A device and method for measuring the permeability of coal and rock that can correct the deviation of measurement values caused by adsorption

Abstract

The present invention belongs to the technical field of seepage testing of coal and rock masses, and specifically discloses a coal and rock permeability measurement device and method capable of correcting the deviation of measurement values caused by adsorption. The device includes a constant temperature box, a triaxial gripper arranged in the constant temperature box, a power gas storage tank, an injection gas storage tank, a vacuum pump, a gas pressure controller, a first switch, a vacuum pump, a second switch, a third switch, a fourth switch, a downstream standard container, a fifth switch, an upstream pressure sensor, a downstream pressure sensor, a temperature sensor and a computer; based on Darcy's law and the principle of mass conservation, combined with the permeability measurement work in two stages of pressure increase and pressure decrease, the deviation of permeability measurement caused by the adsorption of injected gas in the coal and rock mass is corrected, and the problem that the traditional permeability measurement method cannot eliminate the large deviation of permeability measurement caused by gas adsorption is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of seepage testing of coal and rock masses, in particular to a coal and rock permeability measurement device and method capable of correcting the deviation of measurement values caused by adsorption effects. Background Art

[0002] Permeability refers to the ability of a rock to allow a fluid to pass through under a certain pressure difference. Permeability is an important physical parameter involved in fields such as coalbed methane extraction, shale gas extraction, oil extraction, and coal mine gas prevention and control. The types of coal and rock gas permeabilities are diverse, and there are obvious differences in the permeabilities of coal and rock under different fluids, different temperatures, and different medium conditions. The main component of coalbed methane is methane. Coalbed methane extraction uses technologies such as carbon dioxide displacement, liquid nitrogen fracturing, water pressure fracturing, and hydraulic slotting in combination with extraction wells or boreholes to extract the adsorbed and free coalbed methane in the reservoir. Increasing the permeability of coal and rock reservoirs to adsorbed gases (methane, carbon dioxide) is the main way to improve the efficiency of coalbed methane extraction. Therefore, understanding the migration law of adsorbed gases in coal and rock reservoirs can provide important theoretical support for coalbed methane extraction.

[0003] With the rapid development of the research field of coal and rock permeability in the past decade, the laboratory measurement methods of coal and rock permeability have also been enriched and improved. The permeability measurement methods are mainly based on Darcy's law, gas equations, and the law of conservation of mass, and the permeability of coal and rock masses is obtained through the variation relationship between the upstream and downstream pressure differences and time. For example: Zhu Jie, Zhang Ben, Tang Jun, Shao Tangsha. A determination system and method for coal and rock permeability [P]. Beijing: CN111141657A, 2020-05-12; Wang Junguang, Sun Qinglin, Jin Qiao, Yu Qingrong, Liang Bing, Liu Sizhe, Shan Changyan. An experimental device and method for measuring the permeability of low-permeability coal and rock under the action of multi-field coupling [P]. Liaoning: CN110160885A, 2019-08-23; Ke Wenqi, Shi Zaihong, Zhang Rusheng, Xie Xianping, Niu Jun, Li Xin. A simulation device and method for studying coal and rock permeability [P]. Beijing: CN106370576B, 2019-04-02; Zhu Jie. A true triaxial coal and rock three-way deformation and permeability holder [P]. Beijing: CN105806762A, 2016-07-27; Wen Shengming, Hu Aimei, Li Jing, Li Xiangfang, Zhai Yuyang, Peng Zeyang, Zhang Dongling, Xu Min, Miao Yanan. An experimental device for measuring the anisotropic permeability of coal and rock [P]. Beijing: CN205229005U, 2016-05-11. The above-mentioned publicly disclosed permeability measurement methods can accurately measure the permeability of coal and rock masses, and the devices and pipelines involved are simple and easy to operate, and can measure the coal and rock permeability under conditions of long time, different pressures, different confining pressures, different temperatures, different gases, etc.

[0004] In the laboratory measurement of coal and rock permeability, helium, nitrogen, methane or carbon dioxide is generally selected as the gas fluid introduced into the device. Helium is a non-adsorbing gas, and there is no influence of adsorption on permeability when measuring the permeability of coal and rock. However, methane and carbon dioxide are adsorbing gases. When measuring the permeability of coal and rock, part of the gas volume in the injection device flows through the sample and downstream device, and part is adsorbed in the sample. There is a large deviation between the measured permeability value and the actual permeability. No coal and rock permeability measurement method that can correct the above errors has been found in the publicly disclosed permeability measurement methods. There is an urgent need for a coal and rock permeability measurement device and method that can correct the deviation of the measured value caused by adsorption. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a coal and rock permeability measurement device and method that can correct the deviation of the measured value caused by adsorption.

