Device and method for testing migration and conductivity of supercritical carbon dioxide fracturing proppant

Abstract

The present invention discloses a device and method for testing the migration and conductivity of supercritical carbon dioxide fracturing proppants, comprising an experimental clamp, which comprises a first liquid inlet, a second liquid inlet, a confining pressure inlet, an axial pressure inlet, an outer cylinder, an axial piston, a loading plug, a rubber cylinder, a confining pressure chamber, an axial pressure chamber and a liquid outlet; the first liquid inlet is connected to a fluid injection system through a first liquid inlet pipeline, the second liquid inlet is connected to a mixing system through a second liquid inlet pipeline, the confining pressure inlet is connected to a confining pressure pump through a confining pressure pipeline, and the axial pressure inlet is connected to an axial pressure pump through an axial pressure pipeline, an X-ray device is provided on the left side of the experimental clamp, and an imaging device is provided on the right side of the experimental clamp; the mixing system is connected to the fluid injection system and the proppant injection system, and the mixing system is also connected to a gas injection system; the present application solves the problem that existing experimental simulation devices have single functions and cannot accurately simulate experiments.

Description

Technical Field

[0001] The invention belongs to the technical field of mining experimental simulation devices, and in particular relates to a device and method for testing the migration and conductivity of a supercritical carbon dioxide fracturing proppant. Background Art

[0002] Compared to hydraulic fracturing, CO2 fracturing technology shows great potential in coalbed methane extraction. Due to its low viscosity, CO2 easily forms complex fracture networks in coal reservoirs, enhancing reservoir production. Furthermore, CO2 does not contain water during migration, which does not cause water resistance or swelling in clay minerals, thereby affecting the migration path of coalbed methane. Furthermore, CO2 has stronger adsorption properties than CH4, enabling it to displace CH4 molecules from coal, achieving permanent storage of CO2 and increasing coalbed methane recovery.

[0003] Due to the high geothermal temperature, high stress, and high reservoir pressure, coal seam fractures rapidly close under high stress conditions after supercritical CO2 fracturing, making long-term, effective mining difficult. Research has shown that injecting proppants into coal seams can effectively slow fracture closure and improve their conductivity. Therefore, laboratory simulations of supercritical CO2 fracturing and proppant distribution within coal fractures are necessary before field mining to ensure safe and smooth coalbed methane (CBM) extraction. However, due to the complex physical processes involved in proppant transport, most experimental setups for proppant transport assume fractures as vertical flat plates. This simplifies the basic fracture morphology and allows for more intuitive observation of proppant distribution within the fractures. However, coal fractures after supercritical CO2 fracturing exhibit a diverse and highly complex morphology, with apertures ranging from millimeters to micrometers. Therefore, a device and method for testing proppant migration and conductivity during supercritical CO2 fracturing is needed that can accurately simulate supercritical CO2 fracturing and proppant distribution within coal fractures to ensure safe and smooth CBM extraction. Summary of the Invention

[0004] In order to overcome the deficiencies in the prior art, the present invention provides a device and method for testing the migration and conductivity of supercritical carbon dioxide fracturing proppants for precise simulation experiments.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A supercritical carbon dioxide fracturing proppant migration and conductivity testing device includes an experimental holder, which includes a first liquid inlet, a second liquid inlet, a confining pressure inlet, an axial pressure inlet, an outer cylinder, an axial piston, a loading plug, a rubber cylinder, a confining pressure cavity, an axial pressure cavity, and a liquid outlet;

[0007] The first liquid inlet is connected to the fluid injection system through a first liquid inlet pipeline, the second liquid inlet is connected to the mixing system through a second liquid inlet pipeline, the confining pressure inlet is connected to the confining pressure pump through a confining pressure pipeline, and the axial pressure inlet is connected to the axial pressure pump through an axial pressure pipeline. An X-ray device is provided on the left side of the experimental holder, and an imaging device is provided on the right side of the experimental holder. The X-ray device emits rays that pass through the experimental holder to form an image on the imaging device;

