Supercritical CO2 fracturing, displacement and sealing integrated experimental device and method

Abstract

The invention provides a supercritical CO2 fracturing, displacement and storage integrated experimental device and method, belongs to the technical field of natural gas development, and is used for solving the problem that a real-time and multidirectional monitoring and evaluation experimental device for simulating a deep unconventional natural gas exploitation process is lacked. The supercritical CO2 fracturing, displacement and sealing integrated experimental device comprises an accommodating cavity, a ground stress simulation system, a gas source supply system, a fracturing fluid preparation system, a temperature control system, a tail gas recovery system, a multi-parameter monitoring system and a displacement effect evaluation system, and can systematically simulate true triaxial ground stress and ground temperature conditions; fracturing, displacement and sequestration experiments of supercritical carbon dioxide on a rock sample are carried out, multi-azimuth and multi-parameter real-time monitoring and quantitative characterization evaluation are carried out on experimental results in the experimental process, and important theoretical research and actual production guiding significance is achieved for development of deep unconventional natural gas and geological sequestration of carbon dioxide.

Description

Technical Field

[0001] The invention belongs to the technical field of natural gas development and particularly relates to a supercritical CO 2 Integrated experimental device and method for fracturing, displacement and sealing. Background Art

[0002] The exploitation of unconventional natural gas (coalbed methane, shale gas, tight gas, etc.) is characterized by diverse lithology types, diverse sedimentary environments, deep burial depths, dense reservoirs, and strong heterogeneity. Its low porosity and low permeability characteristics determine that reservoir fracturing must be carried out to achieve efficient development. Most unconventional natural gas development uses hydraulic fracturing technology, but there are problems such as waste of water resources and environmental pollution. Since supercritical carbon dioxide has the characteristics of both liquid and gas phases of carbon dioxide (such as unique physical and chemical properties such as low viscosity, high diffusivity, and zero surface tension), it can be used for fracturing to reduce the initiation pressure and increase the complexity of the fracture network. It also has advantages in displacement, energy enhancement and pressure maintenance, pollution reduction, carbon dioxide storage, etc. Therefore, supercritical carbon dioxide (supercritical CO 2 ) has become an ideal alternative to fracturing fluid, effectively solving the problem of water shortage and difficulty in hydraulic fracturing in unconventional natural gas-rich areas.

[0003] Supercritical carbon dioxide fracturing technology has broad application prospects in the exploitation of unconventional natural gas such as shale gas, and is an effective way to achieve large-scale carbon emission reduction in the future. Combining supercritical carbon dioxide fracturing, displacement, and storage with improving the recovery rate of unconventional natural gas has the dual role of sealing carbon emissions and reducing emissions and realizing the resource utilization of carbon dioxide. Therefore, it is urgent to develop an experimental device and method to simulate and analyze the entire process and evaluate the effects. Existing supercritical carbon dioxide fracturing-displacement-storage devices are generally designed for a single process. Not only are they single in function, the equipment is scattered, and they cannot fully simulate actual working conditions for systematic research, but the experimental phenomena are not intuitive, there are few real-time monitoring parameters, and the operating accuracy is poor, which limits the formulation of experimental plans. For example, in terms of fracturing, there are designs for supercritical carbon dioxide transmission pipelines, circulating fracturing devices, variable-size loading systems, etc., but the selection of fracturing fluids available for testing is limited and the fracturing method is single; in terms of displacement, subcritical carbon dioxide is mostly used to displace coalbed methane and shale gas, and the focus is on analyzing the composition and content of mixed gases, avoiding the fact that carbon dioxide changes in multiple phases in practice; in terms of storage, the focus is on increasing the storage capacity and monitoring the degree of damage to rocks by supercritical carbon dioxide to evaluate the safety of storage, but this process often lacks diversified evaluation indicators and novel monitoring methods. In addition, there is a lack of effective utilization or timely recovery units for the waste gas generated at the end of the experiment. Therefore, there are few composite multifunctional unconventional natural gas extraction simulation experimental devices that can simultaneously simulate deep high-temperature and high-pressure environmental conditions, evaluate and monitor the real-time effects of parameters and phenomena, and have a full-process, integrated device with a green recycling unit for experimental waste gas. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present invention is to provide a supercritical CO 2 The integrated experimental device and method for fracturing, displacement and sealing can continuously carry out fracturing, displacement and sealing experiments on rock samples under simulated true triaxial geostress and geotemperature conditions, and conduct multi-directional, multi-parameter, integrated real-time monitoring and quantitative evaluation of the experimental process and results.

[0005] In order to solve the above problems, the present invention provides a supercritical CO 2The integrated experimental device for fracturing, displacement and sealing includes a containing chamber, a geostress simulation system, a gas source supply system, a fracturing fluid preparation system, a temperature control system, an exhaust gas recovery system, a multi-parameter monitoring system and a displacement effect evaluation system. The containing chamber is used to contain rock samples. The geostress simulation system is connected to the containing chamber. The geostress simulation system is used to apply pressure to the rock samples to simulate the three-dimensional stress conditions underground. The gas source supply system is connected to the containing chamber. The gas source supply system is used to supply the gas source required for fracturing, displacement, permeability testing and sealing to the rock samples. The fracturing fluid preparation system is connected between the gas source supply system and the containing chamber. The fracturing fluid preparation system is used to prepare fracturing fluid and inject the fracturing fluid into the rock sample. The temperature control system is used to adjust the temperature of the containing chamber and the fracturing fluid preparation system to simulate the reservoir temperature at different depths underground and different fracturing fluid injection temperatures. The exhaust gas recovery system is connected to the containing chamber. The exhaust gas recovery system is used to recover the gas discharged from the containing chamber. The multi-parameter monitoring system is used to monitor and record the changes in various parameters of rock sample properties and fracturing fluid status during fracturing, displacement and sealing in real time. The displacement effect evaluation system can quantitatively evaluate the displacement effect based on the parameters obtained by the multi-parameter monitoring system.

[0006] Optionally, an injection port and a discharge port are provided on the accommodating chamber. An injection assembly is provided on the injection port. The discharge port is connected to the tail gas recovery system. The injection assembly includes: a three-way joint and a fracturing pipe. The three-way joint includes a first interface, a second interface and a third interface. The gas source supply system and the fracturing fluid preparation system are connected in parallel to the first interface. The multi-parameter monitoring system is connected to the second interface. The fracturing pipe includes a first end and a second end. The first end is connected to the third interface. The second end is closed. On the outer circumference of the fracturing pipe, a first sealing ring, a second sealing ring and a third sealing ring are sequentially provided from the first end to the second end. Perforations are provided on the pipe wall of the fracturing pipe. The perforations are located between the second sealing ring and the third sealing ring. The second end of the fracturing pipe extends into the accommodating chamber from the injection port and is inserted into the fracturing hole on the rock sample. The first sealing ring, the second sealing ring and the third sealing ring are sealed and connected to the inner wall of the fracturing hole. The fracturing pipe is sealed and connected to the injection port and can be raised and lowered in the fracturing hole.

[0007] Optionally, the ground stress simulation system includes: a first direction loading assembly, a second direction loading assembly and a third direction loading assembly. The first direction loading assembly includes a first loading plate, a first piston rod and a first driving device. The first loading plate is arranged on both sides of the rock sample in the first direction. One end of the first piston rod is connected to the first loading plate. One end of the first piston rod away from the first loading plate is connected to the first driving device. The second direction loading assembly includes a second loading plate, a second piston rod and a second driving device. The second loading plate is arranged on both sides of the rock sample in the second direction. One end of the second piston rod is connected to the second loading plate. One end of the second piston rod away from the second loading plate is connected to the second driving device. The third direction loading assembly includes a third loading plate, a third piston rod and a third driving device. The third loading plate is arranged on both sides of the rock sample in the third direction. One end of the third piston rod is connected to the third loading plate. One end of the third piston rod away from the third loading plate is connected to the third driving device. The first loading plate, the second loading plate and the third loading plate are respectively provided with mounting holes. Part of the detection end of the multi-parameter monitoring system contacts the surface of the rock sample through the mounting hole.

[0008] Optionally, the gas source supply system includes: a carbon dioxide storage device, a methane storage device, a helium storage device, a first pressure reducing valve and a pressure booster. The carbon dioxide storage device, the methane storage device and the helium storage device are connected in parallel to the inlet of the first pressure reducing valve. The outlet of the first pressure reducing valve is connected to the fracturing fluid preparation system through the pressure booster.

[0009] Optionally, the fracturing fluid preparation system includes: at least one intermediate container, a first driving pump, a stirring device, a second driving pump and a foam generator. The intermediate container is connected to the gas source supply system. The intermediate container is used to load carbon dioxide. The first driving pump is connected to the intermediate container. The first driving pump is used to increase the carbon dioxide output pressure of the intermediate container. The stirring device includes a feeding port and a discharge port. The output end of the intermediate container is connected to the feeding port. The discharge port is connected to the accommodating chamber to inject fracturing fluid into the rock sample in the accommodating chamber. The second driving pump is connected between the stirring device and the water source. The second driving pump is used to introduce the water source into the stirring device. The foam generator is connected to the stirring device. The foam generator is used to prepare foam and add the foam to the stirring device.

