A comprehensive performance testing device for proppants for fractures and its testing method

Abstract

The present application provides a comprehensive performance testing device and testing method for proppants for fractures. The fluid injection mechanism is connected to the fractures in the rock sample hermetically arranged in the triaxial loading mechanism, and is used to inject matrix, proppants, and stimulants into the fractures in the rock sample respectively; the fluid backflow mechanism is connected to the fractures in the rock sample, and is used to store the fluid after flowing back from the fractures in the rock sample; the rock sample is hermetically arranged in the triaxial loading mechanism, and the triaxial loading mechanism is used to apply axial pressure and confining pressure to the rock sample respectively to simulate the triaxial stress state borne by the deep underground reservoir and fractures; the test result acquisition and analysis mechanism is used to collect data and images during the comprehensive performance testing of proppants to analyze and evaluate the change in the conductivity of proppants before and after expansion. The device and the testing method can simulate the triaxial stress state borne by the reservoir and fractures, and can realize the comprehensive testing of the migration, expansion, and conductivity of self-expanding proppants in rock fractures.

Description

Technical Field

[0001] This application relates to the field of deep underground structure transformation, and particularly to a comprehensive performance testing device and testing method for proppants for fractures. Background Art

[0002] In the process of transforming and developing underground structures such as oil and gas, geothermal energy, and minerals, fracturing the reservoir is an important means to increase the reservoir permeability and improve production. Proppants are an important part of the reservoir fracturing transformation technology. After fractures are generated through fracturing, proppants need to be injected into the fractures to keep the fractures open and prevent them from closing after the pressure is released. The reasonable use of proppants can enhance the stability of the fractures, effectively optimize the fracture network, improve the exploitation efficiency of underground resources, reduce the impact on the environment, and ensure the sustainability of engineering projects.

[0003] Conductivity is the most important indicator to measure the improvement of the permeability of reservoir fractures by proppants. Conducting tests and evaluations on the conductivity of proppants through experiments is a prerequisite for selecting the appropriate type of proppants and optimizing process parameters such as particle size and concentration in reservoir fracturing transformation. Currently, the main testing method for proppant conductivity is the petroleum and natural gas industry standard "SY∕T 6302-2019 Testing Method for Proppant Conductivity" issued by the National Energy Administration. The device used is a fracture conductivity tester developed according to API standards. This method uses two rock plates in the conductivity chamber to simulate the reservoir, evenly lays proppants between the two rock plates to simulate the effect of proppants on fractures, applies a uniform normal pressure to the rock plates to simulate the closing pressure of the fractures, measures the pressure difference between the inlet and outlet of the fractures during fluid displacement, and calculates the permeability of the fractures and the conductivity of proppants through Darcy's law.

[0004] This method has multiple problems: ① The proppants are pre-filled in the fractures in a uniformly laid manner, which is difficult to reflect the migration process of proppants in the fractures during the actual engineering proppant injection process and is also difficult to observe the distribution pattern of proppants in the fractures; ② The rock plates only bear normal pressure and are in a state of uniaxial (directional) loading, unable to reflect the triaxial stress state of the reservoir in actual engineering, resulting in only the most idealized tensile fractures being able to be simulated, and more complex fractures such as shear fractures cannot be simulated; ③ New proppant tests such as temperature change or chemical reagent-induced expansion cannot be carried out, making it difficult to observe the expansion effect and evaluate the change in conductivity before and after expansion.

[0005] Therefore, how to achieve the comprehensive testing of the in-situ migration, expansion, and conductivity of self-expanding proppants is of great significance for the process design and engineering application of this new type of proppant under complex geological conditions. Summary of the Invention

[0006] One of the purposes of this application is to provide a comprehensive performance testing device and method for proppants for fractures, which can achieve the comprehensive testing of the in-fracture migration, expansion and conductivity of self-expanding proppants, and evaluate the change in the conductivity of proppants before and after expansion.

[0007] The technical solution of this application is as follows:

[0008] A comprehensive performance testing device for proppants for fractures includes a fluid injection mechanism, a fluid backflow mechanism, a triaxial loading mechanism and a test result acquisition and analysis mechanism; the fluid injection mechanism is connected to a fracture in a rock sample sealed in the triaxial loading mechanism, and is used to inject matrix, proppants and activator into the fracture in the rock sample respectively. The matrix is used to transport the proppants into the fracture in the rock sample, and the activator is used to stimulate the expansion of the proppants; the fluid backflow mechanism is connected to the fracture in the rock sample and is used to store the fluid after it flows back from the rock sample fracture; the rock sample is sealed in the triaxial loading mechanism, and the triaxial loading mechanism is used to apply axial pressure and confining pressure to the rock sample respectively to simulate the triaxial stress state borne by deep underground reservoirs and fractures; the test result acquisition and analysis mechanism is used to collect data and images during the comprehensive performance test of the proppants to analyze and evaluate the change in the conductivity of the proppants before and after expansion.

[0009] As a technical solution of this application, the fluid injection mechanism includes a matrix storage tank, an activator storage tank, a first high-pressure plunger pump, a second high-pressure plunger pump, a fluid heating and temperature control device, and a proppant addition tank; the matrix storage tank and the first high-pressure plunger pump are connected through a first pneumatic valve and a first connecting pipe; the activator storage tank and the second high-pressure plunger pump are connected through a second pneumatic valve and a second connecting pipe; the first high-pressure plunger pump is connected to the inlet of the fluid heating and temperature control device through a third pneumatic valve and a third connecting pipe for transporting the matrix injection source to the fluid heating and temperature control device; the second high-pressure plunger pump is connected to the inlet of the fluid heating and temperature control device through a fourth pneumatic valve and a fourth connecting pipe for transporting the activator injection source to the fluid heating and temperature control device; the fluid heating and temperature control device is connected to the top end inside the fracture of the rock sample through a fifth pneumatic valve, a sixth pneumatic valve and a fifth connecting pipe; the top end of the proppant addition tank is connected to the upper part of the fifth connecting pipe through a seventh pneumatic valve and a sixth connecting pipe, and the bottom end is connected to the lower part of the fifth connecting pipe through an eighth pneumatic valve and a seventh connecting pipe; the fifth pneumatic valve is between the fluid heating and temperature control device and the sixth connecting pipe; the sixth pneumatic valve is between the sixth connecting pipe and the seventh connecting pipe.

[0010] As a technical solution of this application, a first fluid pressure sensor is provided at the inlet of the fluid heating and temperature control device.

[0011] As a technical solution of the present application, a mass flow meter, a safety valve, a second fluid pressure sensor, and a first fluid temperature sensor are sequentially arranged on the fifth connecting pipe; the second fluid pressure sensor is used to monitor the pressure of the fluid in the fifth connecting pipe in real time; the first fluid temperature sensor is used to monitor the temperature of the fluid in the fifth connecting pipe in real time.

[0012] As a technical solution of the present application, the fluid backflow mechanism includes a fluid recovery tank; the fluid recovery tank is connected to the bottom inside of the crack of the rock sample through an eighth connecting pipe; a ninth pneumatic valve, a volume flow meter, a second fluid temperature sensor, a third fluid pressure sensor, and a pressure regulating valve are sequentially arranged on the eighth connecting pipe from near to far away from the rock sample; the third fluid pressure sensor is used to monitor the pressure of the fluid in the eighth connecting pipe in real time; the second fluid temperature sensor is used to monitor the temperature of the fluid in the eighth connecting pipe in real time; the pressure regulating valve is used to adjust the backflow pressure at the crack outlet of the rock sample in real time.

[0013] As a technical solution of the present application, the triaxial loading mechanism includes a sealing cylinder, an axial hydraulic transmission component, an upper sealing pad, a lower sealing pad, and a circumferential hydraulic transmission component; the rock sample is hermetically arranged in the pressure chamber of the sealing cylinder; the upper sealing pad is arranged on the top of the rock sample; the lower sealing pad is arranged at the bottom of the rock sample; one end of the axial hydraulic transmission component extends into the pressure chamber and is drivingly connected to the top of the upper sealing pad for applying axial pressure to the rock sample; the hydraulic end of the circumferential hydraulic transmission component is connected to the pressure chamber for injecting liquid into the pressure chamber to apply confining pressure to the rock sample.

[0014] As a technical solution of the present application, the sealing cylinder includes a cylinder body, an upper cover, a base, and a clamp; the cylinder body is fastened to the base through the clamp; the upper cover is covered on the top of the cylinder body.

[0015] As a technical solution of the present application, the axial hydraulic transmission component includes a first servo hydraulic pump, a ninth connecting pipe, an axial hydraulic actuator, and a pressure rod; the first servo hydraulic pump is connected to the axial hydraulic actuator through the ninth connecting pipe; the axial hydraulic actuator is drivingly connected to the top of the pressure rod; the top of the pressure rod extends out of the upper cover, and the lower part is hermetically clamped in the cylinder body and extends into the pressure chamber and is movably arranged on the top of the upper sealing pad up and down.

[0016] As a technical solution of the present application, the circumferential hydraulic transmission assembly includes a second servo hydraulic pump and a tenth connecting pipe; the second servo hydraulic pump is connected to the bottom of the pressure chamber through the tenth connecting pipe for injecting liquid into the pressure chamber.

[0017] As a technical solution of the present application, the rock sample is composed of two semi-cylinders, and has the crack penetrating the top and bottom and extending along the axial direction in the middle.

[0018] As a technical solution of the present application, the test result acquisition and analysis mechanism includes a fiber Bragg grating strain sensor, a high-pressure sealed fiber optic connector, a transmission optical fiber, a fiber Bragg grating demodulator, a CT ray source, a CT detector, and an electronic computer; the fiber Bragg grating strain sensors are evenly wound on the outer peripheral side of the rock sample, and the ends are led out through the high-pressure sealed fiber optic connectors and connected to the fiber Bragg grating demodulator through the transmission optical fiber; the fiber Bragg grating demodulator is used for demodulating the received optical signal and performing quasi-distributed measurement of the circumferential strain of the rock sample by means of wavelength division multiplexing; the CT ray source and the CT detector are respectively arranged on the opposite sides outside the triaxial loading mechanism at intervals, and the X-rays emitted by the CT ray source pass through the rock sample and are received by the CT detector to obtain the image of the distribution of the proppant in the crack of the rock sample; the electronic computer is respectively electrically connected to the fiber Bragg grating demodulator and the CT detector for receiving and storing the collected data.