[0008] The mixing system is connected to the fluid injection system via a third liquid inlet pipeline, is connected to the proppant injection system via a fourth liquid inlet pipeline, and is also connected to the gas injection system;

[0009] Before the experiment, gas is introduced into the mixing system through the gas injection system to test the air tightness of the device. After the air tightness is qualified, supercritical carbon dioxide and proppant sand-carrying fluid are injected into the experimental holder through the fluid injection system, proppant injection system and mixing system to carry out experimental simulation.

[0010] The fluid injection system includes a CO2 gas cylinder, which is connected to a booster pump via a first gas pipeline, which is connected to a CO2 storage tank via a second gas pipeline, which is connected to a fracturing pump via a first delivery pipeline, which is connected to a first liquid inlet pipeline, and a pressure gauge is provided on the CO2 storage tank;

[0011] The first gas pipeline is provided with a gas valve, the second gas pipeline is connected to a cooling coil, the cooling coil is connected to a CO2 storage tank, and the CO2 storage tank is arranged in a first water bath thermostatic tank so that the CO2 in the CO2 storage tank is in liquid state;

[0012] A first liquid suction valve is provided on the first delivery pipeline, a delivery branch is connected to the first delivery pipeline between the first liquid suction valve and the CO2 storage tank, a second liquid suction valve is provided on the delivery branch, the delivery branch is connected to a first servo pump, the first servo pump is connected to the mixing system through the second delivery pipeline, and a heater is provided on the second delivery pipeline.

[0013] The proppant injection system includes a proppant supply tank, the proppant supply tank is connected to a mixing tank via a third delivery pipeline, a first discharge valve of the mixing tank is connected to a screw conveyor, and a second discharge valve of the screw conveyor is connected to the mixing system;

[0014] A magnetic stirrer is provided in the mixing tank to fully stir the proppant.

[0015] The mixing system includes a second water bath thermostatic tank, an intermediate container is arranged in the second water bath thermostatic tank, the intermediate container is connected to a second servo pump through a fourth delivery pipeline, and the second servo pump is connected to the second liquid inlet pipeline.

[0016] The second delivery pipeline is connected to the left end of the tee, the right end of the tee is connected to the third liquid inlet pipeline, the third liquid inlet pipeline is connected to the intermediate container, after the liquid CO2 enters the intermediate container, it is heated to a supercritical state in the second water bath thermostatic tank, the lower end of the tee is connected to the third gas pipeline, the third gas pipeline is connected to the gas injection system, and the third liquid inlet pipeline is provided with a third liquid suction valve;

[0017] The fracturing pump is connected to the left end of the four-way pipe through the fracturing pipe, the right end of the four-way pipe is connected to the first liquid inlet pipe, the upper end of the four-way pipe is connected to the discharge pipe, the discharge pipe is connected to the second discharge valve of the screw conveyor, and the lower end of the four-way pipe is connected to the intermediate container through the fourth liquid inlet pipe. The second liquid inlet pipe is provided with a fourth suction valve.

[0018] The bottom end of the intermediate container is connected to a first liquid outlet pipe, which is connected to a first waste liquid pool outside the second water bath thermostatic tank, and a liquid outlet valve is provided on the first liquid outlet pipe;

[0019] A first pressure sensor and a first temperature sensor for monitoring the pressure and temperature in the intermediate container are installed on the intermediate container.

[0020] The gas injection system includes a methane cylinder, a nitrogen cylinder and a helium cylinder. The methane cylinder is connected to a methane outlet branch pipe, the nitrogen cylinder is connected to a nitrogen outlet branch pipe, and the helium cylinder is connected to a helium outlet branch pipe. The methane outlet branch pipe, the nitrogen outlet branch pipe and the helium outlet branch pipe are connected to a third gas transmission pipe.