[0010] Optionally, the temperature control system includes: a first temperature controller and a second temperature controller. The first temperature controller is connected to the fracturing fluid preparation system. The first temperature controller is used to simulate different fracturing fluid injection temperatures. The second temperature controller is connected to the accommodation chamber. The second temperature controller is used to simulate reservoir temperatures at different depths underground.

[0011] Optionally, the tail gas recovery system includes: a condenser and a filter. The tail gas recovery system is used to separate, condense, purify and recover carbon dioxide, methane and helium exhausted during the experiment.

[0012] Optionally, the multi-parameter monitoring system includes an integrated multi-parameter sensor. The integrated multi-parameter sensor includes: an acoustic emission monitoring device for real-time monitoring of the micro-crack activity inside the rock sample during fracturing, displacement and sealing. A wave velocity monitoring device for measuring the wave velocity change of the rock sample to obtain the change of the mechanical parameters of the rock sample. A resistivity measuring device for measuring the resistivity value of the rock sample at different water saturations to obtain the exponential relationship between saturation and resistivity. A fiber grating temperature stress strain monitoring device for real-time monitoring of the surface temperature, stress and strain of the rock sample during fracturing, displacement and sealing. A digital speckle detection device for obtaining the displacement field and strain field on the surface of the rock sample to obtain the dynamic changes of the initiation, evolution, expansion and elastic-plastic stages of cracks in the rock sample. A nuclear magnetic resonance detection device for obtaining the displacement efficiency of the rock sample at different water contents. A pressure difference monitoring device for monitoring the pressure difference between the upstream and downstream of the accommodating cavity. A gas leakage monitoring device for monitoring gas leakage in the rock sample.

[0013] Optionally, the displacement effect evaluation system includes: a gas phase spectrometer disposed between the accommodating chamber and the tail gas recovery system.

[0014] The present invention also provides a supercritical CO 2 The integrated experimental method of fracturing, displacement and storage uses the above-mentioned supercritical CO 2 The integrated experimental device for fracturing, displacement and sealing includes the following steps:

[0015] preparing a rock sample and placing the rock sample in a receiving cavity;

[0016] Obtain the permeability of rock samples before fracturing;

[0017] Injecting methane gas into rock samples to simulate in situ methane occurrence;

[0018] Conduct fracturing experiments on rock samples;

[0019] Displace the methane in the rock sample, obtain the displacement effect and recover the displaced mixed gas;

[0020] Obtain the permeability of rock samples after fracturing;

[0021] The rock samples are sealed and a prediction and evaluation model for leakage risk is established.

[0022] Beneficial Effects

[0023] 1. The supercritical CO provided by the present invention 2The integrated experimental device for fracturing, displacement and sealing includes a containing chamber, a ground stress simulation system, a gas source supply system, a fracturing fluid preparation system, a temperature control system, a tail gas recovery system, a multi-parameter monitoring system and a displacement effect evaluation system. The containing chamber is used to contain rock samples. The ground stress simulation system is used to simulate underground three-dimensional stress conditions. The gas source supply system is used to supply the gas source required for fracturing, displacement, permeability testing and sealing to the rock samples. The fracturing fluid preparation system is used to prepare fracturing fluid and inject the fracturing fluid into the rock sample. The temperature control system is used to adjust the temperature of the containing chamber and the fracturing fluid preparation system to simulate the reservoir temperature at different depths underground and different fracturing fluid injection temperatures. The tail gas recovery system is used to recover the gas discharged from the containing chamber. The multi-parameter monitoring system is used to monitor and record the changes in various parameters of the properties of rock samples and the state of fracturing fluid in real time during fracturing, displacement and sealing. The displacement effect evaluation system can quantitatively evaluate the displacement effect based on the parameters obtained by the multi-parameter monitoring system. Using the supercritical CO 2 The integrated experimental device for fracturing, displacement and storage can systematically simulate true triaxial geostress and geothermal conditions, conduct fracturing, displacement and storage experiments of supercritical carbon dioxide on rock samples, and conduct multi-directional and multi-parameter real-time monitoring and quantitative characterization evaluation of the experimental results during the experiment. It has important theoretical research and practical production guidance significance for the development of deep unconventional natural gas and geological storage of carbon dioxide.

[0024] 2. The supercritical CO provided by the present invention 2 The integrated experimental method of fracturing, displacement and storage uses the above-mentioned experimental device to continuously complete the experimental process of fracturing, displacement and storage on the same experimental device, which is conducive to improving the experimental efficiency and data consistency, and can simulate complex conditions such as underground true triaxial stress and ground temperature, provide an experimental environment close to actual working conditions, and improve the reliability and applicability of experimental results. It can also quantitatively evaluate the permeability changes of rock samples before and after fracturing by different types of fracturing fluids and the effect of in-situ methane displacement, and establish a prediction and evaluation model for automatic feedback and correction of storage leakage risks when carbon dioxide is stored for a long time. The overall real-time monitoring system with multi-parameter and high-precision sensors organically integrated provides intuitive and rich experimental data from multiple angles. In addition, a tail gas recovery system is designed to realize the recycling and utilization of experimental gases. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A supercritical CO according to an embodiment of the present invention is provided 2 System diagram of the integrated experimental device for fracturing, displacement and sealing;

[0026] Figure 2 A supercritical CO according to an embodiment of the present invention is provided 2 Schematic diagram of the structure of the integrated experimental device for fracturing, displacement and sealing;

[0027] Figure 3 A schematic diagram of the structure of a fracturing pipe according to an embodiment of the present invention;

[0028] Figure 4 A schematic diagram of the structure of a loading plate according to an embodiment of the present invention;

[0029] Figure 5 A schematic diagram of a multi-parameter monitoring system according to an embodiment of the present invention;

[0030] Figure 6 A supercritical CO according to an embodiment of the present invention is provided 2 Flowchart of the integrated experimental method of fracturing, displacement and storage.

[0031] The reference numerals are:

[0032] 01. Accommodation chamber; 02. Ground stress simulation system; 03. Gas supply system; 04. Fracturing fluid preparation system; 05. Temperature control system; 06. Tail gas recovery system; 07. Multi-parameter monitoring system; 08. Displacement effect evaluation system;

[0033] 1. Carbon dioxide storage device; 2. Methane storage device; 3. Helium storage device; 4. Three-way connector; 5. First pressure reducing valve; 6. Supercharger; 7. Third intermediate container; 8. Second intermediate container; 9. First intermediate container; 10. First drive pump; 11. Second drive pump; 12. First flow sensor; 13. First temperature sensor; 14. First pressure sensor; 15. Stirring device; 16. Foam generator; 17. First temperature controller; 18. Upstream chamber; 19. Second pressure sensor; 20. Second temperature sensor; 21. Second flow sensor sensor; 22, second pressure reducing valve; 23, first direction loading assembly; 24, rock sample; 25, fracturing pipe; 26, high-precision camera; 27, downstream chamber; 28, second temperature controller; 29, back pressure valve; 30, sixth pressure sensor; 31, third flow sensor; 32, first drive device; 33, second drive device; 34, third drive device; 35, integrated multi-parameter sensor; 36, gas phase spectrometer; 37, gas recovery device; 38, third pressure sensor; 39, fourth pressure sensor; 40, fifth pressure sensor;

[0034] 231. first loading plate; 232. first piston rod;

[0035] 2311, mounting hole;

[0036] 251, positioning nut; 252, first sealing ring; 253, second sealing ring; 254, third sealing ring; 255, perforation;

[0037] 351. Acoustic emission monitoring device; 352. Wave velocity monitoring device; 353. Resistivity measuring device; 354. Fiber Bragg grating temperature stress strain monitoring device; 355. Digital speckle detection device; 356. Nuclear magnetic resonance detection device; 357. Pressure difference monitoring device; 358. Gas leakage monitoring device;

[0038] 0901~0915 are the first stop valve to the fifteenth stop valve. DETAILED DESCRIPTION

[0039] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0040] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0041] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like 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 a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0042] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0043] In the first aspect, this embodiment provides a supercritical CO 2 Integrated experimental device for fracturing, displacement and storage. Figure 1 A supercritical CO provided in this embodiment 2 System diagram of the integrated experimental device for fracturing, displacement and storage.

