Simulation test system and method for hole collapse process of gas extraction drill hole

Abstract

The invention relates to a simulation test system and a simulation test method for a hole collapse process of a gas extraction drill hole. The simulation test system for the hole collapse process of the gas extraction drill hole comprises a simulation box, a test gas circuit and a monitoring assembly, the simulation box comprises a box body, a hydraulic cylinder and a spillplate; threaded holes are formed in the middle of the front face of the box body according to the gas extraction drilling hole distribution rule. The threaded hole is in threaded connection with a threaded plug; the threaded holes comprise a main drill hole and a plurality of auxiliary drill holes; the hydraulic cylinders are arranged on the top and the right side of the box body; the output end of the hydraulic cylinder hermetically penetrates through the box body and is vertically provided with a push plate; the push plate comprises an upper pressing plate matched with the horizontal section of the box body and a side push plate matched with the vertical section of the box body; the spillplate comprises a horizontal plate and a vertical plate which are integrated; the horizontal plate is horizontally and slidably connected with the upper pressing plate; and the vertical plate is in vertical sliding connection with the side push plate. The simulation box provided by the invention is more beneficial to research of gas hole collapse factors. The test method of the test system can realize mutual verification of each monitoring data, and avoids inaccuracy of a single index.

Description

Technical Field

[0001] This invention relates to the technical field of gas drainage testing, and in particular to a simulation test system and method for the borehole collapse process in gas drainage. Background Technology

[0002] Borehole collapse in gas drainage refers to the phenomenon of borehole subsidence during gas drainage. Collapse reduces gas drainage efficiency and severely restricts gas control effectiveness. Many factors influence borehole collapse, such as the physical and mechanical properties of the drainage medium, ground stress, and gas pressure. Studying these influencing factors is crucial for understanding the evolution characteristics of borehole collapse, clarifying the collapse mechanism, and providing important guidance for optimizing on-site borehole support schemes and adjusting borehole layout parameters. Chinese patent CN105781616B, which describes a borehole dynamic instability monitoring system and method during coal seam drilling, provides a laboratory simulation and reproduction device for the borehole dynamic instability process. However, this patent can only simulate vertical ground stress and cannot simulate the superposition of vertical and horizontal ground stresses during drilling. Furthermore, this patent is only applicable to single-bore gas drainage simulation and cannot simulate borehole collapse under the superimposed influence of multiple boreholes. Therefore, this patent's research on the factors influencing borehole collapse in gas drainage remains insufficient. Summary of the Invention

[0003] The purpose of this invention is to solve the above-mentioned problems and provide a simulation test system and test method for the borehole collapse process in gas extraction.

[0004] The technical solution of this invention is as follows: A simulation test system for the collapse process of a gas drainage borehole includes a simulation chamber, a test gas path, and a monitoring component. The test gas path is used for evacuating the simulated coal sample material inside the simulation chamber, injecting simulated gas into the simulation chamber, and extracting the simulated gas. After injecting simulated gas into the simulation chamber, the simulated coal seam material forms a simulated coal seam. The commonly used simulated gas is carbon dioxide. The monitoring component is used to monitor the collapse of the simulated coal seam inside the simulation chamber. The simulation chamber includes a chamber body, a hydraulic cylinder, and a coal baffle plate. Threaded holes are arranged in the center of the front of the chamber body according to the borehole layout pattern of gas drainage boreholes. Threaded holes are threaded with threaded plugs to maintain the closed state inside the simulation chamber, which is beneficial to the formation of the simulated coal seam. The threaded holes include a main borehole and several auxiliary boreholes. During simulated drilling, the threaded plugs of the threaded holes are removed, and a drilling rig is used to drill through the threaded holes to drill the simulated coal seam. Then, the threaded plugs are reinstalled to seal the threaded holes. The removed threaded plugs correspond to the main borehole. The simulation chamber includes boreholes and auxiliary boreholes; monitoring is only conducted on the collapse of the main borehole to study the collapse of borehole groups; hydraulic cylinders are located at the top and right side of the chamber; the output end of the hydraulic cylinders is sealed through the chamber and a push plate is vertically installed; the hydraulic cylinders drive the push plate to move, simulating the compression of the coal seam by in-situ stress; the push plate includes an upper pressure plate matching the horizontal section of the chamber and a side push plate matching the vertical section of the chamber; the upper pressure plate presses down to simulate the downward vertical in-situ stress; the side push plate pushes horizontally to simulate the leftward horizontal in-situ stress; the coal retaining plate includes an integral horizontal plate and a vertical plate; the horizontal plate is horizontally slidably connected to the upper pressure plate; the vertical plate is vertically slidably connected to the side push plate; the coal retaining plate can block the intersection of the upper pressure plate and the side push plate, and ensure that the downward press of the upper pressure plate and the leftward push of the side push plate are carried out simultaneously to simulate the state of simultaneous application of vertical and horizontal in-situ stress; this simulation chamber can simulate both the state of borehole groups and the state of simultaneous application of vertical and horizontal in-situ stress, which is beneficial for the study of gas collapse factors.

[0005] Preferably, the horizontal plate has a horizontal elongated hole; the upper pressure plate is threaded with a sliding screw A; the sliding screw A passes through the horizontal elongated hole, establishing a connection between the upper pressure plate and the coal retaining plate, and realizing a horizontal sliding fit between the upper pressure plate and the coal retaining plate; the vertical plate has a vertical elongated hole; the side push plate is threaded with a sliding screw B; the sliding screw B passes through the vertical elongated hole, establishing a connection between the side push plate and the coal retaining plate, and realizing a vertical sliding fit between the side push plate and the coal retaining plate; this structure is simple and easy to manufacture.

