Physical simulation test device and method for array horizontal wellbore deformation under injection-production conditions

Abstract

The present invention discloses a physical simulation test device and method for borehole deformation of an array of horizontal wells under injection-production conditions, including a carrier frame, a test box, an injection gas pressurization system, a stress loading system, a negative pressure drainage system, and a data monitoring system. The main body of the device is fixed to the carrier frame for easy support and movement. The test box includes a loading chamber, a heating plate, and a borehole plug, which can simulate the formation environment and borehole. The injection gas pressurization system includes a pneumatic pipeline, an injection gas control valve, a gas pipe multi-way joint, a nitrogen cylinder, and a pressure gauge to simulate the injection gas conditions and supply pressure for the stress loading system. The stress loading system includes a sealing rubber pad and a stress loading chamber to apply a stress environment. The negative pressure drainage system includes a solid-gas separation device and a negative pressure machine. The data monitoring system includes a computer, a stress sensor, a temperature sensor, a micro camera, and a gas flow meter, which can monitor the stress, temperature, borehole deformation, and gas drainage volume in the specimen in real time. This invention can study the borehole failure mechanism under injection-production conditions to guide injection-production design.

Description

Technical Field

[0001] The invention relates to the technical field of coal-bed methane mining in underground coal mines, and in particular to a physical simulation test device and method for deformation of array horizontal wellbores under injection-production conditions. Background Art

[0002] Coalbed methane is a self-generated and self-stored unconventional natural gas that is formed in and stored in coal seams. It is mainly composed of methane (more than 95%) and a very small amount of heavier hydrocarbons (mostly ethane and propane) as well as nitrogen and carbon dioxide.

[0003] There are two main methods for extracting coalbed methane underground in coal mines: First, in-layer extraction, the drilling site is arranged in the working tunnel of the mined coal seam, and the in-layer boreholes (wellbores) are arranged along the mining direction of the coal seam, and coalbed methane extraction is implemented. Usually, the length of the in-layer wellbore is directly related to the extraction volume. The longer the wellbore length, the greater the extraction volume. Second, through-layer extraction, the drilling site is arranged outside the mined coal seam, mainly for inclined coal seams with high gas content and good permeability. Regardless of in-layer extraction or through-layer extraction, array wellbore arrangement is required, and then coalbed methane is extracted by injecting nitrogen in some wellbores and extracting coalbed methane in some wellbores under negative pressure. In addition, the wellbores for extracting coalbed methane underground in coal mines are only hundreds of meters to several hundred meters. In order to reduce the cost of hole construction and the resistance of coalbed methane flowing into the wellbore, these wellbores are generally open holes.

[0004] During the extraction of coalbed methane, the gas is first desorbed from the adsorbed state, and then diffuses and seeps into the extraction wellbore. Under the influence of ground stress, temperature and gas flow, due to the soft coal rock and easy migration of coal powder, the open hole wellbore will suffer from serious collapse, creep shrinkage, coal powder blockage and other complex instability problems, resulting in the scrapping of coalbed methane extraction holes and significantly reducing the coalbed methane extraction operation. Therefore, studying the gas flow in the process of coalbed methane extraction by gas injection under the action of stress and temperature, and conducting research on the deformation and damage characteristics of coalbed methane extraction wellbore can help determine the reasonable extraction wellbore layout, ensure the stability of the wellbore during coalbed methane extraction, and achieve safe and efficient extraction of coalbed methane.

[0005] The research on borehole stability considering the actual situation of coal seam gas extraction by injecting gas into multiple boreholes in underground coal mines lacks relevant physical simulation devices and corresponding methods. Currently, the analysis methods for borehole deformation, failure, and instability usually test the mechanical and seepage characteristics of standard cylindrical coal and rock specimens (raw coal / formed coal) to obtain the physical and mechanical properties of reservoir coal and rock, and then calculate or numerically simulate the deformation and failure of coal seam boreholes through theoretical models. These methods are based on certain assumptions for experiments and model construction, so there are certain limitations in engineering practical applications and cannot directly and accurately reflect the engineering reality. Some scholars have invented physical simulation test devices for the deformation of coal seam gas extraction boreholes considering the influence of stress and temperature, but these devices only have a single borehole design and do not have the function of arranging multiple boreholes, nor do they consider the conditions of gas injection and extraction. Therefore, they cannot realize the simulation of borehole deformation and failure tests under the condition of arranging multiple boreholes for gas injection and extraction in underground coal mines.

[0006] To make up for the lack of physical model test devices and methods for studying the deformation and failure of multiple boreholes for gas injection and extraction of coal seam gas in underground coal mines, the present invention introduces a physical simulation test device and method for the deformation of multiple horizontal boreholes considering the multi-field coupling effect of in-situ stress, temperature, and gas injection seepage. Summary of the Invention

[0007] The purpose of the present invention is to provide a physical simulation test device and method for the deformation of multiple horizontal boreholes under injection-production conditions based on actual working conditions for the research on the deformation and failure mechanism of multiple horizontal boreholes for coal seam gas under injection-production conditions. It can solve the problem of the deformation and failure mechanism of multiple horizontal boreholes in underground coal mines under injection-production conditions described in the above technical background, reveal the borehole failure law under the influence of various factors, and provide guidance for the layout and injection-production design of multiple boreholes for coal seam gas injection and extraction.

