Deep in-situ coal body water locking strength testing device, testing method and evaluation method

Abstract

The application discloses a kind of deep in-situ coal body water lock strength testing device, including pressurized gas injection system, air-tightness detection system, vacuum pumping system, desorption testing system, water injection system, permeability testing system, data acquisition system.The application also provides a kind of deep in-situ coal body water lock strength testing device testing method and evaluation method.The application establishes in-situ coal body water lock strength experimental testing device and testing method under the condition of deep high stress, high ground temperature and high gas pressure, and proposes double evaluation indexes of coal permeability damage coefficient λ and coal gas retention coefficient η, constructs a set of water lock strength quantitative evaluation method, which can accurately evaluate the water lock strength of deep in-situ coal body after water injection, master the water lock damage law of hydraulic measures to coal reservoir, and provide basis for actual coal seam gas enhanced extraction, gas disaster control and other operation decisions.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of deep coal seam gas hydraulic exploitation and coal mine gas disaster water injection prevention and control, and particularly relates to a deep in-situ coal body water lock strength testing device, a testing method and an evaluation method. BACKGROUND

[0002] The stress of deep coal in-situ occurrence environment increases, and the ground temperature rises, which leads to large gas flow resistance in the coal body. Hydraulic fracturing and coal seam water injection are often used to change the permeability of the coal body, enhance the gas desorption and migration capacity, and improve the coal seam gas extraction rate. During the coal body water injection process, the liquid enters the gas-containing coal body and is adsorbed on the surface of the coal body organic matter. The water saturation of the reservoir rises, the liquid-gas interfacial tension increases, the fluid viscosity is enhanced, and then the gas phase flow resistance increases, the gas phase permeability of the gas-containing coal body decreases, and serious water lock damage is caused. In the exploitation of deep coal and gas resources, the water lock damage after the coal body water injection can cause the gas extraction capacity to decrease, the operation cost to increase, the economic benefit of the gas reservoir development to be poor, and other problems, which seriously affects the development and evaluation of the gas-containing coal body. Therefore, accurately evaluating the water lock strength of the gas-containing coal body has great significance for further mastering the water lock effect in the coal field and guiding the field application development.

[0003] At present, the evaluation method of water lock damage of oil reservoir is relatively mature, and the commonly used static core flow experiment method and rock sample immersion method mainly monitor the change rule of permeability before and after water lock of core, and then evaluate the water lock strength. Compared with oil reservoir, coal reservoir has strong adsorption, and a large amount of adsorbed and free gas is stored in situ coal body under the control of ground stress and ground temperature. The gas-liquid exchange principle and water lock property of gas-containing coal reservoir under the action of water injection are significantly different from those of oil reservoir, so the water lock evaluation method of oil reservoir cannot be completely applied to gas-containing coal reservoir. The water injection target of coal reservoir is to strengthen gas extraction, improve recovery efficiency and reduce gas content, so the retention degree of gas in coal body after water injection can be used as a macro effect of water lock evaluation, which can more directly express the change rule of gas extraction capacity after water lock, and combined with the water lock damage strength of permeability of gas-containing coal reservoir, a comprehensive water lock evaluation index including the sealing strength of coal reservoir and the desorption inhibition strength of gas is formed. The patent with publication number CN215678199U discloses a water lock damage testing device, which comprises a geological environment simulation module for placing samples and providing a simulated geological environment; a liquid phase injection module for injecting liquid into the sample; a gas phase injection module for injecting gas into the sample; a test module comprising a resistivity test unit for obtaining sample resistivity data and an acoustic wave test unit for obtaining sample longitudinal and transverse wave data; the test module is connected with the geological environment simulation module, the liquid phase injection module and the gas phase injection module, and is used for determining the water lock damage data of the sample according to the resistivity data and the longitudinal and transverse wave data measured under different environments. The water lock damage testing device provided by the patent simulates the geological environment of the sample, the fracturing fluid injection and flowback process, obtains the resistivity data and the longitudinal and transverse wave data of the sample under different environments, and then determines the water lock damage data of the sample. The water lock damage testing device in the patent has inconsistent test conditions with the actual field, single evaluation index, poor applicability and lack of continuous research on coal body adsorption gas, water injection and water lock. SUMMARY

[0004] The present application is directed to the above-mentioned deficiencies in the prior art, and proposes a deep in-situ coal body water lock strength testing device, testing method and evaluation method.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0006] The deep in-situ coal body water lock strength testing device comprises a pressurized gas injection system, a gas tightness detection system, a vacuum pumping system, a desorption testing system, a water injection system, a permeability testing system and a data acquisition system.

[0007] The pressurized gas injection system includes a methane cylinder, a booster pump, a booster pump inlet valve, a booster pump outlet valve, a high-pressure storage tank, a first pressure regulating valve, and a first high-pressure shut-off valve. The booster pump is connected to the methane cylinder via a first pipeline, and a booster pump inlet valve is installed on the first pipeline. The booster pump is connected to the inlet of the high-pressure storage tank via a second pipeline, and a booster pump outlet valve is installed on the second pipeline. A first branch pipeline is installed on the outlet of the high-pressure storage tank, and a first pressure regulating valve and a first high-pressure shut-off valve are installed on the first branch pipeline.

[0008] The airtightness detection system includes a helium cylinder, a second pressure regulating valve, and a high-pressure shut-off valve. The helium cylinder is connected to a third pipeline after merging with the first branch pipeline through a second branch pipeline. A second pressure regulating valve and a second high-pressure shut-off valve are installed on the second branch pipeline.

[0009] The desorption test system includes a high and low temperature program control box, a reference tank, a high-pressure coal sample tank, a ninth high-pressure shut-off valve, a first temperature sensor, a first pressure sensor, a second pressure sensor, a first pneumatic valve, a second pneumatic valve, and a third pneumatic valve. The reference tank and the high-pressure coal sample tank are placed in the high and low temperature program control box. The air inlet of the reference tank is connected to the third pipeline, and the air outlet of the reference tank is connected to the fourth pipeline. A fifth pipeline and the first temperature sensor are installed above the high-pressure coal sample tank, and the air inlet pipeline is connected to the bottom of the high-pressure coal sample tank. A ninth high-pressure shut-off valve is installed on the air inlet pipeline, and the ninth high-pressure shut-off valve is placed inside the high and low temperature program control box.

[0010] The water injection system includes a high-pressure water injection pump and an eighth high-pressure shut-off valve. The outlet of the high-pressure water injection pump is connected to the air inlet pipe through a sixth pipe, and an eighth high-pressure shut-off valve is installed on the sixth pipe.

[0011] The permeability testing system includes a triaxial holder, silicone oil, a stress pump, a constant temperature water bath, a second temperature sensor, an inlet pressure sensor, an outlet pressure sensor, a fifth high-pressure shut-off valve, a sixth high-pressure shut-off valve, a seventh high-pressure shut-off valve, and a fourth pneumatic valve. The triaxial holder is placed in the constant temperature water bath and is filled with silicone oil. The bottom of the triaxial holder has a first port and a second port. The first port is connected to the stress pump through a seventh pipeline, and the second port is connected to the inlet pipeline through an eighth pipeline. A fifth high-pressure shut-off valve is installed on the seventh pipeline, and a sixth high-pressure shut-off valve is installed on the eighth pipeline. The outlet at the top of the triaxial holder is connected to a ninth pipeline. An outlet pressure sensor and a fourth pneumatic valve are installed on the ninth pipeline, and the inlet pipeline is connected to the inlet pressure sensor.

[0012] The vacuum system includes a vacuum pump, a vacuum gauge, a third high-pressure shut-off valve, and a third pneumatic valve; the vacuum pump is connected to the vacuum gauge inlet via a tenth pipeline, and the vacuum gauge outlet is provided with an eleventh pipeline, on which the third high-pressure shut-off valve and the third pneumatic valve are installed.

[0013] The fourth and fifth pipelines are both connected to the eleventh pipeline, and the air intake pipeline is connected to the eleventh and twelfth pipelines. A high-pressure shut-off valve and a ninth pneumatic valve are installed on the twelfth pipeline.

[0014] It also includes: a thirteenth pipeline, a third branch pipeline, a fourth branch pipeline, a fifth branch pipeline, a sixth branch pipeline, a seventh branch pipeline, a fifth pneumatic valve, a sixth pneumatic valve, a seventh pneumatic valve, an eighth pneumatic valve, a vent valve, a first flow sensor, a second flow sensor, a third flow sensor, and a fourth flow sensor; the ninth and eleventh pipelines are both connected to the thirteenth pipeline at their ends, and the thirteenth pipeline is sequentially connected to the third branch pipeline, the fourth branch pipeline, the fifth branch pipeline, the sixth branch pipeline, and the seventh branch pipeline; a vent valve is installed at the end of the third branch pipeline; a fifth pneumatic valve and a first flow sensor are installed on the fourth branch pipeline; a sixth pneumatic valve and a second flow sensor are installed on the fifth branch pipeline; a seventh pneumatic valve and a third flow sensor are installed on the sixth branch pipeline; and an eighth pneumatic valve and a fourth flow sensor are installed on the seventh branch pipeline.

[0015] The first pressure sensor, the second pressure sensor, the inlet pressure sensor, the outlet pressure sensor, the first temperature sensor, the second temperature sensor, the first flow sensor, the second flow sensor, the third flow sensor, the fourth flow sensor, the first pneumatic valve, the second pneumatic valve, the third pneumatic valve, the fourth pneumatic valve, the fifth pneumatic valve, the sixth pneumatic valve, the seventh pneumatic valve, the eighth pneumatic valve, and the ninth pneumatic valve are all connected to the data acquisition system.

[0016] Furthermore, the methane in the methane cylinder has a purity of 99.999%, and the helium in the helium cylinder has a purity of 99.999%.

[0017] Furthermore, the second temperature sensor is placed inside the triaxial clamp cavity, and the second temperature sensor is used to monitor the internal temperature of the triaxial clamp.

[0018] Furthermore, the silicone oil fills the cavity of the triaxial clamp.