[0021] The methane outlet branch pipe is provided with a first outlet valve and a first pressure reducing valve, the nitrogen outlet branch pipe is provided with a second outlet valve and a second pressure reducing valve, and the helium outlet branch pipe is provided with a third outlet valve and a third pressure reducing valve.

[0022] The liquid outlet of the experimental holder is connected to a filter device through a second liquid outlet pipe, the filter device is connected to a second waste liquid tank through a third liquid outlet pipe, a drain valve is provided on the third liquid outlet pipe, and a flow meter is provided on the second liquid outlet pipe;

[0023] A second temperature sensor and a second pressure sensor for monitoring temperature and pressure are mounted on the experimental holder;

[0024] The first temperature sensor, the second temperature sensor, the first pressure sensor, the second pressure sensor, the imaging device and the flow meter are all connected to a data acquisition device, which includes a signal receiver and a display.

[0025] The testing method based on the above-mentioned supercritical carbon dioxide fracturing proppant migration and conductivity testing device includes the following steps:

[0026] (1) Keep the CO2 storage tank, intermediate container and experimental holder completely sealed, open the helium cylinder and the third outlet valve, introduce helium into the device, and check the air tightness of the device;

[0027] (2) Place the core to be tested in the experimental holder, turn on the X-ray instrument, imaging device and data acquisition device, scan the core to be tested, and obtain the initial image of the core;

[0028] (3) Turn on the confining pressure pump and the axial pressure pump to apply corresponding pressure to the core;

[0029] (4) Turn on the heater and set the temperature of the second water bath thermostat to ≥40°C;

[0030] (5) Keep the second suction valve, the third suction valve, and the second discharge valve closed, and keep the gas delivery valve open. Turn on the booster pump to pressurize the CO2, and deliver the pressurized CO2 gas to the CO2 storage tank through the cooling coil. Set the temperature of the first water bath thermostat to less than -0.15°C to keep the CO2 in a liquid state.

[0031] (6) Open the first suction valve and the fracturing pump to perform liquid CO2 fracturing on the stressed core, and simultaneously use an X-ray machine to monitor the crack expansion characteristics in real time, and a data acquisition device to record pressure information;

[0032] (7) Close the first suction valve and open the first discharge valve and the second discharge valve at the same time to transport the proppant in the mixing tank to the intermediate container via the screw conveyor;

[0033] (8) Open the second suction valve and the third suction valve to transfer the pressurized liquid CO2 into the intermediate container and make it supercritical in the second water bath thermostat;

[0034] (9) Open the fourth suction valve and the second servo pump to inject the sand-carrying fluid mixed with supercritical CO2 and proppant into the fractured core, and simultaneously use an X-ray machine to scan the core, and the data acquisition device obtains the distribution of the proppant in the fracture;

[0035] (10) Close the second suction valve, open the liquid outlet valve and the drain valve, discharge the CO2 and proppant in the intermediate container, and discharge the CO2 in the experimental holder. After the discharge, close the liquid outlet valve and the drain valve, and open the third gas outlet valve, introduce helium into the intermediate container, and apply axial pressure and confining pressure to the core again. Measure its permeability with a flow meter, and analyze the conductivity of the proppant under different closing pressures;

[0036] (11) After the experiment is completed, close all valves, open the liquid outlet valve and drain valve, discharge all gases, and clean the intermediate container.

