Supercritical carbon dioxide composite fracturing crack monitoring experiment system

Abstract

The invention discloses a supercritical carbon dioxide composite fracturing crack monitoring experiment system which comprises an experiment box, a composite injection device, an optical fiber monitoring device, a true triaxial confining pressure loading device and a base. The experiment box is arranged on the top of the base; the true triaxial confining pressure loading device comprises an X-axis loading assembly, a Y-axis loading assembly and a Z-axis loading assembly; the X-axis loading assembly, the Y-axis loading assembly and the Z-axis loading assembly are respectively arranged at the upper part, the rear part and the right part of the experiment box; a high-temperature heating plate is arranged outside the experiment box. According to the invention, a deep reservoir high-temperature and high-pressure environment can be constructed, supercritical carbon dioxide composite fracturing experiments under different geological conditions can be realized, strain in a crack propagation process in rock can be monitored in real time, real-time crack initiation and propagation states of cracks can be accurately captured, a three-dimensional crack propagation finite element model can be remodeled, and the fracture propagation efficiency can be improved. The problem that the real-time crack initiation and expansion process in the high-temperature and high-pressure reservoir environment is difficult to finely capture is solved.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas reservoir development, and more specifically to a supercritical carbon dioxide composite fracturing crack monitoring experimental system. Background Art

[0002] Supercritical carbon dioxide fracturing is a "green" fracturing technology. Domestic and foreign practical results show that the use of this technology to develop unconventional deep oil and gas reservoirs is conducive to reducing water resource consumption, improving reservoirs and reducing the greenhouse effect, and reducing rock fracturing pressure. However, supercritical carbon dioxide has many unique physical and chemical properties, which will deteriorate rock strength, reduce rock porosity and increase permeability, etc., and increase the complexity of fractures.

[0003] At present, in order to achieve high temperature function, large-scale true triaxial fracturing devices generally process large-space working chambers to meet the heating function, but the cost is relatively high. In addition, the crack morphology produced by supercritical carbon dioxide injection into large-scale rocks can only be observed by CT scanning or manual cutting of the rocks after fracturing. The cost of CT scanning is relatively high, and manual cutting can easily damage the crack morphology and cannot capture the crack expansion process in real time. Therefore, the technical difficulty of real-time expansion of cracks in large-scale specimens makes it difficult to clarify the crack initiation and expansion behavior, which affects theoretical characterization and factor analysis, and is not conducive to the design of a green solution combining fracturing and storage. To this end, the present invention proposes a supercritical carbon dioxide composite fracturing crack monitoring experimental system. Summary of the invention

[0004] In view of this, the present invention provides a supercritical carbon dioxide composite fracturing crack monitoring experimental system, the purpose of which is to solve the problems existing in the prior art.

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

[0006] A supercritical carbon dioxide composite fracturing crack monitoring experimental system comprises: an experimental box, a composite injection device for injecting fracturing medium into a rock sample, an optical fiber monitoring device for monitoring the internal crack state of the rock sample, a true triaxial confining pressure loading device and a base; the experimental box is arranged on the top of the base; the true triaxial confining pressure loading device comprises an X-axis loading component, a Y-axis loading component and a Z-axis loading component; the X-axis loading component, the Y-axis loading component and the Z-axis loading component are respectively arranged above, behind and to the right of the experimental box; a high-temperature heating plate is arranged on the outside of the experimental box.

[0007] Preferably, the number of the high-temperature heating plates is four; the four high-temperature heating plates are respectively arranged on the front side, the rear side, the left side and the upper side of the experimental box.

[0008] Preferably, the X-axis loading assembly comprises an X-axis loading hydraulic cylinder and an X-axis loading plate; the X-axis loading hydraulic cylinder is arranged on the top of the corresponding high-temperature heating plate; and the X-axis loading plate is arranged at the output end of the X-axis loading hydraulic cylinder.

[0009] Preferably, the Y-axis loading assembly includes a Y-axis loading hydraulic cylinder and a Y-axis loading plate; a rear support plate is provided on the rear side of the base; the Y-axis loading hydraulic cylinder is arranged on the rear support plate; and the Y-axis loading plate is arranged at the output end of the Y-axis loading hydraulic cylinder.

[0010] Preferably, the Z-axis loading assembly includes a Z-axis loading hydraulic cylinder and a Z-axis loading plate; a right support plate is provided on the right side of the base; the Z-axis loading hydraulic cylinder is arranged on the right support plate; the Z-axis loading plate is arranged at the output end of the Z-axis loading hydraulic cylinder; the Z-axis loading plate is an L-shaped structure; a sample port corresponding to the Z-axis loading plate is opened on the front side of the experimental box.

