Reservoir pressure springback simulation device in sea area hydrate exploitation and experimental method

Abstract

The invention relates to the field of safe exploitation of natural gas hydrates, in particular to a reservoir pressure rebound simulation device and an experimental method in sea area hydrate exploitation. According to the technical scheme, the device comprises a multi-section continuous high-pressure reaction hold-down module, a top window module, a low-temperature control module, a data acquisition module, a gas-liquid injection system, a gas-liquid recovery system and a steel cylinder set, and the multi-section continuous high-pressure reaction hold-down module is formed by connecting five sections of single hold-down devices end to end; 60 pressure and temperature monitoring sub-areas are configured in the axial direction and the tangential direction in total, a rock core can be prepared through two methods of integrated pressing and five-time sectional pressing, and a reservoir pressure rebound phenomenon simulation experiment can be carried out in situ. The problems that a traditional device can only simulate a discontinuous reservoir with fixed porosity and the internal temperature and pressure monitoring precision is low are solved, and the device has important theoretical and practical significance on reservoir stability control, mining strategy and reservoir transformation scheme optimization during hydrate mining.

Description

Technical Field

[0001] The present invention relates to the field of safe exploitation of natural gas hydrates, and particularly to a simulation device and experimental method for reservoir pressure rebound during the exploitation of hydrates in the sea area. Background Art

[0002] During the exploitation of natural gas hydrates in the sea area, the pressure reduction method is the preferred method in current domestic and international trial production projects and also the most promising method in the future due to its advantages such as simple application, high cost-effectiveness, and no additional energy input. Along with the pressure reduction, the hydrate phase equilibrium is broken, and the hydrates in the reservoir medium begin to decompose into natural gas and water, and accumulate and migrate in the reservoir pores. However, during this process, there will be a phenomenon of local pore pressure rebound in the hydrate reservoir, which makes it difficult to control the wellbore pressure during exploitation, seriously affects the exploitation efficiency and strategy, and even may trigger marine geological disasters such as the rupture of the shallow overlying formation of the reservoir.

[0003] During the exploitation of natural gas hydrates in the sea area, the driving forces for the migration of gas and water in the reservoir mainly come from the continuous in-situ accumulation of the decomposition products of hydrates, resulting in an increase in the local pore pressure of the reservoir. Only when the pore pressure reaches a certain value will the decomposition products start to migrate to the adjacent pores in the direction of the production well. That is, the pore pressure represents the pressure head of the local area, and the change in pore pressure can reflect the process of the accumulation of decomposition products in the in-situ pores and their migration to the adjacent pores. Specifically, in the initial stage of hydrate decomposition in the reservoir, when the increase in the local pore pressure potential energy is greater than the driving forces consumed by gas and water migration, gas and water will migrate to the adjacent pores; when the sensible heat in the local area of the reservoir is rapidly consumed and not replenished in time, the hydrate decomposition rate will rapidly decrease. Once the increase in the local pore pressure potential energy is less than the driving forces required for gas and water migration, the phenomenon of local pore pressure rebound will occur.

[0004] During the hydrate decomposition process, an accurate description of the heat transfer and migration of gas and water in a reservoir with non-uniform porosity distribution helps to develop safe and efficient natural gas hydrate production methods. The phenomenon of pore pressure rebound in local areas of the reservoir has been confirmed by numerical experiments and laboratory hydrate decomposition experiments. When the local pressure exceeds the shear stress of the reservoir, layered fractures may even occur in the local area and formation outburst may occur (for shallow buried hydrate reservoirs), which is extremely unfavorable to the reservoir stability. However, most current studies focus on how to efficiently extract natural gas from the reservoir, and there is a lack of analysis on the change of pore pressure in local areas of the reservoir during the hydrate decomposition process, resulting in extremely unclear strong coupling relationships among the thermal-fluid-solid-chemical multi-physical fields in the reservoir during the hydrate production process. There is even a blank state for the relevant experimental equipment that takes the appearance and prevention of pore pressure rebound in local areas of the reservoir as the research focus. At the same time, the existing hydrate reservoir production simulation devices can only achieve the pressing and testing of a single-section core with a fixed porosity and cannot achieve the free combination and continuous integrated testing of cores with different porosities and permeabilities, making it difficult to effectively simulate the pore pressure rebound phenomenon in local areas of the reservoir.

[0005] To sum up, during the hydrate pressure reduction production process, the causes and laws of the pore pressure rebound phenomenon in local areas of the reservoir are not clearly understood, there is a lack of prevention methods for the reservoir pore pressure rebound, and the relationship between the reservoir pore pressure rebound and the fracture of the shallow overlying formation of the reservoir is not clear, which seriously affects the smooth progress of the pressure reduction strategy optimization, reservoir transformation plan, and implementation plan. Therefore, there is an urgent need for an experimental device that can achieve the integrated pressing and testing of cores with significantly different porosities in multiple sections and accurately monitor the multi-dimensional temperature and pressure in the cores to meet the effective simulation and in-depth exploration of the pore pressure rebound phenomenon in the reservoir. Summary of the Invention

[0006] The purpose of the present invention is to provide a reservoir pressure rebound simulation device and experimental method for hydrate production in the sea area aiming at the above-mentioned defects existing in the prior art, which can prepare a long horizontal cylindrical core with a high degree of integration, continuity, and significantly different porosities in multiple sections, and in-situ carry out hydrate formation and decomposition experiments in the core, so as to study the mechanism of pore pressure rebound in the hydrate reservoir.

[0007] A reservoir pressure rebound simulation device for hydrate production in the sea area mentioned in the present invention has the following technical solution: it includes a low-temperature control module and a data acquisition module. Among them, it also includes a multi-section continuous high-pressure reaction pressing and holding module, a top window module, a gas-liquid injection system, a gas-liquid recovery system, and a steel cylinder set. The steel cylinder set is made of multiple solid cylinders of stainless steel material; The external part of the multi - stage continuous high - pressure reaction clamping module consists of a steel double - layer cooling cylinder body, an axial head pressing sub - module, and an axial tail sealing sub - module; the internal part of the multi - stage continuous high - pressure reaction clamping module consists of a series of single - stage clamping devices connected end to end; the steel double - layer cooling cylinder body has a double - layer structure, and a water - bath annulus is embedded between the outer wall and the inner wall of the cooling cylinder body for circulating coolant; a coolant inlet is embedded above the side of the cooling cylinder body in the axial head direction, and a coolant outlet is embedded below the side of the cooling cylinder body in the axial tail direction. More than one set of single - stage clamping devices are installed in the inner cavity of the steel double - layer cooling cylinder body. An axial head pressing sub - module is installed at one end of the steel double - layer cooling cylinder body, and an axial tail sealing sub - module is installed at the other end. The top window module consists of a through - type switchable cylindrical window and a switch control valve rod. The through - type switchable cylindrical window is embedded in a pressure application / feedback leather sleeve, a segmented confining pressure chamber, a cylindrical steel body sleeve, and a steel double - layer cooling cylinder body in a through - type manner from the inside out. A set of embedded spherical valves is installed at the inner bottom of the through - type switchable cylindrical window, and a switch control valve rod is connected to the embedded spherical valves to control the opening and closing of the embedded spherical valves. The gas - liquid injection system consists of a high - purity methane high - pressure gas cylinder, a high - purity carbon dioxide high - pressure gas cylinder, a gas booster device, an intermediate gas cylinder during injection, a liquid container, a liquid injection pump, a gas - liquid flow T - shaped three - way, and a vacuum pump. The high - purity methane high - pressure gas cylinder and the high - purity carbon dioxide high - pressure gas cylinder are connected to the intermediate gas cylinder during injection through pipelines and the gas booster device, and then sent into the gas - liquid injection pipeline of the axial head pressing sub - module through pipelines and the gas - liquid flow T - shaped three - way; the liquid container is connected to the gas - liquid flow T - shaped three - way through a pipeline and the liquid injection pump. The gas - liquid recovery system includes an outlet pressure control valve, a primary gas - liquid separation tank, a secondary gas - liquid separation tank, a gas drying device, a gas mass flow controller and an accumulator, a methane concentration sensor, a gas recovery gas cylinder, and a liquid recovery container. The outer end of the gas - liquid discharge pipeline of the axial tail sealing sub - module is connected to the primary gas - liquid separation tank through the outlet pressure control valve. The side line of the primary gas - liquid separation tank is connected to the secondary gas - liquid separation tank through a pipeline. The top of the primary gas - liquid separation tank is connected to the gas recovery gas cylinder through the gas drying device, the gas mass flow controller and the accumulator, and the methane concentration sensor. The bottoms of the primary gas - liquid separation tank and the secondary gas - liquid separation tank are respectively connected to the liquid recovery container.

