Carbon dioxide foam fracturing and displacement mining experimental device and method of hydrate

Abstract

The application discloses a hydrate carbon dioxide foam fracturing and displacement mining experimental device and method, wherein the device comprises a fracturing reaction kettle cavity module, a foam preparation and injection module, a gas supply module, a stress loading module, a back pressure and output metering module, a temperature control module and a data acquisition module; the fracturing reaction kettle cavity module is arranged in a low-temperature environment formed by the temperature control module; the foam preparation and injection module, the gas supply module and the back pressure and output metering module are connected with the fluid passage of the fracturing reaction kettle cavity module through pipelines and valves; the stress loading module is connected with the loading end surfaces of the axial two ends of the fracturing reaction kettle cavity module, and constant closing stress is synchronously applied to the two ends of the sample; and the data acquisition module synchronously collects pressure, temperature, displacement, flow and image information in the fracturing process. Through the above arrangement, the carbon dioxide foam controllable fracturing, crack dynamic observation and displacement effect evaluation can be integrated.

Description

Experimental Apparatus and Method for Carbon Dioxide Foam Fracturing and Displacement Extraction of Hydrates Technical Field

[0001] This invention belongs to the technical field of natural gas hydrate extraction and carbon dioxide sequestration, specifically relating to an experimental apparatus and method for carbon dioxide foam fracturing and displacement extraction of hydrates. Background Technology

[0002] Natural gas hydrates are cage-like crystals formed by gas and water under low temperature and high pressure. They are widely distributed in deep-sea sediments and polar permafrost, containing enormous methane reserves and possessing significant energy value. Under suitable conditions, carbon dioxide can replace methane hydrates in reservoirs, achieving synergy between energy extraction and carbon sequestration. However, in most marine areas, hydrates are found in shallow, fine-grained sediments with poor permeability and low strength. Mining disturbances easily lead to the migration of fine particles and the risk of sand production, resulting in unstable flow channels and limiting seepage efficiency and production capacity. Simultaneously, the carbon dioxide replacement process is limited by small contact area, insufficient mass transfer channels, and slow reaction kinetics, making it difficult to improve replacement efficiency. Therefore, fracturing to enhance fracture-pore connectivity and expand the reaction interface holds promise for synergistically improving hydrate extraction efficiency and carbon sequestration effects along the fracture creation, mass transfer, and replacement / storage pathways.

[0003] Hydraulic fracturing is an important means to improve seepage conditions and increase production capacity in hydrate reservoirs. Compared with conventional water-based fracturing, carbon dioxide foam fracturing uses less liquid phase, has easier control over filtration loss, and causes less potential damage to fine-grained sediments. Simultaneously, the collapse-reorganization and gas-liquid synergistic effect of foam in pores and fractures is beneficial for inducing microfractures and expanding seepage channels. Introducing carbon dioxide foam fracturing into hydrate sediment modification can simultaneously enhance permeability and create fractures, providing a more effective channel foundation for subsequent mass transfer and replacement / storage processes of injected carbon dioxide. Furthermore, fracturing often requires the injection of proppant to form a propped-fill layer. Besides maintaining fracture aperture, proppant can also inhibit fine-grain migration and particle production through particle bridging and sieving, thus achieving a sand control effect.

[0004] Existing fracturing experimental devices for hydrate sediments mostly focus on fracturability verification and static fracture characterization, making it difficult to achieve stable preparation and precise injection control of carbon dioxide foam under low temperature and high pressure conditions. Fracturing and subsequent carbon dioxide replacement processes are usually separate experimental stages and cannot be carried out continuously in the same device, which restricts the quantitative evaluation of the effect of fracturing on mass transfer channels and replacement efficiency. At the same time, the dynamic fracture propagation process lacks in-situ visualization observation methods, and it is difficult to collect and correlate key parameters such as pressure, temperature, and displacement simultaneously.

[0005] Therefore, there is an urgent need to develop an integrated experimental device and method that combines controlled fracturing with carbon dioxide foam, dynamic observation of fractures, and evaluation of replacement effects. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the present invention aims to provide an experimental device and method for carbon dioxide foam fracturing and displacement mining of hydrates, which can integrate controlled carbon dioxide foam fracturing, dynamic observation of fractures and evaluation of displacement effect.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] An experimental device for carbon dioxide foam fracturing and displacement mining of hydrates includes a fracturing reactor chamber module, a foam preparation and injection module, a gas supply module, a stress loading module, a back pressure and production metering module, a temperature control module, and a data acquisition module.

[0009] The fracturing reactor cavity module is set in the low-temperature environment formed by the temperature control module, constituting the core reaction space for in-situ synthesis and fracturing modification of hydrates;

[0010] The foam preparation and injection module, the gas supply module, and the back pressure and output metering module are interconnected with the fluid channel of the fracturing reactor cavity module through pipelines and valves, respectively, to realize full-process control of fracturing medium injection, gas supply and output metering;

[0011] The stress loading module is connected to the loading end faces of the two axial ends of the fracturing reactor cavity module, and is used to simultaneously apply and maintain a constant closing stress to both ends of the sample to simulate the formation closing stress on the fracture during the exploitation of hydrate reservoirs.

[0012] The data acquisition module is used to synchronously acquire pressure, temperature, displacement, flow rate, and image information during the fracturing process.

[0013] Furthermore, the fracturing reactor cavity module is used to accommodate and confine hydrate deposit samples, providing a closed reaction space for in-situ synthesis and fracturing of hydrates under low temperature and high pressure conditions. The fracturing reactor cavity module includes a reactor body assembly, an end cap assembly, a sapphire cylinder, a first loading plate, and a second loading plate. The reactor body assembly consists of an upper reactor body and a lower reactor body forming a pressure-bearing main body. The end cap assembly includes an upper reactor cover and a lower reactor cover, which are respectively sealed to the upper reactor body and the lower reactor body. The sapphire cylinder is located in the observation area between the upper reactor body and the lower reactor body to achieve visual observation of the entire fracture propagation process. The first loading plate and the second loading plate are arranged opposite each other along the sample axial direction and are slidably fitted into the upper reactor body and the lower reactor body, respectively. The first loading plate, the upper reactor body, and the upper reactor cover together form an upper sealed cavity, and the second loading plate, the lower reactor body, and the lower reactor cover together form a lower sealed cavity. The upper and lower sealed cavities are respectively connected to the hydraulic circuit of the stress loading module to transmit axial closing stress.