[0006] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0007] One of the objects of the present invention is to provide a coal and rock permeability measurement device that can correct the deviation of the measured value caused by adsorption, including a constant temperature box and a triaxial gripper arranged in the constant temperature box;

[0008] The triaxial gripper is composed of an upstream metal pad, a downstream metal pad, a rubber sleeve, an axial pressure liquid chamber and a circumferential pressure liquid chamber; the coal and rock sample to be measured is located inside the rubber sleeve, and the upstream metal pad and the downstream metal pad are located at both ends of the rubber sleeve. The upstream metal pad and the downstream metal pad are in close contact with both ends of the coal and rock sample to be measured; both the upstream metal pad and the downstream metal pad are cylindrical, and gas channels are arranged along the axial part; the circumferential pressure liquid chamber is located on the outer wall of the rubber sleeve; the axial pressure liquid chamber is located at both axial ends of the circumferential pressure liquid chamber; the axial pressure liquid chamber is connected to an axial pressure pump through a pressure liquid pipeline, and the output end of the axial pressure pump is connected to a third switch. The circumferential pressure liquid chamber is connected to a circumferential pressure pump through a pressure liquid pipeline, and the output end of the circumferential pressure pump is connected to a fourth switch;

[0009] Outside the constant temperature box, there are a power gas storage tank, an injection gas storage tank and a vacuum pump. The power gas storage tank and the injection gas storage tank are respectively connected to a gas pressure controller through gas pipelines. The power gas storage tank provides power for the gas pressure controller, and the injection gas storage tank provides a gas source for the gas pressure controller. The output end of the gas pressure controller is connected to the gas channel of the upstream metal spacer through a gas pipeline. A first switch is provided on the gas pipeline between the gas pressure controller and the upstream metal spacer; the vacuum pump is connected to the gas channels of the gas pressure controller and the upstream metal spacer through a gas pipeline. A second switch is provided on the gas pipeline connected to the input end of the vacuum pump; the end of the gas channel of the downstream metal spacer is connected to a downstream standard container through a gas pipeline. The downstream standard container is arranged inside the constant temperature box. A fifth switch is provided on the gas pipeline between the downstream standard container and the downstream metal spacer;

[0010] An upstream pressure sensor is provided on the gas pipeline between the first switch and the upstream metal spacer. A downstream pressure sensor is provided on the gas pipeline between the fifth switch and the downstream metal spacer. A temperature sensor is provided inside the constant temperature box. The upstream pressure sensor, the downstream pressure sensor and the temperature sensor are respectively connected to a computer through data transmission lines.

[0011] Further, the coal sample to be measured is cylindrical.

[0012] Further, the temperature control inside the constant temperature box is from normal temperature to 100.0 °C, the adjustment accuracy is 0.1 °C, and the automatic temperature control accuracy is ±0.5 °C.

[0013] Further, the inner wall of the rubber sleeve is an aluminized film rubber sleeve, and the coating thickness is 0.1 mm.

[0014] Preferably, the power gas storage tank is a nitrogen gas tank, and the injection gas storage tank is a carbon dioxide gas tank.

[0015] The second object of the present invention is to provide a coal and rock permeability measurement method capable of correcting the deviation of the measurement value caused by the adsorption effect, including the following steps:

[0016] S1. Measurement preparation: Process and polish the coal rock body to be measured into a standard cylinder. Put the cylindrical coal sample to be measured into a drying oven for drying. The drying temperature is 60 °C and the drying time is 24 h; the dried cylindrical coal sample to be measured is loaded into a triaxial holder with a rubber sleeve;

[0017] S2. Measurement Initial Condition Setting: Turn on the thermostat, adjust the temperature value T and feedback it to the computer through the temperature sensor; Turn on the third switch and the fourth switch, and inject pressure liquid with the set axial pressure of σ1 and circumferential pressure of σ2 into the axial pressure liquid chamber and circumferential pressure liquid chamber in the triaxial holder through the axial pressure pump and the circumferential pressure pump respectively; Turn off the first switch, turn on the second switch and the fifth switch, turn on the vacuum pump, and conduct vacuum treatment on the coal sample to be measured for 12 hours; Turn off the second switch, turn on the first switch, turn on the gas pressure controller, and set the output pressure P of the gas pressure controller through the computer; As the gas injection progresses, the gas pressure downstream of the coal sample to be measured will increase slowly until the upstream and downstream pressures of the coal sample to be measured are equal and both are P; The upstream gas pressure value is measured by the upstream pressure sensor, and the measurement data is collected by the computer in real time; The downstream gas pressure value is measured by the downstream pressure sensor, and the measurement data is collected by the computer in real time;

[0018] S3. Permeability Measurement in the Pressure Increase Stage: Set the output pressure of the gas pressure controller to P through the computer I = P + ΔP, where ΔP ≦ 0.1P, and record the time at this moment as the initial gas injection time; As the gas injection progresses, the gas pressure downstream will gradually increase, and the upstream gas pressure value is measured by the upstream pressure sensor, and the measurement data is collected by the computer in real time. The downstream gas pressure value is measured by the downstream pressure sensor, and the measurement data is collected by the computer in real time; When the upstream and downstream pressures are equal and both are P I , the measurement work of this step ends;