[0008] The physical simulation test device for the deformation of multiple horizontal boreholes under injection-production conditions provided by the present invention mainly includes a bearing frame, a test box, a gas injection and pressurization system, a stress loading system, a negative pressure extraction system, and a data monitoring system.

[0009] The bearing frame includes a test box fixing frame (2), universal wheels (18), rotating hinges (19), flipping hinges (24), pins (25), fixed support feet (27), and extended crossbars (39).

[0010] The test box includes a loading chamber (3), heating plates (33), fixing nuts (40), and borehole plugs (41).

[0011] The gas injection and pressurization system includes a gas injection pipeline (1), a pneumatic multi-way interface (11), a gas injection control valve (15) for the stress loading system, a gas injection control valve (16) for the test chamber, a connecting air pipe (20), an air pipe threaded connector (22), a gas cylinder (23), a three-way interface (30), a gas cylinder pressure gauge (36), a gas injection pressure gauge (46) for the stress loading system, and a gas injection pressure gauge (47) for the test chamber.

[0012] The stress loading system includes a sealing rubber pad (5), a stress loading chamber (6), and a connecting nut (42);

[0013] The negative pressure extraction system includes a solid-gas separation device (9), a negative pressure machine (10), a gas flow meter (13), a negative pressure machine pressure gauge (31), and an extraction pump (43).

[0014] The data monitoring system includes a computer (12), a modem (17), a stress sensor (21), a micro camera (44), and a temperature sensor (45).

[0015] Furthermore, the carrier frame includes a test chamber fixing frame (2), universal wheels (18), a rotary hinge (19), a flip hinge (24), a bolt (25), a fixed support leg (27), and an extended cross bar (39); Universal wheels (18) are installed at the bottom of the carrier frame for easy movement of the equipment; The extended cross bar (39) can be used as a manual handle for the movement and rotation of the equipment; When loading and unloading samples, the fixed support leg (27) can play a role in supporting and stabilizing, and at the same time, the steering of the carrier frame is more flexible through the rotary hinge (19), the flip hinge (24) is convenient for opening the stress loading system to facilitate loading and unloading of samples, and the bolt (25) is used to fix the stress loading system to ensure its stability and reliability.

[0016] Furthermore, the test chamber includes a loading chamber (3), a heating plate (33), a fixing nut (40), and a drilling plug (41); The loading chamber (3) is a box with five sides closed and one side open, and there are connecting holes (4) for connecting the stress sensor (21) and the temperature sensor (45) at the top. The edge of the open side is connected to the stress loading system with screw holes (48). 15 gas injection holes (7) and gas extraction holes (8) with a diameter of 20 mm and a spacing of 70 mm are arranged in an array on the front of the loading chamber (3). The gas injection holes (7) and gas extraction holes (8) can be blocked by threaded connection with the drilling plug (41) as needed. At the same time, the gas injection holes (7) and gas extraction holes (8) can be interchanged in function to simulate different extraction wellbore layouts; The heating plate (33) is located at the rear of the loading chamber (3) and consists of an electric heating wire (34), an electric wire (37), and a power control switch (35); The fixing nut (40) can fix the stress sensor (21) and the temperature sensor (45) by threaded connection.

[0017] Furthermore, the gas injection and pressurization system includes a gas injection pipeline (1), a pneumatic multi-pass interface (11), a gas injection control valve (15) for the stress loading system, a gas injection control valve (16) for the test chamber, a connecting air pipe (20), a pipe threaded connector (22), a gas cylinder (23), a tee joint (30), a gas cylinder pressure gauge (36), a gas injection pressure gauge (46) for the stress loading system, and a gas injection pressure gauge (47) for the test chamber; the tee joint (30) connects the gas injection control valve (15) for the stress loading system, the gas injection control valve (16) for the test chamber, and the gas cylinder (23); when the gas injection control valve (15) for the stress loading system is opened, gas will be injected into the stress loading system for three-way stress loading, and the loading pressure can be obtained by reading the gas injection pressure gauge (46) for the stress loading system; when the gas injection control valve (16) for the test chamber is opened, gas will be injected into the test chamber through the connecting air pipe (20), pneumatic multi-pass interface (11), and threaded connector (22) connected according to the test design to simulate the actual situation of gas injection for coalbed methane extraction, and the gas injection pressure can be obtained by reading the gas injection pressure gauge (47) for the test chamber.

[0018] Furthermore, the stress loading system includes a sealing rubber pad (5), a stress loading chamber (6), and a connecting nut (42); nut through holes (28) are provided around the stress loading chamber (6) in the stress loading system, and the connecting nut (42) can pass through the nut through holes (28) to be connected to the sealing rubber pad (5) and the loading chamber (3) to form a sealed cavity. An air injection screw hole (29) is provided on the right side of the stress loading chamber (6), which is connected to the gas injection and pressurization system to provide gas pressure for the stress loading chamber and transmit it to the test chamber through the sealing rubber pad to apply a three-way stress load to the specimen in the test chamber.

[0019] Furthermore, the negative pressure extraction system includes a solid-gas separation device (9), a negative pressure machine (10), a negative pressure machine pressure gauge (31), and a extraction pump (43); a solid-gas separation device (9) is connected to the front end of the air inlet (49) of the negative pressure machine to separate solids and prevent damage to the machine; the negative pressure machine pressure gauge (31) can monitor the pore pressure of the specimen under test in real time; the extraction pump (43) sucks the gas in the pores of the specimen in the test chamber to form a negative pressure to simulate the actual conditions of negative pressure extraction of coalbed methane.