[0019] Furthermore, the first flow sensor measures flow rate in the range of 0–80 L / min with an accuracy of 5%; the second flow sensor measures flow rate in the range of 0–3000 mL / min with an accuracy of 0.2%; the third flow sensor measures flow rate in the range of 0–500 mL / min with an accuracy of 0.2%; and the fourth flow sensor measures flow rate in the range of 0–50 mL / min with an accuracy of 0.2%.

[0020] This invention also provides a testing method for a deep in-situ coal body water-lock strength testing device, which is implemented using the aforementioned deep in-situ coal body water-lock strength testing device and includes the following steps:

[0021] a. Prepare and dry No. 1 and No. 2 pillar coals: Collect coal cores from the coal reservoir to be evaluated. Two pillar coals must be prepared for each core, numbered No. 1 and No. 2, for coal gas content testing and permeability testing, respectively. Place both No. 1 and No. 2 pillar coals at 105℃ for continuous drying until the coal weight no longer changes, indicating drying is complete. Weigh the No. 1 pillar coal as coal weight G. m1 The weight of coal in pillar No. 2 is coal weight G. m2 ;

[0022] b. Perform an airtightness test on the testing device: Close all high-pressure shut-off valves and pneumatic valves of the testing device, then sequentially open the second high-pressure shut-off valve and the second pressure regulating valve. Fill the reference tank and high-pressure coal sample tank with helium gas, and read the helium pressures from the first and second pressure sensors as P. h1 P h2 Close the second pressure regulating valve and the second high-pressure shut-off valve, and continuously observe the first and second pressure sensors for 12 hours. h1 P h2 If the value remains unchanged, confirming that the airtightness of the testing device is good, the testing work can begin.

[0023] c. Place the dried No. 1 coal column in a high-pressure coal sample container and perform vacuum degassing on the desorption test system: Place the dried No. 1 coal column in a high-pressure coal sample container, close the first high-pressure shut-off valve, the second high-pressure shut-off valve, the ninth high-pressure shut-off valve, the third pneumatic valve, and the ninth pneumatic valve, open the first pneumatic valve, the second pneumatic valve, and the third high-pressure shut-off valve, start the vacuum pump and vacuum gauge to perform vacuum degassing on the desorption test system, when the vacuum gauge shows that the vacuum degree drops below 10Pa, close the first pneumatic valve, the second pneumatic valve, and the third high-pressure shut-off valve in sequence, and then turn off the vacuum pump;

[0024] d. Adjust the temperature of the high and low temperature program control box to the formation temperature t of the deep in-situ environment of the coal reservoir to be evaluated: Turn on the high and low temperature program control box and set the temperature to the formation temperature t of the deep in-situ environment of the coal reservoir to be evaluated. At this time, the first temperature sensor displays t.

[0025] e. Methane is pressurized by the booster pump and then fed into the high-pressure storage tank: Start the booster pump, open the booster pump inlet valve, and after the methane is pressurized by the booster pump, open the booster pump outlet valve to input methane gas at a pressure of not less than 10MPa into the high-pressure storage tank. Then, close the booster pump inlet valve, the booster pump, and the booster pump outlet valve in sequence.

[0026] f. Charge methane into the reference tank: First open the first high-pressure shut-off valve, and after 1 minute, open the first pressure regulating valve. The high-pressure gas storage tank charges methane into the reference tank. When the first pressure sensor displays P... c1 At this time, the first pressure regulating valve and the first high-pressure shut-off valve are closed in sequence, and P is then closed. c1 Not less than twice the simulated in-situ gas pressure P of the coal reservoir to be evaluated;

[0027] g. Methane is introduced into the high-pressure coal sample container to achieve methane adsorption equilibrium in column 1 of the high-pressure coal sample container, and the amount of coal gas adsorbed by column 1 before water injection, Q, is calculated. sx Open the second pneumatic valve, and after 1 minute, open the first pneumatic valve to quickly inject methane into the high-pressure coal sample tank. Then, close the first and second pneumatic valves sequentially. During this period, methane gas is repeatedly replenished into the high-pressure coal sample tank through the reference tank. When the pressure displayed by the second pressure sensor remains unchanged for 12 hours, it indicates that the methane adsorption in column 1 has reached equilibrium. At this time, the reading of the second pressure sensor is P, where P is the gas pressure simulating the in-situ environment of the coal reservoir to be evaluated. After the gas injection is completed, record the pressure displayed by the first pressure sensor as P. c2 ;

[0028] The total amount of methane injected into the high-pressure coal sample tank from the reference tank is calculated according to formula (1), which is the amount of coal gas adsorption Q of column No. 1 before water injection. sx :

[0029]

[0030] In the formula: Q sx —Gas adsorption capacity of No. 1 pillar coal before water injection, ml / g; V c —The sum of the volumes of the reference tank and the inflation pipeline, in ml, wherein the inflation pipeline includes the pipeline between the third high-pressure shut-off valve and the third pneumatic valve, the fourth pipeline, the pipeline between the second pneumatic valve and the eleventh pipeline, and the pipeline between the ninth pneumatic valve and the eleventh pipeline; P c1 —Before filling the high-pressure coal sample container with gas, the first pressure sensor monitors the equilibrium pressure of the reference container, in MPa; P c2 —After gas injection is completed, the first pressure sensor monitors the equilibrium pressure of the reference tank, in MPa; Z c1 —Under pressure P c1 The compressibility factor of methane at temperature t, dimensionless; Z c2 —Under pressure P c2The compressibility factor of methane at temperature t is dimensionless; t—the experimental temperature set in the high and low temperature program control box, i.e., the formation temperature of the deep in-situ environment of the coal reservoir to be evaluated, in °C.

[0031] h. Injecting water into the No. 1 column of coal, which has reached methane adsorption equilibrium, into the high-pressure coal sample container: Start the high-pressure water injection pump, and sequentially open the eighth and ninth high-pressure shut-off valves to inject water into the No. 1 column of coal, which has reached methane adsorption equilibrium. The weight of the injected water is G. s1 Stop water injection and sequentially close the ninth high-pressure shut-off valve, the eighth high-pressure shut-off valve, and the high-pressure water injection pump.

[0032] i. After water injection, the No. 1 coal column naturally desorbs methane for 24 hours. Calculate the coal body gas retention coefficient η: After 24 hours of water injection, sequentially open the vent valve and the third pneumatic valve. Free methane in the high-pressure coal sample tank is rapidly released outward along the pipeline. When the second pressure sensor shows zero pressure, quickly close the vent valve. Simultaneously, the data acquisition system issues commands to control the fifth, sixth, seventh, and eighth pneumatic valves, automatically switching the control of the first, second, third, and fourth flow sensors according to the methane flow rate V. The desorption time lasts for 24 hours. Then, close the second and third pneumatic valves. The desorption process is complete. The cumulative desorption amount recorded by the first, second, third, and fourth flow sensors is the desorption amount Q of the No. 1 coal column naturally desorbing methane for 24 hours after water injection. sj ;

[0033] The gas retention coefficient η of the coal body is calculated using formulas (2) to (4), specifically:

[0034] The gas content of dry No. 1 pillar coal under normal pressure is calculated using formula (2) as Q. g :

[0035]

[0036] In the formula: Q g —Gas content of No. 1 pillar coal under normal pressure, ml / g; a—Adsorption constant, ml / g; b—Adsorption constant, MPa -1 A ad —Ash content (%) of the deep in-situ environment of the coal reservoir to be evaluated; M ad —Moisture content of the deep in-situ environment of the coal reservoir to be evaluated, %;

[0037] The gas content of No. 1 pillar coal under water-lock conditions is calculated as Q using formula (3). s :

[0038] Q s =Q sx -Q sj (3)

[0039] In the formula: Q s —Gas content of No. 1 pillar coal under water-locked conditions, ml / g; Q sx —Gas adsorption capacity of No. 1 pillar coal before water injection, ml / g; Q sj —The amount of coal pillar No. 1 naturally desorbed after 24 hours of water injection, in ml / g;

[0040] Due to the water-locking effect, coal gas is retained in the pores. Under normal pressure, the gas content of water-bearing coal is greater than that of dry coal. The coal gas retention coefficient η is calculated using formula (4):

[0041]

[0042] Where: η—coal gas retention coefficient, %; Q s —Gas content of No. 1 pillar coal under water-locked conditions, ml / g; Q g —Gas content of No. 1 pillar coal dried under normal pressure, ml / g; Q sx —Gas adsorption capacity of No. 1 pillar coal before water injection, ml / g; Q sj — Desorption amount of No. 1 pillar coal after natural desorption for 24 hours after water injection, ml / g; a— Adsorption constant, ml / g; b— Adsorption constant, MPa -1 A ad —Ash content (%) of the deep in-situ environment of the coal reservoir to be evaluated; M ad —Moisture content of the deep in-situ environment of the coal reservoir to be evaluated, %;

[0043] j. After drying, the No. 2 pillar coal is sealed and placed in a triaxial clamp, and then subjected to water bath constant temperature control: The No. 2 pillar coal is sealed with heat shrink tubing and then placed in a triaxial clamp. The constant temperature water bath is started and the water bath temperature is set to the formation temperature t of the deep in-situ environment of the coal reservoir to be evaluated. At this time, the second temperature sensor displays t.

[0044] k. Apply axial pressure P to the No. 2 coal pillar using a stress pump. y1 and confining pressure P y2 To achieve the in-situ stress of the deep environment of the coal reservoir to be evaluated: open the fifth high-pressure shut-off valve and start the stress pump to apply axial pressure P to the No. 2 pillar coal. y1 and confining pressure P y2 When axial pressure P y1 and confining pressure P y2 After reaching the in-situ stress of the deep environment where the coal reservoir to be evaluated is located, the stress pump operating intensity is kept constant.