[0037] The present invention first introduces helium into the device through a helium cylinder to test the airtightness of the entire device, scans the core and records the initial image through an X-ray device, an imaging device and a data acquisition device, then performs liquid CO2 fracturing on the core and uses the X-ray device to monitor the crack expansion characteristics in real time, and heats the CO2 through a second water bath thermostat to make the CO2 supercritical. Then, a sand-carrying fluid mixed with supercritical CO2 and proppant is introduced into the core, and the distribution of the proppant in the fracture is scanned again. Finally, the permeability is measured using a flow meter, and the conductivity of the proppant under different closing pressures is analyzed. The present application is simple to operate and can not only realize CO2 fracturing of the core, but also simulate the migration and conductivity of the proppant in the fracture, so as to reveal the migration mechanism of low-viscosity fracturing fluid and the transport mechanism of the proppant in the fracture, and obtain the optimal preferred solution and laying method of the proppant. It effectively solves the technical problem that the existing experimental simulation device has a single function and cannot accurately simulate experiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a structural schematic diagram of the present invention;

[0039] Figure 2 is an enlarged view of the fluid injection system of the present invention;

[0040] Figure 3 is an enlarged view of the proppant injection system of the present invention;

[0041] Figure 4 is an enlarged view of the mixing system of the present invention;

[0042] Figure 5 is an enlarged view of the gas injection system of the present invention;

[0043] Figure 6 It is a structural schematic diagram of the experimental clamp in the present invention. DETAILED DESCRIPTION

[0044] Example 1

[0045] like Figure 1-6 As shown, the supercritical carbon dioxide fracturing proppant migration and conductivity testing device of the present invention includes an experimental holder 1, which includes a first liquid inlet 2, a second liquid inlet 3, a confining pressure inlet 4, an axial pressure inlet 5, an outer cylinder 6, an axial piston 7, a loading plug 8, a rubber cylinder 9, a confining pressure chamber 10, an axial pressure chamber 11 and a liquid outlet 12;

[0046] The first liquid inlet 2 is connected to the fluid injection system 21 through the first liquid inlet pipe 13, the second liquid inlet 3 is connected to the mixing system 15 through the second liquid inlet pipe 14, the confining pressure inlet 4 is connected to the confining pressure pump 16 through the confining pressure pipeline, and the axial pressure inlet 5 is connected to the axial pressure pump 17 through the axial pressure pipeline. An X-ray device 18 is provided on the left side of the experimental clamp 1, and an imaging device 19 is provided on the right side of the experimental clamp 1. The X-ray device 18 emits rays through the experimental clamp 1 to form an image on the imaging device 19; in addition, the experimental clamp 1 is also connected to a vacuum pump 83.

[0047] The mixing system 15 is connected to the fluid injection system 21 via a third liquid inlet pipe 20 and is connected to the proppant injection system 23 via a fourth liquid inlet pipe 22. The mixing system 15 is also connected to the gas injection system 24.

[0048] Before the experiment, gas is introduced into the mixing system 15 through the gas injection system 24 to test the air tightness of the device. After the air tightness is qualified, supercritical carbon dioxide and proppant-carrying fluid are injected into the experimental holder 1 through the fluid injection system 21, the support and injection system 23 and the mixing system 15 to perform experimental simulation.

[0049] The fluid injection system 21 includes a CO2 gas cylinder 25, which is connected to a booster pump 28 via a first gas pipeline 27, and the booster pump 28 is connected to a CO2 storage tank 26 via a second gas pipeline 29. The CO2 storage tank 26 is connected to a fracturing pump 31 via a first delivery pipeline 30, and the fracturing pump 31 is connected to the first liquid inlet pipeline 13. A pressure gauge 33 is provided on the CO2 storage tank 26;

[0050] The first gas delivery pipe 27 is provided with a gas delivery valve 34, the second gas delivery pipe 29 is connected to a cooling coil 35, and the cooling coil 35 is connected to the CO2 storage tank 26. The CO2 storage tank 26 is placed in a first water bath thermostatic tank 36, so that the CO2 in the CO2 storage tank 26 is in a liquid state;

[0051] A first suction valve 37 is provided on the first delivery pipeline 30, and a delivery branch pipe 38 is connected to the first delivery pipeline 30 between the first suction valve 37 and the CO2 storage tank 26. A second suction valve 39 is provided on the delivery branch pipe 38, and the delivery branch pipe 38 is connected to a first servo pump 40. The first servo pump 40 is connected to the mixing system 15 through a second delivery pipeline 41, and a heater 42 is provided on the second delivery pipeline 41.