[0020] Further, the data monitoring system includes a computer (12), a gas flowmeter (13), a modem (17), a stress sensor (21), a micro camera (44), and a temperature sensor (45); the stress sensor (21) and the temperature sensor (45) can be connected to the modem (17) through the connection holes (4) at the top of the loading chamber (3) and then connected to the USB interface of the computer (12) to achieve digital acquisition and recording of stress and temperature. The micro camera (44) extends into the specimen through the gas injection hole (7) or the gas extraction hole (8) on the front side of the loading chamber (3) to photograph the wellbore size before and after the test to analyze the wellbore deformation, and the video signal can be transmitted through the local area network and recorded in the computer (12); the gas flowmeter (13) is connected to the negative pressure gauge (10) by threads to observe the gas flow change in real time;

[0021] Further, this device and this method can constitute a physical simulation test method for the deformation of an array of horizontal wellbores under injection-production conditions, including the following steps:

[0022] S1: Through geological exploration, geological data analysis, and on-site investigation of coalbed methane extraction technical solutions, determine the borehole spacing, borehole diameter, and gas injection method for the physical simulation test of the deformation of an array of horizontal wellbores under injection-production conditions, and obtain parameters such as the moisture content of coal samples, gas injection pressure, loading stress, and test temperature in the physical simulation test;

[0023] S2: Prepare coal samples with a particle size less than 200 mesh and mix them with a certain amount of water to form a pulverized coal sample with the test-designed moisture content;

[0024] S3: Rotate the bearing frame, place the test box vertically, remove the stress loading chamber (6), seal the screw holes (48) around the loading chamber with transparent tape, and then layer by layer fill the pulverized coal sample. Each layer is compacted to the designed density with a pressing plate. Place the stress sensor (21) and the temperature sensor (45) at the positions where monitoring is required, and then continue to fill the pulverized coal sample according to the above method until the specimen production is completed;

[0025] S4: Uncover the transparent tape on the side of the loading chamber (3), connect the loading chamber (3), the sealing rubber pad (5), and the stress loading chamber (6) through the fixing nut (40), tighten the fixing nut (40), and connect the stress sensor (21) and the temperature sensor (45) to the modem (17) to complete the installation of the stress loading system and the pressure and temperature monitoring device;

[0026] S5: According to the test design requirements such as the determined borehole spacing, borehole diameter, and gas injection method, use the borehole plug (41) to block the unnecessary gas injection holes (7) and gas extraction holes (8), drill the gas injection and extraction boreholes that meet the test design dimensions, and use the micro camera (44) to penetrate into the wellbore to record the borehole shape before the test and record the image information in the computer (12);

[0027] S6: According to the simulation test design scheme, connect the gas injection pressurization system to the gas injection hole (7) through the gas injection pipeline (1), connect the negative pressure extraction system to the gas production hole (8), turn off the negative pressure machine (10), and reset the gas flowmeter (13).

[0028] S7: Connect the gas cylinder filled with methane with a concentration of 99.9% to the gas injection pressurization system, open the gas injection control valve (16) of the test chamber, and let the methane gas flow into the loading chamber (3) to fill the pores of the specimen, and keep the gas pressure at the test design value for 24 hours to enable the specimen to fully adsorb methane gas.

[0029] S8: Replace the methane gas cylinder with a nitrogen gas cylinder, open the gas injection control valve (15) of the stress loading system, inject high-pressure nitrogen into the stress loading chamber (6), make the injection pressure reach the test design value and remain stable; start the heating plate (33) to heat to the test temperature.

[0030] S9: Turn on the negative pressure machine (10), simulate the negative pressure extraction operation under the condition of gas injection for coalbed methane extraction, and at the same time start the acquisition of stress and temperature signals, and record the readings of the negative pressure gauge (31) of the negative pressure machine and the gas flowmeter (13) in real time. When the gas flowmeter (13) stabilizes and fluctuates within a very small range, stop the test, turn off the acquisition of stress and temperature signals of the computer, and turn off the negative pressure machine (10), the gas injection control valve (15) of the stress loading system and the gas injection control valve (16) of the test chamber.

[0031] S10: Open the gas production hole (8), use the micro camera (44) to go deep into the wellbore to the image acquisition position before the test to photograph its shape, and record the image information into the computer (12) for comparative analysis of the deformation of the borehole before and after the test.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] (1) The size of the cuboid specimen used in this device is larger than that of the conventional cylindrical specimen, and it is closer to the actual occurrence situation of the coal seam. And it can drill a borehole with a maximum diameter of 20 mm, which can simulate the wellbore deformation situation of the coalbed methane reservoir under the gas injection pressure and in-situ stress state, and can more accurately simulate the damage situation of the extraction hole during the extraction process of actual coalbed methane during the test.

[0034] (2) This device can complete a series of complex test operation processes such as sensor embedding, briquette specimen pressing, simulated wellbore, and stress loading by using its own loading system. It is convenient to use, simple to operate, has high practicability and wide applicability, and can complete various experimental studies related to rock mechanics and petroleum engineering.

