A test method for proppant migration caused by gas extraction after hydraulic sand fracturing

Abstract

The present invention discloses a test method for proppant migration caused by gas extraction after hydraulic sand fracturing. The test device includes an injection assembly, a fracture assembly, a fixing assembly, and a negative pressure extraction assembly. The injection assembly is used to inject fracturing fluid containing proppant into the fracture assembly. The fracture assembly is used to simulate the reaction of rock with fractures after the injection of the fluid. The fixing assembly not only supports and fixes the fracture assembly but also adjusts the inclination angle of the fracture assembly. The negative pressure extraction assembly is used to simulate the gas extraction process. The test method also includes the following steps: S1: test preparation; S2: load application; S3: fracturing; S4: fracturing completion; S5: negative pressure extraction; and S6: repeating the test. The test method realistically simulates proppant migration caused by negative pressure extraction of gas after hydraulic fracturing to increase the permeability of the coal seam, thereby providing a basis for the state of cracks in the coal seam after hydraulic fracturing and negative pressure extraction of gas, and for repeating hydraulic fracturing.

Description

Technical Field

[0001] The invention belongs to the technical field of coal seam hydraulic fracturing and permeability enhancement gas extraction, and particularly relates to a test method for proppant migration caused by gas extraction after hydraulic sand fracturing. Background Art

[0002] Hydraulic fracturing, a primary method for increasing oil and gas well production, has been widely used in surface coalbed methane (CBM) development and, in recent years, has also begun to be applied underground in coal mines. Hydraulic fracturing of coal rock can achieve widespread decompression, increase coal rock permeability, improve gas extraction efficiency, release coal seam gas pressure, and modify the physical and mechanical properties of the coal, thereby reducing the risk of coal and gas outbursts. This approach also assists in gas management in coal seams with low permeability and unprotected seams. Conventional hydraulic fracturing methods for increasing coal seam permeability suffer from shortcomings such as uneven fracturing, low fracturing rates, limited fracturing coverage, and easy fracture closure. Hydraulic sand fracturing is often used to maintain the continuous opening of coal rock fractures to achieve both permeability enhancement and gas extraction. However, existing research focuses primarily on the migration and placement of proppants in coal rock before and during hydraulic sand fracturing. However, limited research has examined the migration and placement of proppants after hydraulic sand fracturing, particularly during negative pressure gas extraction. Summary of the Invention

[0003] The present invention intends to provide a test method for proppant migration caused by gas extraction after hydraulic sand fracturing, which truly simulates the situation where proppant migration is caused by gas negative pressure extraction after hydraulic fracturing of coal seam permeability enhancement, thereby providing a basis for the state of cracks appearing in the coal seam after hydraulic fracturing of coal seam permeability enhancement and gas negative pressure extraction, and for re-hydraulic fracturing.

[0004] To this end, the technical solution adopted by the present invention is: a test method for proppant migration caused by gas extraction after hydraulic sand fracturing, including a test device, the test device including an injection component, a fracture component, a fixing component and a negative pressure extraction component, the injection component is used to inject fracturing fluid with proppant into the fracture component, the fracture component is used to simulate the reaction of rock with fractures after liquid injection, the fixing component can not only realize the support and fixation of the fracture component, but also adjust the inclination angle of the fracture component, and the negative pressure extraction component is used to simulate the gas extraction process; the fracture component includes an upper fracture plate and a lower fracture plate arranged relatively to each other, the left ends of the upper fracture plate and the lower fracture plate are extended forward and backward with notches for fracturing fluid injection, the upper fracture plate can move up and down, and the upper fracture plate is loaded with a normal load from the fixing component, the lower fracture plate can move left and right, and the lower fracture plate is loaded with a tangential load from the fixing component;

[0005] The following test steps are also included:

[0006] S1: Test preparation: Connect all parts of the test device completely, check that they are correct, and then load the injection assembly with the predetermined proppant and fracturing fluid;

[0007] S2: Load application: applying a predetermined normal load to the upper crack plate and a predetermined tangential load to the lower crack plate through the fixing assembly, while making the crack assembly reach a predetermined inclination and tilt;