[0019] S4. Permeability Measurement in the Pressure Decrease Stage: Set the output pressure of the gas pressure controller to P through the computer, and record the time at this moment as the initial gas injection time; As the gas injection progresses, the gas pressure downstream of the sample will gradually decrease, and the upstream gas pressure value P D up (t) is measured by the upstream pressure sensor, and the measurement data is collected by the computer in real time; The downstream gas pressure value P D dn (t) is measured by the downstream pressure sensor, and the measurement data is collected by the computer in real time; When the upstream and downstream pressures are equal and both are P, the measurement work of this step ends;

[0020] S5. Data Processing: Since ΔP is much smaller than the bulk modulus of the sample, the changes in the height and cross-sectional area of the sample caused by the gas pressure changes in the pressure increase stage and the pressure decrease stage are negligible, and the relationship between the permeability and the gas pressure satisfies:

[0021]

[0022] In the formula: is the ideal value of the upstream gas pressure when the injection gas is assumed to be an ideal non-adsorbing gas and the injection time is t during the pressure increase stage;

[0023] is the ideal value of the downstream gas pressure when the injection gas is assumed to be an ideal non-adsorbing gas and the injection time is t during the pressure increase stage;

[0024] is the ideal value of the upstream gas pressure when the injection gas is assumed to be an ideal non-adsorbing gas and the injection time is t during the pressure decrease stage;

[0025] is the ideal value of the downstream gas pressure when the injection gas is assumed to be an ideal non-adsorbing gas and the injection time is t during the pressure decrease stage;

[0026] ΔP is the difference between the initial injection pressure P I during the pressure increase stage and the measured pressure P;

[0027] t is the experimental relative time during the pressure increase stage and the pressure decrease stage;

[0028] k I is the permeability of the sample during the pressure increase stage;

[0029] k D is the permeability of the sample during the pressure decrease stage;

[0030] μ is the viscosity coefficient of the injection gas;

[0031] β is the compressibility coefficient of the injection gas;

[0032] L is the height of the sample;

[0033] A is the cross-sectional area of the sample;

[0034] V dn is the volume of the downstream standard container;

[0035] Since gas is continuously injected upstream, there is:

[0036]

[0037] In the formula: is the measured value of the upstream gas pressure when the injection time is t during the pressure increase stage;

[0038] is the measured value of the upstream gas pressure when the injection time is t during the pressure decrease stage;

[0039] The measured downstream pressure data satisfies:

[0040]

[0041] In the formula: is the measured value of the downstream gas pressure at the injection time t during the pressure increase stage;

[0042] is the change in the downstream gas pressure caused by the adsorption of the injected gas by the sample at the injection time t during the pressure increase stage;

[0043] is the measured value of the downstream gas pressure at the injection time t during the pressure decrease stage;

[0044] is the change in the downstream gas pressure caused by the adsorption of the injected gas by the sample at the injection time t during the pressure decrease stage;

[0045] Since ΔP << P, it is assumed that the permeability of the sample during the pressure increase and decrease stages is equal and constant k; therefore, at a temperature of T, a confining pressure of σ, and an injection pressure of P, the permeability of the sample is k, satisfying:

[0046] v I = v D (9)

[0047] k = K I = k D (10)

[0048] Assuming that the gas adsorption rate of the sample remains unchanged, and the gas adsorption rates of the sample during the pressure increase and decrease stages are equal and constant, there is:

[0049]

[0050] Combining equations (7), (8), and (11) gives:

[0051]

[0052] Adding equations (1) and (3) gives:

[0053]

[0054] Substituting equation (12) into equation (13) gives:

[0055]

[0056] Equations (15) and (16) are the corrected formulas for measuring the permeability of coal and rock by the transient method. Substitute the pressure data measured during the pressure increase and decrease stages into equation (16) and fit with respect to time to obtain v I , and substitute the obtained v I value into equation (15) to obtain the permeability k;

[0057]

[0057] After the measurement, close the power gas storage tank and the injection gas storage tank, turn off the first switch, turn off the pressure controller, the thermostat, and the computer. Adjust the output pressures of the axial pressure pump and the circumferential pressure pump to 0, turn off the third switch and the fourth switch, take out the coal sample to be measured, and reset and clean the equipment.

[0058] Compared with the prior art, the present invention is composed of a thermostat, a triaxial gripper, a coal sample to be measured, a gas pressure control system, a confining pressure control system, and a data acquisition system. Based on Darcy's law and the principle of mass conservation, combined with the permeability measurement work in two stages of pressure increase and pressure decrease, it corrects the deviation of permeability measurement caused by the adsorption of injected gas in the coal and rock mass, and proposes a coal and rock permeability measurement device and method that can correct the deviation of the measured value caused by the adsorption effect. It solves the problem that the traditional permeability measurement method cannot eliminate the large deviation of permeability measurement caused by gas adsorption. Experimenters can add a series of detection technologies on the basis of this invention, such as temperature control, displacement sensing, acoustic emission, tracer, CT scanning and other technologies, to realize the measurement of various parameters of the seepage of adsorbed gas in the coal and rock mass under multiple physical fields. The connecting pipeline structure of the present invention is simple and the operation difficulty is low, which is worthy of popularization and application in the field of coal and rock mass permeability measurement technology. Description of the Drawings

[0059] Figure 1 It is a schematic diagram of the working principle of the present invention.

