Supercritical carbon dioxide composite fracturing experimental device and experimental method

Abstract

The application provides a supercritical carbon dioxide composite fracturing experimental device and an experimental method. The experimental device comprises a core holder and a carbon dioxide supply device. The core holder comprises a clamping mechanism and a pressure applying mechanism. The clamping mechanism comprises a left core chamber and a right core chamber. The pressure applying mechanism is used for applying pressure to a rock sample between the left core chamber and the right core chamber. The left end face of the right core chamber is provided with a preflush injection port. The carbon dioxide supply device is in communication with the preflush injection port. The right end face of the left core chamber is provided with a preflush discharge port. The left core chamber is further provided with a fracturing fluid injection port. The space between the left core chamber and the right core chamber is in communication with the fracturing fluid injection port. The fracturing fluid injection port can inject fracturing fluid into the space between the left core chamber and the right core chamber, thereby solving the technical problem that it is difficult to completely simulate supercritical CO2 composite fracturing under a laboratory scale.

Description

Technical Field

[0001] The present invention relates to the technical field of unconventional oil and gas production, and in particular to a supercritical carbon dioxide composite fracturing experimental device and an experimental method. Background Art

[0002] Hydraulic fracturing is a key method for the economic development of low- and ultra-low-permeability reservoirs. It is essential for the development of shale oil reservoirs. However, current shale oil fracturing suffers from disadvantages such as water sensitivity, significant water consumption, and associated pollution. CO2 waterless fracturing technology can enable the efficient development of low-pressure-sensitive oil and gas reservoirs. Supercritical CO2 fracturing, a form of waterless fracturing, can be applied to the development of shale oil, shale gas, and coalbed methane. Compared to other conventional fracturing fluids, supercritical CO2 has stronger solubility, diffusion, and permeability. Its fracture pressure is 30%-80% of that of other fracturing fluids, and the specific energy required for rock fracture is 20%-50% of that of other methods. Supercritical CO2 offers significant advantages for fracturing shale.

[0003] Combining the advantages of supercritical CO2 fracturing and hydraulic fracturing, supercritical CO2 hybrid fracturing leverages supercritical CO2's low surface tension, low viscosity, high diffusion coefficient, and low damage rate during the pre-fracturing phase to create a branching fracture network and enhance energy and efficiency. Hydraulic fracturing is then used to create primary fractures and improve the fracture network's conductivity, thereby increasing the stimulated volume, increasing crude oil mobility, and near-wellbore formation pressure, effectively utilizing shale oil and boosting reservoir production. Supercritical CO2 pre-injection can effectively reduce the uniaxial compressive and tensile strength of reservoir rock and create new micropores and microcracks. During the supercritical CO2 injection process, the CO2 reacts with certain minerals in the presence of formation water, forming large corrosion pores. Furthermore, due to long-term corrosion, existing fractures gradually expand, creating new fractures and leading to a sharp decrease in rock strength.

[0004] In supercritical CO2 composite fracturing, supercritical CO2 is first injected, and then water-based fracturing fluid is injected for fracturing. Currently, during the research and development process, there are technical problems that make it difficult to fully simulate actual oil field development at a laboratory scale. Summary of the Invention

[0005] The purpose of the present invention is to provide a supercritical carbon dioxide composite fracturing experimental device and experimental method to alleviate the technical problem that it is difficult to fully simulate supercritical CO2 composite fracturing at a laboratory scale.

[0006] The above-mentioned purpose of the present invention can be achieved by adopting the following technical solutions:

[0007] The present invention provides a supercritical carbon dioxide composite fracturing experimental device, comprising: a core holder and a carbon dioxide supply device, wherein the core holder comprises a clamping mechanism and a pressure mechanism, wherein the clamping mechanism comprises a left core chamber and a right core chamber, wherein the clamping mechanism is capable of fixing a rock sample between the left core chamber and the right core chamber, and wherein the pressure mechanism is used to apply pressure to the rock sample between the left core chamber and the right core chamber;

[0008] The left end face of the right core chamber is provided with a pre-fluid injection port, and the carbon dioxide supply device is connected to the pre-fluid injection port; the right end face of the left core chamber is provided with a pre-fluid discharge port, and the left core chamber is also provided with a fracturing fluid injection port, and the space between the left core chamber and the right core chamber is connected to the fracturing fluid injection port, and the fracturing fluid injection port can inject fracturing fluid into the space between the left core chamber and the right core chamber.

