Experimental apparatus for simulating fracturing of deep coalbed methane reservoirs and methods of use thereof

Abstract

The present application relates to experimental device for simulating deep coal measures gas reservoir fracturing and its using method, the experimental device, including experimental tank and several groups of fracturing device, experimental tank is used for containing simulation coal seam, the inside of simulation coal seam is evenly buried several microseismic detection probes, microseismic detection probe communication connection signal analysis device outside experimental tank, is used for analysing the fracture propagation of coal seam after fracturing coal seam;A vertical fracturing well is pre-buried in simulation coal seam;The fracturing device includes water tank, sand tank and booster pump, water tank, sand tank and parallel inlet pipe, booster pump is connected on the upstream side of conveying pipe, the outlet of conveying pipe is connected with the inlet of fracturing well, for providing fracturing water, fracturing sand to simulation coal seam;The outside of experimental tank is equipped with confining pressure device, for providing hydraulic oil to experimental tank, and the hydraulic oil provides confining pressure to simulation coal seam, to control the buried depth environment of coal seam.

Description

Technical Field

[0001] This invention belongs to the field of geological gas reservoir fracturing development technology, specifically relating to an experimental device for simulating deep coal-bearing gas reservoir fracturing and its usage method. Background Technology

[0002] The exploration, development, and utilization of natural gas is a crucial bridge for the transition from traditional fossil fuels to new energy sources. Coalbed methane (CBM) is an important component of unconventional natural gas. my country possesses vast deep CBM resources, but they are buried at depths of approximately 2000 meters. The depth of CBMs that can be industrially developed in my country reaches around 2000 meters, and the industry is gradually moving towards higher and more stable production. Fracturing is a critical step in deep CBM wells, but it presents challenges such as high temperatures, high ground stress, high fracturing pressure, and difficulty in propagating artificial fractures, leading to a series of problems. Currently, ultra-large-scale ultimate fracturing with "large fluid volume, large displacement, and large sand ratio" in deep CBM wells has gained widespread acceptance in the industry. However, the cost of ultra-large-scale ultimate fracturing is extremely high. Determining the threshold for ultra-large-scale fracturing in deep CBM wells would significantly reduce development costs. However, research on the threshold for fracturing scale in exploration is still in the experimental stage. While simulation experiments can be conducted on coal samples and blocks, accurate simulations of coal seam fracturing are not yet possible. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides an experimental apparatus and its method for simulating the fracturing of deep coal-bearing gas reservoirs, used to simulate the fracturing conditions of deep coal seams.

[0004] Firstly, the experimental apparatus for simulating fracturing in deep coal-bearing gas reservoirs includes an experimental tank and several sets of fracturing devices. The experimental tank is used to contain a simulated coal seam. Several microseismic detection probes are uniformly embedded inside the simulated coal seam. The microseismic detection probes are communicatively connected to a signal analysis device outside the experimental tank to analyze the propagation of fractures in the coal seam after fracturing. A vertical fracturing well is pre-embedded in the simulated coal seam.

[0005] The fracturing device includes a water tank, a sand tank, and a booster pump. The water tank and sand tank are connected to the inlet of a parallel delivery pipe. The booster pump is connected to the upstream side of the delivery pipe. The outlet of the delivery pipe is connected to the inlet of the fracturing well. It is used to supply slickwater and quartz sand to the simulated coal seam.

[0006] The experimental tank is equipped with a confining pressure device to supply hydraulic oil to the experimental tank. The hydraulic oil provides confining pressure to the simulated coal seam in order to control the burial depth environment of the coal seam.

[0007] Optionally, the water tank of the fracturing device is filled with slickwater, and the sand tank is filled with quartz sand. The slickwater and quartz sand are used to simulate coal seams for fracturing. The outlets of the water tank and the sand tank are respectively equipped with valves and a first flow meter to control the flow rates of the slickwater and the quartz sand.

[0008] Optionally, a mixing agitator is provided downstream of the water tank and sand tank, with the inlet of the mixing agitator connected in parallel to the water tank and sand tank, and the outlet of the mixing agitator connected to the inlet of the conveying pipe.

[0009] Optionally, a multi-way valve and a second flow meter are sequentially installed at the inlet of the fracturing well. The number of passages of the multi-way valve is equal to the number of groups of fracturing devices, which can control the amount of fracturing material that finally enters the fracturing well.

[0010] Optionally, the experimental tank is a cube with a detachable tank cover on top, which can be sealed to the top edge of the experimental tank.

[0011] During the experiment, a rubber sleeve was laid inside the experimental tank. The rubber sleeve consists of a separable sleeve body and a sleeve cover. The sleeve body includes a bottom surface and four surrounding sides. The sleeve body encloses a cubic space. After the coal sample is filled into the space, it is compacted to obtain a simulated coal seam.