[0008] S3: Perform fracturing; start the injection assembly to inject the fracturing fluid with proppant into the gap between the upper fracture plate and the lower fracture plate at a predetermined rate;

[0009] S4: completing the fracturing; when the injection time of the fracturing fluid with proppant reaches a predetermined time, the injection is stopped, and the distribution position of the proppant when the fracturing fluid with proppant stops moving between the upper fracture plate and the lower fracture plate is recorded;

[0010] S5: Negative pressure extraction: Start the negative pressure extraction component and conduct a negative pressure extraction simulation. At the same time, record the secondary migration and placement of the proppant, the vertical displacement of the upper fracture plate, and the horizontal displacement of the lower fracture plate during the entire extraction process.

[0011] S6: Repeat the test; clean the fracturing fluid and proppant in the test device to restore the test device to its initial state, and then repeat steps S3-S5 after changing different extraction negative pressures to obtain the migration pattern of the proppant in the fracturing fluid with proppant during the negative pressure extraction process after fracturing.

[0012] As a preferred embodiment of the above scheme, the fixing assembly includes a lower pressure plate arranged below the lower crack plate, a height-adjustable support assembly is arranged below the lower pressure plate, an upper pressure plate is arranged above the lower pressure plate through support bolts, the upper pressure plate is located above the upper crack plate, and a number of normal load springs are arranged between the upper pressure plate and the upper crack plate, a row of tightening bolts that can be pressed against the right side of the upper crack plate are arranged on the right side of the lower pressure plate, and a tangential load assembly for simulating the tangential load when the lower crack plate moves to the right is also arranged on the right side of the lower pressure plate.

[0013] Further preferably, the tangential load assembly includes a tangential load spring, one end of the tangential load spring is against the right side surface of the lower crack plate, and the other end of the tangential load spring is sleeved on the guide column located between the lower pressure plate and the lower crack plate, and a distance is left between the guide column and the lower crack plate.

[0014] Further preferably, the support assembly includes four support rods arranged between the lower pressure plate and the ground and distributed in a rectangular shape, the support rods including a fixed sleeve, a telescopic rod that can move up and down in the fixed sleeve is arranged in the fixed sleeve, a fastening sleeve is arranged outside the telescopic rod, the lower end of the fastening sleeve is provided with an internal thread, the outer side of the upper end of the fixed sleeve is provided with an external thread matching the internal thread, a rubber tube is provided between the fastening sleeve and the telescopic rod, and a gasket is provided between the upper end of the rubber tube and the upper end of the fastening sleeve. When the fastening sleeve is tightened on the fixed sleeve, the rubber tube will be squeezed, thereby fixing the length of the telescopic rod.

[0015] Further preferably, the lower pressure plate is a rectangular plate, the support rod is arranged at the four corners of the lower pressure plate, and two relatively arranged clamps are provided at the upper and lower ends of the support rod, and spherical grooves are provided in the clamps. Ball head bolts fixed to the ground are clamped in the two spherical grooves at the lower end, and ball head clamps that can be fixed at the corners of the lower pressure plate are clamped in the two spherical grooves at the upper end.

[0016] Further preferably, the injection assembly includes a fracturing fluid tank set on the ground through a support column, an injection pipe is provided on the fracturing fluid tank, the end of the injection pipe is set parallel to the notch, and a plurality of liquid outlet holes for injecting liquid into the notch are provided, the injection pipe is provided with a water pump that can drive the flow of liquid, and the injection pipe is also provided with a proppant injection pipe for adding proppant into the injection pipe, the upper end of the proppant injection pipe is provided with a proppant adding assembly for quantitatively adding proppant to the liquid in the injection pipe, and the end of the injection pipe is provided with an injection fixed pipe that can be fixed at the left end of the fixed assembly and is used to ensure that the liquid in the injection pipe is injected into the notch.

[0017] Further preferably, the proppant adding assembly includes a proppant storage tank, and a proppant screw conveyor is provided at the lower end of the proppant storage tank, one end of the proppant screw conveyor is connected to the lower end of the proppant storage tank, and the other end is connected to the upper end of the proppant injection pipe.