[0009] In a preferred embodiment, the pressure-applying mechanism includes an outer cylinder and a rubber sleeve, the two ends of the rubber sleeve are respectively sleeved outside the left core chamber and the right core chamber, and the rubber sleeve is arranged in the outer cylinder, and a confining pressure annulus is provided between the outer wall of the rubber sleeve and the outer cylinder.

[0010] In a preferred embodiment, the left core chamber and the right core chamber are respectively sleeved with tapered sleeves; the rubber sleeve includes a central portion and an end portion, the outer diameter of the end portion is larger than the outer diameter of the central portion, the end portion is sleeved outside the tapered sleeve, and the central portion is sleeved outside the left core chamber and the right core chamber.

[0011] In a preferred embodiment, the pressure mechanism includes a limiting mechanism, an axial pressure cylinder and an axial pressure piston. The limiting mechanism is connected to the left core chamber to prevent the left core chamber from moving to the left. The axial pressure piston is installed on the axial pressure cylinder and connected to the right core chamber to drive the right core chamber to move to the left.

[0012] In a preferred embodiment, the prepad injection port is disposed at the center of the right core chamber, and the prepad discharge port is offset from the center of the left core chamber.

[0013] In a preferred embodiment, the fracturing fluid injection port includes a fracturing fluid injection channel and a fracturing pipe, the fracturing fluid injection channel is connected to the fracturing pipe, the fracturing pipe is installed on the right end face of the left core chamber, and the fracturing pipe at least partially extends to the space between the left core chamber and the right core chamber.

[0014] In a preferred embodiment, the fracturing tube is disposed at the center of the left core chamber.

[0015] In a preferred embodiment, the core holder comprises a plug, and the plug is provided with fracturing holes, seepage holes and radial grooves.

[0016] In a preferred embodiment, the carbon dioxide supply device includes a carbon dioxide gas cylinder, a booster pump and a constant temperature water bath.

[0017] The present invention provides a supercritical carbon dioxide composite fracturing experimental method, which adopts the above-mentioned supercritical carbon dioxide composite fracturing experimental device. The experimental method comprises: injecting supercritical carbon dioxide into the rock sample through the pre-fluid injection port; and injecting fracturing fluid into the rock sample through the fracturing fluid injection port.

[0018] The characteristics and advantages of the present invention are:

[0019] During the experiment, a pressure mechanism was used to simulate formation stress conditions. Supercritical carbon dioxide was injected into the rock sample through the pre-fluid injection port and discharged from the pre-fluid discharge port, achieving pre-injection of supercritical carbon dioxide. The fracturing fluid injection port was used to inject post-water-based fracturing fluid, allowing fluid injection at both ends to achieve pre-injection supercritical CO2 injection and post-water-based fracturing fluid fracturing, simulating an integrated process of pre-injection supercritical CO2 and fracturing in oil and gas reservoirs. The actual simulated formation state remained unchanged during the experiment. The pre-fluid injection port allowed for pre-injection of supercritical CO2 under simulated formation conditions to study the effects of supercritical CO2 on reservoir properties. After the pre-injection of supercritical CO2, the fracturing fluid injection port and the pre-fluid discharge port allowed for in-situ hydraulic fracturing under the same simulated formation conditions, simulating an integrated process of pre-injection supercritical CO2 and fracturing in oil and gas reservoirs, conforming to the operating conditions of actual oil and gas field development, and thus ensuring more realistic and accurate experimental results. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0021] Figure 1 A schematic diagram of the structure of the supercritical carbon dioxide composite fracturing experimental device provided by the present invention;

[0022] Figure 2 A schematic diagram of the clamping mechanism in the supercritical carbon dioxide composite fracturing experimental device provided by the present invention;

[0023] Figure 3 This is a schematic diagram of the structure of the plug in the supercritical carbon dioxide composite fracturing experimental device provided by the present invention;

[0024] Figure 4 This is a schematic diagram of the carbon dioxide supply device in the supercritical carbon dioxide composite fracturing experimental device provided by the present invention.

