High-low-temperature high-pressure rock three-axis measuring system and method for measuring permeability of frozen rock based on high-low-temperature high-pressure rock three-axis measuring system

Abstract

The invention discloses a high-low-temperature high-pressure rock triaxial measurement system and a method for measuring permeability of frozen rock based on the system. The method comprises the following steps: measuring basic data of a rock test piece, and assembling the test piece to a measuring system; at normal temperature, applying a confining pressure value and osmotic pressure to the test piece by using a measuring system to enable the osmotic pressure to reach a first target value, and measuring the permeability of the rock test piece; the rock test piece is cooled, meanwhile, the high-low-temperature high-pressure rock triaxial measurement system is controlled to maintain the confining pressure of the rock test piece unchanged, and the osmotic pressure of the rock test piece is controlled to be a second target value; and when the temperature of the rock test piece is reduced to a preset temperature, controlling the osmotic pressure of the rock at a third target value, and measuring the permeability of the rock test piece at the preset temperature. According to the invention, gas is selected as a medium to measure the permeability at low temperature, so that the problem that liquid as the medium affects the measurement result is solved, and the device has an important promotion effect on scientific research and engineering practice in the field of low-temperature geotechnical engineering.

Description

Technical Field

[0001] The invention belongs to the field of low-temperature geotechnical engineering, and in particular is a high-low-temperature and high-pressure rock triaxial measurement system and a method for measuring the permeability of frozen rocks using the system. Background Art

[0002] With the growing demand for liquefied natural gas (LNG) as a clean energy source, the innovation and development of its underground storage design has become the key to energy security. The airtightness and stability of underground LNG storage are crucial to ensuring energy supply. Given the extremely low temperature characteristics of underground LNG storage, the rock formation where the storage is located may be affected by low temperature, causing rock damage, which in turn poses a threat to the integrity of the storage structure. Therefore, in-depth research on the evolution of rock permeability under low temperature and revealing the specific impact of low temperature on rock airtightness and stability of underground LNG storage are of great significance to ensure the long-term safe operation of LNG storage.

[0003] Existing studies on the permeability characteristics of rocks under low temperature have failed to comprehensively monitor and record the changes in permeability before and after low temperature during the measurement process. These key parameters are crucial for an accurate and in-depth understanding of the permeability behavior of rocks under low temperature conditions. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] The invention aims to solve the problem that the permeability of frozen rocks cannot be directly measured under low temperature.

[0006] (II) Technical solution

[0007] In order to solve the above technical problems, the first aspect of the present invention proposes a method for measuring the permeability of frozen rocks based on a high-low-temperature and high-pressure rock triaxial measurement system, which comprises the following steps:

[0008] S1. Measure basic data of a rock specimen, and assemble the rock specimen to the high-low-temperature and high-pressure rock triaxial measurement system;

[0009] S2. At room temperature, using the high-low-temperature and high-pressure rock triaxial measurement system, applying a confining pressure value and an osmotic pressure to the rock specimen, so that the osmotic pressure reaches a first target value, and measuring the permeability of the rock specimen;

[0010] S3, cooling the rock specimen, and controlling the high-low-temperature and high-pressure rock triaxial measurement system to maintain the confining pressure of the rock specimen unchanged, and controlling the osmotic pressure of the rock specimen at a second target value;

[0011] S4. When the temperature of the rock sample drops to a predetermined temperature, the osmotic pressure of the rock is controlled at a third target value, and the permeability of the rock sample at the predetermined temperature is measured.

[0012] According to a preferred embodiment of the present invention, the first target value and the third target value are equal, and the second target value is smaller than the first target value.

[0013] According to a preferred embodiment of the present invention, the second target value is one third of the first target value.

[0014] According to a preferred embodiment of the present invention, in step S2 and step S4, gas is used as the measuring medium of the permeability.

[0015] According to a preferred embodiment of the present invention, the permeability measurement method is a pulse decay permeability measurement method, using a gas medium, and the permeability measurement formula is described by the following equation:

[0016]

[0017] Among them, L s is the sample height, d is the sample diameter, A s is the cross-sectional area of ​​the sample, μ is the viscosity coefficient of the permeation medium, β is the compressibility coefficient of the permeation medium, V is the volume of the container storing the gas medium, ΔP i is the initial pressure difference, ΔP f is the final pressure difference, and Δt is the measurement time.

[0018] According to a preferred embodiment of the present invention, in step S3, the confining pressure actuator is replenished with oil before cooling to ensure that there is enough oil to maintain the confining pressure during the cooling process.