[0052] The proppant injection system 23 includes a proppant supply tank 43, which is connected to a mixing tank 45 via a third delivery pipe 44. A first discharge valve 46 of the mixing tank 45 is connected to a screw conveyor 47, and a second discharge valve 48 of the screw conveyor 47 is connected to the mixing system 15.

[0053] A magnetic stirrer 49 is provided in the mixing tank 45 to fully stir the proppant.

[0054] The mixing system 15 includes a second water bath thermostatic tank 50 . An intermediate container 51 is provided in the second water bath thermostatic tank 50 . The intermediate container 51 is connected to a second servo pump 53 via a fourth delivery pipe 52 . The second servo pump 53 is connected to the second liquid inlet pipe 14 .

[0055] The second delivery pipeline 41 is connected to the left end of the tee 54, the right end of the tee 54 is connected to the third liquid inlet pipeline 20, and the third liquid inlet pipeline 20 is connected to the intermediate container 51. After the liquid CO2 enters the intermediate container 51, it is heated to a supercritical state in the second water bath 50. The lower end of the tee 54 is connected to the third gas pipeline 57, which is connected to the gas injection system 24. The third liquid inlet pipeline 20 is provided with a third liquid suction valve 58.

[0056] The fracturing pump 31 is connected to the left end of the four-way pipe 55 through the fracturing pipe, the right end of the four-way pipe 55 is connected to the first liquid inlet pipe 13, the upper end of the four-way pipe 55 is connected to the discharge pipe, the discharge pipe is connected to the second discharge valve 48 of the screw conveyor 47, and the lower end of the four-way pipe 55 is connected to the intermediate container 51 through the fourth liquid inlet pipe 22. A fourth suction valve 71 is provided on the second liquid inlet pipe 14.

[0057] The bottom end of the intermediate container 51 is connected to a first liquid outlet pipe 60 , which is connected to a first waste liquid pool 61 outside the second water bath thermostatic tank 50 . A liquid outlet valve 62 is provided on the first liquid outlet pipe 60 .

[0058] A first pressure sensor 63 and a first temperature sensor 64 are mounted on the intermediate container 51 for monitoring the pressure and temperature in the intermediate container 51 .

[0059] The gas injection system 24 includes a methane gas cylinder 67, a nitrogen gas cylinder 68, and a helium gas cylinder 69. The methane gas cylinder 67 is connected to a methane outlet branch pipe, the nitrogen gas cylinder 68 is connected to a nitrogen outlet branch pipe, and the helium gas cylinder 69 is connected to a helium outlet branch pipe. The methane outlet branch pipe, the nitrogen outlet branch pipe, and the helium outlet branch pipe are connected to the third gas transmission pipe 57.

[0060] The methane outlet branch pipe is provided with a first outlet valve 70 and a first pressure reducing valve 74 , the nitrogen outlet branch pipe is provided with a second outlet valve 72 and a second pressure reducing valve 75 , and the helium outlet branch pipe is provided with a third outlet valve 73 and a third pressure reducing valve 76 .

[0061] The liquid outlet 12 of the experimental holder 1 is connected to a filter device 85 via a second liquid outlet pipe, and the filter device 85 is connected to a second waste liquid tank 84 via a third liquid outlet pipe. A drain valve 79 is provided on the third liquid outlet pipe, and a flow meter 80 is provided on the second liquid outlet pipe.

[0062] A second temperature sensor 66 and a second pressure sensor 65 for monitoring temperature and pressure are mounted on the experimental holder 1;

[0063] The first temperature sensor 64 , the second temperature sensor 66 , the first pressure sensor 63 , the second pressure sensor 65 , the imaging device 19 and the flow meter 80 are all connected to a data acquisition device, which includes a signal receiver 81 and a display 82 .

