Rock high-temperature and high-pressure two-phase flow test device and method based on in-situ CT scanning

Abstract

The present invention belongs to the field of rock physics test equipment, and in particular relates to a high-temperature, high-pressure, two-phase flow test apparatus and method for rock based on in-situ CT scanning. The sample apparatus includes a core clamping system, a two-phase flow injection system, a confining pressure system, a backpressure system, and a heating system. The core clamping system includes a core clamp and a heat-shrinkable sleeve for wrapping the core, and the core clamping system is fixed to the stage of the CT scanning system. The two-phase flow injection system includes an air injection pump and a brine pump. The confining pressure system includes a confining pressure pump. The backpressure system includes a backpressure pump. A pipeline is used to connect two three-way valves above and below the core clamp to form a bypass line. The present invention arranges three-way valves upstream and downstream of the core clamp, and then connects the two three-way valves with a pipeline to form a parallel bypass line, which can be used to eliminate two-phase flow dead volume in the pipeline. Based on this, the test method can be applied simultaneously to calculate fluid phase saturation using the fluid volume method and the CT grayscale value method, and verify and calibrate each other.

Description

Technical Field

[0001] The present invention belongs to the field of rock physics test devices, and in particular relates to a rock high-temperature and high-pressure two-phase flow test device and method based on in-situ CT scanning. Background Art

[0002] Deep energy storage and recovery projects, such as deep oil and gas extraction, geological storage of carbon dioxide, and underground natural gas / hydrogen storage, are crucial for promoting sustainable energy development. The flow and distribution characteristics of multiphase fluids within multiscale porous fracture structures in deep formations are directly influenced by the rock pore structure and system wettability. Large variations in the size, number, and permeability of rock pore throats can cause localized rock heterogeneity, directly impacting the flow and capture of gas-liquid two-phase fluids. Relative permeability refers to the effective permeability of a single phase when multiple phases of fluid coexist in a rock. It is a function of phase saturation, wettability, and pore structure, reflecting the interactions between the phases. Traditional multiphase flow tests can calculate phase saturation during the seepage phase using methods such as nuclear magnetic resonance and resistivity, but they cannot reveal the multiphase flow paths or the distribution patterns of fluids within the microscopic pore structure from the core microscopic pore structure. Given the complex physical and chemical reactions that occur during gas-liquid two-phase displacement, it is unknown whether the coupled reactions of the rock-brine-gas system alter the pore structure and how this influences the seepage parameters.

[0003] In recent years, the development of CT scanning technology has provided a technique for visually characterizing the three-dimensional pore structure of rocks. This technology, combined with in-situ gas-liquid two-phase flow displacement devices, can precisely characterize the rock pore structure and the seepage paths of the gas-liquid two-phase fluid. Furthermore, through digital image processing, algorithms, and image segmentation, local measurement and statistical analysis of the fluid phase can be performed. Digital core processing technology can be used to construct core pore network models, quantify seepage parameters, and characterize seepage paths; capillary forces, phase saturation, wetting contact angles, and other parameters can be precisely counted and calculated. Therefore, compared to traditional relative permeability tests, the use of in-situ CT scanning and digital image processing technology can reveal the saturation-relative permeability phenomenon in relative seepage from a microscopic perspective, providing key scientific evidence for the seepage test results. Summary of the Invention

[0004] The present invention provides a high-temperature and high-pressure two-phase flow test device and method for rocks based on in-situ CT scanning. The device and method can be simultaneously applied to the calculation of fluid phase saturation using a fluid volume method and a CT grayscale value method, and can verify and calibrate each other. The test device includes a core clamping system, a two-phase flow injection system, a confining pressure system, a back pressure system, and a heating system. The core clamping system includes a core clamp and a heat shrink tubing for wrapping the core. The top and bottom surfaces of the heat shrink tubing are respectively provided with a through hole. The heat shrink tubing is disposed in the internal cavity of the core clamp. The top surface of the core clamp is provided with one through hole, and the bottom surface is provided with three through holes. The core clamping system is fixed to the rotating stage of the CT scanning system by a clamp.