[0019] As a technical solution of the present application, the arrangement direction of the fiber Bragg grating in the fiber Bragg grating strain sensor is set at an angle with the horizontal cross-section of the rock sample.

[0020] As a technical solution of the present application, the matrix includes supercritical carbon dioxide.

[0021] A comprehensive performance test method for a proppant for cracks, which is tested by using the comprehensive performance test device for a proppant for cracks described above, includes the following steps:

[0022] S1, installing the rock sample in the comprehensive performance test device for a proppant for cracks, and respectively applying confining pressure and axial pressure to the rock sample to make the rock sample reach the set triaxial stress state;

[0023] S2, injecting the proppant into the crack of the rock sample and making the proppant migrate in the crack;

[0024] S3, testing the flow conductivity of the proppant before expansion;

[0025] S4, exciting the proppant in the crack to make the proppant expand;

[0026] S5. Conduct a diversion performance test on the expanded proppant.

[0027] S6. Evaluate the diversion performance of the environmentally responsive self - expanding proppant.

[0028] As a technical solution of the present application, in step S1, it specifically includes the following steps:

[0029] S11. Before the test, cut the cylindrical rock into two symmetrical semi - cylinders, clean the two semi - cylinders and dry them in a drying oven.

[0030] S12. Install a lower sealing spacer on the base of the pressure chamber of the cylinder body of the triaxial loading mechanism, and lay a nylon filter screen with a mesh diameter smaller than the proppant particle size on the lower sealing spacer; piece the two semi - cylinders together to form the rock sample and install it on the lower sealing spacer, then install an upper sealing spacer on the top of the rock sample, and wrap a heat - shrinkable tube around the outside of the rock sample; connect the fluid injection mechanism to the inlet of the crack through the upper sealing spacer, and connect the fluid back - flow mechanism to the outlet of the crack through the lower sealing spacer.

[0031] S13. Wind and install a fiber - optic grating strain sensor on the outer peripheral side of the rock sample, lead out the fiber - optic grating strain sensor from the high - pressure sealed fiber - optic connectors respectively installed on the top and bottom of the base in sequence, and connect it to the fiber - optic grating demodulator through the transmission optical fiber; cover the top of the cylinder body with an upper cover for sealing the cylinder body, and install a pressure rod in the upper cover that is in transmission connection with the first servo - hydraulic pump in the triaxial loading mechanism, and the pressure rod extends into the pressure chamber and is on the top of the upper sealing spacer.

[0032] S14. Apply axial pressure to the rock sample through the first servo - hydraulic pump so that the pressure rod contacts the upper sealing spacer; inject silicone oil into the pressure chamber through the second servo - hydraulic pump in the triaxial loading mechanism to load the rock sample to the target confining pressure, and at the same time drive the axial hydraulic actuator connected to the first servo - hydraulic pump to continue loading the rock sample to the target axial pressure so that the rock sample is in the target triaxial stress state.

[0033] As a technical solution of the present application, in step S2, it specifically includes the following steps:

[0034] S21. Configure the environmentally responsive self - expanding proppant according to a pre - designed proppant injection plan and place it in the proppant addition tank in the fluid injection mechanism.

[0035] S22. Open the first pneumatic valve and the third pneumatic valve in the fluid injection mechanism, start the first high-pressure plunger pump in the fluid injection mechanism, and pump the liquid carbon dioxide in the matrix storage tank in the fluid injection mechanism into the fluid heating and temperature control device in the fluid injection mechanism to generate supercritical carbon dioxide at a specified temperature and pressure.

[0036] S23. Close the seventh pneumatic valve and the eighth pneumatic valve in the fluid injection mechanism, open the sixth pneumatic valve in the fluid injection mechanism, and close the ninth pneumatic valve in the fluid backflow mechanism; open the fifth pneumatic valve behind the fluid heating and temperature control device, and continuously inject supercritical carbon dioxide into the cracks of the rock sample until the reading of the second fluid pressure sensor in the fluid injection mechanism reaches the target value.

[0037] S24. Open the ninth pneumatic valve and adjust the pressure regulating valve in the fluid backflow mechanism so that the reading of the third fluid pressure sensor in the fluid backflow mechanism reaches the target value.

[0038] S25. Add the proppant to the proppant addition tank, open the seventh pneumatic valve and the eighth pneumatic valve so that the proppant is injected into the cracks along with the supercritical carbon dioxide.

[0039] S26. Continuously record the parameters measured by the mass flowmeter, the volume flowmeter, the second fluid pressure sensor, the third fluid pressure sensor, the first fluid temperature sensor, and the second fluid temperature sensor.

[0040] S27. Real-time monitor the circumferential strain of the rock sample through the fiber Bragg grating strain sensor in the test result acquisition and analysis mechanism, and convert the monitored data into the distribution W of the crack opening along the height of the rock sample according to the following formula f (z):

[0041] ;

[0042] In the formula: D is the diameter of the rock sample; ε o (z) is the distribution of the reading of the fiber Bragg grating strain sensor along the height of the rock sample, with the unit of 1; α is the angle between the distribution direction of the fiber Bragg grating in the fiber Bragg grating strain sensor and the horizontal cross-section of the rock sample.

[0043] S28. When the measured flow rate, fluid pressure, and fluid temperature reach complete stability, close the first high-pressure plunger pump, the first pneumatic valve, and the third pneumatic valve, and close the seventh pneumatic valve and the eighth pneumatic valve to evacuate the supercritical carbon dioxide in the cracks.

[0044] S29. Start the CT ray source in the test result acquisition and analysis mechanism to emit X-rays to scan the rock sample, receive and obtain the image of the proppant distribution in the fracture through the CT detector in the test result acquisition and analysis mechanism, and analyze to obtain the proppant distribution in the fracture.

[0045] As a technical solution of the present application, in step S3, it specifically includes the following steps:

[0046] S31. Pump liquid carbon dioxide into the fluid heating and temperature controller in the fluid injection mechanism through the first high-pressure plunger pump and the matrix storage tank in the fluid injection mechanism to generate supercritical carbon dioxide; close the seventh pneumatic valve and the eighth pneumatic valve in the fluid injection mechanism, and open the fifth pneumatic valve and the sixth pneumatic valve in the fluid injection mechanism; open the ninth pneumatic valve in the fluid return mechanism, and open the pressure regulating valve in the fluid return mechanism to the maximum so that the reading of the third fluid pressure sensor in the fluid return mechanism is 1 atmosphere, so that supercritical carbon dioxide flows through the fracture diverted by the proppant.

[0047] S32. Continuously record the parameters measured by the mass flowmeter, the volume flowmeter, the second fluid pressure sensor, the third fluid pressure sensor, the first fluid temperature sensor, and the second fluid temperature sensor; after the flow in the fracture is stable, if the reading of the volume flowmeter is q and the reading of the second fluid pressure sensor is p i , then the average conductivity of the fracture is calculated according to the following formula;

[0048] ;

[0049] In the formula: q is the reading of the volume flowmeter; μ is the kinematic viscosity of supercritical carbon dioxide, mPa·s; H is the height of the rock sample, cm; D is the diameter of the rock sample, cm; p i is the reading of the second fluid pressure sensor; p 0 is 101 kPa;

[0050] S33. Real-time monitor the circumferential strain of the rock sample through the fiber Bragg grating strain sensor in the test result acquisition and analysis mechanism, and convert the monitored data into the distribution W of the fracture aperture along the height of the rock sample according to the following formula f (z):

[0051] ;

[0052] In the formula: D is the diameter of the rock sample; ε o$(z)$ is the distribution of the readings of the fiber Bragg grating strain sensor along the height of the rock sample, with the unit of 1; $\alpha$ is the angle between the distribution direction of the fiber Bragg grating in the fiber Bragg grating strain sensor and the horizontal cross-section of the rock sample;

[0053] Then the average permeability $K$ of the fracture measured before the proppant expands f1 is calculated according to the following formula:

[0054] ;

[0055] In the formula: $F$ f is the average conductivity of the fracture; $H$ is the height of the rock sample; $W$ f $(z)$ is the distribution of the fracture aperture along the height of the rock sample; $z$ is the height coordinate of different positions of the rock sample.

[0056] As a technical solution of the present application, in step S4, it specifically includes the following steps:

[0057] S41, storing the pre-configured activator solution in the activator storage tank in the fluid injection mechanism;

[0058] S42, opening the second pneumatic valve and the fourth pneumatic valve in the fluid injection mechanism, starting the second high-pressure plunger pump in the fluid injection mechanism, and pumping the activator solution in the activator storage tank into the fluid heating and temperature controller in the fluid injection mechanism to make the activator solution reach the target pressure and temperature;

[0059] S43, closing the seventh pneumatic valve and the eighth pneumatic valve in the fluid injection mechanism, opening the fifth pneumatic valve and the sixth pneumatic valve in the fluid injection mechanism, and opening the ninth pneumatic valve in the fluid backflow mechanism, and continuously injecting the activator solution into the fracture to stimulate the expansion of the proppant in the fracture;

[0060] S44, continuously recording the parameters measured by the mass flowmeter, the volume flowmeter, the second fluid pressure sensor, the third fluid pressure sensor, the first fluid temperature sensor, and the second fluid temperature sensor;

[0061] S45, using the fiber Bragg grating strain sensor in the test result acquisition and analysis mechanism to continuously monitor the circumferential strain of the rock sample, and converting the monitored data into the distribution $W$ of the fracture aperture along the height of the rock sample according to the following formula f $(z)$:

[0062] ;

[0063] In the formula: $D$ is the diameter of the rock sample; $\varepsilon$ o$(z)$ is the distribution of the readings of the fiber Bragg grating strain sensor along the height of the rock sample, with the unit of 1; $\alpha$ is the angle between the distribution direction of the fiber Bragg grating in the fiber Bragg grating strain sensor and the horizontal cross-section of the rock sample;

[0064] S46. When the measured flow rate, fluid pressure, and fluid temperature reach complete stability, close the second high-pressure plunger pump, the second pneumatic valve, and the fourth pneumatic valve, stop the injection of the activator solution, and drain the activator solution in the rock sample;

[0065] S47. Start the CT ray source in the test result acquisition and analysis mechanism to emit X-rays to scan the rock sample, receive and obtain the image of the proppant distributed in the fracture through the CT detector in the test result acquisition and analysis mechanism, analyze and obtain the swelling condition of the proppant in the fracture and the change in the aperture of the fracture caused thereby, and compare and verify the analysis result with the monitoring result of the fiber Bragg grating strain sensor.