[0008] Preferably, the above-mentioned axial head pressure application sub-module is composed of an axial head steel sealing cylinder seat and an axial head steel pressure application cylinder seat. The annular space between the two is the axial pressure chamber. The axial head steel sealing cylinder seat is embedded with an axial pressure injection head and an axial pressure injection pipeline. The axial pressure injection head is connected to an axial pressure injection device through a stainless steel ventilation pipeline for applying pressure to the axial pressure chamber; the axial head steel pressure application cylinder seat is embedded with a gas-liquid injection pipeline for injecting gas and liquid into the core.

[0009] Preferably, the above-mentioned axial tail sealing sub-module is composed of an axial tail steel sealing cylinder seat and an axial tail steel fixing cylinder seat. The axial tail steel fixing cylinder seat is embedded with a gas-liquid discharge pipeline for discharging the gas and liquid generated after the hydrate decomposition in the core.

[0010] Preferably, the above-mentioned single-body pressure holding device is composed of a cylindrical steel body sleeve, an embedded confining pressure injection / feedback probe, a segmented confining pressure chamber, a pressure application / feedback leather sleeve, and a core filling space from outside to inside; The embedded confining pressure injection / feedback probe is penetrated and embedded in the steel double-layer cooling cylinder body and the cylindrical steel body sleeve. The tail of each embedded confining pressure injection / feedback probe corresponds to an independent segmented confining pressure chamber, and the head is connected with an independent probe pressure gauge and an independent high-pressure ball valve. The embedded confining pressure injection / feedback probe is divided into two groups, the upper half and the lower half, and is respectively connected in parallel to two confining pressure injection devices through stainless steel ventilation pipelines; The pressure application / feedback leather sleeve is between the segmented confining pressure chamber and the core filling space, and the core filling space is filled with the mixed material required for pressing the core or the finished pressed core.

[0011] Preferably, the above-mentioned single-body pressure holding device has five sections. The segmented confining pressure chamber of each section of the single-body pressure holding device is evenly divided into 3 small sections axially. Each small section of the confining pressure chamber is evenly divided into 4 sections with the radii at the positions of 45°, 135°, 225°, and 315° in the circumferential cross-section as the midlines. Each section of the confining pressure chamber is separated by a confining pressure annulus partition plate; there are 12 segmented confining pressure chambers in each section of the single-body pressure holding device, and there are 60 segmented confining pressure chambers in the whole multi-section continuous high-pressure reaction pressure holding module, and their quantities and positions are exactly corresponding to the embedded confining pressure injection / feedback probes.

[0012] Preferably, the above-mentioned steel cylinder set is composed of 4 solid cylinders made of stainless steel, namely the first steel cylinder, the second steel cylinder, the third steel cylinder, and the fourth steel cylinder, with lengths of 1600 mm, 1200 mm, 800 mm, and 400 mm respectively, all with a diameter of 200 mm and a pressure resistance range of 0 to 40 MPa. They are respectively used as the extended section of the axial head steel pressure cylinder seat during the process of five-stage segmented core pressing in the first single-body pressing device, the second single-body pressing device, the third single-body pressing device, and the fourth single-body pressing device to conduct axial pressure to the core pressing material.