[0005] The two-phase flow injection system includes an air injection pump and a brine pump, wherein the brine pump inlet is connected to the brine container through a pipeline, the air injection pump inlet is connected to the gas cylinder through a pipeline, the brine pump outlet and the air injection pump outlet are respectively connected to a first three-way valve through a pipeline, and the first three-way valve is connected to a first three-way joint, a second three-way valve, a third three-way joint, a through hole on the bottom surface of the core holder, and a through hole on the bottom surface of the heat shrink sleeve through pipelines in sequence;

[0006] The confining pressure system includes a confining pressure pump, the inlet of the confining pressure pump is connected to the deionized water container through a pipeline, and the outlet of the confining pressure pump is connected to the second two-way valve and the through hole on the bottom surface of the core holder in sequence through a pipeline;

[0007] The back pressure system includes a back pressure pump, the inlet of the back pressure pump is connected to the brine container through a pipeline, and the outlet of the back pressure pump is connected to the back pressure valve, the second three-way joint, the third three-way valve, the top surface through hole of the core holder, and the top surface through hole of the heat shrink sleeve in sequence through a pipeline;

[0008] The second three-way valve and the third three-way valve are connected by a pipeline to form a bypass pipeline; the first three-way joint and the second three-way joint are connected by a pipeline with a pressure sensor; the vacuum pump is connected to the first two-way valve and the third three-way joint in sequence through the pipeline; and a heating system is wound around a core holder, wherein a thermocouple is provided in the core holder.

[0009] Preferably, the back pressure valve is also connected to a separation system, and the separation system is used to separate gas and liquid; the back pressure system is used to regulate the pore pressure of the core.

[0010] Preferably, it also includes a computer, which is used to collect and store test data, including pressure data from the pressure sensor and temperature data from the thermocouple. The data line of the thermocouple is connected to the computer after being led out from the through hole on the bottom surface of the core holder, and the data line of the pressure sensor is connected to the computer.

[0011] Based on the above-mentioned rock high-temperature and high-pressure two-phase flow test device, the rock high-temperature and high-pressure two-phase flow test method includes the following steps:

[0012] (1) Determine the core size and core pore volume V p , drying the core;

[0013] (2) placing the core into a heat shrink tubing and fixing it by heat shrinking, machining a through hole on the top and bottom surfaces of the heat shrink tubing, and placing the heat shrink tubing in the inner cavity of the core holder; assembling a high-temperature and high-pressure two-phase flow test apparatus for rocks; and heating the core to a set temperature through a heating system;

[0014] (3) Open the second two-way valve and the confining pressure pump to inject deionized water into the core holder so that the deionized water completely wraps the heat shrink tubing, gradually increase the confining pressure to the first confining pressure, and close the second two-way valve and the confining pressure pump;

[0015] (4) Perform CT dry scanning, and use Avizo to segment the scan data into air phase and rock phase. Take the average grayscale value of the air phase as the CT number, and calculate the average grayscale value of the air CT. a , take the average gray value of rock phase as CT number, calculate the average gray value CT of rock r , take the average grayscale value of the entire image as

[0016] (5) Open the first three-way valve, the second three-way valve, and the third three-way valve; open the first two-way valve, use a vacuum pump to evacuate the air in the pipeline, and close the first two-way valve; close the connection between the first three-way valve and the air pump, close the bypass line directly connecting the second three-way valve and the third three-way valve, and inject brine through the brine pump to replace the air in the core pores to ensure that the core is completely saturated with water;

[0017] (6) setting the core pore pressure to a predetermined pressure by a back pressure pump, and raising the confining pressure to a second confining pressure by a confining pressure pump;

[0018] (7) With the first three-way valve and the air pump connection closed and the bypass line directly connected to the second three-way valve and the third three-way valve closed, inject brine into the core at various flow rates using a brine pump, record the pressure value of the pressure sensor to obtain the upstream and downstream pressure difference of the core, and calculate the absolute permeability K of the core;

[0019] Close the pipeline with the core holder between the second and third three-way valves, and open the bypass pipeline directly connecting the second and third three-way valves; close the connection between the first three-way valve and the brine pump, open the connection between the first three-way valve and the air pump, and drain the water in the pipeline through the air pump;

[0020] (8) Open the first three-way valve and close the bypass line directly connecting the second and third three-way valves; turn on the gas injection pump and the brine pump; inject brine and the selected gas into the core at the set ratio; first inject the brine into the core according to the first ratio until the steady state condition is reached, and record the injected brine volume Vz,i＝1 The amount of brine separated by the separation system V c,i＝1 ;