[0060] Figure 2 It is a diagram of the axial pressure transmission route.

[0061] Figure 3 It is a diagram of the circumferential pressure transmission route.

[0062] Figure 4 It is a diagram of the power gas flow route.

[0063] Figure 5 It is a diagram of the injection gas flow route.

[0064] Reference numerals in the drawings: 1 - triaxial gripper; 2 - coal sample to be measured; 3 - thermostat; 101 - upstream metal spacer; 102 - rubber sleeve; 103 - downstream metal spacer; 104 - axial pressure liquid chamber; 105 - circumferential pressure liquid chamber; 201 - axial pressure pump; 202 - circumferential pressure pump; 203 - pressure liquid pipeline; 301 - power gas storage tank; 302 - injection gas storage tank; 303 - gas pressure controller; 304 - downstream standard container; 305 - vacuum pump; 306 - gas pipeline; 401 - computer; 402 - upstream pressure sensor; 403 - downstream pressure sensor; 404 - temperature sensor; 405 - data transmission line. Detailed Description of the Invention

[0065] To make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the invention.

[0066] As Figure 1 shown, this embodiment exemplarily shows a coal and rock permeability measurement device capable of correcting the deviation of the measured value caused by the adsorption effect, including a constant temperature box 3 and a triaxial gripper 1 arranged in the constant temperature box 3; the constant temperature box 3 in this embodiment is a photosynthetic constant temperature box, which adopts the methods of automatic temperature control and water bath heating, the temperature control is adjusted from normal temperature to 100.0 °C, the adjustment accuracy is 0.1 °C, and the automatic temperature control accuracy is ±0.5 °C.

[0067] The described three-axis gripper 1 (the three-axis gripper 1 can directly select the gripper with the model number 19123Φ50-100, the product specification is Φ50-100mm, and the working pressure is 0-50MPa) consists of an upstream metal spacer 101, a downstream metal spacer 103, a rubber sleeve 102, an axial pressure liquid chamber 104, and a circumferential pressure liquid chamber 105; the coal sample 2 to be measured is located inside the rubber sleeve 102. The coal sample 2 to be measured is cylindrical, generally set to be 100mm long and 50mm in diameter, and its surface is polished. The function of the rubber sleeve 102 is on the one hand to transfer the pressure of the circumferential pressure liquid chamber 105 to the sample 2, and on the other hand to protect the sample 2, isolating the pressure liquid in the circumferential pressure liquid chamber 105 from the sample 2; in some embodiments, the rubber sleeve 102 is a rubber sleeve with an inner aluminized foil film, and the coating thickness is 0.1mm, aiming to prevent small molecule adsorptive gases from entering the rubber sleeve 102 and the circumferential pressure liquid chamber 105 from the sample 2; the upstream metal spacer 101 and the downstream metal spacer 103 are located inside the two ends of the rubber sleeve 102, and the upstream metal spacer 101 and the downstream metal spacer 103 are in close contact with the two ends of the coal sample 2 to be measured; both the upstream metal spacer 101 and the downstream metal spacer 103 are cylindrical, and gas channels are arranged along the axial part; the circumferential pressure liquid chamber 105 is located on the outer wall of the rubber sleeve 102; the axial pressure liquid chamber 104 is located at the axial two ends of the circumferential pressure liquid chamber 105; the axial pressure liquid chamber 104 is connected to an axial pressure pump 201 through a pressure liquid pipeline 203, and the output end of the axial pressure pump 201 is connected to a third switch (III). The circumferential pressure liquid chamber 105 is connected to a circumferential pressure pump 202 through a pressure liquid pipeline, and the output end of the circumferential pressure pump 202 is connected to a fourth switch (IV); in this embodiment, the axial pressure pump 201, the circumferential pressure pump 202, the pressure liquid pipeline 203, the third switch (III), and the fourth switch (IV) together constitute a confining pressure control system. The axial pressure pump 201 and the circumferential pressure pump 202 respectively inject pressurized liquid into the axial pressure liquid chamber 104 and the circumferential pressure liquid chamber 105 through the pressure liquid pipeline 203. The axial pressure transmission route is: axial pressure pump 201 → axial pressure liquid chamber 104 → upstream metal spacer 101 → axial direction of sample 2, as Figure 2 shown. The circumferential pressure transmission route is: circumferential pressure pump 202 → circumferential pressure liquid chamber 105 → rubber sleeve 102 → circumferential direction of sample 2, as Figure 3 shown. The axial pressure pump 201 and the circumferential pressure pump 202 in this embodiment both belong to metering pumps, adopt plunger loading, and select the model 65D SyringePump, with a pressure range of 0.07-138MPa and a pressure accuracy of 0.1% FS.

