Ultralow-temperature high-pressure seepage and deformation test device and method based on in-situ CT scanning

Abstract

The invention belongs to the field of rock physical test devices, and particularly relates to an in-situ CT scanning-based ultralow-temperature high-pressure seepage and deformation test device and method.The sample device comprises a rock core clamping system, a seepage injection system, a confining pressure system, a back pressure system, a pressure acquisition system and a temperature control system, the rock core clamping system comprises a titanium alloy double-layer rock core holder and a heat-shrinkable sleeve for wrapping a rock core, and the rock core clamping system is fixed on a rotary objective table of the CT scanning system through a clamp; the seepage injection system comprises a gas phase injection pump; the backpressure system comprises a backpressure control pump; the confining pressure system comprises a nitrogen confining pressure pump; the pressure acquisition system comprises a computer and a Keller differential pressure sensor; the temperature control system comprises a Dewar flask. The method comprises a seepage test method and a deformation test method. According to the device and the method, a transient method permeability test and a pore water frost heaving-rock matrix cold contraction nonlinear coupling deformation test at ultralow temperature can be performed, and a theoretical basis is provided for construction of an underground liquefied natural gas reservoir.

Description

Technical Field

[0001] The invention belongs to the field of rock physics test devices, and in particular relates to an ultra-low temperature and high pressure seepage and deformation test device and method based on in-situ CT scanning. Background Art

[0002] Natural gas is a widely used clean energy. At present, the main storage form of liquefied natural gas is ground storage tanks, which have the problems of large footprint, small reserves, high evaporation rate and poor safety. Abandoned mines have rich underground space resources. Reusing abandoned mines and tunnels to reconstruct underground liquefied natural gas storage can effectively solve the problem of large-scale storage of natural gas. Underground liquefied natural gas storage has the advantages of large reserves, saving ground space and high safety.

[0003] The conversion of abandoned shafts and tunnels into liquefied natural gas storage involves an ultra-low temperature storage environment of -162°C. Studying the evolution of water frost heave, rock shrinkage deformation and permeability under ultra-low temperature environment is crucial for the safety and stability of the storage. Conventional low-temperature triaxial rock mechanics testing machines such as the utility model CN210923346U can simulate temperatures above -30°C, but it is difficult to achieve the ultra-low temperature (-162°C) environment of liquefied natural gas. In addition, to study the evolution of water frost heave, rock shrinkage deformation and permeability under ultra-low temperature, it is necessary to intuitively observe the changes in the microstructure inside the rock.

[0004] In recent years, in-situ CT imaging technology has been widely used in the field of geotechnical engineering as a visual non-destructive detection method. Invention CN114965076A proposes a sediment skeleton micro-deformation measurement device based on CT imaging in the seepage process of low-temperature hydrate mining, but does not involve ultra-low temperature (-162℃) injection and production environment. The main problem is that it is difficult to achieve ultra-low temperature and high pressure in CT while taking into account the CT imaging quality.

[0005] Therefore, in order to solve the above problems, an ultra-low temperature and high-pressure titanium alloy clamp with inner layer loading and outer layer temperature control was developed to meet the ultra-low temperature (-162℃) and high pressure (30MPa) experimental conditions, achieve precise temperature control (error less than ±0.05℃), and is suitable for in-situ CT scanning, which is of great significance for the study of rock deformation and permeability evolution under ultra-low temperature. Summary of the invention

[0006] The present invention provides an ultra-low temperature and high pressure seepage and deformation test device based on in-situ CT scanning, including a core clamping system, a seepage injection system, a confining pressure system, a back pressure system, a pressure acquisition system and a temperature control system;

[0007] The core clamping system comprises a titanium alloy double-layer core clamp and a heat shrink sleeve for wrapping the core inside, the titanium alloy double-layer core clamp comprises an internal cavity and an annular cavity surrounding the internal cavity; two through holes are arranged on the top surface of the heat shrink sleeve, and one through hole is arranged on the bottom surface, and the heat shrink sleeve is arranged in the internal cavity of the titanium alloy double-layer core clamp; three through holes are arranged on the top of the titanium alloy double-layer core clamp, two of which correspond to the two through holes on the top of the heat shrink sleeve, and one is arranged on the annular cavity; three through holes are arranged on the bottom of the titanium alloy double-layer core clamp, one of which corresponds to the through hole at the bottom of the heat shrink sleeve, one is arranged on the annular cavity, and the other is arranged in the internal cavity and located outside the heat shrink sleeve; the core clamping system is fixed to the rotating stage of the CT scanning system by a clamp;

