In-situ testing device for gas-liquid two-phase permeability after hydraulic fracturing

Abstract

The utility model discloses an in-situ testing device for gas-liquid two-phase permeability after hydraulic fracturing, and belongs to the field of unconventional oil and gas development engineering. The device comprises a fluid injection system, a sample loading system, a ground stress loading system, a fracturing system, a fluid recovery system and a data acquisition and processing system, the fluid injection system, the sample loading system and the fluid recovery system are sequentially connected, the crustal stress loading system is connected with the sample loading system through a rigid pressure head and applies three-dimensional crustal stress to a test piece, and the fracturing system is connected with the sample loading system through a fracturing pipeline and applies liquid injection pressure to the test piece; the fluid injection system, the ground stress loading system and the fracturing system are respectively in electric signal connection with the data acquisition and processing system through transmission cables. The gas-liquid two-phase permeability testing device can be used for respectively testing the gas-liquid two-phase permeability under the conditions of different lithology, different ground stress, different fracturing parameters and different permeability parameters, and can more truly reflect the gas-liquid two-phase fluid migration condition in the unconventional oil and gas discharge and production stage.

Description

Technical Field

[0001] This utility model relates to an in-situ testing device for gas-liquid two-phase permeability after hydraulic fracturing, which belongs to the field of unconventional oil and gas development engineering. Background Technology

[0002] my country possesses abundant reserves of coalbed methane, shale gas, and tight sandstone gas; however, most reservoirs have low permeability, necessitating hydraulic fracturing for reservoir stimulation. The post-fracturing drainage phase involves the co-transport of water / oil and natural gas within the fracture network; that is, the actual operating conditions correspond to the permeation of gas-liquid two-phase fluids within the fracture network after reservoir fracturing. Accurately obtaining the gas-liquid two-phase permeability during the drainage phase after fracturing in low-permeability reservoirs is crucial for fracturing parameter setting and production capacity prediction.

[0003] Current methods for determining the permeability of low-permeability reservoirs mainly include well testing, well logging prediction, indirect testing, and laboratory core testing. Well testing is primarily for homogeneous reservoirs and has a limited testing range. Well logging prediction relies mainly on empirical data for parameters and struggles to overcome the impact of drilling fluid contamination on permeability calculations. Indirect prediction requires manually defining geological strength factors, leading to significant subjectivity and yielding mostly point-based data. Laboratory core testing offers advantages such as low cost and ease of operation, but it cannot account for the impact of fracturing on permeability and is more suitable for testing intact core samples. Furthermore, none of the above methods can accurately determine the true permeability of the gas-liquid two-phase system under drainage conditions. Utility Model Content

[0004] To address the issue of gas-liquid two-phase permeability during the drainage stage after hydraulic fracturing in unconventional oil and gas reservoirs, this invention provides an in-situ testing device for gas-liquid two-phase permeability after hydraulic fracturing. This invention can separately measure the gas-liquid two-phase permeability under different lithologies, different geostresses, different fracturing parameters, and different permeability parameters.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] An in-situ testing device for gas-liquid two-phase permeability after hydraulic fracturing includes a fluid injection system, a sample loading system, a geostress loading system, a fracturing system, a fluid recovery system, and a data acquisition and processing system. The sample loading system holds the test sample (specimen). The fluid injection system, sample loading system, and fluid recovery system are connected sequentially via guide lines according to the permeability test fluid seepage direction. The geostress loading system is connected to the sample loading system via a rigid pressure head, applying triaxial geostress to the specimen in the sample loading system. The fracturing system is connected to the sample loading system via a fracturing pipeline, applying injection pressure to the specimen in the sample loading system. The fluid injection system, geostress loading system, and fracturing system are each electrically connected to the data acquisition and processing system via transmission cables.

[0007] The data acquisition and processing system is a high-performance computer with adjustable parameters, capable of acquiring the flow and pressure of constant flow and constant pressure pumps, and capable of analyzing data programs. It can adjust and acquire fluid injection parameters, geostress parameters, fracturing parameters, and fluid recovery parameters in real time.

[0008] The fluid injection system includes a liquid injection module and a gas injection module. The liquid injection module includes a liquid storage container, a liquid delivery tube, and a constant flow and constant pressure injection pump. The gas injection module includes a gas storage cylinder, a gas injection safety valve, a gas delivery tube, and a constant flow and constant pressure injection pump. The liquid injection module and the gas injection module are connected to the sample loading system via the liquid delivery tube and the gas delivery tube, respectively, through a tee and a flow guide line. The flow guide line is equipped with a constant flow and constant pressure injection pump. The liquid injection pump, the gas injection pump, and the constant flow and constant pressure injection pump are respectively connected to the high-performance computer electrical signal via transmission cables. The tee is equipped with a liquid delivery valve, a gas delivery valve, and a flow guide valve, respectively.