[0019] The second aspect of the present invention provides a high-low-temperature and high-pressure rock triaxial measurement system, comprising a SCON controller, a confining pressure module, a permeation module, a measurement platform, a refrigerator, a pressure pump station, a water cooler, an air compressor, a data display and recording and command input terminal, and an acoustic emission recorder; the SCON controller is used as a transfer to transmit the instructions of the data display and recording and command input terminal to the measurement system, and is also used to transmit the working status of the measurement system and the sensor data in the system to the data display and recording and command input terminal; the confining pressure module includes a pressure chamber, and provides confining pressure to the rock specimen in the pressure chamber; the permeation module is used to provide permeation pressure to the rock specimen in the pressure chamber; the measurement platform is used to assemble the rock specimen; the refrigerator is used to provide temperature conditions for the pressure chamber; the pressure pump station is used to provide the pressure source used for the measurement system; the water cooler is used to cool the pressure pump station; the air compressor is used to provide pressure support when the pressure chamber is filled / drained. The data display, recording and command input terminal is used to input measurement steps, record measurement data and view the working status of the measurement system; the acoustic emission recorder is used to record the acoustic emission signal of the rock specimen during the measurement process.

[0020] According to a preferred embodiment of the present invention, the confining pressure module also includes an oil drain / replenishment port, an oil drain / flush port valve, a pressure chamber oil drain / replenishment lower valve, a first high-pressure valve, a confining pressure booster, a pressure sensor, a confining pressure silicone oil reservoir, a liquid level pipe, a second high-pressure valve, a third high-pressure valve 11, a pressure chamber oil drain / replenishment upper valve, an air compressor connecting valve, a safety valve and a pressure chamber pressure gauge; the oil drain / replenishment port is used to replenish / discharge the silicone oil in the confining pressure silicone oil reservoir; the oil drain / flush port valve is used to open / close the oil drain / flush port; the pressure chamber oil drain / replenishment lower valve is used for pressure chamber oil filling / drainage pipeline conversion. The first high-pressure valve is used to disconnect / connect the pipeline; the confining pressure booster is used to provide confining pressure to the pressure chamber; the pressure sensor is used to monitor the pipeline pressure; the confining pressure silicone oil reservoir is used to store silicone oil liquid that provides confining pressure; the liquid level tube is used to check whether the confining pressure chamber is filled with oil; the second high-pressure valve is used to disconnect / connect the pipeline; the pressure chamber is used to simulate the environment of the formation rock; the third high-pressure valve is used to disconnect / connect the pipeline; the pressure chamber oil discharge / supply upper valve is used for pressure chamber oil filling / drain pipeline conversion; the air compressor connecting valve is used to open the pressure connection with the air compressor when draining / filling oil; the safety valve is used to prevent the pressure chamber from being over-pressured; the pressure chamber pressure gauge is used to monitor the pressure in the pressure chamber.

[0021] According to a preferred embodiment of the present invention, the permeation module includes a first pressure relief port, a second pressure relief port, a first fine-tuning knob pressure relief port, a second fine-tuning knob pressure relief port, a plurality of pipeline valves, an air source / liquid pressure connecting valve, a first pressure sensor, a second pressure sensor and a differential pressure sensor 33; the first pressure relief port is used to discharge the liquid / gas in the connecting pipeline; the second pressure relief port is used to discharge the liquid / gas in the connecting pipeline; the first fine-tuning knob pressure relief port 18 is used to control the liquid / gas velocity in the discharge connecting pipeline. The second fine-tuning knob pressure relief port is used to control the liquid / gas velocity in the discharge connecting pipeline. The plurality of pipeline valves are used to disconnect / connect the pipeline here. The air source / liquid pressure connecting valve is used to connect or disconnect the air source / liquid pressure; the first pressure sensor is used to monitor the pipeline pressure here; the second pressure sensor is used to monitor the pipeline pressure here; the differential pressure sensor is used to monitor the pressure difference of the pipelines at both ends.

[0022] (III) Beneficial effects

[0023] The present invention can precisely control the measurement conditions and effectively simulate the permeability behavior of on-site rocks in a low-temperature environment.

[0024] The present invention uses the pulse attenuation permeability method to select gas as the medium to measure the permeability at low temperature, thereby solving the problem that the physical and chemical reaction between the liquid as the medium and the clay minerals in the rock, the reduction of low-temperature fluidity and the volume change caused by temperature affect the measurement results. A method for measuring the permeability of frozen rocks under low temperature is provided, which has an important role in promoting scientific research and engineering practice in the field of low-temperature geotechnical engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the overall structure of a high-low-temperature and high-pressure rock triaxial measurement system adopted in an embodiment of the present invention.