[0012] The length, width, and height of the rubber sleeve are equal to the length, width, and height of the internal space of the experimental tank. The five sides of the sleeve and the inside of the sleeve cover are hollow, which is used to fill the inside with fine sand. When hydraulic oil applies confining pressure to the simulated coal seam, the rubber sleeve and the fine sand layer inside it wrap around the outside of the simulated coal seam, isolating the hydraulic oil, and at the same time making the oil pressure act evenly on the coal seam.

[0013] Further optionally, the sleeve is integrally formed, and the five sides of the sleeve and the cover are provided with inner bags 18. The inner bags 18 are used to fill fine sand, and the edges of the inner bags 18 are sealed to prevent fine sand leakage.

[0014] The sleeve cover and the groove cover are respectively provided with a first through hole and a second through hole at the position of the fracturing well, allowing the fracturing well to pass through the sleeve cover and the groove cover in sequence before connecting to the fracturing device.

[0015] Optionally, the upper surface of the sleeve is covered with a rubber cap layer, the rubber cap layer is a vertical well sleeve corresponding to the position of the fracturing well, the top of the well sleeve is provided with a third through hole, the fracturing well passes through the sleeve and enters the well sleeve, and drives the well sleeve to pass through the second through hole, the height of the third through hole is higher than the second through hole, so that the well sleeve can pass through the slot cover.

[0016] Optionally, the confining pressure device includes a hydraulic oil tank and several hydraulic oil pipes. Several oil inlets are evenly provided on the top surface of the tank cover near its own edge for connecting the hydraulic oil pipes and injecting hydraulic oil into the experimental tank.

[0017] A simulated coal seam internal pressure sensor is used to monitor the confining pressure of the simulated coal seam in real time, which guides the injection volume of hydraulic oil; an oil drain port is provided at the bottom of the experimental tank.

[0018] Secondly, the method of using the experimental apparatus for simulating fracturing in deep coal-bearing gas reservoirs includes the following steps:

[0019] (1) Fill the inner bag 18 at the bottom of the rubber sleeve with fine sand, then heat-seal the edge of the inner bag 18, put the rubber sleeve into the test tank, and spread the fine sand at the bottom of the sleeve evenly.

[0020] At the same time, the inner bags 18 on all four sides of the sleeve are kept open only at the top to facilitate filling the inner bags 18 with fine sand.

[0021] (2) A fracturing well is pre-set inside the rubber sleeve, then coal samples are filled inside the rubber sleeve, and microseismic detection probes are evenly buried. At the same time, fine sand is filled into the inner bags 18 on the four sides of the sleeve to ensure that the thickness of the coal seam before compaction is the same as the height of the fine sand in the inner bags 18 on the four sides; then the coal seam is compacted.

[0022] Repeat step (2), fill the coal sample in layers, and then compact it in layers to obtain a simulated coal seam;

[0023] (3) Fill the inner bag 18 of the cover with fine sand and then heat-press and seal it; place the cover above the simulated coal seam so that the fracturing well passes through the cover and the rubber cover layer in sequence; then lay the fine sand in the cover flat, and its thickness is equal to the thickness of the fine sand in the bottom surface of the cover; then connect the edge of the cover with the top edge of the cover and heat-press to close it to form a complete rubber cover.

[0024] (4) Place the trench cover on the top of the experimental trench, so that the fracturing well with the well casing passes through the trench cover and seals the trench cover to the experimental trench; then seal the well casing and the trench cover at the position of the third through hole, and then bond the top of the well casing to the outer side of the fracturing well.

[0025] (5) Check the air tightness of the experimental tank and fracturing device, and then inject hydraulic oil into the experimental tank through the oil inlet according to the gas reservoir burial depth. The hydraulic oil is evenly pressurized to each surface of the simulated coal seam through the rubber sleeve and the fine sand layer inside it to simulate the confining pressure conditions of the real strata.

[0026] (6) Turn on the microseismic detection probe and signal analysis device. When the confining pressure of the simulated coal seam reaches the experimental requirements, stop the input of hydraulic oil, start the fracturing device, and first input slickwater into the fracturing well to carry out pre-hydraulic fracturing.

[0027] (7) Turn on the sand tank and mixing agitator to input a mixture of slickwater and quartz sand into the fracturing well for sand-carrying hydraulic fracturing;

[0028] (8) Close the sand tank and mixing agitator, and then separately inject slickwater into the fracturing well to perform displacement hydraulic fracturing;

[0029] In steps (6), (7), and (8), the propagation of the hydraulic fracturing fractures in the simulated coal seam is continuously monitored using a microseismic detection probe and a signal analysis device.