[0045] 1. Charge methane into the triaxial holder and balance the methane adsorption of the No. 2 column coal: Open the sixth high-pressure shut-off valve, the ninth high-pressure shut-off valve, the seventh high-pressure shut-off valve, and the ninth pneumatic valve. After 1 minute, open the first pneumatic valve to quickly charge methane into the triaxial holder. Then, close the first pneumatic valve and the ninth pneumatic valve in sequence. During this period, repeatedly replenish the triaxial holder with methane through the reference tank. When the pressure sensor at the inlet end and the pressure sensor at the outlet end simultaneously show that the pressure remains unchanged for 12 hours, it indicates that the methane adsorption of the No. 2 column coal is balanced. At this time, the readings of the pressure sensor at the inlet end and the pressure sensor at the outlet end both reach pressure P, which is the gas pressure of the simulated in-situ environment of the coal reservoir to be evaluated.

[0046] m. Calculate the permeability k of the dried No. 2 coal pillar containing gas. g The system sequentially opens the fourth, ninth, and first pneumatic valves. Simultaneously, it activates the data acquisition system and issues commands to control the fifth, sixth, seventh, and eighth pneumatic valves. Based on the methane flow rate V, it automatically switches control between the first, second, third, and fourth flow sensors. Once the methane flow through column 2 stabilizes, the first, second, third, and fourth flow sensors collect the stable flow rate as the gas flow rate Q at the outlet of the triaxial clamp. The pressure sensor at the inlet displays the pressure value P at the second port of the triaxial clamp. g1 The pressure value displayed by the outlet pressure sensor 904 is the gas pressure P at the outlet of the triaxial clamp. g2 ; Calculate the permeability k of the gas-containing dry No. 2 pillar coal according to formula (5). g ;

[0047]

[0048] In the formula: k g —Permeability of dry No. 2 pillar coal containing gas, 10 -15 m 2 Q—Gas flow rate at the outlet of the three-axis clamp, ml / s; P a —Atmospheric pressure, MPa; μ—Dynamic viscosity of gas, MPa·s; L2—Length of pillar coal No. 2, cm; A—Cross-sectional area of ​​pillar coal No. 2, cm² 2 ;P g1 —Gas pressure at the second port of the triaxial gripper, MPa; P g2 —Gas pressure at the outlet of the triaxial clamp, MPa;

[0049] n. Continue to replenish methane to column 2 of coal in the triaxial clamp until column 2 coal adsorbs methane to equilibrium: close the fourth pneumatic valve, and continue to replenish methane to column 2 of coal in the triaxial clamp using the reference tank. When the pressure sensor at the inlet end and the pressure sensor at the outlet end simultaneously display pressure P and remain unchanged for 12 hours, it indicates that column 2 coal adsorbs methane to equilibrium. Then close the first pneumatic valve, the ninth pneumatic valve, the ninth high-pressure shut-off valve, and the seventh high-pressure shut-off valve.

[0050] o. Inject water into the No. 2 column coal, which has already been balanced by adsorbed methane, in the three-axis clamp: Turn on the high-pressure water injection pump, open the eighth high-pressure shut-off valve, and inject water into the No. 2 column coal, which has already been balanced by adsorbed methane. The weight of the injected water is G. s2 Stop water injection and shut off the eighth high-pressure shut-off valve and the high-pressure water injection pump in sequence.

[0051] p. Calculate the coal permeability k under waterlock conditions after water injection. s After 24 hours of water injection, the fourth pneumatic valve, the ninth high-pressure shut-off valve, the ninth pneumatic valve, and the first pneumatic valve are opened sequentially. Simultaneously, the data acquisition system is activated, and commands are issued to control the fifth, sixth, seventh, and eighth pneumatic valves. The first, second, third, and fourth flow sensors are automatically switched according to the methane flow rate V. Once the methane flow through column No. 2 stabilizes, the first, second, third, and fourth flow sensors collect the stable flow rate as the gas flow rate Q at the outlet of the triaxial clamp. The pressure sensor at the inlet displays the pressure value as the gas pressure P at the second port of the triaxial clamp. s1 The pressure value displayed by the pressure sensor at the outlet is the gas pressure P at the outlet of the triaxial clamp. s2 ; Calculate the coal permeability k under water-locked conditions after water injection according to formula (6). s ;

[0052]

[0053] In the formula: k s —Coal permeability under water-locked state after water injection, 10 -15 m 2 Q—Gas flow rate at the outlet of the three-axis clamp, ml / s; P a —Atmospheric pressure, MPa; μ—Dynamic viscosity of gas, MPa·s; L2—Length of pillar coal No. 2, cm; A—Cross-sectional area of ​​pillar coal No. 2, cm² 2 ;P s1 —Gas pressure at the second port of the triaxial gripper, MPa; P s2 —Gas pressure at the outlet of the triaxial clamp, MPa;

[0054] q. Calculate the coal permeability damage coefficient λ: k is calculated according to formulas (5) and (6). g and k s The coal permeability damage coefficient λ is calculated according to formula (7);

[0055]

[0056] Where: λ—coal permeability damage coefficient, %; k g —Permeability of dry No. 2 pillar coal containing gas, 10 -15 m 2 ;k s —Coal permeability under water-locked state after water injection, 10 -15 m 2 ;

[0057] r. The experimental testing process has ended.

[0058] Furthermore, the weight G of the injected water in step h s1 Not greater than the weight G of No. 1 coal pillar m1 15%.

[0059] Furthermore, the weight G of the injected water in step o s2 No more than the weight of No. 2 coal pillar G m2 15%.

[0060] Furthermore, in steps i and m, the principle for automatically switching the control of the first, second, third, and fourth flow sensors according to the methane flow rate V is as follows: when 3000 mL / min ≤ V < 80 L / min, the fifth pneumatic valve automatically opens, and the first flow sensor monitors and records the methane flow rate and desorption amount; when 500 mL / min ≤ V < 3000 mL / min, the sixth pneumatic valve automatically opens, and the second flow sensor monitors and records the methane flow rate and desorption amount; when 50 mL / min ≤ V < 500 mL / min, the seventh pneumatic valve automatically opens, and the third flow sensor monitors and records the methane flow rate and desorption amount; when 0 < V < 50 mL / min, the eighth pneumatic valve automatically opens, and the fourth flow sensor monitors and records the methane flow rate and desorption amount.

[0061] This invention also provides a method for evaluating the water-locking strength of deep in-situ coal bodies. Based on the coal gas retention coefficient η and coal permeability damage coefficient λ obtained according to the aforementioned test method, the water-locking strength of deep in-situ coal bodies is comprehensively evaluated according to Table 1.

[0062] Table 1. Comprehensive Evaluation Table of Water Lock Strength in Deep In-situ Coal Seams

[0063] Coal gas retention coefficient η (%) Coal permeability damage coefficient λ (%) Deep in-situ coal water lock strength evaluation grade ≤10 ≤5 None 10～40 5～30 Weak 40～80 30～60 Medium ≥80 70～100 Strong .

[0064] Compared with existing technologies, the present invention has the following advantages by adopting the above technical solution:

[0065] This invention establishes an experimental testing device and method for the water-lock strength of in-situ coal seams under deep, high-stress, high-temperature, and high-gas-pressure conditions. It also proposes a dual evaluation index of coal permeability damage coefficient λ and coal gas retention coefficient η, constructing a quantitative evaluation method for water-lock strength. This method can accurately evaluate the water-lock strength of in-situ gas-bearing coal seams after water injection, providing scientific guidance for the application of hydraulic measures in coal seams. Specific beneficial effects are as follows:

[0066] (1) The deep in-situ coal water lock strength testing device of the present invention can realize the coal gas content test and permeability test through a set of devices, obtain the coal gas retention coefficient η and the coal permeability damage coefficient λ, realize the comprehensive evaluation of the coal sample water lock strength, and the experimental test and data acquisition have basically realized automation and precision, and the operation is simple, the results are accurate and the operation is efficient.

[0067] (2) This invention establishes a dual index and evaluation rule for the coal gas retention coefficient η and the coal permeability damage coefficient λ. The coal gas retention coefficient η characterizes the intensity of the influence of water injection on the gas extraction capacity of the coal reservoir, and the coal permeability damage coefficient λ realizes the quantitative transformation of the coal reservoir's own properties under the influence of water lock. The combination of the two achieves a comprehensive evaluation of the water lock intensity of the coal reservoir, and the results are more realistic, more accurate and more reliable.

[0068] (3) This invention can realize the whole process test of coal adsorption of gas, post-water injection, and desorption after water lock in the in-situ environment of deep high ground stress, high ground temperature and high gas pressure. It can accurately reflect the impact of water injection on gas migration and sealing of gas-bearing coal reservoirs under the influence of the formation environment. It can accurately evaluate the degree of water lock damage to coal reservoirs in different in-situ environments, and grasp the law of water lock damage to coal reservoirs by hydraulic measures. It provides a basis for decision-making on actual coal seam gas enhanced extraction, gas disaster management and other operations. Attached Figure Description

[0069] Figure 1 This is a schematic diagram of the deep in-situ coal body water-lock strength testing device of the present invention;

[0070] Figure 2 This is a schematic diagram of the connection of the data acquisition system of the deep in-situ coal body water-lock strength testing device of the present invention;

[0071] Figure 3 This is a flowchart of the testing method for the deep in-situ coal body water-lock strength testing device of the present invention;

[0072] In the diagram: 1 - Methane cylinder; 201 - Booster pump inlet valve; 202 - Booster pump outlet valve; 203 - First high-pressure shut-off valve; 204 - Second high-pressure shut-off valve; 205 - Third high-pressure shut-off valve; 206 - Fourth high-pressure shut-off valve; 207 - Fifth high-pressure shut-off valve; 208 - Sixth high-pressure shut-off valve; 209 - Seventh high-pressure shut-off valve; 210 - Eighth high-pressure shut-off valve; 211 - Ninth high-pressure shut-off valve;