[0011] Preferably, a guide plate is provided below the Z-axis loading plate; the left side of the guide plate is fixedly connected to the left inner wall of the experimental box; and the right side of the guide plate is fixedly connected to the right support plate.

[0012] Preferably, a bearing plate is provided on the front side, the lower side and the left inner wall of the experimental box.

[0013] Preferably, the composite injection device comprises a supercritical carbon dioxide storage tank, a water storage tank and a control valve; the supercritical carbon dioxide storage tank and the water storage tank are both connected to the control valve; and the control valve is connected to the rock sample through an injection pipe.

[0014] Preferably, the composite injection device further comprises a liquid carbon dioxide cylinder, a cooling and boosting pump and a heater; the liquid carbon dioxide cylinder, the cooling and boosting pump, the heater and the supercritical carbon dioxide storage tank are connected in sequence.

[0015] Preferably, the optical fiber monitoring device comprises a computer and an optical fiber signal demodulator; the computer is electrically connected to the optical fiber signal demodulator; and the optical fiber signal demodulator is connected to the rock sample via a high temperature resistant optical fiber.

[0016] Compared with the prior art, the present invention has achieved the following technical effects: the present invention can construct a high-temperature and high-pressure environment for deep reservoirs, realize supercritical carbon dioxide composite fracturing experiments under different geological conditions, and monitor the strain in the rock during the crack expansion process in real time, accurately capture the real-time crack initiation and expansion state, and reshape the three-dimensional crack expansion finite element model, thereby solving the problem that the real-time crack initiation and expansion process is difficult to accurately capture in the high-temperature and high-pressure reservoir environment. The research results are helpful to characterize the crack initiation and expansion characteristics of supercritical carbon dioxide composite fracturing in high-temperature and high-pressure reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic structural diagram of a supercritical carbon dioxide composite fracturing crack monitoring experimental system of the present invention;

[0018] Figure 2 It is a schematic diagram of the present invention at a viewing angle after removing the composite injection device and the optical fiber monitoring device;

[0019] Figure 3 It is a schematic diagram of the present invention from another perspective after removing the composite injection device and the optical fiber monitoring device;

[0020] Figure 4 This is a schematic diagram from one perspective inside the experimental box;

[0021] Figure 5 This is a schematic diagram of the inside of the experimental box from another perspective;

[0022] Figure 6 It is a structural schematic diagram of a high temperature heating plate;

[0023] In the figure: 1. Experiment box; 2. Base; 3. High temperature heating plate; 301. Heating plate body; 302. Electric heating rod; 4. X-axis loading hydraulic cylinder; 5. X-axis loading plate; 6. Y-axis loading hydraulic cylinder; 7. Y-axis loading plate; 8. Rear support plate; 9. Z-axis loading hydraulic cylinder; 10. Z-axis loading plate; 11. Right support plate; 12. Sample port; 13. Loading plate; 14. Supercritical carbon dioxide storage tank; 15. Water storage tank; 16. Control valve; 17. Injection pipe; 18. Liquid carbon dioxide cylinder; 19. Cooling booster pump; 20. Heater; 21. Computer; 22. Optical fiber signal demodulator; 23. High temperature resistant optical fiber; 24. Rock sample; 25. Guide plate; 26. Thermal insulation board; 27. Pressure buffer plate; 28. Support frame; 29. ​​Rubber limiter; 30. Hydraulic control device. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Example

[0026] Reference Figure 1-6As shown, the present invention discloses a supercritical carbon dioxide composite fracturing crack monitoring experimental system, comprising: an experimental box 1, a composite injection device for injecting fracturing medium into a rock sample 24, an optical fiber monitoring device for monitoring the internal crack state of the rock sample 24, a true triaxial confining pressure loading device and a base 2; the experimental box 1 is arranged on the top of the base 2; the true triaxial confining pressure loading device comprises an X-axis loading component, a Y-axis loading component and a Z-axis loading component; the X-axis loading component, the Y-axis loading component and the Z-axis loading component are respectively arranged above, behind and to the right of the experimental box 1, for applying load to the rock sample 24 to simulate a high-pressure environment; a high-temperature heating plate 3 is arranged on the outside of the experimental box 1, for heating the experimental box 1 to form a high-temperature environment in the experimental box 1.

[0027] The above-mentioned technical scheme can construct a high-temperature and high-pressure environment in the deep reservoir through a true triaxial confining pressure loading device and a high-temperature heating plate, and realize supercritical carbon dioxide composite fracturing experiments under different geological conditions. At the same time, the optical fiber monitoring device can monitor the strain during the expansion of cracks inside the rock sample and accurately capture the real-time initiation and expansion status of the cracks.