[0030] (9) Close the fracturing device, microseismic detection probe and signal analysis device, open the drain port to drain the hydraulic oil and reduce the confining pressure inside the experimental tank; after draining the oil, open the tank cover, take out the simulated coal seam wrapped in the rubber sleeve, and end the experiment.

[0031] Optionally, in step (1), after the fine sand on the bottom surface of the casing is laid flat, the thickness of the fine sand on the bottom surface is 3-6% of the simulated coal seam thickness.

[0032] Optionally, step (2) may also include burying a pressure sensor in the coal seam.

[0033] Optionally, in steps (1) and (3), the fine sand is leveled using a scraper and a conventional level to lay and level the fine sand layer on the bottom surface of the sleeve and in the sleeve cover.

[0034] Optionally, in step (3), there is a certain gap between the edge of the inner bag 18 of the cover and the edge of the cover, for example, 0.5-1cm, to facilitate the connection between the cover and the cover body.

[0035] Optionally, the discharge rate of the slickwater can be set to different quantities, while other process conditions remain unchanged. Steps (6)-(8) can be performed to select the most suitable fracturing fluid discharge rate.

[0036] Adjust the timing of pre-fracturing and displacement fracturing, keeping other process conditions unchanged, and proceed with steps (6)-(8) to select the optimal total amount of fracturing fluid.

[0037] By adjusting the particle size of the quartz sand while keeping other process conditions unchanged, and performing steps (6)-(8), the most suitable particle size of the quartz sand can be selected.

[0038] Adjust the time of hydraulic fracturing with sand, keep other process conditions unchanged, and proceed with steps (6)-(8) to select the most suitable total amount of quartz sand.

[0039] Optionally, in step (9), the rubber sleeve is mechanically cut open to remove the fine sand and simulated coal seam from the inner bag 18, the simulated coal seam is broken, and the microseismic detection probe, pressure sensor, and fracturing well are removed. After cleaning, they can be reused, but the rubber sleeve cannot be reused. Each time the experimental conditions are changed, the simulated coal seam needs to be remade. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the experimental apparatus used to simulate the fracturing of deep coal-bearing gas reservoirs.

[0041] Figure 2 This is a schematic diagram of the experimental tank and the rubber sleeve;

[0042] Figure 3 This is a diagram illustrating the cover and its inner pocket.

[0043] In the attached diagram, 1-experimental tank, 2-simulated coal seam, 3-microseismic detection probe, 4-signal analysis device, 5-fractured well, 6-water tank, 7-sand tank, 8-booster pump, 9-delivery pipe, 10-first flow meter, 11-mixing agitator, 12-multi-way valve, 13-second flow meter, 14-tank cover, 15-rubber sleeve, 16-sleeve body, 17-sleeve cover, 18-inner bag, 19-oil inlet, 20-first through hole, 21-second through hole, 22-third through hole, 23-rubber cap layer, 24-well casing. Detailed Implementation

[0044] This embodiment provides an experimental apparatus for simulating fracturing in deep coal-bearing gas reservoirs, such as... Figures 1-3 As shown, the test tank includes an experimental tank 1 and several sets of fracturing devices. The experimental tank 1 is used to accommodate a simulated coal seam 2. Several microseismic detection probes 3 are uniformly embedded inside the simulated coal seam 2. The microseismic detection probes 3 are connected to a signal analysis device 4 outside the experimental tank 1 to analyze the expansion of the coal seam fractures after fracturing. A vertical fracturing well 5 is pre-embedded in the simulated coal seam 2.

[0045] The fracturing device includes a water tank 6, a sand tank 7, and a booster pump 8. The water tank 6 and the sand tank 7 are connected to the inlet of a parallel conveying pipe 9. The booster pump 8 is connected to the upstream side of the conveying pipe 9. The outlet of the conveying pipe 9 is connected to the inlet of the fracturing well 5 and is used to provide slickwater and quartz sand to the simulated coal seam 2.

[0046] The experimental tank 1 is equipped with a confining pressure device on its exterior, which is used to supply hydraulic oil to the experimental tank 1. The hydraulic oil provides confining pressure to the simulated coal seam 2 to control the burial depth environment of the coal seam.

[0047] Optionally, the water tank 6 of the fracturing device is filled with slickwater, and the sand tank 7 is filled with quartz sand. The slickwater and quartz sand are used to fracturing the simulated coal seam 2. The outlets of the water tank 6 and the sand tank 7 are respectively equipped with valves and a first flow meter 10 to control the flow rates of the slickwater and the quartz sand.