[0013] Preferably, the present invention adopts an integrated pressing method to prepare five sections of cores with different porosities connected end to end and an experimental method, including the following process: First, a core with non-uniformly distributed porosity is prepared by an integrated pressing method in a multi-stage continuous high-pressure reaction pressing module, mainly including the following steps: a1. Check and confirm that all high-pressure ball valves and the ball valves of the injection and recovery systems are all closed, and check and confirm that the right end of the multi-stage continuous high-pressure reaction pressing module is completely sealed by the axial tail sealing sub-module; remove the axial head pressing sub-module, and pull the tail end of the pluggable steel temperature probe in the second to fifth single-body pressing devices to the inner wall of the pressure application / feedback leather sleeve at the lower end of the core filling space to ensure the tightness of the core filling space in the second to fifth single-body pressing devices; insert the first steel cylinder to the left boundary of the core filling space in the first single-body pressing device, and at the same time open the through-type switchable cylindrical window at the top of the first single-body pressing device, and pour the quartz mortar liquid and clay mixture of the first ratio through the top window, where the mass ratio of quartz sand to clay is 5:5 and the water-cement ratio is 0.5; then close the top window and let the mixture stand for a period of time. a2. Open the through-type switchable cylindrical window at the top of the second single-body pressing device, quickly pull the first steel cylinder to the left boundary of the core filling space in the second single-body pressing device, and at the same time quickly pour the quartz mortar liquid and clay mixture of the second ratio through the top window, where the mass ratio of quartz sand to clay is 5:5 and the water-cement ratio is 0.9, insert the pluggable steel temperature probe of the second single-body pressing device to the initial position, then close the top window and let the mixture stand for a period of time. a3. Open the through-type switchable cylindrical window at the top of the third monomer holding device, quickly draw the first steel cylinder to the left boundary of the core filling space of the third monomer holding device, and at the same time quickly pour the quartz mortar liquid and clay mixture with the 3rd ratio through the top window. Among them, the mass ratio of quartz sand to clay is 6:4, and the water-cement ratio is 1. Insert the pluggable steel temperature probe of the third monomer holding device to the initial position, then close the top window, and let the mixture stand for a period of time; a4. Open the through-type switchable cylindrical window at the top of the fourth monomer holding device, quickly draw the first steel cylinder to the left boundary of the core filling space of the fourth monomer holding device, and at the same time quickly pour the quartz mortar liquid and clay mixture with the 4th ratio through the top window. Among them, the mass ratio of quartz sand to clay is 7:3, and the water-cement ratio is 1.1. Insert the pluggable steel temperature probe of the fourth monomer holding device to the initial position, then close the top window, and let the mixture stand for a period of time; a5. Open the through-type switchable cylindrical window at the top of the fifth monomer holding device, quickly draw the first steel cylinder to the left boundary of the core filling space of the fifth monomer holding device, and at the same time quickly pour the quartz mortar liquid and clay mixture with the 5th ratio through the top window. Among them, the mass ratio of quartz sand to clay is 8:2, and the water-cement ratio is 1.2. Insert the pluggable steel temperature probe of the fifth monomer holding device to the initial position, close the top window, and let the mixture stand for a period of time; Then quickly draw out the first steel cylinder, quickly assemble and seal the axial head pressure sub-module at the left end of the multi-stage continuous high-pressure reaction holding module, apply a pressure of 10 MPa to both the axial pressure chamber and the segmented confining pressure chamber at the same time, and continuously press the mixture in the core filling space of the 5-section monomer holding device for 8 hours, so as to form a core in the shape of an integral long horizontal cylinder with 5 sections of significantly different porosities in the multi-stage continuous high-pressure reaction holding module. The non-uniformly distributed porosity in the core decreases gradually from left to right in each section; Secondly, the generation of hydrates in the continuous integral long core with significant differences in porosity in multiple sections includes the following steps: b1. Release the pressure in the axial pressure chamber and the segmented confining pressure chamber to 0 MPa, and use a vacuum pump to pump the pressure in the core filling space and the transfer gas cylinder during the injection process to -0.1 MPa; b2. Close all the ball valves on the liquid injection line side of the gas-liquid flow T-shaped three-way. Use a high-purity methane high-pressure gas cylinder and a gas booster device to make the pressure of methane gas in the transfer gas cylinder during the injection process reach 10 MPa; Then use the pressure difference between the transfer gas cylinder and the core filling space during the injection process to inject methane into the core. Stop injecting methane when the pressure in the segmented confining pressure chamber reaches 8 MPa; b3. Close all the ball valves on one side of the gas-liquid flow T-shaped three-way injection line. Use a liquid injection pump to inject pure water into the core filling space. Stop injecting pure water when the pressure in the segmented confining pressure chamber reaches 10 MPa, and then close all the ball valves on one side of the gas-liquid flow T-shaped three-way liquid injection line. b4. Let the core stand for 1 hour to ensure that the pure water in the core is saturated with methane. Repeat step b2, inject a small amount of methane into the core again, and stabilize the pressure in the segmented confining pressure chamber at 10 MPa. Then close all the ball valves on one side of the gas-liquid flow T-shaped three-way liquid injection line. b5. Turn on the refrigerating water bath circulation machine, set the target water bath temperature to 1°C, and let the coolant continuously cool down and circulate in the water bath annulus inside the steel double-layer cooling cylinder. Monitor the temperature at the temperature monitoring points on the pluggable steel temperature probe in the core filling space in real time. A sudden increase in a certain temperature indicates the formation of hydrates in that sub-region of the core. b6. After the temperatures at all the temperature monitoring points have all shown an upward trend, continue to maintain the target water bath temperature of 1°C and let the coolant circulate for 30 minutes to ensure that the hydrates formed in the integral long core with significantly different porosities in multiple segments are annealed and enter a stable state. Finally, the decomposition of hydrates in the continuous integral long core with significantly different porosities in multiple segments, that is, the simulation of the hydrate pressure reduction production process, includes the following steps: c1. Check and ensure that all the ball valves of the gas-liquid recovery system are closed. Then open the ball valve between the gas-liquid discharge pipeline and the first-stage gas-liquid separation tank. During the process of the pressure reduction in the core, the hydrates gradually decompose into methane gas and water, and migrate to one end of the gas-liquid discharge pipeline in the non-uniform distributed pores in the integral long core. After passing through the outlet pressure control valve, it flows into the first-stage gas-liquid separation tank. Use the data acquisition system to record in real time the temperature and pressure changes in the sub-regions of the core that can be monitored in the multi-segment continuous high-pressure reaction pressure holding module, and monitor the area where the pressure rebound phenomenon occurs in the core during the hydrate decomposition process and the change law of the pressure rebound. c2. When the pressure in the first-stage gas-liquid separation tank reaches stability, open the ball valve between the first-stage gas-liquid separation tank and the second-stage gas-liquid separation tank. c3. When the pressure in the second-stage gas-liquid separation tank reaches stability, open all the ball valves at the back of the first-stage gas-liquid separation tank and the second-stage gas-liquid separation tank in sequence. The methane gas flows into the gas recovery gas cylinder through the gas drying device, the gas mass flow controller and the accumulator, and the methane concentration sensor. c4. After the pressure in the gas recovery gas cylinder stabilizes, inject carbon dioxide gas into the core filling space through the gas-liquid injection system, so that all the remaining methane gas in the core and the two gas-liquid separation tanks flows into the gas recovery gas cylinder; when the methane concentration sensor monitors that the methane concentration is 0, close the spherical valve at the front end of the gas recovery gas cylinder, close the spherical valve at the rear end of the high-purity carbon dioxide high-pressure gas cylinder, open the discharge valves at the lower ends of the first-stage gas-liquid separation tank and the second-stage gas-liquid separation tank, discharge the carbon dioxide gas outdoors, and discharge the water into the liquid recovery container.