[0028] In this embodiment, the number of the high-temperature heating plates 3 is four; the four high-temperature heating plates 3 are respectively arranged at the front side, the rear side, the left side and the upper side of the experimental box 1 .

[0029] In this embodiment, the high temperature heating plate 3 includes a heating plate body 301 and a plurality of electric heating rods 302 ; the plurality of electric heating rods 302 are arranged inside the heating plate body 301 .

[0030] In this embodiment, a heat preservation and insulation board 26 is provided on the front side, the rear side and the left side of the high temperature heating plate 3 of the experimental box 1 away from the experimental box 1 for heat preservation and insulation.

[0031] In this embodiment, a temperature sensor is provided inside the experimental box 1 for detecting the internal temperature of the experimental box 1 .

[0032] In this embodiment, the X-axis loading assembly includes an X-axis loading hydraulic cylinder 4 and an X-axis loading plate 5; the X-axis loading hydraulic cylinder 4 is arranged on the top of the corresponding high-temperature heating plate 3; the X-axis loading plate 5 is arranged at the output end of the X-axis loading hydraulic cylinder 4; the X-axis loading plate 5 is located inside the experimental box 1; when in use, the X-axis loading plate 5 is driven to move by the X-axis loading hydraulic cylinder 4 to apply a load to the rock sample 24.

[0033] In this embodiment, the Y-axis loading assembly includes a Y-axis loading hydraulic cylinder 6 and a Y-axis loading plate 7; a rear support plate 8 is provided on the rear side of the base 2; the Y-axis loading hydraulic cylinder 6 is arranged on the rear support plate 8; the Y-axis loading plate 7 is arranged at the output end of the Y-axis loading hydraulic cylinder 6; the Y-axis loading plate 7 is located inside the experimental box 1; when in use, the Y-axis loading plate 7 is driven to move by the Y-axis loading hydraulic cylinder 6 to apply a load to the rock sample 24.

[0034] In this embodiment, the Z-axis loading assembly includes a Z-axis loading hydraulic cylinder 9 and a Z-axis loading plate 10; a right support plate 11 is provided on the right side of the base 2; the Z-axis loading hydraulic cylinder 9 is arranged on the right support plate 11; the Z-axis loading plate 10 is arranged at the output end of the Z-axis loading hydraulic cylinder 9; the Z-axis loading plate 10 is an L-shaped structure; a sample port 12 corresponding to the Z-axis loading plate 10 is opened on the front side of the experimental box 1; when in use, the rock sample 24 is placed on the Z-axis loading plate 10, and the rock sample 24 is manually adjusted to align with the sample port 12, and then the Z-axis loading hydraulic cylinder 9 drives the Z-axis loading plate 10 to move toward the experimental box 1, and the Z-axis loading plate 10 drives the rock sample 24 to move toward the experimental box 1 until the rock sample 24 moves to the preset position in the experimental box 1, and the load can be applied to the rock sample 24 through the X-axis loading assembly, the Y-axis loading assembly and the Z-axis loading assembly.

[0035] In this embodiment, a guide plate 25 is provided under the Z-axis loading plate 10; the left side of the guide plate 25 is fixedly connected to the left inner wall of the experimental box 1; the right side of the guide plate 25 is fixedly connected to the right support plate 11; when in use, the Z-axis loading hydraulic cylinder 9 drives the Z-axis loading plate 10 to move along the guide plate 25.

[0036] In this embodiment, supporting plates 13 are provided on the front side, lower side and left inner wall of the experimental box 1; the supporting plate 13 located on the front inner wall of the experimental box 1 corresponds to the Y-axis loading plate 7; the supporting plate 13 located on the lower inner wall of the experimental box 1 corresponds to the X-axis loading plate 5; the supporting plate 13 located on the lower inner wall of the experimental box 1 is located below the guide plate 25; the supporting plate 13 located on the left inner wall of the experimental box 1 corresponds to the Z-axis loading plate 10.

[0037] In this embodiment, pressure buffer plates 27 are provided on the side of the load-bearing plate 13 on the front inner wall of the experimental box 1 close to the rock sample 24, on the side of the load-bearing plate 13 on the left inner wall of the experimental box 1 close to the rock sample 24, on the side of the X-axis loading plate 5 close to the rock sample 24, and on the side of the Y-axis loading plate 7 close to the rock sample 24.

[0038] In this embodiment, the pressure buffer plate 27 is made of silicone material.