[0025] Description of Figure Numbers:

[0026] 10. Core holder; 11. Heating tile;

[0027] 21, left ventricle; 22, right ventricle;

[0028] 311. Pre-fluid injection port; 312. Pre-fluid discharge pipe;

[0029] 32. Fracturing fluid injection port; 321. Fracturing fluid injection channel; 322. Fracturing pipe;

[0030] 41. Outer cylinder; 411. Confining pressure annulus;

[0031] 42. Rubber sleeve; 421. Center portion; 422. End portion; 423. Tapered portion;

[0032] 43. Taper sleeve;

[0033] 50. Limiting mechanism; 51. Left pressure cap; 52. Spacer;

[0034] 61, axial pressure cylinder; 611, piston chamber; 62, axial pressure piston;

[0035] 71. First O-ring; 73. Second O-ring;

[0036] 72. Plug; 721. Fracturing hole; 722. Seepage hole; 723. Radial groove;

[0037] 80. Carbon dioxide supply device; 81. Carbon dioxide cylinder; 82. Booster pump; 83. Constant temperature water bath;

[0038] 84. Back pressure valve. DETAILED DESCRIPTION

[0039] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0040] The reservoir transformation mechanism of pre-supercritical CO2 composite fracturing includes: first, supercritical CO2 is injected into the formation to influence the reservoir and form a complex fracture network; then different types of fracturing fluids carrying proppants are injected into the fracture network in sequence to perform hydraulic sand fracturing to expand and support the fracture network, thereby achieving the effects of complex fracture network volume transformation, effective fracture network support, and formation energy enhancement in the formation, especially shale reservoirs.

[0041] In order to further study the characteristics of supercritical CO2 composite fracturing, the inventors developed a supercritical carbon dioxide composite fracturing experimental device and a supercritical carbon dioxide composite fracturing experimental method.

[0042] Option 1

[0043] The present invention provides a supercritical carbon dioxide composite fracturing experimental device, such as Figure 1-Figure 2 As shown, the experimental device includes: a core clamp 10 and a carbon dioxide supply device 80, the core clamp 10 includes a clamping mechanism and a pressure mechanism, the clamping mechanism includes a left core chamber 21 and a right core chamber 22, the clamping mechanism can fix the rock sample between the left core chamber 21 and the right core chamber 22, and the pressure mechanism is used to apply pressure to the rock sample between the left core chamber 21 and the right core chamber 22; the left end face of the right core chamber 22 is provided with a pre-fluid injection port 311, and the carbon dioxide supply device 80 is connected to the pre-fluid injection port 311; the right end face of the left core chamber 21 is provided with a pre-fluid discharge port, and the left core chamber 21 is also provided with a fracturing fluid injection port 32, the space between the left core chamber 21 and the right core chamber 22 is connected to the fracturing fluid injection port 32, and the fracturing fluid injection port 32 can inject fracturing fluid into the space between the left core chamber 21 and the right core chamber 22.

[0044] During the experiment, a rock sample was installed between the left core chamber 21 and the right core chamber 22, and a pressure mechanism was used to simulate formation stress conditions. Supercritical carbon dioxide was injected into the rock sample through the pre-fluid injection port 311 and discharged through the pre-fluid discharge port, achieving pre-injection of supercritical carbon dioxide. The fracturing fluid injection port 32 was used to inject post-injection water-based fracturing fluid. Fluid injection at both ends allowed for pre-injection supercritical CO2 and post-injection water-based fracturing fluid fracturing, simulating an integrated process of pre-injection supercritical CO2 and fracturing in an oil and gas reservoir. The actual state of the simulated formation remained unchanged during the experiment, resulting in more realistic and accurate experimental results.

[0045] Through this supercritical carbon dioxide composite fracturing experimental device, the pre-fluid injection port 311 can be used to perform pre-supercritical CO2 injection under simulated formation conditions to study the impact of supercritical CO2 on reservoir properties; the fracturing fluid injection port 32 and the pre-fluid discharge port can be used to perform in-situ hydraulic fracturing under the same simulated formation conditions after the pre-supercritical CO2 injection is completed, simulating the integrated process of pre-supercritical CO2 injection and fracturing in oil and gas reservoirs, which meets the operating conditions of actual oil and gas field development.