[0006] Furthermore, both the horizontal and vertical elongated holes are countersunk hole structures; the bolt head of sliding screw A is embedded in the horizontal elongated hole; the bolt head of sliding screw B is embedded in the vertical elongated hole; the horizontal and vertical sliding of the coal retaining plate is smoother.

[0007] Furthermore, the box body includes a detachably connected box cover and box wall; a vertical elongated hole penetrates the lower end of the vertical plate; the box cover can be opened when filling the coal sample simulation material; when the box cover is closed, the sliding screw B can slide into the vertical elongated hole to establish a vertical sliding connection between the coal retaining plate and the side push plate.

[0008] Furthermore, the left end of the horizontal plate and the lower end of the vertical plate are both chamfered, which is beneficial for the upper pressure plate and the side push plate to squeeze the simulated coal seam.

[0009] Furthermore, the enclosure also includes a bottom that is detachably connected to the enclosure walls to facilitate the processing and assembly of the enclosure; the enclosure lid, enclosure walls, and enclosure bottom are connected using bolts and nuts.

[0010] Furthermore, the monitoring components include stress sensors; these stress sensors are embedded inside the simulated coal seam, located at the top and left and right sides of the main borehole, to monitor the collapse of the main borehole; this monitoring process includes the collapse during drilling and the drilling process after drilling; a cable passage hole is provided on the back of the box; the cable passage hole is sealed with a pressure-resistant cable connector that connects to the stress sensor to maintain the closed state inside the simulation box, making it more similar to the real situation of gas drainage boreholes.

[0011] Furthermore, a permeable steel plate is embedded at the bottom of the chamber; the bottom of the permeable steel plate is provided with a grid-shaped ventilation groove; the ventilation groove is provided with an air passage that runs through the outside of the chamber; the air passage is connected to the test air path; through the permeable steel plate, ventilation grid, and air passage, the vacuuming of the simulation chamber and the injection of simulated gas can be achieved, and it is also conducive to simulating the adsorption of carbon dioxide by the coal seam; as for the simulated gas extraction, the test air path can be directly extracted through the main borehole, which is closer to the actual situation of gas extraction.

[0012] Furthermore, the test gas path includes valve A, valve B, valve C, valve D, a carbon dioxide cylinder, a flow meter, and a vacuum pump; the gas path is connected to one end of valve A; the other end of valve A is connected to one end of valve B and one end of valve C respectively; the other end of valve B is connected to the carbon dioxide cylinder; one end of the flow meter is detachably connected to the main borehole, and the other end is connected to one end of valve D; the other ends of valves D and C are connected to the vacuum pump; valves A and C are opened, valves B and D are closed, and the vacuum pump is started to evacuate the interior of the simulation chamber to prevent air in the coal sample simulation material from affecting the test results; valves A and B are opened, valve C is closed, and carbon dioxide simulated gas from the carbon dioxide cylinder is injected into the simulated coal seam inside the simulation chamber; the flow meter is connected to the main borehole, valves A and C are closed, valve D is opened, and the vacuum pump is started to simulate the gas extraction process, with the flow meter monitoring the extraction speed.

[0013] Furthermore, the monitoring components include a DIC camera and a computer connected to the DIC camera; the front of the enclosure has a window; the simulation enclosure also includes a baffle and a transparent plate; the transparent plate is detachably installed at the window; a threaded hole is located in the middle of the transparent plate; inside the enclosure, the simulated coal seam in contact with the transparent plate is sprayed with speckled patterns; the DIC camera projects onto the transparent plate; the baffle has the same outline as the transparent plate and is closed in the middle; the DIC camera can photograph the speckled pattern of the coal seam before drilling through the transparent plate, and then photograph the speckled pattern of the coal seam after drilling; the two are compared by the computer to macroscopically monitor the collapse of the gas drainage borehole; the baffle can replace the transparent plate and is used to close the window of the enclosure when filling the coal sample simulation material; compared with the transparent plate, the baffle does not have a threaded hole, which allows the interface between the simulated coal seam and the baffle to form a complete plane, which is beneficial for simulating the coal seam conditions.

[0014] Furthermore, the simulation box also includes an annular cover plate and connecting screws; the annular cover plate is set to correspond to the window and fastens to the baffle / transparent plate; the connecting screws pass through the annular cover plate and are threaded to the edge of the window; the annular cover plate can be removed to replace the baffle / transparent plate.

[0015] Furthermore, the inner walls of the window and the annular cover are both recessed hole structures that match the baffle; the baffle / transparent plate is embedded in the recessed hole structure of the window and the recessed hole structure of the annular cover to increase the sealing effect at the window, so as to conform to the actual gas extraction site conditions.

[0016] A test method for the above-mentioned gas drainage borehole collapse process simulation test system includes the following steps:

[0017] ①Preparation of simulated coal seams

[0018] Install the baffle on the window to ensure the chamber walls are sealed, facilitating the filling of the prepared coal sample simulation material. Open the chamber lid and fill the chamber with the prepared coal sample simulation material to simulate coal seam conditions. When the coal sample simulation material reaches the corresponding depth, embed stress sensors at the corresponding positions. Connect the stress sensors to the pressure-resistant cable connector. The stress sensors are positioned above, below, left, and right of the predetermined main borehole to prepare for monitoring. After the coal sample simulation material has initially solidified, cure it. After curing, remove the baffle and spray speckle pattern onto the coal sample simulation material facing the window to prepare for speckle image capture using a DIC camera. Install the corresponding transparent plate filled with threaded plugs according to the simulation test requirements. Different transparent plates are used for different drilling patterns. The hydraulic cylinder moves the upper pressure plate and side push plate synchronously, squeezing the coal sample simulation material to make the in-situ stress on the coal sample simulation material close to the actual occurrence of coal seams. By controlling the output power of the hydraulic cylinder, the pushing force of the push plate is controlled, thereby changing the in-situ stress on the coal sample simulation material. After the coal sample simulation material reaches the required in-situ stress for the test, the hydraulic cylinder is closed. Valves A and C are opened, and valves B and D are closed. A vacuum pump is used to extract the air from the coal sample simulation material, preparing for the carbon dioxide gas to simulate methane adsorption. Valve C and the vacuum pump are closed, and valve B and the carbon dioxide cylinder are opened. Carbon dioxide gas enters the chamber, simulating the methane adsorption balance of the coal seam. Using carbon dioxide gas to simulate methane in the coal seam is safe and reliable. After waiting for a period of time, valve B and the carbon dioxide cylinder are closed, and the simulated coal seam preparation is complete.