[0021] Perform CT scanning, segment the gas phase and liquid phase using Avizo, and take the grayscale average of the entire image as Take the average value of the gas phase grayscale as the CT number and calculate the CT g , take the average value of liquid grayscale as CT number, calculate CT w ;

[0022] Close the pipeline with the core holder between the second and third three-way valves, and open the bypass pipeline directly connecting the second and third three-way valves; close the connection between the first three-way valve and the brine pump, open the connection between the first three-way valve and the air pump, drain the water in the pipeline through the air pump, and record the discharged dead water volume V s,i＝1 ;

[0023] (9) Repeat step (8) and inject brine and selected gas into the core simultaneously at the 2nd to 8th ratios; after completing the test at each ratio, record the cumulative volume of brine injected by the end of the test at the i-th ratio. The cumulative outflow volume of brine separated by the separation system until the i-th ratio test is completed The cumulative dead volume of brine discharged from the pipeline by the end of the i-th ratio test After completing the test at each ratio, perform CT scans respectively and calculate the grayscale average value of the entire image of the i-th ratio test. Gas phase grayscale average CT g , Liquid grayscale average CT w ;

[0024] (10) Calculate gas and liquid saturation;

[0025] First, the fluid volume method is used to calculate the gas and liquid saturations

[0026]

[0027] S g,I =1-S w,i

[0028] Where, V is the cumulative volume of brine injected by the end of the i-th ratio test, p is the core pore volume, is the cumulative outflow volume of saline by the end of the i-th ratio test, S is the cumulative dead volume of brine discharged from the pipeline by the end of the i-th ratio test; w,i Expressed as the liquid phase saturation of the i-th ratio test, S g,iIt is expressed as the gas phase saturation of the i-th ratio test;

[0029] Second, calculate the gas and liquid saturation based on the CT grayscale value

[0030]

[0031] S w,i =1-S g,i

[0032] Where, is the core porosity, Indicates the grayscale average value of the entire image during dry scanning, CT r Indicates the average grayscale value of rock during dry scanning, CT a Indicates the average grayscale value of the air phase during dry scanning; Indicates the grayscale average value of the entire image in the i-th ratio test, CT g Average grayscale value of test gas phase, CT w Average grayscale value of the test liquid;

[0033] (11) Liquid saturation accuracy check: for each ratio of liquid saturation, the results calculated by the fluid volume method and the CT gray value method are compared. Since the liquid saturation calculated by the fluid volume method is too large, if the liquid saturation value calculated based on the CT gray value is greater than the liquid saturation value calculated by the volume method, the liquid saturation calculated by the volume method is taken as the final liquid saturation value for that ratio; if the liquid saturation value calculated based on the CT gray value is less than the liquid saturation value calculated by the volume method, the liquid saturation calculated by the volume method is taken as the final liquid saturation value for that ratio;

[0034] Preferably, in step (8), the first ratio is that the volume fraction of gas accounts for 0.0 of the total volume, and the gas injection pump does not need to be turned on during the test.

[0035] Preferably, in step (9), the volume fraction of gas in the second to eighth ratios gradually increases to the total volume, wherein the eighth ratio is 1.0, and the gas injection pump does not need to be turned on during the test.

[0036] Preferably, the method further comprises step (12), wherein the steady-state relative permeability is calculated by Darcy's law.

[0037]

[0038] Among them, k w,i and k g,i are the relative permeabilities of the liquid and gas phases in the i-th ratio test, q w,i and q g,i are the Darcy velocities of the liquid and gas phases in the i-th scale test, u w and u qare the fluid viscosities of the liquid and gas phases, respectively; L is the core length; ΔP is the pressure loss along the core length; and K is the absolute permeability of the core.