[0014] Furthermore, the fracturing reactor cavity module also includes a fracturing pipe, the upper end of which is fixedly connected to the upper reactor cover and communicates with the top of the upper reactor cover. The fracturing pipe passes through the first loading plate, and a sealing structure is provided between the fracturing pipe and the hole in the first loading plate. The fracturing pipe is used for injecting carbon dioxide foam and subsequent depressurization mining.

[0015] Furthermore, the data acquisition module includes a fifth pressure sensor, a second temperature sensor, a third temperature sensor, a displacement sensor, and an illumination camera assembly; the fifth pressure sensor is located at the interface connecting the fracturing reactor cavity module with the foam preparation and injection module and the gas supply module; the second and third temperature sensors are respectively located inside the upper and lower reactor bodies; the displacement sensor is located on the first or second loading plate; the illumination camera assembly is distributed around the sapphire cylinder, and the camera end of the illumination camera assembly photographs the sapphire cylinder.

[0016] Furthermore, the foam preparation and injection module is used to mix carbon dioxide gas with a liquid medium under controlled conditions to form carbon dioxide foam, and inject the carbon dioxide foam into the fracturing reactor cavity module; the foam preparation and injection module includes a carbon dioxide cylinder, at least two piston containers arranged in series, a horizontal flow pump, a foam generator, and a sand adding device;

[0017] The carbon dioxide cylinder is connected to the gas inlet of the foam generator via a pressure reducing valve and a mass flow controller, and is used to provide carbon dioxide for foam preparation and subsequent experimental processes.

[0018] The piston container is equipped with a piston plate that divides the internal space of the piston container into an upper chamber and a lower chamber. The lower chamber is connected to the horizontal flow pump, and the upper chamber is connected to the foam generator and the injection channel of the fracturing reactor cavity module. The upper chamber is used to store the foam base liquid or the prepared foam. The reciprocating motion of the piston plate enables the foam base liquid to be quantitatively mixed with carbon dioxide gas under controlled flow conditions. Foam generation and pressurized delivery are completed through step-by-step gas replenishment and pressure increase, thereby obtaining stable carbon dioxide foam and realizing its injection into the fracturing reactor cavity module.

[0019] The sand-adding device is located between the outlet of the foam generator and the injection channel of the fracturing reactor cavity module, and is used to mix the proppant with carbon dioxide foam and then inject it into the sample.

[0020] Furthermore, the stress loading module includes an axial pressure pump, an axial pressure fluid injection pipeline, and a hydraulic control system; the axial pressure pump is connected to the upper sealing cavity and the lower sealing cavity of the fracturing reactor cavity module via the axial pressure fluid injection pipeline; the hydraulic control system controls the hydraulic pressure of the upper sealing cavity and the lower sealing cavity to simultaneously apply a constant closing stress to both ends of the sample.

[0021] Furthermore, the gas supply module includes a methane cylinder, a high-pressure gas storage tank, and a vacuum system; the methane cylinder is connected to the fracturing reactor cavity module via a pressure reducing valve, a high-pressure gas storage tank, and a mass flow controller, and is used for supplying methane gas during the in-situ synthesis stage of hydrates; the vacuum system is located at the connection interface between the methane cylinder and the fracturing reactor cavity module, and is used to evacuate the reaction system composed of the methane cylinder and the high-pressure gas storage tank before the experiment to eliminate air interference.

[0022] Furthermore, the backpressure and production metering module includes a filter, a backpressure device, a gas-liquid separator, and a decomposed gas storage tank connected in sequence. The backpressure device is connected to the production channel of the fracturing reactor chamber module through the filter. The filter is used to isolate particles carried by the produced fluid, and the backpressure device is used to accurately control the bottom hole flowing pressure during the depressurization production stage. The gas-liquid separator is used to separate the gas and liquid components in the produced fluid. The gas separated by the gas-liquid separator is metered by a flow meter and then enters the decomposed gas storage tank. The liquid separated by the gas-liquid separator is weighed and metered to achieve accurate measurement of the gas and water production from hydrate decomposition. The decomposed gas storage tank is equipped with a sampling port for component analysis of the produced gas during the decomposition process.

[0023] A method for carbon dioxide foam fracturing and displacement mining of hydrates, using the aforementioned carbon dioxide foam fracturing and displacement mining experimental apparatus, includes the following steps:

[0024] S1: Sample loading and stress loading

[0025] The hydrate sediment sample was filled into the fracturing reactor cavity module and sealed. The temperature control module was activated to regulate the ambient temperature of the fracturing reactor cavity module, and the stress loading module was used to apply axial closing stress to the sample in the fracturing reactor cavity module, so that the sample was in a controlled stress environment simulating the formation.

[0026] S2: Hydrate formation

[0027] The target gas is introduced into the cavity module of the fracturing reactor and the set conditions are maintained so that the sample forms hydrates in the cavity module of the fracturing reactor.

[0028] S3: Step-by-step preparation of carbon dioxide foam

[0029] Carbon dioxide gas is supplied to the foam generator and foam base liquid is introduced through the foam preparation and injection module, and quantitative gas-liquid mixing is achieved under controlled conditions. By adopting the step-by-step gas replenishment and pressure increase method, the resulting carbon dioxide foam can reach the target injection state while maintaining the predetermined foam quality or gas-liquid ratio, thereby obtaining stable carbon dioxide foam.

[0030] S4: Foam Injection Fracturing and Displacement

[0031] The carbon dioxide foam obtained in S3 is injected into the fracturing reactor cavity module. The stress loading module applies injection drive to the sample in the fracturing reactor cavity module to induce fracturing and achieve fracture propagation. The data acquisition module acquires the pressure and displacement response characteristics and fracture propagation feature points in the multi-view visualization image of the fracturing reactor cavity module to identify and control the stage of the sample fracturing process. After stopping the injection of carbon dioxide foam into the fracturing reactor cavity module, the well is shut in, so that the carbon dioxide in the fracturing reactor cavity module reacts with the hydrate on the fracture wall to generate carbon dioxide hydrate and release methane.

[0032] S5: Backpressure Control and Output Separation Metering

[0033] The backpressure and output metering module reduces the bottom flow pressure of the fracturing reactor chamber module, inducing hydrate decomposition and producing methane gas; and the output fluid is separated, recovered and metered.