[0019] ② Drilling construction and borehole collapse monitoring

[0020] An initial speckle image was captured through a transparent plate using a DIC camera, serving as a comparison for speckle images captured after drilling. Power was supplied to the stress sensor via a pressure-resistant cable connector, and data was transmitted. The threaded plugs corresponding to the selected threaded holes were removed sequentially, and the drill was used to drill through the open threaded holes, simulating a real gas extraction borehole. After drilling, the inside of the borehole was cleaned with high-pressure gas, and the threaded plugs were immediately installed on the threaded holes for sealing. After drilling the main borehole, a wireless borehole inspection device was inserted into the main borehole.

[0021] Remove the threaded plug from the main borehole; connect the flow meter to the main borehole in a sealed manner; open valve C, start the vacuum pump, and simulate gas extraction; monitor the extraction speed of the vacuum pump with the flow meter; use a DIC camera to take another comparative speckle image;

[0022] The stress sensor collects the stress changes around the main borehole during the entire drilling process and after the borehole is completed, realizing borehole stress monitoring; the speckle image is compared with the initial speckle image to realize borehole strain monitoring; the wireless borehole inspection device transmits the video of borehole deformation and collapse to the acquisition software on the computer in real time, realizing borehole visualization monitoring.

[0023] ③ Obtain the collapse rate

[0024] The borehole collapse rate is determined using a computer based on DIC data, stress sensor data, and endoscopic video.

[0025] The beneficial effects of this invention are as follows: The gas drainage borehole collapse simulation test system of this invention has the following advantages:

[0026] (1) The coal retaining plate of the present invention can move synchronously with the upper pressure plate and the side push plate to simulate the state of the coal seam being simultaneously subjected to vertical and horizontal ground stress; and the threaded holes are arranged according to the common drilling method, so that the simulation box can simulate the state of the borehole group; the simulation box of the present invention is more conducive to the study of gas collapse hole factors.

[0027] (2) The vertical elongated hole of the present invention penetrates the lower end of the vertical plate; when filling the coal sample simulation material, the box cover can be opened; when the box cover is closed, the sliding screw B can slide into the vertical elongated hole to establish a vertical sliding connection between the coal blocking plate and the side push plate.

[0028] (3) The window of the present invention and the transparent plate installed on the window can intuitively monitor the speckle pattern by drilling the radial cross section.

[0029] The experimental system's testing method can use stress sensors to collect stress changes around the main borehole throughout the drilling process and after borehole formation, enabling borehole stress monitoring; comparing the speckle image with the initial speckle image to monitor borehole strain; and using a wireless borehole sight to transmit the data externally for visualized monitoring inside the borehole, thus enabling multi-index monitoring. The various monitoring data are cross-validated to avoid the inaccuracy of a single index. Attached Figure Description

[0030] Figure 1 This is the front view of the simulation chamber;

[0031] Figure 2 yes Figure 1 AA section view;

[0032] Figure 3 yes Figure 2 BB cross-sectional view;

[0033] Figure 4 yes Figure 3 CC section view;

[0034] Figure 5 yes Figure 3 DD sectional view;

[0035] Figure 6 This is a common method for drilling group hole layout;

[0036] Figure 7 It is a 3D view of the simulation chamber;

[0037] Figure 8 This is a schematic diagram of a simulation test system for the borehole collapse process in gas drainage drilling;

[0038] In the diagram: 111. Threaded hole, 1111. Main drilled hole, 1112. Auxiliary drilled hole, 112. Threaded plug, 113. Cable guide hole, 1131. Pressure-resistant cable connector, 1141. Ventilation steel plate, 1142. Ventilation slot, 1143. Air passage, 115. Box cover, 116. Box wall, 117. Box bottom, 118. Window, 12. Hydraulic cylinder, 121. Upper pressure plate, 1211. Sliding screw armor, 122. Side push 1221. Sliding screw B, 131. Horizontal plate, 1311. Horizontal elongated hole, 132. Vertical plate, 1321. Vertical elongated hole, 14. Chamfer, 15. Transparent plate, 16. Annular cover plate, 161. Vertical longitudinal brace, 17. Connecting screw, 18. Sealing ring, 21. Valve A, 22. Valve B, 23. Valve C, 24. Valve D, 25. Carbon dioxide cylinder, 26. Flow meter, 27. Vacuum pump. Detailed Implementation

