A test method for the effect of rock mass fracture surface strength on proppant embedment and migration

Abstract

The application discloses a kind of rock mass fracture surface strength influence proppant embedding and migration test method, including mainly by injection component, fracture component and fixed component composition test device, the injection component is used to be injected into the fracture component with the fracturing fluid of proppant, the fixed component not only can realize the support fixation of fracture component, can also adjust the inclination angle of fracture component;It further includes the following steps: S1: test preparation;S2: load application;S3: carry out fracturing;S4: complete fracturing;S5: repeat test. By replacing the fracture plate of different materials, the strength of the fracture surface and the rock formation is changed, so that the proppant fracture seepage test of different strength rock formation fracture can be simulated, so that the embedding and migration law of proppant during the hydraulic sand fracturing process and after fracturing of different strength rock formation can be observed, to provide reliable theory and experimental basis for further fracturing operation.

Description

Technical Field

[0001] This invention belongs to the field of unconventional energy hydraulic fracturing mining technology, specifically relating to a test method for the influence of rock fracture surface strength on proppant embedding and migration. Background Technology

[0002] Large-scale volumetric fracturing is a crucial means for the economical and efficient development of unconventional oil and gas. The conductivity of fracturing fractures has a significant impact on the stimulation effect and stable production period. Besides factors such as closure stress, proppant particle size, and rock mechanical properties, the degree of proppant embedding into the fracture surface has a significant influence on conductivity. Under effective stress, proppant embedding reduces the width of the propped fracture, thereby decreasing its conductivity and weakening the permeability enhancement effect. Therefore, it is necessary to study proppant embedding during fracturing operations, analyze the factors affecting proppant embedding, and propose corresponding countermeasures to provide reliable theoretical and experimental basis for further fracturing operations. Existing experimental methods mostly involve studying proppant embedding in rock cores under constant pressure and uniform propping conditions. These methods have three significant shortcomings: First, under engineering conditions, the fracture aperture is non-uniform, and the proppant entering the fracture with the fracturing fluid is also non-uniformly distributed, resulting in non-uniform embedding and stress concentration. Second, after hydraulic fracturing with proppant, fractures in engineering rock masses are prone to shear slip under proppant conditions, and the embedding and sliding trajectories of proppant under uniaxial compression and shear loading conditions differ significantly. Third, rocks exhibit significant individual differences, leading to large dispersion in experimental data. Summary of the Invention

[0003] This invention aims to provide a test method for the influence of rock fracture surface strength on proppant embedding and migration, and to conduct proppant fracture seepage tests simulating different rock fracture surface strengths, so as to provide reliable theoretical and experimental basis for further hydraulic fracturing operations.

[0004] Therefore, the technical solution adopted by the present invention is as follows: a test method for the influence of rock fracture surface strength on proppant embedding and migration, comprising a test device, the test device comprising an injection component, a fracture component, and a fixing component, the injection component being used to inject fracturing fluid containing proppant into the fracture component, the fracture component being used to simulate the reaction of rock mass with fractures after fluid injection, the fixing component not only supporting and fixing the fracture component, but also adjusting the tilt angle of the fracture component; the fracture component comprising an upper fracture plate and a lower fracture plate arranged opposite each other, the left ends of the upper fracture plate and the lower fracture plate having notches for fracturing fluid injection extending forward and backward, the upper fracture plate being able to move up and down, and a normal load from the fixing component being applied to the upper fracture plate, the lower fracture plate being able to move left and right, and a tangential load from the fixing component being applied to the lower fracture plate;

[0005] It also includes the following test steps:

[0006] S1: Test preparation; Connect all components on the test device and, after checking that everything is correct, fill the injection assembly with the predetermined proppant and fracturing fluid.

[0007] S2: Load application; A predetermined normal load is applied to the upper fracture plate and a predetermined tangential load is applied to the lower fracture plate by means of a fixed component, while the fracture component reaches a predetermined tilt angle and inclination.

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

[0009] S4: Complete fracturing; When the fracturing fluid with proppant is injected for the predetermined time, stop the injection and record the distribution position of the proppant when the fracturing fluid with proppant stops moving between the upper and lower fracture plates. At the same time, observe and record the proppant embedding and changes during the sliding of the lower fracture plate under the condition of constant initial load.