[0046] A pre-fluid injection port 311 is provided at one end of the core holder 10, and a fracturing fluid injection port 32 and a pre-fluid discharge port are provided at the other end. Fluid can be injected at both ends to realize pre-supercritical CO2 injection + post-water-based fracturing fluid fracturing, simulating the pre-supercritical CO2 injection-fracturing integrated process of oil and gas reservoirs.

[0047] like Figure 1 and Figure 2 As shown, the pressure-applying mechanism includes an outer cylinder 41 and a rubber sleeve 42. The two ends of the rubber sleeve 42 are respectively sleeved outside the left core chamber 21 and the right core chamber 22. The rubber sleeve 42 is disposed within the outer cylinder 41, and a confining pressure annulus 411 is defined between the outer wall of the rubber sleeve 42 and the outer cylinder 41. A rock sample is installed between the left core chamber 21 and the right core chamber 22. The rubber sleeve 42 surrounds the rock sample. High-pressure fluid is injected into the confining pressure annulus 411, and the rubber sleeve 42 exerts confining pressure on the rock sample, simulating the confining pressure conditions of the formation.

[0048] Furthermore, a tapered sleeve 43 is respectively provided outside the left core chamber 21 and the right core chamber 22; the rubber sleeve 42 includes a central portion 421 and an end portion 422, the outer diameter of the end portion 422 is larger than the outer diameter of the central portion 421, the end portion 422 is provided outside the tapered sleeve 43, and the central portion 421 is provided outside the left core chamber 21 and the right core chamber 22. The tapered sleeve 43 and the rubber sleeve 42 are sealed to ensure the sealing of the confining pressure annulus 411. Figure 1 As shown, the right end face of the tapered sleeve 43 located on the left side is inclined radially inward toward the right, and a tapered portion 423 that matches the right end face is provided between the central portion 421 and the end portion 422 of the rubber sleeve 42; the left end face of the tapered sleeve 43 located on the right side is inclined radially inward toward the left, and a tapered portion 423 that matches the left end face is provided between the central portion 421 and the end portion 422 of the rubber sleeve 42.

[0049] In some embodiments, the pressure mechanism includes a limit mechanism 50, an axial pressure cylinder 61, and an axial pressure piston 62. The limit mechanism 50 is connected to the left core chamber 21 to prevent the left core chamber 21 from moving leftward. The axial pressure piston 62 is mounted on the axial pressure cylinder 61 and connected to the right core chamber 22 to drive the right core chamber 22 to move leftward. The axial pressure cylinder 61 is provided with a piston cavity 611. The axial pressure piston 62 moves rightward and drives the right core chamber 22 to apply axial pressure to the rock sample, simulating the axial pressure conditions of the formation.

[0050] The core holder 10 is also provided with surrounding heating tiles 11 to simulate the high temperature and high pressure environment of a real reservoir, so as to more accurately simulate the actual reservoir conditions of oil field development.

[0051] like Figure 2 As shown, the pad injection port 311 is located at the center of the right core chamber 22, while the pad discharge port is offset from the center of the left core chamber 21. The fracturing fluid injection port 32 includes a fracturing fluid injection channel 321 and a fracturing tube 322. The fracturing fluid injection channel 321 communicates with the fracturing tube 322, which is mounted on the right end face of the left core chamber 21. The fracturing tube 322 at least partially extends into the space between the left and right core chambers 21, 22. Furthermore, the fracturing tube 322 is located at the center of the left core chamber 21. The fracturing tube 322 simulates a fracturing well, improving the accuracy of the experimental results.

[0052] Specifically, the core holder 10 is sealed mainly by the left pressure cap 51, the spacer 52 and the first O-ring 71. In one embodiment, the core holder 10 has an overall length of no more than 600 mm, is relatively small, and is easy to transport and place.

[0053] Through the supercritical carbon dioxide composite fracturing experimental device, supercritical CO2 is injected into the core holder 10, and the rock sample is immersed in the supercritical CO2 environment inside the core holder 10 for a predetermined time. Specifically, the CO2 is heated to a first preset temperature and pressurized to a first preset pressure before being injected into the core holder 10; the temperature of the confining annulus 411 is monitored in real time, and when the difference between the actual temperature and the second preset temperature exceeds a preset temperature threshold, the internal space of the core holder 10 is heated to maintain the temperature within the preset temperature threshold of the second preset temperature; the pressure of the internal space of the core holder 10 is monitored in real time, and when the difference between the actual pressure and the second preset pressure exceeds a preset pressure threshold, CO2 is injected into the internal space of the core holder 10 to maintain the pressure within the preset pressure threshold of the second preset pressure.