[0039] Example 1: See Figure 1-8 A simulation test system for the collapse process of a gas drainage borehole includes a simulation chamber, a test gas circuit, and a monitoring component. The test gas circuit is used for evacuating the simulated coal sample material inside the simulation chamber, injecting simulated gas into the simulation chamber, and extracting the simulated gas. After the simulated gas is injected into the simulation chamber, the simulated coal seam material forms a simulated coal seam. The commonly used simulated gas is carbon dioxide. The monitoring component is used to monitor the collapse of the simulated coal seam inside the simulation chamber. The simulation chamber includes a chamber body, a hydraulic cylinder 12, and a coal baffle plate. Threaded holes 111 are arranged in the center of the front of the chamber body according to the borehole layout pattern of gas drainage boreholes. A threaded connection with a threaded plug 112 is used to maintain the sealed state inside the simulation chamber, which is beneficial for simulating coal seam formation. The threaded hole 111 includes a main borehole 1111 and several auxiliary boreholes 1112. During simulated drilling, the threaded plug 112 of the threaded hole 111 is removed, and the simulated coal seam is drilled through the threaded hole 111 using a drilling rig. Then, the threaded plug 112 is reinstalled to seal the threaded hole 111. The removed threaded plug 112 corresponds to the main borehole 1111 and the auxiliary boreholes 1112. Only the collapse of the main borehole 1111 is monitored to study the collapse of the borehole group. See [link to documentation]. Figure 6Common borehole layout methods include single-row parallel drilling, double-row parallel drilling, and double-row three-hole drilling. A single-row parallel drilling consists of a row of equally spaced holes; the middle hole is the main borehole 1111, and the others are auxiliary boreholes 1112. A double-row parallel drilling consists of two rows of holes arranged in an array; the middle hole in the lower row is the main borehole 1111, and the others are auxiliary boreholes 1112. A double-row three-hole drilling consists of two rows of staggered holes; the middle hole in the lower row is the main borehole 1111, and the others are auxiliary boreholes 1112. Hydraulic cylinders 12 are located at the top and right side of the housing. The output end of the hydraulic cylinder 12 is sealed and penetrates the housing, with a push plate vertically installed. The hydraulic cylinder 12 drives the push plate to move, simulating the compression of a coal seam by in-situ stress. The push plate includes an upper pressure plate 1 that matches the horizontal cross-section of the housing. 21 and a side push plate 122 matching the vertical cross section of the box; the upper pressure plate 121 presses down to simulate the vertical downward ground stress; the side push plate 122 pushes horizontally to simulate the horizontal leftward ground stress; the coal retaining plate includes an integral horizontal plate 131 and a vertical plate 132; the horizontal plate 131 is horizontally slidably connected to the upper pressure plate 121; the vertical plate 132 is vertically slidably connected to the side push plate 122; the coal retaining plate can block the intersection of the upper pressure plate 121 and the side push plate 122, and ensure that the downward pressing of the upper pressure plate 121 and the leftward pushing of the side push plate 122 are carried out simultaneously to simulate the state of simultaneous application of vertical and horizontal ground stress; this simulation box can simulate both the state of borehole groups and the state of simultaneous application of vertical and horizontal ground stress, which is beneficial to the study of gas collapse borehole factors.

[0040] Compared with the prior art, the coal retaining plate of the present invention can move synchronously with the upper pressure plate 121 and the side push plate 122 to simulate the state of the coal seam being simultaneously subjected to vertical and horizontal ground stress; and the threaded holes 111 are arranged according to the common drilling method, so that the simulation box can simulate the state of the borehole group; the simulation box of the present invention is more conducive to the study of gas collapse hole factors.

[0041] In this embodiment, there are two hydraulic cylinders 12 and two lower pressure plates installed on the top of the box, which can well cover the horizontal cross section of the box, so that the simulated coal seam inside the box is uniformly squeezed.

[0042] The horizontal plate 131 has a horizontal elongated hole 1311; the upper pressure plate 121 is threadedly connected to a sliding screw A 1211; the sliding screw A 1211 passes through the horizontal elongated hole 1311, establishing a connection between the upper pressure plate 121 and the coal retaining plate, and realizing a horizontal sliding fit between the upper pressure plate 121 and the coal retaining plate; the vertical plate 132 has a vertical elongated hole 1321; the side push plate 122 is threadedly connected to a sliding screw B 1221; the sliding screw B 1221 passes through the vertical elongated hole 1321, establishing a connection between the side push plate 122 and the coal retaining plate, and realizing a vertical sliding fit between the side push plate 122 and the coal retaining plate; this structure is simple and easy to manufacture.

[0043] Both the horizontal elongated hole 1311 and the vertical elongated hole 1321 are countersunk hole structures; the bolt head of the sliding screw A 1211 is embedded in the horizontal elongated hole 1311; the bolt head of the sliding screw B 1221 is embedded in the vertical elongated hole 1321; the horizontal and vertical sliding of the coal retaining plate is smoother.

[0044] The box body includes a detachably connected box cover 115 and box wall 116; a vertical elongated hole 1321 penetrates the lower end of the vertical plate 132; when filling with coal sample simulation material, the box cover 115 can be opened; when the box cover 115 is closed, the sliding screw 1221 can slide into the vertical elongated hole 1321 to establish a vertical sliding connection between the coal retaining plate and the side push plate 122.

[0045] The left end of the horizontal plate 131 and the lower end of the vertical plate 132 are both provided with chamfers 14, which are beneficial for the upper pressure plate 121 and the side push plate 122 to squeeze the simulated coal seam.

[0046] The enclosure also includes a bottom 117 that is detachably connected to the enclosure wall 116 to facilitate the processing and assembly of the enclosure; the enclosure cover 115, enclosure wall 116, and enclosure bottom 117 are connected by bolts and nuts.

[0047] The monitoring components include stress sensors; the stress sensors are embedded inside the simulated coal seam, located at the top and left and right sides of the main borehole 1111, to monitor the collapse of the main borehole 1111; the monitoring process includes the collapse during the drilling process and the collapse after drilling; a cable passage hole 113 is provided on the back of the box; a pressure-resistant cable connector 1131 connected to the stress sensor is sealed in the cable passage hole 113 to maintain the closed state inside the simulation box, which is closer to the real situation of gas drainage boreholes.