[0068] Outside the constant temperature incubator 3, there are a power gas storage tank 301, an injection gas storage tank 302, and a vacuum pump 305. The power gas storage tank 301 and the injection gas storage tank 302 are respectively connected to a gas pressure controller 303 through a gas pipeline 306. The power gas storage tank 301 provides power for the gas pressure controller 303, and the injection gas storage tank 302 provides a gas source for the gas pressure controller 303. In this embodiment, the power gas storage tank 301, the injection gas storage tank 302, the gas pressure controller 303, the vacuum pump 305, the downstream standard container 304, the gas pipeline 306, the first switch (I), the second switch (II), and the fifth switch (V) together form a gas pressure control system; the power gas storage tank 301 is a nitrogen tank, the injection gas storage tank 302 is a carbon dioxide tank, and the output end of the gas pressure controller 303 is connected to the gas passage of the upstream metal pad 101 through the gas pipeline 306. A first switch (I) is provided on the gas pipeline 306 between the gas pressure controller 303 and the upstream metal pad 101; the vacuum pump 305 is connected to the gas passages of the gas pressure controller 303 and the upstream metal pad 101 through the gas pipeline 306. A second switch (II) is provided on the gas pipeline 306 connected to the input end of the vacuum pump 305. In this embodiment, the vacuum pump 305 is of model 550D vacuum pump, with a power of 220V / 50Hz, a power of 320W, and a capacitance of 20μF; the end of the gas passage of the downstream metal pad 103 is connected to a downstream pressure sensor 403 through the gas pipeline 306. The downstream pressure sensor 403 is arranged inside the constant temperature incubator 3. A fifth switch (V) is provided on the gas pipeline 306 between the downstream pressure sensor 403 and the downstream metal pad 103; the gas flow route is divided into a power gas flow route and an injection gas flow route. The power gas flow route is: power gas storage tank 301 → gas pressure controller 303, as Figure 4 shown. The injection gas flow route is: injection gas storage tank 302 → gas pressure controller 303 → upstream metal pad 101 → sample 2 → downstream metal pad 103 → downstream standard container 304, as Figure 5 shown.

[0069] On the gas pipeline 306 between the first switch (I) and the upstream metal spacer 101, an upstream pressure sensor 402 is provided, and the upstream pressure sensor 402 is used to measure the gas pressure in the upstream pipeline; on the gas pipeline 306 between the fifth switch (V) and the downstream metal spacer 103, a downstream pressure sensor 403 is provided, and the downstream pressure sensor 403 is used to measure the gas pressure in the downstream pipeline; a temperature sensor 404 is provided in the thermostat, and is used to measure the temperature in the thermostat 3; the upstream pressure sensor 402, the downstream pressure sensor 403, and the temperature sensor 404 are respectively connected to the computer 401 through a data transmission line 405. In this embodiment, the upstream pressure sensor 402, the downstream pressure sensor 403, the temperature sensor 404, the computer 401, and the data transmission line 405 together constitute a data acquisition system.

[0070] During actual use, both the upstream pressure sensor 402 and the downstream pressure sensor 403 in this embodiment are selected as general industrial pressure sensors of model PTX5072, with a range of 0.1 - 10 MPa and a measurement accuracy of 0.1% FS. The temperature sensor 404 is selected as an NTC thermistor of model, with a size of 5×25 mm, a resistance value of 10K (25 °C), a measurement temperature range of -40 - 300 °C, and a measurement accuracy of 1%. The gas pressure controller 303 is selected as a regulator of model ER5000, with a weight of 1.4 kg, an operating temperature of -30 °C to 75 °C, a maximum output pressure of 30000 psi, an inlet pressure range of 1 psi to 120 psi, an accuracy of 0.1%, a pressure boost response time of 257 ms from 10 psi to 90 psi, and a pressure drop response time of 552 ms from 92 psi to 10 psi. Both the gas pipeline 306 and the pressure liquid pipeline 203 are seamless stainless steel pipes, with an outer diameter of Φ3 mm and a wall thickness of 0.5 mm.

[0071] Embodiment 2

[0072] This embodiment uses the adsorptive gas CO2 to measure the permeability of the sample. The experimental conditions are an injection pressure of 3.0 MPa, an axial pressure of 6.0 MPa, a confining pressure of 6.0 MPa, and a temperature of 30 °C. As Figure 1 shown, specifically, it is a method for measuring the coal and rock permeability that can correct the deviation of the measured value caused by the adsorption effect, including the following steps:

[0073] S1. Measurement preparation: Process and polish the coal and rock body to be measured into a standard cylinder, place the cylindrical coal sample 2 to be measured in a drying oven for drying, with a drying temperature of 60 °C and a drying time of 24 h; put the dried cylindrical coal sample 2 to be measured into the triaxial holder 1 with a rubber sleeve 102.