[0035] (3)The device is provided with a circular hole with a diameter of 0 - 20 mm on its horizontal side, which can be used for drilling holes when pressing specimens, gas injection holes, simulating the seepage of coalbed methane, laying sensor leads, and observing and recording the deformation and failure conditions of the drilled holes in real time, etc.

[0036] Other advantages, objectives, and features of the present invention will be partially reflected by the following description, and partially will also be understood by those skilled in the art through the research and practice of the present invention. Brief Description of the Drawings

[0037] Figure 1 It is a front view structural schematic diagram of the physical simulation test device for the deformation of an array of horizontal wellbores under injection and production conditions of the present invention.

[0038] Figure 2 It is a schematic diagram of the main structure disassembly of the physical simulation test device for the deformation of an array of horizontal wellbores under injection and production conditions of the present invention.

[0039] Figure 3 It is a schematic diagram of the heating structure of the physical simulation test device for the deformation of an array of horizontal wellbores under injection and production conditions of the present invention.

[0040] Figure 4 It is a schematic diagram of the gas injection and pressurization system structure of the physical simulation test device for the deformation of an array of horizontal wellbores under injection and production conditions of the present invention.

[0041] Figure 5 It is a schematic diagram of the stress loading system structure of the physical simulation test device for the deformation of an array of horizontal wellbores under injection and production conditions of the present invention.

[0042] Figure 6 It is a schematic diagram of the structure of the vacuum pump and gas flowmeter of the physical simulation test device for the deformation of an array of horizontal wellbores under injection and production conditions of the present invention.

[0043] Figure 7 It is a schematic diagram of the structure of the extraction hole, stress, and temperature sensors of the physical simulation test device for the deformation of an array of horizontal wellbores under injection and production conditions of the present invention.

[0044] Figure 8 It is a schematic diagram of the structure of the computer and micro camera of the physical simulation test device for the deformation of an array of horizontal wellbores under injection and production conditions of the present invention.

[0045] Figure 9 It is a connection schematic diagram of the physical simulation test device for the deformation of an array of horizontal wellbores under injection and production conditions of the present invention.

[0046] Figure 10 It is a physical diagram of the physical simulation test device for the deformation of an array of horizontal wellbores under injection and production conditions of the present invention.

[0047] Figure 11This is a physical object diagram of the gas injection pressurization system of the physical simulation test device for array horizontal wellbore deformation under injection-production conditions of the present invention.

[0048] Figure 12 This is a physical object diagram of the stress loading system of the physical simulation test device for array horizontal wellbore deformation under injection-production conditions of the present invention.

[0049] Figure 13 This is a physical object diagram of the negative pressure machine and gas flowmeter of the physical simulation test device for array horizontal wellbore deformation under injection-production conditions of the present invention.

[0050] Figure 14 This is a physical object diagram of the drainage holes and stress sensors of the physical simulation test device for array horizontal wellbore deformation under injection-production conditions of the present invention.

[0051] Figure 15 This is a physical object diagram of the connection of each system of the physical simulation test device for array horizontal wellbore deformation under injection-production conditions of the present invention.

[0052] Figure 16 This is a comparison diagram of the deformation of the drainage holes before and after gas injection production when the borehole spacing is 210mm.

[0053] Figure 17 This is a curve graph of the area change rate of the drainage holes after the test when the borehole spacing is 210mm.

[0054] Figure 18 This is a curve graph of the change of the internal stress in coal samples in different regions under injection-production conditions.

[0055] Figure 19 This is a curve graph of the change of the gas flow rate at the wellbore outlet under different borehole spacings.

[0056] Figure 20 This is a curve graph of the change of the monitored temperature in different regions of the specimen under injection-production conditions.

[0057] Figure 21 This is a comparison diagram of the wellbore shrinkage in the field and the wellbore shrinkage in the physical simulation test under injection-production conditions.

[0058] In the figure: 1. Gas injection pipeline; 2. Fixed frame of test chamber; 3. Loading chamber; 4. Connection hole; 5. Sealing rubber pad; 6. Stress loading chamber; 7. Gas injection hole; 8. Gas extraction hole; 9. Solid-gas separation device; 10. Negative pressure machine; 11. Pneumatic multi-way interface; 12. Computer; 13. Gas flowmeter; 14. Multi-way negative pressure interface; 15. Control valve of stress loading system; 16. Control valve of test chamber; 17. Modem; 18. Universal wheel; 19. Rotating hinge; 20. Connecting air pipe; 21. Stress sensor; 22. Threaded connection head of air pipe; 23. Gas cylinder; 24. Flipping hinge; 25. Bolt; 26. Threaded interface of negative pressure machine; 27. Fixed support leg; 28. Threaded through hole; 29. Gas injection screw hole; 30. Three-way interface; 31. Pressure gauge of negative pressure gauge; 32. Air outlet of negative pressure machine; 33. Heating plate; 34. Electric heating wire; 35. Power control switch; 36. Pressure gauge of gas cylinder; 37. Electric wire; 38. Extraction pipeline; 39. Extended cross bar; 40. Fixed nut; 41. Drilling plug; 42. Connecting nut; 43. Extraction pump; 44. Miniature camera; 45. Temperature sensor; 46. Pressure gauge of gas injection for stress loading system; 47. Pressure gauge of gas injection for test chamber; 48. Screw hole; 49. Air inlet of negative pressure machine. Detailed implementation manners

[0059] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0060] In the drawings, the size and thickness of each component shown are arbitrarily shown, and the present invention does not limit the size and thickness of each component. To make the illustration clearer, the size of some parts in the drawings is appropriately exaggerated.