[0064] Example 2

[0065] The testing method based on the above-mentioned supercritical carbon dioxide fracturing proppant migration and conductivity testing device includes the following steps:

[0066] (1) Keep the CO2 storage tank 26, the intermediate container 51 and the experimental holder 1 completely sealed, open the helium cylinder 69 and the third outlet valve 73, and introduce helium into the device to test the airtightness of the device;

[0067] (2) Place the core to be tested in the experimental holder 1, turn on the X-ray instrument 18, the imaging device 19 and the data acquisition device, scan the core to be tested, and obtain an initial image of the core;

[0068] (3) Start the confining pressure pump 16 and the axial pressure pump 17 to apply corresponding pressure to the core;

[0069] (4) Turn on the heater 42 and set the temperature of the second water bath thermostat 50 to ≥40°C for one hour;

[0070] (5) Keep the second suction valve 39, the third suction valve 58, and the second discharge valve 48 closed, and keep the gas delivery valve 34 open. Turn on the booster pump 28 to pressurize the CO2, and deliver the pressurized CO2 gas to the CO2 storage tank 26 through the cooling coil 35. Set the temperature of the first water bath thermostat 36 to less than -0.15°C to keep the CO2 in a liquid state.

[0071] (6) Open the first suction valve 37 and the fracturing pump 31 to perform liquid CO2 fracturing on the stressed core, and simultaneously use the X-ray device 18 to monitor the crack expansion characteristics in real time, and the data acquisition device records the pressure information;

[0072] (7) Close the first liquid suction valve 37 and open the first discharge valve 46 and the second discharge valve 48 at the same time to convey the proppant in the mixing tank 45 to the intermediate container 51 via the screw conveyor 47;

[0073] (8) Open the second suction valve 39 and the third suction valve 58 to transfer the pressurized liquid CO2 into the intermediate container 51 and to form a supercritical state in the second water bath thermostatic tank 50;

[0074] (9) Open the fourth suction valve 71 and the second servo pump 53 to inject the sand-carrying fluid mixed with supercritical CO2 and proppant into the fractured core, and simultaneously use the X-ray device 18 to scan the core, and the data acquisition device obtains the distribution of the proppant in the fracture;

[0075] (10) Close the second suction valve 39, open the liquid outlet valve 62 and the drain valve 79, discharge the CO2 and proppant in the intermediate container 51, and discharge the CO2 in the experimental holder 1. After the discharge, close the liquid outlet valve 62 and the drain valve 79, and open the third gas outlet valve 73, introduce helium into the intermediate container 51, and apply axial pressure and confining pressure to the core again. Measure its permeability with the flow meter 80, and analyze the conductivity of the proppant under different closing pressures;

[0076] (11) After the experiment is completed, close all valves, open the liquid outlet valve 62 and the drain valve 79, discharge all gases, and clean the intermediate container 51.

[0077] The present invention first introduces helium into the device via a helium cylinder 69 to test the overall airtightness of the device. The core is scanned and an initial image is recorded using an X-ray instrument 18, an imaging device 19, and a data acquisition device. The core is then subjected to liquid CO2 fracturing and the crack expansion characteristics are monitored in real time using the X-ray instrument 18. The CO2 is heated in a second water bath 50 to a supercritical state. A sand-carrying fluid mixed with supercritical CO2 and proppant is then introduced into the core. The core is scanned again to obtain the distribution of the proppant in the fracture. Finally, a flow meter 80 is used to measure permeability and analyze the proppant's conductivity at different closure pressures. The present invention is simple to operate and can not only perform CO2 fracturing on the core, but also simulate the migration and conductivity of the proppant in the fracture, thereby revealing the migration mechanism of low-viscosity fracturing fluid and the transport mechanism of the proppant in the fracture, and obtaining the optimal proppant optimization scheme and laying method. This effectively solves the technical problem of existing experimental simulation devices having a single function and being unable to accurately simulate experiments.