[0039] The beneficial technical effects of the present invention are as follows: The test apparatus of the present invention employs three-way valves installed upstream and downstream of the core holder, and then connects these three-way valves with pipelines to form a parallel bypass line, which can be used to eliminate dead volume in two-phase flow. Furthermore, the test method of the present invention can be applied simultaneously to calculate fluid phase saturation using the fluid volume method and the CT grayscale value method, and both can be verified and calibrated. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The accompanying drawings that constitute the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0041] Figure 1 This is an overall schematic diagram of the rock high-temperature and high-pressure two-phase flow test device based on in-situ CT scanning of the present invention;

[0042] Explanation of the accompanying symbols: 1. Heat shrink tubing; 2. Core holder; 3. Vacuum pump; 4. First three-way valve; 5. Second three-way valve; 6. Third three-way valve; 7. First three-way connector; 8. Second three-way connector; 9. Third three-way connector; 10. Back pressure valve; 11. Back pressure pump; 12. Confining pressure pump; 13. Air injection pump; 14. Brine pump; 15. Computer; 16. Separation system; 17. Heating system; 18. Thermocouple; 19. CT scanning system; 20. Pressure sensor; 21. First two-way valve; 22. Second two-way valve. DETAILED DESCRIPTION

[0043] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0044] Example 1

[0045] like Figure 1 As shown, the rock high-temperature and high-pressure two-phase flow test device based on in-situ CT scanning of the present invention includes a core clamping system, a two-phase flow injection system, a confining pressure system, a back pressure system and a heating system; the core clamping system includes a core clamp 2 and a heat shrink tubing 1 for wrapping the core inside, the top and bottom surfaces of the heat shrink tubing 1 are respectively provided with a through hole, the heat shrink tubing 1 is arranged in the internal cavity of the core clamp 2, the top surface of the core clamp 2 is provided with one through hole, and the bottom surface of the core clamp 2 is provided with three through holes; the core clamping system is fixed to the rotating stage of the CT scanning system 19 by a clamp;

[0046] The two-phase flow injection system includes an air injection pump 13 and a brine pump 14. The inlet of the brine pump 14 is connected to the brine container through a pipeline, the inlet of the air injection pump 13 is connected to the gas cylinder through a pipeline, the outlet of the brine pump 14 and the outlet of the air injection pump 13 are respectively connected to the first three-way valve 4 through pipelines, and the first three-way valve 4 is connected to the first three-way joint 7, the second three-way valve 5, the third three-way joint 9, the bottom through hole of the core holder 2, and the bottom through hole of the heat shrink sleeve 1 through pipelines in sequence;

[0047] The confining pressure system includes a confining pressure pump 12, the inlet of the confining pressure pump 12 is connected to the deionized water container through a pipeline, and the outlet of the confining pressure pump 12 is connected to the second two-way valve 22 and the through hole on the bottom surface of the core holder 2 in sequence through a pipeline;

[0048] The back pressure system includes a back pressure pump 11, the inlet of the back pressure pump 11 is connected to the brine container via a pipeline, and the outlet of the back pressure pump 11 is connected to the back pressure valve 10, the second three-way joint 8, the third three-way valve 6, the through hole on the top surface of the core holder 2, and the through hole on the top surface of the heat shrink sleeve 1 via a pipeline in sequence; the back pressure valve 10 is also connected to the separation system 16, which is used to separate gas and liquid; the back pressure system is used to regulate the pore pressure of the core;

[0049] The second three-way valve 5 and the third three-way valve 6 are connected by a pipeline to form a bypass pipeline for eliminating the two-phase flow dead volume in the pipeline; the first three-way connector 7 and the second three-way connector 8 are connected by a pipeline with a pressure sensor 20, and the pressure sensor 20 is used to monitor the upstream and downstream pressure difference of the core; the vacuum pump 3 is connected to the first two-way valve 21 and the third three-way connector 9 in sequence through the pipeline; a heating system 17 is wrapped around the core holder 12, and a thermocouple (or temperature sensor) 18 is provided in the core holder 2 to monitor the internal temperature of the core holder 2;

[0050] It also includes a computer 15, which is used to collect and store test data, including pressure data from the pressure sensor 20 and temperature data from the thermocouple 18. The data line of the thermocouple 18 is connected to the computer 15 after being led out from the through hole on the bottom surface of the core holder 2. The data line of the pressure sensor 20 is connected to the computer 15.

[0051] The back pressure pump 11 , the confining pressure pump 12 , the air injection pump 13 and the brine pump 14 are ISCO high-precision plunger pumps.