[0009] The sample loading system includes a loading base, a cuboid sleeve with a top opening, a top sleeve, a left pressure plate, a front pressure plate, a right pressure plate, a rear pressure plate, and a top pressure plate. The loading base has four bolt holes symmetrically located at its four corners for connecting to the underlying stress loading system. The left, front, right, and rear pressure plates are connected to the loading base via four horizontal sliding supports. The cuboid sleeve and top sleeve are used to seal the specimen and also to prevent shear stress on the specimen surface caused by uneven stress during stress loading. The various pressure plates are designed to evenly distribute the pressure head of the stress loading system. Specifically, the specimen has a cuboid structure, and the sample loading system is symmetrical. The flow guide line on the left side of the system injects fluid, while the flow guide line on the right side connects to a fluid recovery system for fluid extraction. Specifically, the left flow guide line connects to the specimen via the left pressure plate with a central perforation and the cuboid sleeve, while the right flow guide line connects to the specimen via the right pressure plate with a central perforation and the cuboid sleeve.

[0010] The geostress loading system includes a loading base, a left-side pressure head, a front pressure head, a right-side pressure head, a rear pressure head, and an upper pressure head. The pressure heads, positioned in five directions, are connected to hydraulic cylinders via hydraulic lines. Each hydraulic line is equipped with a safety valve and a pressure gauge. Each pressure head directly presses against the corresponding pressure plate of the sample loading system. The loading base is fixed to the loading base of the sample loading system by four bolts. The hydraulic cylinders are electrically connected to a high-performance computer via transmission cables. The pressure heads are controlled by the opening and closing of each safety valve, thereby achieving graded and alternating loading of triaxial geostress and preventing the specimen from being crushed due to uneven stress during geostress loading.

[0011] The fracturing system includes an active water container, an active water input pipe, an active water constant flow and constant pressure pump, a sand mixing fluid container, a sand mixing fluid input pipe, a sand mixing fluid constant flow and constant pressure pump, a mixed fluid input pipe, a mixing tank, a support frame, a motor, a fracturing fluid constant flow and constant pressure pump, and fracturing pipelines. A fracturing safety valve is installed on the fracturing pipelines. The support frame fixes the mixing tank via a rotating shaft, which is connected to the support frame via a hinged support. The motor is connected to the rotating shaft via a drive shaft, which drives the rotating shaft to rotate, thus causing the mixing tank to reciprocate. The sand mixing fluid container contains a mixture of water and proppant, mixing the proppant (quartz sand, ceramsite, etc.) used in the fracturing process with water so that it can be pumped into the mixing tank using the sand mixing fluid constant flow and constant pressure pump. The active water constant flow and constant pressure pump, the sand mixing fluid constant flow and constant pressure pump, and the fracturing fluid constant flow and constant pressure pump are each electrically connected to a high-performance computer via transmission cables.

[0012] The fluid recovery system includes a liquid recovery module and a gas recovery module. The liquid recovery module includes a flow guide line, a liquid collection bottle, and a liquid metering balance. The flow guide line is equipped with a fluid collection safety valve and a gas-liquid collection pressure gauge. The gas recovery module includes a gas output pipe, a drainage gas collection bottle, a drainage pipe, a drainage container, and a drainage metering balance. The liquid collection bottle is connected to the drainage gas collection bottle through the gas output pipe, and the drainage gas collection bottle is connected to the drainage container through the drainage pipe.

[0013] A fracturing hole is set vertically downward at the center of the top of the specimen. The fracturing line is inserted into the fracturing hole and sealed with high-strength epoxy resin. Before sealing, a certain length of bare hole needs to be left at the bottom of the hole as a fracturing section. After sealing, let it stand at room temperature for 48 hours.

[0014] The in-situ stress loading system applies different in-situ stresses to the specimen, with the maximum in-situ stress along the left-right direction, the minimum in-situ stress along the vertical direction, and the intermediate principal stress along the front-back direction; the in-situ stress loading value in each direction is controlled to achieve graded stable loading of the three-dimensional in-situ stress.

[0015] The fracturing system is used to fracturing the specimen. The active water input pipe and the sand mixing fluid input pipe are connected to the mixed fluid input pipe respectively. The active water in the active water container and the sand mixing fluid in the sand mixing fluid container are input into the mixing tank. After being stirred, the mixed fluid enters the fracturing hole of the specimen through the fracturing pipeline.