[0048] Optionally, a mixing agitator 11 is provided downstream of the water tank 6 and the sand tank 7, with the inlet of the mixing agitator 11 connected in parallel to the water tank 6 and the sand tank 7, and the outlet of the mixing agitator 11 connected to the inlet of the conveying pipe 9.

[0049] During fracturing, slickwater can be used alone, or slickwater and quartz sand can be mixed evenly in the mixer 11 before being fed into the fracturing well 5.

[0050] Optionally, the booster pump 8 is connected downstream of the mixing agitator 11 and is capable of pressurizing a single slickwater or a mixture of slickwater and quartz sand.

[0051] Optionally, a multi-way valve 12 and a second flow meter 13 are sequentially installed at the inlet of the fracturing well 5. The number of passages of the multi-way valve 12 is equal to the number of groups of fracturing devices, which can control the amount of fracturing material that finally enters the fracturing well 5.

[0052] The fracturing well 5 of the present invention has several sets of fracturing devices connected in parallel at the inlet to provide fracturing conditions for the fracturing well 5. Since the present invention needs to simulate the ultra-large-scale extreme fracturing situation of geological gas reservoirs, a single booster pump 8 in the laboratory cannot meet this requirement. By superimposing the pressure of several sets of fracturing devices, the requirements of ultra-large-scale extreme fracturing can be achieved.

[0053] Optionally, the experimental tank 1 is a cube with a detachable tank cover 14 on the top, and the tank cover 14 is sealed to the top edge of the experimental tank 1.

[0054] During the experiment, a rubber sleeve 15 was laid inside the experimental tank 1. The rubber sleeve 15 includes a separable sleeve body 16 and a sleeve cover 17. The sleeve body 16 includes a bottom surface and four surrounding sides. The sleeve body 16 encloses a cubic space. After the coal sample is filled into the space, it is compacted to obtain a simulated coal seam 2.

[0055] The length, width, and height of the rubber sleeve 15 are equal to the length, width, and height of the internal space of the experimental tank 1. The five sides of the sleeve body 16 and the interior of the cover 17 are hollow and used to fill the interior with fine sand 18. When hydraulic oil applies confining pressure to the simulated coal seam, the rubber sleeve 15 and the fine sand 18 inside it wrap around the outside of the simulated coal seam 2, isolating the hydraulic oil. At the same time, the oil pressure is evenly applied to the coal seam, making the confining pressure environment of the coal seam more in line with the actual situation and the experimental accuracy is higher.

[0056] Further optionally, the sleeve 16 is integrally formed, and the five sides of the sleeve 16 and the cover 17 are provided with inner bags 18. The inner bags 18 are used to fill fine sand 18. The edges of the inner bags 18 are sealed to prevent the fine sand 18 from leaking. For example, the inner bags 18 are pressed by hot pressing process.

[0057] The sleeve cover 17 and the groove cover 14 are respectively provided with a first through hole 20 and a second through hole 21 at the position corresponding to the fracturing well 5, allowing the fracturing well 5 to pass through the sleeve cover 17 and the groove cover 14 in sequence, and then connect to the fracturing device.

[0058] Optionally, the upper surface of the cover 17 is covered with a rubber cover layer 23. The rubber cover layer 23 corresponds to the vertical well sleeve 24 of the fracturing well 5. The top of the well sleeve 24 is provided with a third through hole 22. After the fracturing well 5 passes through the cover 17, it enters the well sleeve 24 and drives the well sleeve 24 to pass through the second through hole 21. The height of the third through hole 22 is higher than that of the second through hole 21, so that the well sleeve 24 can pass through the groove cover 14.

[0059] Optionally, the well sleeve 24 and the rubber cover 23 are integrally formed, so that the bottom of the well sleeve 24 and the rubber cover 23 are seamlessly connected. When the tank cover 14 is placed on the top surface of the experimental tank 1 and sealed, the well sleeve 24 is sealed at the position of the second through hole 21 to prevent the hydraulic oil entering the experimental tank 1 from the first through hole 20 into the inside of the cover 17 and from overflowing along the well sleeve 24 from the third through hole 22.

[0060] Figure 2 The rubber cover layer 23 and the sleeve cover 17 are separated and drawn as flat plates to clearly show the structure of the rubber sleeve.

[0061] Preferably, the length of the well sleeve 24 inside the experimental tank 1 is greater than the distance between the first through hole 20 and the second through hole 21. That is, the well sleeve 24 has extra space and wrinkles inside the experimental tank 1. In this way, when hydraulic oil is filled into the experimental tank 1 and presses the rubber cover 23 and the sleeve cover 17 downward, the upper part of the well sleeve 24 is sealed to the second through hole 21, and the lower part has room to extend. This avoids the well sleeve 24 from being unable to extend under force and breaking off, causing hydraulic oil to leak to the outside of the simulated coal seam 2 and / or the tank cover 14.