[0052] Example 2

[0053] Based on the rock high-temperature and high-pressure two-phase flow test device of Example 1, the present invention further proposes a rock high-temperature and high-pressure two-phase flow test method based on in-situ CT scanning, comprising the following steps:

[0054] (1) The core was cleaned with methanol for 5 hours, and then placed in a drying oven at 373K for 24 hours. The diameter and length of the core were measured and recorded, and the dry weight of the core was weighed m0. The core was then vacuumed and completely saturated with water, and the core mass m1 was weighed again. The pore volume V of the core can be calculated. p ; Place the core in a drying oven at 373K and dry it again for 24 hours; In this embodiment, the core diameter is 12mm and the length is 72mm;

[0055] (2) Place the core into the heat shrink tubing 1 and heat shrink it to fix it. The heat shrink tubing 1 wraps the entire core. A through hole is made on the top and bottom surfaces of the heat shrink tubing 1. The heat shrink tubing 1 is set in the inner cavity of the core holder 2. Assemble the rock high temperature and high pressure two-phase flow test device based on in-situ CT scanning ( Figure 1 ); The core is heated to a set temperature by a heating system 17, and the temperature is monitored by a thermocouple 18;

[0056] (3) Open the second two-way valve 22, then start the confining pressure pump 12 and inject deionized water into the core holder 2 at a flow rate of 0.1-2 mL / min so that the deionized water completely wraps the heat shrink tubing 1, gradually increase the confining pressure to 2 MPa, and close the second two-way valve 22 and the confining pressure pump 12;

[0057] (4) Perform CT dry scanning, and use Avizo to segment the scan data into air phase and rock phase. Take the average grayscale value of the air phase as the CT number, and calculate the average grayscale value of the air CT. a , take the average gray value of rock phase as CT number, calculate the average gray value CT of rock r , take the average grayscale value of the entire image as

[0058] (5) Open the first three-way valve 4, the second three-way valve 5, and the third three-way valve 6; open the first two-way valve 21, use the vacuum pump 3 to evacuate the air in the pipeline, and close the first two-way valve 21; close the connection between the first three-way valve 4 and the air pump 13, close the bypass line directly connecting the second three-way valve 5 and the third three-way valve 6, and inject more than 200 pore volumes of 30 wt% KI brine through the brine pump 14 at a flow rate of 0.5-2 mL / min to replace the air in the core pores and ensure that the core is completely water saturated;

[0059] (6) The core pore pressure is set to 13 MPa by the back pressure pump 11, and the confining pressure is increased to 15 MPa by the confining pressure pump 12, and the effective stress is maintained at 2 MPa;

[0060] (7) With the connection between the first three-way valve 4 and the air pump 13 closed and the bypass line directly connecting the second three-way valve 5 and the third three-way valve 6 closed, 30 wt% KI brine was injected into the core at various flow rates through the brine pump 14. The pressure value of the pressure sensor 20 was recorded to obtain the upstream and downstream pressure difference of the core. The absolute permeability K of the core was determined based on the core size, the upstream and downstream pressure difference of the core, the flow rate, and the fluid viscosity.

[0061] Close the pipeline with the core holder 2 between the second three-way valve 5 and the third three-way valve 6, and open the bypass pipeline directly connecting the second three-way valve 5 and the third three-way valve 6; close the connection between the first three-way valve 4 and the brine pump 14, open the connection between the first three-way valve 4 and the air pump 13, and drain the water in the pipeline (except the water in the pipeline with the core holder 2 between the second three-way valve 5 and the third three-way valve 6) through the air pump 13;

[0062] (8) Open the first three-way valve 4 and close the bypass line directly connecting the second three-way valve 5 and the third three-way valve 6; turn on the gas injection pump 13 and the brine pump 14; inject 30 wt% KI brine and gas (hydrogen or methane, the same below) into the core at the same time in a set ratio; first inject the core according to the first ratio, wherein the first ratio is that the volume fraction of gas accounts for 0.0 of the total volume (at this time, it is not necessary to turn on the gas injection pump 13), the total injection flow rate is 2 mL / min, the injection continues for at least 24 hours to reach a steady-state condition, and the pressure difference measured by the pressure sensor 20 remains stable for 8 hours, and the amount of 30 wt% KI brine injected V is recorded. z,i＝1 The amount of 30wt% KI brine separated by the separation system V c,i＝1 ;

[0063] Perform CT scanning, segment the gas phase (hydrogen or methane) and liquid phase using Avizo, and take the grayscale average of the entire image as Take the average grayscale value of the gas phase (hydrogen or methane) as the CT number and calculate the CT g , take the average value of liquid grayscale as CT number, calculate CT w ;