[0008] The seepage injection system comprises a gas phase injection pump, the outlet of which is connected to the second two-way valve, the first three-way connector, the bottom through hole of the core holder, and the bottom through hole of the heat shrink sleeve in sequence through pipelines;

[0009] The back pressure system comprises a back pressure control pump, the outlet of which is connected to the back pressure valve, the sixth two-way valve, the second three-way connector, the small gas tank, the fifth two-way valve, the through hole on the top surface of the core holder, and the through hole on the top surface of the heat shrink sleeve in sequence through a pipeline;

[0010] The confining pressure system comprises a nitrogen confining pressure pump, the inlet of the nitrogen confining pressure pump is connected to the nitrogen bottle through a pipeline, and the outlet of the nitrogen confining pressure pump is connected to the first two-way valve and the through hole arranged in the inner cavity and outside the heat shrinkable sleeve on the bottom surface of the core holder through a pipeline in sequence;

[0011] The pressure acquisition system includes a computer and a Keller pressure differential sensor connected thereto, and two ends of a pipeline where the Keller pressure differential sensor is located are respectively connected to a first three-way connector and a second three-way connector;

[0012] The temperature control system includes a Dewar flask, which is connected in sequence to a pressure and flow controller, an open nitrogen tank, an airflow temperature controller, a third two-way valve, and a through hole arranged in an annular cavity at the bottom of a titanium alloy double-layer core holder through a stainless steel nitrogen pipeline wrapped in an insulation tube. The Dewar flask also includes a PID controller, which is respectively connected to the pressure and flow controller, the airflow temperature controller, and an ultra-low temperature resistant thermocouple, and the ultra-low temperature resistant thermocouple is wrapped in an ultra-low temperature resistant heat shrink tubing.

[0013] Preferably, the back pressure valve is also connected to the recovery tank via a pipeline.

[0014] Preferably, a nitrogen coil is provided in the open nitrogen tank.

[0015] Preferably, the temperature control system further comprises a recovery tank, which is connected in sequence to the fourth two-way valve and the through hole arranged in the annular cavity at the top of the titanium alloy double-layer core clamp through pipelines.

[0016] Preferably, the CT scanning system is a YXLON FF35 high-resolution micron CT scanning system.

[0017] Based on the ultra-low temperature and high pressure seepage and deformation test device described above, the present invention further proposes an ultra-low temperature and high pressure seepage and deformation test method based on in-situ CT scanning, including a seepage test method and a deformation test method, wherein the seepage test method comprises the following steps:

[0018] S1: Prepare several cores, clean them with methanol, put them in a drying oven to dry, measure and record the diameter and length of the cores; then evacuate the cores and fully saturate them with water;

[0019] S2: Place the saturated cores in a drying oven for natural evaporation, obtain the preset saturation through quality control method, make different cores reach different saturation, and smear the core surface with vaseline; take cores with different saturation in turn for subsequent tests;

[0020] S3: Place the core into the heat shrink tubing and fix it by heat shrinking, the heat shrink tubing wraps the entire core, two through holes are processed on the top surface of the heat shrink tubing and one through hole is processed on the bottom surface, and the heat shrink tubing is set in the inner cavity of the core holder; assemble the ultra-low temperature and high pressure seepage and deformation test device based on in-situ CT scanning;

[0021] S4: Open the first two-way valve, start the confining pressure pump and gradually increase the confining pressure to the first pressure;