[0014] Preferably, the present invention adopts a five-stage segmented preparation method for five cores with different porosities connected end to end and an experimental method, including the following processes: First, prepare a core with non-uniform porosity distribution in the multi-stage continuous high-pressure reaction pressing module by means of five-stage segmented pressing. This pressing method realizes the non-uniform porosity distribution in the large-section core by precisely controlling two factors: the mixing material ratio of the small-section core pressing and the pressing time of the small-section core. It is suitable for experiments that require a large porosity difference condition, and mainly includes the following steps: S1. Check and confirm that all high-pressure ball valves and spherical valves of the injection and recovery systems are closed, and check and confirm that the right end of the multi-stage continuous high-pressure reaction pressing module is completely sealed by the axial tail sealing sub-module; remove the axial head pressing sub-module, and pull the tail ends of the pluggable steel temperature probes in the second to fifth monomer pressing devices to the inner wall of the pressure application / feedback leather sleeve at the lower end of the core filling space; insert the first steel cylinder into the left boundary of the core filling space of the first monomer pressing device, and quickly assemble and seal the axial head pressing sub-module at the left end of the multi-stage continuous high-pressure reaction pressing module; open the through-type switchable cylindrical window at the top of the first monomer pressing device, and pour in a fixed ratio of quartz mortar liquid and clay mixed material through the top window, where the mass ratio of quartz sand to clay is 8:2 and the water-binder ratio is 1.2; then close the top window, insert the pluggable steel temperature probe of the first monomer pressing device to the initial position, and apply a pressure of 10 MPa to both the axial pressure chamber and the segmented confining pressure chamber at the same time, and continuously press the mixed material in the core filling space of the first monomer pressing device for 1 hour; S2. Release the pressures in the axial compression chamber and the segmented confining pressure chamber to 0 MPa. Remove the axial head pressing sub-module, extract the first steel cylinder, and insert the second steel cylinder at the left boundary of the core filling space of the second single-body holding device. Quickly assemble and seal the axial head pressing sub-module. Open the through-type switchable cylindrical window at the top of the second single-body holding device, and pour in the quartz mortar liquid and clay mixture with the same ratio as in step S1 through the top window. Then close the top window, insert the pluggable steel temperature probe of the second single-body holding device to the initial position, apply a pressure of 10 MPa to both the axial compression chamber and the segmented confining pressure chamber simultaneously, and press the mixture in the second single-body holding device and the formed core in the first single-body holding device for 1 hour. S3. Release the pressures in the axial compression chamber and the segmented confining pressure chamber to 0 MPa. Remove the axial head pressing sub-module, extract the second steel cylinder, and insert the third steel cylinder at the left boundary of the core filling space of the third single-body holding device. Quickly assemble and seal the axial head pressing sub-module. Open the through-type switchable cylindrical window at the top of the third single-body holding device, and pour in the quartz mortar liquid and clay mixture with the same ratio as in step S1 through the top window. Then close the top window, insert the pluggable steel temperature probe of the third single-body holding device to the initial position, apply a pressure of 10 MPa to both the axial compression chamber and the segmented confining pressure chamber simultaneously, and press the mixture in the third single-body holding device and the formed cores in the first single-body holding device and the second single-body holding device for 1 hour. S4. Release the pressures in the axial compression chamber and the segmented confining pressure chamber to 0 MPa. Remove the axial head pressing sub-module, extract the third steel cylinder, and insert the fourth steel cylinder at the left boundary of the core filling space of the fourth single-body holding device. Quickly assemble and seal the axial head pressing sub-module. Open the through-type switchable cylindrical window at the top of the fourth single-body holding device, and pour in the quartz mortar liquid and clay mixture with the same ratio as in step S1 through the top window. Then close the top window, insert the pluggable steel temperature probe of the fourth single-body holding device to the initial position, apply a pressure of 10 MPa to both the axial compression chamber and the segmented confining pressure chamber simultaneously, and press the mixture in the fourth single-body holding device and the formed cores in the first single-body holding device, the second single-body holding device, and the third single-body holding device for 1 hour. S5. Release the pressures in the axial compression chamber and the segmented confining pressure chamber to 0 MPa. Remove the axial head pressing sub-module, extract the fourth steel cylinder, quickly assemble and seal the axial head pressing sub-module. Open the through-type switchable cylindrical window at the top of the fifth single-body holding device, and pour in the quartz mortar liquid and clay mixture with the same ratio as in step S1 through the top window. Then close the top window, insert the pluggable steel temperature probe of the fifth single-body holding device to the initial position, apply a pressure of 10 MPa to both the axial compression chamber and the segmented confining pressure chamber simultaneously, and press the mixture in the fifth single-body holding device and the formed rock cores in the first, second, third, and fourth single-body holding devices for 4 hours. After the pressing is completed, a rock core in the shape of an integrated long horizontal cylinder with 5 segments of significantly different porosities is formed in the multi-segment continuous high-pressure reaction holding module. The mixture ratios used for pressing each small segment of the rock core are exactly the same, but the pressing times for the 5 small segments of the rock core are 4, 5, 6, 7, and 8 hours from left to right. Therefore, the non-uniformly distributed porosities in the integrated long horizontal cylinder-shaped rock core decrease gradually from left to right in each segment.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention provides a top window module, which consists of a through-type switchable cylindrical window at the top of the single-body holding device and a switch control valve rod. During the pressing process of a large segment of rock core with non-uniformly distributed porosities, it provides conditions for injecting different mixtures into the single-body holding devices at different positions. (2) The present invention provides a multi-segment continuous high-pressure reaction holding module composed of five single-body holding devices connected end to end. Each single-body holding device is provided with a pluggable steel temperature probe at the bottom. Combining the top window module, the steel cylinder set, and the experimental method provided by the present invention, an integrated long horizontal cylinder rock core with a high degree of integration, continuity, and significantly different porosities in multiple segments can be prepared by two methods: integrated pressing and five-stage segmented pressing. Moreover, the free combination of small segments of rock core with different porosities can be controlled, providing conditions for the long-distance continuous migration of the fluid after hydrate decomposition in a porous medium with non-uniformly distributed and complex and variable porosities, and effectively simulating the reservoir pressure rebound phenomenon during the hydrate production process. (3) The present invention innovatively provides 12 segmented confining pressure chambers, 12 embedded confining pressure injection / feedback probes, and 6 pluggable steel temperature probes in each single-body holding device. The temperature and pressure in a total of 60 fan-shaped columnar sub-regions in the axial and tangential dimensions of the entire rock core in the multi-segment continuous high-pressure reaction holding module can be independently monitored, enabling fine monitoring of the specific location where the pressure rebound phenomenon occurs and the pressure fluctuation changes in the integrated long horizontal cylinder rock core with significantly different porosities in multiple segments. Description of the Drawings

[0016] Figure 1 is a schematic diagram of the overall system of the present invention; Figure 2 is a front structural schematic diagram of the multi-stage continuous high-pressure reaction pressing module mentioned in the present invention; Figure 3 is a structural schematic diagram of the steel cylinder set mentioned in the present invention; Figure 4 is a structural schematic diagram of the steel double-layer cooling cylinder of the present invention; Figure 5 is a spread structural schematic diagram of the axial head pressure application sub-module, 5-section monomer pressing device, and axial tail sealing sub-module installed in the steel double-layer cooling cylinder; Figure 6 is a cross-sectional schematic diagram of the multi-stage continuous high-pressure reaction pressing module of the present invention; Figure 7 is a curve schematic diagram of the core pore pressure rebound phenomenon that appears in the multi-stage continuous high-pressure reaction pressing module during the experimental process of simulating the pressure reduction extraction of hydrates in the present invention; In the above figure: 1 - multi-stage continuous high-pressure reaction pressing module, 2 - steel double-layer cooling cylinder, 3 - axial head pressure application sub-module, 4 - axial tail sealing sub-module, 5 - outer wall of the cooling cylinder, 6 - inner wall of the cooling cylinder, 7 - water bath annulus, 8 - coolant inlet, 9 - coolant outlet, 10 - axial head steel sealing cylinder seat, 11 - axial head steel pressure application cylinder seat, 12 - axial pressure chamber, 13 - axial pressure injection head, 14 - axial pressure injection pipeline, 15 - stainless steel ventilation pipeline, 16 - axial pressure injection device, 17 - gas-liquid injection pipeline, 18 - sealing bolt, 19 - axial tail steel sealing cylinder seat, 20 - axial tail steel fixing cylinder seat, 21 - gas-liquid discharge pipeline, 22 - cylindrical steel body sleeve, 23 - embedded confining pressure injection / feedback probe, 24 - segmented confining pressure chamber, 25 - pressure application / feedback leather sleeve, 26 - core filling space, 27 - fifth monomer pressing device, 28 - fourth monomer pressing device, 29 - third monomer pressing device, 30 - second monomer pressing device, 31 - first monomer pressing device, 32 - first axial small section of the cylindrical steel body sleeve, 33 - second axial small section of the cylindrical steel body sleeve, 34 - third axial small section of the cylindrical steel body sleeve; 43 - Through - type switchable cylindrical window, 44 - Wrench at the top of the valve stem, 45 - Switch - controlled valve stem, 46 - Plug - in steel temperature probe, 47 - Thermometer, 48 - Probe pressure gauge, 49 - High - pressure ball valve, 50 - Confining pressure injection device, 51 - Confining pressure annulus separation steel plate, 52 - Embedded spherical valve, 53 - First steel temperature probe monitoring point, 54 - Second steel temperature probe monitoring point, 55 - Data transmission line, 56 - Refrigerated water bath circulation machine, 57 - Coolant input pipeline, 58 - Coolant discharge pipeline, 59 - Pressure gauge in the gas - liquid injection system, 60 - Pressure gauge in the gas - liquid recovery system, 61 - Electronic scale, 62 - Data acquisition module, 63 - Computer, 64 - High - purity methane high - pressure gas cylinder, 65 - High - purity carbon dioxide high - pressure gas cylinder, 66 - Pressure reducing valve, 67 - Gas boosting device, 68 - Intermediate gas cylinder during injection process, 69 - Process control valve, 70 - Liquid container, 71 - Liquid injection pump, 72 - Gas - liquid flow T - shaped tee, 73 - Vacuum pump, 74 - Spherical valve, 75 - Outlet pressure control valve, 76 - First - stage gas - liquid separation tank, 77 - Second - stage gas - liquid separation tank, 78 - Gas drying device, 79 - Gas mass flow controller and accumulator, 80 - Methane concentration sensor, 81 - Gas recovery gas cylinder, 82 - Liquid recovery container, 84 - Drying net, 85 - First steel cylinder, 86 - Second steel cylinder, 87 - Third steel cylinder, 88 - Fourth steel cylinder. Specific implementation mode