[0010] S5: Repeat the test; clean the fracturing fluid and proppant inside the test device to restore the test device to its initial state, and then repeat steps S2-S4 after replacing the upper and lower fracture plates with different strengths to obtain the proppant embedding and migration laws of fracture plates with different strengths during hydraulic fracturing and after fracturing.

[0011] As a preferred embodiment of the above solution, the fixing assembly includes a lower bearing plate disposed below the lower split plate, a height-adjustable support assembly disposed below the lower bearing plate, an upper bearing plate disposed above the lower bearing plate by support bolts, the upper bearing plate being located above the upper split plate, and a plurality of normal load springs disposed between the upper bearing plate and the upper split plate, a row of clamping bolts being disposed on the right side of the lower bearing plate that can abut against the right side surface of the upper split plate, and a tangential load assembly for simulating tangential load when the lower split plate moves to the right being disposed on the right side of the lower bearing plate.

[0012] Further preferably, the tangential load assembly includes a tangential load spring, one end of which rests against the right side of the lower slit plate, and the other end of which is sleeved on a guide post located between the lower bearing plate and the lower slit plate, with a distance between the guide post and the lower slit plate.

[0013] Further preferably, the support assembly includes four support rods arranged in a rectangular pattern between the lower pressure plate and the ground. Each support rod includes a fixed sleeve, inside which is a telescopic rod that can move up and down. A fastening sleeve is provided outside the telescopic rod. The lower end of the fastening sleeve has an internal thread, and the upper outer side of the fixed sleeve has an external thread that matches the internal thread. A rubber tube is provided between the fastening sleeve and the telescopic rod. 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 onto the fixed sleeve, it will compress the rubber tube, thereby fixing the length of the telescopic rod.

[0014] Further preferably, the lower bearing plate is a rectangular plate, and the support rod is set at the four corners of the lower bearing plate. The upper and lower ends of the support rod are each provided with two opposing clamps. The clamps are provided with spherical grooves. The two spherical grooves at the lower end clamp ball head bolts fixed to the ground, and the two spherical grooves at the upper end clamp ball head clamping parts that can be fixed at the corners of the lower bearing plate.

[0015] Further preferably, the injection assembly includes a fracturing fluid tank mounted on the ground via a support column, an injection pipe mounted on the fracturing fluid tank, the end of the injection pipe being parallel to the notch and having multiple liquid outlet holes for injecting liquid into the notch, a water pump for driving the liquid flow mounted on the injection pipe, a proppant injection pipe for adding proppant into the injection pipe, a proppant addition assembly for quantitatively adding proppant to the liquid in the injection pipe at the upper end of the proppant injection pipe, and an injection fixing pipe that can be fixed to the left end of the fixing assembly and is used to ensure that the liquid in the injection pipe is injected into the notch.

[0016] Further preferably, the proppant addition 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.

[0017] Further preferably, the right end of the injection fixing tube is provided with a rectangular groove for the upper and lower slit plates to extend into, and the upper slit plate can move up and down within the rectangular groove. A sealing protrusion extending forward and backward is inserted above the left end of the upper slit plate. The upper end of the sealing protrusion is fitted with an upper and lower sealing ring. The upper wall of the rectangular groove is provided with a sealing strip groove for the sealing protrusion to be inserted and can move up and down, and the upper and lower sealing rings are located within the sealing strip groove. The front and rear side walls of the rectangular groove are provided with retaining strips to ensure that the lower slit plate is in close contact with the lower wall of the rectangular groove. The lower end of the retaining strip contacts the upper end of the lower slit plate, and the upper end of the retaining strip is pressed against the upper slit plate by a micro spring.

[0018] In a further preferred embodiment, the top surface of the lower slit plate is provided with protrusions extending to the left and right on both the front and rear sides. The upper end of the protrusion is fitted with left and right sealing rings. The bottom surface of the upper slit plate is provided with sealing grooves corresponding to the positions of the protrusions, and the left and right sealing rings are located in the sealing grooves.