[0061] As Figure 1As shown in the figure, the present invention provides a physical simulation test device and method for array horizontal wellbores under injection-production conditions. The tee joint (30) is connected to the gas cylinder (23), the stress loading system control valve (15), and the test chamber control valve (16). The stress loading system control valve (15) is connected to the gas injection pipeline (1). The gas injection pipeline (1) is connected to the stress loading chamber (6) in a threaded manner through the gas injection screw hole (29). The test chamber control valve (16) is connected to the gas injection hole (7) of the test chamber through the connecting gas pipe (20). The stress loading system control valve (15) and the test chamber control valve (16) can be opened to inject the gas in the gas cylinder (23) into the stress loading chamber (6) and the loading chamber (3), providing the triaxial stress required for the test and simulating the actual situation of coalbed methane extraction by gas injection. The loading pressure can be obtained by reading the gas injection pressure gauge (46) of the stress loading system, and the gas injection pressure can be obtained by reading the gas injection pressure gauge (47) of the test chamber; the stress sensor (21) and the temperature sensor (45) can be connected to the modem (17) through the connection hole (4) at the top of the loading chamber (3) and then connected to the computer USB interface to realize the digital acquisition and recording of stress and temperature; 15 gas injection holes (7) and gas production holes (8) with a diameter of 20 mm and a spacing of 70 mm are arranged in an array on the front of the loading chamber (3). The micro camera (44) extends into the specimen through the gas injection hole (7) or the gas production hole (8) on the front side of the loading chamber (3) to photograph the borehole size before and after the test to analyze the borehole deformation; the heating plate (33) is located at the rear side of the loading chamber (3) and consists of an electric heating wire (34), a wire (37), and a power control switch (35) to provide the test temperature; the gas production hole (8) is connected to the negative pressure machine (10) through the extraction pipeline (38) and the multi-pass negative pressure interface. A solid-gas separation device (9) is connected to the front end of the air inlet (49) of the negative pressure machine to separate solids and prevent damage to the machine; the gas flowmeter (13) is connected to the outlet (32) of the negative pressure gauge in a threaded manner to observe the change of gas flow in real time; the negative pressure machine pressure gauge (31) can monitor the pore pressure of the specimen to be tested in real time. See the physical diagram of the device in Figure 10 。

[0062] This example also discloses a physical simulation test method for the deformation of array horizontal wellbores under injection-production conditions. Taking different wellbore spacings as examples, this method includes the following steps:

[0063] S1: Through geological exploration, geological data analysis, and investigation of on-site coalbed methane extraction technical solutions, determine that the wellbore spacings for the physical simulation test of the deformation of array horizontal wellbores under injection-production conditions are 70 mm, 140 mm, and 210 mm, the wellbore diameter is 10 mm, and the gas injection method is long-hole gas injection, and obtain parameters such as the moisture content of the coal sample, gas injection pressure, loading stress, and test temperature in the physical simulation test;

[0064] S2: Prepare a coal sample with a particle size less than 200 mesh and mix it with a certain amount of water to form a pulverized coal sample with the designed moisture content for the test;

[0065] S3: Rotate the carrier frame, place the test chamber vertically, remove the stress loading chamber (6), seal the screw holes (48) around the loading chamber with transparent tape, then load the pulverized coal samples layer by layer. For each layer loaded, compact it to the designed density using a pressing plate, place stress sensors (21) and temperature sensors (45) at the positions where monitoring is required, and then continue to load the pulverized coal samples according to the above method until the sample production is completed;

[0066] S4: Remove the transparent tape on the side of the loading chamber (3), connect the loading chamber (3), the sealing rubber gasket (5) and the stress loading chamber (6) through the fixing nuts (40), tighten the fixing nuts (40), and connect the stress sensors (21) and temperature sensors (45) to the modem (17) to complete the installation of the stress loading system and the pressure and temperature monitoring device;

[0067] S5: According to the test design requirements of the determined wellbore spacing, use the borehole plug (41) to block the unnecessary gas injection holes (7) and gas extraction holes (8), drill the gas injection and gas extraction wellbores that meet the test design dimensions, and use a micro camera (44) to go deep into the wellbore to record the shape of the wellbore before the test, and record the image information into the computer (12);

[0068] S6: According to the simulation test design scheme, connect the gas injection pressurization system to the gas injection hole (7) through the gas injection pipeline (1), connect the negative pressure extraction system to the gas extraction hole (8), close the negative pressure machine (10), and zero the gas flowmeter (13);

[0069] S7: Connect the gas cylinder filled with methane with a concentration of 99.9% to the gas injection pressurization system, open the gas injection control valve (16) of the test chamber, let the methane gas flow into the loading chamber (3) to fill the pores of the sample, and keep the gas pressure at the test design value for 24 hours to allow the sample to fully adsorb the methane gas;

[0070] S8: Replace the methane gas cylinder with a nitrogen gas cylinder, open the gas injection control valve (15) of the stress loading system, inject high-pressure nitrogen into the stress loading chamber (6) to make the injection pressure reach the test setting value and keep it stable; start the heating plate (33) to heat to 38°C;

[0071] S9: Open the negative pressure machine (10) to simulate the negative pressure extraction operation under the condition of injecting gas to produce coalbed methane. At the same time, start the acquisition of stress and temperature signals, and record the readings of the pressure gauge (31) of the negative pressure machine and the gas flowmeter (13) in real time. When the gas flowmeter (13) stabilizes and fluctuates within a very small range, stop the test, close the acquisition of stress and temperature signals of the computer, and close the negative pressure machine (10), the gas injection control valve (15) of the stress loading system and the gas injection control valve (16) of the test chamber;

[0072] S10: Open the gas extraction hole (8), use a micro camera (44) to go deep into the wellbore to the image acquisition position before the test to photograph its shape, and record the image information into the computer (12) for comparative analysis of the deformation of the wellbore before and after the test.