[0064] Close the pipeline with the core holder 2 between the second three-way valve 5 and the third three-way valve 6, and open the bypass pipeline directly connecting the second three-way valve 5 and the third three-way valve 6; close the connection between the first three-way valve 4 and the brine pump 14, open the connection between the first three-way valve 4 and the air pump 13, and drain the water in the pipeline (except the water in the pipeline with the core holder 2 between the second three-way valve 5 and the third three-way valve 6) through the air pump, and record the discharged dead water volume V s,i＝1 ;

[0065] (9) Repeat step (8) and inject 30 wt% KI brine and gas into the core simultaneously in the second to eighth ratios, wherein the volume fraction of gas in the second to eighth ratios is 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, and 1.0, respectively (the brine pump 14 does not need to be turned on in the eighth ratio); after completing the test at each ratio, record the cumulative injected volume of 30 wt% KI brine up to the completion of the test at the i-th ratio. The cumulative outflow volume of 30 wt% KI brine separated by the separation system until the i-th ratio test is completed By the end of the i-th ratio test, the pipeline has discharged a total of 30wt% KI brine dead volume. After completing the test at each ratio, perform CT scans respectively and calculate the grayscale average value of the entire image of the i-th ratio test. Gas phase grayscale average CT g , Liquid grayscale average CT w ;

[0066] (10) Calculate gas and liquid saturation;

[0067] First, the fluid volume method is used to calculate the gas and liquid saturations

[0068]

[0069] S g,i =1-S w,i

[0070] Where, V is the cumulative injection volume of 30 wt% KI brine until the i-th ratio test is completed, p is the core pore volume, is the cumulative outflow volume of 30 wt% KI saline by the end of the i-th ratio test, S is the dead volume of 30wt% KI brine discharged from the pipeline by the end of the i-th ratio test; w,i Expressed as the liquid phase saturation of the i-th ratio test, S g,i It is expressed as the gas phase saturation of the i-th ratio test;

[0071] Second, calculate the gas and liquid saturation based on the CT grayscale value

[0072]

[0073] S w,i =1-S g,i

[0074] Where, is the core porosity, Indicates the grayscale average value of the entire image during dry scanning, CT r Indicates the average grayscale value of rock during dry scanning, CT a Indicates the average grayscale value of the air phase during dry scanning; Indicates the grayscale average value of the entire image in the i-th ratio test, CT g Average grayscale value of test gas phase, CT w Average grayscale value of the test liquid;

[0075] (11) Liquid saturation accuracy check: for each ratio of liquid saturation, the results calculated by the fluid volume method and the CT gray value method are compared. Since the liquid saturation calculated by the fluid volume method is too large (the dead water in the pipeline with the core holder 2 between the second three-way valve 5 and the third three-way valve 6 cannot be removed), if the liquid saturation value calculated based on the CT gray value is greater than the liquid saturation value calculated by the volume method, the liquid saturation calculated by the volume method is taken as the final liquid saturation value under the ratio. If the liquid saturation value calculated based on the CT gray value is less than the liquid saturation value calculated by the volume method, the liquid saturation calculated by the volume method is taken as the final liquid saturation value under the ratio.

[0076] (12) Calculation of steady-state relative permeability using Darcy's law

[0077]

[0078] Among them, k w,i and k g,i are the relative permeabilities of the liquid and gas phases in the i-th ratio test, q w,i and q g,i are the Darcy velocities of the liquid and gas phases in the i-th scale test, u w and u q are the fluid viscosities of the liquid phase and gas phase respectively, L is the core length, ΔP is the pressure loss along the core length (the pressure value of the pressure sensor 20 obtains the pressure difference between the upstream and downstream of the core), and K is the absolute permeability of the core.

[0079] Of course, the above description is only a preferred embodiment of the present invention, and the present invention is not limited to the above-mentioned embodiments. It should be noted that all equivalent substitutions and obvious deformation forms made by any technician familiar with this field under the guidance of this specification fall within the substantive scope of this specification and should be protected by the present invention.