[0019] In a further preferred embodiment, a base plate located within a fixing assembly is disposed below the lower slit plate, and a plurality of rollers extending forward and backward are disposed on the base plate at intervals from left to right.

[0020] The beneficial effects of this invention are as follows: by replacing the fracture plate with one of different materials, the strength of the fracture surface and the rock layer can be changed, which can simulate the proppant fracture seepage test of rock layer fractures of different strengths. This allows us to observe the proppant embedding and migration law of rock layers of different strengths during and after hydraulic fracturing, providing a reliable theoretical and experimental basis for further fracturing operations. Attached Figure Description

[0021] Figure 1 This is a flowchart of the present invention.

[0022] Figure 2 This is a three-dimensional schematic diagram of the experimental apparatus in this invention. Figure 1 .

[0023] Figure 3 This is a three-dimensional schematic diagram of the experimental apparatus in this invention. Figure 2 .

[0024] Figure 4 This is a schematic diagram of the experimental device in this invention.

[0025] Figure 5 for Figure 4 The left view.

[0026] Figure 6 This is a schematic diagram of the support rod in this invention.

[0027] Figure 7 This is a schematic diagram of the liquid injection fixing tube in this invention.

[0028] Figure 8 for Figure 4 A magnified view of N in the diagram.

[0029] Figure 9 for Figure 2 A magnified view of M. Detailed Implementation

[0030] The present invention will be further described below with reference to the embodiments and accompanying drawings:

[0031] like Figures 1-9As shown, a variable fracturing fluid density-controlled proppant-directed movement test device mainly consists of an injection component A, a fracture component B, and a fixing component C. The injection component A is used to inject fracturing fluid containing proppant into the fracture component B. The fracture component B is used to simulate the reaction of fractured rock mass after fluid injection. The fixing component C not only supports and fixes the fracture component but also adjusts its tilt angle, enabling the device to simulate the seepage test of proppant-containing fracturing fluid in fractures with different dip angles or inclinations. Simultaneously, by applying a normal load to the upper fracture plate and a tangential load to the lower fracture plate, the device causes the upper and lower fracture plates to move during fracturing fluid seepage. This causes the stress on the upper and lower fracture plates to change with the movement of the corresponding plates. Therefore, this application not only simulates the initial stress field during seepage but also the stress changes during seepage, thus enabling it to realistically simulate the seepage of proppant-containing fracturing fluid in fractures.

[0032] The specific structure of fracture assembly B includes an upper fracture plate 1 and a lower fracture plate 2 arranged opposite each other. Both the upper fracture plate 1 and the lower fracture plate 2 have notches for fracturing fluid injection extending forward and backward at their left ends. 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.

[0033] The specific structure of the fixing component C includes a lower bearing plate 3 located below the lower split plate 2, and a height-adjustable support component located below the lower bearing plate 3. An upper bearing plate 4 is mounted above the lower bearing plate 3 via support bolts 5, and the upper bearing plate 4 is positioned above the upper split plate 1. To achieve the loading of normal loads on the upper split plate, several normal load springs 6 are provided between the upper bearing plate 4 and the upper split plate 1. The number and specifications of the normal load springs can be varied as needed. In this embodiment, 18 normal load springs are evenly arranged between the upper bearing plate 4 and the upper split plate 1. To prevent the upper split plate from moving left or right, a row of clamping bolts 7 is provided on the right side of the lower bearing plate 3 to abut against the right side of the upper split plate 1.

[0034] To facilitate the initial tangential load when the lower fracture plate moves left and right, a tangential load assembly is provided on the right side of the lower bearing plate 3 to simulate the tangential load when the lower fracture plate 2 moves to the right. The tangential load assembly includes a tangential load spring 8, with one end resting against the right side of the lower fracture plate 2 and the other end fitted onto a guide post 9 located between the lower bearing plate 3 and the lower fracture plate 2. A distance is maintained between the guide post 9 and the lower fracture plate 2 to ensure the lower fracture plate can move left and right. To facilitate changing the distance between the guide post and the lower fracture plate, a bolt extending from the right end of the lower bearing plate to the left is provided on the guide post. A nut for adjusting the compression of the tangential load spring is also provided on this bolt to achieve compression.