[0062] Optionally, the confining pressure device includes a hydraulic oil tank and several hydraulic oil pipes. Several oil inlets 19 are evenly provided on the top surface of the tank cover 14 near its own edge for connecting the hydraulic oil pipes and injecting hydraulic oil into the experimental tank 1.

[0063] A pressure sensor inside the simulated coal seam 2 is used to monitor the confining pressure of the simulated coal seam 2 in real time and to guide the injection volume of hydraulic oil; an oil drain port is provided at the bottom of the experimental tank 1.

[0064] The microseismic detection probe 3 and signal analysis device 4 mentioned are commonly used microseismic detection probes 3 and signal analysis devices 4 in the field of distributed microseismic monitoring, which can detect coal seam fracture information.

[0065] Optionally, the bottom of the fracturing well 5 is sealed, and several output holes are evenly arranged on the side for inputting fracturing fluid into the simulated coal seam 2.

[0066] The method of using the experimental apparatus for simulating fracturing in deep coal-bearing gas reservoirs includes the following steps:

[0067] (1) Fill the inner bag 18 at the bottom of the sleeve 16 of the rubber sleeve 15 with fine sand 18. After the fine sand 18 is laid flat, the thickness of the fine sand 18 at the bottom is 3% of the thickness of the simulated coal seam 2. Then, heat-press the edge of the inner bag 18 at the bottom and put the rubber sleeve 15 into the experimental tank 1. Lay the fine sand 18 at the bottom of the sleeve 16 flat.

[0068] At the same time, the inner bags 18 on all four sides of the sleeve 16 are kept open only at the top to facilitate filling the inner bags 18 with fine sand 18.

[0069] (2) A fracturing well 5 is pre-set inside the rubber sleeve 15, and then a coal sample is filled inside the rubber sleeve 15. Microseismic detection probes 3 and pressure sensors are evenly buried. At the same time, fine sand 18 is filled into the inner bags 18 on the four sides of the sleeve 16 to ensure that the thickness of the coal seam before compaction is the same as the height of the fine sand 18 in the inner bags 18 on the four sides; then the coal seam is compacted.

[0070] Repeat step (2), fill coal samples in layers, and then compact them in layers to obtain simulated coal seam 2; the coal seam can be compacted using a conventional device with mechanical pressing function, or it can be compacted manually.

[0071] (3) Fill the inner bag 18 of the cover 17 with fine sand 18, and then heat-press and seal it. There is a 0.5cm gap between the edge of the inner bag 18 of the cover 17 and the edge of the cover 17, so as to facilitate the connection between the cover 17 and the cover body 16.

[0072] Place the cover 17 above the simulated coal seam 2, so that the fracturing well 5 passes through the cover 17 and the rubber cover layer 23 in sequence. Then, lay the fine sand 18 inside the cover 17 flat, with a thickness equal to the thickness of the fine sand 18 inside the bottom surface of the sleeve body 16. Then, connect the edge of the cover 17 with the top edge of the sleeve body 16 and heat-press to close it, forming a complete rubber sleeve 15.

[0073] In steps (1) and (3), the fine sand 18 is leveled using a scraper and a conventional level to lay and level the fine sand 18 layer on the bottom surface of the sleeve 16 and the sleeve cover 17.

[0074] (4) Cover the top of the test tank 1 with the tank cover 14, so that the fracturing well 5 with the well sleeve 24 passes through the tank cover 14 and seal the tank cover 14 with the test tank 1; then seal the well sleeve 24 and the tank cover 14 at the position of the third through hole 22, and then bond the top of the well sleeve 24 to the outer side of the fracturing well 5.

[0075] (5) Check the air tightness of the experimental tank 1 and the fracturing device. Then, according to the burial depth of the gas reservoir, inject hydraulic oil into the experimental tank 1 through the oil inlet 19. The hydraulic oil is evenly pressurized to each surface of the simulated coal seam 2 through the rubber sleeve 15 and the fine sand 18 layer inside it to simulate the confining pressure conditions of the real strata.