[0073] 3 - Booster pump; 401 - First pressure regulating valve; 402 - Second pressure regulating valve; 5 - High-pressure gas storage tank; 6 - Reference tank; 7 - High-pressure coal sample tank; 701 - Inlet pipe; 8 - High and low temperature program control box; 901 - First pressure sensor; 902 - Second pressure sensor; 903 - Inlet pressure sensor; 904 - Outlet pressure sensor; 10 - Triaxial clamp; 11 - Silicone oil; 12 - Stress pump; 13 - Constant temperature water bath; 141 - First temperature sensor; 142 - Second temperature sensor; 15 - ... 16 - Flow sensor; 17 - Second flow sensor; 18 - Third flow sensor; 191 - Fourth flow sensor; 192 - First pneumatic valve; 193 - Second pneumatic valve; 194 - Third pneumatic valve; 195 - Fifth pneumatic valve; 196 - Sixth pneumatic valve; 197 - Seventh pneumatic valve; 198 - Eighth pneumatic valve; 199 - Ninth pneumatic valve; 20 - Exhaust valve; 21 - Helium cylinder; 22 - Vacuum pump; 23 - Vacuum gauge; 24 - Data acquisition system; 25 - High-pressure water injection pump;

[0074] 26 - First pipe; 27 - Second pipe; 28 - Third pipe; 29 - First branch pipe; 30 - Second branch pipe; 31 - Fourth pipe; 32 - Fifth pipe; 33 - Sixth pipe; 34 - Seventh pipe; 35 - Eighth pipe; 36 - Ninth pipe; 37 - Tenth pipe; 38 - Eleventh pipe; 39 - Twelfth pipe; 40 - Thirteenth pipe; 41 - Third branch pipe; 42 - Fourth branch pipe; 43 - Fifth branch pipe; 44 - Sixth branch pipe; 45 - Seventh branch pipe. Detailed Implementation

[0075] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0076] Example 1

[0077] Please see Figure 1 - Figure 2The deep in-situ coal body water lock strength testing device includes a pressurized gas injection system, an air tightness testing system, a vacuum system, a desorption testing system, a water injection system, a permeability testing system, and a data acquisition system.

[0078] The pressurized gas injection system includes a methane cylinder 1, a booster pump 3, a booster pump inlet valve 201, a booster pump outlet valve 202, a high-pressure storage tank 5, a first pressure regulating valve 401, and a first high-pressure shut-off valve 203. The booster pump 3 is connected to the methane cylinder 1 via a first pipeline 26, and the booster pump inlet valve 201 is installed on the first pipeline 26. The booster pump 3 is connected to the inlet of the high-pressure storage tank 5 via a second pipeline 27, and the booster pump outlet valve 202 is installed on the second pipeline 27. A first branch pipeline 29 is installed on the outlet of the high-pressure storage tank 5, and the first pressure regulating valve 401 and the first high-pressure shut-off valve 203 are installed on the first branch pipeline 29.

[0079] The airtightness detection system includes a helium cylinder 21, a second pressure regulating valve 402, and a second high-pressure shut-off valve 204. The helium cylinder 21 is connected to the third pipeline 28 after merging with the first branch pipeline 29 through the second branch pipeline 30. The second pressure regulating valve 402 and the second high-pressure shut-off valve 204 are installed on the second branch pipeline 30.

[0080] The desorption test system includes a high and low temperature program control box 8, a reference tank 6, a high-pressure coal sample tank 7, a ninth high-pressure shut-off valve 211, a first temperature sensor 141, a first pressure sensor 901, a second pressure sensor 902, a first pneumatic valve 191, a second pneumatic valve 192, and a third pneumatic valve 193. The reference tank 6 and the high-pressure coal sample tank 7 are placed in the high and low temperature program control box 8. The air inlet of the reference tank 6 is connected to the third pipeline 28, and the air outlet of the reference tank 6 is connected to the fourth pipeline 31. A fifth pipeline 32 and the first temperature sensor 141 are installed above the high-pressure coal sample tank 7, and the lower part of the high-pressure coal sample tank 7 is connected to the air inlet pipeline 701. The ninth high-pressure shut-off valve 211 is installed on the air inlet pipeline 701 and is placed inside the high and low temperature program control box 8.

[0081] The water injection system includes a high-pressure water injection pump 25 and an eighth high-pressure shut-off valve 210. The water outlet of the high-pressure water injection pump 25 is connected to the air inlet pipe 701 through the sixth pipe 33, and the eighth high-pressure shut-off valve 210 is installed on the sixth pipe 33.

[0082] The permeability testing system includes a triaxial clamp 10, silicone oil 11, a stress pump 12, a constant temperature water bath 13, a second temperature sensor 142, an inlet pressure sensor 903, an outlet pressure sensor 904, a fifth high-pressure shut-off valve 207, a sixth high-pressure shut-off valve 208, a seventh high-pressure shut-off valve 209, and a fourth pneumatic valve 194. The triaxial clamp 10 is placed in the constant temperature water bath 13, and the inside of the triaxial clamp 10 is filled with silicone oil 11. The bottom end of the triaxial clamp 10 is provided with a first port and a second port. The first port is connected to the stress pump 12 through a seventh pipe 34. The stress pump 12 inputs vacuum pump oil into the triaxial clamp 10 through the first port, and the second port is connected to the air inlet pipe 701 through the eighth pipe 35. Air is introduced into the triaxial clamp 10 through the second port. A fifth high-pressure shut-off valve 207 is installed on the seventh pipe 34, and a sixth high-pressure shut-off valve 208 is installed on the eighth pipe 35. The air outlet at the top of the triaxial clamp 10 is connected to the ninth pipe 36. An air outlet pressure sensor 904 and a fourth pneumatic valve 194 are installed on the ninth pipe 36. The air inlet pipe 701 is connected to the air inlet pressure sensor 903.

[0083] The vacuum system includes a vacuum pump 22, a vacuum gauge 23, a third high-pressure shut-off valve 205, and a third pneumatic valve 193. The vacuum pump 22 is connected to the inlet of the vacuum gauge 23 through a tenth pipe 37. The outlet of the vacuum gauge 23 is provided with an eleventh pipe 38. The third high-pressure shut-off valve 205 and the third pneumatic valve 193 are provided on the eleventh pipe 38.

[0084] The fourth pipe 31 and the fifth pipe 32 are both connected to the eleventh pipe 38. The intake pipe 701 is connected to the eleventh pipe 38 through the twelfth pipe 39. A high-pressure shut-off valve 206 and a ninth pneumatic valve 199 are installed on the twelfth pipe 39.

[0085] It also includes: the thirteenth pipe 40, the third branch pipe 41, the fourth branch pipe 42, the fifth branch pipe 43, the sixth branch pipe 44, the seventh branch pipe 45, the fifth pneumatic valve 195, the sixth pneumatic valve 196, the seventh pneumatic valve 197, the eighth pneumatic valve 198, the vent valve 20, the first flow sensor 15, the second flow sensor 16, the third flow sensor 17, and the fourth flow sensor 18; the ends of the ninth pipe 36 and the eleventh pipe 38 are both connected to the thirteenth pipe 40, and the thirteenth pipe 40 is sequentially connected to the third... Branch pipes 41, 42, 43, 44, and 45 are provided. A drain valve 20 is installed at the end of the third branch pipe 41. A fifth pneumatic valve 195 and a first flow sensor 15 are installed on the fourth branch pipe 42. A sixth pneumatic valve 196 and a second flow sensor 16 are installed on the fifth branch pipe 43. A seventh pneumatic valve 197 and a third flow sensor 17 are installed on the sixth branch pipe 44. An eighth pneumatic valve 198 and a fourth flow sensor 18 are installed on the seventh branch pipe 45.

[0086] The first pressure sensor 901, the second pressure sensor 902, the inlet pressure sensor 903, the outlet pressure sensor 904, the first temperature sensor 141, the second temperature sensor 142, the first flow sensor 15, the second flow sensor 16, the third flow sensor 17, the fourth flow sensor 18, the first pneumatic valve 191, the second pneumatic valve 192, the third pneumatic valve 193, the fourth pneumatic valve 194, the fifth pneumatic valve 195, the sixth pneumatic valve 196, the seventh pneumatic valve 197, the eighth pneumatic valve 198, and the ninth pneumatic valve 199 are all connected to the data acquisition system 24.

[0087] The methane in the methane cylinder 1 has a purity of 99.999%, and the helium in the helium cylinder 21 has a purity of 99.999%.

[0088] The second temperature sensor 142 is placed inside the cavity of the triaxial clamp 10 and is used to monitor the internal temperature of the triaxial clamp 10.

[0089] The silicone oil 11 fills the cavity of the triaxial clamp 10. The stress pump 12 uses the silicone oil 11 as a power medium to simultaneously apply axial pressure and confining pressure to the triaxial clamp 10, which is used to simulate the in-situ stress of the deep environment of the coal reservoir to be evaluated.

[0090] The first flow sensor 15 measures flow rate in the range of 0–80 L / min with an accuracy of 5%; the second flow sensor 16 measures flow rate in the range of 0–3000 mL / min with an accuracy of 0.2%; the third flow sensor 17 measures flow rate in the range of 0–500 mL / min with an accuracy of 0.2%; and the fourth flow sensor 18 measures flow rate in the range of 0–50 mL / min with an accuracy of 0.2%.

[0091] In this invention, the first pipe 26, the second pipe 27, the third pipe 28, the first branch pipe 29, the second branch pipe 30, the fourth pipe 31, the fifth pipe 32, the sixth pipe 33, the seventh pipe 34, the eighth pipe 35, the ninth pipe 36, the tenth pipe 37, the eleventh pipe 38, the twelfth pipe 39, the thirteenth pipe 40, the third branch pipe 41, the fourth branch pipe 42, the fifth branch pipe 43, the sixth branch pipe 44, the seventh branch pipe 45, and the intake pipe 701 are all high-pressure pipes with a diameter of 2mm.