[0022] S5: Open the second two-way valve, the first three-way connector, the fifth two-way valve, the second three-way connector and the sixth two-way valve; open the gas phase injection pump to maintain the second pressure of upstream injection, open the back pressure control pump to pressurize to the second pressure, and wait for the upstream and downstream pressure difference measured by the Keller differential pressure sensor to be zero; increase the gas phase injection pump pressure to the third pressure, and gradually increase the back pressure control pump pressure to the third pressure until the pressure difference measured by the Keller differential pressure sensor gradually decreases to zero, record the pressure difference attenuation, and the permeability is calculated according to the following formula

[0023]

[0024] Where k is the permeability, α is the slope of the pressure drop curve, and μ g is the gas viscosity, L is the core length, c g is the gas compressibility, V down is the volume of the small gas tank, A is the cross-sectional area of ​​the core;

[0025] S6: Close the first three-way connector, the second two-way valve, the fifth two-way valve, the second three-way connector, the sixth two-way valve, and the gas phase injection pump;

[0026] Turn on the temperature control system, open the Dewar flask valve, and let the nitrogen pass through the pressure and flow controller and then through the copper tube in the open liquid nitrogen tank to cool down to the first temperature, and then pass through the pipeline into the air flow temperature controller to raise the temperature to the required temperature, and let the nitrogen pass through the third two-way valve into the through hole at the bottom of the annular cavity of the low-temperature resistant core holder, and slowly cool the core to multiple preset low temperatures in sequence through the annular cavity, and keep the constant temperature at each temperature level for a certain time, and refer to step S5 to calculate the permeability at different temperatures;

[0027] The deformation test method comprises the following steps:

[0028] B1: Prepare several cores, clean them with methanol, put them in a drying oven to dry, measure and record the diameter and length of the cores; then evacuate the cores and fully saturate them with water;

[0029] B2: Place the saturated cores in a drying oven for natural evaporation, obtain the preset saturation through quality control method, and make different cores reach different saturation; smear the core surface with vaseline; take cores with different saturation from low to high for subsequent tests;

[0030] B3: Place the core into the heat shrink tubing and fix it by heat shrinking, wrap the entire core with the heat shrink tubing, and set the heat shrink tubing in the inner cavity of the core holder; assemble the ultra-low temperature and high pressure seepage and deformation test device based on in-situ CT scanning;

[0031] B4: The simulated formation pressure is the fourth pressure, and the pore pressure is the fifth pressure, that is, the effective stress is the fourth pressure minus the fifth pressure; open the first two-way valve, start the nitrogen confining pressure pump and gradually increase the confining pressure to the effective stress;

[0032] B5: Scan the core at room temperature using CT;

[0033] B6: Turn on the temperature control system, and use the temperature control system to slowly cool the core to multiple preset low temperature levels in sequence, and keep the temperature constant for a certain period of time at each temperature level, and scan the core through CT;

[0034] B7: Data processing: AVIZO image processing software is used to pre-process the high-precision CT images of cores with different water saturations and obtained under different temperature conditions, mainly including image cropping, correction and image noise reduction.

[0035] Preferably, in step B8, taking the core CT image at room temperature as a reference, the digital volume technology is used to first mesh the image before deformation and mark each subdomain, then the coordinates between the freezing process image and the reference image are tracked, and the position changes between the rock images at different freezing temperatures and the reference image are monitored to obtain the deformation of the subdomain; all subdomains are calculated and analyzed to obtain the global deformation information inside the core at different freezing temperatures, and the volume frost heave or contraction coefficient at the corresponding freezing temperature is further calculated to analyze the nonlinear change stage and mode of freezing deformation; based on the watershed segmentation method of mathematical morphology topology theory, the rock particles and pores in the CT images at different temperatures are segmented, the pore water frost heave strain and the rock matrix contraction strain are studied in different regions, and the nonlinear competition and coupling law of pore water frost heave-rock matrix contraction at ultra-low temperature is analyzed.

[0036] The beneficial technical effect of the present invention is that the test device of the present invention can carry out transient permeability test and nonlinear coupled deformation test of pore water frost heave and rock matrix contraction under ultra-low temperature, providing a theoretical basis for the construction of underground liquefied natural gas storage.