[0017] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not used to limit the present invention.

[0018] Example 1. Refer to Figures 1 - 7 A reservoir pressure rebound simulation device in marine gas hydrate exploitation mentioned in the present invention has the following technical solution: It includes a low - temperature control module and a data acquisition module. Among them, it also includes a multi - stage continuous high - pressure reaction holding module 1, a top window module, a gas - liquid injection system, a gas - liquid recovery system, and a steel cylinder set. The steel cylinder set is made of multiple solid cylinders of stainless steel material; The multi-stage continuous high-pressure reaction pressing module 1 is externally composed of a steel double-layer cooling cylinder 2, an axial head pressing sub-module 3, and an axial tail sealing sub-module 4; the multi-stage continuous high-pressure reaction pressing module 1 is internally composed of a series of single pressing devices connected end to end; the steel double-layer cooling cylinder 2 is a double-layer structure, and a water bath annulus 7 is embedded between the outer wall 5 and the inner wall 6 of the cooling cylinder for circulating the coolant; a coolant inlet 8 is embedded above the side of the cooling cylinder in the axial head direction, and a coolant outlet 9 is embedded below the side of the cooling cylinder in the axial tail direction. One or more groups of single pressing devices are installed in the inner cavity of the steel double-layer cooling cylinder 2. The axial head pressing sub-module 3 is installed at one end of the steel double-layer cooling cylinder 2 through a sealing bolt 18, and the axial tail sealing sub-module 4 is installed at the other end through a sealing bolt 18; The top window module consists of a through-type switchable cylindrical window 43 and a switch control valve stem 45. The through-type switchable cylindrical window 43 is embedded in a pressure application / feedback leather sleeve 25, a segmented confining pressure chamber 24, a cylindrical steel sleeve 22, and a steel double-layer cooling cylinder 2 in a through-type manner from the inside out. A group of embedded spherical valves 52 are installed at the bottom inside the through-type switchable cylindrical window 43. A switch control valve stem 45 is connected to the embedded spherical valves 52, and a valve stem top wrench 44 is installed at the top of the switch control valve stem 45 for controlling the opening and closing of the embedded spherical valves 52; The gas-liquid injection system consists of a high-purity methane high-pressure gas cylinder 64, a high-purity carbon dioxide high-pressure gas cylinder 65, a gas booster 67, an intermediate gas cylinder 68 during the injection process, a liquid container 70, a liquid injection pump 71, a gas-liquid flow T-shaped tee 72, and a vacuum pump 73. The high-purity methane high-pressure gas cylinder 64 and the high-purity carbon dioxide high-pressure gas cylinder 65 are connected to the intermediate gas cylinder 68 during the injection process through pipelines and the gas booster 67, and then sent into the gas-liquid injection pipeline 17 of the axial head pressing sub-module 3 through pipelines and the gas-liquid flow T-shaped tee 72; the liquid container 70 is connected to the gas-liquid flow T-shaped tee 72 through a pipeline and the liquid injection pump 71; During the gas injection process, the gas in the high-pressure gas cylinder passes through the pressure reducing valve 66 and is pumped into the transfer gas cylinder 68 during the injection process by the gas booster device 67. Subsequently, under the action of the pressure difference, it successively passes through the process control valve 69, the gas-liquid flow T-shaped tee 72, and the gas-liquid injection pipeline 17 and is thus injected into the core. The transfer gas cylinder 68 during the injection process is used to control the pressure and composition of the injected gas. The pumping pressure of the gas booster device 67 can be adjusted in the range of 0 to 20 MPa, and the flow monitoring range of the process control valve 69 is 0 to 1000 kg / s. During the liquid injection process, the liquid in the liquid container 70 is successively injected into the core through the liquid injection pump 71, the gas-liquid flow T-shaped tee 72, and the gas-liquid injection pipeline 17. The working pressure of the liquid injection pump 71 is 0 - 30 MPa. The vacuum pump 73 is used to evacuate the air in the core filling space 26 and the transfer gas cylinder 68 during the injection process before the experiment starts, and the working pressure is -0.2 to 0.5 MPa.

[0019] The gas-liquid recovery system includes an outlet pressure control valve 75, a primary gas-liquid separation tank 76, a secondary gas-liquid separation tank 77, a gas drying device 78, a gas mass flow controller and accumulator 79, a methane concentration sensor 80, a gas recovery gas cylinder 81, and a liquid recovery container 82. The outer end of the gas-liquid discharge pipeline 21 of the axial tail sealing sub-module 4 is connected to the primary gas-liquid separation tank 76 through the outlet pressure control valve 75. The side line of the primary gas-liquid separation tank 76 is connected to the secondary gas-liquid separation tank 77 through a pipeline and a drying mesh 84. The top of the primary gas-liquid separation tank 76 is connected to the gas recovery gas cylinder 81 through the gas drying device 78, the gas mass flow controller and accumulator 79, and the methane concentration sensor 80. The bottoms of the primary gas-liquid separation tank 76 and the secondary gas-liquid separation tank 77 are respectively connected to the liquid recovery container 82.

[0020] Refer to Figure 2 and Figure 5 As shown in FIGS. and, the axial head pressure application sub-module 3 mentioned in the present invention is composed of an axial head steel sealing cylinder seat 10 and an axial head steel pressure application cylinder seat 11. The annular space between the two is the axial pressure chamber 12. The axial head steel sealing cylinder seat 10 is embedded with an axial pressure injection head 13 and an axial pressure injection pipeline 14. The axial pressure injection head 13 is connected to the axial pressure injection device 16 through a stainless steel ventilation pipeline 15 for applying pressure to the axial pressure chamber 12. The axial head steel pressure application cylinder seat 11 is embedded with a gas-liquid injection pipeline 17 for injecting gas and liquid into the core.

[0021] The above-mentioned axial tail sealing sub-module 4 is composed of an axial tail steel sealing cylinder seat 19 and an axial tail steel fixed cylinder seat 20. The axial tail steel fixed cylinder seat 20 is embedded with a gas-liquid discharge pipeline 21 for discharging the gas and liquid generated after the hydrate decomposition in the core.