[0034] S6: Simultaneous monitoring of multiple parameters during fracturing and replacement processes

[0035] The data acquisition module collects pressure, temperature, displacement, flow rate, and output signals during the fracturing and displacement process within the fracturing reactor chamber module. The illumination camera component continuously images the fracture initiation and propagation process. The data is synchronously recorded and aligned for a unified time reference, and experimental results are output, including initiation pressure, fracture propagation characteristics, carbon dioxide displacement effect, and output behavior.

[0036] Furthermore, in step S4, the carbon dioxide foam obtained in step S3 is injected into the fracturing reactor cavity module using the following method:

[0037] As needed, the proppant and carbon dioxide foam are mixed and injected into the sample in the cavity module of the fracturing reactor through a sand-adding device to form a support to fill the fracture. During the process, the proppant is maintained while inhibiting the migration and production of fine particles.

[0038] The present invention has the following beneficial effects:

[0039] (1) This invention realizes an integrated experiment of the entire process of fracturing, replacement and mining. The entire process of carbon dioxide foam fracturing, proppant laying, well shut-in replacement and depressurization mining is completed continuously in the same reaction chamber, providing direct experimental evidence for quantitatively evaluating the promoting effect of fracturing fractures on carbon dioxide mass transfer efficiency and methane replacement rate.

[0040] (2) By working together with the air bath temperature control and axial stress loading module, the low temperature, high pressure and formation closure stress conditions can be accurately reproduced; the upper and lower loading plate design can apply constant axial stress to both ends of the sample simultaneously, which more realistically reflects the stress state of the crack in the formation.

[0041] (3) A step-by-step gas replenishment and incremental pressurization strategy is adopted. By switching between series piston containers, the foam quality can be controlled and the pressure can be gradually increased. While maintaining a stable gas-liquid ratio, pressurization and delivery are completed, effectively matching the reservoir fracture pressure requirements.

[0042] (4) It has the ability to visualize the dynamic evolution of cracks in situ and monitor multiple parameters simultaneously. Relying on the sapphire cylinder and multi-view camera system, it captures the crack initiation, propagation and proppant migration behavior in real time, and collects them synchronously with pressure, temperature and displacement signals on a unified time reference to achieve precise correlation between mechanical response and morphological evolution. Attached Figure Description

[0043] Figure 1 is a schematic diagram of the experimental device for integrated carbon dioxide foam fracturing and displacement mining of natural gas hydrate reservoirs according to the present invention.

[0044] Figure 2 is an enlarged schematic diagram of the internal structure of the air bath in part A of Figure 1.

[0045] Figure 3 is a schematic diagram of the arrangement of the camera and fill light of the present invention.

[0046] In the diagram: 1. Methane cylinder; 2. First pressure reducing valve; 3. High-pressure gas storage tank; 4. First mass flow controller; 5. Check valve; 6. Vacuum pump; 7. Filter; 8. Sand adding device; 9. Back pressure device; 10. Gas-liquid separator; 11. Dryer; 12. First pressure sensor; 13. First temperature sensor; 14. Decomposed gas storage tank; 15. Mass flow meter; 16. Electronic balance; 17. Second pressure sensor; 18. First horizontal flow pump; 19. First liquid injection container; 20. Back pressure valve; 21. First piston container; 22. Air bath; 23. Third pressure sensor; 24. Second horizontal flow pump; 25. Second liquid injection container; 26. Second piston container 27. Third piston container; 28. Carbon dioxide cylinder; 29. ​​Second pressure reducing valve; 30. Second mass flow controller; 31. Foam generator; 32. Fourth pressure sensor; 33. Upper vessel cover; 34. Pneumatic valve; 35. Upper vessel body; 36. First loading plate; 37. Second temperature sensor; 38. First supplementary light; 39. First camera; 40. Fracturing pipe; 41. Third temperature sensor; 42. Displacement sensor; 43. Lower vessel cover; 44. Second loading plate; 45. Lower vessel body; 46. Sapphire cylinder; 47. Second camera; 48. Second supplementary light; 49. Fifth pressure sensor; 51. Third camera; 52. Fourth camera. Detailed Implementation

[0047] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Terms such as “upper,” “inner,” “middle,” “left,” “right,” and “one” used in this specification are merely for clarity of description and are not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0048] Example 1

[0049] An experimental apparatus for carbon dioxide foam fracturing and displacement mining of hydrates, as shown in Figures 1 to 3, includes a fracturing reactor chamber module, a foam preparation and injection module, a gas supply module, a stress loading module, a back pressure and production metering module, a temperature control module, and a data acquisition module.

[0050] The fracturing reactor chamber module is a pressure-bearing, visualized chamber structure used to contain and confine hydrate deposit samples and conduct fracturing experiments under high pressure.

[0051] The fracturing reactor chamber module is set in a low-temperature environment created by the temperature control module, forming the core reaction space for in-situ synthesis and fracturing modification of hydrates.

[0052] The foam preparation and injection module, gas supply module, and back pressure and output metering module are interconnected with the fluid channels of the fracturing reactor cavity module through pipelines and valves, respectively, to realize full-process control of fracturing medium injection, gas supply and output metering.

[0053] The stress loading module is connected to the loading end faces of both ends of the fracturing reactor cavity module in the axial direction. It is used to apply and maintain a constant closing stress to both ends of the sample to simulate the formation closing stress on the fracture during the exploitation of hydrate reservoirs.

[0054] The data acquisition module is used to synchronously acquire pressure, temperature, displacement, flow rate, and image information during the fracturing process.

[0055] In this embodiment, as shown in Figures 1 and 2, the fracturing reactor cavity module includes a reactor body assembly, an end cap assembly, a sapphire cylinder 46, a first loading plate 36, a second loading plate 44, a fracturing pipe 40, a pneumatic valve 34, a hollow connecting rod, a second temperature sensor 37, a third temperature sensor 41, a fifth pressure sensor 49, and a displacement sensor 42.