[0076] (6) Turn on the microseismic detection probe 3 and signal analysis device 4. When the confining pressure of the simulated coal seam 2 reaches the experimental requirements (at a burial depth of 2000 meters, the vertical stress of the simulated coal seam is 54 MPa, the maximum horizontal principal stress is 89 MPa, and the minimum horizontal principal stress is 50 MPa), stop the input of hydraulic oil, start the six sets of fracturing devices, first input slickwater into the fracturing well 5 to perform pre-fracturing hydraulic fracturing, and the slickwater discharge of each water tank 6 is 2 m³ / s. 3 / min, the injection rate into fractured well 5 is 12m³ / min. 3 / min, injection time 5min;

[0077] (7) Turn on the sand tank 7 and the mixing agitator 11 to input a mixture of slickwater and quartz sand into the fracturing well 5 for sand-carrying hydraulic fracturing; the sand output rate of each sand tank 7 is 0.36m. 3 / min, the amount of sand injected into fractured well 5 is 2.16m. 3 / min, with quartz sand accounting for 18% of the volume, while the slickwater injection discharge rate is maintained at 12m³ / min. 3 / min, injection time 5min;

[0078] (8) Close the sand tank 7 and the mixing agitator 11, and then separately input slickwater into the fracturing well 5. The slickwater discharge rate of each tank 6 is 2m³. 3 / min, injection time 5min, to perform displacement hydraulic fracturing;

[0079] In steps (6), (7), and (8), the propagation of the hydraulic fracturing fractures in the simulated coal seam 2 is continuously monitored using the microseismic detection probe 3 and the signal analysis device 4.

[0080] (9) Close the fracturing device, microseismic detection probe 3 and signal analysis device 4, open the drain port, drain the hydraulic oil, and reduce the confining pressure inside the experimental tank 1; after draining the oil, open the tank cover 14, take out the simulated coal seam 2 wrapped by the rubber sleeve 15, and end the experiment.

[0081] In step (9), the rubber sleeve 15 is mechanically cut open, and the fine sand 18 and simulated coal seam 2 in the inner bag 18 are taken out. The simulated coal seam 2 is broken, and the microseismic detection probe 3, pressure sensor and fractured well 5 are taken out. After cleaning, they can be reused, but the rubber sleeve 15 cannot be reused. The simulated coal seam 2 needs to be remade every time the experimental conditions are changed.

[0082] The discharge capacity of the slickwater was set to different values: 2.5, 3, 3.5, and 4 m. 3 / min, with other process conditions unchanged, proceed with steps (6)-(8) to select the most suitable fracturing fluid discharge rate;

[0083] Adjust the time for pre-fracturing and displacement fracturing to 5, 10, 15, 20, and 25 minutes, while keeping other process conditions unchanged, and proceed with steps (6)-(8) to select the most suitable total amount of fracturing fluid.

[0084] Adjust the particle size of the quartz sand to 40, 60, 80, 100, or 120 mesh, while keeping other process conditions unchanged, and proceed with steps (6)-(8) to select the most suitable quartz sand particle size.

[0085] Adjust the time for hydraulic fracturing with sand to 5, 10, 15, 20, or 25 minutes, while keeping other process conditions unchanged. Then, proceed with steps (6) to (8) to select the most suitable total amount of quartz sand.

[0086] The experimental apparatus and its method for simulating fracturing in deep coalbed methane reservoirs described in this invention can simulate the effects of fracturing fluid flow rate, total fracturing fluid volume, quartz sand particle size, and total quartz sand volume on the fracturing effect of deep coalbed methane wells. Microseismic fracture monitoring technology is used to monitor the impact of these factors on the fracturing effect in real time. Simultaneously, it can also simulate the staged injection sequence of different quartz sand particle sizes during fracturing (in this case, quartz sand of different particle sizes is placed in different sand containers 7, which can be connected in parallel with the mixing agitator 11), optimizing the most suitable quartz sand injection sequence. Furthermore, this experimental apparatus and its method can also simulate fracturing engineering modifications of other types of oil and gas reservoirs (such as shale gas, shale oil, sandstone gas, limestone gas, bauxite gas, etc.) at different depths (i.e., different confining pressures), providing important references for oil and gas fracturing optimization.

[0087] This invention improves the simulation of confining pressure in coal seam 2. Traditional fracturing experiments target loose coal samples or small coal blocks, which are localized parts of the coal seam and cannot demonstrate the fracturing of the entire coal seam under confining pressure. Traditional experiments apply confining pressure to small samples using mechanical compression, but this is unsuitable for whole coal seam samples. Mechanical compression requires at least three surfaces of the coal seam (e.g., the bottom and two adjacent sides) to be compressed, while the other three surfaces remain stationary. Under the interaction of forces, all six surfaces of the coal seam are subjected to forces to simulate confining pressure. However, mechanical compression involves the movement of compression plates. With three adjacent surfaces, the compression plates corresponding to these three surfaces restrict each other during movement. If the compression plates are divided into sections, leakage of the coal sample or fracturing fluid is highly likely, resulting in pressure leakage and experimental failure.