[0074] S2. Measurement Initial Condition Setting: Turn on the thermostatic chamber 3, adjust the temperature value T and feedback it to the computer 401 through the temperature sensor 404; Turn on the third switch (III) and the fourth switch (IV), and inject pressure liquid with an experimentally set axial pressure of σ1 and a circumferential pressure of σ2 into the axial pressure liquid chamber 104 and the circumferential pressure liquid chamber 105 in the triaxial gripper 1 respectively through the axial pressure pump 201 and the circumferential pressure pump 202; Turn off the first switch (I), turn on the second switch (II) and the fifth switch (V), turn on the vacuum pump 305, and perform vacuum treatment on the coal sample 2 to be measured for a duration of 12 h; Turn off the second switch (II), turn on the first switch (I), turn on the gas pressure controller 303, and set the output pressure P of the gas pressure controller 303 through the computer 401; As the gas injection proceeds, the gas pressure downstream of the coal sample 2 to be measured will slowly increase until the upstream and downstream pressures of the coal sample 2 to be measured are equal and both are P; The upstream gas pressure value is measured by the upstream pressure sensor 402, and the measurement data is collected in real time by the computer; The downstream gas pressure value is measured by the downstream pressure sensor 403, and the measurement data is collected in real time by the computer 401;

[0075] S3. Permeability Measurement in the Pressure Increase Stage: Set the output pressure of the gas pressure controller 303 to P through the computer 401 I = P + ΔP, where ΔP ≦ 0.1P, and record the time at this moment as the initial gas injection time; As the gas injection proceeds, the gas pressure downstream will gradually increase, and the upstream gas pressure value is measured by the upstream pressure sensor 402, and the measurement data is collected in real time by the computer 401. The downstream gas pressure value is measured by the downstream pressure sensor 403, and the measurement data is collected in real time by the computer 401; When the upstream and downstream pressures are equal and both are P I the measurement work of this step ends;

[0076] S4. Permeability Measurement in the Pressure Decrease Stage: Set the output pressure of the gas pressure controller 303 to P through the computer 401, and record the time at this moment as the initial gas injection time; As the gas injection proceeds, the gas pressure downstream of the sample will gradually decrease, and the upstream gas pressure value P D up (t) is measured by the upstream pressure sensor 402, and the measurement data is collected in real time by the computer 401; The downstream gas pressure value P D dn (t) is measured by the downstream pressure sensor 403, and the measurement data is collected in real time by the computer 401; When the upstream and downstream pressures are equal and both are P, the measurement work of this step ends;

[0077] S5. Data Processing: Since ΔP is much smaller than the bulk modulus of the sample, the changes in the height and cross-sectional area of the sample caused by the gas pressure changes during the pressure increase and decrease phases are negligible, and the relationship between the permeability and the gas pressure satisfies:

[0078]

[0079] In the formula: is the ideal value of the upstream gas pressure at the injection time t during the pressure increase phase, assuming the injected gas is an ideal non-adsorbing gas;

[0080] is the ideal value of the downstream gas pressure at the injection time t during the pressure increase phase, assuming the injected gas is an ideal non-adsorbing gas;

[0081] is the ideal value of the upstream gas pressure at the injection time t during the pressure decrease phase, assuming the injected gas is an ideal non-adsorbing gas;

[0082] is the ideal value of the downstream gas pressure at the injection time t during the pressure decrease phase, assuming the injected gas is an ideal non-adsorbing gas;

[0083] ΔP is the difference between the initial injection pressure P I during the pressure increase phase and the pressure to be measured P;

[0084] t is the experimental relative time during the pressure increase and decrease phases;

[0085] k I is the permeability of the sample during the pressure increase phase;

[0086] k D is the permeability of the sample during the pressure decrease phase;

[0087] μ is the viscosity coefficient of the injected gas;

[0088] β is the compressibility coefficient of the injected gas;

[0089] L is the height of the sample;

[0090] A is the cross-sectional area of the sample;

[0091] V dn is the volume of the downstream standard container;

[0092] Since gas is continuously injected upstream, there is:

[0093]

[0094] In the formula: is the measured value of the upstream gas pressure at the injection time t during the pressure increase phase;

[0095] is the measured value of the upstream gas pressure when the gas injection time is t during the pressure reduction stage;

[0096] The measured downstream pressure data satisfies:

[0097]

[0098] In the formula: is the measured value of the downstream gas pressure when the gas injection time is t during the pressure increase stage;

[0099] is the change in the downstream gas pressure caused by the adsorption of the injected gas by the sample when the gas injection time is t during the pressure increase stage;

[0100] is the measured value of the downstream gas pressure when the gas injection time is t during the pressure reduction stage;

[0101] is the change in the downstream gas pressure caused by the adsorption of the injected gas by the sample when the gas injection time is t during the pressure reduction stage;

[0102] Since ΔP << P, it is assumed that the permeability of the sample during the pressure increase and pressure reduction stages is equal and is a constant k; therefore, at a temperature of T, a confining pressure of σ, and an injection pressure of P, the permeability of the sample is k and satisfies:

[0103] v I = v D (9)

[0104] k = k I = k D (10)

[0105] Assuming that the gas adsorption rate of the sample remains unchanged and the gas adsorption rates of the sample during the pressure increase and pressure reduction stages are equal and unchanged, there is:

[0106]

[0107] Combining formulas (7), (8), and (11) gives:

[0108]

[0109] Adding formulas (1) and (3) gives:

[0110]

[0111] Substituting formula (12) into formula (13) gives:

[0112]

[0113] Formulas (15) and (16) are the modified formulas for measuring the permeability of coal and rock by the transient method proposed by the present invention. Substitute the pressure data measured in the pressure increase stage and the pressure decrease stage into formula (16), and fit the time to obtain v I , and substitute the obtained v I value into formula (15) to obtain the permeability k;

[0114] S6. After the measurement is completed, close the power gas storage tank and the injection gas storage tank, close the first switch (I), close the gas pressure controller 303, the constant temperature box 3, and the computer 401. Adjust the output pressures of the axial pressure pump 201 and the circumferential pressure pump 202 to 0, close the third switch (III) and the fourth switch (IV), take out the coal sample 2 to be measured, reset the equipment and clean it up.