[0037] The present invention adopts an improved transient method-constant pressure pulse decay method to measure permeability, which reduces the test error and does not require the installation of a gas tank upstream; a low-temperature nitrogen coil contact refrigeration method is adopted to strengthen the control of the nitrogen flow rate and the distribution of the cooling medium, and the nitrogen temperature and flow rate are controlled according to the core temperature to form a PID control system, which can accurately regulate the temperature and cooling rate, and the temperature fluctuation is less than 0.05 degrees Celsius. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings constituting the present invention are used to provide a further understanding of the present invention, and the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, and do not constitute improper limitations on the present invention.

[0039] Figure 1 It is an overall schematic diagram of the ultra-low temperature and high pressure seepage and deformation test device based on in-situ CT scanning of the present invention;

[0040] Explanation of the reference numerals in the accompanying drawings: 1. Ultra-low temperature resistant thermocouple; 2. Ultra-low temperature resistant heat shrink tubing; 3. Titanium alloy double-layer core clamp; 4. First two-way valve; 5. Second two-way valve; 6. First three-way connector; 7. Third two-way valve; 8. Fourth two-way valve; 9. Fifth two-way valve; 10. Small gas tank; 11. Second three-way connector; 12. Sixth two-way valve; 13. Back pressure valve; 14. Recovery tank; 15. Back pressure control pump; 16. Nitrogen confining pressure pump; 17. Gas phase injection pump; 18. Air flow temperature controller; 19. Open nitrogen tank; 20. Dewar flask; 21. Pressure and flow controller; 22. PID controller; 23. Recovery tank; 24. Computer; 25. Keller differential pressure sensor. DETAILED DESCRIPTION

[0041] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0042] Embodiment 1

[0043] like Figure 1 As shown, the ultra-low temperature and high pressure seepage and deformation test device based on in-situ CT scanning of the present invention includes a core clamping system, a seepage injection system, a confining pressure system, a back pressure system, a pressure acquisition system and a temperature control system;

[0044] The core clamping system includes a titanium alloy double-layer core clamp 3 and a heat shrink sleeve 2 for wrapping the core inside, the titanium alloy double-layer core clamp 3 includes an internal cavity and an annular cavity surrounding the internal cavity; the heat shrink sleeve 2 is provided with two through holes on the top surface and one through hole on the bottom surface, and the heat shrink sleeve 2 is arranged in the internal cavity of the titanium alloy double-layer core clamp 3; three through holes are arranged on the top of the titanium alloy double-layer core clamp 3, two of which correspond to the two through holes on the top of the heat shrink sleeve 2, and one is arranged on the annular cavity; three through holes are arranged on the bottom of the titanium alloy double-layer core clamp 3, one of which corresponds to the through hole at the bottom of the heat shrink sleeve 2, one is arranged on the annular cavity, and the other is arranged in the internal cavity and located outside the heat shrink sleeve 2; the core clamping system is fixed to the rotating stage of the CT scanning system by a clamp;

[0045] The seepage injection system includes a gas phase injection pump 17, the inlet of the gas phase injection pump 17 is connected to the gas cylinder through a pipeline, and the outlet of the gas phase injection pump 17 is connected to the second two-way valve 5, the first three-way connector 6, the bottom surface through hole of the core holder 3, and the bottom surface through hole of the heat shrink sleeve 2 in sequence through a pipeline;

[0046] The back pressure system includes a back pressure control pump 15, the outlet of the back pressure control pump 15 is connected to the back pressure valve 13, the sixth two-way valve 12, the second three-way connector 11, the small gas tank 10, the fifth two-way valve 9, the top surface through hole of the core holder 3, and the top surface through hole of the heat shrink sleeve 2 in sequence through a pipeline; the back pressure valve 13 is also connected to the recovery tank 14 through a pipeline;

[0047] The confining pressure system includes a nitrogen confining pressure pump 16, the inlet of the nitrogen confining pressure pump 16 is connected to the nitrogen bottle through a pipeline, and the outlet of the nitrogen confining pressure pump 16 is connected to the first two-way valve 4 and the through hole on the bottom surface of the core holder 3 arranged in the internal cavity and located outside the heat shrinkable sleeve 2 in sequence through a pipeline;