[0018] It is further preferred that the right end of the liquid injection fixed tube is provided with a rectangular groove for the upper and lower crack plates to extend into, and the upper crack plate can move up and down in the rectangular groove, and a sealing ridge extending forward and backward is inserted above the left end of the upper crack plate, and the upper end of the sealing ridge is covered with a circle of upper and lower sealing rings, and the upper wall surface of the rectangular groove is upwardly provided with a sealing strip groove for the sealing strip to be inserted and can move up and down, and the upper and lower sealing rings are located in the sealing strip groove, and the front and rear side walls of the rectangular groove are provided with a clamping strip for ensuring that the lower crack plate is in close contact with the lower wall surface of the rectangular groove, the lower end of the clamping strip is in contact with the upper end of the lower crack plate, and the upper end of the clamping strip is pressed against the upper crack plate through a micro spring.

[0019] Further preferably, the front and rear sides of the top surface of the lower slit plate are both provided with left and right extending protrusions, the upper ends of the protrusions are covered with left and right sealing rings, and the bottom surface of the upper slit plate is provided with sealing grooves at positions corresponding to the protrusions, and the left and right sealing rings are located in the sealing grooves.

[0020] Further preferably, a bottom plate located in the fixed assembly is provided below the lower slit plate, and a plurality of rollers extending forward and backward are provided on the bottom plate at intervals on the left and right sides.

[0021] The beneficial effects of the present invention are: it truly simulates the situation in which proppant migration is caused by negative pressure extraction of gas after hydraulic fracturing to increase the permeability of the coal seam, thereby providing a basis for the state of cracks appearing in the coal seam after hydraulic fracturing to increase the permeability of the coal seam and after negative pressure extraction of gas, and for re-hydraulic fracturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Flowchart of the present invention.

[0023] Figure 2 A three-dimensional schematic diagram of the test device in the present invention Figure 1 .

[0024] Figure 3 A three-dimensional schematic diagram of the test device in the present invention Figure 2 .

[0025] Figure 4 Schematic diagram of the structure of the test device in the present invention.

[0026] Figure 5 for Figure 4 Left view of .

[0027] Figure 6 Schematic diagram of the support rod in the present invention.

[0028] Figure 7 Schematic diagram of the liquid injection fixed tube in the present invention.

[0029] Figure 8 for Figure 4 Enlarged view of N in the figure.

[0030] Figure 9 for Figure 2 Enlarged view of M in the middle. DETAILED DESCRIPTION

[0031] The present invention will be further described below by way of examples and in conjunction with the accompanying drawings:

[0032] like Figures 1-9As shown, a test device for controlling the directional movement of proppants by varying the density of the fracturing fluid is mainly composed of an injection component A, a fracture component B, a fixing component C and a negative pressure extraction component, wherein the injection component A is used to inject the fracturing fluid with proppant into the fracture component B, the fracture component B is used to simulate the reaction of the rock mass with fractures after the injection of the liquid, the fixing component C can not only realize the support and fixation of the fracture component, but also adjust the inclination angle of the fracture component, and the negative pressure extraction component is used to simulate the gas extraction process, so that the device can realize the seepage test of the fracturing fluid with proppant in fractures with different inclinations or dips. At the same time, by loading the normal load on the upper fracture plate and the tangential load on the lower fracture plate, the device will cause the upper and lower fracture plates to move when the fracturing fluid seeps, so that the stress conditions of the upper and lower fracture plates can change with the movement of the corresponding plates. Therefore, the application not only simulates the initial stress field during seepage, but also simulates the stress change during the seepage process, so that the application can truly simulate the seepage of the fracturing fluid with proppant in the fracture.

[0033] The specific structure of the fracture assembly B includes an upper fracture plate 1 and a lower fracture plate 2 arranged relatively to each other in the upper and lower directions. Notches for fracturing fluid injection are extended forward and backward at the left ends of the upper fracture plate 1 and the lower fracture plate 2. The upper fracture plate 1 can move up and down, and is loaded with a normal load from the fixed assembly. The lower fracture plate 2 can move left and right, and is loaded with a tangential load from the fixed assembly.