[0115] The technical solution of the present invention is not limited to the limitations of the above specific embodiments. Any technical deformation made according to the technical solution of the present invention falls within the protection scope of the present invention.

Claims

1. A method for measuring the permeability of coal and rock that can correct the deviation of the measured value caused by adsorption, characterized in that, Measurement is carried out using a coal and rock permeability measurement device that can correct the deviation of the measured value caused by adsorption. The coal and rock permeability measurement device that can correct the deviation of the measured value caused by adsorption includes a constant temperature box and a triaxial gripper arranged in the constant temperature box; the triaxial gripper is composed of an upstream metal spacer, a downstream metal spacer, a rubber sleeve, an axial pressure liquid chamber and a circumferential pressure liquid chamber; the coal sample to be measured is located inside the rubber sleeve, and the upstream metal spacer and the downstream metal spacer are located inside the two end ports of the rubber sleeve, and the upstream metal spacer and the downstream metal spacer are in close contact with both ends of the coal sample to be measured; both the upstream metal spacer and the downstream metal spacer are cylindrical, and gas channels are arranged along the axial part; the circumferential pressure liquid chamber is located on the outer wall of the rubber sleeve; the axial pressure liquid chamber is located at the axial two ends of the circumferential pressure liquid chamber; the axial pressure liquid chamber is connected to an axial pressure pump through a pressure liquid pipeline, and the output end of the axial pressure pump is connected to a third switch, and the circumferential pressure liquid chamber is connected to a circumferential pressure pump through a pressure liquid pipeline, and the output end of the circumferential pressure pump is connected to a fourth switch; Outside the constant temperature box, there are a power gas storage tank, an injection gas storage tank and a vacuum pump. The power gas storage tank and the injection gas storage tank are respectively connected to a gas pressure controller through gas pipelines. The power gas storage tank provides power for the gas pressure controller, and the injection gas storage tank provides a gas source for the gas pressure controller. The output end of the gas pressure controller is connected to the gas channel of the upstream metal spacer through a gas pipeline. A first switch is arranged on the gas pipeline between the gas pressure controller and the upstream metal spacer; the vacuum pump is connected to the gas pressure controller and the gas channel of the upstream metal spacer through a gas pipeline. A second switch is arranged on the gas pipeline connected to the input end of the vacuum pump; the end of the gas channel of the downstream metal spacer is connected to a downstream standard container through a gas pipeline. The downstream standard container is arranged in the constant temperature box. A fifth switch is arranged on the gas pipeline between the downstream standard container and the downstream metal spacer; An upstream pressure sensor is arranged on the gas pipeline between the first switch and the upstream metal spacer, a downstream pressure sensor is arranged on the gas pipeline between the fifth switch and the downstream metal spacer, a temperature sensor is arranged inside the constant temperature box, and the upstream pressure sensor, the downstream pressure sensor and the temperature sensor are respectively connected to a computer through data transmission lines; The coal and rock permeability measurement method that can correct the deviation of the measured value caused by adsorption includes the following steps: S1. Measurement preparation: Process and polish the coal rock body to be measured into a standard cylinder, and place the cylindrical coal sample to be measured in a drying oven for drying. The drying temperature is 60 °C and the drying time is 24 h; the dried cylindrical coal sample to be measured is loaded into a triaxial gripper with a rubber sleeve; S2. Setting of initial measurement conditions: Open the thermostat, adjust the temperature value T and feed it back to the computer through the temperature sensor; open the third switch and the fourth switch, and inject the pressure liquid with the experimentally set axial pressure of σ1 and the annular pressure of σ2 into the axial pressure liquid chamber and the annular pressure liquid chamber in the three-axis clamp through the axial pressure pump and the annular pressure pump respectively; close the first switch, open the second switch and the fifth switch, turn on the vacuum pump, and perform vacuum treatment on the coal sample to be tested for a duration of 12 hours; close the second switch, open the first switch, turn on the gas pressure controller, and set the output pressure P of the gas pressure controller through the computer; as the gas injection proceeds, the gas pressure downstream of the coal sample to be tested will slowly increase until the upstream and downstream pressures of the coal sample to be tested are equal and both are P; the upstream gas pressure value is measured by the upstream pressure sensor, and the measurement data is collected in real time by the computer; the downstream gas pressure value is measured by the downstream pressure sensor, and the measurement data is collected in real time by the computer; S3. Permeability measurement in the boosting stage: Set the output pressure of the gas pressure controller to P by computer I = P + ΔP, where ΔP ≦ 0.1P, and record the time at this moment as the initial gas injection time; As gas injection progresses, the gas pressure downstream will gradually increase, and the gas pressure