[0039] In this embodiment, load sensors are provided between the output end of the X-axis loading hydraulic cylinder 4 and the X-axis loading plate 5, between the output end of the Y-axis loading hydraulic cylinder 6 and the Y-axis loading plate 7, and between the output end of the Z-axis loading hydraulic cylinder 9 and the Z-axis loading plate 10 for obtaining real-time stress loading values.

[0040] In this embodiment, a support frame 28 is disposed at the bottom of the base 2 .

[0041] In this embodiment, the composite injection device includes a supercritical carbon dioxide storage tank 14, a water storage tank 15 and a control valve 16; the supercritical carbon dioxide storage tank 14 and the water storage tank 15 are both connected to the control valve 16; the control valve 16 is connected to a preset injection port on the rock sample 24 through an injection pipe 17; during injection, a variety of injection methods can be provided, including alternating injection of water and supercritical carbon dioxide, pre-injection of supercritical carbon dioxide, and post-injection of supercritical carbon dioxide.

[0042] In this embodiment, the composite injection device further includes a liquid carbon dioxide cylinder 18, a cooling booster pump 19 and a heater 20; the liquid carbon dioxide cylinder 18, the cooling booster pump 19, the heater 20 and the supercritical carbon dioxide storage tank 14 are connected in sequence.

[0043] In this embodiment, the fiber optic monitoring device includes a computer 21 and a fiber optic signal demodulator 22; the computer 21 is electrically connected to the fiber optic signal demodulator 22; the fiber optic signal demodulator 22 is connected to the rock sample 24 through a high-temperature resistant optical fiber 23; the computer 21 has three-dimensional crack expansion and reconstruction software; when in use, the high-temperature resistant optical fiber 23 collects strain data during the crack expansion process inside the rock sample, the fiber optic signal demodulator 22 collects signal demodulation strain values, and the computer 21 controls the collection, storage, analysis and reconstruction process; the fiber optic monitoring device can monitor the strain during the crack expansion process in the rock in real time, accurately capture the real-time crack initiation and expansion status of the crack, and reshape the three-dimensional crack expansion finite element model.

[0044] In this embodiment, the experimental system further includes three hydraulic control devices 30; the three hydraulic control devices 30 are respectively connected to the X-axis loading hydraulic cylinder 4, the Y-axis loading hydraulic cylinder 6 and the Z-axis loading hydraulic cylinder 9.

[0045] In this embodiment, a rubber stopper 29 is provided on the left outer wall of the right support plate 11 ; the rubber stopper 29 is provided corresponding to the Z-axis loading plate 10 .

[0046] In this embodiment, the experimental box 1 includes an upper box plate, a lower box plate, a left box plate, a right box plate, a front box plate and a rear box plate; the upper box plate, the lower box plate, the left box plate, the right box plate, the front box plate and the rear box plate together constitute the experimental box 1.

[0047] Working principle of the present invention:

[0048] 1. Place the rock sample 24 on the Z-axis loading plate 10, connect the injection pipe 17 to the injection port on the rock sample 24, and insert the high-temperature resistant optical fiber 23 into the preset optical fiber channel in the rock sample 24; 2. Manually adjust the position of the rock sample 24 to align the rock sample 24 with the sample port 12 on the experimental box 1; 3. Control the Z-axis loading hydraulic cylinder 9 through the hydraulic control device 30 to push the rock sample 24 to move to the left until the rock sample 24 moves to the preset position in the experimental box 1; 4. Control the Z-axis loading hydraulic cylinder 9 through the hydraulic control device 30 to apply a load to the rock sample 24 until the corresponding load sensor detects a value of 7Mpa, and then stop loading; 5. Control the X-axis loading hydraulic cylinder 4, the Y-axis loading hydraulic cylinder 6 and the Z-axis loading hydraulic cylinder 9 through the hydraulic control device 30 to perform confining pressure loading, and set different loading load value and construct different stress conditions; 6. Turn on the high-temperature heating plate 3 to heat the experimental box 1, so that the temperature in the experimental box 1 rises to the temperature required for the experiment; 7. Start the optical fiber monitoring device and adjust the optical fiber signal demodulator 22 to make the collected strain value accurate; 8. Start the composite injection device and realize different injection methods such as alternating injection of supercritical carbon dioxide and water, pre-injection of supercritical carbon dioxide and post-injection of supercritical carbon dioxide through the control valve; 9. Real-time monitoring of the strain and pressure during the expansion of cracks in the rock during the fracturing process, accurately capture the real-time cracking and expansion state of the cracks, and reshape the three-dimensional crack expansion finite element model; 10. After the experiment, turn off the composite injection system and the high-temperature heating plate 3; 11. Control the X-axis loading hydraulic cylinder 4, the Y-axis loading hydraulic cylinder 6 and the Z-axis loading hydraulic cylinder 9 through the hydraulic control device 30 to unload, and take out the rock sample 24.