[0035] The specific structure of the support assembly includes 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 support rods are inclined inwards and supported on the lower bearing plate. By adjusting the different heights of the four support rods, the fracture assembly can be adjusted to any angle between 0 and 90° relative to the ground. To achieve the telescopic adjustment of the support rods, each support rod 10 includes a fixed sleeve 10a, within which a telescopic rod 10b that can move up and down within the fixed sleeve 10a is installed. To secure the telescopic rod after extension and retraction, a fastening sleeve 10c is fitted over the telescopic rod 10b. The lower end of the fastening sleeve 10c has an internal thread, and correspondingly, the upper outer side of the fixing sleeve 10a has an external thread matching the internal thread. A rubber tube 10d is positioned between the fastening sleeve 10c and the telescopic rod 10b. When the fastening sleeve 10c is tightened onto the fixing sleeve 10a, it compresses the rubber tube 10d, thus fixing the length of the telescopic rod 10b. To prevent direct friction between the upper end of the fastening sleeve and the rubber tube, a gasket 10e is placed between the upper end of the rubber tube 10d and the upper end of the fastening sleeve 10c.

[0036] In this embodiment, the lower bearing plate 3 is a rectangular plate, and the support rods 10 are located at the four corners of the lower bearing plate 3. To facilitate the installation of the support rods, two opposing clamps 11 are provided at both the upper and lower ends of the support rods 10, and the clamps at the upper and lower ends are staggered. Spherical grooves 11a are provided within the clamps 11, and ball-head bolts 12 fixed to the ground are clamped within the two lower spherical grooves 11a. Ball-head clamping members 13, which can be fixed at the corners of the lower bearing plate 3, are clamped within the two upper spherical grooves 11a. Each ball-head clamping member 13 includes two clamping supports 13a, which are respectively fixed to either side forming a corner of the lower bearing plate 3, and are mutually fixed. To achieve the function of clamping support, clamping support 13a includes a ball head located in a spherical groove and a fixing part fixed on the lower pressure plate. 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 support 13a to each other and a second connecting part extending along the first connecting part. The ball head is disposed at the end of the second connecting part.

[0037] The specific structure of injection component A includes a fracturing fluid tank 15 mounted on the ground via a support column 14. An injection pipe 16 is mounted on the fracturing fluid tank 15, with its end parallel to the notch and equipped with multiple outlet holes for injecting fluid into the notch. A water pump 17 is mounted on the injection pipe 16 to facilitate fluid flow. A proppant injection pipe 18 is also mounted on the injection pipe 16 for proppant addition, and a proppant addition assembly for metering proppant into the fluid within the injection pipe 18 is located at the upper end of the proppant injection pipe 18. To ensure accurate injection of fluid into the notch, an injection fixing pipe 19 is mounted at the end of the injection pipe 16 and fixed to the left end of the fixing assembly. Preferably, the upper end of the injection fixing pipe is bolted to the upper pressure plate, and the lower end is bolted to the lower pressure plate.

[0038] The aforementioned proppant addition 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. 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. A fixed amount of proppant is added to a certain amount of liquid through the proppant screw conveyor.

[0039] Because an injection fixing tube is provided at the end of the injection tube, a rectangular groove 19a is provided at the right end of the injection fixing tube 19 to allow the upper slit plate 1 and the lower slit plate 2 to extend into, in order to ensure a seal during injection. The upper slit plate 1 can move up and down within the rectangular groove 19a. To ensure a seal between the upper end of the upper slit plate and the rectangular groove when the upper slit plate moves up and down, a front-to-back extending sealing protrusion 1a is inserted above the left end of the upper slit plate 1, and an upper and lower sealing ring is sleeved on the upper end of the sealing protrusion 1a. At the same time, a sealing strip groove 19b is provided on the upper wall surface of the rectangular groove 19a for the sealing protrusion 1a to be inserted and can move up and down, and the upper and lower sealing rings are always located within the sealing strip groove 19b. In this embodiment, a positioning protrusion 1c is provided at the position of the upper slit plate near the left end. After installation, the left side of the positioning protrusion just abuts 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, which would prevent the upper slit plate from moving up and down normally.