[0022] The above-mentioned single-core pressing device is composed of a cylindrical steel sleeve 22, an embedded confining pressure injection / feedback probe 23, a segmented confining pressure chamber 24, a pressure application / feedback leather sleeve 25, and a core filling space 26 from the outside to the inside; The embedded confining pressure injection / feedback probe 23 is penetrated and embedded in the steel double-layer cooling cylinder 2 and the cylindrical steel sleeve 22. The tail of each embedded confining pressure injection / feedback probe 23 corresponds to an independent segmented confining pressure chamber 24, and the head is connected with an independent probe pressure gauge 48 and an independent high-pressure ball valve 49. The embedded confining pressure injection / feedback probe 23 is divided into two groups, the upper half and the lower half, and is respectively connected in parallel to two confining pressure injection devices 50 through stainless steel gas pipelines 15; The pressure application / feedback leather sleeve 25 is located between the segmented confining pressure chamber 24 and the core filling space 26, and the core filling space 26 is filled with the mixed material required for pressing the core or the finished pressed core.

[0023] Refer to Figure 5 and Figure 6 As shown in the figure, the single-core pressing device mentioned in the present invention has five sections. The segmented confining pressure chamber 24 of each section of the single-core pressing device is evenly divided into 3 small sections axially, namely: the first cylindrical steel sleeve axial small section 32, the second cylindrical steel sleeve axial small section 33, and the third cylindrical steel sleeve axial small section 34. Each small-section confining pressure chamber is evenly divided into 4 sections in the tangential cross-section with the radii at the positions of 45°, 135°, 225°, and 315° of the circumference as the midlines. Each section of the confining pressure chamber is separated by a confining pressure annulus separating steel plate 51; there are 12 segmented confining pressure chambers in each section of the single-core pressing device, and there are 60 segmented confining pressure chambers 24 in the whole multi-section continuous high-pressure reaction pressing module 1, and their quantities and positions completely correspond to the embedded confining pressure injection / feedback probes 23.

[0024] 6 pluggable steel temperature probes 46 are embedded at the bottom of each section of the cylindrical steel sleeve 22. The head of each pluggable steel temperature probe 46 is connected with an independent thermometer 47. At the same time, each pluggable steel temperature probe 46 is provided with 2 temperature monitoring points, specifically the first steel temperature probe monitoring point 53 and the second steel temperature probe monitoring point 54, for monitoring the temperature inside different sub-regions of the core.

[0025] Refer to Figure 3, the steel cylinder set mentioned in the present invention is composed of 4 solid cylinders made of stainless steel, namely the first steel cylinder 85, the second steel cylinder 86, the third steel cylinder 87, and the fourth steel cylinder 88, with lengths of 1600 mm, 1200 mm, 800 mm, and 400 mm respectively, all with a diameter of 200 mm and a pressure resistance range of 0 to 40 MPa. They are respectively used as the extended sections of the axial head steel pressing cylinder seat 11 during the process of five-stage segmented pressing of the core in the first single pressing device 31, the second single pressing device 30, the third single pressing device 29, and the fourth single pressing device 28 to conduct axial pressure to the core pressing material.

[0026] In addition, the low-temperature control module mentioned in the present invention is composed of a refrigerating water bath circulation machine 56, a coolant input pipeline 57, and a coolant discharge pipeline 58. The refrigerating water bath circulation machine 56 can cool the antifreeze coolant inside it, and then pump the coolant into the water bath annulus 7 inside the double-layer steel cooling cylinder 2 through the coolant input pipeline 57 and the coolant input port 8 successively. Affected by its own gravity and the pumping power of the refrigerating water bath circulation machine, the coolant flows towards the coolant discharge port 9 and flows back into the refrigerating water bath circulation machine 56 through the coolant discharge pipeline 58. The temperature control range of the refrigerating water bath circulation machine 56 is -20°C to 50°C.

[0027] The data acquisition module mentioned in the present invention is composed of pressure gauges 59 and 60 in 4 gas-liquid injection systems, pressure gauges 48 of the probe of 60 embedded confining pressure injection / feedback probes 23, pressure gauges 60 in 5 gas-liquid recovery systems, thermometers 47 of 30 pluggable steel temperature probes 46, 3 electronic scales 61, a data transmission line 55, a data acquisition module 62, and a computer 63. All pressure gauges and thermometers are connected to the data acquisition module 62 through the data transmission line 55. The computer 63 records and saves the temperature and pressure data monitored by the acquisition module in real time, and the data recording time interval ranges from 1 to 10 seconds.

[0028] In addition, referring to Figure 7 , it is a schematic curve diagram of the core pore pressure rebound phenomenon that appears in the multi-stage continuous high-pressure reaction pressing module during the experimental process of simulating the depressurization production of hydrates in the present invention. It can be concluded that there is a local core pore pressure rebound phenomenon in the fourth single pressing device and the fifth single pressing device; furthermore, research on the prevention and control methods for reservoir pressure rebound can be carried out.

[0029] In addition, the experimental method of the reservoir pressure rebound simulation device in the exploitation of submarine hydrates mentioned in the present invention mainly includes three experimental stages: the core preparation stage, the hydrate formation stage, and the hydrate decomposition stage. In the core preparation stage, cores with different porosities connected end to end in five sections are prepared by the method of one-piece pressing or five-section segmented pressing, and then hydrate formation and decomposition experiments are carried out, so as to realize the experimental research on the simulation and prevention of the pore pressure rebound phenomenon in the reservoir with non-uniform porosity distribution during the hydrate exploitation process.