[0049] The above description is only a preferred embodiment of the present invention and does not limit the technical scope of the present invention. Therefore, any slight modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A supercritical carbon dioxide composite fracturing crack monitoring experimental system, characterized in that: include: An experimental box (1), a composite injection device for injecting a fracturing medium into a rock sample (24), an optical fiber monitoring device for monitoring the internal crack state of the rock sample (24), a true triaxial confining pressure loading device and a base (2); the experimental box (1) is arranged on the top of the base (2); the true triaxial confining pressure loading device comprises an X-axis loading component, a Y-axis loading component and a Z-axis loading component; the X-axis loading component, the Y-axis loading component and the Z-axis loading component are respectively arranged above, behind and to the right of the experimental box (1); a high-temperature heating plate (3) is provided on the outside of the experimental box (1).

2. A supercritical carbon dioxide composite fracturing crack monitoring experimental system according to claim 1, characterized in that: The number of the high-temperature heating plates (3) is four; the four high-temperature heating plates (3) are respectively arranged on the front side, the rear side, the left side and the upper side of the experimental box (1).

3. A supercritical carbon dioxide composite fracturing crack monitoring experimental system according to claim 2, characterized in that: The X-axis loading assembly comprises an X-axis loading hydraulic cylinder (4) and an X-axis loading plate (5); the X-axis loading hydraulic cylinder (4) is arranged on the top of the corresponding high-temperature heating plate (3); and the X-axis loading plate (5) is arranged at the output end of the X-axis loading hydraulic cylinder (4).

4. A supercritical carbon dioxide composite fracturing crack monitoring experimental system according to claim 1, characterized in that: The Y-axis loading assembly comprises a Y-axis loading hydraulic cylinder (6) and a Y-axis loading plate (7); a rear support plate (8) is provided on the rear side of the base (2); the Y-axis loading hydraulic cylinder (6) is arranged on the rear support plate (8); and the Y-axis loading plate (7) is arranged at the output end of the Y-axis loading hydraulic cylinder (6).

5. The supercritical carbon dioxide composite fracturing crack monitoring experimental system according to claim 1 is characterized in that: The Z-axis loading assembly comprises a Z-axis loading hydraulic cylinder (9) and a Z-axis loading plate (10); a right support plate (11) is provided on the right side of the base (2); the Z-axis loading hydraulic cylinder (9) is arranged on the right support plate (11); the Z-axis loading plate (10) is arranged at the output end of the Z-axis loading hydraulic cylinder (9); the Z-axis loading plate (10) is an L-shaped structure; and a sample port (12) corresponding to the Z-axis loading plate (10) is provided on the front side of the experimental box (1).

6. A supercritical carbon dioxide composite fracturing crack monitoring experimental system according to claim 5, characterized in that: A guide plate (25) is provided below the Z-axis loading plate (10); the left side of the guide plate (25) is fixedly connected to the left inner wall of the experimental box (1); and the right side of the guide plate (25) is fixedly connected to the right support plate (11).

7. The supercritical carbon dioxide composite fracturing crack monitoring experimental system according to claim 1 is characterized in that: The front side, the lower side and the left inner wall of the experimental box (1) are all provided with a bearing plate (13).

8. The supercritical carbon dioxide composite fracturing crack monitoring experimental system according to claim 1, characterized in that: The composite injection device comprises a supercritical carbon dioxide storage tank (14), a water storage tank (15) and a control valve (16); the supercritical carbon dioxide storage tank (14) and the water storage tank (15) are both connected to the control valve (16); and the control valve (16) is connected to the rock sample (24) through an injection pipe (17).

9. A supercritical carbon dioxide composite fracturing crack monitoring experimental system according to claim 8, characterized in that: The composite injection device further comprises a liquid carbon dioxide gas cylinder (18), a cooling and boosting pump (19) and a heater (20); the liquid carbon dioxide gas cylinder (18), the cooling and boosting pump (19), the heater (20) and the supercritical carbon dioxide storage tank (14) are connected in sequence.

10. The supercritical carbon dioxide composite fracturing crack monitoring experimental system according to claim 1, characterized in that: The optical fiber monitoring device comprises a computer (21) and an optical fiber signal demodulator (22); the computer (21) is electrically connected to the optical fiber signal demodulator (22); and the optical fiber signal demodulator (22) is connected to the rock sample (24) via a high temperature resistant optical fiber (23).

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