[0066] As a technical solution of the present application, in step S5, it specifically includes the following steps:

[0067] S51. Pump liquid carbon dioxide into the fluid heating and temperature controller in the fluid injection mechanism through the second high-pressure plunger pump and the matrix storage tank in the fluid injection mechanism to generate supercritical carbon dioxide; close the seventh pneumatic valve and the eighth pneumatic valve in the fluid injection mechanism, open the fifth pneumatic valve and the sixth pneumatic valve in the fluid injection mechanism, and open the ninth pneumatic valve in the fluid return mechanism, and open the pressure regulating valve in the fluid return mechanism to the maximum so that the reading of the third fluid pressure sensor in the fluid return mechanism is 1 atmospheric pressure, so that the supercritical carbon dioxide flows through the fracture diverted by the proppant;

[0068] S52. Continuously record the parameters measured by the mass flowmeter, the volume flowmeter, the second fluid pressure sensor, the third fluid pressure sensor, the first fluid temperature sensor, and the second fluid temperature sensor; after the flow in the fracture is stable, if the reading of the volume flowmeter is q and the reading of the second fluid pressure sensor is p i , then the average conductivity of the fracture is calculated according to the following formula;

[0069] ;

[0070] In the formula: q is the reading of the volume flowmeter; $\mu$ is the kinematic viscosity of supercritical carbon dioxide, mPa·s; H is the height of the rock sample, cm; D is the diameter of the rock sample, cm; p i is the reading of the second fluid pressure sensor; p 0is 101 kPa;

[0071] S53, the circumferential strain of the rock sample is monitored in real time through the fiber Bragg grating strain sensor in the test result acquisition and analysis mechanism, and the data monitored is converted into the distribution W of the crack opening along the height of the rock sample according to the following formula f (z):

[0072] ;

[0073] In the formula: D is the diameter of the rock sample; ε o (z) is the distribution of the fiber Bragg grating strain sensor readings along the height of the rock sample, with the unit of 1; α is the angle between the distribution direction of the fiber Bragg grating in the fiber Bragg grating strain sensor and the horizontal cross-section of the rock sample;

[0074] Then the average permeability K of the crack measured after the proppant expands f2 is calculated according to the following formula:

[0075] ;

[0076] In the formula: F f is the average conductivity of the crack; H is the height of the rock sample; W f (z) is the distribution of the crack opening along the height of the rock sample; z is the height coordinate of different positions of the rock sample.

[0077] As a technical solution of the present application, in step S6, if the average permeability of the crack measured before the proppant expands is K f1 , and the crack permeability measured after the proppant expands is K f2 , then the change in the proppant conductivity performance before and after expansion is:

[0078] ;

[0079] The conductivity performance of the environmentally responsive self-expanding proppant is evaluated according to the obtained change data of the proppant conductivity performance before and after expansion.

[0080] Advantages of the present application:

[0081] (1) The present application provides a comprehensive performance testing device for proppants for fractures. Through a fluid injection mechanism, a fluid backflow mechanism, a triaxial loading mechanism, and a test result acquisition and analysis mechanism, this device can achieve a comprehensive test of the in-fracture migration, expansion, and conductivity of self-expanding proppants. It applies axial pressure and confining pressure to the cut-in-half cylindrical rock samples through the triaxial loading mechanism to simulate the triaxial stress state borne by deep underground reservoirs and fractures. At the same time, during the proppant migration test, the fluid injection mechanism is used to regulate the pressure and temperature of the matrix and carry the proppants into the fractures of the rock samples, and the fluid backflow mechanism is used to adjust and control the backflow pressure at the fracture outlet to simulate the migration of proppants in fractures in actual engineering. During the proppant expansion test, an activator is injected into the fractures of the rock samples through the fluid injection mechanism to stimulate the expansion of the proppants and simulate the effect of proppant expansion on fractures in actual engineering. During the comprehensive performance test, the test result acquisition and analysis mechanism is used to collect, store, and process data and images to monitor the distribution and expansion of proppants in fractures, and observe the distribution of the fracture aperture of the rock samples along the height, so as to evaluate the change in the conductivity of proppants before and after expansion.

[0082] (2) The present application provides a comprehensive performance testing method for proppants for fractures. This method can achieve the effects of temperature-pressure control and injection of proppants, activators, and conductive fluids during the three different test stages of proppant migration, expansion, and conductivity. It can monitor the distribution of the fracture aperture along the height, the distribution and expansion of proppants in fractures, and evaluate the change in the conductivity of proppants before and after expansion. This method realizes a comprehensive test of the in-fracture migration, expansion, and conductivity performance of self-expanding proppants. During the proppant migration test, the fluid injection mechanism is used to regulate the pressure and temperature of the matrix and carry the proppants into the fractures of the rock samples, and the fluid backflow mechanism is used to adjust and control the backflow pressure at the fracture outlet to simulate the migration of proppants in fractures in actual engineering. During the proppant expansion test, an activator is injected into the fractures of the rock samples through the fluid injection mechanism to stimulate the expansion of the proppants and simulate the effect of proppant expansion on fractures in actual engineering. During the comprehensive performance test, the test result acquisition and analysis mechanism is used to collect, store, and process data and images to monitor the distribution and expansion of proppants in fractures, and observe the distribution of the fracture aperture of the rock samples along the height, so as to evaluate the change in the conductivity of proppants before and after expansion. Description of the Drawings

[0083] To more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and thus should not be regarded as a limitation of the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0084] Figure 1 Schematic diagram of the comprehensive performance test device for proppants for fractures provided by the first embodiment of the present application;

[0085] Figure 2 Schematic diagram of rock sample processing provided by the second embodiment of the present application;

[0086] Figure 3 Schematic diagram of the steps of the comprehensive performance test method for proppants for fractures provided by the second embodiment of the present application.

[0087] Icons: 1 - Rock sample; 2 - Matrix storage tank; 3 - Accelerator storage tank; 4 - First high-pressure piston pump; 5 - Second high-pressure piston pump; 6 - Fluid heating temperature controller; 7 - Proppant addition tank; 8 - Mass flowmeter; 9 - First pneumatic valve; 10 - Second pneumatic valve; 11 - Third pneumatic valve; 12 - Fourth pneumatic valve; 13 - Fifth pneumatic valve; 14 - Sixth pneumatic valve; 15 - Seventh pneumatic valve; 16 - Eighth pneumatic valve; 17 - Ninth pneumatic valve; 18 - First fluid pressure sensor; 19 - Safety valve; 20 - Second fluid pressure sensor; 21 - First fluid temperature sensor; 22 - Fluid recovery tank; 23 - Volume flowmeter; 24 - Second fluid temperature sensor; 25 - Third fluid pressure sensor; 26 - Pressure regulating valve; 27 - Upper sealing pad; 28 - Lower sealing pad; 29 - Cylinder body; 30 - Upper cover; 31 - Base; 32 - Clamp; 33 - Axial hydraulic actuator; 34 - Pressure rod; 35 - Servo hydraulic source; 36 - Fiber Bragg grating strain sensor; 37 - High-pressure sealed fiber optic connector; 38 - Transmission optical fiber; 39 - Fiber Bragg grating demodulator; 40 - CT ray source; 41 - CT detector; 42 - Electronic computer; 43 - First connecting pipe; 44 - Second connecting pipe; 45 - Third connecting pipe; 46 - Fourth connecting pipe; 47 - Fifth connecting pipe; 48 - Sixth connecting pipe; 49 - Seventh connecting pipe; 50 - Eighth connecting pipe; 51 - Ninth connecting pipe; 52 - Tenth connecting pipe. Detailed implementation manners

[0088] To make the objectives, technical solutions and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this application. Apparently, the described embodiments are some but not all of the embodiments of this application. Components of the embodiments of this application generally described and illustrated in the figures herein may be arranged and designed in a variety of different configurations.

[0089] Therefore, the detailed description of the embodiments of this application provided in the drawings is not intended to limit the scope of this application which is claimed, but is merely representative of selected embodiments of this application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of this application without creative efforts shall fall within the scope of protection of this application.

[0090] It should be noted that like reference numerals and letters denote like items in the following figures. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0091] In the description of this application, it should be noted that the orientation or positional relationship indicated by terms such as "upper", "lower", etc. is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the inventive product is customarily placed during use. It is only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of this application.

[0092] In addition, in this application, unless otherwise clearly specified and limited, the first feature being above or below the second feature may include the first and second features being in direct contact, or may include the first and second features not being in direct contact but being in contact through additional features therebetween. Moreover, the first feature being above, on top of and over the second feature includes the first feature being directly above and diagonally above the second feature, or merely indicating that the first feature has a higher horizontal height than the second feature. The first feature being below, beneath and under the second feature includes the first feature being directly below and diagonally below the second feature, or merely indicating that the first feature has a lower horizontal height than the second feature.

[0093] In addition, terms such as "horizontal" and "vertical" do not mean that the components are required to be absolutely horizontal or hanging, but may be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but may be slightly inclined.