[0056] The vessel assembly consists of an upper vessel body 35 and a lower vessel body 45, forming the pressure-bearing main body. The end cap assembly includes an upper vessel cap 33 and a lower vessel cap 43, which are connected to the upper vessel body 35 and the lower vessel body 45 respectively via flanges and secured with screws. Sealing rings are also provided at the connections to ensure reliable sealing. The upper vessel body 35 and the lower vessel body 45 clamp and fix the sapphire cylinder 46 using flanges and studs, placing the sapphire cylinder 46 in the observation area between the upper vessel body 35 and the lower vessel body 45 for visualized observation of the entire crack propagation process.

[0057] The first loading plate 36 and the second loading plate 44 are arranged opposite each other along the axial direction of the sample and are slidably fitted within the upper vessel body 35 and the lower vessel body 45, respectively. Double-layer sealing rings are provided on the outer circumferential surfaces of both the first loading plate 36 and the second loading plate 44 to achieve sealing during movement. The first loading plate 36, the upper vessel body 35, and the upper vessel cover 33 together form an upper sealing cavity, while the second loading plate 44, the lower vessel body 45, and the lower vessel cover 43 together form a lower sealing cavity. Both the upper vessel cover 33 and the lower vessel cover 43 are provided with axial pressure hydraulic inlet and outlet channels that communicate with the upper and lower sealing cavities, respectively, so that the upper and lower sealing cavities are connected to the hydraulic circuit of the stress loading module through the axial pressure inlet and outlet channels to transmit axial closing stress.

[0058] The upper end of the fracturing pipe 40 is fixed to the upper vessel cover 33 by threaded connection or welding, and the upper end of the fracturing pipe 40 is connected to the top surface of the upper vessel cover 33; the fracturing pipe 40 passes through the hole of the first loading plate 36, and a sealing structure is set between the fracturing pipe 40 and the hole of the first loading plate 36 to ensure the sealing of the connection position during the movement of the first loading plate 36; the upper end of the fracturing pipe 40 is connected to the pneumatic valve 34, and is also connected to the foam preparation and injection module and the back pressure and production metering module respectively, so as to realize the flow path switching under different working conditions; at the same time, the fracturing pipe 40 is used to simulate the wellbore channel, and serves as the carbon dioxide foam injection channel for fracturing medium and the gas production channel for subsequent depressurization and extraction.

[0059] The top surface of the second loading plate 44 in contact with the sediment is also equipped with a filter screen, which is used to intercept solid sediments precipitated from the fluid. The second loading plate 44 is fixedly connected to the hollow connecting rod, which passes through the lower vessel cover 43 and is provided with a sealing structure at the exit position. The bottom end of the hollow connecting rod that passes through the lower vessel cover 43 is connected to the gas supply module. A gas channel is formed inside the hollow connecting rod, and the gas channel is connected to the sediment sample through the through hole in the second loading plate 44, so that the gas can pass through the hollow connecting rod, through the through hole in the second loading plate 44 and enter the interior of the sediment sample.

[0060] The second temperature sensor 37 and the third temperature sensor 41 are respectively installed on the inner walls of the upper vessel 35 and the lower vessel 45 to monitor the internal temperature. The displacement sensor 42 is installed on the first loading plate 36 or the second loading plate 44 to monitor the axial loading displacement. In this embodiment, the displacement sensor 42 is installed on the hollow connecting rod to reduce the influence of the cavity on the displacement sensor 42. The fifth pressure sensor 49 is installed at the interface between the fracturing reactor cavity module and the foam preparation and injection module and the gas supply module to monitor the internal pressure of the fracturing reactor cavity module. The fifth pressure sensor 49, the second temperature sensor 37, the third temperature sensor 41 and the displacement sensor 42 are all electrically connected to the data acquisition and processing module for the correlation analysis of the fracture initiation and propagation process and the fracturing-displacement response characteristics in subsequent experiments. The data acquisition and processing module can be a data acquisition processor.

[0061] In this embodiment, the foam preparation and injection module is used to mix carbon dioxide gas with liquid medium under controlled conditions to form carbon dioxide foam, and then inject the carbon dioxide foam into the fracturing reactor cavity module.

[0062] The foam preparation and injection module includes a carbon dioxide cylinder 28, a second pressure reducing valve 29, a second mass flow controller 30, a foam generator 31, a second horizontal flow pump 24, a second liquid injection container 25, a second piston container 26, a third piston container 27, a sand adding device 8, and a fourth pressure sensor 32.

[0063] The carbon dioxide cylinder 28 is connected to the gas inlet of the foam generator 31 after passing through the second pressure reducing valve 29 and the second mass flow controller 30. Carbon dioxide gas is output from the carbon dioxide cylinder 28, and after being reduced and stabilized by the second pressure reducing valve 29, the flow rate is regulated by the second mass flow controller 30 and enters the gas inlet of the foam generator 31 at a set flow rate to provide a gas source for the preparation of carbon dioxide foam.

[0064] The second piston container 26 and the third piston container 27 are respectively connected to the two ends of the foam generator 31. Both the second piston container 26 and the third piston container 27 are piston-type isolated pressurization structures. Taking the structure of the second piston container 26 as an example: the second piston container 26 is provided with a piston plate inside, which divides the internal space of the second piston container 26 into an upper chamber and a lower chamber; the upper chamber is used to store the fracturing fluid base fluid or the prepared carbon dioxide foam. The upper chamber is connected to the injection channel of the foam generator 31 and the fracturing reactor cavity module through pipelines, and the flow path is selected and switched through a valve group; the lower chamber is used to contain the working fluid and is connected to the second horizontal flow pump 24. The lower chamber is isolated from the upper chamber to achieve medium isolation between the working fluid and the fracturing fluid base fluid / foam.

[0065] The inlet of the second horizontal flow pump 24 is connected to the second liquid injection container 25. The second horizontal flow pump 24 draws in working fluid from the second liquid injection container 25 and injects or discharges it into the lower chamber of the second piston container 26 and the third piston container 27 to drive the piston plate to reciprocate, thereby pressurizing and pushing the fluid in the upper chamber.

[0066] During the foam preparation process, carbon dioxide gas and base liquid are quantitatively mixed under controlled conditions through the reciprocating motion of the piston plate and the switching of the valve group. The foam pressure and stability are gradually increased by stepwise gas replenishment and pressurization to obtain carbon dioxide foam that meets the requirements of fracturing injection. After the prepared carbon dioxide foam is switched between the valve group and the pneumatic valve 34, it enters the injection channel of the fracturing reactor cavity module to realize the foam fracturing injection of the sample.

