of the fuel tank 6 through the observation window.

[0038] In some embodiments of the present invention, the bottom of the oil tank 6 is mounted on the first base 5 via a plurality of shock-absorbing legs 16 , and the shock-absorbing legs 16 are provided to reduce the influence of the running vibration of the oil supply pump 7 on the oil tank 6 .

[0039] In some embodiments of the present invention, the shock absorbing legs 16 are adaptive shock absorbing legs.

[0040] like Figure 4 and Figure 5As shown, as some embodiments of the present invention, the shock-absorbing leg 16 includes a bottom plate 17, a first cylinder body 18, a second cylinder body 19, a piston rod 20, an energy storage member 21, a piston 22 and a split block 23, the first cylinder body 18 and the second cylinder body 19 are fixedly mounted on the bottom plate 17, the second cylinder body 19 is sleeved on the outside of the first cylinder body 18, the second cylinder body 19 and the outside of the first cylinder body 18 and the bottom plate 17 are surrounded to form a third chamber 35, the piston 22 is slidably arranged in the first cylinder body 18, the bottom of the piston rod 20 is fixedly mounted on the piston 22, the top of the piston rod 20 is fixedly mounted on the oil tank 6, and the bottom plate 17 is fixedly mounted on the first base 5; the energy storage member 21 is divided into two parts at both ends. The first cylinder 18 is fixedly connected to the first cylinder 18 and the piston rod 20; the first cylinder 18 is fixedly installed with a partition block 23, which is arranged below the piston 22. The partition block 23 divides the position below the piston 22 in the first cylinder 18 into a first chamber 32 and a second chamber 34. The second chamber 34 is below the partition block 23. The second chamber 34 is connected to the third chamber 35 through the second connecting hole 31 at the bottom of the first cylinder 18. The first chamber 32 and the second chamber 34 are filled with liquid medium, and the third chamber 35 is also provided with liquid medium; the partition block 23 is provided with no less than two throttle holes 26, and the throttle holes 26 are used to connect the first chamber 32 with the second chamber 34. In this way, during the vibration process, the piston rod 20 slides up and down relative to the first cylinder 18, and the piston rod 20 drives the piston 22 to slide up and down, so that the medium in the first chamber 32 is exchanged with the second chamber 34 through the throttle hole 26, so as to achieve the absorption of vibration energy. The first cylinder 18 is circular in the interior. The piston 22 is a circular block. The energy storage member 21 may be sleeved on the outside of the piston rod 20 , and the energy storage member 21 may be a coil spring.

[0041] like Figures 4 to 7 As shown, in some embodiments of the present invention, since the amount of hydraulic oil inside the oil tank 6 changes during the operation of the system, the weight of the oil tank 6 changes. Different damping needs to be adjusted for shock-absorbing legs 16 of different weights to adapt to the shock-absorbing requirements of oil tanks 6 of different weights. Therefore, an opening self-adjusting mechanism is provided on the dividing block 23, and the opening self-adjusting mechanism is used to adjust the opening of the throttle hole 26.

[0042] As some embodiments of the present invention, the opening self-adjusting mechanism includes a first mounting groove 29 arranged on the dividing block 23 and a second mounting groove 30 arranged at the center position of the first mounting groove 29, an adjusting disk 25 is fixedly installed on the outside of the up and down sliding adjusting member 24 inside the second mounting groove 30, the first outlet of the throttle hole 26 is arranged on the side wall of the first mounting groove 29, and the outer ring of the adjusting disk 25 abuts against the side wall of the first mounting groove 29; the second outlet of the throttle hole 26 is arranged below the dividing block 23; the adjusting member 24 is elastically mounted on the dividing block 23; the upper edge of the adjusting disk 25 is higher than the first outlet of the throttle hole 26, and the lower edge of the adjusting disk 25 is arranged below the upper end of the first outlet of the throttle hole 26. Specifically, if the weight of the oil tank 6 is relatively large, the damping required will be relatively large. At this time, the pressure inside the first chamber 32 will increase, so the adjusting member 24 will move toward the inside of the second mounting groove 30, thereby driving the adjusting disk 25 to move downward, and the area covered by the side wall of the adjusting disk 25 on the throttle hole 26 will increase, so that the first outlet connecting area of ​​the throttle hole 26 will become smaller, thereby increasing the damping. If the hydraulic oil inside the oil tank 6 decreases, the pressure inside the first chamber 32 will decrease, so that the adjusting member 24 will move away from the dividing block 23 under the action of elasticity, so that the first connecting hole 28 moves upward, and the area of ​​the first outlet of the throttle hole 26 covered by the outer wall of the first connecting hole 28 is reduced, so that the first outlet area of ​​the throttle hole 26 is increased, and the damping is reduced to meet the low-weight shock absorption requirements.