[0092] Example 2

[0093] Reference Figure 3 A testing method for a deep in-situ coal body water-lock strength testing device, implemented using the deep in-situ coal body water-lock strength testing device in Example 1, includes the following steps:

[0094] a. Prepare and dry No. 1 and No. 2 pillar coals: Collect coal cores from the coal reservoir to be evaluated, and prepare pillar coals with a diameter of 5 cm and a height of 10 cm. Two pillar coals must be prepared for each coal core, numbered No. 1 and No. 2, for coal gas content testing and permeability testing, respectively. Place both No. 1 and No. 2 pillar coals at 105℃ for continuous drying until the coal weight no longer changes, which is considered as the drying is complete. Weigh the No. 1 pillar coal as the coal weight G. m1 The weight of coal in pillar No. 2 is coal weight G. m2 ;

[0095] b. Perform an airtightness test on the testing device: Close all high-pressure shut-off valves and pneumatic valves of the testing device, and sequentially open the second high-pressure shut-off valve 204 and the second pressure regulating valve 402. Fill the reference tank 6 and the high-pressure coal sample tank 7 with helium gas, and read the helium pressure of the first pressure sensor 901 and the second pressure sensor 902 as P. h1 P h2 Close the second pressure regulating valve 402 and the second high-pressure shut-off valve 204, and continuously observe the first pressure sensor 901 and the second pressure sensor 902 for 12 hours. h1 P h2 If the value remains unchanged, confirming that the airtightness of the testing device is good, the testing work can begin.

[0096] c. Place the dried No. 1 coal column into the high-pressure coal sample container 7 and perform vacuum degassing on the desorption test system: Place the dried No. 1 coal column into the high-pressure coal sample container 7, close the first high-pressure shut-off valve 203, the second high-pressure shut-off valve 204, the ninth high-pressure shut-off valve 211, the third pneumatic valve 193, and the ninth pneumatic valve 199, open the first pneumatic valve 191, the second pneumatic valve 192, and the third high-pressure shut-off valve 205, start the vacuum pump 22 and the vacuum gauge 23 to perform vacuum degassing on the desorption test system, when the vacuum gauge 23 shows that the vacuum degree drops below 10Pa, close the first pneumatic valve 191, the second pneumatic valve 192, and the third high-pressure shut-off valve 205 in sequence, and then turn off the vacuum pump 22;

[0097] d. Adjust the temperature of the high and low temperature program control box 8 to the formation temperature t of the deep in-situ environment of the coal reservoir to be evaluated: turn on the high and low temperature program control box 8 and set the temperature to the formation temperature t of the deep in-situ environment of the coal reservoir to be evaluated. At this time, the first temperature sensor 141 displays t.

[0098] e. Methane is pressurized by the booster pump and then input into the high-pressure storage tank 5: Start the booster pump 3, open the booster pump inlet valve 201, after the methane is pressurized by the booster pump 3, open the booster pump outlet valve 202, and input methane gas with a pressure of not less than 10MPa into the high-pressure storage tank 5. Then, close the booster pump inlet valve 201, booster pump 3, and booster pump outlet valve 202 in sequence.

[0099] f. Filling reference tank 6 with methane: First open the first high-pressure shut-off valve 203, and after 1 minute, open the first pressure regulating valve 401. High-pressure gas storage tank 5 fills reference tank 6 with methane. When the first pressure sensor 901 displays P... c1 At this time, the first pressure regulating valve 401 and the first high-pressure shut-off valve 203 are closed in sequence, and P is then closed. c1 Not less than twice the simulated in-situ gas pressure P of the coal reservoir to be evaluated;

[0100] g. Methane is introduced into the high-pressure coal sample container 7 to achieve methane adsorption equilibrium in column 1 of the high-pressure coal sample container 7, and the amount of coal gas adsorbed by column 1 before water injection, Q, is calculated. sx Open the second pneumatic valve 192. After 1 minute, open the first pneumatic valve 191 to quickly inject methane into the high-pressure coal sample tank 7. Then, sequentially close the first pneumatic valve 191 and the second pneumatic valve 192. During this period, methane gas is repeatedly supplied to the high-pressure coal sample tank 7 through the reference tank 6. When the pressure displayed by the second pressure sensor 902 remains unchanged for 12 hours, it indicates that the methane adsorption in column 1 has reached equilibrium. At this time, the reading of the second pressure sensor 902 is P, where P is the gas pressure simulating the in-situ environment of the coal reservoir to be evaluated. After the gas injection is completed, record the pressure displayed by the first pressure sensor 901 as P. c2 ;

[0101] The total amount of methane injected into the high-pressure coal sample tank 7 from the reference tank 6 is calculated according to formula (1), which is the amount of coal gas adsorption Q of column 1 before water injection. sx :

[0102]

[0103] In the formula: Q sx —Gas adsorption capacity of No. 1 pillar coal before water injection, ml / g; V c —The volume of reference tank 6 and the inflation pipeline, in ml, wherein the inflation pipeline includes the pipeline between the third high-pressure shut-off valve 205 and the third pneumatic valve 193, the fourth pipeline 31, the pipeline between the second pneumatic valve 192 and the eleventh pipeline 38, and the pipeline between the ninth pneumatic valve 199 and the eleventh pipeline 38; P c1 —Before filling the high-pressure coal sample container 7 with gas, the first pressure sensor 901 monitors the equilibrium pressure of the reference container, in MPa; P c2 —After gas injection is completed, the first pressure sensor 901 monitors the equilibrium pressure of the reference tank 6, in MPa; Z c1 —Under pressure P c1 The compressibility factor of methane at temperature t, dimensionless; Z c2 —Under pressure P c2 The compressibility factor of methane at temperature t is dimensionless; t—the experimental temperature set by the high and low temperature program control box 8, i.e., the formation temperature of the deep in-situ environment of the coal reservoir to be evaluated, in °C.

[0104] h. Injecting water into the No. 1 column of coal, which has been balanced by adsorbed methane, in the high-pressure coal sample container 7: Start the high-pressure water injection pump 25, and sequentially open the eighth high-pressure shut-off valve 210 and the ninth high-pressure shut-off valve 211 to inject water into the No. 1 column of coal that has been balanced by adsorbed methane. The weight of the injected water is G. s1 Stop water injection and close the ninth high-pressure shut-off valve 211, the eighth high-pressure shut-off valve 210, and the high-pressure water injection pump 25 in sequence.

[0105] i. After water injection, the No. 1 coal column naturally desorbs methane for 24 hours. Calculate the coal body gas retention coefficient η: After 24 hours of water injection, sequentially open the vent valve 20 and the third pneumatic valve 193. Free methane in the high-pressure coal sample tank 7 is rapidly released outward along the pipeline. When the second pressure sensor 902 displays zero pressure, quickly close the vent valve 20. Simultaneously, the data acquisition system 24 issues commands to control the fifth pneumatic valve 195, the sixth pneumatic valve 196, the seventh pneumatic valve 197, and the eighth pneumatic valve 198, automatically switching control of the first flow sensor 15, the second flow sensor 16, the third flow sensor 17, and the fourth flow sensor 18 according to the methane flow rate V. The desorption time lasts for 24 hours. Then close the second pneumatic valve 192 and the third pneumatic valve 193. The desorption process is complete. The cumulative desorption amount recorded by the first flow sensor 15, the second flow sensor 16, the third flow sensor 17, and the fourth flow sensor 18 is the desorption amount Q of the No. 1 coal column naturally desorbing methane for 24 hours after water injection. sj ;

[0106] The gas retention coefficient η of the coal body is calculated using formulas (2) to (4), specifically:

[0107] The gas content of dry No. 1 pillar coal under normal pressure is calculated using formula (2) as Q. g :

[0108]

[0109] In the formula: Q g —Gas content of No. 1 pillar coal under normal pressure, ml / g; normal pressure is specifically 0.1 MPa; a—Adsorption constant, ml / g; b—Adsorption constant, MPa -1 A ad —Ash content (%) of the deep in-situ environment of the coal reservoir to be evaluated; M ad —Moisture content of the deep in-situ environment of the coal reservoir to be evaluated, %;

[0110] The gas content of No. 1 pillar coal under water-lock conditions is calculated as Q using formula (3). s :

[0111] Q s =Q sx -Q sj (3)

[0112] In the formula: Q s —Gas content of No. 1 pillar coal under water-locked conditions, ml / g; Q sx —Gas adsorption capacity of No. 1 pillar coal before water injection, ml / g; Q sj —The amount of coal pillar No. 1 naturally desorbed after 24 hours of water injection, in ml / g;

[0113] Due to the water-locking effect, coal gas is retained in the pores. Under normal pressure, the gas content of water-bearing coal is greater than that of dry coal. The coal gas retention coefficient η is calculated using formula (4):

[0114]

[0115] Where: η—coal gas retention coefficient, %; Q s —Gas content of No. 1 pillar coal under water-locked conditions, ml / g; Q g —Gas content of No. 1 pillar coal dried under normal pressure, ml / g; Q sx —Gas adsorption capacity of No. 1 pillar coal before water injection, ml / g; Q sj — Desorption amount of No. 1 pillar coal after natural desorption for 24 hours after water injection, ml / g; a— Adsorption constant, ml / g; b— Adsorption constant, MPa -1 A ad —Ash content (%) of the deep in-situ environment of the coal reservoir to be evaluated; M ad —Moisture content of the deep in-situ environment of the coal reservoir to be evaluated, %;

[0116] j. After drying, the No. 2 pillar coal is sealed and placed in the triaxial clamp 10, and water bath constant temperature control is performed: The No. 2 pillar coal is sealed with heat shrink tubing and then placed in the triaxial clamp 10. The constant temperature water bath 13 is started and the water bath temperature is set to the formation temperature t of the deep in-situ environment of the coal reservoir to be evaluated. At this time, the second temperature sensor 142 displays t.

[0117] k. Apply axial pressure P to the No. 2 coal pillar via stress pump 12. y1 and confining pressure P y2 To achieve the in-situ stress of the deep environment of the coal reservoir to be evaluated: open the fifth high-pressure shut-off valve 207 and start the stress pump 12 to apply axial pressure P to the No. 2 pillar coal. y1 and confining pressure P y2 When axial pressure P y1 and confining pressure P y2 After reaching the in-situ in-depth environment of the coal reservoir to be evaluated, the in-situ stress is obtained through actual on-site testing, and the operating intensity of stress pump 12 is kept constant.