[0067] The sand-adding device 8 is located between the outlet of the foam generator 31 and the injection channel of the fracturing reactor cavity module, and is used to mix the proppant and carbon dioxide foam and inject it into the sample when needed.

[0068] The fourth pressure sensor 32 is installed on the connecting pipeline between the outlet of the foam generator 31 and the injection channel of the fracturing reactor cavity module. It is used to monitor the pipeline pressure changes in real time during the foam preparation and injection process, and is connected to the data acquisition and processing module to achieve synchronous recording.

[0069] In this embodiment, the temperature control module is an air bath 22, which consists of a constant temperature refrigeration unit, a circulating fan, and an insulation cavity. The insulation cavity has a cubic structure, and the entire fracturing reactor cavity module is placed inside the insulation cavity. The constant temperature refrigeration unit adopts a cascade refrigeration system, which drives low-temperature air to circulate within the insulation cavity through a circulating fan, thereby achieving uniform temperature control of the entire fracturing reactor cavity module.

[0070] In this embodiment, the stress loading module is used to apply and maintain a stable axial closing stress on the fracturing reactor cavity module to simulate reservoir in-situ stress conditions. The stress loading module includes an axial pressure pump, an axial pressure fluid injection pipeline, and a hydraulic control system; the axial pressure pump is connected to the upper and lower sealing cavities of the fracturing reactor cavity module via the axial pressure fluid injection pipeline; the hydraulic control system controls the hydraulic pressure in the upper and lower sealing cavities to simultaneously apply a constant closing stress to both ends of the sample.

[0071] The axial pressure pump adopts a first parallel flow pump 18; the hydraulic control system includes a first injection container 19, a back pressure valve 20, a first piston container 21 and a second pressure sensor 17, and the first piston container 21 is a piston-type isolated pressurization structure.

[0072] The inlet of the first horizontal flow pump 18 is connected to the first injection container 19, and the outlet of the first horizontal flow pump 18 is connected to the lower chamber of the first piston container 21 through the back pressure valve 20. The back pressure valve 20 is also connected to the first injection container 19. The upper chamber of the first piston container 21 is connected to the upper sealing chamber and the lower sealing chamber of the fracturing reactor cavity module through the axial pressure liquid injection pipeline.

[0073] The first horizontal flow pump 18, acting as an axial pressure pump, provides hydraulic pressure to drive the working fluid from the first injection container 19 through the back pressure valve 20 into the lower chamber of the first piston container 21. The back pressure valve 20 is used for pressure limiting and stabilization; when the circuit pressure exceeds a set value, it automatically releases pressure, and the released fluid flows back to the first injection container 19, thus forming a closed hydraulic pressure stabilization circuit to ensure the stability of the axial loading pressure. The upper chamber of the first piston container 21 is filled with axial pressure fluid and is connected to the upper and lower sealed chambers of the fracturing reactor cavity module through an axial pressure fluid injection pipeline. The lower chamber of the first piston container 21 is connected to the back pressure valve 20. Through the pressure transmission action of the piston plate, the first piston container 21 simultaneously applies and maintains a constant axial closing stress at both ends of the sample.

[0074] The second pressure sensor 17 is installed at the axial pressure fluid injection pipeline between the upper cavity of the first piston container 21 and the upper and lower sealing cavities of the fracturing reactor cavity module. It is used to monitor the axial loading pressure in real time and is connected to the data acquisition and processing module to achieve synchronous recording.

[0075] In this embodiment, the gas supply module includes a methane cylinder 1, a first pressure reducing valve 2, a high-pressure gas storage tank 3, a first mass flow controller 4, a check valve 5, and a vacuum system. The methane cylinder 1 is connected to the fracturing reactor cavity module via the pressure reducing valve, the high-pressure gas storage tank 3, and the mass flow controller. Thus, the methane gas source is generated by the methane cylinder 1, and after pressure reduction, pressure stabilization, and flow control, it is connected to the fracturing reactor cavity module for supplying methane during the in-situ synthesis stage of hydrates. The vacuum system uses a vacuum pump 6, which is located at the connection interface between the methane cylinder 1 and the fracturing reactor cavity module. The vacuum pump 6 is used to evacuate the reaction system composed of the methane cylinder 1 and the high-pressure gas storage tank 3 before the experiment to eliminate air interference.

[0076] In this embodiment, the back pressure and production metering module includes a filter 7, a back pressure device 9, a gas-liquid separator 10, a dryer 11, a first pressure sensor 12, a first temperature sensor 13, a decomposed gas storage tank 14, a mass flow meter 15, and an electronic balance 16. The filter 7 is located between the fracturing pipe 40 and the back pressure device 9 to filter particles entrained in the produced fluid. The back pressure device 9 is connected to the production channel (i.e., the fracturing pipe 40) of the fracturing reactor chamber module and is used to regulate and stabilize the outlet pressure to precisely control the bottom hole flowing pressure during the depressurization stage, thus achieving precise control of back pressure conditions. The fluid produced from the production channel of the fracturing reactor chamber module enters the gas-liquid separator 10 for gas-liquid separation. The gas phase is dehydrated by the dryer 11, metered by the mass flow meter 15, and enters the decomposed gas storage tank 14. The liquid phase is weighed by the electronic balance 16, thereby achieving simultaneous quantitative measurement of gas and liquid production. The first pressure sensor 12 and the first temperature sensor 13 are both installed on the decomposed gas storage tank 14 to monitor the pressure and temperature parameters inside the tank in real time. The decomposed gas storage tank 14 is also equipped with a sampling port for subsequent gas component analysis.

[0077] The data acquisition module of the present invention includes a first pressure sensor 12, a second pressure sensor 17, a third pressure sensor 23, a fourth pressure sensor 32, a fifth pressure sensor 49, a first temperature sensor 13, a second temperature sensor 37, a third temperature sensor 41, a displacement sensor 42, a first mass flow controller 4, a second mass flow controller 30, a mass flow meter 15, and an illumination camera assembly, which are used to synchronously acquire pressure, temperature, displacement, flow rate, and image information during the fracturing process.