[0048] The pressure acquisition system includes a computer 24 and a Keller pressure differential sensor 25 connected thereto. The two ends of the pipeline where the Keller pressure differential sensor 25 is located are respectively connected to the first three-way connector 6 and the second three-way connector 11; the Keller pressure differential sensor 25 is used to monitor the pressure difference between the upstream and downstream of the core;

[0049] The temperature control system includes a Dewar flask 20, which is connected to a pressure and flow controller 21, an open nitrogen tank 19, an airflow temperature controller 18, a third two-way valve 7, and a through hole arranged in the annular cavity at the bottom of a titanium alloy double-layer core holder 3 in sequence through a stainless steel nitrogen pipeline wrapped in an insulation tube. It also includes a PID controller 22, which is respectively connected to the pressure and flow controller 21, the airflow temperature controller 18, and an ultra-low temperature resistant thermocouple 1, and the ultra-low temperature resistant thermocouple 1 is wrapped in an ultra-low temperature resistant heat shrinkable sleeve 2; it also includes a recovery tank 14, and the recovery tank 23 is connected to the fourth two-way valve 8 and the through hole arranged in the annular cavity at the top of the titanium alloy double-layer core holder 3 through a pipeline.

[0050] Among them, a nitrogen coil is arranged in the open nitrogen tank 19 .

[0051] Among them, the CT scanning system uses the YXLON FF35 high-resolution micron CT scanning system.

[0052] Embodiment 2

[0053] Based on the ultra-low temperature and high pressure seepage and deformation test device of the first embodiment, the present invention further proposes an ultra-low temperature and high pressure seepage and deformation test method based on in-situ CT scanning, including a seepage test method and a deformation test method, wherein the seepage test method comprises the following steps:

[0054] S1: Prepare several cores, wash them with methanol for 5 hours, put the cores in a drying oven at 105°C and dry them (until the mass change does not exceed 0.1%), measure and record the diameter and length of the cores; in this embodiment, the core diameter is 10 mm and the length is 20 mm; then vacuum the cores and completely saturate them with water, and the solution is a 20% mass fraction KI solution;

[0055] S2: Place the saturated core in a drying oven at 50°C for natural evaporation, obtain a preset saturation (such as 20%, 40%, 60%, 80%, 100%) through quality control method, make different cores reach different saturations, and smear the core surface with vaseline; take cores with different saturations in turn for subsequent tests;

[0056] S3: Put the core into the heat shrinkable tube 2 and fix it by heat shrinking. The heat shrinkable tube 2 wraps the entire core. Two through holes are processed on the top surface of the heat shrinkable tube 2 and one through hole is processed on the bottom surface. The heat shrinkable tube 2 is set in the inner cavity of the core holder 3; assemble the ultra-low temperature and high pressure seepage and deformation test device based on in-situ CT scanning ( Figure 1 );

[0057] S4: Open the first two-way valve 4, start the confining pressure pump 16 and gradually increase the confining pressure to 4 MPa;

[0058] S5: Open the second two-way valve 5, the first three-way connector 6, the fifth two-way valve 9, the second three-way connector 11 and the sixth two-way valve 12; open the gas phase injection pump 17 to maintain the upstream injection pressure at 0.4 MPa, open the back pressure control pump 15 to pressurize to 0.4 MPa, and wait for the upstream and downstream pressure difference measured by the Keller pressure difference sensor to be zero; close the sixth two-way valve 12, increase the gas phase injection pump pressure by 0.4 MPa, until the pressure difference measured by the Keller pressure difference sensor 25 gradually decreases to zero, record the pressure difference attenuation, and the permeability can be calculated according to the following formula

[0059]

[0060] Where k is the permeability, α is the slope of the pressure differential decay curve (lnΔp~t, Δp is the upstream and downstream pressure difference, t is the test time), μ g is the gas viscosity, L is the core length, c g is the gas compressibility, V down is the volume of the small gas tank, A is the cross-sectional area of ​​the core;

[0061] S6: Close the first three-way connector 6, the second two-way valve 5, the fifth two-way valve 9, the second three-way connector 11, the sixth two-way valve 12, and the gas phase injection pump 17;