[0030] Among them, the method for preparing cores with different porosities connected end to end in five sections by the one-piece pressing method and the experimental method of the present invention include the following processes: First, cores with non-uniform porosity distribution are prepared by the one-piece pressing method in the multi-section continuous high-pressure reaction pressing module 1, which mainly includes the following steps: a1. Check and confirm that all high-pressure ball valves 49 and the ball valves 74 of the injection and recovery system are all closed, and check and confirm that the right end of the multi-section continuous high-pressure reaction pressing module 1 is completely sealed by the axial tail sealing sub-module 4; remove the axial head pressure application sub-module 3, and pull the tail ends of the pluggable steel temperature probes 46 in the second to fifth monomer pressing devices 30-27 to the inner wall of the pressure application / feedback leather sleeve 25 at the lower end of the core filling space 26 to ensure the tightness of the core filling space 26 in the second to fifth monomer pressing devices 30-27; insert the first steel cylinder 85 to the left boundary of the core filling space 26 of the first monomer pressing device 31, and at the same time open the through-type switchable cylindrical window 43 at the top of the first monomer pressing device 31, and pour the quartz sand mortar liquid and clay mixture material with the first ratio through the top window. Among them, the mass ratio of quartz sand to clay is 5:5, and the water-cement ratio is 0.5; then close the top window and let the mixture stand for a period of time; a2. Open the through-type switchable cylindrical window 43 at the top of the second monomer pressing device 30, quickly pull the first steel cylinder 85 to the left boundary of the core filling space 26 of the second monomer pressing device 30, and at the same time quickly pour the quartz sand mortar liquid and clay mixture material with the second ratio through the top window. Among them, the mass ratio of quartz sand to clay is 5:5, and the water-cement ratio is 0.9. Insert the pluggable steel temperature probe 46 of the second monomer pressing device 30 to the initial position, then close the top window and let the mixture stand for a period of time; a3. Open the through-type switchable cylindrical window 43 at the top of the third monomer holding device 29, quickly draw the first steel cylinder 85 to the left boundary of the core filling space 26 of the third monomer holding device 29, and at the same time quickly pour the quartz mortar liquid and clay mixture material with the 3rd ratio through the top window. Among them, the mass ratio of quartz sand to clay is 6:4, and the water-cement ratio is 1. Insert the pluggable steel temperature probe 46 of the third monomer holding device 29 to the initial position, then close the top window, and let the mixture stand for a period of time; a4. Open the through-type switchable cylindrical window 43 at the top of the fourth monomer holding device 28, quickly draw the first steel cylinder 85 to the left boundary of the core filling space 26 of the fourth monomer holding device 28, and at the same time quickly pour the quartz mortar liquid and clay mixture material with the 4th ratio through the top window. Among them, the mass ratio of quartz sand to clay is 7:3, and the water-cement ratio is 1.1. Insert the pluggable steel temperature probe 46 of the fourth monomer holding device 28 to the initial position, then close the top window, and let the mixture stand for a period of time; a5. Open the through-type switchable cylindrical window 43 at the top of the fifth monomer holding device 27, quickly draw the first steel cylinder 85 to the left boundary of the core filling space 26 of the fifth monomer holding device 27, and at the same time quickly pour the quartz mortar liquid and clay mixture material with the 5th ratio through the top window. Among them, the mass ratio of quartz sand to clay is 8:2, and the water-cement ratio is 1.2. Insert the pluggable steel temperature probe 46 of the fifth monomer holding device 27 to the initial position, close the top window, and let the mixture stand for a period of time; Then quickly draw out the first steel cylinder 85, quickly assemble and seal the axial head pressing sub-module 3 at the left end of the multi-stage continuous high-pressure reaction holding module 1, apply a pressure of 10 MPa to both the axial pressure chamber 12 and the segmented confining pressure chamber 24 at the same time, and continuously press the mixture in the core filling space 26 of the 5-stage monomer holding device for 8 hours, so as to form an integrated long horizontal cylinder-shaped core with 5 significantly different porosities in the multi-stage continuous high-pressure reaction holding module 1, and the non-uniformly distributed porosity in the core decreases gradually from left to right; Secondly, the formation of hydrates in the continuous integrated long core with significantly different porosities in multiple stages includes the following steps: b1. Release the pressure in the axial pressure chamber 12 and the segmented confining pressure chamber 24 to 0 MPa, and use the vacuum pump 73 to pump the pressure in the core filling space 26 and the transfer gas cylinder 68 during the injection process to -0.1 MPa; b2. Close all the ball valves 74 on the liquid injection line side of the gas-liquid flow T-shaped tee 72. Use the high-purity methane high-pressure gas cylinder 64 and the gas booster 67 to make the pressure of the methane gas in the transfer gas cylinder 68 during the injection process reach 10 MPa. Subsequently, use the pressure difference between the transfer gas cylinder 68 during the injection process and the core filling space 26 to inject methane into the core. Stop injecting methane when the pressure in the segmented confining pressure chamber 24 reaches 8 MPa. b3. Close all the ball valves 74 on the gas injection line side of the gas-liquid flow T-shaped tee 72. Use the liquid injection pump 71 to inject pure water into the core filling space 26. Stop injecting pure water when the pressure in the segmented confining pressure chamber 24 reaches 10 MPa, and then close all the ball valves 74 on the liquid injection line side of the gas-liquid flow T-shaped tee 72. b4. Let the core stand still for 1 hour to ensure that the pure water in the core is saturated with methane. Repeat step b2 to inject a small amount of methane into the core again to make the pressure in the segmented confining pressure chamber 24 stable at 10 MPa. Subsequently, close all the ball valves 74 on the liquid injection line side of the gas-liquid flow T-shaped tee 72. b5. Turn on the refrigerated water bath circulation machine 56, set the water bath target temperature to 1 °C, and make the coolant continuously cool down and circulate in the water bath annulus 7 in the steel double-layer cooling cylinder 2. Real-time monitor the temperature at the temperature monitoring points on the pluggable steel temperature probe 46 in the core filling space 26. A sudden increase in a certain temperature indicates the formation of hydrates in that sub-region of the core. b6. After the temperatures of all the temperature monitoring points have all shown an upward trend, continue to maintain the water bath target temperature of 1 °C and let the coolant circulate for 30 minutes to ensure that the hydrates formed in the integral long core with significantly different porosities in multiple segments are annealed and enter a stable state. Finally, the decomposition of hydrates in the continuous integral long core with significantly different porosities in multiple segments, that is, the simulation of the hydrate pressure reduction production process, includes the following steps: c1. Check and ensure that all the ball valves 74 of the gas-liquid recovery system are closed. Subsequently, open the ball valve 74 between the gas-liquid discharge pipeline 21 and the first-stage gas-liquid separation tank 76. The hydrates gradually start to decompose into methane gas and water during the process of the pressure reduction in the core, and migrate to one end of the gas-liquid discharge pipeline 21 in the non-uniformly distributed pores in the integral long core, and flow into the first-stage gas-liquid separation tank 76 after passing through the outlet pressure control valve 75. Use the data acquisition system to record in real time the temperature and pressure changes in the sub-regions of the core that can be monitored in the multi-segment continuous high-pressure reaction pressure holding module 1, and monitor the area where the pressure rebound phenomenon occurs in the core during the hydrate decomposition process and the change law of the pressure rebound. c2. When the pressure in the first-stage gas-liquid separation tank 76 reaches stability, open the ball valve 74 between the first-stage gas-liquid separation tank 76 and the second-stage gas-liquid separation tank 77. c3. After the pressure in the secondary gas-liquid separation tank 77 reaches stability, successively open all the spherical valves 74 at the rear ends of the primary gas-liquid separation tank 76 and the secondary gas-liquid separation tank 77. Methane gas flows into the gas recovery gas cylinder 81 through the gas drying device 78, the gas mass flow controller and accumulator 79, and the methane concentration sensor 80; c4. After the pressure in the gas recovery gas cylinder 81 reaches stability, inject carbon dioxide gas into the core filling space 26 through the gas-liquid injection system, so that all the remaining methane gas in the core and the two gas-liquid separation tanks flows into the gas recovery gas cylinder 81. When the methane concentration sensor 80 monitors that the methane concentration is 0, close the spherical valve 74 at the front end of the gas recovery gas cylinder 81, close the spherical valve 74 at the rear end of the high-purity carbon dioxide high-pressure gas cylinder 65, open the discharge valves at the lower ends of the primary gas-liquid separation tank 76 and the secondary gas-liquid separation tank 77, discharge the carbon dioxide gas to the outside, and discharge the water to the liquid recovery container 82.