[0078] As shown in Figure 3, the lighting and camera assembly includes a first camera 39, a second camera 47, a third camera 51, a fourth camera 52, a first supplementary light 38, and a second supplementary light 48. The first camera 39, the second camera 47, the third camera 51, and the fourth camera 52 are arranged at equal intervals at four positions around the periphery of the fracturing reactor cavity module, and the lenses of the four cameras are all facing the sapphire cylinder 46. The relative positions of the upper part of the fracturing reactor cavity module are respectively coordinated with the first supplementary light 38 and the second supplementary light 48 to achieve multi-view synchronous imaging of the fracture propagation process.

[0079] Example 2

[0080] A method for carbon dioxide foam fracturing and displacement mining of hydrates, using the experimental apparatus for carbon dioxide foam fracturing and displacement mining of hydrates as described in Example 1, includes the following steps:

[0081] S1: Sample loading and stress loading

[0082] The pipelines of the fracturing reactor cavity module, foam preparation and injection module, gas supply module, stress loading module, back pressure and production metering module, temperature control module, and data acquisition module are connected and their sealing is checked. After the aqueous solution and sediment skeleton are thoroughly mixed to form a hydrate sediment sample, it is filled into the fracturing reactor cavity module in layers and compacted layer by layer. The first loading plate 36 and the second loading plate 44 are installed and positioned. The air bath 22 is started to bring the reactor cavity to the target temperature and stabilize it. The sample temperature is monitored and recorded by the second temperature sensor 37 and the third temperature sensor 41. Then the stress loading module is started to establish a pressure-stabilized loading circuit through the first horizontal flow pump 18, the first liquid injection container 19, the back pressure valve 20, and the first piston container 21. A preset axial closed stress is applied synchronously to both ends of the sample and maintained, so that the sample is in a controlled stress environment simulating the formation. The axial loading pressure is monitored and recorded by the second pressure sensor 17.

[0083] S2: Hydrate formation

[0084] Vacuum pump 6 is used to evacuate the fracturing reactor module and its connecting pipelines. While maintaining the target temperature and axial closure stress, methane is introduced into the fracturing reactor module through the gas supply module. During this process, methane enters the gas channel of the fracturing reactor module from methane cylinder 1, passing sequentially through the first pressure reducing valve 2, the high-pressure gas storage tank 3, the first mass flow controller 4, and the check valve 5, thus supplying methane to the sample inside the chamber and pressurizing the chamber. During hydrate formation, the pressure of the fracturing reactor module is monitored by the fifth pressure sensor 49. When the pressure, temperature, and other signals within the fracturing reactor module stabilize or meet preset criteria, it is determined that hydrate formation has met experimental requirements. The amount of hydrate formed can be characterized by the cumulative gas supply recorded by the first mass flow controller 4.

[0085] S3: Step-by-step preparation of carbon dioxide foam

[0086] The fracturing fluid base fluid is prepared by dissolving foam stabilizer, foaming agent, and dye in pure water through the foam preparation and injection module, and then placed in the upper chamber of the third piston container 27. The fracturing fluid base fluid may also contain thickener, salts, or other functional additives. During the process, carbon dioxide gas is output from carbon dioxide cylinder 28, depressurized and stabilized by the second pressure reducing valve 29, and its flow rate is regulated by the second mass flow controller 30 before entering the foam generator 31. The second horizontal flow pump 24 is activated to drive the piston plate of the third piston container 27 to move at a set flow rate, causing the base fluid and carbon dioxide to mix in the foam generator 31 to generate carbon dioxide foam, which is then introduced into the upper chamber of the second piston container 26.

[0087] This embodiment uses a step-by-step gas replenishment and pressurization method to prepare foam: the second piston container 26 and the third piston container 27 are switched alternately to achieve foam transfer and mixing. During the container switching process, carbon dioxide is slowly replenished into the target container and pressurized simultaneously. If necessary, the non-working second piston container 26 or third piston container 27 is depressurized and reset from the bottom before entering the next round of gas replenishment and pressurization. The above cycle is repeated until the foam pressure reaches the target injection pressure. The pressure is monitored and recorded by the fourth pressure sensor 32 during the carbon dioxide foam preparation and injection process.

[0088] In the above process, carbon dioxide foams of different qualities can be obtained by adjusting the amount of fracturing fluid base fluid and the gas supply flow rate of the second mass flow controller 30.

[0089] In this embodiment, the proppant can be mixed with carbon dioxide foam and injected into the sample in the fracturing reactor cavity module by the sand adding device 8 as needed to form a propped filling crack. During the process, while maintaining the flow channel, it inhibits the migration of fine particles and particle production. This facilitates the comparative evaluation of the sand control effect of proppant particle size, laying concentration and injection regime.

[0090] S4: Foam Injection Fracturing and Displacement

[0091] After the foam preparation is completed and the target injection pressure is reached, the valve group is switched and the pneumatic valve 34 is opened, so that the carbon dioxide foam obtained in S3 is injected into the sample through the fracturing pipe 40, inducing the initiation of the fracture and promoting the expansion of the fracture, thereby realizing the fracturing transformation.

[0092] During the process, the proppant and carbon dioxide foam can be mixed by the sand adding device 8, so that the proppant enters the crack along with the carbon dioxide foam and forms a propping filling layer, which can inhibit fine particle migration and particle production while maintaining the flow channel. Then, the sample is injected to form a propping filling crack.

[0093] After fracturing is completed, the valve group is switched to the well-shutting stage, which is maintained for a period of time under the set temperature, pressure and back pressure conditions, so that the injected carbon dioxide comes into contact with the hydrate and carbon dioxide-methane replacement occurs.

[0094] During the carbon dioxide foam injection fracturing and well shut-off replacement process, the injection side pressure is recorded simultaneously by the fourth pressure sensor 32, the reactor pressure is recorded by the fifth pressure sensor 49, the axial loading pressure is recorded by the second pressure sensor 17, the displacement is recorded by the displacement sensor 42, and the temperature signals are recorded by the second temperature sensor 37 and the third temperature sensor 41. The sapphire cylinder 46 is visualized and recorded by the camera illumination unit to obtain the pressure and displacement response characteristics in the fracturing reactor cavity module and the crack propagation feature points in the multi-view visualization images, so as to identify and control the stage of the sample fracturing process.

[0095] After stopping the injection of carbon dioxide foam into the fracturing reactor chamber module, the well is shut in, allowing the carbon dioxide in the fracturing reactor chamber module to undergo a displacement reaction with the hydrate on the fracture wall to generate carbon dioxide hydrate and release methane.

