Rock high-temperature and high-pressure two-phase flow 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 a rock high-temperature and high-pressure two-phase flow test device and method based on in-situ CT scanning. The sample device comprises a rock core clamping system, a two-phase flow injection system, a confining pressure system, a back pressure system and a heating system; the rock core clamping system comprises a rock core holder and a heat-shrinkable sleeve, and the interior of the heat-shrinkable sleeve is used for wrapping a rock core; the rock core clamping system is fixed on an objective table of the CT scanning system; the two-phase flow injection system comprises an air injection pump and a brine pump; the confining pressure system comprises a confining pressure pump; the backpressure system comprises a backpressure pump; the two three-way valves on the upper and lower parts of the core holder are connected through pipelines to form a bypass pipeline; the three-way valves are arranged on the upstream and downstream of the core holder, and the two three-way valves are connected through the pipeline to form a parallel bypass pipeline which can be used for eliminating the dead volume of two-phase flow in the pipeline. On the basis, the test method can be simultaneously applied to a fluid volumetric method and a CT gray value method to calculate the fluid phase saturation and mutually verify and calibrate the fluid phase saturation.

Description

Technical Field

[0001] The 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 production projects, such as deep oil and gas production, geological storage of carbon dioxide, and underground storage of natural gas / hydrogen, are important guarantees for promoting sustainable energy development. The flow and distribution characteristics of multiphase fluids in multi-scale pore fracture structures in deep formations are directly affected by the pore structure of the rock and the wettability of the system. The large differences in the number of rock pore throat sizes and permeability will cause local rock heterogeneity, which directly affects the flow and capture of gas-liquid two-phase fluids. Relative permeability refers to the effective permeability of a phase when multiphase fluids exist simultaneously in the rock. It is a function of phase saturation, wettability, and pore structure, reflecting the laws of mutual influence and action of each phase of fluid. Traditional multiphase seepage tests can calculate the phase saturation of the core in the seepage stage through nuclear magnetic resonance methods, resistivity methods, etc., but it is impossible to reveal the multiphase seepage path and the distribution law of fluids in the microscopic pore structure from the microscopic pore structure of the core. For the complex physical and chemical reactions that occur during the displacement process of gas-liquid two-phase flow, it is unknown whether the coupled reaction of the rock-brine-gas system changes the pore structure and the influence law on the seepage parameters.

[0003] In recent years, the development of CT scanning technology has provided a visualization characterization technology for the three-dimensional pore structure of rocks. This technology combined with the in-situ gas-liquid two-phase flow displacement device can accurately characterize the rock pore structure and the seepage path of the gas-liquid two-phase fluid. In addition, local measurement and statistical analysis of the fluid phase can be performed through digital image processing and algorithm and image segmentation. Through digital core processing technology, a core pore network model can be constructed, seepage parameters can be quantified, and seepage paths can be characterized; capillary force, phase saturation, wetting contact angle, etc. can be precisely counted and calculated. Therefore, compared with 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 results of seepage tests. Summary of the invention

[0004] The present invention provides a rock high-temperature and high-pressure two-phase flow test device and method based on in-situ CT scanning, which can be simultaneously applied to the calculation of fluid phase saturation by a fluid volume method and a CT gray value method, and can verify and calibrate each other. The test device 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 an internal heat shrinkable sleeve for wrapping the core, the top surface and the bottom surface of the heat shrinkable sleeve are respectively provided with a through hole, the heat shrinkable sleeve is arranged in the internal cavity of the core clamp, the top surface of the core clamp is provided with a 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 comprises an injection pump and a brine pump, wherein the inlet of the brine pump is connected to the brine container through a pipeline, the inlet of the injection pump is connected to the gas cylinder through a pipeline, the outlet of the brine pump and the outlet of the injection pump are respectively connected to the first three-way valve through pipelines, and the first three-way valve is sequentially connected to the first three-way joint, the second three-way valve, the third three-way joint, the bottom through hole of the core holder, and the bottom through hole of the heat shrink sleeve through pipelines;

[0006] The confining pressure system comprises 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 comprises 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 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;

[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; the heating system is wound around the core holder, and a thermocouple is arranged 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 of the pressure sensor and temperature data of 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.