[0118] 1. Introduce methane into the triaxial clamp 10 and balance the methane adsorption of the No. 2 column coal: Open the sixth high-pressure shut-off valve 208, the ninth high-pressure shut-off valve 211, the seventh high-pressure shut-off valve 209, and the ninth pneumatic valve 199. After 1 minute, open the first pneumatic valve 191 to quickly introduce methane into the triaxial clamp 10. Then, close the first pneumatic valve 191 and the ninth pneumatic valve 199 in sequence. During this period, repeatedly supplement the triaxial clamp 10 with methane through the reference tank 6. When the pressure sensor 903 at the inlet end and the pressure sensor 904 at the outlet end simultaneously show that the pressure remains unchanged for 12 hours, it indicates that the methane adsorption of the No. 2 column coal is balanced. At this time, the readings of the pressure sensor 903 at the inlet end and the pressure sensor 904 at the outlet end both reach pressure P, which is the gas pressure of the simulated in-situ environment of the coal reservoir to be evaluated.

[0119] m. Calculate the permeability k of the dried No. 2 coal pillar containing gas. g The system sequentially opens the fourth pneumatic valve 194, the ninth pneumatic valve 199, and the first pneumatic valve 191. Simultaneously, the data acquisition system 24 is activated and commands are issued to control the fifth pneumatic valve 195, the sixth pneumatic valve 196, the seventh pneumatic valve 197, and the eighth pneumatic valve 198. The system automatically switches between the first flow sensor 15, the second flow sensor 16, the third flow sensor 17, and the fourth flow sensor 18 according to the methane flow rate V. Once the methane flow through the No. 2 coal column stabilizes, the first flow sensor 15, the second flow sensor 16, the third flow sensor 17, and the fourth flow sensor 18 collect the stable flow rate as the gas flow rate Q at the outlet of the triaxial clamp 10. The pressure sensor 903 at the inlet displays the pressure value as the gas pressure P at the second port of the triaxial clamp 10. g1 The pressure value displayed by the outlet pressure sensor 904 is the gas pressure P at the outlet of the triaxial clamp 10. g2 ; Calculate the permeability k of the gas-containing dry No. 2 pillar coal according to formula (5). g ;

[0120]

[0121] In the formula: k g —Permeability of dry No. 2 pillar coal containing gas, 10 -15 m 2 Q—Gas flow rate at the outlet of the three-axis clamp 10, ml / s; P a —Atmospheric pressure, MPa, valued at 0.1 MPa; μ—Dynamic viscosity of gas fluid, MPa·s; L2—Length of pillar coal No. 2, cm, valued at 10 cm; A—Cross-sectional area of ​​pillar coal No. 2, cm² 2 The value is 19.625cm. 2 ;P g1 —Gas pressure at the second port of the triaxial clamp 10, MPa; P g2—Gas pressure at the outlet of the triaxial clamp 10, MPa;

[0122] n. Continue to replenish methane to the No. 2 column coal in the triaxial clamp 10 until the adsorption of methane in the No. 2 column coal reaches equilibrium: close the fourth pneumatic valve 194, and continue to replenish methane to the No. 2 column coal in the triaxial clamp 10 using the reference tank 6. When the pressure sensor 903 at the inlet end and the pressure sensor 904 at the outlet end simultaneously display a pressure of P and remain unchanged for 12 hours, it indicates that the adsorption of methane in the No. 2 column coal has reached equilibrium. Then close the first pneumatic valve 191, the ninth pneumatic valve 199, the ninth high-pressure shut-off valve 211, and the seventh high-pressure shut-off valve 209.

[0123] o. Inject water into the No. 2 column coal, which has already been balanced by adsorbed methane, in the triaxial clamp 10: Turn on the high-pressure water injection pump 25, open the eighth high-pressure shut-off valve 210, and inject water into the No. 2 column coal, which has already been balanced by adsorbed methane. The weight of the injected water is G. s2 Stop water injection and close the eighth high-pressure shut-off valve 210 and the high-pressure water injection pump 25 in sequence.

[0124] p. Calculate the coal permeability k under waterlock conditions after water injection. s After 24 hours of water injection, the fourth pneumatic valve 194, the ninth high-pressure shut-off valve 211, the ninth pneumatic valve 199, and the first pneumatic valve 191 are opened sequentially. Simultaneously, the data acquisition system 24 is activated and commands are issued to control the fifth pneumatic valve 195, the sixth pneumatic valve 196, the seventh pneumatic valve 197, and the eighth pneumatic valve 198. The first flow sensor 15, the second flow sensor 16, the third flow sensor 17, and the fourth flow sensor 18 are automatically switched according to the methane flow rate V. Once the methane flow through the No. 2 coal column stabilizes, the first flow sensor 15, the second flow sensor 16, the third flow sensor 17, and the fourth flow sensor 18 collect the stable flow rate as the gas flow rate Q at the outlet of the triaxial clamp 10. The pressure sensor 903 at the inlet displays the pressure value as the gas pressure P at the second port of the triaxial clamp 10. s1 The pressure value displayed by the outlet pressure sensor 904 is the gas pressure P at the outlet of the triaxial clamp 10. s2 ; Calculate the coal permeability k under water-locked conditions after water injection according to formula (6). s ;

[0125]

[0126] In the formula: k s —Coal permeability under water-locked state after water injection, 10 -15 m 2 Q—Gas flow rate at the outlet of the three-axis clamp 10, ml / s; P a—Atmospheric pressure, MPa, valued at 0.1 MPa; μ—Dynamic viscosity of gas fluid, MPa·s; L2—Length of pillar coal No. 2, cm, valued at 10 cm; A—Cross-sectional area of ​​pillar coal No. 2, cm² 2 The value is 19.625cm. 2 ;P s1 —Gas pressure at the second port of the triaxial clamp 10, MPa; P s2 —Gas pressure at the outlet of the triaxial clamp 10, MPa;

[0127] q. Calculate the coal permeability damage coefficient λ: k is calculated according to formulas (5) and (6). g and k s The coal permeability damage coefficient λ is calculated according to formula (7);

[0128]

[0129] Where: λ—coal permeability damage coefficient, %; k g —Permeability of dry No. 2 pillar coal containing gas, 10 -15 m 2 ;k s —Coal permeability under water-locked state after water injection, 10 -15 m 2 ;

[0130] r. The experimental testing process has ended.

[0131] The weight G of the injected water in step h s1 Not greater than the weight G of No. 1 coal pillar m1 15%.

[0132] The weight G of the injected water in step o s2 No more than the weight of No. 2 coal pillar G m2 15%.

[0133] In steps i and m, the principle for automatically switching the control of the first flow sensor 15, the second flow sensor 16, the third flow sensor 17, and the fourth flow sensor 18 according to the methane flow rate V is as follows: when 3000 mL / min ≤ V < 80 L / min, the fifth pneumatic valve 195 automatically opens, and the first flow sensor 15 monitors and records the methane flow rate and desorption amount; when 500 mL / min ≤ V < 3000 mL / min, the sixth pneumatic valve 196 automatically opens, and the second flow sensor 16 monitors and records the methane flow rate and desorption amount; when 50 mL / min ≤ V < 500 mL / min, the seventh pneumatic valve 197 automatically opens, and the third flow sensor 17 monitors and records the methane flow rate and desorption amount; when 0 < V < 50 mL / min, the eighth pneumatic valve 198 automatically opens, and the fourth flow sensor 18 monitors and records the methane flow rate and desorption amount.

[0134] Example 3

[0135] A method for evaluating the water-locking strength of deep in-situ coal bodies, using the coal gas retention coefficient η and coal permeability damage coefficient λ obtained according to the test method in Example 2 above, and comprehensively evaluating the water-locking strength of deep in-situ coal bodies according to Table 1:

[0136] Table 1. Comprehensive Evaluation Table of Water Lock Strength in Deep In-situ Coal Seams

[0137] Coal gas retention coefficient η (%) Coal permeability damage coefficient λ (%) Deep in-situ coal water lock strength evaluation grade ≤10 ≤5 None 10～40 5～30 Weak 40～80 30～60 Medium ≥80 70～100 Strong .

[0138] When the test results of the coal gas retention coefficient η and the coal permeability damage coefficient λ are not within the numerical range of the same row in Table 1, the evaluation level of the deep in-situ water-lock strength corresponding to the larger of the two test results shall be used as the judgment result. For example, when the test result of the coal gas retention coefficient η is 50% and the test result of the coal permeability damage coefficient λ is 20%, the evaluation level of the deep in-situ water-lock strength corresponding to the coal gas retention coefficient η shall be used as the judgment result, that is, the evaluation level of the deep in-situ coal water-lock strength is "medium".