[0096] In this embodiment, multiple fracturing-steaming cycles can be implemented as needed to improve fracture conductivity and replacement efficiency.

[0097] S5: Backpressure Control and Output Separation Metering

[0098] After fracturing, the flow path is switched to the back pressure and production metering module. The produced fluid enters the back pressure device 9 through the fracturing pipe 40 and filter 7 to achieve outlet pressure regulation and stable back pressure. During the back pressure production process, the produced fluid is filtered by filter 7 to intercept entrained solid particles. After the experiment, the intercepted particles can be collected and weighed, and the particle production rate and its variation with operating conditions can be characterized by combining the production curve, which is used to evaluate the sand production situation and the sand control effect of the proppant filling layer.

[0099] After the produced fluid is separated by the gas-liquid separator 10, the gas phase is dehydrated by the dryer 11 and then measured by the mass flow meter 15 before entering the decomposed gas storage tank 14; the liquid phase is weighed by the electronic balance 16, thereby obtaining the gas production and liquid production data. The first pressure sensor 12 and the first temperature sensor 13 on the decomposed gas storage tank 14 are used to monitor the tank pressure and temperature; the sampling port of the decomposed gas storage tank 14 is used for subsequent gas component analysis to achieve the separation, recovery and measurement of the produced fluid.

[0100] S6: Simultaneous monitoring of multiple parameters during fracturing and replacement processes

[0101] Throughout the experiment, the data acquisition module collected, recorded, and stored multi-source signals, including pressure, temperature, displacement, flow rate, and output, from the fracturing and displacement processes within the fracturing reactor chamber. Time alignment analysis was performed on the multi-source data using a unified time reference. An illumination camera assembly continuously imaged 46 visual sections of the sapphire cylinder from multiple perspectives. The acquired image data was recorded synchronously with the aforementioned sensor signals and used for correlation analysis of the fracture initiation and propagation processes and the fracturing-displacement response characteristics.

[0102] The steps of the above-described experimental method for carbon dioxide foam fracturing and displacement mining of hydrates are merely one embodiment of the present invention and do not constitute a limitation on the scope of protection of the present invention. Optionally, the foam injection medium of the present invention can be extended from carbon dioxide foam to other gas foams or mixed gas foams, such as carbon dioxide / nitrogen mixed gas foam; the fracturing fluid base fluid can also be formulated differently or have different functional components added according to experimental requirements.

[0103] Meanwhile, this invention can study fracture closure behavior, sand production risk, and sand control effect under different closure stress conditions by changing parameters such as proppant particle size and proppant concentration, and compare and evaluate these results with output interception and metering. Optionally, this invention can implement multiple rounds of gas and fracturing fluid injection and modification operations, including re-injection after hydrate decomposition to conduct repeated fracturing and displacement experiments.

[0104] The embodiments of the present invention are not limited thereto. Based on the above description of the present invention, and using common technical knowledge and conventional means in the field, the present invention can be modified, replaced or combined in various other forms without departing from the basic technical idea of ​​the present invention, and all such modifications, replacements or combinations fall within the scope of protection of the present invention.

Claims

1. An experimental apparatus for carbon dioxide foam fracturing and displacement mining of hydrates, characterized in that, The system includes a fracturing reactor chamber module, a foam preparation and injection module, a gas supply module, a stress loading module, a back pressure and production metering module, a temperature control module, and a data acquisition module. The fracturing reactor chamber module is located in the low-temperature environment created by the temperature control module, forming the core reaction space for in-situ hydrate synthesis and fracturing modification. The fracturing reactor chamber module is used to contain and confine hydrate deposit samples, providing a closed reaction space for in-situ hydrate synthesis and fracturing modification under low-temperature and high-pressure conditions. The fracturing reactor chamber module includes a reactor body assembly, an end cap assembly, a sapphire cylinder, a first loading plate, and a second loading plate. The reactor body assembly consists of an upper reactor body and a lower reactor body forming the pressure-bearing main body. The end cap assembly includes an upper reactor cap and an end cap assembly. The lower vessel cover is sealed to the upper and lower vessel bodies, respectively. A sapphire cylinder is positioned in the observation area between the upper and lower vessel bodies to visualize the entire crack propagation process. The first and second loading plates are arranged axially opposite to each other within the upper and lower vessel bodies, respectively slidingly fitted within them. The first loading plate, upper vessel body, and upper vessel cover together form an upper sealed cavity, while the second loading plate, lower vessel body, and lower vessel cover together form a lower sealed cavity. Both the upper and lower sealed cavities are connected to the hydraulic circuit of the stress loading module to transmit axial closing stress. The foam preparation and injection module, the gas supply module, and the back pressure and output metering module are respectively connected via… Pipelines and valves are interconnected with the fluid channels of the fracturing reactor cavity module, enabling full-process control of fracturing medium injection, gas supply, and product metering. The foam preparation and injection module is used to mix carbon dioxide gas with a liquid medium under controlled conditions to form carbon dioxide foam, and then inject the carbon dioxide foam into the fracturing reactor cavity module. The foam preparation and injection module includes a carbon dioxide cylinder, at least two piston containers arranged in series, a horizontal flow pump, a foam generator, and a sand adding device. The carbon dioxide cylinder is connected to the gas inlet of the foam generator via a pressure reducing valve and a mass flow controller to provide carbon dioxide for foam preparation and subsequent experimental processes. The piston container is equipped with a piston plate, which controls the flow of the carbon dioxide inlet. The internal space of the plug container is divided into an upper chamber and a lower chamber, wherein the lower chamber is connected to the horizontal flow pump, the upper chamber is connected to the foam generator, and the upper chamber is connected to the injection channel of the fracturing reactor cavity module. The upper chamber is used to store the foam base liquid or the prepared foam. The piston plate reciprocates to achieve quantitative mixing of the foam base liquid with carbon dioxide gas under controlled flow conditions, and completes foam generation and pressurized delivery through step-by-step gas replenishment and pressure increase, thereby obtaining stable carbon dioxide foam and realizing injection into the fracturing reactor cavity module. The sand adding device is set between the outlet of the foam generator and the injection channel of the fracturing reactor cavity module, and is used to mix the proppant and carbon dioxide foam and then inject it into the sample.The stress loading module connects to the loading end faces of both axial ends of the fracturing reactor chamber module, and is used to simultaneously apply and maintain a constant closing stress at both ends of the sample to simulate the formation closing stress experienced by the fracture during hydrate reservoir exploitation. The data acquisition module is used to simultaneously acquire pressure, temperature, displacement, flow rate, and image information during the fracturing process. The data acquisition module includes a fifth pressure sensor, a second temperature sensor, a third temperature sensor, a displacement sensor, and an illumination camera assembly. The fifth pressure sensor is located at the interface connecting the fracturing reactor chamber module with the foam preparation and injection module and the gas supply module. The second and third temperature sensors are respectively located inside the upper and lower reactor bodies. The displacement sensor is located on the first or second loading plate. The illumination camera assembly is distributed around the sapphire cylinder, and the camera end of the illumination camera assembly photographs the sapphire cylinder.