value P I up (t) is measured by the upstream pressure sensor, and the measurement data is collected in real time by the computer. The gas pressure value P I dn (t) is measured by the downstream pressure sensor, and the measurement data is collected in real time by the computer; Wait until the pressures upstream and downstream are equal and both are P I , and the measurement work for this step ends; S4. Permeability measurement during the pressure reduction stage: Set the output pressure of the gas pressure controller to P through the computer, and record the time at this moment as the initial gas injection time; as the gas injection progresses, the gas pressure downstream of the sample will gradually decrease, and the gas pressure value P D up (t) is measured by the upstream pressure sensor, and the measurement data is collected in real time by the computer; the gas pressure value P D dn (t) is measured by the downstream pressure sensor, and the measurement data is collected in real time by the computer; when the upstream and downstream pressures are equal and both are P, the measurement work of this step ends; S5. Data processing: Since ΔP is much smaller than the bulk modulus of the sample, the changes in the height and cross-sectional area of the sample caused by the changes in gas pressure during the pressure increase and pressure decrease stages are negligible, and the relationship between permeability and gas pressure satisfies: In the formula: is the ideal value of the upstream gas pressure at the time t of the gas injection time in the pressure boosting stage assuming that the injected gas is an ideal non-adsorbing gas; When the injected gas is assumed to be an ideal non-adsorbing gas, the ideal value of the downstream gas pressure at time t during the pressure increase stage when injecting gas; The ideal value of the upstream gas pressure at time t during the gas injection in the pressure reduction stage, assuming that the injected gas is an ideal non-adsorbing gas; Assume that the injected gas is an ideal non-adsorbing gas. When the injection time is t during the pressure reduction stage, the ideal value of the downstream gas pressure; ΔP is the difference between the initial gas injection pressure P during the pressure boosting stage and the pressure P to be measured; I ​ t is the relative experimental time of the boost phase and the depressurization phase; k I is the permeability of the sample in the boosting stage; k D is the permeability of the sample during the pressure reduction stage; μ is the viscosity coefficient of the injected gas; β is the compression factor of the injected gas; L is the height of the sample; A is the cross-sectional area of the sample; V dn is the volume of the downstream standard container; Since gas injection is continuously carried out upstream, there are: In the formula: is the measured value of the upstream gas pressure at the injection time t during the pressure boosting stage; When the gas injection time in the pressure reduction stage is t, the measured value of the upstream gas pressure; The measured downstream pressure data meets: Wherein: is the measured value of the downstream gas pressure at time t during the gas injection stage of pressure boost; When the gas injection time in the pressure boosting stage is t, it is the change in the downstream gas pressure caused by the adsorption of the injected gas by the sample; is the measured value of the downstream gas pressure when the gas injection time is t during the pressure reduction stage; Δp is the change in the downstream gas pressure caused by the adsorption of the injected gas by the sample at the injection gas time t during the pressure reduction stage; Since ΔP< <P,设定升压和降压阶段样品的渗透率相等且为常数k;因此,在温度为T、围压为σ、注气压力为P的情况下,该样品的渗透率为k,满足: v I = v D (9) k = k I = k D (10) Assuming that the adsorption rate of the sample to the gas remains unchanged, and the adsorption rate of the sample to the gas is equal and unchanged during the pressure increase and pressure decrease stages, we have: Formulas (7), (8) (11) are combined to obtain: Adding formula (1) and (3) together, we get: Substituting formula (12) into formula (13) yields: Formulas (15) and (16) are the corrected formulas for measuring the permeability of coal and rock by the transient method. Substitute the pressure data measured in the pressure increase stage and the pressure decrease stage into formula (16), and fit the time to obtain v I , and substitute the obtained v I value into formula (15) to obtain the permeability k; S6. After the measurement is completed, close the power gas tank and the injection gas tank, turn off the first switch, turn off the pressure controller, the constant temperature box, and the computer, adjust the output pressure of the axial pressure pump and the annular pressure pump to 0, turn off the third switch and the fourth switch, take out the coal sample to be tested, reset the equipment and clean it.

2. The method for measuring the permeability of coal and rock capable of correcting the deviation of the measured value caused by the adsorption effect according to claim 1, characterized in that: The temperature control in the constant temperature box is adjusted to room temperature ~ 100.0°C, the adjustment accuracy is 0.1°C, and the automatic temperature control accuracy is ±0.5°C.

3. The coal and rock permeability measurement method capable of correcting the deviation of measurement values caused by adsorption according to claim 1, characterized in that: The inner wall of the rubber sleeve is coated with an aluminum foil film, and the coating thickness is 0.1 mm.

4. The coal and rock permeability measurement method for correcting the deviation of measurement values caused by adsorption according to claim 1, characterized in that: The power gas storage tank is a nitrogen tank, and the injection gas storage tank is a carbon dioxide tank.

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