[0040] To ensure a seal between the lower end of the lower slit plate and the rectangular groove, a retaining strip 22 is provided on the front and rear side walls of the rectangular groove 19a to ensure that the lower slit plate 2 is in close contact with the lower wall of the rectangular groove 19a. The lower end of the retaining strip 22 contacts the upper end of the lower slit plate, and the upper end of the retaining strip 22 is pressed against the upper slit plate 1 by a micro spring 23. The compressed micro spring ensures that the lower end of the lower slit plate is always in contact with the lower inner wall of the rectangular groove.

[0041] To ensure the seal between the upper and lower slit plates on the front and rear sides, protrusions 2a extending to the left and right are provided on both the front and rear sides of the top surface of the lower slit plate 2. At the same time, a sealing groove 1b is provided on the bottom surface of the upper slit plate 1 at the position corresponding to the protrusions 2a. Left and right sealing rings are sleeved on the upper end of the protrusions 2a, and the left and right sealing rings are always located in the sealing groove.

[0042] In this embodiment, the retaining strip is designed in a gate shape, and a small recess is provided at the upper end of the retaining strip corresponding to the position where the micro-spring is installed. Since the lower slit plate can move to the right, retaining strip grooves for inserting the retaining strip are vertically provided on the left and right side walls of the rectangular groove to facilitate the fixing of the retaining strip. At the same time, an extension section that can be inserted into the retaining strip groove is provided horizontally at either end of the retaining strip. To facilitate the processing of the sealing strip groove and the two retaining strip grooves, a ring of grooves is provided in the rectangular groove. The groove located on the upper inner wall of the rectangular groove is the sealing strip groove, and the grooves located on the front and rear inner walls of the rectangular groove are the retaining strip grooves. To ensure sealing, sealing strips are filled in both the retaining strip grooves and the grooves located on the lower inner wall of the rectangular groove, and the cross-section of the sealing strips is circular.

[0043] To reduce friction when the lower slit plate moves to the right, a base plate 24 located within the fixing assembly is provided below the lower slit plate 2. At the same time, several rollers 24a extending forward and backward are provided on the base 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 slit plate.

[0044] To better observe the movement of the proppant-supported fracturing fluid, both the upper and lower pressure plates are made of transparent material, such as plexiglass. Ideally, the device should also be equipped with a high-speed camera. For convenient fracturing fluid recovery, a fracturing groove 3a is provided within the lower pressure plate. Both the upper and lower fracture plates are positioned within this groove. A collection tank 3b is located at the right end of the groove and is connected to the outside via a collection pipe. A pressure gauge and flow meter are installed at the end of the injection pipe, and strain gauge sensors for measuring stress are installed between each spring and the fracture plate.

[0045] Based on the above-mentioned test apparatus, a test method for assessing the influence of rock fracture surface strength on proppant embedding and migration includes the following test steps:

[0046] Step 1: Test preparation; Connect all components on the test device and, after checking that everything is correct, fill the predetermined amount of proppant into the proppant storage tank in the injection component and fill the fracturing fluid into the fracturing tank.

[0047] Step 2: Load Application; A predetermined normal load is applied to the upper fracture plate and a predetermined tangential load to the lower fracture plate using the fixing components, simultaneously bringing the fracture assembly to a predetermined tilt angle and inclination. Specifically, the normal load springs are compressed by tightening the support bolts, causing the normal load on the upper fracture plate to reach a predetermined value; the normal load is the combined elastic force of all normal load springs. By changing the distance between the fixing column and the diameter of the lower fracture plate, the compression of the tangential load springs is altered, causing the tangential load on the lower fracture plate to reach a predetermined value; the normal load is the combined elastic force of all tangential load springs. By adjusting the height of the four support rods, the fracture assembly can reach the predetermined tilt angle and inclination, ensuring that the fracture surface between the upper and lower fracture plates reaches the predetermined tilt angle and inclination.