2. The experimental apparatus for carbon dioxide foam fracturing and displacement mining of hydrates as described in claim 1, characterized in that, The fracturing reactor cavity module also includes a fracturing pipe. The upper end of the fracturing pipe is fixedly connected to the upper reactor cover and communicates with the top of the upper reactor cover. The fracturing pipe passes through the first loading plate. A sealing structure is provided between the fracturing pipe and the hole in the first loading plate. The fracturing pipe is used for injecting carbon dioxide foam and subsequent depressurization mining.

3. The experimental apparatus for carbon dioxide foam fracturing and displacement mining of hydrates as described in claim 1, characterized in that, The stress loading module includes an axial pressure pump, an axial pressure fluid injection pipeline, and a hydraulic control system. The axial pressure pump is connected to the upper and lower sealing cavities of the fracturing reactor cavity module via the axial pressure fluid injection pipeline. The hydraulic control system controls the hydraulic pressure in the upper and lower sealing cavities to apply a constant closing stress to both ends of the sample simultaneously.

4. The experimental apparatus for carbon dioxide foam fracturing and displacement mining of hydrates as described in claim 1, characterized in that, The gas supply module includes a methane cylinder, a high-pressure gas storage tank, and a vacuum system. The methane cylinder is connected to the fracturing reactor cavity module via a pressure reducing valve, a high-pressure gas storage tank, and a mass flow controller, and is used to supply methane gas during the in-situ synthesis stage of hydrates. The vacuum system is located at the connection interface between the methane cylinder and the fracturing reactor cavity module, and is used to evacuate the reaction system composed of the methane cylinder and the high-pressure gas storage tank before the experiment to eliminate air interference.

5. The experimental apparatus for carbon dioxide foam fracturing and displacement mining of hydrates as described in claim 1, characterized in that, The backpressure and production metering module includes a filter, a backpressure device, a gas-liquid separator, and a decomposed gas storage tank connected in sequence. The backpressure device is connected to the production channel of the fracturing reactor chamber module through the filter. The filter is used to isolate particles carried by the produced fluid, and the backpressure device is used to accurately control the bottom hole flowing pressure during the depressurization production stage. The gas-liquid separator is used to separate the gas and liquid components in the produced fluid. The gas separated by the gas-liquid separator is metered by a flow meter and then enters the decomposed gas storage tank. The liquid separated by the gas-liquid separator is weighed and metered to achieve accurate measurement of the gas and water production from hydrate decomposition. The decomposed gas storage tank is equipped with a sampling port for component analysis of the produced gas during the decomposition process.

6. A method for carbon dioxide foam fracturing and displacement mining of hydrates, employing the experimental apparatus for carbon dioxide foam fracturing and displacement mining of hydrates as described in claim 1, characterized in that, The process includes the following steps: S1: Sample loading and stress loading. The hydrate deposit sample is loaded into the fracturing reactor cavity module and sealed. The temperature control module is activated to regulate the ambient temperature of the fracturing reactor cavity module, and the stress loading module applies axial closing stress to the sample within the fracturing reactor cavity module, placing the sample in a controlled stress environment simulating the formation. S2: Hydrate formation. Target gas is introduced into the fracturing reactor cavity module and the set conditions are maintained, allowing the sample to form hydrates within the cavity module. S3: Stepwise gas supply for carbon dioxide foam preparation. Carbon dioxide gas is supplied to the foam generator and foam base liquid is introduced through the foam preparation and injection module, achieving quantitative gas-liquid mixing under controlled conditions. Stepwise gas supply and pressure increment are used to ensure that the obtained carbon dioxide foam maintains the predetermined foam quality or gas-liquid ratio while reaching the target injection state, thereby obtaining stable carbon dioxide foam. S4: Foam injection fracturing and displacement. The carbon dioxide foam obtained in S3 is injected into the fracturing reactor cavity module, and the stress loading module applies pressure to the sample within the fracturing reactor cavity module. The system is driven by an injection mechanism to induce fracturing and promote fracture propagation. A data acquisition module obtains pressure and displacement response characteristics within the fracturing reactor chamber module, as well as fracture propagation feature points in multi-view visualization images, to identify and control the stage of the sample fracturing process. After stopping the injection of carbon dioxide foam into the fracturing reactor chamber module, a shut-in process is initiated, causing carbon dioxide within the fracturing reactor chamber module to undergo a displacement reaction with hydrates on the fracture wall, generating carbon dioxide hydrates and releasing methane. S5: Backpressure control and production separation and metering. A backpressure and production metering module reduces the bottom flow pressure of the fracturing reactor chamber module, inducing hydrate decomposition and producing methane gas. The produced fluid is then separated, recovered, and metered. S6: Multi-parameter synchronous monitoring of fracturing and displacement processes. A data acquisition module collects pressure, temperature, displacement, flow rate, and production signals during the fracturing and displacement process within the fracturing reactor chamber module. A lighting camera assembly continuously images the fracture initiation and propagation process. Data is synchronously recorded and aligned using a unified time reference, outputting experimental results on initiation pressure, fracture propagation characteristics, carbon dioxide displacement effect, and production behavior.

7. The experimental method for carbon dioxide foam fracturing and displacement mining of hydrates as described in claim 6, characterized in that, In step S4, the carbon dioxide foam obtained in step S3 is injected into the fracturing reactor cavity module using the following method: as needed, the proppant and carbon dioxide foam are mixed by a sand-adding device and then injected into the sample in the fracturing reactor cavity module to form a support filling the fracture. During the process, while maintaining the flow channel, it inhibits the migration of fine particles and particle production.

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