[0026] Figure 2 It is a schematic diagram of the principle of the confining pressure module of the high-temperature and high-pressure rock triaxial measurement system adopted in one embodiment of the present invention.

[0027] Figure 3 It is a schematic diagram of the principle of a permeability module of a high-low-temperature and high-pressure rock triaxial measurement system adopted in an embodiment of the present invention.

[0028] Figure 4 It is a flow chart of a method for measuring the permeability of frozen rocks based on a high-low-temperature and high-pressure rock triaxial measurement system of the present invention.

[0029] 1. Oil drain / supply port, 2. Oil drain / flush port valve, 3. Pressure chamber oil drain / supply lower valve, 4. High-pressure valve, 5. Confining pressure booster, 6. Pressure sensor, 7. Confining pressure silicone oil reservoir, 8. Liquid level tube 9. High-pressure valve, 10. Pressure chamber, 11. High-pressure valve, 12. Pressure chamber oil drain / supply upper valve, 13. Air compressor connecting valve, 14. Safety valve, 15. Pressure chamber pressure gauge, 16, 17. Pressure relief port, 18, 19. Fine-tuning knob pressure relief port, 20, 21. 22, 24, 26, 27, 29, 30, 31, 32, pipeline valve, 23, gas source / liquid pressure connecting valve, 25, 28 pressure sensor, 33, differential pressure sensor, 34, backup power supply, 35, SCON controller, 36, confining pressure module, 37, penetration module, 38, measurement platform, 39, refrigerator, 40, pressure pump station, 41, water cooler, 42, air compressor, 43, data display and recording and command input terminal, 44, acoustic emission recorder DETAILED DESCRIPTION

[0030] In general, the present invention proposes a method for measuring the permeability of frozen rocks by using a pulse attenuation permeability measurement method based on the principle of one-dimensional non-steady-state fluid dynamics, by applying a transient pressure pulse to a rock sample and monitoring its attenuation response inside the rock sample, and then using a mathematical model to quantitatively analyze the permeability.

[0031] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0032] The present invention proposes an innovative measurement method based on a high-low-temperature and high-pressure rock triaxial measurement system, which is specifically designed to accurately measure the permeability of frozen rocks under low-temperature conditions.

[0033] Figure 1 FIG. 1 is a schematic diagram of the overall structure of a high-low-temperature and high-pressure rock triaxial measurement system used in an embodiment of the present invention. Figure 1 As shown, the high-low-temperature and high-pressure rock triaxial measurement system includes a backup power supply 34, a SCON controller 35 (serial port controller 35), a confining pressure module 36, a permeation module 37, a measurement platform 38, a refrigerator 39, a pressure pump station 40, a water cooler 41, an air compressor 42, a data display and recording and command input terminal 43 and an acoustic emission recorder 44.

[0034] The backup power supply 34 is used to maintain the power supply of the SCON controller to prevent sudden power failure.

[0035] The SCON controller 35 is used as a transfer to transmit the instructions of the data display, recording and instruction input terminal 43 to the measurement system, and is also used to transmit the working status of the measurement system and the sensor data in the system to the data display, recording and instruction input terminal 43.

[0036] The confining pressure module 36 is used to provide confining pressure to the rock specimen in the pressure chamber.

[0037] The penetration module 37 is used to provide penetration pressure to the rock specimen in the pressure chamber.

[0038] The measuring platform 38 is used to assemble rock specimens.

[0039] The refrigerator 39 is used to provide temperature conditions for the pressure chamber.

[0040] The pressure pump station 40 is used to provide a pressure source for the measurement system.

[0041] The water cooler 41 is used to cool the pressure pump station.

[0042] The air compressor 42 is used to provide pressure support when filling / draining oil in the pressure chamber.

[0043] The data display, recording and command input terminal 43 is used to input measurement steps, record measurement data and view the working status of the measurement system.

[0044] The acoustic emission recorder 44 is used to record the acoustic emission signal of the rock specimen during the measurement process.

[0045] Figure 2 FIG. 1 is a schematic diagram of the confining pressure module principle of the high-temperature and high-pressure rock triaxial measurement system used in an embodiment of the present invention. Figure 2 As shown, the confining pressure module includes an oil drain / fill port 1, an oil drain / flush port valve 2, a pressure chamber oil drain / fill lower valve 3, a first high-pressure valve 4, a confining pressure booster 5, a pressure sensor 6, a confining pressure silicone oil reservoir 7, a liquid level tube 8, a second high-pressure valve 9, a pressure chamber 10, a third high-pressure valve 11, a pressure chamber oil drain / fill upper valve 12, an air compressor connecting valve 13, a safety valve 14 and a pressure chamber pressure gauge 15.