Claims

1. Rock high-temperature and high-pressure two-phase flow test device based on in-situ CT scanning, characterized by: The core clamping system comprises a core clamping system, a two-phase flow injection system, a confining pressure system, a back pressure system and a heating system; the core clamping system comprises a core clamp and a heat shrink tubing for wrapping the core inside, the top and bottom surfaces of the heat shrink tubing are respectively provided with a through hole, the heat shrink tubing is arranged in the internal cavity of the core clamping system, the top surface of the core clamping system is provided with one through hole, and the bottom surface of the core clamping system is provided with three through holes; the core clamping system is fixed to the rotating stage of the CT scanning system by a clamp; The two-phase flow injection system includes an air injection pump and a brine pump, wherein the brine pump inlet is connected to the brine container through a pipeline, the air injection pump inlet is connected to the gas cylinder through a pipeline, the brine pump outlet and the air injection pump outlet are respectively connected to a first three-way valve through a pipeline, and the first three-way valve is connected to a first three-way joint, a second three-way valve, a third three-way joint, a through hole on the bottom surface of the core holder, and a through hole on the bottom surface of the heat shrink sleeve through pipelines in sequence; The confining pressure system includes a confining pressure pump, the inlet of the confining pressure pump is connected to the deionized water container through a pipeline, and the outlet of the confining pressure pump is connected to the second two-way valve and the through hole on the bottom surface of the core holder in sequence through a pipeline; The back pressure system includes a back pressure pump, the inlet of the back pressure pump is connected to the brine container through a pipeline, and the outlet of the back pressure pump is connected to the back pressure valve, the second three-way joint, the third three-way valve, the top surface through hole of the core holder, and the top surface through hole of the heat shrink sleeve in sequence through a pipeline; The second three-way valve and the third three-way valve are connected by a pipeline to form a bypass pipeline; the first three-way joint and the second three-way joint are connected by a pipeline with a pressure sensor; the vacuum pump is connected to the first two-way valve and the third three-way joint in sequence through the pipeline; and a heating system is wound around a core holder, wherein a thermocouple is provided in the core holder.

2. The rock high-temperature and high-pressure two-phase flow test device according to claim 1 is characterized in that: The back pressure valve is also connected to a separation system, which is used to separate gas and liquid; the back pressure system is used to regulate the pore pressure of the core.

3. The rock high-temperature and high-pressure two-phase flow test device according to claim 2, characterized in that: It also includes a computer, which is used to collect and store test data, including pressure data from the pressure sensor and temperature data from the thermal couple. The data line of the thermocouple is connected to the computer after being led out from the through hole on the bottom surface of the core holder, and the data line of the pressure sensor is connected to the computer.