[0048] Step 3: Perform fracturing; start the water pump and proppant screw conveyor, mix the fracturing fluid with the proppant, and inject it into the space between the upper and lower fracture plates at a predetermined rate through the notch.

[0049] Step 4: Complete fracturing; After the fracturing fluid with proppant has been injected for the predetermined time, stop the injection, that is, turn off 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 and lower fracture plates. At the same time, observe and record the proppant embedding and changes during the sliding of the lower fracture plate under constant load, and record the vertical displacement of the upper fracture plate and the horizontal displacement of the lower fracture plate, 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.

[0050] Step 5: Repeat the test; clean the fracturing fluid and proppant inside the test device to restore the test device to its initial state. Then, after replacing the upper and lower fracture plates with different strengths, repeat steps 2 to 4 to obtain the proppant embedding and migration patterns of fracture plates with different strengths during hydraulic fracturing and after fracturing.

[0051] When replacing the upper and lower fracture plates, the upper bearing plate can be removed. During repeated tests, it is necessary to ensure that the normal load, tangential load, fracture surface dip angle and dip direction, and fracturing fluid injection rate remain unchanged.

Claims

1. A test method for assessing the influence of rock fracture surface strength on proppant embedding and migration, characterized in that: The test apparatus includes an injection component (A), a fracture component (B), and a fixing component (C). The injection component (A) is used to inject fracturing fluid with proppant into the fracture component (B). The fracture component (B) is used to simulate the reaction of a rock mass with fractures after fluid injection. The fixing component (C) can not only support and fix the fracture component, but also adjust the tilt angle of the fracture component. The fracture component (B) includes an upper fracture plate (1) and a lower fracture plate (2) arranged opposite 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. The upper fracture plate (1) can move up and down and is loaded with a normal load from the fixing component. The lower fracture plate (2) can move left and right and is loaded with a tangential load from the fixing component. The fixing component (C) includes a lower bearing plate (3) disposed below the lower crack plate (2), a height-adjustable support component disposed below the lower bearing plate (3), an upper bearing plate (4) disposed above the lower bearing plate (3) by support bolts (5), the upper bearing plate (4) is located above the upper crack plate (1), and a number of normal load springs (6) are disposed between the upper bearing plate (4) and the upper crack plate (1), a row of clamping bolts (7) that can abut against the right side of the upper crack plate (1) is disposed on the right side of the lower bearing plate (3), and a tangential load component for simulating the tangential load when the lower crack plate (2) moves to the right is also disposed on the right side of the lower bearing plate (3); The tangential load assembly includes a tangential load spring (8), one end of which rests against the right side of the lower slit plate (2), and the other end of which is sleeved on a guide post (9) located between the lower bearing plate (3) and the lower slit plate (2), with a distance between the guide post (9) and the lower slit plate (2). It also includes the following test steps: S1: Experiment preparation; After connecting all the components of the test device and verifying that everything is correct, fill the injection assembly with the predetermined proppant and fracturing fluid. S2: Load applied; A predetermined normal load is applied to the upper fracture plate by fixing the assembly, and a predetermined tangential load is applied to the lower fracture plate, while the fracture assembly reaches a predetermined tilt angle and dip. S3: Perform hydraulic fracturing; Start the injection assembly to inject fracturing fluid with proppant into the space between the upper and lower fracture plates at a predetermined rate through the notch; S4: Fracturing completed; When the proppant-supported fracturing fluid injection time reaches the predetermined time, the injection is stopped, and the distribution position of the proppant is recorded when the proppant-supported fracturing fluid stops moving between the upper and lower fracture plates. At the same time, the proppant embedding and changes during the sliding of the lower fracture plate under the condition of constant initial load are observed and recorded. S5: Repeat the experiment; Clean the fracturing fluid and proppant inside the test device to restore the test device to its initial state. Then, after replacing the upper and lower fracture plates with different strengths, repeat steps S2-S4 to obtain the proppant embedding and migration patterns of fracture plates with different strengths during hydraulic fracturing and after fracturing.