[0034] The specific structure of the fixing assembly C includes a lower pressure plate 3 arranged below the lower crack plate 2, and a height-adjustable support assembly is arranged below the lower pressure plate 3. An upper pressure plate 4 is arranged above the lower pressure plate 3 through a support bolt 5, and the upper pressure plate 4 is located above the upper crack plate 1. In order to realize the loading of the normal load on the upper crack plate, a number of normal load springs 6 are arranged between the upper pressure plate 4 and the upper crack plate 1, and the normal load springs can be set in different numbers and springs of different specifications as needed. In this embodiment, 18 normal load springs are evenly arranged between the upper pressure plate 4 and the upper crack plate 1. In order to prevent the upper crack plate from moving left and right, a row of tightening bolts 7 that can be pressed against the right side of the upper crack plate 1 are arranged on the right side of the lower pressure plate 3.

[0035] At the same time, in order to facilitate the lower crack plate to have an initial tangential load when moving left and right, a tangential load assembly is also provided on the right side of the lower pressure plate 3 for simulating the tangential load when the lower crack plate 2 moves to the right. The specific structure of the tangential load assembly includes a tangential load spring 8, and one end of the tangential load spring 8 is against the right side of the lower crack plate 2, and the other end of the tangential load spring 8 is sleeved on the guide column 9 between the lower pressure plate 3 and the lower crack plate 2. At the same time, to ensure that the lower crack plate can move left and right, a distance is left between the guide column 9 and the lower crack plate 2. In order to facilitate the change of the distance between the guide column and the lower crack plate, the guide column and the bolt extending from the right end of the lower pressure plate to the left, and in order to realize the compression of the tangential load spring, a nut for adjusting the compression amount of the tangential load spring can also be provided on the bolt.

[0036] The support assembly comprises four support rods 10 arranged in a rectangular pattern between the lower bearing plate 3 and the ground. The distance between the lower ends of the four support rods is greater than the distance between their upper ends, meaning the rods are tilted inward and supported on the lower bearing plate. Adjusting the four support rods at different heights allows the fracture assembly to be adjusted to any angle between 0 and 90 degrees relative to the ground. To achieve telescopic adjustment, the support rods 10 include fixed sleeves 10a, within which is located a telescopic rod 10b capable of moving up and down within the sleeve. To secure the telescopic rod after extension and retraction, a tightening sleeve 10c is fitted over the telescopic rod 10b. The lower end of the tightening sleeve 10c has an internal thread, and the upper end of the fixed sleeve 10a has a corresponding external thread that matches the internal thread. A rubber tube 10d is installed between the tightening sleeve 10c and the telescopic rod 10b. When the tightening sleeve 10c is tightened onto the fixed sleeve 10a, it squeezes the rubber tube 10d, thereby fixing the length of the telescopic rod 10b. To prevent the upper end of the tightening sleeve from rubbing against the rubber tube, a gasket 10e is placed between the upper ends of the rubber tube 10d and the upper ends of the tightening sleeve 10c.

[0037] In this embodiment, the lower pressure plate 3 is a rectangular plate, and the support rod 10 is arranged at the four corners of the lower pressure plate 3. In order to realize the installation of the support rod, two relatively arranged clamps 11 are provided at the upper and lower ends of the support rod 10, and the clamps at the upper and lower ends are staggered. A spherical groove 11a is provided in the clamp 11, and a ball head bolt 12 fixed to the ground is clamped in the two spherical grooves 11a at the lower end. A ball head clamping member 13 that can be fixed at the corners of the lower pressure plate 3 is clamped in the two spherical grooves 11a at the upper end. The ball head clamping member 13 includes two clamping supports 13a, and the two clamping supports 13a are respectively fixed on any side surface forming the corner of the lower pressure plate 3, and the two clamping supports 13a are fixed to each other. In order to realize the function of the clamping support, the clamping support 13a includes a ball head located in the spherical groove and a fixing part fixed on the lower pressure plate, and the fixing part and the ball head are connected by a connecting part. The connecting part includes a first connecting part for fixing the two clamping supports 13a to each other and a second connecting part extending along the first connecting part. The ball head is arranged on the end of the second connecting part.