[0078] This embodiment does not impose any formal restrictions on the shape, material, structure, etc. of the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are within the scope of protection of the technical solution of the present invention.

Claims

1. A supercritical carbon dioxide fracturing proppant migration and conductivity testing device, characterized by: The experimental holder includes a first liquid inlet, a second liquid inlet, a confining pressure inlet, an axial pressure inlet, an outer cylinder, an axial piston, a loading plug, a rubber cylinder, a confining pressure cavity, an axial pressure cavity and a liquid outlet; The first liquid inlet is connected to the fluid injection system through a first liquid inlet pipeline, the second liquid inlet is connected to the mixing system through a second liquid inlet pipeline, the confining pressure inlet is connected to the confining pressure pump through a confining pressure pipeline, and the axial pressure inlet is connected to the axial pressure pump through an axial pressure pipeline. An X-ray device is provided on the left side of the experimental holder, and an imaging device is provided on the right side of the experimental holder. The X-ray device emits rays that pass through the experimental holder to form an image on the imaging device; The mixing system is connected to the fluid injection system via a third liquid inlet pipeline, is connected to the proppant injection system via a fourth liquid inlet pipeline, and is also connected to the gas injection system; The fluid injection system includes a CO2 gas cylinder, which is connected to a booster pump via a first gas pipeline, which is connected to a CO2 storage tank via a second gas pipeline, which is connected to a fracturing pump via a first delivery pipeline, which is connected to a first liquid inlet pipeline, and a pressure gauge is provided on the CO2 storage tank; The first gas pipeline is provided with a gas valve, the second gas pipeline is connected to a cooling coil, the cooling coil is connected to a CO2 storage tank, and the CO2 storage tank is arranged in a first water bath thermostatic tank so that the CO2 in the CO2 storage tank is in liquid state; A first liquid suction valve is provided on the first delivery pipeline, a delivery branch is connected to the first delivery pipeline between the first liquid suction valve and the CO2 storage tank, a second liquid suction valve is provided on the delivery branch, the delivery branch is connected to a first servo pump, the first servo pump is connected to the mixing system through a second delivery pipeline, and a heater is provided on the second delivery pipeline; The proppant injection system includes a proppant supply tank, which is connected to a mixing tank via a third delivery pipeline. A first discharge valve of the mixing tank is connected to a screw conveyor, and a second discharge valve of the screw conveyor is connected to the mixing system. A magnetic stirrer is provided in the mixing tank to fully stir the proppant. The mixing system includes a second water bath thermostatic tank, an intermediate container is provided in the second water bath thermostatic tank, the intermediate container is connected to a second servo pump via a fourth delivery pipeline, and the second servo pump is connected to the second liquid inlet pipeline; The bottom end of the intermediate container is connected to a first liquid outlet pipe, which is connected to a first waste liquid pool outside the second water bath thermostatic tank, and a liquid outlet valve is provided on the first liquid outlet pipe; The intermediate container is equipped with a first pressure sensor and a first temperature sensor for monitoring the pressure and temperature in the intermediate container; The liquid outlet of the experimental holder is connected to a filter device through a second liquid outlet pipe, the filter device is connected to a second waste liquid tank through a third liquid outlet pipe, a drain valve is provided on the third liquid outlet pipe, and a flow meter is provided on the second liquid outlet pipe; A second temperature sensor and a second pressure sensor for monitoring temperature and pressure are mounted on the experimental holder; The first temperature sensor, the second temperature sensor, the first pressure sensor, the second pressure sensor, the imaging device and the flow meter are all connected to a data acquisition device, which includes a signal receiver and a display.