[0062] Turn on the temperature control system. At this time, open the Dewar flask valve 20. The nitrogen passes through the pressure and flow control device and then cools down to about -180°C through the copper tube in the open liquid nitrogen tank 19. Then, it passes through the pipeline into the air flow temperature controller 18 to heat up to the required temperature. The nitrogen passes through the third two-way valve 7 into the through hole at the bottom of the annular cavity of the low-temperature resistant core holder 3, passes through the annular cavity, and then is discharged from the annular cavity through the fourth two-way valve 8. The core is slowly cooled to a total of 6 temperature levels of 0°C, -20°C, -40°C, -80°C, -120°C, and -160°C in sequence, and the temperature is kept constant for 30 minutes at each temperature level. Refer to step S5 to calculate the permeability at different temperatures;

[0063] The deformation test method comprises the following steps:

[0064] B1: Prepare several cores, wash them with methanol for 5 hours, put the cores in a drying oven at 105°C to dry them (until the mass change does not exceed 0.1%), measure and record the diameter and length of the cores; in this embodiment, the core diameter is 10 mm and the length is 20 mm; then evacuate the cores and completely saturate them with water, and the solution is a 20% mass fraction KI solution;

[0065] B2: Place the saturated core in a drying oven at 50°C for natural evaporation, and obtain the preset saturation through the quality control method, so that different cores reach different saturations (0%, 20%, 40%, 60%, 80%, 100%), and the core with a saturation of 0% is in a completely dry state; apply vaseline on the surface of the core; take cores with different saturations from low to high in turn for subsequent tests;

[0066] B3: Place the core into the heat shrink tube 2 and heat shrink it to fix it. The heat shrink tube 2 wraps the entire core. The heat shrink tube 1 is set in the inner cavity of the core holder 2; assemble the ultra-low temperature and high pressure seepage and deformation test device based on in-situ CT scanning ( Figure 1 );

[0067] B4: simulate formation pressure of 20 MPa, pore pressure of 5 MPa, that is, effective stress of about 15 MPa; open the first two-way valve 3, start the nitrogen confining pressure pump 14 and gradually increase the confining pressure to 15 MPa;

[0068] B5: Scanning the core at room temperature using the YXLON FF35 high-resolution micron CT.

[0069] B6: Turn on the temperature control system, and slowly cool the core to the preset temperatures of 0℃, -20℃, -40℃, -80℃, -120℃, and -160℃ in total. Keep the temperature constant for more than 10 minutes at each temperature level, and scan the core with the YXLON FF35 high-resolution micron CT.

[0070] Each CT scan was performed at the same location, and each scan lasted 40 minutes;

[0071] B7: Data processing: AVIZO image processing software is used to pre-process high-precision CT images of cores with different water saturations and obtained under different temperature conditions, mainly including image cropping, correction and image noise reduction;

[0072] Taking the core CT image at room temperature as the benchmark, the digital volume correlation (DVC) technology is used to first mesh the image before deformation and mark each subdomain, then track the coordinates between the freezing process image and the benchmark image, and monitor the position change between the rock image at different freezing temperatures and the benchmark image, so as to obtain the deformation of the subdomain; all subdomains are calculated and analyzed to obtain the global deformation information inside the core at different freezing temperatures, and the volume expansion or contraction coefficient at the corresponding freezing temperature is further calculated to analyze the nonlinear change stage and mode of freezing deformation;

[0073] Based on the watershed segmentation method of mathematical morphology topology theory, the rock particles and pores in CT images at different temperatures are segmented, the pore water frost heave strain and rock matrix contraction strain are studied in different regions, and the nonlinear competition and coupling laws of pore water frost heave and rock matrix contraction under ultra-low temperature are analyzed.

[0074] Of course, the above description is only a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It should be noted that all equivalent substitutions and obvious deformation forms made by any technician familiar with the field under the guidance of this specification fall within the essential scope of this specification and should be protected by the present invention.