[0038] The specific structure of the injection assembly A includes a fracturing fluid tank 15 mounted on the ground via a support column 14. An injection pipe 16 is provided on the fracturing fluid tank 15. The end of the injection pipe 16 is arranged parallel to the notch and is provided with multiple outlet holes for injecting liquid into the notch. To facilitate the flow of liquid in the injection pipe, a water pump 17 is provided on the injection pipe 16. To enable the addition of proppant, a proppant injection pipe 18 is also provided on the injection pipe 16. At the same time, a proppant addition assembly is provided at the upper end of the proppant injection pipe 18 for quantitatively adding proppant to the liquid in the injection pipe. To ensure that the liquid in the injection pipe 16 can be accurately injected into the notch, an injection fixed pipe 19 is provided at the end of the injection pipe 16 and is fixed to the left end of the fixed assembly. Preferably, the upper end of the injection fixed pipe is fixed to the upper pressure plate by bolts, and the lower end of the injection fixed pipe is fixed to the lower pressure plate by bolts.

[0039] The above-mentioned proppant adding assembly includes a proppant storage tank 20, and a proppant screw conveyor 21 is provided at the lower end of the proppant storage tank 20, that is, one end of the proppant screw conveyor 21 is connected to the lower end of the proppant storage tank 20, and the other end is connected to the upper end of the proppant injection pipe 18, so that a fixed amount of proppant is added to a certain amount of liquid through the proppant screw conveyor.

[0040] The negative pressure extraction component D includes a negative pressure pump 25, a tee 26 is arranged between the injection pipe and the injection fixed pipe, and the other end of the tee is provided with a negative pressure pipe 27 connected to the negative pressure pump, and one end of the tee connected to the injection pipe and the other end of the tee connected to the negative pressure pipe are both provided with valves for realizing switching, and a pressure gauge for measuring the negative pressure on the negative pressure pipe is provided on the negative pressure pipe.

[0041] Since a liquid injection fixing tube is provided at the end of the liquid injection tube, to ensure sealing during liquid injection, a rectangular groove 19a for the upper and lower slit plates 1 and 2 to extend into is provided at the right end of the liquid injection fixing tube 19, and the upper slit plate 1 can move up and down within the rectangular groove 19a. To ensure sealing between the upper end of the upper slit plate and the rectangular groove when the upper slit plate moves up and down, a sealing ridge 1a extending forward and backward is inserted above the left end of the upper slit plate 1, and the upper end of the sealing ridge 1a is covered with a circle of upper and lower sealing rings. At the same time, a sealing strip groove 19b for the sealing ridge 1a to be inserted into and capable of moving up and down is provided on the upper wall surface of the rectangular groove 19a, and the upper and lower sealing rings are always located in the sealing strip groove 19b. In this embodiment, a positioning protrusion 1c is provided near the left end of the upper slit plate. After installation, the left side of the positioning protrusion just rests against the right side of the liquid injection fixing tube, thereby preventing the tightening bolt from over-pressing the upper and lower sealing rings during installation, thereby causing the upper slit plate to be unable to move up and down normally.

[0042] In order to ensure the sealing between the lower end of the lower crack plate and the rectangular groove, a clamping strip 22 is provided on the front and rear side walls of the rectangular groove 19a to ensure that the lower crack plate 2 is in close contact with the lower wall surface of the rectangular groove 19a. The lower end of the clamping strip 22 is in contact with the upper end of the lower crack plate, and the upper end of the clamping strip 22 is pressed against the upper crack plate 1 through the micro spring 23. The compressed micro spring ensures that the lower end of the lower crack plate is always in contact with the lower inner wall of the rectangular groove.

[0043] In order to ensure the sealing between the front and rear sides of the upper and lower crack plates, left and right extending protrusions 2a are provided on the front and rear sides of the top surface of the lower crack plate 2. At the same time, a sealing groove 1b is provided on the bottom surface of the upper crack plate 1 at the position corresponding to the protrusion 2a. Left and right sealing rings are arranged on the upper ends of the protrusions 2a, and the left and right sealing rings are always located in the sealing grooves.