[0139] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A deep in-situ coal seam water-lock strength testing device, characterized in that, It includes a pressurization and gas injection system, an airtightness testing system, a vacuum system, a desorption testing system, a water injection system, a permeability testing system, and a data acquisition system; The pressurized gas injection system includes a methane cylinder, a booster pump, a booster pump inlet valve, a booster pump outlet valve, a high-pressure storage tank, a first pressure regulating valve, and a first high-pressure shut-off valve. The booster pump is connected to the methane cylinder via a first pipeline, and a booster pump inlet valve is installed on the first pipeline. The booster pump is connected to the inlet of the high-pressure storage tank via a second pipeline, and a booster pump outlet valve is installed on the second pipeline. A first branch pipeline is installed on the outlet of the high-pressure storage tank, and a first pressure regulating valve and a first high-pressure shut-off valve are installed on the first branch pipeline. The airtightness testing system includes a helium cylinder, a second pressure regulating valve, and a second high-pressure shut-off valve. The helium cylinder is connected to a third pipeline after merging with the first branch pipeline through a second branch pipeline. A second pressure regulating valve and a second high-pressure shut-off valve are installed on the second branch pipeline. The desorption test system includes a high and low temperature program control box, a reference tank, a high-pressure coal sample tank, a ninth high-pressure shut-off valve, a first temperature sensor, a first pressure sensor, a second pressure sensor, a first pneumatic valve, a second pneumatic valve, and a third pneumatic valve. The reference tank and the high-pressure coal sample tank are placed in the high and low temperature program control box. The air inlet of the reference tank is connected to the third pipeline, and the air outlet of the reference tank is connected to the fourth pipeline. A fifth pipeline and the first temperature sensor are installed above the high-pressure coal sample tank, and the air inlet pipeline is connected to the bottom of the high-pressure coal sample tank. A ninth high-pressure shut-off valve is installed on the air inlet pipeline, and the ninth high-pressure shut-off valve is placed inside the high and low temperature program control box. The water injection system includes a high-pressure water injection pump and an eighth high-pressure shut-off valve. The outlet of the high-pressure water injection pump is connected to the air inlet pipe through a sixth pipe, and an eighth high-pressure shut-off valve is installed on the sixth pipe. The permeability testing system includes a triaxial holder, silicone oil, a stress pump, a constant temperature water bath, a second temperature sensor, an inlet pressure sensor, an outlet pressure sensor, a fifth high-pressure shut-off valve, a sixth high-pressure shut-off valve, a seventh high-pressure shut-off valve, and a fourth pneumatic valve. The triaxial holder is placed in the constant temperature water bath and is filled with silicone oil. The bottom of the triaxial holder has a first port and a second port. The first port is connected to the stress pump through a seventh pipeline, and the second port is connected to the inlet pipeline through an eighth pipeline. A fifth high-pressure shut-off valve is installed on the seventh pipeline, and a sixth high-pressure shut-off valve is installed on the eighth pipeline. The outlet at the top of the triaxial holder is connected to a ninth pipeline. An outlet pressure sensor and a fourth pneumatic valve are installed on the ninth pipeline, and the inlet pipeline is connected to the inlet pressure sensor. The vacuum system includes a vacuum pump, a vacuum gauge, a third high-pressure shut-off valve, and a third pneumatic valve; the vacuum pump is connected to the vacuum gauge inlet via a tenth pipeline, and the vacuum gauge outlet is provided with an eleventh pipeline, on which the third high-pressure shut-off valve and the third pneumatic valve are installed. The fourth and fifth pipelines are both connected to the eleventh pipeline, and the air intake pipeline is connected to the eleventh and twelfth pipelines. A fourth high-pressure shut-off valve and a ninth pneumatic valve are installed on the twelfth pipeline. It also includes: a thirteenth pipeline, a third branch pipeline, a fourth branch pipeline, a fifth branch pipeline, a sixth branch pipeline, a seventh branch pipeline, a fifth pneumatic valve, a sixth pneumatic valve, a seventh pneumatic valve, an eighth pneumatic valve, a vent valve, a first flow sensor, a second flow sensor, a third flow sensor, and a fourth flow sensor; the ninth and eleventh pipelines are both connected to the thirteenth pipeline at their ends, and the thirteenth pipeline is sequentially connected to the third branch pipeline, the fourth branch pipeline, the fifth branch pipeline, the sixth branch pipeline, and the seventh branch pipeline. A vent valve is installed at the end of the third branch pipeline, a fifth pneumatic valve and a first flow sensor are installed on the fourth branch pipeline, a sixth pneumatic valve and a second flow sensor are installed on the fifth branch pipeline, a seventh pneumatic valve and a third flow sensor are installed on the sixth branch pipeline, and an eighth pneumatic valve and a fourth flow sensor are installed on the seventh branch pipeline. The first pressure sensor, the second pressure sensor, the inlet pressure sensor, the outlet pressure sensor, the first temperature sensor, the second temperature sensor, the first flow sensor, the second flow sensor, the third flow sensor, the fourth flow sensor, the first pneumatic valve, the second pneumatic valve, the third pneumatic valve, the fourth pneumatic valve, the fifth pneumatic valve, the sixth pneumatic valve, the seventh pneumatic valve, the eighth pneumatic valve, and the ninth pneumatic valve are all connected to the data acquisition system.

2. The deep in-situ coal seam water-lock strength testing device as described in claim 1, characterized in that, The methane in the methane cylinder has a purity of 99.999%, and the helium in the helium cylinder has a purity of 99.999%.

3. The deep in-situ coal seam water-lock strength testing device as described in claim 1, characterized in that, The second temperature sensor is placed inside the cavity of the triaxial clamp and is used to monitor the internal temperature of the triaxial clamp.

4. The deep in-situ coal seam water-lock strength testing device as described in claim 1, characterized in that, The silicone oil fills the cavity of the triaxial clamp.

5. The deep in-situ coal seam water-lock strength testing device as described in claim 1, characterized in that, The first flow sensor has a flow rate range of 0–80 L / min and an accuracy of 5%; the second flow sensor has a flow rate range of 0–3000 mL / min and an accuracy of 0.2%; the third flow sensor has a flow rate range of 0–500 mL / min and an accuracy of 0.2%; and the fourth flow sensor has a flow rate range of 0–50 mL / min and an accuracy of 0.2%.

6. A testing method for a deep in-situ coal body water-lock strength testing device, implemented using the deep in-situ coal body water-lock strength testing device as described in any one of claims 1-5, characterized in that, Includes the following steps: a. Prepare and dry No. 1 and No. 2 pillar coals: Collect coal cores from the coal reservoir to be evaluated. Two pillar coals must be prepared for each core, numbered No. 1 and No. 2, for coal gas content testing and permeability testing, respectively. Place both No. 1 and No. 2 pillar coals at 105℃ for continuous drying until the coal weight no longer changes, indicating drying is complete. Weigh the No. 1 pillar coal as coal weight G. m1 The weight of coal in pillar No. 2 is coal weight G. m2 ; b. Perform an airtightness test on the testing device: Close all high-pressure shut-off valves and pneumatic valves of the testing device, then sequentially open the second high-pressure shut-off valve and the second pressure regulating valve. Fill the reference tank and high-pressure coal sample tank with helium gas, and read the helium pressure readings from the first and second pressure sensors. P h1 , P h2 Close the second pressure regulating valve and the second high-pressure shut-off valve, and continuously observe the first and second pressure sensors for 12 hours. P h1 , P h2 The value remains unchanged, confirming that the airtightness of the testing device is good, and the testing work begins; c. Place the dried No. 1 coal column in a high-pressure coal sample container and perform vacuum degassing on the desorption test system: Place the dried No. 1 coal column in a high-pressure coal sample container, close the first high-pressure shut-off valve, the second high-pressure shut-off valve, the ninth high-pressure shut-off valve, the third pneumatic valve, and the ninth pneumatic valve, open the first pneumatic valve, the second pneumatic valve, and the third high-pressure shut-off valve, start the vacuum pump and vacuum gauge to perform vacuum degassing on the desorption test system, when the vacuum gauge shows that the vacuum degree drops below 10Pa, close the first pneumatic valve, the second pneumatic valve, and the third high-pressure shut-off valve in sequence, and then turn off the vacuum pump; d. Adjust the temperature of the high and low temperature program control box to the formation temperature of the deep in-situ environment of the coal reservoir to be evaluated. t 0: Turn on the high and low temperature program control box and set the temperature to the formation temperature of the deep in-situ environment of the coal reservoir to be evaluated. t 0, at this time the first temperature sensor displays 0. t 0; e. Methane is pressurized by the booster pump and then fed into the high-pressure storage tank: Start the booster pump, open the booster pump inlet valve, and after the methane is pressurized by the booster pump, open the booster pump outlet valve to input methane gas at a pressure of not less than 10MPa into the high-pressure storage tank. Then, close the booster pump inlet valve, the booster pump, and the booster pump outlet valve in sequence. f. Charge methane into the reference tank: First open the first high-pressure shut-off valve, and after 1 minute, open the first pressure regulating valve. The high-pressure gas storage tank charges methane into the reference tank. When the first pressure sensor displays [value missing]... P c1 At this time, the first pressure regulating valve and the first high-pressure shut-off valve are closed in sequence. P c1 Not lower than the simulated in-situ gas pressure of the coal reservoir to be evaluated P 2 times; g. Introduce methane into the high-pressure coal sample container to achieve methane adsorption equilibrium in column 1 of the high-pressure coal sample container, and calculate the amount of coal gas adsorbed by column 1 before water injection. Q sx Open the second pneumatic valve, and after 1 minute, open the first pneumatic valve to quickly fill the high-pressure coal sample container with methane. Then, sequentially close the first and second pneumatic valves. During this period, repeatedly replenish the high-pressure coal sample container with methane gas through the reference container. When the pressure displayed by the second pressure sensor remains constant for 12 hours, it indicates that the methane adsorption in column 1 has reached equilibrium. At this point, the reading of the second pressure sensor is [value missing]. P , P To simulate the gas pressure in the in-situ environment of the coal reservoir to be evaluated; after gas injection, the pressure displayed by the first pressure sensor was recorded as follows. P c2 ; The total amount of methane injected into the high-pressure coal sample tank from the reference tank is calculated according to formula (1), which is the amount of coal gas adsorption in column No. 1 before water injection. Q sx : ； In the formula: Q sx —Gas adsorption capacity of No. 1 pillar coal before water injection, ml / g; V c —The sum of the volumes of the reference tank and the inflation pipeline, in ml, wherein the inflation pipeline includes the pipeline between the third high-pressure shut-off valve and the third pneumatic valve, the fourth pipeline, the pipeline between the second pneumatic valve and the eleventh pipeline, and the pipeline between the ninth pneumatic valve and the eleventh pipeline. P c1 —Before filling the high-pressure coal sample tank with gas, the first pressure sensor monitors the balance pressure of the reference tank, in MPa; P c2 —After the gas injection is completed, the first pressure sensor monitors the balance pressure of the reference tank, in MPa; Z c1 —Under pressure P c1 and temperature t The compressibility factor of methane at 0°C is dimensionless. Z c2 —Under pressure P c2 and temperature t The compressibility factor of methane at 0°C is dimensionless. t 0—The experimental temperature set by the high and low temperature program control box, i.e., the formation temperature of the deep in-situ environment of the coal reservoir to be evaluated, in °C; h. Injecting water into the No. 1 column of coal, which has reached methane adsorption equilibrium, into the high-pressure coal sample container: Start the high-pressure water injection pump, and sequentially open the eighth and ninth high-pressure shut-off valves to inject water into the No. 1 column of coal, which has reached methane adsorption equilibrium. The weight of the injected water is G. s1 Stop water injection and sequentially close the ninth high-pressure shut-off valve, the eighth high-pressure shut-off valve, and the high-pressure water injection pump. i. After water injection, the No. 1 coal column naturally desorbs methane for 24 hours, and the gas retention coefficient of the coal body is calculated. η After 24 hours of water injection, the vent valve and the third pneumatic valve are opened sequentially. Free methane in the high-pressure coal sample tank is rapidly released outward along the pipeline. When the second pressure sensor shows zero pressure, the vent valve is quickly closed. Simultaneously, the data acquisition system sends commands to control the fifth, sixth, seventh, and eighth pneumatic valves, automatically switching the control of the first, second, third, and fourth flow sensors according to the methane flow rate V. The desorption time lasts for 24 hours. Then, the second and third pneumatic valves are closed, completing the desorption process. The cumulative desorption amount recorded by the first, second, third, and fourth flow sensors is the amount of methane naturally desorbed from the No. 1 column coal after 24 hours of water injection. Q sj ; The gas retention coefficient of the coal body is calculated using formulas (2) to (4). η Specifically: The gas content of dry No. 1 pillar coal under normal pressure was calculated using formula (2). Q g : ； In the formula: Q g —Gas content of No. 1 pillar coal dried under normal pressure, ml / g; a —Adsorption constant, ml / g; b —Adsorption constant, MPa -1 ; A ad —Ash content of the deep in-situ environment of the coal reservoir to be evaluated, % M ad —Moisture content of the deep in-situ environment of the coal reservoir to be evaluated, % The gas content of No. 1 pillar coal under water-lock conditions is calculated using formula (3). Q s : ； In the formula: Q s —Gas content of No. 1 pillar coal under water-locked conditions, ml / g; Q sx —Gas adsorption capacity of No. 1 pillar coal before water injection, ml / g; Q sj —The amount of coal pillar No. 1 naturally desorbed after 24 hours of water injection, in ml / g; Due to the water-locking effect, coal gas is retained in the pores. Under normal pressure, the gas content of water-bearing coal is greater than that of dry coal. The coal gas retention coefficient is calculated using formula (4). η : ； In the formula: η —Gas retention coefficient in coal seam, % Q s —Gas content of No. 1 pillar coal under water-locked conditions, ml / g; Q g —Gas content of No. 1 pillar coal dried under normal pressure, ml / g; Q sx —Gas adsorption capacity of No. 1 pillar coal before water injection, ml / g; Q sj —The amount of coal pillar No. 1 naturally desorbed after 24 hours of water injection, in ml / g; a —Adsorption constant, ml / g; b —Adsorption constant, MPa -1 ; A ad —Ash content of the deep in-situ environment of the coal reservoir to be evaluated, % M ad —Moisture content of the deep in-situ environment of the coal reservoir to be evaluated, % j. After drying, the No. 2 pillar coal is sealed and placed in a triaxial holder, and then subjected to water bath temperature control: The No. 2 pillar coal is sealed with heat shrink tubing, then placed in the triaxial holder, and the temperature-controlled water bath is activated, setting the water bath temperature to the formation temperature of the deep in-situ environment of the coal reservoir being evaluated. t 0, at this time the second temperature sensor displays 0. t 0; k. Apply axial pressure to the No. 2 coal pillar using a stress pump. P y1 and confining pressure P y2 To achieve the in-situ stress of the deep coal reservoir being evaluated: open the fifth high-pressure shut-off valve and start the stress pump to apply axial pressure to the No. 2 pillar coal. P y1 and confining pressure P y2 When axial compression P y1 and confining pressure P y2 After reaching the in-situ stress of the deep environment where the coal reservoir to be evaluated is located, the stress pump operating intensity is kept constant.