Claims

1. An ultra-low temperature and high pressure seepage and deformation test device based on in-situ CT scanning, comprising a core clamping system, a seepage injection system, a confining pressure system, a back pressure system, a pressure acquisition system and a temperature control system; characterized in that: The core clamping system comprises a titanium alloy double-layer core clamp and a heat shrink sleeve for wrapping the core inside, the titanium alloy double-layer core clamp comprises an internal cavity and an annular cavity surrounding the internal cavity; two through holes are arranged on the top surface of the heat shrink sleeve, and one through hole is arranged on the bottom surface, and the heat shrink sleeve is arranged in the internal cavity of the titanium alloy double-layer core clamp; three through holes are arranged on the top of the titanium alloy double-layer core clamp, two of which correspond to the two through holes on the top of the heat shrink sleeve, and one is arranged on the annular cavity; three through holes are arranged on the bottom of the titanium alloy double-layer core clamp, one of which corresponds to the through hole at the bottom of the heat shrink sleeve, one is arranged on the annular cavity, and the other is arranged in the internal cavity and located outside the heat shrink sleeve; the core clamping system is fixed to the rotating stage of the CT scanning system by a clamp; The seepage injection system comprises a gas phase injection pump, the outlet of which is connected to the second two-way valve, the first three-way connector, the bottom through hole of the core holder, and the bottom through hole of the heat shrink sleeve in sequence through pipelines; The back pressure system comprises a back pressure control pump, the outlet of which is connected to the back pressure valve, the sixth two-way valve, the second three-way connector, the small gas tank, the fifth two-way valve, the through hole on the top surface of the core holder, and the through hole on the top surface of the heat shrink sleeve in sequence through a pipeline; The confining pressure system comprises a nitrogen confining pressure pump, the inlet of the nitrogen confining pressure pump is connected to the nitrogen bottle through a pipeline, and the outlet of the nitrogen confining pressure pump is connected to the first two-way valve and the through hole arranged in the inner cavity and outside the heat shrinkable sleeve on the bottom surface of the core holder through a pipeline in sequence; The pressure acquisition system includes a computer and a Keller pressure differential sensor connected thereto, and two ends of a pipeline where the Keller pressure differential sensor is located are respectively connected to a first three-way connector and a second three-way connector; The temperature control system includes a Dewar flask, which is connected in sequence to a pressure and flow controller, an open nitrogen tank, an airflow temperature controller, a third two-way valve, and a through hole arranged in an annular cavity at the bottom of a titanium alloy double-layer core holder through a stainless steel nitrogen pipeline wrapped in an insulation tube. The Dewar flask also includes a PID controller, which is respectively connected to the pressure and flow controller, the airflow temperature controller, and an ultra-low temperature resistant thermocouple, and the ultra-low temperature resistant thermocouple is wrapped in an ultra-low temperature resistant heat shrink tubing.

2. The test device according to claim 1, characterized in that: The back pressure valve is also connected to the recovery tank through a pipeline.

3. The test device according to claim 1, characterized in that: A nitrogen coil is arranged in the open nitrogen tank.

4. The test device according to claim 1, characterized in that: The temperature control system also includes a recovery tank, which is connected to the fourth two-way valve and the through hole arranged in the annular cavity at the top of the titanium alloy double-layer core clamp in sequence through pipelines.

5. The test device according to claim 1, characterized in that: The CT scanning system uses the YXLON FF35 high-resolution micron CT scanning system.