[0048] The bottom of the chamber is fitted with a permeable steel plate 1141; the bottom of the permeable steel plate 1141 is provided with a grid-shaped ventilation groove 1142; the ventilation groove 1142 is provided with an air passage 1143 that penetrates the outside of the chamber; the air passage 1143 is connected to the test air path; through the permeable steel plate 1141, the ventilation grid, and the air passage 1143, the vacuuming of the simulation chamber and the injection of simulated gas can be realized, and it is also conducive to simulating the adsorption of carbon dioxide by the coal seam; as for the simulated gas extraction, the test air path can be directly extracted through the main borehole 1111, which is closer to the actual situation of gas extraction.

[0049] The test gas path includes valve A 21, valve B 22, valve C 23, valve D 24, carbon dioxide cylinder 25, flow meter 26, and vacuum pump 27; gas passage 1143 is connected to one end of valve A 21; the other end of valve A 21 is connected to one end of valve B 22 and one end of valve C 23 respectively; the other end of valve B 22 is connected to carbon dioxide cylinder 25; one end of flow meter 26 is detachably connected to the main borehole 1111, and the other end is connected to one end of valve D 24; the other ends of valve D 24 and valve C 23 are connected to vacuum pump 27; open valve A 21. Vacuum pump 27 is started to evacuate the interior of the simulation chamber by closing valves 23, 22 and 24 to prevent air in the coal sample simulation material from affecting the test results; valves 21 and 22 are opened and valve 23 is closed, and carbon dioxide simulated gas from carbon dioxide cylinder 25 is injected into the simulated coal seam inside the simulation chamber; flow meter 26 is connected to the main borehole 1111, valves 21 and 23 are closed and valve 24 is opened, vacuum pump 27 is started to simulate the gas extraction process, and flow meter 26 monitors the extraction speed.

[0050] The monitoring components include a DIC camera and a computer connected to the DIC camera; the front of the enclosure has a window 118; the simulation enclosure also includes a baffle and a transparent plate 15; the transparent plate 15 is detachably installed in the window 118; a threaded hole 111 is located in the middle of the transparent plate 15; inside the enclosure, the simulated coal seam connected to the transparent plate 15 is sprayed with speckle patterns; the DIC camera projects onto the transparent plate 15; the baffle has the same outline as the transparent plate 15, and is closed in the middle; the DIC camera can photograph the speckle pattern of the coal seam before drilling through the transparent plate 15, and then photograph the speckle pattern of the coal seam after drilling. The two are compared by a computer to macroscopically monitor the collapse of the gas drainage borehole; the DIC camera can take pictures of the coal seam speckle before drilling through the transparent plate 15, and then take pictures of the coal seam speckle after drilling; the two are compared by a computer to macroscopically monitor the collapse of the gas drainage borehole; the baffle can replace the transparent plate 15 and is used to close the box window 118 when filling the coal sample simulation material; compared with the transparent plate 15, the baffle does not have a threaded hole 111, which can make the interface between the simulated coal seam and the baffle form a complete plane, which is beneficial to the simulation of coal seam conditions.

[0051] This embodiment can also be applied to gas extraction simulation in single-hole drilling.

[0052] The working principle of this embodiment is as follows: The test gas path is used for evacuating the simulated coal sample material inside the simulation chamber, injecting simulated methane gas into the simulation chamber, and extracting simulated methane gas; after injecting simulated methane gas into the simulation chamber, the simulated coal seam material forms a simulated coal seam; the commonly used simulated methane gas is carbon dioxide; the monitoring component is used to monitor the collapse of the simulated coal seam inside the simulation chamber; the threaded plug 112 is used to maintain the closed state inside the simulation chamber, which is beneficial to the formation of the simulated coal seam; during simulated drilling, the threaded plug 112 of the threaded hole 111 is removed, and the drilling rig is used to drill the simulated coal seam through the threaded hole 111; then the threaded plug 112 is reinstalled to seal the threaded hole 111; the removed threaded plug 112 corresponds to the main drill. The main borehole 1111 and auxiliary borehole 1112 are used for monitoring the collapse of the main borehole 1111 to study the collapse of the borehole group. The hydraulic cylinder 12 drives the push plate to move, simulating the compression of the coal seam by the ground stress. The upper pressure plate 121 presses down to simulate the vertical downward ground stress. The side push plate 122 pushes horizontally to simulate the horizontal leftward ground stress. The coal retaining plate can block the intersection of the upper pressure plate 121 and the side push plate 122, and ensure that the downward pressing of the upper pressure plate 121 and the leftward pushing of the side push plate 122 are carried out simultaneously to simulate the state of simultaneous application of vertical and horizontal ground stress. This simulation box can simulate the state of the borehole group and the state of simultaneous application of vertical and horizontal ground stress, which is beneficial to the study of gas collapse factors. Sliding screw A 1211 engages with the horizontal elongated hole 1311 to establish a connection between the upper pressure plate 121 and the coal retaining plate, achieving a horizontal sliding fit between the upper pressure plate 121 and the coal retaining plate; sliding screw B 1221 engages with the vertical elongated hole 1321 to establish a connection between the side push plate 122 and the coal retaining plate, achieving a vertical sliding fit between the side push plate 122 and the coal retaining plate; the vertical elongated hole 1321 penetrates the lower end of the vertical plate 132; when filling the coal sample simulation material, the box cover 115 can be opened; when the box cover 115 is closed, sliding screw B 1221 can slide into the vertical elongated hole 1321, establishing a vertical sliding connection between the coal retaining plate and the side push plate 122. The left end of the horizontal plate 131 and the lower end of the vertical plate 132 are both provided with chamfers 14, which facilitates the compression of the simulated coal seam by the upper pressure plate 121 and the side push plate 122. Stress sensors monitor the collapse of the main borehole 1111; this monitoring process includes the collapse during drilling and the collapse after drilling; the pressure-resistant cable connector 1131 maintains the closed state inside the simulation box, which is closer to the real situation of gas drainage drilling; the ventilated steel plate 1141, the ventilation grid, and the gas channel 1143 can realize the vacuuming of the simulation box and the injection of simulated gas, and are conducive to simulating the adsorption of carbon dioxide by the coal seam; as for the simulated gas drainage, the test gas path can be directly extracted through the main borehole 1111, which is closer to the actual situation of gas drainage.Open valves A 21 and C 23, close valves B 22 and D 24, and start vacuum pump 27 to evacuate the interior of the simulation chamber to prevent air inside the coal sample simulation material from affecting the test results; open valves A 21 and B 22, close valve C 23, and inject carbon dioxide simulated gas from carbon dioxide cylinder 25 into the simulated coal seam inside the simulation chamber; connect flow meter 26 to the main borehole 1111, close valves A 21 and C 23, open valve D 24, start vacuum pump 27 to simulate the gas extraction process, and flow meter 26 monitors the extraction speed. The DIC camera can capture images of coal seam speckle patterns before drilling and after drilling through the transparent plate 15. The images are then compared with a computer to monitor the collapse of gas drainage boreholes macroscopically. The baffle can replace the transparent plate 15 and is used to close the box window 118 when filling the coal sample simulation material. Compared with the transparent plate 15, the baffle does not have threaded holes 111, which allows the interface between the simulated coal seam and the baffle to form a complete plane, which is beneficial for simulating coal seam conditions.