[0044] like Figure 1 As shown, the supercritical CO 2 The integrated experimental device for fracturing, displacement and sealing includes: a containing chamber 01, a geostress simulation system 02, a gas source supply system 03, a fracturing fluid preparation system 04, a temperature control system 05, an exhaust gas recovery system 06, a multi-parameter monitoring system 07 and a displacement effect evaluation system 08. The containing chamber 01 is used to contain rock samples. The geostress simulation system 02 is connected to the containing chamber 01. The geostress simulation system 02 is used to apply pressure to the rock sample to simulate the three-dimensional stress conditions underground. The gas source supply system 03 is connected to the containing chamber 01. The gas source supply system 03 is used to supply the gas source required for fracturing, displacement, permeability testing and sealing to the rock sample. The fracturing fluid preparation system 04 is connected between the gas source supply system 03 and the containing chamber 01. The fracturing fluid preparation system 04 is used to prepare the fracturing fluid and inject the fracturing fluid into the rock sample. The temperature control system 05 is used to adjust the temperature of the containing chamber 01 and the fracturing fluid preparation system 04 to simulate the reservoir temperature at different depths underground and different fracturing fluid injection temperatures. The tail gas recovery system 06 is connected to the accommodating chamber 01. The tail gas recovery system 06 is used to recover the gas discharged from the accommodating chamber 01. The multi-parameter monitoring system 07 is used to monitor and record the changes in various parameters of the rock sample properties and the state of the fracturing fluid in real time during the fracturing, displacement and sealing process. The displacement effect evaluation system 08 can quantitatively evaluate the displacement effect based on the parameters obtained by the multi-parameter monitoring system 07.

[0045] In this embodiment, the shape of the rock sample is a cube with a side length of 5 cm to 30 cm, which can meet the needs of experiments of different scales and requirements.

[0046] The supercritical CO 2 The integrated experimental device for fracturing, displacement and sealing includes a containing chamber 01, a ground stress simulation system 02, a gas source supply system 03, a fracturing fluid preparation system 04, a temperature control system 05, an exhaust gas recovery system 06, a multi-parameter monitoring system 07 and a displacement effect evaluation system 08. The containing chamber 01 is used to contain rock samples. The ground stress simulation system 02 is used to simulate underground three-dimensional stress conditions. The gas source supply system 03 is used to supply the gas source required for fracturing, displacement, permeability testing and sealing to the rock samples. The fracturing fluid preparation system 04 is used to prepare fracturing fluid and inject the fracturing fluid into the rock samples. The temperature control system 05 is used to adjust the temperature of the containing chamber 01 and the fracturing fluid preparation system 04 to simulate the reservoir temperature at different depths underground and different fracturing fluid injection temperatures. The exhaust gas recovery system 06 is used to recover the gas discharged from the containing chamber 01. The multi-parameter monitoring system 07 is used to monitor and record the changes in various parameters of the properties of rock samples and the state of fracturing fluid in real time during fracturing, displacement and sealing. The displacement effect evaluation system 08 can quantitatively evaluate the displacement effect according to the parameters obtained by the multi-parameter monitoring system 07.2 The integrated experimental device for fracturing, displacement and storage can systematically simulate true triaxial geostress and geothermal conditions, conduct fracturing, displacement and storage experiments of supercritical carbon dioxide on rock samples, and conduct multi-directional and multi-parameter real-time monitoring and quantitative characterization evaluation of the experimental results during the experiment. It has important theoretical research and practical production guidance significance for the development of deep unconventional natural gas and geological storage of carbon dioxide.

[0047] Figure 2 A supercritical CO provided in this embodiment 2 Schematic diagram of the structure of the integrated experimental device for fracturing, displacement and storage. Figure 3 A schematic diagram of the structure of a fracturing pipe provided in this embodiment. Figures 1 to 3 As shown, an injection port and a discharge port are provided on the accommodating chamber 01. An injection assembly is provided on the injection port. The discharge port is connected to the tail gas recovery system 06. The injection assembly includes: a three-way joint 4 and a fracturing pipe 25. The three-way joint 4 includes a first interface, a second interface and a third interface. The gas source supply system 03 and the fracturing fluid preparation system 04 are connected in parallel to the first interface. The multi-parameter monitoring system 07 is connected to the second interface. The fracturing pipe 25 includes a first end and a second end. The first end is connected to the third interface. The second end is closed. On the outer periphery of the fracturing pipe 25, a first sealing ring 252, a second sealing ring 253 and a third sealing ring 254 are provided in sequence from the first end to the second end. A perforation 255 is provided on the pipe wall of the fracturing pipe 25. The perforation 255 is located between the second sealing ring 253 and the third sealing ring 254. The second end of the fracturing pipe 25 extends into the accommodating chamber 01 from the injection port and is inserted into the fracturing hole on the rock sample 24. The first sealing ring 252, the second sealing ring 253 and the third sealing ring 254 are sealed and connected to the inner wall of the fracturing hole. The fracturing pipe 25 is sealed and connected to the injection port and can be raised and lowered in the fracturing hole.

[0048] The fracturing tube 25 of this embodiment includes a first sealing ring 252, a second sealing ring 253, a third sealing ring 254 and a perforation 255. The first sealing ring 252 is used to initially seal the fracturing hole. The perforation 255 is located between the second sealing ring 253 and the third sealing ring 254. The second sealing ring 253 and the third sealing ring 254 cooperate with the inner wall of the fracturing hole to form a closed space, which can seal the high-pressure gas output by the perforation 255 so that the fracturing fluid in the fracturing tube 25 can be injected into the gap of the rock sample 24. The fracturing tube 25 is sealed and connected to the injection port and can be raised and lowered in the fracturing hole. During the fracturing experiment, after the first section of the rock sample 24 is fracturing, the fracturing tube 25 is adjusted to move up. When the third sealing ring 254 moves to the position of the second sealing ring 253 when the first section is fracturing, the fracturing fluid can continue to be injected to carry out the fracturing test of the next section, thereby realizing the staged fracturing process.

[0049] It should be noted that the fracturing tube 25 and the injection port can be sealed and connected by a positioning nut 251. After the fracturing of the first section is completed, the positioning nut 251 on the fracturing tube 25 is adjusted, and then the position of the fracturing tube 25 in the fracturing hole can be adjusted. There are multiple perforations 255 on the fracturing tube 25, and the multiple perforations 255 are evenly distributed along the circumference of the fracturing tube 25 to ensure that the fracturing fluid is evenly injected into the rock sample 24. For example, the number of perforations 255 is six. For example, the fracturing tube 25 is preferably made of stainless steel, and the inner diameter of the fracturing tube is preferably 2 cm.

[0050] Figure 4 A schematic diagram of the structure of a loading plate provided in this embodiment. Figures 1 to 4 As shown, the ground stress simulation system 02 includes: a first direction loading component 23, a second direction loading component and a third direction loading component. The first direction loading component 23 includes a first loading plate 231, a first piston rod 232 and a first driving device 32. The first loading plate 231 is arranged on both sides of the rock sample 24 in the first direction. One end of the first piston rod 232 is connected to the first loading plate 231. The end of the first piston rod 232 away from the first loading plate 231 is connected to the first driving device 32. The second direction loading component includes a second loading plate, a second piston rod and a second driving device 33. The second loading plate is arranged on both sides of the rock sample 24 in the second direction. One end of the second piston rod is connected to the second loading plate. The end of the second piston rod away from the second loading plate is connected to the second driving device 33. The third direction loading component includes a third loading plate, a third piston rod and a third driving device 34. The third loading plate is arranged on both sides of the rock sample 24 in the third direction. One end of the third piston rod is connected to the third loading plate. The end of the third piston rod away from the third loading plate is connected to the third driving device 34. The first loading plate 231 , the second loading plate and the third loading plate are respectively provided with mounting holes 2311 . Part of the detection end of the multi-parameter monitoring system 07 contacts the surface of the rock sample 24 through the mounting holes 2311 .

[0051] The geostress simulation system 02 of this embodiment can realize accurate application and control of three-dimensional stress on the rock sample 24, and is used to simulate complex three-dimensional stress conditions underground. A third pressure sensor 38, a fourth pressure sensor 39, and a fifth pressure sensor 40 are respectively arranged at the output ends of the first driving device 32, the second driving device 33, and the third driving device 34, for real-time monitoring and data recording of stress applied in the first direction, the second direction, and the third direction.

[0052] In this embodiment, the third loading plate located on the upper surface of the rock sample 24 is made of high-strength pressure-resistant transparent material (such as polycarbonate PC) to form a visualization window for visual monitoring of the fracturing process; the first loading plate and the second loading plate are made of high-strength steel material to ensure the stability and safety of the system.

[0053] like Figure 4 As shown, the mounting hole 2311 of this embodiment is a stepped hole, the end close to the rock sample 24 is a small diameter hole section, and the end away from the rock sample 24 is a large diameter hole section. An internal thread is configured on the inner wall of the small diameter hole section to meet the installation requirements of various detection ends and lead wires of the multi-parameter monitoring system 07 during the fracturing process. By realizing the channel integration of multiple monitoring means, the overall structure of the experimental device is significantly simplified, and its operation convenience and practicality are improved. In addition, in this embodiment, the surfaces of the various detection ends of the multi-parameter monitoring system 07 that contact the rock sample 24 are coated with a special coupling agent, so that these detection ends can be in close contact with the surface of the rock sample 24, ensuring sensitive reception of detection signals during the experiment.