[0016] The method of using the above-mentioned in-situ gas-liquid two-phase permeability testing device after hydraulic fracturing includes the following steps:

[0017] S1: Assemble the in-situ testing device for gas-liquid two-phase permeability after hydraulic fracturing;

[0018] S2: Prepare the rock sample specimen to be tested according to the dimensions of the cuboid rubber sleeve;

[0019] S3: Place the specimen inside the cuboid rubber sleeve of the sample loading system, adjust the position of the top rubber sleeve and each pressure plate, and apply ground stress to the specimen through the ground stress loading system;

[0020] S4: Check the airtightness of the entire device;

[0021] S5: Fracturing the specimen using a fracturing system;

[0022] S6: Shut down the fracturing system, start the fluid injection system and fluid recovery system, and conduct a post-fracturing gas-liquid two-phase permeability test;

[0023] S7: Analyze the test data based on the data acquisition and processing system, and calculate the gas-liquid two-phase permeability using the permeability calculation formula.

[0024] The specific implementation steps are described in the examples.

[0025] The beneficial effects of this utility model are:

[0026] (1) This utility model can test the effect of sand content in fracturing fluid on the permeability of specimens after hydraulic fracturing;

[0027] (2) This utility model can measure the gas-liquid two-phase permeability under different lithology, different geostress, different fracturing parameters, and different permeability parameters respectively;

[0028] (3) This utility model can test the permeability before and after hydraulic fracturing respectively, and provide guidance for optimizing hydraulic fracturing construction parameters by comparison;

[0029] (4) This utility model can measure the permeability of gas and liquid phases separately, and can more realistically reflect the nature of gas and liquid phase fluid migration in the unconventional oil and gas drainage stage.

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of this utility model.

[0032] Figure 2 This is a schematic diagram of the fluid injection system of this utility model.

[0033] Figure 3 This is a partial cross-sectional view (front view) of the sample loading system of this utility model.

[0034] Figure 4 This is a left view of the sample loading system of this utility model.

[0035] Figure 5 yes Figure 4 Top view.

[0036] Figure 6 This is a schematic diagram of the ground stress loading system of this utility model.

[0037] Figure 7 This is a schematic diagram of the fracturing system of this utility model.

[0038] Figure 8 This is a schematic diagram of the fluid recovery system of this utility model.

[0039] Figure 9 This is a diagram showing the combination of the various systems of this utility model.

[0040] In the diagram: 1 is the fluid injection system, 2 is the sample loading system, 3 is the geostress loading system, 4 is the fracturing system, 5 is the fluid recovery system, 6 is the data acquisition and processing system, 7 is the diversion pipeline, 8 is the fracturing pipeline, 9 is the rigid pressure head, and 10 is the transmission cable.

[0041] 11 is a liquid storage container, 12 is a liquid guide tube, 13 is a liquid injection constant flow and constant pressure pump, 14 is a liquid guide valve, 15 is a gas storage cylinder, 16 is a gas injection safety valve, 17 is a gas guide tube, 18 is a gas injection constant flow and constant pressure pump, 19 is a gas guide valve, 111 is a three-way valve, 112 is a flow guide valve, and 113 is a flow injection constant flow and constant pressure pump.

[0042] 21 is the specimen, 22 is the fracturing hole, 23 is the left pressure plate, 24 is the right pressure plate, 25 is the top pressure plate, 26 is the loading base, 27 is the cuboid rubber sleeve, 28 is the top rubber sleeve, 29 is the horizontal sliding support, 211 is the bolt, 212 is the rear pressure plate, and 213 is the front pressure plate.

[0043] 31 is the left safety valve, 32 is the front safety valve, 33 is the right safety valve, 34 is the rear safety valve, 35 is the upper safety valve, 36 is the left pressure gauge, 37 is the front pressure gauge, 38 is the right pressure gauge, 39 is the rear pressure gauge, 311 is the upper pressure gauge, 312 is the loading base, 313 is the left hydraulic line, 314 is the front hydraulic line, 315 is the right hydraulic line, 316 is the rear hydraulic line, 317 is the upper hydraulic line, 91 is the left pressure head, 92 is the front pressure head, 93 is the right pressure head, 94 is the rear pressure head, and 95 is the upper pressure head.