[0094] In the description of the present application, it should also be noted that unless otherwise clearly specified and defined, the terms "arranged", "connected", and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0095] First Embodiment:

[0096] Please refer to Figure 1 , the present application provides a comprehensive performance testing device for proppants for fractures, which can realize the comprehensive testing of the in-fracture migration, expansion, and flow conductivity of self-expanding proppants; it mainly includes a fluid injection mechanism, a fluid backflow mechanism, a triaxial loading mechanism, and a test result acquisition and analysis mechanism; wherein, the fluid injection mechanism is connected to the fracture in the rock sample 1 sealed in the triaxial loading mechanism, and is used to inject matrix, proppant, and activator into the fracture in the rock sample 1 respectively. The matrix is used to transport the proppant into the fracture in the rock sample 1, and the activator is used to stimulate the expansion of the proppant; at the same time, the fluid backflow mechanism is connected to the fracture in the rock sample 1 and is used to store the fluid after it flows back from the fracture in the rock sample 1; and, the rock sample 1 is sealed in the triaxial loading mechanism, and the triaxial loading mechanism is used to apply axial pressure and confining pressure to the rock sample 1 respectively to simulate the triaxial stress state borne by the deep underground reservoir and the fracture; in addition, the test result acquisition and analysis mechanism is used to collect data and images during the comprehensive performance testing of the proppant to analyze and evaluate the change in the flow conductivity of the proppant before and after expansion. And, the matrix can be supercritical carbon dioxide.

[0097] It should be noted that it respectively applies axial pressure and confining pressure to the cylindrical rock sample 1 cut in half through a triaxial loading mechanism to simulate the triaxial stress state borne by deep underground reservoirs and fractures. At the same time, it designs a set of fluid injection mechanism and fluid backflow mechanism, which can realize the temperature-pressure control and injection of proppant, activator, and diversion fluid respectively in three different test stages of proppant migration, expansion, and diversion. At the same time, during the proppant migration test, it regulates the pressure and temperature of the matrix through the fluid injection mechanism and carries the proppant into the fracture of the rock sample 1, and adjusts and controls the backflow pressure at the fracture outlet through the fluid backflow mechanism to simulate the migration of proppant in the fracture in actual engineering. During the proppant expansion test, it injects the activator into the fracture of the rock sample 1 through the fluid injection mechanism to stimulate the expansion of the proppant and simulate the effect of proppant expansion on the fracture in actual engineering. During the comprehensive performance test, it collects, stores, and processes data and images through the test result acquisition and analysis mechanism to monitor the distribution and expansion of the proppant in the fracture and observe the distribution of the fracture aperture of the rock sample 1 along the height, so as to evaluate the change in the proppant diversion performance before and after expansion. And it establishes a set of test result acquisition and analysis mechanism, which can monitor the distribution of the fracture aperture along the height through the fiber Bragg grating strain sensor 36 and monitor the distribution and expansion of the proppant in the fracture through CT scanning, correct the calculation formula of the average fracture permeability based on the change in the aperture, and finally evaluate the change in the proppant diversion performance before and after expansion.

[0098] Furthermore, the fluid injection mechanism includes a matrix storage tank 2, an activator storage tank 3, a first high-pressure plunger pump 4, a second high-pressure plunger pump 5, a fluid heating and temperature controller 6, and a proppant addition tank 7; the matrix storage tank 2 and the first high-pressure plunger pump 4 are connected through a first pneumatic valve 9 and a first connecting pipe 43; the activator storage tank 3 and the second high-pressure plunger pump 5 are connected through a second pneumatic valve 10 and a second connecting pipe 44; the first high-pressure plunger pump 4 is connected to the inlet of the fluid heating and temperature controller 6 through a third pneumatic valve 11 and a third connecting pipe 45 for delivering a matrix injection source to the fluid heating and temperature controller 6; the second high-pressure plunger pump 5 is connected to the inlet of the fluid heating and temperature controller 6 through a fourth pneumatic valve 12 and a fourth connecting pipe 46 for delivering an activator injection source to the fluid heating and temperature controller 6; and, a first fluid pressure sensor 18 is provided at the inlet of the fluid heating and temperature controller 6; the fluid heating and temperature controller 6 is connected to the top end inside the crack of the rock sample 1 through a fifth pneumatic valve 13, a sixth pneumatic valve 14, and a fifth connecting pipe 47; the top end of the proppant addition tank 7 is connected to the upper part of the fifth connecting pipe 47 through a seventh pneumatic valve 15 and a sixth connecting pipe 48, and the bottom end is connected to the lower part of the fifth connecting pipe 47 through an eighth pneumatic valve 16 and a seventh connecting pipe 49; the fifth pneumatic valve 13 is between the fluid heating and temperature controller 6 and the sixth connecting pipe 48; the sixth pneumatic valve 14 is between the sixth connecting pipe 48 and the seventh connecting pipe 49. And, a mass flow meter 8, a safety valve 19, a second fluid pressure sensor 20, and a first fluid temperature sensor 21 are sequentially provided on the fifth connecting pipe 47; the second fluid pressure sensor 20 is used to monitor the pressure of the fluid in the fifth connecting pipe 47 in real time; the first fluid temperature sensor 21 is used to monitor the temperature of the fluid in the fifth connecting pipe 47 in real time.

[0099] Therefore, the matrix injection source and the activator injection source are connected in parallel and then connected to the fluid heating and temperature controller 6 with a first fluid pressure sensor 18 in front, and then discharged by the fifth pneumatic valve 13; then connected to a parallel pipeline jointly constituted by a seventh pneumatic valve 15, an eighth pneumatic valve 16, a proppant addition tank 7, and a sixth pneumatic valve 14, and then connected to the crack of the rock sample 1 in the pressure chamber of the triaxial loading mechanism after passing through a mass flow meter 8, a second fluid pressure sensor 20, and a first fluid temperature sensor 21.

[0100] It should be noted that the first high-pressure plunger pump 4 and the second high-pressure plunger pump 5 can continuously inject water, carbon dioxide, and various acid-base solutions within the range of 0-80 MPa; in the fluid heating and temperature control device 6, the coil can be heated by a water bath, and the constant temperature heating of the water in the cabin is controlled by the heater and the electric thermostat therein, thereby adjusting the temperature of the fluid flowing through the coil, and the temperature adjustment range is from room temperature to 100 °C; the first fluid pressure sensor 18 and the safety valve 19 can monitor the pressure of the pipeline fluid in real time, and the measurement ranges of both are 0-100 MPa, and the accuracy is ±0.5%; the second temperature sensor can monitor the temperature of the pipeline fluid in real time, the measurement range is -50-300 °C, and the accuracy is ±0.5%.

[0101] Furthermore, the fluid backflow mechanism includes a fluid recovery tank 22; wherein, the fluid recovery tank 22 is connected to the bottom inside of the crack of the rock sample 1 through an eighth connecting pipe 50; at the same time, a ninth pneumatic valve 17, a volumetric flowmeter 23, a second fluid temperature sensor 24, a third fluid pressure sensor 25, and a pressure regulating valve 26 are sequentially arranged on the eighth connecting pipe 50 from near to far away from the rock sample 1; in addition, the third fluid pressure sensor 25 is used to monitor the pressure of the fluid in the eighth connecting pipe 50 in real time; the second fluid temperature sensor 24 is used to monitor the temperature of the fluid in the eighth connecting pipe 50 in real time; the pressure regulating valve 26 is used to adjust the backflow pressure at the crack outlet of the rock sample 1 in real time.

[0102] After the fluid flows back from the rock sample 1 in the pressure chamber of the triaxial loading system, it is discharged into the fluid recovery tank 22 through the ninth pneumatic valve 17, the volumetric flowmeter 23, the third fluid pressure sensor 25, the second fluid temperature sensor 24, and the pressure regulating valve 26. The ninth pneumatic valve 17 controls whether the fluid in the rock sample 1 is discharged; the third fluid pressure sensor 25 can monitor the pressure of the pipeline fluid in real time, and its measurement range is 0-100 MPa, and the accuracy is ±0.5%; and, its second temperature sensor can monitor the temperature of the pipeline fluid in real time, and its measurement range is -50-300 °C, and the accuracy is ±0.5%; the pressure regulating valve 26 can adjust the backflow pressure at the crack outlet in real time, and its adjustment range upper limit is the upstream injection pressure, and the lower limit is 0; in addition, the fluid recovery tank 22 is used to store the fluid flowing back from the rock sample 1.

[0103] Furthermore, the triaxial loading mechanism includes a sealing cylinder, a servo hydraulic source 35, an axial hydraulic transmission assembly, an upper sealing cushion block 27, a lower sealing cushion block 28, and a circumferential hydraulic transmission assembly; wherein, the sealing cylinder includes a cylinder body 29, an upper cover 30, a base 31, and a clamp 32, and its cylinder body 29 is fastened to the base 31 through the clamp 32; the upper cover 30 is covered on the top of the cylinder body 29; the rock sample 1 is composed of two semi-cylinders and has a crack penetrating the top and bottom and extending axially in the middle, and the rock sample 1 is hermetically arranged in the pressure chamber of the sealing cylinder; at the same time, the upper sealing cushion block 27 is arranged on the top of the rock sample 1; the lower sealing cushion block 28 is arranged at the bottom of the rock sample 1; the fifth connecting pipe 47 passes through the bottom and top of the base 31 and extends into the pressure chamber, and passes through the top middle of the upper sealing pad from one side of the upper sealing pad and is connected to the top of the crack; the eighth connecting pipe 50 passes through the bottom and top of the base 31 and extends into the pressure chamber, and passes through the top middle of the lower sealing pad from one side of the lower sealing pad and is connected to the bottom of the crack; in addition, the servo hydraulic source 35 is respectively hydraulically connected to the axial hydraulic transmission assembly and the circumferential hydraulic transmission assembly; one end of the axial hydraulic transmission assembly extends into the pressure chamber and is drivingly connected to the top of the upper sealing cushion block 27 for applying axial pressure to the rock sample 1; and, the hydraulic end of the circumferential hydraulic transmission assembly is connected to the pressure chamber for injecting liquid into the pressure chamber to apply confining pressure to the rock sample 1.