[0054] In some examples, the first direction, the second direction, and the third direction are respectively the X direction (the left and right sides of the rock sample 24), the Y direction (the front and rear sides of the rock sample 24), and the Z direction (the upper and lower sides of the rock sample 24). The first driving device 32, the second driving device 33, and the third driving device 34 can all use servo pumps, and the maximum output pressure of the servo pump can be set to 100 MPa, which can meet the simulation requirements under most geological conditions.

[0055] In some embodiments, Figure 1 and Figure 2 As shown, the gas source supply system 03 includes: a carbon dioxide storage device 1, a methane storage device 2, a helium storage device 3, a first pressure reducing valve 5 and a supercharger 6. The carbon dioxide storage device 1, the methane storage device 2, and the helium storage device 3 are connected in parallel to the inlet of the first pressure reducing valve 5. The outlet of the first pressure reducing valve 5 is connected to the fracturing fluid preparation system 04 through the supercharger 6. The carbon dioxide storage device 1, the methane storage device 2, and the helium storage device 3 in this embodiment are gas cylinders. The first pressure reducing valve 5 is used to accurately control the output pressure of the carbon dioxide storage device 1, the methane storage device 2, and the helium storage device 3. The supercharger 6 is used to pressurize the gas in the carbon dioxide storage device 1, the methane storage device 2, and the helium storage device 3 to a set initial pressure.

[0056] In this embodiment, a first stop valve 0901 is provided at the outlet of the carbon dioxide storage device 1, a second stop valve 0902 is provided at the outlet of the methane storage device 2, and a third stop valve 0903 is provided at the outlet of the helium storage device 3. By controlling the opening and closing of the first stop valve 0901, the second stop valve 0902, and the third stop valve 0903, the type of gas output to the first pressure reducing valve 5 can be switched.

[0057] In some embodiments, Figure 1 and Figure 2 As shown, the fracturing fluid preparation system 04 includes: at least one intermediate container, a first drive pump 10, a stirring device 15, a second drive pump 11 and a foam generator 16. The intermediate container is connected to the gas source supply system 03. The intermediate container is used to load carbon dioxide. The first drive pump 10 is connected to the intermediate container. The first drive pump 10 is used to increase the carbon dioxide output pressure of the intermediate container. The stirring device 15 includes a feeding port and a discharge port. The output end of the intermediate container is connected to the feeding port. The discharge port is connected to the accommodating chamber 01 to inject fracturing fluid into the rock sample 24 in the accommodating chamber 01. The second drive pump 11 is connected between the stirring device 15 and the water source. The second drive pump 11 is used to introduce the water source into the stirring device 15. The foam generator 16 is connected to the stirring device 15. The foam generator 16 is used to prepare foam and add the foam to the stirring device 15.

[0058] The fracturing fluid preparation system 04 of this embodiment can prepare a variety of fracturing fluids, such as carbon dioxide in different phases, water, water-carrying proppants, water-carrying carbon dioxide-carrying proppants, etc., to simulate different fracturing methods. The intermediate container is used to store the high-pressure carbon dioxide prepared by the supercharger. It is understandable that the number of intermediate containers can be set to multiple and each has a different volume. Such a setting can meet the injection requirements of different fracturing volumes and is conducive to achieving accurate control of the injection amount.

[0059] For example, Figure 2 As shown, there are three intermediate containers, namely, the first intermediate container 9, the second intermediate container 8, and the third intermediate container 7. The gas inlets of the first intermediate container 9, the second intermediate container 8, and the third intermediate container 7 are connected in parallel to the gas outlet of the supercharger 6. The first driving pump 10 is connected in parallel to the first intermediate container 9, the second intermediate container 8, and the third intermediate container 7. The gas inlets of the first intermediate container 9, the second intermediate container 8, and the third intermediate container 7 are respectively provided with a sixth stop valve 0906, a fifth stop valve 0905, and a fourth stop valve 0904. By controlling the opening and closing of the sixth stop valve 0906, the fifth stop valve 0905, and the fourth stop valve 0904, the carbon dioxide discharged from the supercharger 6 can be stored in any intermediate container.

[0060] Preferably, the volumes of the first intermediate container 9 , the second intermediate container 8 , and the third intermediate container 7 are 0.5 L, 1.5 L, and 2.5 L, respectively.

[0061] The foam generator 16 of this embodiment is used to generate the foam required in the proppant transportation process, and inject the prepared foam into the stirring device 15. The stirring device 15 is used to evenly mix the fracturing fluid, the proppant and the foam according to a set ratio.

[0062] The first driving pump 10 is used to directly inject the different phases of carbon dioxide stored in the intermediate container into the rock sample 24 at a set displacement, or to inject the different phases of carbon dioxide stored in the intermediate container into the stirring device 15, so as to mix the fracturing fluid and the proppant in the stirring device 15 and inject them into the rock sample 24. The second driving pump 11 can separately inject water or water-carrying proppant mixed fracturing fluid into the rock sample 24 or the stirring device 15 at a set displacement, so as to achieve mixed injection of fracturing fluid and proppant. Through the organic combination of the first driving pump 10 and the second driving pump 11, different phases of carbon dioxide, water or a mixture of the two or a proppant mixed fracturing fluid can be separately injected into the rock sample 24 at a set displacement. Preferably, the intermediate container adopts a plunger-type intermediate container, and the first driving pump 10 and the second driving pump 11 adopt plunger pumps.

[0063] In some examples, such as Figure 2 As shown, the output end of the second driving pump 11 is provided with a tenth stop valve 0910, which is used to control the disconnection or connection of the output pipeline of the second driving pump. The inlet of the foam generator 16 is provided with an eleventh stop valve 0911; the intermediate container and the accommodating chamber 01 are provided with a twelfth stop valve 0912 and a thirteenth stop valve 0913 in sequence; the discharge port of the stirring device 15 is provided with a fourteenth stop valve 0914; the discharge port of the accommodating chamber 01 is provided with a fifteenth stop valve 0915. By controlling the opening and closing of the tenth stop valve 0910, the eleventh stop valve 0911, the twelfth stop valve 0912, the thirteenth stop valve 0913, the fourteenth stop valve 0914 and the fifteenth stop valve 0915, the flow direction of various media in the pipeline can be controlled.

[0064] like Figure 1 and Figure 2As shown, the fracturing fluid preparation system 4 of this embodiment also includes: a first pressure sensor 14, a first temperature sensor 13, and a first flow sensor 12, which are sequentially arranged at the output end of the intermediate container, for accurately monitoring the initial output pressure, temperature, and flow of the fracturing fluid; and a second pressure sensor 19, a second temperature sensor 20, and a second flow sensor 21, which are sequentially arranged at the inlet end of the accommodating chamber 01, for accurately monitoring the injection pressure, temperature, and flow of the fracturing fluid mixed with proppants. Through the visualization window on the accommodating chamber 01, the second pressure sensor 19, and the second temperature sensor 20, the state and phase change process of carbon dioxide under different temperature and pressure conditions can be observed in real time, and the continuous phase change of carbon dioxide and the influence of carbon dioxide under these states on fracturing and proppant migration processes can be studied.

[0065] In addition, if Figure 2 As shown, in this embodiment, an upstream chamber 18 is provided upstream of the second pressure sensor 19, which enables the fracturing fluid to smoothly enter the rock sample 24 in the accommodating chamber 01. A second pressure reducing valve 22 is provided downstream of the second flow sensor 21 for adjusting the injection pressure of the fracturing fluid. The discharge port of the accommodating chamber 01 is provided with a downstream chamber 27, a back pressure valve 29, a sixth pressure sensor 30 and a third flow sensor 31 in sequence; the downstream chamber 27 is used to adjust the discharge pressure of the accommodating chamber 01 to avoid fluid turbulence or impact, thereby protecting downstream equipment; by adjusting the opening degree of the back pressure valve 29, the flow and pressure of the fluid in the pipeline can be controlled, thereby achieving the purpose of controlling the system pressure stability.

[0066] In some embodiments, Figure 1 and Figure 2 As shown, the temperature control system 05 includes: a first temperature controller 17 and a second temperature controller 28. The first temperature controller 17 is connected to the fracturing fluid preparation system 04. The first temperature controller 17 is used to simulate different fracturing fluid injection temperatures. The second temperature controller 28 is connected to the accommodation chamber 01. The second temperature controller 28 is used to simulate reservoir temperatures at different depths underground.