[0044] 41 is the active water container, 42 is the sand mixing fluid container, 43 is the active water input pipe, 44 is the sand mixing fluid input pipe, 45 is the active water constant flow and constant pressure pump, 46 is the sand mixing fluid constant flow and constant pressure pump, 47 is the mixed fluid input pipe, 48 is the mixing tank, 49 is the support, 411 is the motor, 412 is the drive shaft, 413 is the rotating shaft, 414 is the hinged support, 415 is the fracturing fluid constant flow and constant pressure pump, and 416 is the fracturing safety valve;

[0045] 51 is a fluid collection safety valve, 52 is a gas output pipe, 53 is a gas-liquid collection pressure gauge, 54 is a drain pipe, 55 is a liquid collection bottle, 56 is a drain gas collection bottle, 57 is a drain container, 58 is a liquid metering balance, and 59 is a drain metering balance. Detailed Implementation

[0046] To make the above-mentioned objectives, features, and advantages of this utility model more apparent and understandable, the technical solution of this utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0047] In the description of this utility model, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model. Example

[0048] like Figure 1-9As shown, an in-situ testing device for gas-liquid two-phase permeability after hydraulic fracturing includes a fluid injection system 1, a sample loading system 2, a ground stress loading system 3, a fracturing system 4, a fluid recovery system 5, and a data acquisition and processing system 6. The fluid injection system 1, sample loading system 2, and fluid recovery system 5 are connected sequentially through a guide pipeline according to the fluid permeation direction. The ground stress loading system 3 applies triaxial ground stress to the specimen 21 in the sample loading system 2 through a rigid pressure head 9. The fracturing system 4 applies injection pressure to the specimen 21 in the sample loading system 2 through a fracturing pipeline 8. The fluid injection system 1, ground stress loading system 3, and fracturing system 4 are electrically connected to the data acquisition and processing system 6 through transmission cables 10. The data acquisition and processing system is a high-performance computer with adjustable parameters, capable of acquiring constant flow and pressure pump flow and pressure, and capable of data analysis programs.

[0049] The fluid injection system 1 includes a liquid injection module and a gas injection module. The liquid injection module includes a liquid storage container 11, a liquid guide tube 12, and a liquid injection constant flow and constant pressure pump 13. The gas injection module includes a gas storage cylinder 15, a gas injection safety valve 16, a gas guide tube 17, and a gas injection constant flow and constant pressure pump 18. The liquid injection module and the gas injection module are connected to the sample loading system 2 via a T-junction 111 and a flow guide line 7. The T-junction 111 is equipped with a liquid guide valve 14, a gas guide valve 19, and a flow guide valve 112. The flow guide line 7 is equipped with a liquid injection constant flow and constant pressure pump 113.

[0050] The sample loading system 2 includes a loading base 26, a cuboid rubber sleeve 27 with a top opening, a top rubber sleeve 28, a left pressure plate 23, a front pressure plate 213, a right pressure plate 24, a rear pressure plate 212, and a top pressure plate 25. The loading base 26 has four bolt holes symmetrically arranged at its four corners for connecting to the ground stress loading system 3 below it. The left pressure plate 23, front pressure plate 213, right pressure plate 24, and rear pressure plate 212 are connected to the loading base 26 via four horizontal sliding supports 29. The cuboid rubber sleeve 27 and the top rubber sleeve 28 are used to wrap and seal the specimen 21, and another purpose is to prevent the specimen from being damaged during ground stress loading. The surface of the specimen is subjected to shear stress due to uneven force. The purpose of the four side pressure plates and the top pressure plate is to uniformly transfer the pressure of the rigid pressure head 9 of the ground stress loading system 3. The specimen 21 is a cuboid structure, and the sample loading system 2 is a left-right symmetrical structure. The guide pipe 7 on the left side of the sample loading system 2 is used to inject fluid, and the guide pipe 7 on the right side is connected to the fluid recovery system 5 to discharge fluid. Specifically, the guide pipe 7 on the left side is connected to the specimen 21 through the left pressure plate 23 with the central perforation and the cuboid rubber sleeve 27, and the guide pipe 7 on the right side is connected to the specimen 21 through the right pressure plate 24 with the central perforation and the cuboid rubber sleeve 27.

[0051] The ground stress loading system 3 includes a loading base 312, a left pressure head 91, a front pressure head 92, a right pressure head 93, a rear pressure head 94, and an upper pressure head 95. The left pressure head 91 is connected to a hydraulic cylinder (not shown in the figure) via a left hydraulic line 313. The left hydraulic line 313 is equipped with a left safety valve 31 and a left pressure gauge 36. The front pressure head 92 is connected to a hydraulic cylinder via a front hydraulic line 314. The front hydraulic line 314 is equipped with a front safety valve 32 and a front pressure gauge 37. The right pressure head 93 is connected to a hydraulic cylinder via a right hydraulic line 315. The right hydraulic line 315 is equipped with a right safety valve 33 and a right pressure gauge 38. The rear pressure head 94 is connected to a hydraulic cylinder via a rear hydraulic line 316. The hydraulic cylinder has a rear safety valve 34 and a rear pressure gauge 39 on the rear hydraulic line 316. The upper pressure head 95 is connected to the hydraulic cylinder through the upper hydraulic line 317, which is equipped with an upper safety valve 35 and an upper pressure gauge 311. The pressure heads in each direction directly press against the corresponding pressure plates of the sample loading system 2. The loading base 312 is fixed to the loading base 26 through the four bolt holes of the sample loading system 2 by four bolts 211. The hydraulic cylinder is electrically connected to the high-performance computer through the transmission cable 10. The pressure heads are controlled by the opening and closing of each safety valve, thereby realizing the graded and alternating loading of ground stress in the vertical, left and right and front and back directions, and avoiding the specimen from being crushed due to uneven force during the ground stress loading process.