[0054] like Figure 3 As shown, the plug 72 is provided with a fracturing hole 721, a seepage hole 722, and a radial groove 723. The fracturing tube 322 is sealed in contact with the fracturing hole 721 via a second O-ring 73. The radial groove 723 serves as a flow channel for the pad fluid on the left side of the rock sample. The seepage hole 722 communicates with the radial groove 723 and serves as a pad fluid discharge port. The pad fluid discharge pipe 312 is connected to the seepage hole 722.

[0055] In some embodiments, the carbon dioxide supply device 80 includes a carbon dioxide gas cylinder 81, a booster pump 82 and a constant temperature water bath 83. Figure 4As shown, the pre-fluid injection port 311 is connected to a booster pump 82 for pre-injecting supercritical CO2. The pre-fluid discharge pipe 312 is connected to a back-pressure valve 84 for controlling the injection rate. The booster pump 82, in conjunction with a constant-temperature water bath 83, heats and pressurizes the CO2 before it enters the core holder 10, bringing it to a supercritical state. Specifically, the booster pump 82 includes a gas booster, an air compressor, an air dryer, a boost controller, a CO2 monitoring alarm, and a gas pressure reducer.

[0056] The operating steps of the carbon dioxide supply device 80 are as follows: (1) Start the air compressor to ensure that sufficient power is provided to the pneumatic components of the system; (2) Open the constant temperature water bath 83 and adjust the temperature to the required temperature for the experiment; (3) Open the valve of the carbon dioxide cylinder 81, inflate 3 to 5 MPa of gas into the system, check the sealing of the pipeline, and turn on the CO2 concentration monitoring and alarm system; (4) Install the rock sample and apply the confining pressure to the design value, connect the fracturing pipe 322 and the transmission pipeline, and check the sealing; (5) Adjust the boost pointer to the design value, turn on the boost switch, and check whether the pressure gauge is working normally; (6) Slowly open the boost valve to ensure that the experimental pipeline is unobstructed; (7) Continue to increase the CO2 pressure until the rock sample is fractured, close the boost valve and equipment switch, and unload the rock sample confining pressure; (8) When the confining pressure cylinder pressure indicates 0, remove the confining pressure cover, take out the rock sample, record the data, and complete the experiment. To ensure experimental safety, the system boost pressure value shall not exceed 60% of the design value, that is, the maximum boost pressure shall not exceed 60MPa (the design value is 100MPa).

[0057] The working steps of the supercritical carbon dioxide composite fracturing experimental device include:

[0058] (1) Unscrew the left pressure cap 51 of the holder, remove the left pressure cap 51 and the spacer 52 from the left core chamber 21, load the prepared rock sample into the core holder 10, then install the spacer 52 into the left core chamber 21, and tighten the left pressure cap 51;

[0059] (2) Open the annular pressure vent and the annular pressure liquid inlet valve connected to the confining pressure annulus 411, and inject liquid into the confining pressure annulus 411 of the clamp. When the air in the confining pressure annulus 411 is completely discharged, tighten the annular pressure vent plug;

[0060] (3) Turn on the power switch of the control box surrounding the heating tile 11, set the required heating temperature on the temperature control instrument, turn on the heating switch to start heating; during heating, the liquid expands due to the increase in temperature, and the pressure will continue to increase, which is a normal phenomenon; if the pressure increases too quickly and exceeds the working pressure, the annular pressure vent should be opened in time to vent it to ensure that the pressure in the confining pressure annulus 411 does not exceed the working pressure;

[0061] (4) According to the experimental requirements, if the pressure cannot meet the required value when heated to the required temperature, the pressure in the confining pressure annulus 411 can be increased to the required pressure value by a high-pressure injection pump, and then the annular pressure liquid inlet valve is closed, and then the temperature is heated to the required experimental temperature and pressure value;

[0062] (5) Open the axial pressure inlet valve connected to the piston chamber 611 of the axial pressure cylinder 61, apply axial pressure to the end face of the rock sample, and apply axial pressure according to the experimental requirements;