[0067] The temperature control system 05 of this embodiment is used to simulate reservoir temperature conditions at different depths underground and different fracturing fluid injection temperatures, and includes a first temperature controller 17 and a second temperature controller 28. The second temperature controller 28 can form a stable temperature field around the rock sample 24 by electric heating, and the temperature range is from room temperature to 300 degrees Celsius; the temperature range of the first temperature controller 17 is -25 degrees Celsius to 100 degrees Celsius, which can meet the temperature requirements of different types of fracturing fluids (low-temperature liquid carbon dioxide, supercritical carbon dioxide, water, and a mixture of the above fracturing fluids). The temperature control system 05 of this embodiment can accurately control the temperature, and the control error does not exceed ±0.5°C.

[0068] In some embodiments, Figure 1 and Figure 2 As shown, the tail gas recovery system 06 includes a gas recovery device 37, and the gas recovery device 37 includes a condenser and a filter. The tail gas recovery system 06 is used to separate, condense and purify the carbon dioxide, methane and helium discharged from the containing chamber 01 during the experiment, and recycle them to the gas source supply system 03 for reuse.

[0069] The tail gas recovery system 06 of this embodiment includes an integrated condenser and a filter. Through the cooperation of the condenser and the filter, the carbon dioxide, methane and helium emitted during the experiment can be separated, condensed and purified, and directly reused after recovery.

[0070] Figure 5 A schematic diagram of a multi-parameter monitoring system 07 provided in this embodiment. In some embodiments, Figure 1 and Figure 5 As shown, the multi-parameter monitoring system 07 includes an integrated multi-parameter sensor 35. The integrated multi-parameter sensor 35 includes: an acoustic emission monitoring device 351, which is used to monitor the internal micro-crack activity of the rock sample 24 in real time during the fracturing, displacement and sealing process. A wave velocity monitoring device 352, which is used to measure the wave velocity change of the rock sample 24 to obtain the mechanical parameter change of the rock sample 24. A resistivity measuring device 353, which is used to measure the resistivity value of the rock sample 24 at different water saturations to obtain the exponential relationship between saturation and resistivity. A fiber grating temperature stress strain monitoring device 354, which is used to monitor the surface temperature, stress and strain of the rock sample 24 in real time during the fracturing, displacement and sealing process. A digital speckle detection device 355, which is used to obtain the displacement field and strain field on the surface of the rock sample 24, so as to obtain the dynamic changes of the initiation, evolution, expansion and elastic-plastic stages of the cracks in the rock sample 24. A nuclear magnetic resonance detection device 356, which is used to obtain the displacement efficiency of the rock sample 24 at different water contents. The pressure difference monitoring device 357 is used to monitor the pressure difference between the upstream and downstream of the containing chamber 01. The gas leakage monitoring device 358 is used to monitor the gas leakage in the rock sample 24.

[0071] The multi-parameter monitoring system 07 of this embodiment is equipped with a variety of high-precision sensors and organically integrated. It can monitor and record the changes of various parameters in the process of fracturing, displacement and sealing in real time, provide comprehensive experimental data support, and can monitor and record the changes of various parameters of rock properties and fracturing fluid state in the process of fracturing-displacement-sealing in real time. Through the integrated multi-parameter sensor 35, a composite sensor with integrated temperature, pressure, strain and acoustic emission measurement functions is used to reduce the complexity of sensor installation and connection, and ensure the consistency of measurement points and data synchronization. Each sensor node is equipped with a low-power wireless communication module, using ZigBee (a wireless communication technology applied to short distances and low rates) or LoRa (a low-power wide area network communication technology) technology to ensure the stability of data transmission and long-distance transmission capabilities, reduce wiring requirements, and improve the flexibility of experimental layout. And using automated data acquisition and processing software, the system can automatically collect, store and analyze experimental data. At the same time, using remote monitoring software, the system can remotely monitor the experimental status in real time on Android and iOS platforms, and display current experimental information and sensor output data. The system supports data transmission through a local wireless network or Ethernet connection. Among them:

[0072] The acoustic emission monitoring device 351 uses a highly sensitive acoustic emission sensor to monitor the micro-crack activity inside the rock during fracturing, displacement and sealing in real time;

[0073] The wave velocity monitoring device 352 is used to measure the wave velocity changes of the rock sample and analyze the changes of the mechanical parameters of the rock through inversion calculation;

[0074] The resistivity measuring device 353 is used to measure the resistivity value of the rock sample at different water saturations and obtain the relationship between saturation and resistivity index;

[0075] The fiber Bragg grating temperature stress strain monitoring device 354 is used to monitor the surface temperature, stress and strain of the specimen in real time during the fracturing-displacement-sealing process;

[0076] The digital speckle detection device 355 analyzes the speckle image on the sample surface through digital image correlation (DIC) software, calculates the displacement field, strain field and other data on the sample surface, and analyzes the dynamic changes of the crack initiation, evolution, expansion and elastic-plastic stage of the specimen during the experiment.

[0077] The nuclear magnetic resonance detection device 356 can indirectly obtain real-time data of the methane adsorption state based on the nuclear magnetic resonance T2 spectrum and calculate the displacement efficiency of samples with different water contents.

[0078] The pressure difference monitoring device 357 is used to monitor the pressure difference between the upstream and downstream of the test piece in real time during the transient permeability measurement process.

[0079] The gas leakage monitoring device 358 can monitor the leakage of carbon dioxide and methane in real time. Once a leakage is detected, the alarm mechanism will be triggered immediately to ensure the safety of the experimenters.

[0080] In addition, the multi-parameter monitoring system 07 of this embodiment can inject supercritical carbon dioxide at a set pressure into the rock sample 24 after the displacement is completed to simulate the deep reservoir carbon dioxide storage process, and use a variety of monitoring methods to monitor the changes in various parameters of the rock during the storage process in real time. The wave velocity monitoring device 352, the acoustic emission monitoring device 351, and the fiber grating temperature stress strain monitoring device 354 are used to monitor the changes in the mechanical parameters of the rock sample 24 in real time to ensure the safety and effectiveness of the storage process. The data obtained by the multi-parameter monitoring system 07 can be used to feedback and correct the prediction and evaluation model of the carbon dioxide storage leakage risk, and to predict the long-term storage stability.

[0081] In some embodiments, Figure 1 and Figure 2 As shown, the displacement effect evaluation system 08 includes: a gas phase spectrometer 36, which is arranged between the accommodating chamber 01 and the tail gas recovery system 06. The displacement effect evaluation system 08 of this embodiment is used to simulate the process of carbon dioxide displacing methane in unconventional reservoirs and the effect evaluation, and adopts the third flow sensor 31, the nuclear magnetic resonance detection device 356, and the gas phase spectrometer 36 to detect the methane displacement amount, carbon dioxide / methane displacement ratio, and methane extraction pure amount under different water content states in the dynamic displacement process in real time. It has high sensitivity and high resolution, can quickly and accurately measure the concentration changes of each component, quantitatively evaluate the displacement effect, and clarify the relationship between the displacement evaluation index and the displacement time.

[0082] When using the experimental device of this embodiment to perform permeability test experiments, a combination of steady-state method and transient method can be used, or different test modes can be flexibly selected according to experimental needs, so that the permeability of rock samples before and after fracturing can be accurately measured. -16 m 2 It is recommended to use the steady-state method to measure rock permeability, otherwise, the transient method is used. The third flow sensor 31 is used for the test requirements of the steady-state method; the organic combination of the upstream chamber 18, the downstream chamber 27, the sixth pressure sensor 30, and the pressure difference monitoring device 357 can realize the transient method to measure the permeability, ensuring the accuracy and reliability of the test results; the back pressure valve 29 is used to control the downstream output fluid pressure of the accommodating chamber 01, and control it above 7.38MPa to simulate the whole process of carbon dioxide seepage in a supercritical state.

[0083] The above supercritical CO 2The integrated experimental device for fracturing, displacement and storage was introduced. The experimental device significantly improved the technical level and practicality of the integrated experimental instrument for supercritical carbon dioxide fracturing, displacement and storage through the accommodating chamber 01, ground stress simulation system 02, gas source supply system 03, fracturing fluid preparation system 04, temperature control system 05, tail gas recovery system 06, multi-parameter monitoring system 07 and displacement effect evaluation system 08. This not only enhances the function and performance of the experiment, but also makes the experimental operation more convenient, improves the accuracy and reliability of the experimental data, and provides a more efficient, intelligent and environmentally friendly experimental means for the development and research of unconventional natural gas.

[0084] This embodiment also provides a supercritical CO 2 The integrated experimental method of fracturing, displacement and storage uses the supercritical CO 2 Integrated experimental device for fracturing, displacement and storage. Figure 6 A supercritical CO provided in this embodiment 2 Flowchart of the integrated experimental method of fracturing, displacement and storage.