[0053] Example 2: Example 2 is basically the same as Example 1, and the similarities will not be repeated. The difference is that the simulation box also includes an annular cover plate 16 and connecting screws 17; the annular cover plate 16 is set to correspond to the window 118 and is fastened to the baffle / transparent plate 15; the connecting screws 17 pass through the annular cover plate 16 and are threaded to the edge of the window 118; the annular cover plate 16 can be removed to replace the baffle / transparent plate 15.

[0054] The inner walls of window 118 and annular cover 16 are both recessed hole structures that match the baffle; the baffle / transparent plate 15 is embedded in the recessed hole structure of window 118 and the recessed hole structure of annular cover 16 to increase the sealing effect at window 118, so as to conform to the actual gas extraction site conditions.

[0055] The annular cover plate 16 has several vertical braces 161 in the middle to improve the structural strength of the annular cover plate 16 and thus enhance its support capacity for the baffle / transparent plate 15. In this embodiment, there are four vertical braces 161.

[0056] Sealing rings 18 are provided between the hydraulic cylinder 12 and the simulation box, between the box cover 115 and the box wall 116, between the box wall 116 and the box bottom 117, and between the window 118 and the baffle / transparent plate 15 to increase the sealing effect of the simulation box.

[0057] Example 3: A test method for a gas drainage borehole collapse simulation test system as described in Example 1 includes the following steps:

[0058] ①Preparation of simulated coal seams

[0059] Install the baffle on window 118 to ensure the box wall 116 is closed, facilitating the filling of the prepared coal sample simulation material; open the box cover 115 and fill the box with the prepared coal sample simulation material to simulate coal seam conditions; when the coal sample simulation material is filled to the corresponding depth, embed a stress sensor at the corresponding position; the stress sensor is electrically connected to the pressure-resistant cable connector 1131; the stress sensor is positioned above, below, left, and right of the predetermined main borehole 1111, in preparation for monitoring using the stress sensor; after the coal sample simulation material has initially solidified, cure the coal sample simulation material; after curing, remove the baffle and spray speckle pattern on the coal sample simulation material facing window 118, in preparation for taking speckle images using a DIC camera; according to the simulation test requirements, install the corresponding transparent plate 15 filled with threaded plugs 112; Different drilling and hole layout methods are used, with different transparent plates 15. The hydraulic cylinder 12 is driven to move the upper pressure plate 121 and the side push plate 122 synchronously, compressing the coal sample simulation material to make the ground stress on the coal sample simulation material close to the actual occurrence of the coal seam. After the coal sample simulation material is compressed to a certain extent, the hydraulic cylinder 12 is closed. Valves A 21 and C 23 are opened, and valves B 22 and D 24 are closed. The vacuum pump 27 is used to extract the air from the coal sample simulation material to prevent residual air in the chamber from interfering with the test results. Valve C 23 is closed, the vacuum pump 27 is opened, and valve B 22 and the carbon dioxide cylinder 25 are opened, allowing carbon dioxide gas to enter the chamber and simulate the gas adsorption balance of the coal seam. The carbon dioxide gas simulates the gas in the coal seam, which is safe and reliable. After a period of time, valve B 22 and the carbon dioxide cylinder 25 are closed, and the simulated coal seam preparation is complete.

[0060] Before curing the coal sample simulation material, after the coal sample simulation material has been initially consolidated, the baffle can be removed to allow ventilation at window 118, which is beneficial to the curing of the coal sample simulation material.

[0061] In this embodiment, the coal sample simulation materials include 62.5 silicate cement, 40-80 mesh coal powder, ultra-80 mesh coal powder, sodium humate, and water. Among these, "coal powder gradation," "mass percentage of silicate cement," and "mass percentage of sodium humate" are important preparation factors. "Coal powder gradation" refers to the mass ratio of 40-80 mesh coal powder to ultra-80 mesh coal powder; "mass percentage of silicate cement" is the percentage of silicate cement mass in the total solid mass; and "mass percentage of sodium humate" is the percentage of sodium humate mass in the total solid mass. Each of these three preparation factors has four levels, employing a three-factor, four-level approach. The orthogonal method yielded 16 formulation schemes for solid materials, which comprehensively covered the main effects and interactive influences of the three preparation factors, reducing the experimental workload. The solid materials were then mixed with water at a mass ratio of 2.7:1, and a coal sample simulation material was obtained by casting. Different levels of the three preparation factors resulted in different robustness coefficients in the coal sample simulation material, providing material support for the simulation experiment of borehole collapse in gas drainage.