[0063] (6) Open the pre-inlet and outlet valves of the core holder 10, inject supercritical carbon dioxide into the core through the pre-fluid injection port 311, and record the inlet and outlet pressures and outlet flow in real time to obtain experimental data such as permeability;

[0064] (7) opening the fracturing control system and the fracturing valve, injecting the fracturing fluid into the fracturing pipe 322 through the fracturing fluid pipe, controlling the injection pressure through the fracturing control system to fracture the rock sample, and closing the fracturing valve after the fracturing is completed;

[0065] (8) After the experimental reaction is completed, turn off the heating switch; after the temperature of the temperature control instrument drops to room temperature, remove the pad 52 and the left pressure cap 51, take out the rock sample, and then install the pad 52 and the left pressure cap 51 to restore the initial state of the experiment.

[0066] In one embodiment, during the application of axial pressure, the ratio of the axial pressure loading area to the end surface area of ​​the rock sample is 1.1856:1, that is, when the gauge pressure is 42.17 MPa, the stress on the end surface of the Φ50 core is 50 MPa.

[0067] When conducting an experiment using this supercritical carbon dioxide composite fracturing experimental device, supercritical CO2 is injected beforehand; the rock sample is dynamically immersed in the supercritical CO2 environment inside the core holder 10 for a predetermined time; then a hydraulic fracturing experiment is performed on the rock sample; and based on the experimental data, the fracturing parameters of the rock sample are obtained. Specifically, the rock sample is placed inside the core holder 10; a certain confining pressure and axial pressure are applied to the rock sample to fix the rock sample and simulate the actual stress state of the formation; the core holder 10 is vacuumed; the core inside the holder is saturated with water to achieve the actual water saturation state of the reservoir; and the interior of the core holder 10 is heated to a preset temperature to reach the target reservoir temperature and maintain it for a predetermined period of time.

[0068] The supercritical carbon dioxide composite fracturing experimental device is used to simulate the actual formation temperature, ground stress and other conditions. During the overall injection-fracturing experiment, the rock sample remains in situ to simulate the formation state, allowing for efficient and accurate injection-fracturing experiments and simulating the integrated process of pre-supercritical CO2 injection-fracturing in oil and gas reservoirs. It has the following advantages:

[0069] (1) A pre-fluid injection port 311 is provided at one end of the core holder 10, which can be used to perform pre-supercritical CO2 injection under simulated formation temperature and stress conditions to study the effects of supercritical CO2-water-rock interaction on reservoir properties;

[0070] (2) There is a fracturing fluid injection port 32 and a pre-fluid discharge port at the other end of the core holder 10, so that the rock sample after the pre-supercritical carbon dioxide injection can be directly subjected to secondary hydraulic fracturing in situ under the same simulated formation conditions without removing the rock sample, which conforms to the process operation process and conditions of actual oil field development;

[0071] (3) During the entire experimental process, the rock samples are kept in a core holder 10, maintaining the same temperature and stress conditions. No disassembly or adjustment is required during the experiment. A series of pre-injection fracturing experiments are carried out in situ under simulated formation conditions, which is conducive to ensuring the effective conduct of the experiment.

[0072] Option 2

[0073] The present invention provides a supercritical carbon dioxide composite fracturing experimental method, which uses the above-mentioned supercritical carbon dioxide composite fracturing experimental device. The experimental method includes: injecting supercritical carbon dioxide into the rock sample through the pre-fluid injection port 311; and injecting fracturing fluid into the rock sample through the fracturing fluid injection port 32.

[0074] During the experiment, a pressure mechanism was used to simulate formation stress conditions. Supercritical carbon dioxide was injected into the rock sample through the pre-fluid injection port 311 and discharged through the pre-fluid discharge port, achieving pre-supercritical carbon dioxide injection. The fracturing fluid injection port 32 was used to inject post-water-based fracturing fluid, allowing fluid injection at both ends to achieve pre-supercritical CO2 injection and post-water-based fracturing fluid fracturing, simulating an integrated pre-supercritical CO2 injection and fracturing process for oil and gas reservoirs. The actual simulated formation conditions remained unchanged during the experiment. The pre-fluid injection port 311 allowed for pre-supercritical CO2 injection under simulated formation conditions to study the effects of supercritical CO2 on reservoir properties. After the pre-supercritical CO2 injection, the fracturing fluid injection port 32 and the pre-fluid discharge port allowed for in-situ hydraulic fracturing under the same simulated formation conditions, simulating an integrated pre-supercritical CO2 injection and fracturing process for oil and gas reservoirs. This conforms to the operating conditions of actual oil and gas field development, ensuring more realistic and accurate experimental results.