[0073] The test results obtained according to the above embodiments and the implementation effects are analyzed as follows:

[0074] Using this device to carry out the test on the influence law of different wellbore spacings on wellbore stability under gas injection mining conditions, the results show that:

[0075] When the wellbore spacing is 210 mm, the overall condition of the wellbore is good, only a very small amount of coal powder flows out, the wellbore stability is good, and after the gas injection mining is stable, the deformation of the wellbore is small, and there is no overall collapse or sealing. When the wellbore spacing is 140 mm, obvious changes occur in the formed wellbore. During the extraction process, a certain amount of coal powder flows out, and partial collapse appears in the wellbore. After the gas injection mining is stable in some wellbores, the deformation of the wellbore is large, but there is no phenomenon of borehole shrinkage and sealing. When the wellbore spacing is 70 mm, after the wellbore is arranged, the overall wellbore is affected, obvious deformation appears, and coal and rock fall off the wall of some wellbores. After the gas injection mining is stable, the wellbore almost shows different degrees of collapse or borehole shrinkage and sealing.

[0076] It can be seen from Figure 16 that when the wellbore spacing is 210 mm, the overall condition of the wellbore is good, only accompanied by a very small amount of coal powder flowing out, and the wellbore stability is good. After the gas injection mining is stable, the deformation of the wellbore is small, and there is no overall collapse or borehole shrinkage and sealing. It can be seen from Figure 17 that due to gas injection and negative pressure extraction, the coal powder on the surface of some wellbores is sucked out, causing partial minor deformation on the surface of the wellbore, showing a situation where the cross-sectional area of the wellbore is reduced. The reduction amount is between 20% and 30%, which has little impact on the overall stability of the wellbore, and the average equal ratio area change rate is -28.1109%.

[0077] It can be seen from Figure 18 that during the whole process of gas injection mining, the stress applied by the stress loading system changes little and remains at about 2.5 MPa, indicating that the stress loading system of this device has good stability. In oil and gas drilling, when the wellbore is formed, the stress around the wellbore will redistribute, and the circumferential stress of the wellbore is higher than the original in-situ stress of the formation. According to Figure 18 the initial point of the circumferential stress curve around the gas extraction hole in Figure 18The characteristics of the stress change with time around the wellbore near the gas intake hole are consistent. As the distance affected by the deformation and failure of the wellbore gradually expands, it will also cause the stress at the midpoint of the connection between the injection and production hole centers to decrease with time. This result is also consistent with Figure 18 the situation of the stress change with time at the midpoint of the connection between the injection and production hole centers in

[0078] Through the test results with different wellbore spacings, when the wellbore spacings are 210 mm, 140 mm, and 70 mm respectively, the average gas flow rates are approximately 3.87 SLPM, 3.42 SLPM, and 3.04 SLPM (as Figure 19 shown). The average gas flow rate will change with the change of the wellbore area. When the wellbore spacing is 210 mm, the deformation of the wellbore is small, and there is no overall collapse, shrinkage and sealing, etc. Therefore, the average gas flow rate is large. When the wellbore spacing is 140 mm, partial collapse occurs in the wellbore. After the injection and production are stable in some wellbores, the deformation of the wellbore is large, which hinders the gas flow channel, but the wellbore does not show the phenomenon of shrinkage and sealing, so it has a certain impact on the average gas flow rate. When the wellbore spacing is 70 mm, due to the influence of gas injection and extraction and the stress between wellbores, the wellbore becomes unstable, causing the wellbore to deform, resulting in situations such as collapse, shrinkage and sealing, so the average gas flow rate is small.

[0079] Generally, for every 100-meter decrease in formation depth, the temperature will increase by 3°C. The buried depth of the coal seam simulated in this test is about 370 meters, and the surface temperature is 24°C. It is calculated that the temperature of the specimen set in this physical simulation test is 38°C. From Figure 20 it can be seen that the monitored temperature of the heating plate is about 38°C, with a change within 0.2°C, indicating that the temperature control of the device is good. During the injection and production test process, the injected gas is normal-temperature nitrogen. With the continuous heat exchange, the temperature at the midpoint of the connection line between the injection and production hole centers and the temperature around the wellbore near the gas intake hole will both decrease, and the temperature at the midpoint of the connection line between the injection and production hole centers closer to the injection hole is lower than the temperature around the wellbore near the gas intake hole, and the decrease rate is faster. However, as time increases, due to the heat exchange gradually reaching equilibrium, the temperature at the midpoint of the connection line between the injection and production hole centers and the temperature around the wellbore near the gas intake hole will eventually tend to be stable. Thus, Figure 20 the shown change of the temperature at the midpoint of the connection line between the injection and production hole centers and the temperature around the wellbore near the gas intake hole with time conforms to the actual heat exchange law, and the physical model test of simulating the formation temperature can be carried out using this device.