[0062] The four levels of pulverized coal gradation are: 1:4, 2:3, 3:2, and 4:1.

[0063] The four levels of silicate cement quality percentage are: 11%, 19%, 27%, and 35%.

[0064] The four levels of sodium humate by mass were 0.2%, 0.4%, 0.6%, and 0.8%.

[0065] ② Drilling construction and borehole collapse monitoring

[0066] An initial speckle image is captured through a transparent plate 15 using a DIC camera, serving as a comparison object for speckle images captured after drilling. Power is supplied to the stress sensor via a pressure-resistant cable connector 1131, and data is transmitted. The threaded plugs 112 corresponding to the selected threaded holes 111 are removed sequentially, and a drilling rig is used to drill through the open threaded holes 111, simulating a real gas extraction borehole. After drilling, the inside of the borehole is cleaned with high-pressure gas, and the threaded plugs 112 are immediately installed on the threaded holes 111 for sealing. After drilling the main borehole 1111, a wireless borehole inspection device is inserted into the main borehole 1111.

[0067] Remove the threaded plug 112 from the main borehole 1111; connect the flow meter 26 to the main borehole 1111 in a sealed manner; open valve C 23 and start the vacuum pump 27 to simulate gas extraction; the flow meter 26 monitors the extraction speed of the vacuum pump 27; use a DIC camera to take another comparative speckle image.

[0068] The stress sensor collects the stress changes around the main borehole 1111 throughout the drilling process and after the borehole is completed, realizing borehole stress monitoring; the speckle image is compared with the initial speckle image to realize borehole strain monitoring; the wireless borehole inspection device transmits the video of borehole deformation and collapse to the acquisition software on the computer in real time, realizing borehole visualization monitoring.

[0069] A quick connector can be used to connect the flow meter 26 to the main borehole 1111, which can effectively prevent the hose connecting the flow meter 26 from rotating and quickly establish a connection.

[0070] ③ Obtain the collapse rate

[0071] The borehole collapse rate is determined using a computer based on DIC data, stress sensor data, and endoscopic video.

[0072] DIC data: Based on the matching results of the speckle images, the full-field displacement field (u) is automatically calculated by computer. x u y Then, the shear strain field is solved using the partial derivatives of the displacement field to generate a shear strain contour map. Analysis shows that when the shear strain around the hole is greater than or equal to the critical shear strain threshold, hole collapse is considered to have begun.

[0073] The strain field around the hole tends to stabilize, indicating that the hole collapse has ended.

[0074] Extract the radial displacement of all measuring points near the borehole boundary (where r=R), and calculate the average radial displacement. The equivalent radius after the hole collapses Substitute into the formula for calculating the collapse rate η= The collapse rate η can be calculated.

[0075] Stress sensor: After drilling, the stress sensor detects a sudden decrease in stress gradient. In the near-hole area (the area outside the borehole and R away from the hole wall, where R is the borehole radius), the tangential and radial stress of the sensor drop sharply. In the middle hole area (the area outside the borehole and R-3R away from the hole wall), the tangential stress of the sensor increases. In the far hole area (the area outside the borehole and more than 3R away from the hole wall), the stress sensor stabilizes, indicating that the hole collapse has begun.

[0076] When all stress sensor readings stabilize, with error fluctuations less than 1%, and this continues for a period of time, the hole collapse is considered terminated.

[0077] First, based on the locations of sensors with near-zero stress values ​​at the top and sides, determine the top collapse height and the side collapse depths. Then, calculate the percentage of volume change after breakage relative to the borehole cross-section based on the fracture expansion coefficient of similar materials, thereby calculating the collapse rate η.

[0078] Endoscopic video: It was observed that tiny particles (particle size > 0.5 mm) were beginning to peel off from the borehole wall or new cracks appeared on the borehole wall, indicating that the borehole was beginning to collapse.

[0079] If there is no further spalling on the borehole wall, the collapse volume is stable, or the collapsed borehole section is stable, the borehole collapse is considered terminated.

[0080] The borehole collapse rate is determined by comparing photos of intact boreholes with photos of borehole collapse termination.

[0081] Based on the collapse rate, borehole collapse can be classified into complete borehole, slight collapse, severe collapse, and blockage. A borehole collapse of <10% is defined as a complete borehole; a collapse of 10% to 30% is defined as a slight collapse; a collapse of 30% to 70% is defined as a severe collapse; and a collapse of >70% is defined as a blockage.

[0082] In step ②, after removing the threaded plug 112 and before drilling, a threaded drill sleeve is threadedly connected to the corresponding threaded hole 111; the drill is then used to drill through the drill sleeve; after drilling is completed, the drill sleeve is replaced with the threaded plug 112. The drill sleeve protects the threads of the threaded hole 111, ensuring the continued use of the transparent plate 15.

Claims

1. A simulation test system for borehole collapse process in gas drainage, comprising a simulation chamber, a test gas path, and monitoring components; characterized in that, The simulation box includes a box body, a hydraulic cylinder, and a coal retaining plate. Threaded holes are arranged in the center of the front of the box body according to the drilling pattern of gas extraction boreholes. Threaded holes are connected to threaded plugs. The threaded holes include one main borehole and several auxiliary boreholes. The hydraulic cylinder is located at the top and right side of the box body. The output end of the hydraulic cylinder is sealed and penetrates the box body, with a push plate vertically installed. The push plate includes an upper pressure plate matching the horizontal section of the box body and a side push plate matching the vertical section of the box body. The coal retaining plate includes an integral horizontal plate and a vertical plate. The horizontal plate is horizontally slidably connected to the upper pressure plate; the vertical plate is vertically slidably connected to the side push plate.