[0046] The oil drain / replenishment port 1 is used to replenish / discharge the silicone oil in the confining pressure cabinet.

[0047] The oil drain / flush port valve 2 is used to open / close the oil drain / flush port.

[0048] The pressure chamber oil drain / supply lower valve 3 is used for switching the pressure chamber oil filling / draining pipeline.

[0049] The first high-pressure valve 4 is used to disconnect / connect the pipeline there.

[0050] The confining pressure booster 5 is used to provide confining pressure to the pressure chamber.

[0051] The pressure sensor 6 is used to monitor the pipeline pressure here.

[0052] The confining pressure silicone oil storage 7 is used to store silicone oil liquid that provides confining pressure.

[0053] The liquid level tube 8 is used to check whether the oil filling of the confining pressure chamber is completed.

[0054] The second high-pressure valve 9 is used to disconnect / connect the pipeline here.

[0055] The pressure chamber 10 is used to simulate the environment of formation rocks.

[0056] The third high-pressure valve 11 is used to disconnect / connect the pipeline here.

[0057] The pressure chamber oil drain / supply upper valve 12 is used for switching the pressure chamber oil filling / draining pipeline.

[0058] The air compressor connecting valve 13 is used to open the pressure connection with the air compressor when draining / filling oil.

[0059] The safety valve 14 is used to prevent the pressure chamber from being over-pressured.

[0060] The pressure chamber pressure gauge 15 is used to monitor the pressure in the pressure chamber.

[0061] Figure 3 FIG. 1 is a schematic diagram of the principle of the permeability module of the high-temperature and high-pressure rock triaxial measurement system used in one embodiment of the present invention. Figure 3 As shown, the permeation module includes a first pressure relief port 16, a second pressure relief port 17, a first fine-tuning knob pressure relief port 18, a second fine-tuning knob pressure relief port 19, a plurality of pipeline valves 20, 21, 22, 24, 26, 27, 29, 30, 31, 32, an air source / liquid pressure connecting valve 23, a first pressure sensor 25, a second pressure sensor 28 and a differential pressure sensor 33.

[0062] The first pressure relief port 16 is used to discharge the liquid / gas in the communicating pipe.

[0063] The second pressure relief port 17 is used to discharge the liquid / gas in the communicating pipe.

[0064] The first fine-tuning knob pressure relief port 18 is used to control the liquid / gas velocity in the discharge communication pipeline.

[0065] The second fine-tuning knob pressure relief port 19 is used to control the liquid / gas velocity in the discharge communication pipeline.

[0066] A plurality of pipeline valves 20, 21, 22, 24, 26, 27, 29, 30, 31, 32 are used to disconnect / connect the pipelines therein.

[0067] The gas source / liquid pressure communication valve 23 is used to connect or disconnect the gas source / liquid pressure.

[0068] The first pressure sensor 25 is used to monitor the pipeline pressure there.

[0069] The second pressure sensor 28 is used to monitor the pipeline pressure there.

[0070] The pressure difference sensor 33 is used to monitor the pressure difference between the two ends of the pipeline.

[0071] Figure 4 This is a flow chart of the method for measuring the permeability of frozen rock based on the high-low-temperature and high-pressure rock triaxial measurement system of the present invention. Figure 4 As shown, the method of the present invention comprises the following steps:

[0072] S1. Measure basic data of a rock specimen, and assemble the rock specimen to the high-low-temperature and high-pressure rock triaxial measurement system.

[0073] In order to carry out triaxial measurement of low-temperature rocks, the present invention first measures basic data of rock specimens.

[0074] In order to reveal the differences in the permeability behavior of rocks under low temperature conditions, this step preferably selects multiple rock specimens with different basic conditions.

[0075] Specifically, step S1 includes:

[0076] S1.1 Measure the basic data of rock specimens.

[0077] In the present invention, the basic data of the rock specimen includes the height L of the rock specimen s , the diameter d of the rock specimen, the cross-sectional area A of the rock specimen s .

[0078] S1.2. Drain water and oil from the pipelines of the high-temperature, low-pressure and rock triaxial measurement system.

[0079] Close the pipeline valves 20 and 21 of the high-low-temperature and high-pressure rock triaxial measurement system, open the pipeline valves 22, 24, 26, 27, 29, 30, 31, and 32, open the gas source / liquid pressure connecting valve 23, and connect to the gas source pressure to drain the pipeline from the gas pipe connection end to the test piece end (the purpose of this step is to empty the liquid in the pipeline to prevent the retained liquid in the pipeline from affecting the permeability measurement results).