[0104] The axial hydraulic transmission assembly includes a first servo hydraulic pump, a ninth connecting pipe 51, an axial hydraulic actuator 33, and a pressure rod 34; the servo hydraulic source 35 is connected to the first servo hydraulic pump, and the first servo hydraulic pump is connected to the axial hydraulic actuator 33 through the ninth connecting pipe 51; the axial hydraulic actuator 33 is drivingly connected to the top of the pressure rod 34; the top of the pressure rod 34 extends out of the upper cover 30, and the lower part is hermetically clamped in the cylinder body 29 and extends into the pressure chamber and is movably arranged on the top of the upper sealing pad.

[0105] The circumferential hydraulic transmission assembly includes a second servo hydraulic pump and a tenth connecting pipe 52; the servo hydraulic source 35 is connected to the second servo hydraulic pump; the second servo hydraulic pump is connected to the bottom of the pressure chamber through the tenth connecting pipe 52 for injecting liquid into the pressure chamber.

[0106] It should be noted that the servo hydraulic source 35 is powered by an independent first servo hydraulic pump and a second servo hydraulic pump respectively to provide axial pressure and confining pressure. The first servo hydraulic pump applies axial pressure to the rock sample 1 in the pressure chamber through the axial hydraulic actuator 33 and the pressure rod 34. The second servo hydraulic pump injects silicone oil into the pressure chamber through the hydraulic pipeline of the base 31 to apply confining pressure to the rock sample 1. The upper cover 30, the cylinder 29, the clamp 32 and the base 31 can ensure the high-pressure sealing of the pressure chamber. The upper sealing pad 27 and the lower sealing pad 28 can ensure the uniformity of axial pressure loading, and they are respectively connected to the fluid injection mechanism and the fluid backflow mechanism to realize the injection and discharge of the fluid in the rock sample 1. In addition, the maximum axial loading force of the triaxial loading mechanism is 2000 kN, the maximum confining pressure is 70 MPa, and the control accuracy is less than ±1%. The installable rock sample 1 is a cylinder with a size of Φ100 mm×200 mm.

[0107] Furthermore, the test result acquisition and analysis mechanism includes a fiber Bragg grating strain sensor 36, a high-pressure sealed fiber optic connector 37, a transmission optical fiber 38, a fiber Bragg grating demodulator 39, a CT ray source 40, a CT detector 41 and a computer 42. The fiber Bragg grating strain sensor 36 is evenly wound around the outer peripheral side of the rock sample 1, and the end is led out through the high-pressure sealed fiber optic connector 37 on the base 31 and connected to the fiber Bragg grating demodulator 39 through the transmission optical fiber 38. The fiber Bragg grating demodulator 39 is used to demodulate the received optical signal and perform quasi-distributed measurement of the circumferential strain of the rock sample 1 by means of wavelength division multiplexing. The measurement range is 0 - 10000 με, and the measurement accuracy is ±10 με. The CT ray source 40 and the CT detector 41 form an in-situ CT scanning device with a minimum spatial resolution of 1 μm. The CT ray source 40 and the CT detector 41 are respectively arranged at intervals on the opposite outer sides of the cylinder 29, and the X-rays emitted by the CT ray source 40 pass through the rock sample 1 and are received by the CT detector 41. Based on the gray value differences of different materials, a high-precision image of the distribution of the proppant in the cracks of the rock sample 1 can be obtained. The computer 42 is electrically connected to the fiber Bragg grating demodulator 39 and the CT detector 41 respectively, and is used to receive and store the collected data and perform subsequent processing and analysis.

[0108] It should be noted that the arrangement direction of the fiber Bragg grating in the fiber Bragg grating strain sensor 36 is set at an angle to the horizontal cross-section of the rock sample 1.

[0109] Second Embodiment:

[0110] Please refer to Figure 2 and, in conjunction with reference to Figure 1 and Figure 3, this application provides a comprehensive performance test method for proppants for fractures, which can comprehensively test the migration, expansion, and conductivity performance of self-expanding proppants in the fractures of rock sample 1 under triaxial stress state; this method mainly uses the comprehensive performance test device for proppants for fractures in the first embodiment for testing, including the following steps:

[0111] S1. Install rock sample 1 in the comprehensive performance test device for proppants for fractures, and apply confining pressure and axial pressure to rock sample 1 respectively to make rock sample 1 reach the set triaxial stress state;

[0112] S2. Inject proppants into the fracture of rock sample 1 and make the proppants migrate in the fracture;

[0113] S3. Test the conductivity performance of the proppants before expansion;

[0114] S4. Stimulate the proppants in the fracture to make the proppants expand;

[0115] S5. Test the conductivity performance of the proppants after expansion;

[0116] S6. Evaluate the conductivity performance of the environmentally responsive self-expanding proppants.

[0117] In step S1, mainly install rock sample 1 in the triaxial loading mechanism and load confining pressure and axial pressure to make it reach the specified triaxial stress state; it specifically includes the following steps:

[0118] S11. Before the test, cut a Φ100mm×200mm cylindrical rock symmetrically into two semi-cylinders along its longitudinal direction from the diameter direction, and the cut surface is the fracture; clean the two semi-cylinders and dry them in a 70°C drying oven for 12h;

[0119] S12. Install the lower sealing pad 28 on the base 31 of the pressure chamber of the cylinder body 29 of the triaxial loading mechanism, and lay a nylon filter screen with a mesh diameter smaller than the proppant particle size on the lower sealing pad 28; piece the two semi-cylinders together to form rock sample 1 and install it on the lower sealing pad 28, then install the upper sealing pad 27 on the top of rock sample 1, and wrap a heat shrinkable tube outside rock sample 1 to isolate the confining pressure silicone oil; connect the fifth connecting pipe 47 to the inlet of the fracture through the upper sealing pad 27, and connect the eighth connecting pipe 50 to the outlet of the fracture through the lower sealing pad 28; check the airtightness of the fluid pipeline section by section through the first pneumatic valve 9, the second pneumatic valve 10, the third pneumatic valve 11, the fourth pneumatic valve 12, the fifth pneumatic valve 13, the sixth pneumatic valve 14, the seventh pneumatic valve 15, the eighth pneumatic valve 16, the first fluid pressure sensor 18, the second fluid pressure sensor 20, and the third fluid pressure sensor 25 to ensure that the entire fluid pipeline has good sealing;

[0120] S13. Wind and install the fiber Bragg grating strain sensor 36 on the outer peripheral side of the rock sample 1, with the fiber Bragg grating at an angle α to the horizontal plane; lead out the fiber Bragg grating strain sensor 36 from the high-pressure sealed fiber optic connectors 37 respectively installed on the top and bottom of the base 31 in sequence, and connect it to the fiber Bragg grating demodulator 39 via the transmission optical fiber 38; install the upper cover 30 for sealing the cylinder body 29 on the top of the cylinder body 29, install a pressure rod 34 in the upper cover 30 which is drivingly connected to the first servo hydraulic pump in the triaxial loading mechanism, the pressure rod 34 extends into the pressure chamber and is on the top of the upper sealing pad 27, and tighten the clamp 32 to ensure good sealing of the pressure chamber;

[0121] S14. First apply a small axial pressure (0.5 MPa) to the rock sample 1 through the first servo hydraulic pump to make the pressure rod 34 contact the upper sealing pad 27; inject silicone oil into the pressure chamber through the second servo hydraulic pump in the triaxial loading mechanism to load the rock sample 1 to the target confining pressure, and at the same time drive the axial hydraulic actuator 33 connected to the first servo hydraulic pump to continue loading the rock sample 1 to the target axial pressure, so that the rock sample 1 is in the target triaxial stress state.

[0122] In step S2, it is mainly to inject proppants into the rock sample 1, monitor the migration of proppants and their effects on the cracks of the rock sample 1. Here, the matrix carrying proppants is taken as supercritical carbon dioxide as an example; it specifically includes the following steps:

[0123] S21. Configure the environmentally responsive self-expanding proppants according to the pre-designed proppant injection scheme and place them in the proppant addition tank 7 in the fluid injection mechanism;

[0124] S22. Open the first pneumatic valve 9 and the third pneumatic valve 11 in the fluid injection mechanism, start the first high-pressure plunger pump 4 in the fluid injection mechanism, pump the liquid carbon dioxide in the matrix storage tank 2 in the fluid injection mechanism into the fluid heating and temperature control device 6 in the fluid injection mechanism, and at the same time start heating and adjust the temperature to generate supercritical carbon dioxide at the specified temperature and pressure;

[0125] S23. Close the seventh pneumatic valve 15 and the eighth pneumatic valve 16 in the fluid injection mechanism, open the sixth pneumatic valve 14 in the fluid injection mechanism, and close the ninth pneumatic valve 17 in the fluid backflow mechanism; open the fifth pneumatic valve 13 behind the fluid heating and temperature control device 6, and continuously inject supercritical carbon dioxide into the cracks of the rock sample 1 until the reading of the second fluid pressure sensor 20 in the fluid injection mechanism reaches the target value;

[0126] S24. Open the ninth pneumatic valve 17 and adjust the pressure regulating valve 26 in the fluid backflow mechanism to make the reading of the third fluid pressure sensor 25 in the fluid backflow mechanism reach the target value;

[0127] S25, Add proppant into the proppant addition tank 7, and then open the seventh pneumatic valve 15 and the eighth pneumatic valve 16 to inject the proppant into the fracture along with supercritical carbon dioxide;

[0128] S26, Continuously record the parameters measured by the mass flowmeter 8, the volume flowmeter 23, the second fluid pressure sensor 20, the third fluid pressure sensor 25, the first fluid temperature sensor 21, and the second fluid temperature sensor 24;

[0129] S27, Use the fiber Bragg grating strain sensor 36 in the test result acquisition and analysis mechanism to monitor the circumferential strain of the rock sample 1 in real time, and convert the monitored data into the distribution W of the fracture aperture along the height of the rock sample 1 according to the following formula f (z):

[0130] ;

[0131] In the formula: D is the diameter of the rock sample 1, which is generally 10 cm for this device; ε o (z) is the distribution of the fiber Bragg grating strain sensor 36 reading along the height of the rock sample 1, with the unit of 1; α is the angle between the distribution direction of the fiber Bragg grating in the fiber Bragg grating strain sensor 36 and the horizontal cross-section of the rock sample 1;

[0132] S28, When the measured flow rate, fluid pressure, and fluid temperature reach complete stability, it indicates that the distribution of the proppant in the fracture of the rock sample 1 has reached stability. Close the first high-pressure piston pump 4, the first pneumatic valve 9, and the third pneumatic valve 11, and close the seventh pneumatic valve 15 and the eighth pneumatic valve 16 to evacuate the supercritical carbon dioxide in the fracture. At this time, the proppant is embedded in the rock sample 1 on both sides of the fracture due to the confining pressure, providing support for the fracture;

[0133] S29, Start the CT ray source 40 in the test result acquisition and analysis mechanism to emit X-rays to scan the rock sample 1, receive the high-precision image of the proppant distribution in the fracture through the CT detector 41 in the test result acquisition and analysis mechanism, and analyze the distribution of the proppant in the fracture.