6. The ultra-low temperature and high pressure seepage and deformation test method based on in-situ CT scanning adopts the test device according to any one of claims 1 to 5, characterized in that: Including seepage test method and deformation test method; The seepage test method comprises the following steps: S1: Prepare several cores, clean them with methanol, put them in a drying oven to dry, measure and record the diameter and length of the cores; then evacuate the cores and fully saturate them with water; S2: Place the saturated cores in a drying oven for natural evaporation, obtain the preset saturation through quality control method, make different cores reach different saturation, and smear the core surface with vaseline; take cores with different saturation in turn for subsequent tests; S3: Place the core into the heat shrink tubing and fix it by heat shrinking, the heat shrink tubing wraps the entire core, two through holes are processed on the top surface of the heat shrink tubing and one through hole is processed on the bottom surface, and the heat shrink tubing is set in the inner cavity of the core holder; assemble the ultra-low temperature and high pressure seepage and deformation test device based on in-situ CT scanning; S4: Open the first two-way valve, start the confining pressure pump and gradually increase the confining pressure to the first pressure; S5: Open the second two-way valve, the first three-way connector, the fifth two-way valve, the second three-way connector and the sixth two-way valve; open the gas phase injection pump to maintain the second pressure of upstream injection, open the back pressure control pump to pressurize to the second pressure, and wait for the upstream and downstream pressure difference measured by the Keller pressure differential sensor to be zero; close the sixth two-way valve, increase the gas phase injection pump pressure by the third pressure, until the pressure difference measured by the Keller pressure differential sensor gradually decreases to zero, record the pressure differential attenuation, and the permeability is calculated according to the following formula Where k is the permeability, α is the slope of the pressure drop curve, and μ g is the gas viscosity, L is the core length, c g is the gas compressibility, V down is the volume of the small gas tank, A is the cross-sectional area of ​​the core; S6: Close the first three-way connector, the second two-way valve, the fifth two-way valve, the second three-way connector, the sixth two-way valve, and the gas phase injection pump; Turn on the temperature control system, open the Dewar flask valve, and let the nitrogen pass through the pressure and flow controller and then through the copper tube in the open liquid nitrogen tank to cool down to the first temperature, and then pass through the pipeline into the air flow temperature controller to raise the temperature to the required temperature, and let the nitrogen pass through the third two-way valve into the through hole at the bottom of the annular cavity of the low-temperature resistant core holder, and slowly cool the core to multiple preset low temperatures in sequence through the annular cavity, and keep the constant temperature at each temperature level for a certain time, and refer to step S5 to calculate the permeability at different temperatures; The deformation test method comprises the following steps: B1: Prepare several cores, clean them with methanol, put them in a drying oven to dry, measure and record the diameter and length of the cores; then evacuate the cores and fully saturate them with water; B2: Place the saturated cores in a drying oven for natural evaporation, obtain the preset saturation through quality control method, and make different cores reach different saturation; smear the core surface with vaseline; take cores with different saturation from low to high for subsequent tests; B3: Place the core into the heat shrink tubing and fix it by heat shrinking, wrap the entire core with the heat shrink tubing, and set the heat shrink tubing in the inner cavity of the core holder; assemble the ultra-low temperature and high pressure seepage and deformation test device based on in-situ CT scanning; B4: The simulated formation pressure is the fourth pressure, and the pore pressure is the fifth pressure, that is, the effective stress is the fourth pressure minus the fifth pressure; open the first two-way valve, start the nitrogen confining pressure pump and gradually increase the confining pressure to the effective stress; B5: Scan the core at room temperature using CT; B6: Turn on the temperature control system, and use the temperature control system to slowly cool the core to multiple preset low temperature levels in sequence, and keep the temperature constant for a certain period of time at each temperature level, and scan the core through CT; B7: Data processing: AVIZO image processing software is used to pre-process the high-precision CT images of cores with different water saturations and obtained under different temperature conditions, mainly including image cropping, correction and image noise reduction.

7. The test method according to claim 6, characterized in that: In step B8, the core CT image at room temperature is used as a reference, and the image before deformation is first meshed and each subdomain is marked using digital volume technology, and then the coordinates between the freezing process image and the reference image are tracked, and the position changes between the rock images at different freezing temperatures and the reference image are monitored, thereby obtaining the deformation of the subdomain; All subdomains are calculated and analyzed to obtain the global deformation information inside the core at different freezing temperatures, and the volume frost heave or contraction coefficient at the corresponding freezing temperature is further calculated to analyze the nonlinear change stages and modes of freezing deformation. The watershed segmentation method based on mathematical morphology topology theory is used to segment the rock particles and pores in CT images at different temperatures, and the pore water frost heave strain and rock matrix contraction strain are studied in different regions. The nonlinear competition and coupling laws of pore water frost heave and rock matrix contraction under ultra-low temperatures are analyzed.

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