[0052] The fracturing system 4 includes an active water container 41, an active water inlet pipe 43, an active water constant flow and constant pressure pump 45, a sand mixing fluid container 42, a sand mixing fluid inlet pipe 44, a sand mixing fluid constant flow and constant pressure pump 46, a mixed fluid inlet pipe 47, a mixing tank 48, a support 49, an electric motor 411, a fracturing fluid constant flow and constant pressure pump 415, and a fracturing pipeline 8. The active water inlet pipe 43 is connected to the active water container 41 and the active water constant flow and constant pressure pump 45, and the sand mixing fluid inlet pipe 8 is connected to the active water container 41 and the active water constant flow and constant pressure pump 45. Pipe 44 is connected to a sand-mixing fluid container 42 and a sand-mixing fluid constant flow and constant pressure pump 46; the mixed fluid input pipe 47 is sequentially connected to a mixing tank 48, a fracturing fluid constant flow and constant pressure pump 415, and a fracturing pipeline 8, with a fracturing safety valve 416 installed on the fracturing pipeline 8; a support 49 fixes the mixing tank 48 via a rotating shaft 413, and the rotating shaft 413 is connected to the support 49 via a hinged support 414; a motor 411 is connected to the rotating shaft 413 via a transmission shaft 412. The fracturing system is used to fracture the specimen. The active water input pipe and the sand-mixing fluid input pipe are respectively connected to the mixed fluid input pipe, inputting the active water in the active water container and the sand-mixing fluid in the sand-mixing fluid container into the mixing tank. After stirring, the mixed fluid enters the fracturing hole of the specimen through the fracturing pipeline. The purpose of connecting the motor drive shaft to the rotating shaft is to drive the rotating shaft to rotate together, thereby causing the mixing tank to reciprocate. The mixing liquid container contains a mixture of water and proppant. The proppant (quartz sand, ceramsite, etc.) used in the fracturing project is mixed with water so that it can be pumped into the mixing tank using a constant flow and constant pressure pump. In this embodiment, quartz sand is used as the proppant.

[0053] The fluid recovery system 5 includes a liquid recovery module and a gas recovery module. The liquid recovery module includes a flow guide line 7, a liquid collection bottle 55, and a liquid metering balance 58. The flow guide line 7 is equipped with a fluid collection safety valve 51 and a gas-liquid collection pressure gauge 53. The gas recovery module includes a gas output pipe 52, a drainage gas collection bottle 56, a drain pipe 54, a drainage container 57, and a drainage metering balance 59. The liquid collection bottle 55 is connected to the drainage gas collection bottle 56 through the gas output pipe 52, and the drainage gas collection bottle 56 is connected to the drainage container 57 through the drain pipe 54.

[0054] The method for in-situ testing of gas-liquid two-phase permeability after hydraulic fracturing using the above-mentioned testing device specifically includes the following testing steps:

[0055] S1: Assemble the in-situ testing device for gas-liquid two-phase permeability after hydraulic fracturing;

[0056] S2: Prepare rock sample specimen 21 to be tested according to the dimensions of the cuboid rubber sleeve 27;

[0057] S3: Place the specimen 21 inside the cuboid rubber sleeve 27 of the sample loading system 2, adjust the position of the top rubber sleeve 28 and each pressure plate, and apply ground stress to the specimen 21 through the ground stress loading system 3;

[0058] S4: Check the airtightness of the entire device;

[0059] S5: Fracturing specimen 21 using fracturing system 4;

[0060] S6: Shut down fracturing system 4, start fluid injection system 1 and fluid recovery system 5, and conduct gas-liquid two-phase permeability test after fracturing;

[0061] S7: Analyze the test data based on the data acquisition and processing system 6, and calculate the gas-liquid two-phase permeability using the permeability calculation formula.

[0062] Step S2 is as follows: According to the size of the cuboid sleeve 27, the block rock sample to be tested is cut into a cuboid specimen 21 using wire cutting technology. A fracturing hole 22 is drilled vertically downward from the center of the top of the specimen using a drilling rig. The fracturing pipeline 8 is inserted into the fracturing hole 22 and sealed with high-strength epoxy resin. Before sealing, a certain length of bare hole needs to be reserved at the bottom of the fracturing hole as a fracturing section. After sealing, it is left to stand at room temperature for 48 hours.