1. Introduce methane into the triaxial clamp and balance the methane adsorption of column No. 2 coal: Open the sixth, fourth, seventh, and ninth high-pressure shut-off valves, and after 1 minute, open the first pneumatic valve to quickly introduce methane into the triaxial clamp. Then, close the first and ninth pneumatic valves sequentially. During this period, repeatedly replenish the triaxial clamp with methane through the reference tank. When the pressure sensors at both the inlet and outlet ends simultaneously display pressures that remain unchanged for 12 hours, it indicates that the methane adsorption of column No. 2 coal is balanced. At this point, the readings of both the inlet and outlet pressure sensors have reached the required pressure. P , P That is, to simulate the gas pressure in the in-situ environment of the coal reservoir to be evaluated; m. Calculate the permeability of the dried No. 2 pillar coal containing gas. k g The system sequentially opens the fourth, ninth, and first pneumatic valves, while simultaneously activating the data acquisition system and issuing commands to control the fifth, sixth, seventh, and eighth pneumatic valves. Based on the methane flow rate V, it automatically switches control between the first, second, third, and fourth flow sensors. Once the methane flow through column 2 stabilizes, the first, second, third, and fourth flow sensors collect the stable flow rate as the gas flow rate at the outlet of the triaxial clamp. Q The pressure sensor at the inlet end displays the gas pressure at the second port of the triaxial gripper. P g1 The pressure value displayed by the pressure sensor at the outlet is the gas pressure at the outlet of the triaxial clamp. P g2 ; Calculate the permeability of the gas-containing dry No. 2 pillar coal according to formula (5) k g ; ； In the formula: k g —Permeability of dry No. 2 pillar coal containing gas, 10 -15 m 2 ; Q —Gas flow rate at the outlet of the three-axis clamp, ml / s; P a —Atmospheric pressure, MPa; μ — Gas fluid dynamic viscosity, MPa·s; L Length of No. 2 coal pillar, cm; A —Cross-sectional area of ​​No. 2 coal pillar, cm² 2 ; P g1 —Gas pressure at the second port of the triaxial gripper, MPa; P g2 —Gas pressure at the outlet of the triaxial clamp, MPa; n. Continue to replenish methane to column 2 of the triaxial clamp until column 2 reaches methane adsorption equilibrium: Close the fourth pneumatic valve, and continue to replenish methane to column 2 of the triaxial clamp using the reference tank. When both the inlet and outlet pressure sensors simultaneously display a pressure of [value missing], [action missing]. P And it remained unchanged for 12 hours, indicating that the adsorption of methane in the No. 2 column coal was in equilibrium. Then the first pneumatic valve, the ninth pneumatic valve, the fourth high-pressure shut-off valve, and the seventh high-pressure shut-off valve were closed. o. Inject water into the No. 2 column coal, which has already been balanced by adsorbed methane, in the three-axis clamp: Turn on the high-pressure water injection pump, open the eighth high-pressure shut-off valve, and inject water into the No. 2 column coal, which has already been balanced by adsorbed methane. The weight of the injected water is G. s2 Stop water injection and shut off the eighth high-pressure shut-off valve and the high-pressure water injection pump in sequence. p. Calculate the coal permeability under waterlock conditions after water injection. k s After 24 hours of water injection, the fourth pneumatic valve, the fourth high-pressure shut-off valve, the ninth pneumatic valve, and the first pneumatic valve are opened sequentially. Simultaneously, the data acquisition system is activated, and commands are issued to control the fifth, sixth, seventh, and eighth pneumatic valves. The first, second, third, and fourth flow sensors are automatically switched according to the methane flow rate V. Once the methane flow through column No. 2 stabilizes, the first, second, third, and fourth flow sensors collect the stable flow rate as the gas flow rate at the outlet of the triaxial clamp. Q The pressure sensor at the inlet end displays the gas pressure at the second port of the triaxial gripper. P s1 The pressure value displayed by the pressure sensor at the outlet is the gas pressure at the outlet of the triaxial clamp. P s2 ; Calculate the coal permeability under water-locked conditions after water injection according to formula (6). k s ; ； In the formula: k s —Coal permeability under water-locked state after water injection, 10 -15 m 2 ; Q —Gas flow rate at the outlet of the three-axis clamp, ml / s; P a —Atmospheric pressure, MPa; μ — Gas fluid dynamic viscosity, MPa·s; L Length of No. 2 coal pillar, cm; A —Cross-sectional area of ​​No. 2 coal pillar, cm² 2 ; P s1 —Gas pressure at the second port of the triaxial gripper, MPa; P s2 —Gas pressure at the outlet of the triaxial clamp, MPa; q. Calculate the coal permeability damage coefficient λ : Calculated according to formulas (5) and (6) k g and k s The coal permeability damage coefficient is calculated according to formula (7). λ ; ； In the formula: λ — Coal permeability damage coefficient, % k g —Permeability of dry No. 2 pillar coal containing gas, 10 -15 m 2 ; k s —Coal permeability under water-locked state after water injection, 10 -15 m 2 ; r. The experimental testing process has ended.

7. The testing method of the deep in-situ coal seam water-lock strength testing device as described in claim 6, characterized in that, The weight G of the injected water in step h s1 Not greater than the weight G of No. 1 coal pillar m1 15%.

8. The testing method of the deep in-situ coal seam water-lock strength testing device as described in claim 6, characterized in that, The weight G of the injected water in step o s2 No more than the weight of No. 2 coal pillar G m2 15%.

9. The testing method of the deep in-situ coal seam water-lock strength testing device as described in claim 6, characterized in that, In steps i and m, the principle for automatically switching the control of the first, second, third, and fourth flow sensors according to the methane flow rate V is as follows: when 3000 mL / min ≤ V < 80 L / min, the fifth pneumatic valve automatically opens, and the first flow sensor monitors and records the methane flow rate and desorption amount; when 500 mL / min ≤ V < 3000 mL / min, the sixth pneumatic valve automatically opens, and the second flow sensor monitors and records the methane flow rate and desorption amount; when 50 mL / min ≤ V < 500 mL / min, the seventh pneumatic valve automatically opens, and the third flow sensor monitors and records the methane flow rate and desorption amount; when 0 < V < 50 mL / min, the eighth pneumatic valve automatically opens, and the fourth flow sensor monitors and records the methane flow rate and desorption amount.

10. A method for evaluating the water-locking strength of deep in-situ coal bodies, wherein the coal gas retention coefficient is obtained according to the testing method of the deep in-situ coal body water-locking strength testing device as described in any one of claims 6-9. η and coal permeability damage coefficient λ Based on Table 1, the water-locking strength of the deep in-situ coal seam is comprehensively evaluated as follows: 。

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