4. A high-temperature and high-pressure two-phase flow test method for rocks based on in-situ CT scanning, using the high-temperature and high-pressure two-phase flow test apparatus for rocks according to claim 3, characterized in that: The steps include: (1) Determine core size and core pore volume V p , drying the core; (2) Place the core into the heat shrink tubing and fix it by heat shrinking. Make a through hole on the top and bottom surfaces of the heat shrink tubing respectively, and set the heat shrink tubing in the inner cavity of the core holder; assemble the rock high temperature and high pressure two-phase flow test device; heat the core to the set temperature through the heating system; (3) Open the second two-way valve and the confining pressure pump to inject deionized water into the core holder so that the deionized water completely covers the heat shrink tubing, gradually increase the confining pressure to the first confining pressure, and close the second two-way valve and the confining pressure pump; (4) Perform CT dry scanning, and use Avizo to segment the scan data into air phase and rock phase. Take the average grayscale value of the air phase as the CT number, and calculate the average grayscale value of the air CT. a , take the average gray value of rock phase as CT number, calculate the average gray value CT of rock r , take the average grayscale value of the entire image as ; (5) Open the first three-way valve, the second three-way valve, and the third three-way valve; open the first two-way valve, use a vacuum pump to evacuate the air in the pipeline, and close the first two-way valve; close the connection between the first three-way valve and the air pump, close the bypass line directly connecting the second three-way valve and the third three-way valve, and inject brine through the brine pump to replace the air in the core pores to ensure that the core is completely saturated with water; (6) Setting the core pore pressure to a predetermined pressure by a back pressure pump and raising the confining pressure to a second confining pressure by a confining pressure pump; (7) With the first three-way valve and the air pump connection closed and the bypass line directly connected to the second three-way valve and the third three-way valve closed, inject brine into the core at various flow rates through the brine pump, record the pressure value of the pressure sensor to obtain the upstream and downstream pressure difference of the core, and calculate the absolute permeability of the core ; Close the pipeline with the core holder between the second and third three-way valves, and open the bypass pipeline directly connecting the second and third three-way valves; close the connection between the first three-way valve and the brine pump, open the connection between the first three-way valve and the air pump, and drain the water in the pipeline through the air pump; (8) Open the first three-way valve and close the bypass line directly connected to the second and third three-way valves; turn on the gas injection pump and the brine pump; inject brine and the selected gas into the core at the set ratio; first inject the core at the first ratio until the steady state condition is reached, and record the injected brine volume V z,i=1 The amount of brine separated by the separation system V c,i=1 ; Perform CT scanning, segment the gas phase and liquid phase using Avizo, and take the grayscale average of the entire image as Take the average value of the gas phase grayscale as the CT number and calculate , take the average value of liquid grayscale as the CT number, and calculate ; Close the pipeline with the core holder between the second and third three-way valves, and open the bypass pipeline directly connecting the second and third three-way valves; close the connection between the first three-way valve and the brine pump, open the connection between the first three-way valve and the air pump, drain the water in the pipeline through the air pump, and record the discharged dead water volume V s,i=1 ; (9) Repeat step (8) and inject brine and selected gas into the core simultaneously at the 2nd to 8th ratios; after completing the test at each ratio, record the cumulative volume of brine injected by the end of the test at the i-th ratio. , the cumulative outflow volume of brine separated by the separation system until the i-th ratio test is completed , by the end of the i-th ratio test, the cumulative dead volume of brine discharged from the pipeline is ; After completing the test at each ratio, perform CT scans respectively and calculate the grayscale average value of the entire image of the i-th ratio test. , average value of gas phase grayscale , average liquid grayscale value ; (10) Calculate gas and liquid saturation; First, the fluid volume method is used to calculate the gas and liquid saturations , ； ； Where, V is the cumulative volume of brine injected by the end of the i-th ratio test, p is the core pore volume, is the cumulative outflow volume of saline by the end of the i-th ratio test, S is the cumulative dead volume of brine discharged from the pipeline by the end of the i-th ratio test; w,i Expressed as the liquid phase saturation of the i-th ratio test, It is expressed as the gas phase saturation of the i-th ratio test; Second, calculate the gas and liquid saturation based on the CT grayscale value ； ； , ； ； Where, is the core porosity, Indicates the grayscale average value of the entire image during dry scanning, CT r Indicates the average grayscale value of rock during dry scanning, CT a Indicates the average grayscale value of the air phase during dry scanning; Represents the grayscale average value of the entire image in the i-th ratio test, Indicates the average grayscale value of the gas phase, CT w represents the average grayscale value of liquid phase; (11) Liquid saturation accuracy check: for each ratio of liquid saturation, the results calculated by the fluid volume method and the CT gray value method are compared. Since the liquid saturation calculated by the fluid volume method is too large, if the liquid saturation value calculated based on the CT gray value is greater than the liquid saturation value calculated by the volume method, the liquid saturation calculated by the volume method is taken as the final liquid saturation value under this ratio. If the liquid saturation value calculated based on the CT gray value is less than the liquid saturation value calculated by the volume method, the liquid saturation calculated by the volume method is taken as the final liquid saturation value under this ratio.

5. The rock high-temperature and high-pressure two-phase flow test method according to claim 4, characterized in that: In step (8), the first ratio is that the volume fraction of gas accounts for 0.0 of the total volume, and the gas injection pump does not need to be turned on during the test.

6. The rock high-temperature and high-pressure two-phase flow test method according to claim 5, characterized in that: In step (9), the volume fraction of gas in the second to eighth ratios gradually increases to the total volume, wherein the eighth ratio is 1.

0. It is not necessary to start the gas injection pump during the test.

7. The rock high-temperature and high-pressure two-phase flow test method according to any one of claims 4 to 6, characterized in that: It also includes step (12) to calculate the steady-state relative permeability according to Darcy's law ； ； Among them, k w,i and are the relative permeabilities of the liquid and gas phases in the i-th ratio test, q w,i and are the Darcy velocities of the liquid and gas phases in the i-th scale test, u w and u q are the fluid viscosities of the liquid and gas phases, respectively; L is the core length; ΔP is the pressure loss along the core length; and K is the absolute permeability of the core.

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