[0043] In some embodiments of the present invention, the regulating disk 25 is provided with a first communicating hole 28 , so that the medium in the second chamber 34 is communicated with the interior of the first chamber 32 through the throttling hole 26 and then through the first communicating hole 28 .

[0044] In some embodiments of the present invention, a first elastic member 27 is further disposed inside the second mounting groove 30, and both ends of the first elastic member 27 are respectively fixedly mounted on the adjusting member 24 and the bottom of the second mounting groove 30, so that the adjusting member 24 is elastically mounted in the dividing block 23. The first elastic member 27 may be a coil spring.

[0045] The working principle of the present invention is: When in use, first, the heating device 37 is powered on to heat the simulated medium 36. When the simulated medium 36 reaches the simulated temperature, the oil supply pump 7 is powered on to drive the three oil cylinders 8 to squeeze the three sides of the simulated medium 36. After squeezing to the set temperature, the fracturing pumping device 2 injects pressure liquid into the simulated medium 36 through the pressure pipe. During the fracturing process, the CT scanning device 3 obtains the transformed image information of the simulated medium 36, and the fracturing is completed. During operation, the amount of hydraulic oil in the oil tank 6 changes. If the weight of the oil tank 6 is relatively large, the damping required will be relatively large. At this time, the pressure in the first chamber 32 will increase, so the adjusting member 24 moves toward the inside of the second mounting groove 30, thereby driving the adjusting disk 25 to move downward, and the area covered by the side wall of the adjusting disk 25 on the throttle hole 26 will increase, so that the first outlet connecting area of ​​the throttle hole 26 will become smaller, thereby increasing the damping. If the hydraulic oil in the oil tank 6 decreases, the pressure in the first chamber 32 will decrease, so that the adjusting member 24 moves away from the dividing block 23 under the action of elasticity, so that the first connecting hole 28 moves upward, and the area of ​​the first outlet of the throttle hole 26 covered by the outer wall of the first connecting hole 28 is reduced, so that the first outlet area of ​​the throttle hole 26 is increased, and the damping is reduced to meet the low-weight shock absorption requirements.

[0046] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0047] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0048] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0049] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0050] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0051] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A true triaxial hydraulic fracturing test device for low permeability media, characterized in that: include: A fracturing chamber (1); a block-shaped simulated medium (36) is arranged inside the fracturing chamber (1); three surfaces of the simulated medium (36) are attached to three surfaces inside the fracturing chamber (1); the other three surfaces of the simulated medium (36) are attached to three pressing plates (9), each pressing plate (9) is connected to the output end of an oil cylinder (8), the oil cylinder (8) is installed on the fracturing chamber (1), and a fracturing pipe is also arranged at the center of the simulated medium (36); a drainage filter plate (10) is arranged on one side of the pressing plate (9) close to the simulated medium (36); and drainage filter plates (10) are arranged at the positions of the simulated medium (36) inside the fracturing chamber (1); A fracturing pumping device (2), the fracturing pumping device (2) is used to inject fracturing fluid into the fracturing pipe inside the fracturing chamber (1); and a true three-axis loading device (4), wherein the true three-axis loading device (4) provides high-pressure hydraulic oil to three oil cylinders (8).

2. A low permeability medium true triaxial hydraulic fracturing test device according to claim 1, characterized in that: The drainage filter plate (10) comprises a frame (11), a geotextile layer (12) and a pebble cushion layer (13); the geotextile layer (12) and the pebble cushion layer (13) are both arranged inside the frame (11); the pebble cushion layer (13) is close to the simulated medium (36); and the geotextile layer (12) is attached to the pebble cushion layer (13).