[0080] Based on the temperature values, gas flow rate values, average equal ratio area change rate, and stress at different positions from the wellbore obtained from the physical simulation test of the present invention, combined with the actual engineering situation on site, during the coalbed methane extraction process, due to the stress influence between wellbores, being too close or having an irregular arrangement will cause wellbore collapse or instability and sealing, which is in good agreement with the test results of this device (seeFigure 21 ), indicating that the physical simulation test of the deformation and failure of the horizontal wellbore in the coal seam under the condition of gas injection mining carried out by this device has good results. Through the test results obtained by this device, considering the mutual influence of multiple factors, the laws obtained from the test of this device can be used to guide the design and engineering operations of gas injection for coalbed methane extraction in underground coal mines, so as to obtain better coalbed methane extraction benefits.

[0081] The above are only some implementation examples of the present invention, and do not impose any formal restrictions on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments by using the above-disclosed technical content within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A physical simulation test method for the deformation of an array of horizontal wellbores under injection-production conditions, which is realized by using a physical simulation test device for the deformation of an array of horizontal wellbores under injection-production conditions, and is characterized in that, The method includes the following steps: S1: Through geological exploration, geological data analysis, and on-site research on coalbed methane extraction technical solutions, determine that the wellbore spacing for the physical simulation test of array horizontal wellbore deformation under injection and production conditions is 70 mm, 140 mm, and 210 mm, the wellbore diameter is 0 - 20 mm, the gas injection method is long-hole gas injection, and obtain the moisture content of the coal sample, gas injection pressure, loading stress, and test temperature in the physical simulation test; S2: Prepare coal samples with a particle size less than 200 mesh, and mix them with a certain amount of water to form a coal powder sample with the moisture content designed in the test; S3: Rotate the bearing frame, place the test box vertically, remove the stress loading chamber (6), seal the screw holes (48) around the loading chamber with transparent tape, fill the coal powder sample in layers, and compact each layer with a pressing plate to the designed density. Place stress sensors (21) and temperature sensors (45) at the positions where monitoring is required, and then continue to fill the coal powder sample according to the above method until the sample production is completed; S4: Uncover the transparent tape on the side of the loading chamber (3), connect the loading chamber (3), the sealing rubber pad (5), and the stress loading chamber (6) through the fixing nut (40), tighten the fixing nut (40), and connect the stress sensors (21) and temperature sensors (45) to the modem (17) to complete the installation of the stress loading system and the pressure and temperature monitoring device; S5: Use a drilling plug (41) to block the unnecessary gas injection holes (7) and gas extraction holes (8), drill injection and extraction wellbores that meet the test design dimensions, and use a micro camera (44) to go deep into the wellbore to record the wellbore shape before the test, and record the image information into the computer (12); S6: Connect the gas injection pressurization system to the gas injection hole (7) through the gas injection pipeline (1), connect the negative pressure extraction system to the gas extraction hole (8), turn off the negative pressure machine (10), and zero the gas flowmeter (13); S7: Connect the gas cylinder filled with methane with a concentration of 99.9% to the gas injection pressurization system, open the gas injection control valve (16) of the test box, and let the methane gas flow into the loading chamber (3) to fill the pores of the sample; S8: Replace the methane gas cylinder with a nitrogen gas cylinder, open the gas injection control valve (15) of the stress loading system, inject high-pressure nitrogen into the stress loading chamber (6), make the injection pressure reach the test design value and remain stable, and start the heating plate (33) to heat to the test temperature; S9: Turn on the negative pressure machine (10), simulate the negative pressure extraction operation under the condition of injecting gas to extract coalbed methane, and at the same time start the acquisition of stress and temperature signals, and record the readings of the negative pressure gauge (31) of the negative pressure machine and the gas flowmeter (13) in real time. When the gas flowmeter (13) stabilizes and fluctuates within a very small range, stop the test, turn off the acquisition of stress and temperature signals of the computer, and turn off the negative pressure machine (10), the gas injection control valve (15) of the stress loading system, and the gas injection control valve (16) of the test box; S10: Open the gas extraction hole (8), use a micro camera (44) to go deep into the wellbore to the image acquisition position before the test to take its shape, and record the image information into the computer (12) for comparative analysis of the deformation of the wellbore before and after the test; The influence law test of different wellbore spacings on wellbore stability under gas injection production conditions was carried out using the test device and method. The results show that: when the wellbore spacing is 210 mm, the overall condition of the wellbore is good, only a very small amount of coal powder flows out, the wellbore stability is good, and after the gas injection production is stable, the deformation of the wellbore is small, and there is no overall collapse or sealing; when the wellbore spacing is 140 mm, obvious changes occur in the formed wellbore. During the extraction process, a certain amount of coal powder flows out, and partial collapse appears in the wellbore. After the gas injection production is stable, the deformation of some wellbores is large, but there is no phenomenon of borehole shrinkage and sealing; when the wellbore spacing is 70 mm, the overall wellbore is affected after the wellbore is arranged, obvious deformation appears, and coal and rock fall off from the hole wall of some wellbores. After the gas injection production is stable, the wellbore shows different degrees of collapse or borehole shrinkage and sealing.