[0134] In step S3, it is mainly used to test the conductivity of the proppant before expansion, and specifically includes the following steps:

[0135] S31. Pump liquid carbon dioxide into the fluid heating and temperature control device 6 in the fluid injection mechanism through the first high-pressure plunger pump 4 and the matrix storage tank 2 in the fluid injection mechanism to generate supercritical carbon dioxide. Close the seventh pneumatic valve 15 and the eighth pneumatic valve 16 in the fluid injection mechanism, and open the fifth pneumatic valve 13 and the sixth pneumatic valve 14 in the fluid injection mechanism. Open the ninth pneumatic valve 17 in the fluid backflow mechanism, and open the pressure regulating valve 26 in the fluid backflow mechanism to the maximum so that the reading of the third fluid pressure sensor 25 in the fluid backflow mechanism is 1 atmosphere, so that the supercritical carbon dioxide flows through the fractures diverted by the proppant.

[0136] S32. Continuously record the parameters measured by the mass flowmeter 8, the volume flowmeter 23, the second fluid pressure sensor 20, the third fluid pressure sensor 25, the first fluid temperature sensor 21, and the second fluid temperature sensor 24. After the flow in the fracture is stable, if the reading of the volume flowmeter 23 is q (unit: cm 3 / s), and the reading of the second fluid pressure sensor 20 is p i (unit: kPa), then the average conductivity of the fracture (unit: μm 2 ·cm) is calculated according to the following formula;

[0137] ;

[0138] Where: q is the reading of the volume flowmeter 23; μ is the kinematic viscosity of supercritical carbon dioxide, mPa·s; H is the height of the rock sample 1, generally 20 cm for this device; D is the diameter of the rock sample 1, generally 10 cm for this device; p i is the reading of the second fluid pressure sensor 20; p 0 is 101 kPa;

[0139] S33. Real-time monitor the circumferential strain of the rock sample 1 through the fiber Bragg grating strain sensor 36 in the test result acquisition and analysis mechanism, and convert the monitored data into the distribution W f (z) of the fracture aperture along the height of the rock sample 1 according to the following formula:

[0140] ;

[0141] Where: D is the diameter of the rock sample 1; ε o (z) is the distribution of the reading of the fiber Bragg grating strain sensor 36 along the height of the rock sample 1, unit: 1; α is the included angle between the distribution direction of the fiber Bragg grating in the fiber Bragg grating strain sensor 36 and the horizontal cross-section of the rock sample 1;

[0142] Then the average permeability K f1 (unit μm 2 ) of the fracture measured before the proppant expands is calculated according to the following formula:

[0143] ;

[0144] In the formula: F f is the average fracture conductivity; H is the height of the rock sample 1; W f (z) is the distribution of the fracture aperture along the height of the rock sample 1; z is the height coordinate of different positions of the rock sample 1.

[0145] In step S4, it mainly injects the activator solution into the rock sample 1 to stimulate the environmentally responsive self - expanding proppant to expand, and monitors the expansion of the proppant and the evolution process of the fractures in the rock sample 1 caused thereby; specifically, it includes the following steps:

[0146] S41, store the pre - configured activator solution in the activator storage tank 3 in the fluid injection mechanism;

[0147] S42, open the second pneumatic valve 10 and the fourth pneumatic valve 12 in the fluid injection mechanism, start the second high - pressure piston pump 5 in the fluid injection mechanism, pump the activator solution in the activator storage tank 3 into the fluid heating and temperature controller 6 in the fluid injection mechanism, and at the same time start heating and adjust the temperature so that the activator solution reaches the target pressure and temperature;

[0148] S43, close the seventh pneumatic valve 15 and the eighth pneumatic valve 16 in the fluid injection mechanism, open the fifth pneumatic valve 13 and the sixth pneumatic valve 14 in the fluid injection mechanism, and open the ninth pneumatic valve 17 in the fluid back - flow mechanism, and continuously inject the activator solution into the fracture to stimulate the expansion of the proppant in the fracture;

[0149] S44, continuously record the parameters measured by the mass flowmeter 8, the volume flowmeter 23, the second fluid pressure sensor 20, the third fluid pressure sensor 25, the first fluid temperature sensor 21, and the second fluid temperature sensor 24;

[0150] S45, use the fiber - Bragg grating strain sensor 36 in the test result acquisition and analysis mechanism to continuously monitor the circumferential strain of the rock sample 1, and convert the monitored data into the distribution of the fracture aperture along the height of the rock sample 1, W f (z) as follows:

[0151] ;

[0152] In the formula: D is the diameter of the rock sample 1, generally 10 cm for this device; ε o (z) is the distribution of the readings of the fiber - Bragg grating strain sensor 36 along the height of the rock sample 1, with the unit of 1; α is the angle between the distribution direction of the fiber - Bragg grating in the fiber - Bragg grating strain sensor 36 and the horizontal cross - section of the rock sample 1;

[0153] S46. When the measured flow rate, fluid pressure, and fluid temperature reach complete stability, indicating that the proppant no longer expands, the fracture of the rock sample 1 no longer changes, and the overall reaches stability, close the second high-pressure plunger pump 5, the second pneumatic valve 10, and the fourth pneumatic valve 12, stop the injection of the activator solution, and drain the activator solution in the rock sample 1.

[0154] S47. Start the CT ray source 40 in the test result acquisition and analysis mechanism to emit X-rays to scan the rock sample 1. Receive and obtain a high-precision image of the distribution of the proppant in the fracture through the CT detector 41 in the test result acquisition and analysis mechanism. Analyze and obtain the expansion situation of the proppant in the fracture and the change in the aperture of the fracture caused by it, and compare and verify the analysis result with the monitoring result of the fiber Bragg grating strain sensor 36.

[0155] In step S5, its main purpose is to test the conductivity of the proppant after expansion. Still choose supercritical carbon dioxide as the conductive fluid here, which specifically includes the following steps:

[0156] S51. Pump liquid carbon dioxide into the fluid heating and temperature control device 6 in the fluid injection mechanism through the second high-pressure plunger pump 5 and the matrix storage tank 2 in the fluid injection mechanism to generate supercritical carbon dioxide; close the seventh pneumatic valve 15 and the eighth pneumatic valve 16 in the fluid injection mechanism, open the fifth pneumatic valve 13 and the sixth pneumatic valve 14 in the fluid injection mechanism, and open the ninth pneumatic valve 17 in the fluid return mechanism. Open the pressure regulating valve 26 in the fluid return mechanism to the maximum so that the reading of the third fluid pressure sensor 25 in the fluid return mechanism is 1 atmosphere, that is, p o = 101 kPa, so that supercritical carbon dioxide flows through the fracture diverted by the proppant;

[0157] S52. Continuously record the parameters measured by the mass flowmeter 8, the volume flowmeter 23, the second fluid pressure sensor 20, the third fluid pressure sensor 25, the first fluid temperature sensor 21, and the second fluid temperature sensor 24; after the flow in the fracture is stable, if the reading of the volume flowmeter 23 is q and the reading of the second fluid pressure sensor 20 is p i , then the average conductivity of the fracture is calculated according to the following formula;

[0158] ;

[0159] In the formula: q is the reading of the volume flowmeter 23; μ is the kinematic viscosity of supercritical carbon dioxide, mPa·s; H is the height of the rock sample 1, cm; D is the diameter of the rock sample 1, cm; p i is the reading of the second fluid pressure sensor 20; p 0 is 101 kPa;

[0160] S53. The circumferential strain of the rock sample 1 is monitored in real time by the fiber Bragg grating strain sensor 36 in the test result acquisition and analysis mechanism, and the data monitored is converted into the distribution W of the crack opening along the height of the rock sample 1 according to the following formula f (z):

[0161] ;

[0162] In the formula: D is the diameter of the rock sample 1; ε o (z) is the distribution of the readings of the fiber Bragg grating strain sensor 36 along the height of the rock sample 1, with the unit of 1; α is the angle between the distribution direction of the fiber Bragg grating in the fiber Bragg grating strain sensor 36 and the horizontal cross-section of the rock sample 1;

[0163] Then the average permeability K of the crack measured after the proppant expands f2 is calculated according to the following formula:

[0164] ;

[0165] In the formula: F f is the average conductivity of the crack; H is the height of the rock sample 1; W f (z) is the distribution of the crack opening along the height of the rock sample 1; z is the height coordinate of different positions of the rock sample 1.

[0166] In step S6, if the average permeability of the crack measured before the proppant expands is K f1 and the permeability of the crack measured after the proppant expands is K f2 , then the change in the proppant conductivity before and after expansion is:

[0167] ;

[0168] Evaluate the conductivity of the environmentally responsive self-expanding proppant according to the obtained change data of the proppant conductivity before and after expansion.