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

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

[0013] (2) placing the core into the heat shrink tube and fixing it by heat shrinking, machining a through hole on the top and bottom surfaces of the heat shrink tube respectively, and setting the heat shrink tube in the inner cavity of the core holder; assembling the rock high temperature and high pressure two-phase flow test device; 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 connection port between the first three-way valve and the air pump closed and the bypass line directly connecting the second three-way valve and the third three-way valve closed, inject brine into the core at various flow rates through 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 three-way valve and the third three-way valve, and open the bypass pipeline directly connecting the second three-way valve and the third three-way valve; close the connection port between the first three-way valve and the brine pump, open the connection port between the first three-way valve and the air pump, and discharge the water in the pipeline through the air pump;

[0020] (8) Open the first three-way valve, close the bypass line directly connecting the second three-way valve and the third three-way valve; 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 at the first ratio until a 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 grayscale value of the gas phase as the CT number and calculate the CT g , take the average gray value of the liquid phase as the CT number, and calculate the CT w ;

[0022] Close the pipeline with the core holder between the second three-way valve and the third three-way valve, and open the bypass pipeline directly connecting the second three-way valve and the third three-way valve; 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, discharge 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 in 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 salt water 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 gray average CT w ;

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

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

[0026]

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

[0028] In the formula, V is the cumulative volume of brine injected until the i-th ratio test is completed, 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 until the i-th ratio test is completed; w,i It is expressed as the liquid 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 gray value

[0030]

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

[0032] In the formula, 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 It represents the average grayscale value of air phase during dry scanning; represents 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 gray value of the test liquid phase;

[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 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 for the 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 there is no need to start the gas injection pump during the test.

[0035] Preferably, in step (9), the volume fraction of gas in the second ratio to the eighth ratio as a percentage of the total volume gradually increases, 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 phase and the gas phase 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 ratio test, u w and u qare 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, and K is the absolute permeability of the core.

[0039] The beneficial technical effect of the present invention is that the test device of the present invention forms a parallel bypass pipeline by setting a three-way valve upstream and downstream of the core clamp, and then connecting the two three-way valves with a pipeline, which can be used to eliminate the dead volume of the two-phase flow in the pipeline. On this basis, the test method of the present invention can be simultaneously applied to the fluid volume method and the CT gray value method to calculate the fluid phase saturation, and verify the calibration with each other. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The accompanying drawings constituting 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 It 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 reference numerals in the accompanying drawings: 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] Embodiment 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 an internal heat shrinkable sleeve 1 for wrapping the core, the top surface and the bottom surface of the heat shrinkable sleeve 1 are respectively provided with a through hole, the heat shrinkable sleeve 1 is arranged in the internal cavity of the core clamp 2, the top surface of the core clamp 2 is provided with a 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 19 by a clamp;

[0046] The two-phase flow injection system comprises an injection pump 13 and a brine pump 14, wherein the inlet of the brine pump 14 is connected to the brine container through a pipeline, the inlet of the injection pump 13 is connected to the gas cylinder through a pipeline, the outlet of the brine pump 14 and the outlet of the injection pump 13 are respectively connected to the first three-way valve 4 through pipelines, and the first three-way valve 4 is sequentially 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 shrinkable sleeve 1 through pipelines;

[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 through 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 top surface through hole of the core holder 2, and the top surface through hole of the heat shrink sleeve 1 through a pipeline in sequence; the back pressure valve 10 is also connected to the separation system 16, 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;

[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 removing the two-phase flow dead volume in the pipeline; the first three-way joint 7 and the second three-way joint 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 joint 9 in sequence through the pipeline; the heating system 17 is wound around the core holder 12, and the core holder 2 is provided with a thermocouple (or temperature sensor) 18 for monitoring 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 of the pressure sensor 20 and temperature data of 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, and 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] Embodiment 2

[0053] Based on the rock high temperature and high pressure two-phase flow test device of the first embodiment, 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 evacuated and completely saturated with water, and the core mass m1 was weighed again to calculate the core pore volume V. 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) The core is placed in the heat shrink tube 1 and fixed by heat shrinkage. The heat shrink tube 1 wraps the entire core. A through hole is processed on the top and bottom surfaces of the heat shrink tube 1 respectively. The heat shrink tube 1 is set in the inner cavity of the core holder 2; a rock high temperature and high pressure two-phase flow test device based on in-situ CT scanning is assembled ( Figure 1 ); The core is heated to a set temperature by a heating system 17, and the temperature value 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 port 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 30wt% KI brine at a flow rate of 0.5-2mL / min through the brine pump 14 to replace the air in the core pores to ensure that the core is completely saturated with water;

[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 is injected into the core at various flow rates through the brine pump 14, and the pressure value of the pressure sensor 20 is recorded to obtain the upstream and downstream pressure difference of the core. The absolute permeability K of the core is determined according to 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 discharge the water in the pipeline through the air pump 13 (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);