[0044] In this embodiment, the clip is designed in a door-like shape, and a small recess is provided at the upper end of the clip, corresponding to the location where the microspring is installed. Since the lower slit plate can move to the right, to facilitate the fixing of the clip, clip grooves for the clip are provided vertically on the left and right sidewalls of the rectangular groove. At the same time, an extension section that snaps into the clip groove is provided horizontally at either end of the clip. To facilitate the processing of the sealing strip groove and the two clip grooves, a circle of grooves is provided within the rectangular groove. The sealing strip groove is located on the upper inner wall of the rectangular groove, and the clip grooves are located on the front and rear inner walls of the rectangular groove. To ensure sealing, both the clip groove and the groove on the lower inner wall of the rectangular groove are filled with a sealing strip, and the cross-section of the sealing strip is circular.

[0045] In order to reduce the friction when the lower crack plate moves to the right, a bottom plate 24 located in the fixed component is provided below the lower crack plate 2. At the same time, a number of rollers 24a extending forward and backward are provided on the bottom plate 24 at intervals on the left and right, and the upper ends of the rollers are in contact with the bottom surface of the lower crack plate.

[0046] To better observe the movement of the proppant-laden fracturing fluid, the upper and lower pressure plates are made of transparent materials, such as plexiglass, and the device is preferably equipped with a high-speed camera. To facilitate the recovery of the fracturing fluid, a fracturing groove 3a is provided within the lower pressure plate. Both the upper and lower fracture plates are located within the fracturing groove. A collection groove 3b is provided at the right end of the fracturing groove, and the collection groove is connected to the outside world via a collection pipe. A pressure gauge and flow meter are provided at the end of the injection pipe, and a strain gauge sensor for measuring stress is provided between each spring and the fracture plate.

[0047] Based on the above test device, a test method for proppant migration caused by gas extraction after hydraulic sand fracturing includes the following test steps:

[0048] Step 1: Test preparation: Connect all parts of the test device completely. After checking that everything is correct, fill the proppant into the proppant storage tank in the injection assembly and fill the fracturing fluid into the fracturing box.

[0049] Step 2: Load application; apply a predetermined normal load to the upper crack plate and a predetermined tangential load to the lower crack plate through the fixing assembly, and at the same time make the crack assembly reach a predetermined inclination and tendency. Specifically, by twisting the support bolts, the normal load spring is compressed so that the normal load on the upper crack plate reaches a predetermined value, and the normal load is the elastic force of all normal load springs. By changing the distance between the fixing column and the diameter of the lower crack plate, the compression amount of the tangential load spring is changed, so that the tangential load on the lower crack plate reaches a predetermined value, and the normal load is the elastic force of all tangential load springs. By adjusting the height of the four support rods, the crack assembly can reach a predetermined inclination and tendency, that is, the crack surface between the upper crack plate and the lower crack plate reaches a predetermined inclination and tendency.

[0050] Step 3: Perform fracturing; open the valve on the tee pipe connected to the injection pipe, then start the water pump and proppant screw conveyor, mix the fracturing fluid and proppant, and inject them into the gap between the upper and lower fracture plates at a predetermined rate.

[0051] Step 4: Complete fracturing; when the injection time of the fracturing fluid with proppant reaches the predetermined time, stop the injection, that is, close the valve on the tee pipe connected to the injection pipe, and at the same time close the water pump and the proppant screw conveyor, and record the distribution position of the proppant when the fracturing fluid with proppant stops moving between the upper fracture plate and the lower fracture plate.

[0052] Step 5: Negative pressure extraction; simulate negative pressure extraction, that is, set the negative pressure of the negative pressure pump, then open the valve connecting the tee and the negative pressure pipe, and then turn on the negative pressure pump. At the same time, record the secondary migration and laying of the proppant, the upper and lower displacement changes of the upper fracture plate, and the left and right displacement changes of the lower fracture plate during the entire extraction process, so as to obtain the sliding law of the lower fracture plate under the action of the tangential load spring and the non-uniform deformation law of the upper fracture plate during the entire test process. After a certain period of negative pressure extraction, close the corresponding valve and negative pressure pump.

[0053] Step 6: Repeat the test. The fracturing fluid and proppant in the test apparatus are cleaned out, and the apparatus is restored to its initial state. Then, after varying the negative extraction pressure, steps 3 through 5 are repeated to determine the proppant migration patterns during post-fracture negative extraction of the fracturing fluid. During the repeated test, all parameters except the negative extraction pressure must remain constant.