[0169] Therefore, this method realizes the comprehensive test of the in - seam migration, expansion and conductivity performance of self - expanding proppants; during the proppant migration test, the pressure and temperature of the matrix are regulated through the fluid injection mechanism and the proppants are carried into the fracture of rock sample 1, and the back - flow pressure at the fracture outlet is regulated and controlled through the fluid back - flow mechanism to simulate the migration of proppants in the fracture in actual engineering; during the proppant expansion test, an activator is injected into the fracture of rock sample 1 through the fluid injection mechanism to stimulate the expansion of the proppants and simulate the effect of proppant expansion on the fracture in actual engineering; during the comprehensive performance test, data and images are collected, stored and processed through the test result acquisition and analysis mechanism to monitor the distribution and expansion of proppants in the fracture, and to observe the distribution of the fracture aperture of rock sample 1 along the height, so as to evaluate the change in the conductivity performance of proppants before and after expansion.

[0170] The above are only the preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A method for testing the comprehensive performance of a proppant for a fracture, characterized in that: A comprehensive performance testing device for crack proppant is used for testing, and the comprehensive performance testing device for crack proppant comprises a fluid injection mechanism, a fluid return mechanism, a triaxial loading mechanism and a test result collection and analysis mechanism; the fluid injection mechanism is connected to the crack in the rock sample sealed in the triaxial loading mechanism, and is used to inject matrix, proppant and stimulant into the crack in the rock sample respectively, the matrix is ​​used to transport the proppant to the crack in the rock sample, and the stimulant is used to stimulate the expansion of the proppant; the fluid return mechanism is connected to the crack in the rock sample, and is used to store the fluid returned from the crack in the rock sample; the rock sample is sealed in the triaxial loading mechanism, and the triaxial loading mechanism is used to apply axial pressure and confining pressure to the rock sample respectively, so as to simulate the triaxial stress state borne by deep underground reservoirs and cracks; The test result collection and analysis mechanism is used to collect data and images during the proppant comprehensive performance test process to analyze and evaluate changes in the proppant conductivity before and after expansion; The method for testing the comprehensive performance of a fracture proppant comprises the following steps: S1, installing the rock sample in the comprehensive performance testing device for the fracture proppant, and applying confining pressure and axial pressure to the rock sample respectively, so that the rock sample reaches a set triaxial stress state; S2, injecting the proppant into the crack of the rock sample and allowing the proppant to migrate in the crack; which specifically includes the following steps: S21, configuring the environmentally responsive self-expanding proppant according to a pre-designed proppant injection scheme, and placing the proppant in the fluid injection mechanism into a proppant addition tank; S22, opening the first pneumatic valve and the third pneumatic valve in the fluid injection mechanism, starting the first high-pressure plunger pump in the fluid injection mechanism, and pumping the liquid carbon dioxide in the matrix storage tank in the fluid injection mechanism into the fluid heating temperature controller in the fluid injection mechanism to generate supercritical carbon dioxide at a specified temperature and pressure; S23, closing the seventh pneumatic valve and the eighth pneumatic valve in the fluid injection mechanism, opening the sixth pneumatic valve in the fluid injection mechanism, and closing the ninth pneumatic valve in the fluid return mechanism; opening the fifth pneumatic valve after the fluid heating temperature controller, and continuously injecting supercritical carbon dioxide into the cracks of the rock sample until the reading of the second fluid pressure sensor in the fluid injection mechanism reaches the target value; S24, opening the ninth pneumatic valve, and adjusting the pressure regulating valve in the fluid return mechanism so that the reading of the third fluid pressure sensor in the fluid return mechanism reaches the target value; S25, adding the proppant into the proppant adding tank, opening the seventh pneumatic valve and the eighth pneumatic valve, so that the proppant is injected into the fracture along with the supercritical carbon dioxide; S26, continuously recording the parameters measured by the mass flow meter, the volume flow meter, the second fluid pressure sensor, the third fluid pressure sensor, the first fluid temperature sensor, and the second fluid temperature sensor; S27, the circumferential strain of the rock sample is monitored in real time by the fiber Bragg grating strain sensor in the test result collection and analysis mechanism, and the monitored data is converted into the distribution of the crack opening along the height of the rock sample according to the following formula W f (z): ； Where: D is the diameter of the rock sample; ε o (z) is the distribution of the fiber Bragg grating strain sensor readings along the height of the rock sample, with the unit of 1; α is the angle between the distribution direction of the fiber Bragg grating in the fiber Bragg grating strain sensor and the horizontal cross section of the rock sample; S28, when the measured flow rate, fluid pressure and fluid temperature are completely stable, closing the first high-pressure plunger pump, the first pneumatic valve and the third pneumatic valve, and closing the seventh pneumatic valve and the eighth pneumatic valve to exhaust the supercritical carbon dioxide in the fracture; S29, starting the CT ray source in the test result acquisition and analysis mechanism to emit X-rays to scan the rock sample, receiving and obtaining an image of the distribution of the proppant in the fracture through the CT detector in the test result acquisition and analysis mechanism, and analyzing and obtaining the distribution of the proppant in the fracture; S3, performing a conductivity test on the proppant before expansion; S4, stimulating the proppant in the fracture to cause the proppant to expand; S5, performing a conductivity test on the expanded proppant; S6, evaluating the conductivity of the environmentally responsive self-expanding proppant.

2. The method for testing comprehensive properties of crack proppants according to claim 1, characterized in that: The fluid injection mechanism comprises a matrix storage tank, an exciter storage tank, a first high-pressure plunger pump, a second high-pressure plunger pump, a fluid heating temperature controller and a proppant adding tank; the matrix storage tank and the first high-pressure plunger pump are connected through a first pneumatic valve and a first connecting pipe; the exciter storage tank and the second high-pressure plunger pump are connected through a second pneumatic valve and a second connecting pipe; the first high-pressure plunger pump is connected to the inlet of the fluid heating temperature controller through a third pneumatic valve and a third connecting pipe, for conveying a matrix injection source to the fluid heating temperature controller; the second high-pressure plunger pump is connected to the inlet of the fluid heating temperature controller through a fourth pneumatic valve and a fourth connecting pipe. connected to the inlet of the fluid heating thermostat, used for conveying an activator injection source to the fluid heating thermostat; the fluid heating thermostat is connected to the top of the crack of the rock sample through the fifth pneumatic valve, the sixth pneumatic valve and the fifth connecting pipe; the top of the proppant adding tank is connected to the upper part of the fifth connecting pipe through the seventh pneumatic valve and the sixth connecting pipe, and the bottom end is connected to the lower part of the fifth connecting pipe through the eighth pneumatic valve and the seventh connecting pipe; the fifth pneumatic valve is between the fluid heating thermostat and the sixth connecting pipe; the sixth pneumatic valve is between the sixth connecting pipe and the seventh connecting pipe.

3. The method for testing comprehensive properties of crack proppants according to claim 2, characterized in that: A first fluid pressure sensor is arranged at the inlet of the fluid heating temperature controller.

4. The method for testing comprehensive properties of fracture proppants according to claim 2, characterized in that: The fifth connecting pipe is provided with a mass flow meter, a safety valve, a second fluid pressure sensor and a first fluid temperature sensor in sequence; the second fluid pressure sensor is used to monitor the pressure of the fluid in the fifth connecting pipe in real time; the first fluid temperature sensor is used to monitor the temperature of the fluid in the fifth connecting pipe in real time.

5. The method for testing comprehensive properties of fracture proppants according to claim 1, characterized in that: The fluid return mechanism includes a fluid recovery tank; the fluid recovery tank is connected to the bottom of the crack of the rock sample through an eighth connecting pipe; the eighth connecting pipe is provided with a ninth pneumatic valve, a volume flow meter, a second fluid temperature sensor, a third fluid pressure sensor and a pressure regulating valve in sequence from close to to away from the rock sample; the third fluid pressure sensor is used to monitor the pressure of the fluid in the eighth connecting pipe in real time; the second fluid temperature sensor is used to monitor the temperature of the fluid in the eighth connecting pipe in real time; the pressure regulating valve is used to adjust the return pressure at the crack outlet of the rock sample in real time.

6. The method for testing comprehensive properties of fracture proppants according to claim 1, characterized in that: The three-axis loading mechanism includes a sealing cylinder, an axial hydraulic transmission assembly, an upper sealing pad, a lower sealing pad and a circumferential hydraulic transmission assembly; the rock sample is sealed in a pressure chamber of the sealing cylinder; the upper sealing pad is arranged on the top of the rock sample; the lower sealing pad is arranged at the bottom of the rock sample; one end of the axial hydraulic transmission assembly extends into the pressure chamber and is transmission-connected to the top of the upper sealing pad for applying axial pressure to the rock sample; the hydraulic end of the circumferential hydraulic transmission assembly is connected to the pressure chamber for injecting liquid into the pressure chamber to apply confining pressure to the rock sample.

7. The method for testing comprehensive properties of fracture proppants according to claim 6, characterized in that: The sealing cylinder comprises a cylinder body, an upper cover, a base and a clamp; the cylinder body is fastened to the base through the clamp; and the upper cover is arranged on the top of the cylinder body.

8. The method for testing comprehensive properties of fracture proppants according to claim 7, characterized in that: The axial hydraulic transmission assembly includes a first servo hydraulic pump, a ninth connecting pipe, an axial hydraulic transmission and a pressure rod; the first servo hydraulic pump is connected to the axial hydraulic transmission through the ninth connecting pipe; the axial hydraulic transmission is transmission-connected to the top of the pressure rod; the top of the pressure rod extends out of the upper cover, and the lower seal is clamped in the cylinder and extends into the pressure chamber and is movably arranged on the top of the upper sealing gasket.

9. The method for testing comprehensive properties of fracture proppants according to claim 7, characterized in that: The circumferential hydraulic transmission assembly includes a second servo hydraulic pump and a tenth connecting pipe; the second servo hydraulic pump is connected to the bottom of the pressure chamber through the tenth connecting pipe, and is used to inject liquid into the pressure chamber.

10. The method for testing comprehensive properties of fracture proppants according to claim 1, characterized in that: The rock sample is composed of two semi-cylinders, and has a crack in the middle which penetrates through the top and bottom and extends in the axial direction.