[0088] This invention abandons traditional mechanical extrusion and instead uses hydraulic pressure. In order to further ensure that the simulated coal seam 2 is subjected to uniform stress, a rubber sleeve 15 is creatively used to wrap the coal seam. Under pressure, the coal seam can easily damage the rubber sleeve 15. This invention fills the rubber sleeve 15 with fine sand 18 (e.g., 100-120 mesh) to form a layer of fine sand 18, which protects the rubber sleeve 15. At the same time, it makes the hydraulic action surface regular and dense, and the coal seam is subjected to more uniform stress, which is closer to the actual coal seam situation and improves the accuracy of the experiment.

[0089] Each time a layer of coal sample is filled, fine sand 18 is simultaneously filled into the inner bags 18 on the four sides of the sleeve 16. The height of the fine sand 18 is the same as that of the coal sample. After the coal layer is compacted, the fine sand 18 is squeezed and its height increases slightly. When filling the next coal layer, the height of the fine sand 18 is still the same as that of the coal layer. This process is repeated so that after the last layer of coal sample is compacted, the fine sand 18 on all sides is only slightly higher than the simulated coal layer 2 (e.g., 1-5 mm). The extra space can be used to accommodate the sleeve 17 and its fine sand 18 layer. Finally, after the rubber sleeve 15 is closed, the top surface of the coal layer contacts the lower surface of the sleeve 17, and the upper surface of the sleeve 17 is close to the lower surface of the trough cover 14 (e.g., 1-10 mm away).

Claims

1. An experimental apparatus for simulating fracturing in deep coal-bearing gas reservoirs, characterized in that, It includes an experimental tank and several sets of fracturing devices. The experimental tank is used to contain a simulated coal seam. Several microseismic detection probes are uniformly embedded inside the simulated coal seam. The microseismic detection probes are connected to a signal analysis device outside the experimental tank to analyze the propagation of the coal seam fractures after fracturing. A vertical fracturing well is pre-embedded in the simulated coal seam. The fracturing device includes a water tank, a sand tank, and a booster pump. The water tank and sand tank are connected to the inlet of a parallel delivery pipe. The booster pump is connected to the upstream side of the delivery pipe. The outlet of the delivery pipe is connected to the inlet of the fracturing well. It is used to supply slickwater and quartz sand to the simulated coal seam. The experimental tank is equipped with a confining pressure device to supply hydraulic oil to the experimental tank. The hydraulic oil provides confining pressure to the simulated coal seam in order to control the burial depth environment of the coal seam. The experimental tank is a cube with a detachable tank cover on top, which can be sealed to the top edge of the experimental tank. During the experiment, a rubber sleeve was laid inside the experimental tank. The rubber sleeve consists of a separable sleeve body and a sleeve cover. The sleeve body includes a bottom surface and four surrounding sides. The sleeve body encloses a cubic space. After the coal sample is filled into the space, it is compacted to obtain a simulated coal seam. The five sides of the sleeve and the inside of the sleeve cover are hollow, which is used to fill the inside with fine sand. When the hydraulic oil applies confining pressure to the simulated coal seam, the rubber sleeve and the fine sand layer inside wrap around the outside of the simulated coal seam, isolating the hydraulic oil, while making the oil pressure act evenly on the coal seam. The sleeve cover and the groove cover are respectively provided with a first through hole and a second through hole at the position of the fracturing well, allowing the fracturing well to pass through the sleeve cover and the groove cover in sequence before connecting to the fracturing device; The upper surface of the sleeve is covered with a rubber cover layer. The position of the rubber cover layer corresponding to the position of the fracturing well is a vertical well sleeve. The top of the well sleeve is provided with a third through hole. After the fracturing well passes through the sleeve cover, it enters the well sleeve and drives the well sleeve to pass through the second through hole. The height of the third through hole is higher than that of the second through hole, so that the well sleeve can pass through the slot cover. The well casing and the rubber cover are integrally formed, so that the bottom of the well casing and the rubber cover are seamlessly connected. When the tank cover is placed on the top surface of the experimental tank and sealed, the well casing is sealed at the position of the second through hole to prevent the hydraulic oil entering the experimental tank from the first through hole into the inside of the cover and from overflowing from the third through hole along the well casing.

2. The experimental apparatus for simulating fracturing in deep coal-bearing gas reservoirs according to claim 1, characterized in that, The fracturing device has a water tank containing slickwater and a sand tank containing quartz sand. The slickwater and quartz sand are used to simulate coal seams for fracturing. The outlets of the water tank and the sand tank are equipped with valves and a first flow meter, respectively, to control the flow rates of the slickwater and the quartz sand.