[0063] Step S3 specifically involves placing the specimen 21 inside the cuboid sleeve 27 of the sample loading system 2, and sequentially covering the upper surface of the specimen 21 with a top sleeve 28 and a top pressure plate 25. Simultaneously, the left pressure plate 23, front pressure plate 213, right pressure plate 24, and rear pressure plate 212 are pre-contacted with the cuboid sleeve 27 containing the specimen 21, and the four bolts 211 are tightened to fix the sample loading system 2 onto the loading base 312. The designed stress distribution scheme is as follows: maximum stress along the left-right direction, minimum stress along the vertical direction, and the central principal stress along the front-back direction. Then, the left safety valve 31, front safety valve 32, right safety valve 33, rear safety valve 34, and upper safety valve 35 are opened. The hydraulic cylinders are started via a high-performance computer, and the left pressure head 91, front pressure head 92, right pressure head 93, rear pressure head 94, and upper pressure head 95 are simultaneously loaded at the same rate. The left pressure plate 23, front pressure plate 213, right pressure plate 24, rear pressure plate 212, and top pressure plate 25 are pressurized to the minimum ground stress value (the ground stress loading value is read from the pressure gauges of the ground stress loading system). The pressure is stabilized for 10 minutes and the upper safety valve 35 is closed. Then, the left pressure plate 23, front pressure plate 213, right pressure plate 24, and rear pressure plate 212 are pressurized to the intermediate ground stress value at the same rate through the left pressure head 91, front pressure head 92, right pressure head 93, and rear pressure head 94. The pressure is stabilized for 10 minutes and the front safety valve 32 and rear safety valve 34 are closed. Finally, the left pressure plate 23 and right pressure plate 24 are pressurized to the maximum ground stress value at the same rate through the left pressure head 91 and right pressure head 93. The pressure is stabilized for 30 minutes and the left safety valve 31 and right safety valve 33 are closed, thus achieving graded and stable loading of the three-dimensional ground stress.

[0064] Step S4 specifically involves: opening the gas injection safety valve 16, the gas injection constant flow and constant pressure pump 18, the gas guide valve 19, the flow guide valve 112, the gas injection constant flow and constant pressure pump 113, and the fluid collection safety valve 51; setting the gas injection constant flow and constant pressure pump 18 to constant pressure mode, that is, injecting gas into the sample specimen 21 at a constant pressure for 24 hours; then reading the pressure of the recovered fluid through the gas-liquid collection pressure gauge 53; if the reading of the gas-liquid collection pressure gauge 53 remains stable, it indicates that the overall device has good airtightness.

[0065] Step S5 specifically involves: closing the air injection safety valve 16, the air injection constant flow and constant pressure pump 18, the air guide valve 19, the flow guide valve 112, the injection constant flow and constant pressure pump 113, and the fluid collection safety valve 51; clearing the air pressure, drainage, and readings of each metering balance generated in the fluid recovery system 5 in step S4; then opening the activated water constant flow and constant pressure pump 45 and the sand mixing liquid constant flow and constant pressure pump 46; injecting the activated water in the activated water container 41 and the sand mixing liquid in the sand mixing liquid container 42 into the mixing tank 48 in a certain proportion; closing the activated water constant flow and constant pressure pump 45 and the sand mixing liquid constant flow and constant pressure pump 46; starting the motor 411; and moving the mixing tank 48... The active water and sand-mixing liquid inside are stirred evenly to prepare a fracturing fluid with a certain sand content. Then, the fracturing safety valve 416 and the fracturing fluid constant flow and constant pressure pump 415 are opened to inject the fracturing fluid into the fracturing specimen 21 in constant flow mode. After the injection pressure suddenly drops, the fracturing fluid constant flow and constant pressure pump 415 and the fracturing safety valve 416 are immediately closed to stop fracturing. If no fracturing fluid seeps out of the top rubber sleeve 28 after the pressure is completed, it indicates that the sample loading system 2 is well sealed after pressure. Otherwise, the high-strength epoxy resin glue around the top rubber sleeve 28 needs to be cast to reseal it and the airtightness of the device needs to be checked again to ensure that there is no leakage of air and water during the subsequent permeability test.