2. The simulation test system for borehole collapse process in gas drainage according to claim 1, characterized in that: The horizontal plate has a horizontal elongated hole; the upper pressure plate is threaded with a sliding screw A; the sliding screw A passes through the horizontal elongated hole; the vertical plate has a vertical elongated hole; the side push plate is threaded with a sliding screw B; the sliding screw B passes through the vertical elongated hole.

3. The simulation test system for borehole collapse process in gas drainage according to claim 2, characterized in that: The enclosure includes a detachable lid and walls; a vertical elongated hole extends through the lower end of the vertical plate.

4. The simulation test system for borehole collapse process in gas drainage according to claim 3, characterized in that: The monitoring components include a stress sensor; the stress sensor is embedded inside the simulated coal seam, located at the top and sides of the main borehole; a cable passage hole is provided on the back of the housing; the cable passage hole is sealed with a pressure-resistant cable connector that connects to the stress sensor.

5. The simulation test system for borehole collapse process in gas drainage according to claim 4, characterized in that: The bottom of the chamber is fitted with a breathable steel plate; the bottom of the breathable steel plate is provided with a grid-shaped ventilation groove; the ventilation groove is provided with an air passage that runs through the outside of the chamber; the air passage is connected to the test air passage.

6. The simulation test system for borehole collapse process in gas drainage according to claim 5, characterized in that: The test gas path includes valve A, valve B, valve C, valve D, a carbon dioxide cylinder, a flow meter, and a vacuum pump; the gas path is connected to one end of valve A; the other end of valve A is connected to one end of valve B and one end of valve C respectively; the other end of valve B is connected to the carbon dioxide cylinder; one end of the flow meter is detachably connected to the main borehole, and the other end is connected to one end of valve D; the other ends of valves D and C are connected to the vacuum pump.

7. The simulation test system for borehole collapse process in gas drainage according to claim 6, characterized in that: The monitoring components include a DIC camera and a computer connected to the DIC camera; the front of the enclosure has a window; the simulation enclosure also includes a baffle and a transparent plate; the transparent plate is detachably installed in the window; a threaded hole is located in the middle of the transparent plate; inside the enclosure, the simulated coal seam connected to the transparent plate is sprayed with speckled paint; the DIC camera shoots at the transparent plate; the baffle has the same outline as the transparent plate and is closed in the middle.

8. The simulation test system for borehole collapse process in gas drainage according to claim 7, characterized in that: The simulation chamber also includes an annular cover plate and connecting screws; the annular cover plate is set to correspond to the window and is fastened to the baffle / transparent plate; the connecting screws pass through the annular cover plate and are threaded to the edge of the window.

9. The simulation test system for borehole collapse process in gas drainage according to claim 8, characterized in that: The inner walls of the window and the inner walls of the annular cover are both recessed hole structures that match the baffle; the baffle / transparent plate is embedded in the recessed hole structure of the window and the recessed hole structure of the annular cover.

10. A test method for a gas drainage borehole collapse simulation test system as described in claim 9, characterized in that: Includes the following steps: ①Preparation of simulated coal seams Install the baffle on the window to ensure the container walls are sealed. Open the container lid and fill the container with the prepared coal sample simulation material. When the coal sample simulation material reaches the corresponding depth, embed a stress sensor at the corresponding position. Connect the stress sensor to the pressure-resistant cable connector. The stress sensor is positioned above, below, left, and right of the predetermined main borehole. After the coal sample simulation material has initially solidified, cure it. After curing, remove the baffle and spray speckle pattern onto the coal sample simulation material facing the window. Install the corresponding transparent plate filled with threaded plugs according to the simulation test requirements. Different drilling methods require different... A transparent plate is used to drive the hydraulic cylinder, causing the upper pressure plate and side push plate to move synchronously, squeezing the coal sample simulation material so that the in-situ stress on the coal sample simulation material is close to the actual occurrence of coal seams; after the coal sample simulation material reaches the in-situ stress required for the test, the hydraulic cylinder is closed; valves A and C are opened, and valves B and D are closed, and the air inside the coal sample simulation material is extracted using a vacuum pump; valve C and the vacuum pump are closed, and valve B and the carbon dioxide cylinder are opened, allowing carbon dioxide gas to enter the chamber; after a period of time, valve B and the carbon dioxide cylinder are closed, and the preparation of the simulated coal seam is completed; ② Drilling construction and borehole collapse monitoring The initial speckle image is captured through a transparent plate using a DIC camera; power is supplied to the stress sensor via a pressure-resistant cable connector, and data is transmitted; the thread plugs corresponding to the selected threaded holes are removed in sequence, and the drill is used to drill through the open threaded holes; after drilling, the inside of the drill hole is cleaned with high-pressure gas, and the thread plugs are immediately installed on the threaded holes to seal them; after drilling the main hole, a wireless drilling peephole is inserted into the main hole. Remove the threaded plug from the main borehole; connect the flow meter to the main borehole in a sealed manner; open valve C, start the vacuum pump, and simulate gas extraction; use a DIC camera to take another comparative speckle image; The stress sensor collects the stress changes around the main borehole during the entire drilling process and after the borehole is formed, realizing the monitoring of borehole stress; by comparing the speckle image with the initial speckle image, the borehole strain is monitored; the wireless borehole inspection device transmits the video of borehole deformation and collapse in real time to the acquisition software on the computer and displays it to the outside, realizing the visualization monitoring of the borehole. ③ Obtain the collapse rate The borehole collapse rate is determined using a computer based on DIC data, stress sensor data, and endoscopic video.

Images