[0080] After the oil is discharged, close the gas source / liquid pressure connecting valve 23 and the pipeline valves 30 and 31, and open the pipeline valves 20 and 21 and the fine-tuning knob pressure relief ports 18 and 19 to exhaust and relieve pressure.

[0081] S1.3. Assemble the rock specimen to the high-low-temperature and high-pressure rock triaxial measurement system.

[0082] S1.3.1. Assemble the rock specimens after ensuring that there is no liquid in all pipes involved in the permeability test.

[0083] S1.3.2, assemble the sensor to the high-low-temperature and high-pressure rock triaxial measurement system.

[0084] The sensors include a first pressure sensor 25, a second pressure sensor 28 and a differential pressure sensor 33. After the sensors are assembled, they are adjusted to within the measuring range.

[0085] S1.3.4. Measure each sensor, and after the measurement of each sensor is completed, push the measuring platform 38 into the lower part of the pressure chamber 10, then reset each sensor, and then use displacement control to manipulate the axial actuator to contact the upper pressure head of the rock specimen, and finally lower the pressure chamber.

[0086] S2. At room temperature, use the high-low-temperature and high-pressure rock triaxial measurement system to apply confining pressure and osmotic pressure to the rock specimen so that the osmotic pressure reaches a first target value, and measure the permeability of the rock specimen.

[0087] Since the physical and chemical reaction between the liquid as a medium and the clay minerals in the rock, the reduction of low-temperature fluidity and the volume change caused by temperature affect the measurement results, the present invention uses a gas medium. Specifically, step S2 includes:

[0088] S2.1. Oil injection, confining pressure and osmotic pressure application.

[0089] S2.1.1. The steps for filling the pressure chamber with oil are as follows: close the drain / flush port valve 2, adjust the pressure chamber drain / fill upper valve 12 to fill cell; adjust the pressure chamber drain / fill lower valve 3 to fill cell; open the high-pressure valves 4, 9, and 11; open the air compressor connecting valve 13 to connect with the air compressor to fill the pressure chamber with oil.

[0090] S2.1.2. When the liquid level pipe 8 is filled, indicating that the pressure chamber is fully filled with oil, the air compressor connecting valve 13 is closed to cut off the connection with the air compressor, and the high-pressure valves 4 and 9 are closed, and then the target confining pressure can be applied.

[0091] S2.1.3. After the confining pressure is applied, the specimen will inevitably be compressed. At this time, observe the reading of the axial pressure sensor. If the reading is 0 or a negative value, use displacement control to fine-tune the downward movement of the axial actuator. When the axial sensor has a reading, stop pressing immediately.

[0092] S2.1.4. Gas saturate the rock specimen (the purpose of this step is to maintain the balance of internal and external pressures). The detailed operating steps are as follows: close pipeline valves 20 and 21, open pipeline valves 22, 24, 26, 27, 29, 30, 31, and 32, then open the gas source / liquid pressure connecting valve 23 to connect with the pressure gas source, adjust the gas source pressure to the first target value of the osmotic pressure, and then close the gas source / liquid pressure connecting valve 23. Wait until the readings of pressure sensors 25, 28 and differential pressure sensor 33 are stable, and then close pipeline valves 30 and 31 to complete the gas saturation of the specimen.

[0093] S2.2. Permeability measurement (normal temperature).

[0094] The room temperature of the present invention refers to the general indoor temperature, usually 15-25°C.

[0095] S2.2.1. Adjust the osmotic pressure difference. The operation steps are as follows: close the pipeline valves 22 and 24, open the pipeline valve 21 first, then slowly turn the fine-tuning knob pressure relief port 19 to fine-tune the exhaust valve for exhaust. At the same time, observe the reading of the differential pressure sensor 33. When the reading of the differential pressure sensor 33 reaches the target osmotic pressure difference, close the pipeline valve 21 first and then close the fine-tuning knob pressure relief port 19. Wait until the readings of the pressure sensors 25, 28 and the differential pressure sensor 33 are stable, start data recording, and record the initial pressure difference ΔP i , open pipeline valves 30 and 31, the osmotic pressure difference slowly decreases during the test, and when the osmotic pressure difference stabilizes, record the end pressure difference ΔP f .

[0096] The permeability measurement method is a pulse decay permeability measurement method using a gas medium. The permeability measurement formula is described by the following equation:

[0097]

[0098] Among them, L s is the sample height, d is the sample diameter, A s is the cross-sectional area of ​​the sample, μ is the viscosity coefficient of the permeation medium, β is the compressibility coefficient of the permeation medium, V is the volume of the container storing the gas medium, ΔP i is the initial pressure difference, ΔP f is the final pressure difference, and Δt is the measurement time.