[0066] Step S6 specifically involves: opening the gas injection safety valve 16, the liquid guiding valve 14, the gas guiding valve 19, the flow guiding valve 112, and the fluid collection safety valve 51, and then sequentially opening the liquid injection constant pressure pump 13, the gas injection constant pressure pump 18, and the injection constant pressure pump 113 to begin the gas-liquid two-phase permeability test after hydraulic fracturing. Once the reading on the gas-liquid collection pressure gauge 53 stabilizes, data recording begins, and the gas-water injection pressure reading of the injection constant pressure pump 113 is directly read by a high-performance computer. p 1. Read the pressure reading of the recovered fluid from the gas-liquid collection pressure gauge 53. p 2. The liquid seepage mass is read from the liquid metering balance 58. m l The drainage mass is read from the drainage metering balance 59. m w Meanwhile, the seepage time is recorded by a high-performance computer. t .

[0067] Step S7 specifically involves: based on the data obtained in step S6, and using the cubic law, calculating the permeability of liquid and gas in the hydraulic fracture, respectively. The specific calculation method is as follows:

[0068] Liquid permeation rate Q l The calculation is as follows:

[0069] (1)

[0070] Gas permeation velocity Q g The calculation is as follows:

[0071] (2)

[0072] The liquid permeability can then be obtained from the cubic law. k l as follows:

[0073] (3)

[0074] Gas permeability k g as follows:

[0075] (4)

[0076] Substituting the test data into the above formulas (1) to (4) yields the liquid permeability and gas permeability during gas-water two-phase flow after fracturing. The physical meanings of the parameters in the above formulas are as follows: ρ l For the density of the liquid, ρ w The density of water, μ l For the dynamic viscosity of the liquid, μ g For gas dynamic viscosity, L This refers to the seepage path length, i.e., the length of specimen 21; p 0 represents atmospheric pressure. w The equivalent width of the hydraulic fracture is determined as follows: After the gas-water two-phase permeation test is completed, specimen 21 is removed, and the upper and lower surfaces of the hydraulic fracture are scanned using a 3D topography scanner to obtain topography point clouds. Based on the point cloud... x , y , z ) Coordinate calculation for each ( x , y )of z The difference in coordinates represents the hydraulic crack opening at that location. By integrating the hydraulic crack opening at each point along the entire length of specimen 21 and taking the average, the equivalent width of the hydraulic crack can be obtained. w .

[0077] The above embodiments are only used to illustrate and not limit the technical solutions of this utility model. Although the utility model has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the utility model without departing from the spirit and scope of the utility model. Any modifications or partial substitutions should be covered within the scope of the claims of this utility model.

Claims

1. A device for in-situ testing of gas-liquid two-phase permeability after hydraulic fracturing, characterized in that: The system comprises a fluid injection system, a sample loading system, a ground stress loading system, a fracturing system, a fluid recovery system, and a data acquisition and processing system; the sample loading system is loaded with a test piece; the fluid injection system, the sample loading system, and the fluid recovery system are sequentially connected through a flow guide pipeline in the direction of fluid seepage of the permeability test fluid; the ground stress loading system is connected with the sample loading system through a rigid pressure head; the test piece in the sample loading system is subjected to three-way ground stress; the fracturing system is connected with the sample loading system through a fracturing pipeline to apply liquid injection pressure to the test piece in the sample loading system; the fluid injection system, the ground stress loading system, and the fracturing system are respectively connected with the data acquisition and processing system through a transmission cable.

2. The hydraulic fracturing post-frac gas-liquid two-phase permeability in-situ testing apparatus of claim 1, wherein: The fluid injection system comprises a liquid injection module and a gas injection module; the liquid injection module comprises a liquid storage container, a liquid guide pipe, and a liquid injection constant-flow constant-pressure pump; the gas injection module comprises a gas storage cylinder, a gas injection safety valve, a gas guide pipe, and a gas injection constant-flow constant-pressure pump; the liquid injection module and the gas injection module are respectively connected with the sample loading system through the liquid guide pipe and the gas guide pipe, a tee joint, and the flow guide pipeline; the flow guide pipeline is provided with a flow injection constant-flow constant-pressure pump; the tee joint is respectively provided with a liquid guide valve, a gas guide valve, and a flow guide valve.

3. The apparatus of claim 1, wherein: The sample loading system comprises a loading base, a rectangular cuboid rubber sleeve with an open top, a top rubber sleeve, a left side pressing plate, a front side pressing plate, a right side pressing plate, a rear side pressing plate, and a top pressing plate; the loading base is symmetrically provided with four bolt holes at four corners for connecting the ground stress loading system below; the left side pressing plate, the front side pressing plate, the right side pressing plate, and the rear side pressing plate are respectively connected with the loading base through four horizontal sliding supports; the rectangular cuboid rubber sleeve and the top rubber sleeve are used to wrap and seal the test piece; another purpose is to avoid shear stress generated on the surface of the test piece due to uneven stress during the ground stress loading process; the pressing plates are used to uniformly transmit the pressure of the pressure head of the ground stress loading system; specifically, the test piece has a rectangular cuboid structure; the sample loading system has a left-right symmetric structure; the flow guide pipeline on the left side of the sample loading system is used for injecting fluid; the flow guide pipeline on the right side is connected with the fluid recovery system for guiding fluid out; specifically, the flow guide pipeline on the left side is connected with the test piece through the left side pressing plate and the rectangular cuboid rubber sleeve with a central hole; the flow guide pipeline on the right side is connected with the test piece through the right side pressing plate and the rectangular cuboid rubber sleeve with a central hole.