Claims

1. A method for testing proppant migration caused by gas extraction after hydraulic sand fracturing, characterized by: The test device comprises an injection assembly (A), a fracture assembly (B), a fixing assembly (C) and a negative pressure extraction assembly, wherein the injection assembly (A) is used to inject a fracturing fluid with a proppant into the fracture assembly (B), the fracture assembly (B) is used to simulate the reaction of a rock mass with fractures after the liquid is injected, the fixing assembly (C) can not only realize the support and fixation of the fracture assembly, but also adjust the inclination angle of the fracture assembly, and the negative pressure extraction assembly is used to simulate the gas extraction process; the fracture assembly (B) comprises an upper fracture plate (1) and a lower fracture plate (2) arranged relatively to each other, the left ends of the upper fracture plate (1) and the lower fracture plate (2) are provided with notches for fracturing fluid injection extending forward and backward, the upper fracture plate (1) can move up and down, and a normal load from the fixing assembly is loaded on the upper fracture plate (1), and the lower fracture plate (2) can move left and right, and a tangential load from the fixing assembly is loaded on the lower fracture plate (2); The fixing assembly (C) includes a lower pressure plate (3) arranged below the lower crack plate (2), a height-adjustable support assembly is arranged below the lower pressure plate (3), an upper pressure plate (4) is arranged above the lower pressure plate (3) through a support bolt (5), the upper pressure plate (4) is located above the upper crack plate (1), and a plurality of normal load springs (6) are arranged between the upper pressure plate (4) and the upper crack plate (1), a row of tightening bolts (7) that can be pressed against the right side of the upper crack plate (1) are arranged on the right side of the lower pressure plate (3), and a tangential load assembly for realizing tangential load simulation when the lower crack plate (2) moves to the right is also arranged on the right side of the lower pressure plate (3); The tangential load assembly includes a tangential load spring (8), one end of the tangential load spring (8) is against the right side of the lower slit plate (2), and the other end of the tangential load spring (8) is sleeved on a guide column (9) located between the lower pressure plate (3) and the lower slit plate (2), and a distance is left between the guide column (9) and the lower slit plate (2); The following test steps are also included: S1: Experimental preparation; Connect all parts of the test device completely, and after checking that they are correct, fill the injection assembly with the predetermined proppant and fracturing fluid; S2: load application; Applying a predetermined normal load to the upper crack plate and a predetermined tangential load to the lower crack plate through the fixing assembly, while making the crack assembly reach a predetermined inclination angle and tendency; S3: perform fracturing; Start the injection assembly to inject the fracturing fluid with proppant into the gap between the upper fracture plate and the lower fracture plate at a predetermined rate; S4: complete fracturing; When the injection time of the fracturing fluid with proppant reaches a predetermined time, the injection is stopped, and the distribution position of the proppant when the fracturing fluid with proppant stops moving between the upper fracture plate and the lower fracture plate is recorded; S5: negative pressure extraction; Start the negative pressure extraction component and conduct a negative pressure extraction simulation. At the same time, record the secondary migration and placement of the proppant, the vertical displacement of the upper fracture plate, and the horizontal displacement of the lower fracture plate during the entire extraction process. S6: Repeat test; The fracturing fluid and proppant in the test device are cleaned to restore the test device to its initial state. Then, after changing different extraction negative pressures, steps S3-S5 are repeated to obtain the proppant migration pattern of the fracturing fluid with proppant during the negative pressure extraction process after fracturing.

2. The method for testing proppant migration caused by gas extraction after hydraulic sand fracturing according to claim 1, characterized in that: The support assembly comprises four support rods (10) arranged between the lower pressure plate (3) and the ground and distributed in a rectangular shape, the support rods (10) comprising a fixed sleeve (10a), a telescopic rod (10b) capable of moving up and down in the fixed sleeve (10a) being arranged in the fixed sleeve (10a), a fastening sleeve (10c) being arranged outside the telescopic rod (10b), an internal thread being arranged at the lower end of the fastening sleeve (10c), an external thread matching the internal thread being arranged on the outer side of the upper end of the fixed sleeve (10a), a rubber tube (10d) being arranged between the fastening sleeve (10c) and the telescopic rod (10b), a gasket (10e) being arranged between the upper end of the rubber tube (10d) and the upper end of the fastening sleeve (10c), and when the fastening sleeve (10c) is tightened onto the fixed sleeve (10a), the rubber tube (10d) is squeezed, thereby achieving a fixed length of the telescopic rod (10b).