[0099] S2.4.2 After the measurement at room temperature is completed, open the pipeline valves 22 and 24, open the fine-tuning knob pressure relief port 19 and the pipeline valve 21 to exhaust, and at the same time, when the pressure value read by the pressure sensors 25 and 28 is 1 / 10 of the surrounding pressure value used, close the pressure sensors 19 and 21 to stop exhausting (the purpose of this step is to prevent moisture from seeping out of the specimen into the air seepage pipeline during the cooling process, which can ensure the accuracy of the measurement data and avoid blockage of the pipeline due to ice), close the pipeline valves 30 and 31, turn off the gas source pressure, open the gas source / liquid pressure connecting valve 23, open the fine-tuning knob pressure relief port 19 and the pipeline valve 21 to exhaust until the pressure sensors 25, 28 and the pressure difference sensor 33 read 0, and close the fine-tuning knob pressure relief port 19 and the pipeline valve 21.

[0100] S3. Cooling the rock specimen, while controlling the high-low-temperature and high-pressure rock triaxial measurement system to maintain the confining pressure of the rock specimen unchanged, and controlling the osmotic pressure of the rock specimen at a second target value.

[0101] The high-low-temperature and high-pressure rock triaxial measurement system of the present invention supports triaxial measurement of rock specimens under high and low temperature conditions. The low temperature refers to a temperature below zero degrees Celsius. In a specific embodiment of the present invention, the low temperature can reach -40 degrees Celsius.

[0102] Specifically, this step includes the following sub-steps.

[0103] S3.1. Since the liquid that maintains the confining pressure will shrink during the cooling process, it is necessary to replenish the confining pressure actuator with oil so that it has enough oil to maintain the confining pressure.

[0104] S3.2. Lift the axial actuator until there is no force on the upper pressure head of the specimen, and continue to lift the axial actuator according to the approximate range of cooling and deformation of the specimen to leave enough deformation displacement in the axial direction for the specimen.

[0105] S3.3. Turn on the recording instrument of the sensor, set the target temperature value on the cooling instrument, start the instrument and start the temperature change recording.

[0106] S3.4. Maintain the osmotic pressure at a second target value, and ensure that the second target value is lower than the first target value.

[0107] In order to prevent the water in the specimen from penetrating and flowing back into the pipeline during the cooling process, thereby causing measurement errors and blockage of the liquid pipeline due to temperature reduction, and considering the influence of osmotic pressure on confining pressure, the present invention proposes to maintain the osmotic pressure at a second target value and ensure that the second target value is lower than the first target value. Specifically, the patent preferably sets the second target value to one third of the first target value to achieve effective control of the osmotic pressure.

[0108] S4. When the temperature of the rock sample drops to a predetermined temperature, the osmotic pressure of the rock is controlled at a third target value, and the permeability of the rock sample at the predetermined temperature is measured.

[0109] The predetermined temperature refers to a low temperature, generally 0 to -60° C. In this embodiment, the predetermined temperature is -40° C. Specifically, step S4 includes the following sub-steps.

[0110] S4.1. After reaching the target temperature (predetermined temperature), the specimen is gas-saturated (the purpose of this step is to maintain the balance of internal and external pressures). The detailed operation steps are as follows: After the cooling is completed, close the pipeline valves 20 and 21, open the pipeline valves 22, 24, 26, 27, 29, 30, 31, and 32, and then open the gas source / liquid pressure connecting valve 23 to connect with the pressure gas source, adjust the gas source pressure to the third target value of the osmotic pressure, and then close the gas source / liquid pressure connecting valve 23, wait until the readings of the pressure sensors 25, 28 and the pressure difference sensor 33 are stable, close the pipeline valves 30 and 31, and the gas-saturated specimen is completed.

[0111] S4.2. The operation steps for adjusting the osmotic pressure difference are as follows: close the pipeline valves 22 and 24, open the pipeline valve 21 first, then slowly turn the fine-tuning knob pressure relief port 19 to fine-tune the exhaust valve for exhaust while observing the reading of the differential pressure sensor 33. When the reading of the differential pressure sensor 33 reaches the target osmotic pressure difference, close the pipeline valve 21 first and then close the fine-tuning knob pressure relief port 19, wait until the readings of the pressure sensors 25, 28 and the differential pressure sensor 33 are stable, start data recording, and record the initial pressure difference ΔP i , open pipeline valves 30 and 31, the osmotic pressure difference slowly decreases during the measurement process, and when the osmotic pressure difference stabilizes, record the end pressure difference ΔP f The permeability measurement method is still a pulse decay permeability measurement method, using a gas medium. As before, the permeability measurement formula is described by the following equation:

[0112]

[0113] Among them, L s is the sample height, d is the sample diameter, A s is the cross-sectional area of ​​the sample, μ is the viscosity coefficient of the permeation medium used, β is the compressibility coefficient of the permeation medium used, V is the volume of the container storing the gas medium, ΔP i is the initial pressure difference, ΔP f is the final pressure difference, and Δt is the measurement time.