[0062] (8) Open the first three-way valve 4, 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 a set ratio; first inject the core according to the first ratio, the first ratio is that the volume fraction of gas accounts for 0.0 of the total volume (the gas injection pump 13 does not need to be turned on at this time), 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 gray value of the liquid phase as the CT number, and calculate the 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 port between the first three-way valve 4 and the brine pump 14, open the connection port between the first three-way valve 4 and the air pump 13, and discharge 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 for 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 30wt% 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 gray average CT w ;

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

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

[0068]

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

[0070] In the formula, 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 30wt% KI saline by the end of the i-th ratio test, S is the cumulative dead volume of 30wt% KI brine discharged from the pipeline by the end of the i-th ratio test; w,i It is expressed as the liquid 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 gray value

[0072]

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

[0074] In the formula, 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 It represents the average grayscale value of air phase during dry scanning; represents 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 gray value of the test liquid phase;

[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 for 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 for the ratio;

[0076] (12) Calculate the 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 phase and the gas phase 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 ratio test, u w and u q are respectively the fluid viscosities of the liquid phase and the gas phase, 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 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. Rock high temperature and high pressure two-phase flow test device based on in-situ CT scanning, characterized in that: It 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 sleeve for wrapping the core inside, the top surface and the bottom surface of the heat shrink sleeve are respectively provided with a through hole, the heat shrink sleeve is arranged in the inner cavity of the core clamp, the top surface of the core clamp is provided with a 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 through a clamp; The two-phase flow injection system comprises an injection pump and a brine pump, wherein the inlet of the brine pump is connected to the brine container through a pipeline, the inlet of the injection pump is connected to the gas cylinder through a pipeline, the outlet of the brine pump and the outlet of the injection pump are respectively connected to the first three-way valve through pipelines, and the first three-way valve is sequentially connected to the first three-way joint, the second three-way valve, the third three-way joint, the bottom through hole of the core holder, and the bottom through hole of the heat shrink sleeve through pipelines; The confining pressure system comprises 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 comprises 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 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 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; the heating system is wound around the core holder, and a thermocouple is arranged 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, 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.

3. The rock high temperature and high pressure two-phase flow test device according to claim 2 is characterized in that ,, also includes a computer, the computer is used to collect and store test data, including pressure data of the pressure sensor, temperature data of 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, characterized in that: The steps include: (1) Determine the core size and core pore volume V p , drying the core; (2) placing the core into the heat shrink tube and fixing it by heat shrinking, machining a through hole on the top and bottom surfaces of the heat shrink tube respectively, and setting the heat shrink tube in the inner cavity of the core holder; assembling the rock high temperature and high pressure two-phase flow test device; heating the core to a set temperature through a 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 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; (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 connection port between the first three-way valve and the air pump closed and the bypass line directly connecting the second three-way valve and the third three-way valve closed, inject brine into the core at various flow rates through 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; Close the pipeline with the core holder between the second three-way valve and the third three-way valve, and open the bypass pipeline directly connecting the second three-way valve and the third three-way valve; close the connection port between the first three-way valve and the brine pump, open the connection port between the first three-way valve and the air pump, and discharge the water in the pipeline through the air pump; (8) Open the first three-way valve, close the bypass line directly connecting the second three-way valve and the third three-way valve; 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 at the first ratio until a 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 grayscale value of the gas phase as the CT number and calculate the CT g , take the average gray value of the liquid phase as the CT number, and calculate the CT w ; Close the pipeline with the core holder between the second three-way valve and the third three-way valve, and open the bypass pipeline directly connecting the second three-way valve and the third three-way valve; 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, discharge 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 in 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 salt water 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 gray average CT w ; (10) Calculate gas and liquid phase saturation; First, the fluid volume method is used to calculate the gas and liquid saturation S g,i =1-S w,i In the formula, V is the cumulative volume of brine injected until the i-th ratio test is completed, p is the core pore volume, is the cumulative outflow volume of saline until the i-th ratio test is completed, S is the cumulative dead volume of brine discharged from the pipeline until the i-th ratio test is completed; w,i It is expressed as the liquid saturation of the i-th ratio test, S g,i 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 gray value S w,i =1-S g,i In the formula, 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 It represents the average grayscale value of air phase during dry scanning; represents 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 gray value of the test liquid phase; (11) Liquid saturation accuracy verification: 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.

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 there is no need to start the gas injection pump during the test.

6. According to the rock high-temperature and high-pressure two-phase flow test method described in claim 5, in step (9), the volume fraction of gas in the second ratio to the eighth ratio gradually increases, wherein the eighth ratio is 1.0, and the gas injection pump does not need to be turned on 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, further comprising step (12), calculating the steady-state relative permeability by Darcy's law in, k w,i and k g,i are the relative permeabilities of the liquid phase and the gas phase 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 ratio 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, and K is the absolute permeability of the core.

Images