[0085] like Figure 6 As shown, the supercritical CO 2 The integrated experimental method of fracturing, displacement and sealing includes the following steps:

[0086] S1. Prepare a rock sample 24 and place the rock sample 24 in the receiving chamber 01;

[0087] Specifically, the preparation of the rock sample 24 includes: processing a cubic rock sample 24 with a size range of 5 cm to 30 cm, drilling a fracturing hole with a diameter of 2 cm directly above it, and the depth of the fracturing hole is 1 / 2 to 1 / 3 of the side length of the rock sample 24; based on a chemical thermodynamic method for accurately preparing different water contents, a rock sample 24 with a water content of 0 to 10% is prepared.

[0088] Placing the rock sample 24 in the containing chamber 01 includes: cleaning the upper surface of the rock sample 24 to avoid grease or other contaminants, and evenly spraying the upper surface of the sample with white spray paint in a well-ventilated area, ensuring that the spray layer is uniform and without omissions, and that there are no bubbles or defects after the coating dries. After waiting for the white spray paint coating to completely dry, use a black oil pen to evenly apply black spots on the white coating. The size, shape and spacing of the spots can be adjusted according to the requirements of the experiment or the digital speckle detection device 355 test.

[0089] Subsequently, a sensor probe of the fiber Bragg grating temperature stress and strain monitoring device 354 is arranged on each surface of the rock sample 24, and then the rock sample 24 is placed in the accommodating cavity 01, the ground stress simulation system 02 is started, and the output pressures of the first driving device 32, the second driving device 33, and the third driving device 34 are set respectively, and three-dimensional stress is accurately applied to the rock sample 24. The applied stress is monitored and recorded in real time through the third pressure sensor 38, the fourth pressure sensor 39, and the fifth pressure sensor 40; the acoustic emission sensor of the acoustic emission monitoring device 351, the oscilloscope probe of the wave velocity monitoring device 352, the nuclear magnetic resonance signal probe of the nuclear magnetic resonance detection device 356, and the sensor lead wire of the fiber Bragg grating temperature stress and strain monitoring device 354 are installed and fixed in the installation hole 2311 of at least one loading plate among the first loading plate 231, the second loading plate, and the third loading plate. There are wire grooves between the first loading plate 231 and the first piston rod 232, between the second loading plate and the second piston rod, and between the third loading plate and the third piston rod for leading out wires connected to the above-mentioned sensors. The wires are connected to the multi-parameter monitoring system 07 through pipelines.

[0090] S2. Obtaining the permeability of the rock sample 24 before fracturing;

[0091] Specifically, when the permeability of the rock sample 24 exceeds 10 -16 m 2 The permeability of the rock sample 24 is measured using the steady-state method: the helium storage device 3 is opened, the first pressure reducing valve 5 is adjusted, the output gas pressure is set to ensure that the pressure in the system is less than the confining pressure, the helium is connected to the fracturing pipe 25 through a pipeline, and is injected into the rock sample 24 through the fracturing pipe 25. The pressure and flow rate of the gas inlet and outlet during the test are recorded. The test is stopped when the flow rate is stable for a certain period of time, and the permeability of the rock sample 24 before fracturing is calculated using the steady-state method formula.

[0092] When the permeability of the rock sample is less than 10 -16 m 2When the permeability of the rock sample 24 is measured using the transient method: the helium storage device 3 is opened, the first pressure reducing valve 5 is adjusted, the output gas pressure is set (recommended to be 7MPa), and the pressure in the system is ensured to be less than the confining pressure. The helium is connected to the fracturing pipe 25 through the pipeline, and is injected into the rock sample 24 through the fracturing pipe 25, and the rock sample 24 is waited for to be saturated with helium (the saturation time is not less than 5min). The pressure in the system is recorded, which is the pore pressure. The helium storage device 3 is closed, the pressure difference monitoring device 357 is turned on, and a certain amount of gas in the downstream chamber 27 is discharged, so that the gas discharge is stopped when the pressure difference between the upstream chamber 18 and the downstream chamber 27 reaches 0.0689MPa to 0.2067MPa, and then the pressure difference between the upstream chamber 18 and the downstream chamber 27 gradually decreases. When the pressure difference between the upstream chamber 18 and the downstream chamber 27 drops to 1 / 3 of the initial pressure difference, the test is stopped, and the gas is recycled through the tail gas recovery system 06. The downstream pressure of the accommodation chamber 01, the upstream and downstream pressure difference and the time are recorded, and the permeability of the rock sample 24 before fracturing is calculated by the transient method formula.

[0093] Conduct supercritical carbon dioxide permeability test: open the carbon dioxide storage device 1, adjust the first pressure reducing valve 5 to set the output gas pressure, start the supercharger 6, pressurize the carbon dioxide output by the first pressure reducing valve 5 to make its pressure exceed 7.38MPa (supercritical carbon dioxide critical pressure), and store it in an intermediate container (referring to the first intermediate container 9, the second intermediate container 8 or the third intermediate container 7), set the first temperature controller 17 to make its temperature exceed 31°C (supercritical carbon dioxide critical temperature), and finally make the carbon dioxide in the intermediate container in a supercritical state; then adjust the second pressure reducing valve 22 and the back pressure valve 29 to make their output pressure greater than 7.38MPa, so that the carbon dioxide flows in the rock sample 24 in the form of supercritical carbon dioxide, record the pressure and flow rate of the gas inlet and outlet of the containing chamber 01 during the test, stop the test when the flow rate is stable for a certain period of time, and calculate the supercritical CO2 of the rock sample 24 before fracturing by the steady-state method formula. 2 Permeability.

[0094] S3. injecting methane gas into the rock sample 24 to simulate the in-situ methane storage state;

[0095] Specifically, the methane storage device 2 is opened, the first pressure reducing valve 5 and the pressure booster 6 are adjusted, and the methane gas is injected into the rock sample 24 at a preset pressure through the pipeline and the fracturing pipe 25, and the injection time is continued for 7 days. After the methane storage device 2 is closed, the pressure monitored by the second pressure sensor 19 does not change, and it is considered that the rock sample 24 has reached adsorption equilibrium, simulating the in-situ methane storage state.

[0096] S4. Performing a fracturing experiment on the rock sample 24;

[0097] Specifically, the fracturing experiment on the rock sample 24 includes:

[0098] (1) Supercritical carbon dioxide sand fracturing experiment

[0099] The carbon dioxide storage device 1 is turned on, and the first pressure reducing valve 5 is adjusted to control the output pressure of the carbon dioxide storage device 1; the booster 6 is turned on to increase the low-pressure CO outputted by the first pressure reducing valve 5. 2 The pressure is increased to more than 7.38MPa; a first temperature controller 17 is set to make the carbon dioxide temperature exceed 31°C and then be stored in an intermediate container (referring to the first intermediate container 9, the second intermediate container 8 or the third intermediate container 7), so that the supercritical carbon dioxide in the intermediate container is stable at a preset value; the first driving pump 10 is started to push the piston in the intermediate container to move, so that the supercritical carbon dioxide stored in the intermediate container is injected into the stirring device 15 according to the preset displacement; the stirring device 15 and the foam generator 16 are started to fully stir the supercritical carbon dioxide, the proppant and the foam in the stirring device 15 according to the preset proportion, and after being mixed evenly, they are injected into the rock sample 24 through the fracturing pipe 25; the second pressure sensor 19, the second temperature sensor 20 and the second flow sensor 21 are respectively used to monitor the injection pressure, temperature and flow changes of the supercritical carbon dioxide in the sand fracturing process in real time; once the rock sample 24 is broken, the supercritical carbon dioxide The injection pressure and temperature of carbon will change significantly. The phase change of carbon dioxide is monitored through the visualization window on the accommodating chamber 01, the second pressure sensor 19 and the second temperature sensor 20. A high-precision camera 26 combined with a digital speckle detection device 355 is used to monitor the surface strain field changes of the rock sample 24 during the fracturing process in real time through the visualization window on the accommodating chamber 01. An acoustic emission monitoring device 351 is used to monitor the acoustic emission signal inside the rock sample 24 during the fracturing process, and invert the microcrack extension information inside the specimen. A fiber grating temperature stress strain monitoring device 354 is used to monitor the surface temperature, stress and strain data of the rock sample 24. After fracturing the first section, the positioning nut 251 of the fracturing tube 25 is adjusted to move the fracturing tube 25 upward, and the third sealing ring 254 moves to the original height position of the second sealing ring 253, and supercritical carbon dioxide is continuously injected to carry out the next stage of fracturing test to realize the staged fracturing process.