4. The apparatus of claim 1, wherein: The ground stress loading system comprises a loading base, a left side pressure head, a front side pressure head, a right side pressure head, a rear side pressure head, and an upper pressure head; the pressure heads in the five directions are connected with hydraulic oil cylinders through hydraulic pipelines; a safety valve and a pressure gauge are arranged on each hydraulic pipeline; the pressure heads in each direction directly press the corresponding pressing plates of the sample loading system; the loading base is connected with the loading base of the sample loading system through four bolts; the hydraulic oil cylinders are electrically connected with the data acquisition and processing system through a transmission cable; the pressure heads are controlled through the opening and closing of the safety valves, thereby achieving the step-by-step and alternate loading of the three-way ground stress and avoiding the crushing of the test piece due to uneven stress during the ground stress loading process.

5. The hydraulic fracturing post-frac gas-liquid two-phase permeability in-situ testing apparatus of claim 4, wherein: The ground stress loading system applies different ground stresses to the test piece, the maximum ground stress is along the left-right direction, the minimum ground stress is along the vertical direction, and the intermediate principal stress is along the front-back direction; the ground stress loading value in each direction is controlled respectively to realize the step-by-step stable loading of three-directional ground stress.

6. The apparatus of claim 1, wherein: The fracturing system comprises an active water container, an active water input pipe, an active water constant-flow constant-pressure pump, a sand mixing liquid container, a sand mixing liquid input pipe, a sand mixing liquid constant-flow constant-pressure pump, a mixed liquid input pipe, a stirring box, a support, a motor, a fracturing liquid constant-flow constant-pressure pump and a fracturing pipeline, wherein a fracturing safety valve is arranged on the fracturing pipeline, the support fixes the stirring box through a rotating shaft, the rotating shaft is connected with the support through a hinged support, the motor is connected with the rotating shaft through a transmission shaft, and the motor transmission shaft is connected with the rotating shaft to drive the rotating shaft to rotate, so that the stirring box reciprocatingly stirs; the sand mixing liquid container contains a mixed liquid of water and proppant; the active water constant-flow constant-pressure pump, the sand mixing liquid constant-flow constant-pressure pump and the fracturing liquid constant-flow constant-pressure pump are electrically connected with a data acquisition and processing system through transmission cables.

7. The hydraulic fracturing post-frac gas-liquid two-phase permeability in-situ testing apparatus of claim 6, wherein: A fracturing hole is vertically arranged downward at the center of the top of the test piece, the fracturing pipeline is inserted into the fracturing hole and sealed with high-strength epoxy resin glue, and a certain length of bare hole is reserved at the bottom of the hole as a fracturing section before sealing, and the test piece is statically placed at room temperature for 48 hours after sealing.

8. The hydraulic fracturing post-frac gas-liquid two-phase permeability in-situ testing apparatus of claim 6, wherein: The fracturing system is used for fracturing the test piece, the active water input pipe and the sand mixing liquid input pipe are connected with the mixed liquid input pipe, the active water in the active water container and the sand mixing liquid in the sand mixing liquid container are input into the stirring box, and the mixed liquid is stirred and then enters the test piece fracturing hole through the fracturing pipeline.

9. The apparatus of claim 1, wherein: The fluid recovery system comprises a liquid recovery module and a gas recovery module, the liquid recovery module comprises a flow guide pipeline, a liquid collection bottle and a liquid metering balance, the flow guide pipeline is provided with a fluid collection safety valve and a gas-liquid collection pressure gauge, the gas recovery module comprises a gas output pipe, a drainage gas collection bottle, a drainage pipe, a drainage container and a drainage metering balance, the liquid collection bottle is connected with the drainage gas collection bottle through the gas output pipe, and the drainage gas collection bottle is connected with the drainage container through the drainage pipe.

10. The apparatus of claim 1, wherein: The data acquisition and processing system is a high-performance computer with adjustable parameters, constant-flow constant-pressure pump flow and pressure acquisition and data analysis program, which can realize real-time adjustment and acquisition of fluid injection parameters, ground stress parameters, fracturing parameters and fluid recovery parameters.

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