2. The supercritical carbon dioxide fracturing proppant migration and conductivity testing device according to claim 1, characterized in that: The second delivery pipeline is connected to the left end of the tee, the right end of the tee is connected to the third liquid inlet pipeline, the third liquid inlet pipeline is connected to the intermediate container, after the liquid CO2 enters the intermediate container, it is heated to a supercritical state in the second water bath thermostatic tank, the lower end of the tee is connected to the third gas pipeline, the third gas pipeline is connected to the gas injection system, and the third liquid inlet pipeline is provided with a third liquid suction valve; The fracturing pump is connected to the left end of the four-way pipe through the fracturing pipe, the right end of the four-way pipe is connected to the first liquid inlet pipe, the upper end of the four-way pipe is connected to the discharge pipe, the discharge pipe is connected to the second discharge valve of the screw conveyor, and the lower end of the four-way pipe is connected to the intermediate container through the fourth liquid inlet pipe. The second liquid inlet pipe is provided with a fourth suction valve.

3. The supercritical carbon dioxide fracturing proppant migration and conductivity testing device according to claim 2, characterized in that: The gas injection system includes a methane cylinder, a nitrogen cylinder and a helium cylinder. The methane cylinder is connected to a methane outlet branch pipe, the nitrogen cylinder is connected to a nitrogen outlet branch pipe, and the helium cylinder is connected to a helium outlet branch pipe. The methane outlet branch pipe, the nitrogen outlet branch pipe and the helium outlet branch pipe are connected to a third gas transmission pipe. The methane outlet branch pipe is provided with a first outlet valve and a first pressure reducing valve, the nitrogen outlet branch pipe is provided with a second outlet valve and a second pressure reducing valve, and the helium outlet branch pipe is provided with a third outlet valve and a third pressure reducing valve.

4. A testing method based on the supercritical carbon dioxide fracturing proppant migration and conductivity testing device according to any one of claims 1 to 3, characterized in that: (1) Keep the CO2 storage tank, intermediate container and experimental holder completely sealed, open the helium cylinder and the third outlet valve, introduce helium into the device, and check the air tightness of the device; (2) Place the core to be tested in the experimental holder, turn on the X-ray instrument, imaging device and data acquisition device, scan the core to be tested, and obtain the initial image of the core; (3) Turn on the confining pressure pump and the axial pressure pump to apply corresponding pressure to the core; (4) Turn on the heater and set the temperature of the second water bath thermostat to ≥40°C; (5) Keep the second suction valve, the third suction valve, and the second discharge valve closed, and keep the gas delivery valve open. Turn on the booster pump to pressurize the CO2, and deliver the pressurized CO2 gas to the CO2 storage tank through the cooling coil. Set the temperature of the first water bath thermostat to less than -0.15°C to keep the CO2 in a liquid state. (6) Open the first suction valve and the fracturing pump to perform liquid CO2 fracturing on the stressed core, and simultaneously use an X-ray machine to monitor the crack expansion characteristics in real time, and a data acquisition device to record pressure information; (7) Close the first suction valve and open the first discharge valve and the second discharge valve at the same time to transport the proppant in the mixing tank to the intermediate container via the screw conveyor; (8) Open the second suction valve and the third suction valve to transfer the pressurized liquid CO2 into the intermediate container and make it supercritical in the second water bath thermostat; (9) Open the fourth suction valve and the second servo pump to inject the sand-carrying fluid mixed with supercritical CO2 and proppant into the fractured core, and simultaneously use an X-ray machine to scan the core, and the data acquisition device obtains the distribution of the proppant in the fracture; (10) Close the second suction valve, open the liquid outlet valve and the drain valve, discharge the CO2 and proppant in the intermediate container, and discharge the CO2 in the experimental holder. After the discharge, close the liquid outlet valve and the drain valve, and open the third gas outlet valve, introduce helium into the intermediate container, and apply axial pressure and confining pressure to the core again. Measure its permeability with a flow meter, and analyze the conductivity of the proppant under different closing pressures; (11) After the experiment is completed, close all valves, open the liquid outlet valve and drain valve, discharge all gases, and clean the intermediate container.

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