[0100] (2) Supercritical carbon dioxide fracturing experiment

[0101] Open the carbon dioxide storage device 1, adjust the first pressure reducing valve 5; open the booster 6 to increase the low-pressure CO output from the first pressure reducing valve 5. 2The pressure is increased to more than 7.38MPa, and a first temperature controller 17 is set to make its temperature exceed 31°C, and then the supercritical carbon dioxide is stored in an intermediate container (referring to the first intermediate container 9, the second intermediate container 8 or the third intermediate container 7), so that the supercritical carbon dioxide in the intermediate container is stabilized at a preset value; the first driving pump 10 is started to push the piston in the intermediate container to move, so that the supercritical carbon dioxide stored in the intermediate container is injected into the rock sample 24 through the fracturing pipe 25 according to the preset displacement; the second pressure sensor 19, the second temperature sensor 20, and the second flow sensor 21 are respectively used to monitor the changes in the injection pressure, temperature, and flow rate of the supercritical carbon dioxide during the fracturing process in real time; once the rock is broken, the injection pressure and temperature of the supercritical carbon dioxide will change significantly, and the visual window on the accommodating chamber 01, the second temperature sensor 20, and the second flow sensor 21 are used to monitor the injection pressure, temperature, and flow rate of the supercritical carbon dioxide in real time. The pressure sensor 19 and the second temperature sensor 20 monitor the phase change of carbon dioxide; a high-precision camera 26 is used in combination with a digital speckle detection device 355 to monitor the surface strain field changes of the rock sample 24 during the fracturing process in real time through the visualization window on the accommodating chamber 01; an acoustic emission monitoring device 351 is used to monitor the acoustic emission signal inside the rock sample 24 during the fracturing process, and the microcrack extension information inside the rock sample 24 is inverted; a fiber grating temperature stress strain monitoring device 354 is used to monitor the surface temperature, stress and strain data of the rock sample 24; after fracturing the first section, the positioning nut 251 of the fracturing tube 25 is adjusted to move the fracturing tube 25 upward, and the third sealing ring 254 is moved to the original height position of the second sealing ring 253, and supercritical carbon dioxide is continuously injected to carry out the next stage of fracturing test.

[0102] (3) Water-carrying supercritical carbon dioxide-carrying sand fracturing experiment

[0103] Open the carbon dioxide storage device 1, adjust the first pressure reducing valve 5; open the booster 6 to increase the low-pressure CO output from the first pressure reducing valve 5. 2The pressure is increased to more than 7.38MPa; a first temperature controller 17 is set to make its temperature exceed 31°C, and then stored in an intermediate container (referring to the first intermediate container 9, the second intermediate container 8 or the third intermediate container 7), so that the supercritical carbon dioxide in the intermediate container is stable at a preset value; the first drive pump 10 is started to push the piston in the intermediate container to move; at the same time, the second drive pump 11 is started to output high-pressure water, so that supercritical carbon dioxide and high-pressure water are injected into the stirring device 15 according to a preset ratio and displacement; the stirring device 15 and the foam generator 16 are started to fully stir the supercritical carbon dioxide, water, proppant, and foam in the stirring device 15 according to a preset ratio, and after mixing evenly, they are injected into the rock sample 24 through the fracturing pipe 25; the second pressure sensor 19, the second temperature sensor 20, and the second flow sensor 21 are respectively used to monitor the changes in the injection pressure, temperature, and flow of supercritical carbon dioxide during the fracturing process in real time; once the rock is broken, The injection pressure and temperature of supercritical carbon dioxide will change significantly. The phase change of carbon dioxide is monitored through the visualization window on the accommodating chamber 01, the second pressure sensor 19 and the second temperature sensor 20. A high-precision camera 26 combined with a digital speckle detection device 355 is used to monitor the surface strain field changes of the rock sample 24 in real time during the fracturing process through the visualization window on the accommodating chamber 01. An acoustic emission monitoring device 351 is used to monitor the acoustic emission signal inside the rock sample 24 during the fracturing process, and invert the microcrack extension information inside the rock sample 24. A fiber grating temperature stress strain monitoring device 354 is used to monitor the surface temperature, stress and strain data of the rock sample 24. After fracturing the first section, the positioning nut 251 of the fracturing tube 25 is adjusted to move the fracturing tube 25 upward in the fracturing hole until the third sealing ring 254 moves to the original height position of the second sealing ring 253, and supercritical carbon dioxide is continuously injected to carry out the next stage of fracturing test.

[0104] It is understandable that in addition to the above-mentioned fracturing experiments, hydraulic fracturing experiments, water-carrying sand fracturing experiments, liquid carbon dioxide fracturing experiments, etc. can also be carried out.

[0105] S5. displacing methane in the rock sample 24, obtaining the displacement effect and recovering the displaced mixed gas;

[0106] Specifically, after the fracturing experiment is completed, the first drive pump 10 is turned off, the first pressure reducing valve 5 is adjusted to the preset value, and carbon dioxide is continuously injected into the rock sample 24 after fracturing through the fracturing pipe 25, so that the mixed gas displaced by fracturing enters the downstream connecting pipeline through the discharge port of the accommodating chamber 01; a fiber grating temperature stress strain monitoring device 354 is used to monitor the surface temperature, stress and strain of the rock sample 24 during the displacement process in real time; a third flow sensor 31, a nuclear magnetic resonance detection device 356, and a gas phase spectrometer 36 are used to detect the methane displacement amount, carbon dioxide / methane displacement ratio, and methane extraction pure amount under different water content conditions during the dynamic displacement process in real time; the displaced mixed gas is separated, condensed and purified by the tail gas recovery system 06, and directly reused after recovery.

[0107] S6. Obtaining the permeability of the rock sample 24 after fracturing;

[0108] Specifically, due to the complex cracks generated inside the rock sample 24 after fracturing, it has a higher permeability;

[0109] Use the steady-state method to measure the permeability of the rock sample 24 after fracturing: open the helium storage device 3; adjust the first pressure reducing valve 5, set the output gas pressure, ensure that the pressure in the system is less than the confining pressure, and connect the helium to the fracturing pipe 25 through the pipeline, and inject it into the rock sample 24 through the fracturing pipe 25. Record the pressure and flow rate of the gas inlet and outlet of the containing chamber 01 during the test. Stop the test when the flow rate is stable for a certain period of time, and calculate the permeability of the rock sample 24 after fracturing using the steady-state method formula;

[0110] Supercritical CO fracturing test specimens 2 Seepage test:

[0111] The carbon dioxide storage device 1 is opened, the first pressure reducing valve 5 is adjusted, the output gas pressure is set, the supercharger 6 is started, and the carbon dioxide outputted from the first pressure reducing valve 5 is pressurized to make its pressure exceed 7.38 MPa (supercritical carbon dioxide critical pressure); it is stored in an intermediate container (referring to the first intermediate container 9, the second intermediate container 8 or the third intermediate container 7), and the first temperature controller 17 is set to make its temperature exceed 31° C. (supercritical carbon dioxide critical temperature), and finally the carbon dioxide in the intermediate container is in a supercritical state; then the second pressure reducing valve 22 and the back pressure valve 29 are adjusted to make their output pressure greater than 7.38 MPa, so that the carbon dioxide flows in the rock sample 24 in a supercritical carbon dioxide state, and the pressure and flow rate of the gas outlet and inlet of the containing chamber 01 during the test are recorded. When the flow rate is stable for a certain period of time, the test is stopped, and the supercritical CO2 of the rock sample 24 after fracturing is calculated by the steady-state method formula. 2 Permeability.

[0112] S7. Seal the rock sample 24 and establish a prediction and evaluation model for leakage risk.

[0113] Specifically, the carbon dioxide storage device 1 is turned on, and the first pressure reducing valve 5 is adjusted; the supercharger 6 is turned on to increase the low-pressure CO output by the first pressure reducing valve 5. 2 The pressure is increased to more than 7.38MPa, and the first temperature controller 17 is set to make its temperature exceed 31°C, and then it is stored in an intermediate container (referring to the first intermediate container 9, the second intermediate container 8 or the third intermediate container 7), so that the supercritical carbon dioxide in the intermediate container is stable at a preset value; the first driving pump 10 is started to push the piston in the intermediate container to move, so that the supercritical carbon dioxide stored in the intermediate container is continuously injected into the rock sample 24 at a preset pressure, and the injection time is 7 days. When the carbon dioxide storage device 1 is closed, the pressure monitored by the second pressure sensor 19 does not change, and it is considered that the rock sample 24 has reached adsorption equilibrium, simulating the in-situ CO 2 Endogenous environment;

[0114] The wave velocity monitoring device 352 is used to measure the wave velocity changes of the rock sample 24 before and after sealing, and the changes in the mechanical parameters of the rock sample 24 are analyzed by inversion calculation; the resistivity measuring device 353 is used to measure the resistivity values ​​of the rock sample 24 at different water saturations to obtain the relationship between saturation and resistivity index; the fiber Bragg grating temperature stress strain monitoring device 354 is used to monitor the surface temperature, stress and strain of the rock sample 24 in real time during the sealing process; through these data, the prediction and evaluation model of the carbon dioxide storage leakage risk can be fed back and corrected, and the long-term storage stability prediction can be carried out. The gas leakage monitoring device 358 can monitor CO in real time. 2 Once a leak is detected, the alarm mechanism will be triggered immediately.