[0114] At this time, the osmotic pressure is controlled at a third target value to measure the permeability of the rock sample at the predetermined temperature.

[0115] The first target value and the third target value of the osmotic pressure in the present invention are preferably equal, so as to accurately evaluate the change of the permeability properties of the specimen under different temperature conditions. The present invention specifically provides for the standardization of the measurement conditions to ensure that the other measurement conditions except the osmotic pressure remain constant before and after the low temperature action. Through this design, we can compare the permeability properties under different temperature conditions on the same rock specimen, thereby eliminating the interference of other variables and obtaining accurate measurement results.

[0116] S4.3. After the measurement is completed, open the pipeline valves 22, 24, 30, and 31, close the gas source pressure, open the gas source / liquid pressure connecting valve 23, open the fine-tuning knob pressure relief port 19, and exhaust the pipeline valve 21 until the pressure sensors 25, 28, and the pressure difference sensor 33 read 0. After completion, close the pipeline valves 30 and 31.

[0117] In summary, the present invention uses gas medium to improve measurement efficiency, reduce the impact of slippage effect, avoid the physical and chemical reaction between liquid medium and clay minerals in rock, the reduction of low-temperature fluidity and the influence of volume change caused by temperature on the measurement results, and is particularly suitable for permeability measurement of low-permeability dense reservoirs, so that more accurate permeability measurement of rocks can be performed under low-temperature environment, thereby providing a new measurement method for the field of low-temperature geotechnical engineering, in order to obtain more reliable data support and theoretical guidance. The implementation of this method will help optimize engineering design and improve engineering safety, and has important scientific significance and application value for promoting the development of low-temperature geotechnical engineering disciplines.

[0118] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for measuring the permeability of frozen rocks based on a high-low-temperature and high-pressure rock triaxial measurement system, characterized in that: The steps include: S1. Measure basic data of a rock specimen, and assemble the rock specimen to the high-low-temperature and high-pressure rock triaxial measurement system; S2. At room temperature, using the high-low-temperature and high-pressure rock triaxial measurement system, applying a confining pressure value and an osmotic pressure to the rock specimen, so that the osmotic pressure reaches a first target value, and measuring the permeability of the rock specimen; S3, cooling the rock specimen, and controlling the high-low-temperature and high-pressure rock triaxial measurement system to maintain the confining pressure of the rock specimen unchanged, so as to control the osmotic pressure of the rock specimen at a second target value; S4. When the temperature of the rock sample drops to a predetermined temperature, the osmotic pressure of the rock is controlled at a third target value, and the permeability of the rock sample at the predetermined temperature is measured.

2. The method for measuring the permeability of frozen rock based on the high-low-temperature and high-pressure rock triaxial measurement system according to claim 1 is characterized in that: The first target value and the third target value are equal, and the second target value is smaller than the first target value.

3. The method for measuring the permeability of frozen rock based on the high-low-temperature and high-pressure rock triaxial measurement system according to claim 2, characterized in that: The second target value is one third of the first target value.

4. The method for measuring the permeability of frozen rock based on the high-low-temperature and high-pressure rock triaxial measurement system according to claim 2, characterized in that: In step S2 and step S4, gas is used as the measuring medium of the permeability.

5. The method for measuring the permeability of frozen rock based on the high-low-temperature and high-pressure rock triaxial measurement system according to claim 4, characterized in that: The permeability measurement method is a pulse decay permeability measurement method using a gas medium. The permeability measurement formula is described by the following equation: Among them, L s is the sample height, d is the sample diameter, A s is the cross-sectional area of ​​the sample, μ is the viscosity coefficient of the permeation medium, β is the compressibility coefficient of the permeation medium, V is the volume of the container storing the gas medium, ΔP i is the initial pressure difference, ΔP f is the final pressure difference, and Δt is the measurement time.

6. The method for measuring the permeability of frozen rock based on the high-low-temperature and high-pressure rock triaxial measurement system according to claim 1, characterized in that: In step S3, the confining pressure actuator is replenished with oil before cooling to ensure that there is enough oil to maintain the confining pressure during the cooling process.