11. The method for testing comprehensive properties of fracture proppants according to claim 1, characterized in that: The test result collection and analysis mechanism includes a fiber grating strain sensor, a high-pressure sealed fiber optic connector, a transmission fiber, a fiber grating demodulator, a CT ray source, a CT detector and an electronic computer; the fiber grating strain sensor is evenly wound on the outer peripheral side of the rock sample, and the end is led out through the high-pressure sealed fiber optic connector and connected to the fiber grating demodulator through the transmission fiber; the fiber grating demodulator is used to demodulate the received optical signal and perform quasi-distributed measurement of the annular strain of the rock sample by wavelength division multiplexing; the CT ray source and the CT detector are respectively arranged at intervals outside the opposite sides of the three-axis loading mechanism, and the X-rays emitted by the CT ray source pass through the rock sample and are received by the CT detector to obtain an image of the distribution of the proppant in the cracks of the rock sample; the electronic computer is electrically connected to the fiber grating demodulator and the CT detector respectively, and is used to receive and store the collected data.

12. The method for testing comprehensive properties of fracture proppants according to claim 11, characterized in that: The arrangement direction of the fiber Bragg grating in the fiber Bragg grating strain sensor is set at an angle to the horizontal cross section of the rock sample.

13. The method for testing comprehensive properties of fracture proppants according to claim 1, characterized in that: The matrix includes supercritical carbon dioxide.

14. The method for testing comprehensive properties of fracture proppants according to claim 1, characterized in that: In step S1, the following steps are specifically included: S11, before the test, the cylindrical rock is cut into two symmetrical semi-cylinders, and the two semi-cylinders are cleaned and placed in a drying oven for drying; S12, installing a lower sealing pad on the base of the pressure chamber of the cylinder of the triaxial loading mechanism, laying a nylon filter with a mesh diameter smaller than the particle size of the proppant on the lower sealing pad; assembling the two semi-cylinders into the rock sample and installing it on the lower sealing pad, then installing an upper sealing pad on the top of the rock sample, and wrapping a heat shrink tube on the outside of the rock sample; connecting the fluid injection mechanism to the inlet of the fracture through the upper sealing pad, and connecting the fluid return mechanism to the outlet of the fracture through the lower sealing pad; S13, winding and installing a fiber Bragg grating strain sensor on the outer peripheral side of the rock sample, leading out the fiber Bragg grating strain sensor from the high-pressure sealed fiber connectors respectively installed on the top and bottom of the base in sequence, and connecting it to a fiber Bragg grating demodulator via a transmission optical fiber; providing an upper cover for sealing the cylinder body on the top of the cylinder body, installing a pressure rod in transmission connection with the first servo hydraulic pump in the three-axis loading mechanism in the upper cover, and the pressure rod extending into the pressure chamber and being located on the top of the upper sealing pad; S14, applying axial pressure to the rock sample through the first servo hydraulic pump so that the pressure rod contacts the upper sealing pad; injecting silicone oil into the pressure chamber through the second servo hydraulic pump in the triaxial loading mechanism to load the rock sample to the target confining pressure, and at the same time driving the axial hydraulic transmission connected to the first servo hydraulic pump to continue loading the rock sample to the target axial pressure, so that the rock sample is in a target triaxial stress state.

15. The method for testing comprehensive properties of fracture proppants according to claim 1, characterized in that: In step S3, the following steps are specifically included: S31, pumping liquid carbon dioxide into the fluid heating temperature controller in the fluid injection mechanism through the first high-pressure plunger pump and the matrix storage tank in the fluid injection mechanism to generate supercritical carbon dioxide; closing the seventh pneumatic valve and the eighth pneumatic valve in the fluid injection mechanism, and opening the fifth pneumatic valve and the sixth pneumatic valve in the fluid injection mechanism; opening the ninth pneumatic valve in the fluid return mechanism, and opening the pressure regulating valve in the fluid return mechanism to the maximum so that the reading of the third fluid pressure sensor in the fluid return mechanism is 1 atmosphere, so that the supercritical carbon dioxide flows through the fracture guided by the proppant; S32, continuously record the parameters measured by the mass flow meter, the volume flow meter, the second fluid pressure sensor, the third fluid pressure sensor, the first fluid temperature sensor, and the second fluid temperature sensor; after the flow in the fracture stabilizes, if the reading of the volume flow meter is q, the reading of the second fluid pressure sensor is p i , then the average conductivity of the crack is calculated as follows; ； Where: q is the reading of the volume flow meter; μ is the kinematic viscosity of supercritical carbon dioxide, mPa·s; H is the height of the rock sample, cm; D is the diameter of the rock sample, cm; p i is the reading of the second fluid pressure sensor; p0 is 101 kPa; S33, the circumferential strain of the rock sample is monitored in real time by the fiber Bragg grating strain sensor in the test result collection and analysis mechanism, and the monitored data is converted into the distribution of the crack opening along the height of the rock sample according to the following formula: f (z): ； Where: D is the diameter of the rock sample; ε o (z) is the distribution of the fiber Bragg grating strain sensor readings along the height of the rock sample, with the unit of 1; α is the angle between the distribution direction of the fiber Bragg grating in the fiber Bragg grating strain sensor and the horizontal cross section of the rock sample; The average permeability K of the fracture measured before the proppant expansion is f1 Calculate as follows: ； Where: F f is the average conductivity of the fracture; H is the height of the rock sample; W f (z) is the distribution of the fracture opening along the height of the rock sample; z is the height coordinate of different positions of the rock sample.

16. The method for testing comprehensive properties of fracture proppants according to claim 1, characterized in that: In step S4, the following steps are specifically included: S41, storing the pre-configured activator solution in the activator storage tank in the fluid injection mechanism; S42, opening the second pneumatic valve and the fourth pneumatic valve in the fluid injection mechanism, starting the second high-pressure plunger pump in the fluid injection mechanism, and pumping the activator solution in the activator storage tank into the fluid heating temperature controller in the fluid injection mechanism, so that the activator solution reaches the target pressure and temperature; S43, closing the seventh pneumatic valve and the eighth pneumatic valve in the fluid injection mechanism, opening the fifth pneumatic valve and the sixth pneumatic valve in the fluid injection mechanism, and opening the ninth pneumatic valve in the fluid flowback mechanism, and continuously injecting the stimulant solution into the fracture to stimulate the expansion of the proppant in the fracture; S44, continuously recording the parameters measured by the mass flow meter, the volume flow meter, the second fluid pressure sensor, the third fluid pressure sensor, the first fluid temperature sensor, and the second fluid temperature sensor; S45, the circumferential strain of the rock sample is monitored in real time by the fiber Bragg grating strain sensor in the test result collection and analysis mechanism, and the monitored data is converted into the distribution of the crack opening along the height of the rock sample according to the following formula: f (z): ； Where: D is the diameter of the rock sample; ε o (z) is the distribution of the fiber Bragg grating strain sensor readings along the height of the rock sample, with the unit of 1; α is the angle between the distribution direction of the fiber Bragg grating in the fiber Bragg grating strain sensor and the horizontal cross section of the rock sample; S46, when the measured flow rate, fluid pressure and fluid temperature are completely stable, closing the second high-pressure plunger pump, the second pneumatic valve and the fourth pneumatic valve, stopping the injection of the activator solution, and draining the activator solution in the rock sample; S47, start the CT ray source in the test result acquisition and analysis mechanism to emit X-rays to scan the rock sample, receive and obtain the image of the distribution of the proppant in the crack through the CT detector in the test result acquisition and analysis mechanism, analyze and obtain the expansion of the proppant in the crack and the resulting change in the opening of the crack, and compare and verify the analysis result with the monitoring result of the fiber grating strain sensor.

17. The method for testing comprehensive properties of fracture proppants according to claim 1, characterized in that: In step S5, the following steps are specifically included: S51, pumping liquid carbon dioxide into the fluid heating temperature controller in the fluid injection mechanism through the second high-pressure plunger pump and the matrix storage tank in the fluid injection mechanism to generate supercritical carbon dioxide; closing the seventh pneumatic valve and the eighth pneumatic valve in the fluid injection mechanism, opening the fifth pneumatic valve and the sixth pneumatic valve in the fluid injection mechanism, and opening the ninth pneumatic valve in the fluid return mechanism, opening the pressure regulating valve in the fluid return mechanism to the maximum so that the reading of the third fluid pressure sensor in the fluid return mechanism is 1 atmosphere, so that the supercritical carbon dioxide flows through the fracture guided by the proppant; S52, continuously record the parameters measured by the mass flow meter, the volume flow meter, the second fluid pressure sensor, the third fluid pressure sensor, the first fluid temperature sensor, and the second fluid temperature sensor; after the flow in the fracture stabilizes, if the reading of the volume flow meter is q, the reading of the second fluid pressure sensor is p i , then the average conductivity of the crack is calculated as follows; ； Where: q is the reading of the volume flow meter; μ is the kinematic viscosity of supercritical carbon dioxide, mPa·s; H is the height of the rock sample, cm; D is the diameter of the rock sample, cm; p i is the reading of the second fluid pressure sensor; p0 is 101 kPa; S53, the circumferential strain of the rock sample is monitored in real time by the fiber Bragg grating strain sensor in the test result collection and analysis mechanism, and the monitored data is converted into the distribution of the crack opening along the height of the rock sample according to the following formula: f (z): ； Where: D is the diameter of the rock sample; ε o (z) is the distribution of the fiber Bragg grating strain sensor readings along the height of the rock sample, with the unit of 1; α is the angle between the distribution direction of the fiber Bragg grating in the fiber Bragg grating strain sensor and the horizontal cross section of the rock sample; Then the average permeability K of the fracture measured after the proppant expands is f2 Calculate as follows: ； Where: F f is the average conductivity of the fracture; H is the height of the rock sample; W f (z) is the distribution of the fracture opening along the height of the rock sample; z is the height coordinate of different positions of the rock sample.

18. The method for testing comprehensive properties of fracture proppants according to claim 1, characterized in that: In step S6, if the average permeability of the fracture measured before the proppant expansion is K f1 The fracture permeability measured after the proppant expands is K f2 , then the change of the proppant conductivity before and after expansion is: ； The conductivity of the environmentally responsive self-expanding proppant is evaluated based on the obtained data on the change in the conductivity of the proppant before and after expansion.

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