3. The experimental apparatus for simulating fracturing in deep coal-bearing gas reservoirs according to claim 2, characterized in that, A mixing agitator is located downstream of the water tank and sand tank. The inlet of the mixing agitator is connected in parallel to the inlet of the water tank and sand tank, and the outlet of the mixing agitator is connected to the inlet of the conveying pipe.

4. The experimental apparatus for simulating fracturing in deep coal-bearing gas reservoirs according to claim 3, characterized in that, The inlet of the fracturing well is equipped with a multi-way valve and a second flow meter in sequence. The number of passages of the multi-way valve is equal to the number of groups of fracturing devices, which can control the amount of fracturing material that finally enters the fracturing well.

5. The experimental apparatus for simulating fracturing in deep coal-bearing gas reservoirs according to claim 4, characterized in that, The length, width, and height of the rubber sleeve are equal to the length, width, and height of the internal space of the experimental tank.

6. The experimental apparatus for simulating fracturing in deep coal-bearing gas reservoirs according to claim 5, characterized in that, The sleeve is integrally formed, and each of the five sides of the sleeve and the cover is provided with an inner bag. The inner bag is used to fill fine sand, and the edges of the inner bag are sealed to prevent fine sand leakage.

7. The experimental apparatus for simulating fracturing in deep coal-bearing gas reservoirs according to claim 6, characterized in that, The confining pressure device includes a hydraulic oil tank and several hydraulic oil pipes. Several oil inlets are evenly provided on the top surface of the tank cover near the edge of the tank body for connecting the hydraulic oil pipes and injecting hydraulic oil into the experimental tank. The simulated coal seam is equipped with a pressure sensor to monitor the confining pressure of the simulated coal seam in real time, so as to guide the injection volume of hydraulic oil; the bottom of the experimental tank is equipped with an oil drain port.

8. The method of using the experimental apparatus for simulating fracturing in deep coal-bearing gas reservoirs as described in claim 7, characterized in that, Includes the following steps: (1) Fill the inner bag at the bottom of the rubber sleeve with fine sand, then heat-seal the edge of the inner bag at the bottom, put the rubber sleeve into the test tank, and spread the fine sand at the bottom of the sleeve evenly. At the same time, the inner pockets on all four sides of the sleeve should only have their top openings open to facilitate filling the inner pockets with fine sand. (2) A pre-set fracturing well is placed inside the rubber sleeve, and then coal samples are filled inside the rubber sleeve. Microseismic detection probes are evenly buried. At the same time, fine sand is filled into the inner bags on the four sides of the sleeve to ensure that the thickness of the coal seam before compaction is the same as the height of the fine sand in the inner bags on the four sides; then the coal seam is compacted. Repeat step (2), fill the coal sample in layers, and then compact it in layers to obtain a simulated coal seam; (3) Fill the inner bag of the cover with fine sand and then heat-press and seal it; place the cover above the simulated coal seam so that the fracturing well passes through the cover and the rubber cover layer in sequence, then lay the fine sand in the cover flat, and its thickness is equal to the thickness of the fine sand in the bottom surface of the cover; then connect the edge of the cover with the top edge of the cover and heat-press to close it to form a complete rubber cover. (4) Place the trench cover on the top of the experimental trench, so that the fracturing well with the well casing passes through the trench cover and seals the trench cover to the experimental trench; then seal the well casing and the trench cover at the position of the third through hole, and then bond the top of the well casing to the outer side of the fracturing well. (5) Check the airtightness of the experimental tank and fracturing device, and then inject hydraulic oil into the experimental tank through the oil inlet according to the gas reservoir burial depth. The hydraulic oil is evenly pressurized to each surface of the simulated coal seam through the rubber sleeve and the fine sand layer inside it to simulate the confining pressure conditions of the real strata. (6) Turn on the microseismic detection probe and signal analysis device. When the confining pressure of the simulated coal seam reaches the experimental requirements, stop the input of hydraulic oil, start the fracturing device, and first input slickwater into the fracturing well to carry out pre-hydraulic fracturing. (7) Turn on the sand tank and mixing agitator to input a mixture of slickwater and quartz sand into the fracturing well for sand-carrying hydraulic fracturing; (8) Turn off the sand tank and mixing agitator, and then separately inject slickwater into the fracturing well to perform displacement hydraulic fracturing; In steps (6), (7), and (8), the propagation of the hydraulic fracturing fractures in the simulated coal seam is continuously monitored using a microseismic detection probe and a signal analysis device; (9) Close the fracturing device, microseismic detection probe and signal analysis device, open the drain port to drain the hydraulic oil and reduce the confining pressure inside the experimental tank; after draining the oil, open the tank cover, take out the simulated coal seam wrapped in the rubber sleeve, and end the experiment.

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