2. The physical simulation test method for the deformation of an array of horizontal wellbores under injection-production conditions according to claim 1, characterized in that The test device includes: a carrier frame, a test box, a gas injection and pressurization system, a stress loading system, a negative pressure extraction system, and a data monitoring system.

3. The physical simulation test method for the deformation of an array of horizontal wellbores under injection and production conditions according to claim 2, wherein, The carrier frame is composed of a test box fixing frame (2), universal wheels (18), rotary hinges (19), flipping hinges (24), pins (25), fixed support feet (27), and extended crossbars (39); universal wheels (18) are installed at the bottom of the carrier frame to facilitate the movement of the equipment; the extended crossbars (39) are used as manual handles for the movement and rotation of the equipment; when loading and unloading samples, the fixed support feet (27) play a role in supporting and stabilizing, and at the same time, the rotary hinges (19) make the steering of the carrier frame more flexible, the flipping hinges (24) are convenient for opening the stress loading system to facilitate loading and unloading samples, and the pins (25) are used to fix the stress loading system.

4. A physical simulation test method for the deformation of an array of horizontal wellbores under injection-production conditions according to claim 2, characterized in that, The test box is composed of a loading chamber (3), a heating plate (33), fixing nuts (40), and drilling plugs (41); the loading chamber (3) is a box with five sides closed and one side open, and there are connection holes (4) for connecting stress sensors (21) and temperature sensors (45) at the top. The edge of the open side is connected to the stress loading system with screw holes (48). 15 gas injection holes (7) and gas extraction holes (8) with a diameter of 20 mm and a spacing of 70 mm are arranged in an array on the front of the loading chamber. According to needs, the drilling plugs (41) are used to threadedly connect and block the gas injection holes (7) and gas extraction holes (8). At the same time, the gas injection holes (7) and gas extraction holes (8) can interchange functions to simulate different gas extraction drilling arrangements; the heating plate (33) is located at the rear of the loading chamber (3) and is composed of heating wires (34), wires (37), and a power control switch (35); the fixing nuts (40) fix the stress sensors (21) and temperature sensors (45) through threaded connections.

5. The physical simulation test method for the deformation of an array of horizontal wellbores under injection-production conditions according to claim 2, wherein, The gas injection and pressurization system consists of a gas injection pipeline (1), a pneumatic multi-way interface (11), a gas injection control valve (15) for the stress loading system, a gas injection control valve (16) for the test chamber, a connecting air pipe (20), an air pipe threaded connector (22), a gas cylinder (23), a tee joint (30), a gas cylinder pressure gauge (36), a gas injection pressure gauge (46) for the stress loading system, and a gas injection pressure gauge (47) for the test chamber; the tee joint (30) connects the gas injection control valve (15) for the stress loading system, the gas injection control valve (16) for the test chamber, and the gas cylinder (23); when the gas injection control valve (15) for the stress loading system is opened, gas will be injected into the stress loading system for three-way stress loading; when the gas injection control valve (16) for the test chamber is opened, gas will be injected into the test chamber through the connecting air pipe (20), pneumatic multi-way interface (11), and threaded connector (22) connected according to the test design to simulate the actual situation of gas injection for coalbed methane extraction.

6. A physical simulation test method for array horizontal wellbore deformation under injection-production conditions according to claim 2, characterized in that The stress loading system consists of a sealing rubber gasket (5), a stress loading chamber (6), and a connecting nut (42); nut through holes (28) are provided around the stress loading chamber (6) in the stress loading system, and the connecting nut (42) passes through the nut through holes (28) to be connected with the sealing rubber gasket (5) and the loading chamber (3) to form a sealed cavity. An air injection screw hole (29) is provided on the right side of the stress loading chamber (6), which is connected to the gas injection and pressurization system to provide gas pressure for the stress loading chamber (6) and transmit it to the test chamber through the sealing rubber gasket (5) to apply three-way stress loads to the specimens in the test chamber.

7. A physical simulation test method for the deformation of an array of horizontal wellbores under injection-production conditions according to claim 2, characterized in that, The negative pressure extraction system consists of a solid-gas separation device (9), a negative pressure machine (10), a negative pressure machine pressure gauge (31), and a extraction pump (43); the front end of the air inlet (49) of the negative pressure machine is connected with a solid-gas separation device (9) to separate solids and prevent damage to the machine; the negative pressure machine pressure gauge (31) monitors the pore pressure of the specimen being tested in real time; the extraction pump (43) sucks the gas in the pores of the specimen in the test chamber to form a negative pressure to simulate the actual conditions of negative pressure extraction of coalbed methane.

8. A physical simulation test method for the deformation of an array of horizontal wellbores under injection-production conditions according to claim 2, characterized in that The data monitoring system consists of a computer (12), a gas flow meter (13), a modem (17), a stress sensor (21), a micro camera (44), and a temperature sensor (45); the stress sensor (21) and the temperature sensor (45) are connected to the modem (17) through the connection holes (4) at the top of the loading chamber (3) and connected to the USB interface of the computer (12) to realize digital acquisition and recording of stress and temperature. The micro camera (44) extends into the specimen through the air injection hole (7) or gas extraction hole (8) on the front side of the loading chamber (3) to photograph the wellbore size before and after the test to analyze the wellbore deformation, and transmits the video signal through the local area network for recording in the computer (12); the gas flow meter (13) is connected to the negative pressure gauge (10) by threads to observe the change of gas flow in real time.

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