7. A high-low-temperature and high-pressure rock triaxial measurement system, characterized in that: It includes a SCON controller (35), a confining pressure module (36), a permeation module (37), a measuring platform (38), a refrigerator (39), a pressure pump station (40), a water cooler (41), an air compressor (42), a data display and recording and command input terminal (43) and an acoustic emission recorder (44); The SCON controller (35) is used as a transfer to transmit the instructions of the data display, recording and instruction input terminal (43) to the measurement system, and is also used to transmit the working status of the measurement system and the sensor data in the system to the data display, recording and instruction input terminal (43); The confining pressure module (36) comprises a pressure chamber (10) and provides confining pressure to the rock specimen in the pressure chamber; The permeation module (37) is used to provide permeation pressure to the rock specimen in the pressure chamber; The measuring platform (38) is used to assemble the rock specimen; The refrigerator (39) is used to provide temperature conditions for the pressure chamber; The pressure pump station (40) is used to provide a pressure source for the measurement system; The water cooler (41) is used to cool the pressure pump station (40); The air compressor (42) is used to provide pressure support when filling / draining oil in the pressure chamber (10); The data display, recording and command input terminal (43) is used to input measurement steps, record measurement data and view the working status of the measurement system; The acoustic emission recorder (44) is used to record the acoustic emission signal of the rock specimen during the measurement process.

8. The high-low-temperature and high-pressure rock triaxial measurement system according to claim 7, characterized in that: The confining pressure module further comprises an oil drain / replenishment port (1), an oil drain / replenishment port valve (2), a pressure chamber oil drain / replenishment lower valve (3), a first high-pressure valve (4), a confining pressure booster (5), a pressure sensor (6), a confining pressure silicone oil reservoir (7), a liquid level pipe (8), a second high-pressure valve (9), a third high-pressure valve 11, a pressure chamber oil drain / replenishment upper valve (12), an air compressor connecting valve (13), a safety valve (14) and a pressure chamber pressure gauge (15); The oil discharge / replenishment port (1) is used to replenish / discharge the silicone oil in the confining pressure silicone oil reservoir; The oil drain / flush port valve (2) is used to open / close the oil drain / flush port; The pressure chamber oil discharge / supply lower valve (3) is used for switching the pressure chamber oil filling / discharge pipeline; The first high-pressure valve (4) is used to disconnect / connect the pipeline; The confining pressure booster (5) is used to provide confining pressure to the pressure chamber; The pressure sensor (6) is used to monitor the pipeline pressure; The confining pressure silicone oil storage (7) is used to store silicone oil liquid that provides confining pressure; The liquid level tube (8) is used to check whether the oil filling of the confining pressure chamber is completed; The second high-pressure valve (9) is used to disconnect / connect the pipeline; The pressure chamber (10) is used to simulate the environment of the formation rock; The third high-pressure valve (11) is used to disconnect / connect the pipeline; The pressure chamber oil discharge / supply upper valve (12) is used for switching the pressure chamber oil filling / discharge pipeline; The air compressor connecting valve (13) is used to open the pressure connection with the air compressor when draining / filling oil; The safety valve (14) is used to prevent the pressure chamber from being over-pressured; The pressure chamber pressure gauge (15) is used to monitor the pressure in the pressure chamber.

9. The high-low-temperature and high-pressure rock triaxial measurement system according to claim 7, characterized in that: The permeation module comprises a first pressure relief port (16), a second pressure relief port (17), a first fine-tuning knob pressure relief port (18), a second fine-tuning knob pressure relief port (19), a plurality of pipeline valves (20, 21, 22, 24, 26, 27, 29, 30, 31, 32), an air source / liquid pressure communication valve (23), a first pressure sensor (25), a second pressure sensor (28) and a differential pressure sensor 33; The first pressure relief port (16) is used to discharge liquid / gas in the communicating pipe; The second pressure relief port (17) is used to discharge liquid / gas in the communicating pipe; The first fine-tuning knob pressure relief port 18 is used to control the liquid / gas velocity in the discharge communication pipe; The second fine-tuning knob pressure relief port (19) is used to control the liquid / gas velocity in the discharge communication pipeline; The plurality of pipeline valves (20, 21, 22, 24, 26, 27, 29, 30, 31, 32) are used to disconnect / connect the pipelines therein; The gas source / liquid pressure communication valve (23) is used to connect or disconnect the gas source / liquid pressure; The first pressure sensor (25) is used to monitor the pipeline pressure; The second pressure sensor (28) is used to monitor the pipeline pressure; The pressure difference sensor (33) is used to monitor the pressure difference between the two ends of the pipeline.

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