[0075] The above descriptions are only several embodiments of the present invention. Those skilled in the art may make various changes or modifications to the embodiments of the present invention based on the contents disclosed in the application documents without departing from the spirit and scope of the present invention.

Claims

1. A supercritical carbon dioxide composite fracturing experimental device, characterized in that: include: A core holder and a carbon dioxide supply device, wherein the core holder includes a clamping mechanism and a pressure mechanism, wherein the clamping mechanism includes a left core chamber and a right core chamber, the clamping mechanism can fix a rock sample between the left core chamber and the right core chamber, and the pressure mechanism is used to apply pressure to the rock sample between the left core chamber and the right core chamber; The left end face of the right core chamber is provided with a forepad injection port, which is used to inject supercritical CO2 into the rock sample to simulate supercritical CO2 fracturing, and the carbon dioxide supply device is connected to the forepad injection port; the right end face of the left core chamber is provided with a forepad discharge port, which is used to discharge the supercritical CO2, and the left core chamber is also provided with a fracturing fluid injection port, and the space between the left core chamber and the right core chamber is connected to the fracturing fluid injection port, and the fracturing fluid injection port can inject water-based fracturing fluid into the space between the left core chamber and the right core chamber to simulate hydraulic fracturing.

2. The supercritical carbon dioxide composite fracturing experimental device according to claim 1, characterized in that: The pressure mechanism includes an outer cylinder and a rubber sleeve, the two ends of the rubber sleeve are respectively sleeved outside the left core chamber and the right core chamber, and the rubber sleeve is arranged in the outer cylinder, and a confining pressure annulus is provided between the outer wall of the rubber sleeve and the outer cylinder.

3. The supercritical carbon dioxide composite fracturing experimental device according to claim 2, characterized in that: The left core chamber and the right core chamber are respectively covered with tapered sleeves; The rubber sleeve includes a central portion and end portions, the outer diameter of the end portions is larger than the outer diameter of the central portion, the end portions are sleeved outside the tapered sleeve, and the central portion is sleeved outside the left core chamber and the right core chamber.

4. The supercritical carbon dioxide composite fracturing experimental device according to claim 2, characterized in that: The pressure mechanism includes a limiting mechanism, an axial pressure cylinder and an axial pressure piston. The limiting mechanism is connected to the left core chamber to prevent the left core chamber from moving to the left. The axial pressure piston is installed on the axial pressure cylinder and connected to the right core chamber to drive the right core chamber to move to the left.

5. The supercritical carbon dioxide composite fracturing experimental device according to claim 1, characterized in that: The prepad injection port is arranged at the center of the right core chamber, and the prepad discharge port is offset from the center of the left core chamber.

6. The supercritical carbon dioxide composite fracturing experimental device according to claim 5, characterized in that: The fracturing fluid injection port includes a fracturing fluid injection channel and a fracturing pipe, the fracturing fluid injection channel is connected to the fracturing pipe, the fracturing pipe is installed on the right end surface of the left core chamber, and the fracturing pipe at least partially extends to the space between the left core chamber and the right core chamber.

7. The supercritical carbon dioxide composite fracturing experimental device according to claim 6, characterized in that: The fracturing tube is arranged at the center of the left core chamber.

8. The supercritical carbon dioxide composite fracturing experimental device according to claim 1, characterized in that: The core holder comprises a plug, and the plug is provided with a fracturing hole, a seepage hole and a radiation groove.

9. The supercritical carbon dioxide composite fracturing experimental device according to claim 1, characterized in that: The carbon dioxide supply device includes a carbon dioxide gas cylinder, a booster pump and a constant temperature water bath.

10. A supercritical carbon dioxide composite fracturing experimental method, characterized in that: The supercritical carbon dioxide composite fracturing experimental device according to any one of claims 1 to 9 is used, and the experimental method comprises: injecting supercritical carbon dioxide into the rock sample through the pre-fluid injection port; and injecting fracturing fluid into the rock sample through the fracturing fluid injection port.

Images