3. A low permeability medium true triaxial hydraulic fracturing test device according to claim 2, characterized in that: The pressure plate (9) is provided with a drainage cavity (14) at a position close to the frame (11), and the fracturing chamber (1) is also provided with a drainage cavity (14) at a position close to an adjacent frame (11), and all drainage cavities (14) are provided with drainage pipes (15).

4. A low permeability medium true triaxial hydraulic fracturing test device according to claim 1, characterized in that: A heating device (37) is also provided on the fracturing chamber (1), and the heating device (37) is used to heat both sides of the simulated medium (36).

5. A low permeability medium true triaxial hydraulic fracturing test device according to claim 4, characterized in that: The fracturing chamber (1) is also provided with a CT scanning device (3), the CT scanning device (3) comprising a CT radiation source and a CT detector arranged at the front and rear sides of the fracturing chamber (1), and all accessories located in the scanning area are made of carbon fiber material.

6. A low permeability medium true triaxial hydraulic fracturing test device according to any one of claims 1 to 5, characterized in that: The true triaxial loading device (4) comprises a first base (5), an oil tank (6) and an oil supply pump (7) mounted on the first base (5); the output end of the oil supply pump (7) is connected to the input end of three pressing plates (9); the oil supply pump (7) is used to provide high-pressure hydraulic oil to the three pressing plates (9); the input end of the oil supply pump (7) is connected to the bottom of the oil tank (6); and the output end of the oil cylinder (8) is connected to the top of the oil tank (6).

7. A low permeability medium true triaxial hydraulic fracturing test device according to claim 6, characterized in that: The bottom of the oil tank (6) is mounted on the first base (5) via a plurality of shock-absorbing legs (16).

8. A low permeability medium true triaxial hydraulic fracturing test device according to claim 7, characterized in that: The shock-absorbing leg (16) comprises a base plate (17), a first cylinder body (18), a second cylinder body (19), a piston rod (20), an energy storage member (21), a piston (22) and a partition block (23); the first cylinder body (18) and the second cylinder body (19) are fixedly mounted on the base plate (17); the second cylinder body (19) is sleeved on the outside of the first cylinder body (18); the second cylinder body (19) and the outside of the first cylinder body (18) and the base plate (17) enclose a third chamber (35); the piston (22) is slidably arranged in the first cylinder body (18); the bottom of the piston rod (20) is fixedly mounted on the piston (22); the top of the piston rod (20) is fixedly mounted on the oil tank (6); the base plate (17) is fixedly mounted on the first base (5); both ends of the energy storage member (21) are fixedly connected to the second cylinder body (18); A cylinder body (18) and a piston rod (20); a partition block (23) is fixedly installed inside the first cylinder body (18), the partition block (23) is arranged below the piston (22), the partition block (23) divides the position below the piston (22) inside the first cylinder body (18) into a first chamber (32) and a second chamber (34), the second chamber (34) is located below the partition block (23), the second chamber (34) is connected to a third chamber (35) through a second connecting hole (31) at the bottom of the first cylinder body (18), the first chamber (32) and the second chamber (34) are filled with a liquid medium, and the third chamber (35) is also provided with a liquid medium; the partition block (23) is provided with no less than two throttling holes (26), the throttling holes (26) are used to connect the first chamber (32) with the second chamber (34).

9. A low permeability medium true triaxial hydraulic fracturing test device according to claim 8, characterized in that: The dividing block (23) is provided with an opening self-adjusting mechanism, and the opening self-adjusting mechanism is used to adjust the opening of the throttling hole (26).

10. A low permeability medium true triaxial hydraulic fracturing test device according to claim 9, characterized in that: The opening self-adjusting mechanism comprises a first mounting groove (29) arranged on the dividing block (23) and a second mounting groove (30) arranged at the center of the first mounting groove (29); an adjusting disk (25) is fixedly installed on the outside of the upward and downward sliding adjusting member (24) inside the second mounting groove (30); the first outlet of the throttle hole (26) is arranged on the side wall of the first mounting groove (29); the outer ring of the adjusting disk (25) abuts against the side wall of the first mounting groove (29); the second outlet of the throttle hole (26) is arranged below the dividing block (23); the adjusting member (24) is elastically mounted on the dividing block (23); the upper edge of the adjusting disk (25) is higher than the first outlet of the throttle hole (26), and the lower edge of the adjusting disk (25) is arranged below the upper end of the first outlet of the throttle hole (26).

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