2. The test method for the influence of rock fracture surface strength on proppant embedding and migration according to claim 1, characterized in that: The support assembly includes four support rods (10) arranged in a rectangular pattern between the lower pressure plate (3) and the ground. Each support rod (10) includes a fixed sleeve (10a). A telescopic rod (10b) that can move up and down inside the fixed sleeve (10a) is provided inside the fixed sleeve (10a). A fastening sleeve (10c) is provided outside the telescopic rod (10b). The lower end of the fastening sleeve (10c) is provided with an internal thread. The upper outer side of the fixed sleeve (10a) is provided with an external thread that matches the internal thread. A rubber tube (10d) is provided between the fastening sleeve (10c) and the telescopic rod (10b). A gasket (10e) is provided between the upper end of the rubber tube (10d) and the upper end of the fastening sleeve (10c). When the fastening sleeve (10c) is tightened onto the fixed sleeve (10a), the rubber tube (10d) will be squeezed, thereby fixing the length of the telescopic rod (10b).

3. The test method for the influence of rock fracture surface strength on proppant embedding and migration according to claim 2, characterized in that: The lower bearing plate (3) is a rectangular plate. The support rod (10) is located at the four corners of the lower bearing plate (3). The upper and lower ends of the support rod (10) are provided with two opposing clamps (11). The clamps (11) are provided with spherical grooves (11a). The two spherical grooves (11a) at the lower end are clamped with ball head bolts (12) fixed on the ground. 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 bearing plate (3).

4. The test method for the influence of rock fracture surface strength on proppant embedding and migration as described in claim 1, characterized in that: The injection assembly (A) includes a fracturing fluid tank (15) mounted on the ground via a support column (14). The fracturing fluid tank (15) is equipped with an injection pipe (16). The end of the injection pipe (16) is parallel to the notch and has multiple outlet holes for injecting liquid into the notch. The injection pipe (16) is equipped with a water pump (17) that can drive the flow of liquid. The injection pipe (16) is also equipped with a proppant injection pipe (18) for adding proppant into the injection pipe. The upper end of the proppant injection pipe (18) is equipped with a proppant addition assembly for quantitatively adding proppant to the liquid in the injection pipe. The end of the injection pipe (16) is equipped 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 test method for the influence of rock fracture surface strength on proppant embedding and migration according to claim 4, characterized in that: The proppant addition 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). 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).

6. The test method for the influence of rock fracture surface strength on proppant embedding and migration according to claim 4, characterized in that: The right end of the injection fixing tube (19) is provided with a rectangular groove (19a) into which the upper slit plate (1) and the lower slit plate (2) extend. The upper slit plate (1) can move up and down within the rectangular groove (19a). A sealing protrusion (1a) extending forward and backward is inserted above the left end of the upper slit plate (1). The upper end of the sealing protrusion (1a) is fitted with an upper and lower sealing ring. The upper wall of the rectangular groove (19a) is provided with a sealing protrusion (1a) extending forward and backward. 1a) A sealing strip groove (19b) that can be inserted and moved up and down, and the upper and lower sealing rings are located in the sealing strip groove (19b). The front and rear side walls of the rectangular groove (19a) are provided with a retaining strip (22) to ensure that the lower slit plate (2) and the lower wall of the rectangular groove (19a) are in close contact. The lower end of the retaining strip (22) is in contact with the upper end of the lower slit plate, and the upper end of the retaining strip (22) is pressed against the upper slit plate (1) by a micro spring (23).

7. The test method for the influence of rock fracture surface strength on proppant embedding and migration according to claim 1, characterized in that: The lower slit plate (2) has protrusions (2a) extending to the left and right on both the front and rear sides of its top surface. The upper end of the protrusion (2a) is fitted with left and right sealing rings. The bottom surface of the upper slit plate (1) is provided with a sealing groove (1b) corresponding to the position of the protrusion (2a). The left and right sealing rings are located in the sealing groove.

8. The test method for the influence of rock fracture surface strength on proppant embedding and migration according to claim 1, characterized in that: Below the lower slit plate (2) is a base plate (24) located within the fixing assembly, and several rollers (24a) extending forward and backward are arranged on the base plate (24) at intervals on the left and right.

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