3. The method for testing proppant migration caused by gas extraction after hydraulic sand fracturing according to claim 2, characterized in that: The lower pressure plate (3) is a rectangular plate, and the support rod (10) is arranged at the four corners of the lower pressure plate (3). The upper and lower ends of the support rod (10) are each provided with two relatively arranged clamps (11), and a spherical groove (11a) is provided in the clamp (11). The two spherical grooves (11a) at the lower end are clamped with ball head bolts (12) fixed on the ground, and the two spherical grooves (11a) at the upper end are clamped with ball head clamping parts (13) that can be fixed at the corners of the lower pressure plate (3).

4. The method for testing proppant migration caused by gas extraction after hydraulic sand fracturing according to claim 1, characterized in that: The injection assembly (A) includes a fracturing fluid tank (15) arranged on the ground through a support column (14), an injection pipe (16) is arranged on the fracturing fluid tank (15), the end of the injection pipe (16) is arranged parallel to the notch, and a plurality of liquid outlet holes for injecting liquid into the notch are provided, the injection pipe (16) is provided with a water pump (17) capable of driving the flow of liquid, and the injection pipe (16) is also provided with a proppant injection pipe (18) for adding proppant into the injection pipe, the upper end of the proppant injection pipe (18) is provided with a proppant adding assembly for quantitatively adding proppant into the liquid in the injection pipe, and the end of the injection pipe (16) is provided with an injection fixing pipe (19) that can be fixed to the left end of the fixing assembly and is used to ensure that the liquid in the injection pipe (16) is injected into the notch.

5. The method for testing proppant migration caused by gas extraction after hydraulic sand fracturing according to claim 4, characterized in that: The proppant adding assembly comprises a proppant storage tank (20), a proppant screw conveyor (21) is provided at the lower end of the proppant storage tank (20), one end of the proppant screw conveyor (21) is communicated with the lower end of the proppant storage tank (20), and the other end is communicated with the upper end of the proppant injection pipe (18).

6. The method for testing proppant migration caused by gas extraction after hydraulic sand fracturing according to claim 4, characterized in that: The right end of the injection fixed tube (19) is provided with a rectangular groove (19a) for the upper crack plate (1) and the lower crack plate (2) to extend into, and the upper crack plate (1) can move up and down in the rectangular groove (19a). A sealing ridge (1a) extending forward and backward is inserted above the left end of the upper crack plate (1). The upper end of the sealing ridge (1a) is covered with a circle of upper and lower sealing rings. The upper wall surface of the rectangular groove (19a) is provided with a sealing ridge (1a) for the sealing ridge (1a) to extend upward. 1a) is inserted into a sealing strip groove (19b) that can move up and down, and the upper and lower sealing rings are located in the sealing strip groove (19b), and the front and rear side walls of the rectangular groove (19a) are provided with a clamping strip (22) for ensuring that the lower crack plate (2) is in close contact with the lower wall surface of the rectangular groove (19a), the lower end of the clamping strip (22) is in contact with the upper end of the lower crack plate, and the upper end of the clamping strip (22) is pressed against the upper crack plate (1) through a micro spring (23).

7. The method for testing proppant migration caused by gas extraction after hydraulic sand fracturing according to claim 1, characterized in that: The front and rear sides of the top surface of the lower slit plate (2) are both provided with protrusions (2a) extending left and right, and the upper ends of the protrusions (2a) are covered with left and right sealing rings. The bottom surface of the upper slit plate (1) is provided with sealing grooves (1b) at positions corresponding to the protrusions (2a), and the left and right sealing rings are located in the sealing grooves.

8. The method for testing proppant migration caused by gas extraction after hydraulic sand fracturing according to claim 1, characterized in that: A bottom plate (24) located in the fixed assembly is provided below the lower slit plate (2), and a plurality of rollers (24a) extending forward and backward are provided on the bottom plate (24) at intervals on the left and right sides.

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