[0115] The integrated experimental method of fracturing, displacement and sealing of this embodiment utilizes the above-mentioned experimental device, and can continuously complete the experimental process of fracturing, displacement and sealing on the same experimental device, which is conducive to improving the experimental efficiency and consistency of data, and can simulate complex conditions such as underground true triaxial stress and ground temperature, provide an experimental environment close to the actual working conditions, and improve the reliability and applicability of the experimental results. And it is possible to quantitatively evaluate the permeability changes of rock samples 24 before and after fracturing by different types of fracturing fluids and the effect of in-situ methane displacement. When establishing long-term storage of carbon dioxide, the prediction and evaluation model of the risk of leakage of storage is automatically fed back and corrected. The overall real-time monitoring system with multi-parameter and high-precision sensors organically integrated is adopted to provide intuitive and rich experimental data from multiple angles. In addition, a tail gas recovery system is designed to realize the recycling and utilization of experimental gas.

[0116] It is easy for those skilled in the art to understand that, under the premise of no conflict, the above-mentioned advantageous methods can be freely combined and superimposed.

[0117] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention. The above are only preferred embodiments of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and variations can be made without departing from the technical principles of the present invention, and these improvements and variations should also be regarded as the protection scope of the present invention.

Claims

1. A supercritical CO2 fracturing, displacement and storage integrated experimental device, characterized in that: include: A holding chamber, used for holding a rock sample; A geostress simulation system connected to the accommodating cavity; the geostress simulation system is used to apply pressure to the rock sample to simulate underground three-dimensional stress conditions; An air source supply system is connected to the accommodating chamber; the air source supply system is used to supply the rock sample with the air source required for fracturing, displacement, permeability testing and sealing; A fracturing fluid preparation system is connected between the gas source supply system and the accommodating chamber; the fracturing fluid preparation system is used to prepare fracturing fluid and inject the fracturing fluid into the rock sample; A temperature control system, used to adjust the temperature of the containing chamber and the fracturing fluid preparation system to simulate reservoir temperatures at different depths underground and different fracturing fluid injection temperatures; An exhaust gas recovery system connected to the accommodating chamber; the exhaust gas recovery system is used to recover the gas discharged from the accommodating chamber; A multi-parameter monitoring system for real-time monitoring and recording the changes in various parameters of the rock sample properties and the state of the fracturing fluid during fracturing, displacement and sealing; The displacement effect evaluation system can quantitatively evaluate the displacement effect according to the parameters obtained by the multi-parameter monitoring system.

2. The supercritical CO2 fracturing, displacement and storage integrated experimental device according to claim 1 is characterized in that: The accommodating chamber is provided with an injection port and a discharge port; the injection port is provided with an injection assembly; the discharge port is connected to the exhaust gas recovery system; The injection assembly comprises: a three-way joint and a fracturing pipe; The three-way joint includes a first interface, a second interface and a third interface; the gas source supply system and the fracturing fluid preparation system are connected in parallel to the first interface; the multi-parameter monitoring system is connected to the second interface; The fracturing pipe comprises a first end and a second end; the first end is connected to the third interface; the second end is closed; on the outer circumference of the fracturing pipe, a first sealing ring, a second sealing ring and a third sealing ring are arranged in sequence from the first end to the second end; a perforation is arranged on the pipe wall of the fracturing pipe; the perforation is located between the second sealing ring and the third sealing ring; The second end of the fracturing pipe extends from the injection port into the accommodating cavity and is inserted into the fracturing hole on the rock sample; the first sealing ring, the second sealing ring and the third sealing ring are sealedly connected to the inner wall of the fracturing hole; The fracturing pipe is sealed and connected to the injection port and can be raised and lowered in the fracturing hole.

3. The supercritical CO2 fracturing, displacement and storage integrated experimental device according to claim 1 is characterized in that: The geostress simulation system comprises: The first direction loading assembly comprises a first loading plate, a first piston rod and a first driving device; the first loading plate is arranged on both sides of the rock sample in the first direction; one end of the first piston rod is connected to the first loading plate; and one end of the first piston rod away from the first loading plate is connected to the first driving device; The second direction loading assembly comprises a second loading plate, a second piston rod and a second driving device; the second loading plate is arranged on both sides of the rock sample in the second direction; one end of the second piston rod is connected to the second loading plate; and one end of the second piston rod away from the second loading plate is connected to the second driving device; A third direction loading assembly comprises a third loading plate, a third piston rod and a third driving device; the third loading plate is arranged on both sides of the rock sample in the third direction; one end of the third piston rod is connected to the third loading plate; and one end of the third piston rod away from the third loading plate is connected to the third driving device; The first loading plate, the second loading plate and the third loading plate are respectively provided with mounting holes; a part of the detection end of the multi-parameter monitoring system contacts the surface of the rock sample through the mounting holes.

4. The supercritical CO2 fracturing, displacement and storage integrated experimental device according to claim 1 is characterized in that: The gas source supply system comprises: a carbon dioxide storage device, a methane storage device, a helium storage device, a first pressure reducing valve and a booster; The carbon dioxide storage device, the methane storage device, and the helium storage device are connected in parallel to the inlet of the first pressure reducing valve; the outlet of the first pressure reducing valve is connected to the fracturing fluid preparation system through the booster.

5. The supercritical CO2 fracturing, displacement and storage integrated experimental device according to claim 1 is characterized in that: The fracturing fluid preparation system comprises: At least one intermediate container connected to the gas source supply system; the intermediate container is used to load carbon dioxide; a first driving pump connected to the intermediate container; the first driving pump is used to increase the carbon dioxide output pressure of the intermediate container; A stirring device, comprising a feeding port and a discharging port; the output end of the intermediate container is connected to the feeding port; the discharging port is connected to the containing chamber, so as to inject fracturing fluid into the rock sample in the containing chamber; A second driving pump is connected between the stirring device and the water source; the second driving pump is used to introduce the water source into the stirring device; A foam generator is connected to the stirring device; the foam generator is used to prepare foam and add the foam into the stirring device.

6. The supercritical CO2 fracturing, displacement and storage integrated experimental device according to claim 1 is characterized in that: The temperature control system comprises: A first temperature controller connected to the fracturing fluid preparation system; the first temperature controller is used to simulate different fracturing fluid injection temperatures; The second temperature controller is connected to the containing cavity; the second temperature controller is used to simulate the reservoir temperature at different depths underground.

7. The supercritical CO2 fracturing, displacement and storage integrated experimental device according to claim 1 is characterized in that: The tail gas recovery system comprises: a condenser and a filter; the tail gas recovery system is used to separate, condense, purify and recover carbon dioxide, methane and helium exhausted during the experiment.

8. The supercritical CO2 fracturing, displacement and storage integrated experimental device according to claim 1 is characterized in that: The multi-parameter monitoring system includes an integrated multi-parameter sensor; the integrated multi-parameter sensor includes: An acoustic emission monitoring device for real-time monitoring of the internal microcrack activity of the rock sample during the fracturing, displacement and sealing process; A wave velocity monitoring device, used to measure the wave velocity change of the rock sample to obtain the change of the mechanical parameters of the rock sample; A resistivity measuring device, used to measure the resistivity value of the rock sample at different water saturations to obtain an exponential relationship between saturation and resistivity; A fiber Bragg grating temperature stress and strain monitoring device is used to monitor the surface temperature, stress and strain of the rock sample in real time during fracturing, displacement and sealing; A digital speckle detection device, used to obtain the displacement field and strain field on the surface of the rock sample, so as to obtain the dynamic changes of the initiation, evolution, expansion and elastic-plastic stages of cracks in the rock sample; A nuclear magnetic resonance detection device, used to obtain the displacement efficiency of the rock sample at different water contents; A pressure difference monitoring device, used to monitor the pressure difference between the upstream and downstream of the accommodating chamber; A gas leakage monitoring device is used to monitor the gas leakage in the rock sample.

9. The supercritical CO2 fracturing, displacement and storage integrated experimental device according to claim 1 is characterized in that: The displacement effect evaluation system comprises: A gas phase spectrometer is arranged between the accommodating chamber and the tail gas recovery system.

10. A supercritical CO2 fracturing, displacement, and storage integrated experimental method, using the supercritical CO2 fracturing, displacement, and storage integrated experimental device as described in any one of claims 1 to 9, characterized in that: The method comprises the following steps: Preparing a rock sample, and placing the rock sample in the containing cavity; Obtaining the permeability of the rock sample before fracturing; injecting methane gas into the rock sample to simulate the in-situ methane occurrence state; performing a fracturing experiment on the rock sample; displacing methane in the rock sample, obtaining a displacing effect and recovering the displaced mixed gas; Obtaining the permeability of the rock sample after fracturing; The rock samples are sealed and a prediction and evaluation model for leakage risk is established.

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