[0031] Example 2. The experimental method of the reservoir pressure rebound simulation device in the exploitation of marine hydrates mentioned in the present invention is different from that in Example 1 in that: In this example, a five-stage segmented method is used to prepare five sections of cores with different porosities connected end to end and the experimental method, including the following process: First, in the multi-stage continuous high-pressure reaction pressing module 1, prepare a core with non-uniform porosity distribution through a five-stage segmented pressing method. This pressing method realizes the non-uniform porosity distribution in the large-section core by precisely controlling two factors: the mixing material ratio of the small-section core pressing and the pressing time of the small-section core. It is suitable for experiments that require a large porosity difference condition, and mainly includes the following steps: S1. Check and confirm that all high-pressure ball valves 49 and ball valves 74 of the injection and recovery system are completely closed. Check and confirm that the right end of the multi-stage continuous high-pressure reaction holding module 1 is completely sealed by the axial tail sealing sub-module 4. Remove the axial head pressure application sub-module 3, and pull the tail end of the pluggable steel temperature probe 46 in the second to fifth monomer holding devices 30 to 27 to the inner wall of the pressure application / feedback leather sleeve 25 at the lower end of the core filling space 26. Insert the first steel cylinder 85 to the left boundary of the core filling space 26 of the first monomer holding device 31, and quickly assemble and seal the axial head pressure application sub-module 3 at the left end of the multi-stage continuous high-pressure reaction holding module 1. Open the through-switchable cylindrical window 43 at the top of the first monomer holding device 31, and pour in the quartz mortar liquid and clay mixture with a fixed ratio through the top window. Among them, the mass ratio of quartz sand to clay is 8:2, and the water-cement ratio is 1.2. Then close the top window, insert the pluggable steel temperature probe 46 of the first monomer holding device 31 to the initial position, and apply a pressure of 10 MPa to both the axial pressure chamber 12 and the segmented confining pressure chamber 24 at the same time, and continuously press the mixture in the core filling space 26 of the first monomer holding device 31 for 1 hour. S2. Release the pressure in the axial pressure chamber 12 and the segmented confining pressure chamber 24 to 0 MPa, remove the axial head pressure application sub-module 3, pull out the first steel cylinder 85 and insert the second steel cylinder 86 to the left boundary of the core filling space 26 of the second monomer holding device 30, and quickly assemble and seal the axial head pressure application sub-module 3. Open the through-switchable cylindrical window 43 at the top of the second monomer holding device 30, and pour in the quartz mortar liquid and clay mixture with the same ratio as in step S1 through the top window. Then close the top window, insert the pluggable steel temperature probe 46 of the second monomer holding device 30 to the initial position, apply a pressure of 10 MPa to both the axial pressure chamber 12 and the segmented confining pressure chamber 24 at the same time, and press the mixture in the second monomer holding device 30 and the formed core in the first monomer holding device 31 for 1 hour at the same time. S3. Release the pressures in the axial pressure chamber 12 and the segmented confining pressure chamber 24 to 0 MPa, remove the axial head pressing sub-module 3, extract the second steel cylinder 86 and insert the third steel cylinder 87 into the left boundary of the core filling space 26 of the third single-body holding device 29. Quickly assemble and seal the axial head pressing sub-module 3. Open the through-type switchable cylindrical window 43 at the top of the third single-body holding device 29, and pour in the quartz mortar liquid and clay mixture with the same ratio as in step S1 through the top window. Then close the top window, insert the pluggable steel temperature probe 46 of the third single-body holding device 29 to the initial position, apply a pressure of 10 MPa simultaneously to the axial pressure chamber 12 and the segmented confining pressure chamber 24, and press the mixture in the third single-body holding device 29 and the formed cores in the first single-body holding device 31 and the second single-body holding device 30 for 1 hour. S4. Release the pressures in the axial pressure chamber 12 and the segmented confining pressure chamber 24 to 0 MPa, remove the axial head pressing sub-module 3, extract the third steel cylinder 87 and insert the fourth steel cylinder 88 into the left boundary of the core filling space 26 of the fourth single-body holding device 28. Quickly assemble and seal the axial head pressing sub-module 3. Open the through-type switchable cylindrical window 43 at the top of the fourth single-body holding device 28, and pour in the quartz mortar liquid and clay mixture with the same ratio as in step S1 through the top window. Then close the top window, insert the pluggable steel temperature probe 46 of the fourth single-body holding device 28 to the initial position, apply a pressure of 10 MPa simultaneously to the axial pressure chamber 12 and the segmented confining pressure chamber 24, and press the mixture in the fourth single-body holding device 28 and the formed cores in the first single-body holding device 31, the second single-body holding device 30 and the third single-body holding device 29 for 1 hour. S5. Release the pressures in the axial compression chamber 12 and the segmented confining pressure chamber 24 to 0 MPa, remove the axial head pressing sub-module 3, extract the fourth steel cylinder 88, quickly assemble and seal the axial head pressing sub-module 3; open the through-switchable cylindrical window 43 at the top of the fifth single body pressing device 27, and pour in the quartz mortar liquid and clay mixture with the same ratio as in step S1 through the top window; then close the top window, insert the pluggable steel temperature probe 46 of the fifth single body pressing device 27 to the initial position, apply a pressure of 10 MPa to both the axial compression chamber 12 and the segmented confining pressure chamber 24, and simultaneously press the mixture in the fifth single body pressing device 27 and the formed rock cores in the first single body pressing device 31, the second single body pressing device 30, the third single body pressing device 29 and the fourth single body pressing device 28 for 4 hours; after the pressing is completed, a rock core in the shape of an integral long horizontal cylinder with 5 segments of significantly different porosities is formed in the multi-stage continuous high-pressure reaction pressing module 1. The mixture ratios used for pressing each small segment of the rock core are exactly the same, but the pressing times for the 5 small segments of the rock core are 4, 5, 6, 7, and 8 hours from left to right respectively. Therefore, the non-uniformly distributed porosities in the integral long horizontal cylinder-shaped rock core decrease gradually from left to right in each segment.

[0032] As described above, only some of the preferred embodiments of the present invention are provided. Any person skilled in the art may modify the above-described technical solution or modify it into an equivalent technical solution. Therefore, any corresponding simple modification or equivalent transformation made according to the technical solution of the present invention falls within the scope of protection required by the present invention.

Claims

1. A simulation device for reservoir pressure rebound in marine hydrate exploitation, comprising a low-temperature control module and a data acquisition module, characterized in that: It also includes a multi-stage continuous high-pressure reaction clamping module (1), a top window module, a gas-liquid injection system, a gas-liquid recovery system, and a steel cylinder set. The steel cylinder set is made of multiple solid cylinders of stainless steel material; The external part of the multi-stage continuous high-pressure reaction clamping module (1) consists of a steel double-layer cooling cylinder body (2), an axial head pressure application sub-module (3), and an axial tail sealing sub-module (4); the internal part of the multi-stage continuous high-pressure reaction clamping module (1) is composed of multiple single-stage clamping devices connected end to end; the steel double-layer cooling cylinder body (2) is of a double-layer structure, and a water bath annulus (7) is embedded between the outer wall (5) of the cooling cylinder body and the inner wall (6) of the cooling cylinder body for circulating the coolant; a coolant inlet (8) is embedded above the side of the cooling cylinder body in the axial head direction, and a coolant outlet (9) is embedded below the side of the cooling cylinder body in the axial tail direction. One or more groups of single-stage clamping devices are installed in the inner cavity of the steel double-layer cooling cylinder body (2). An axial head pressure application sub-module (3) is installed at one end of the steel double-layer cooling cylinder body (2), and an axial tail sealing sub-module (4) is installed at the other end; The top window module consists of a through-type switchable cylindrical window (43) and a switch control valve rod (45). The through-type switchable cylindrical window (43) is embedded in a pressure application / feedback leather sleeve (25), a segmented confining pressure chamber (24), a cylindrical steel body sleeve (22), and a steel double-layer cooling cylinder body (2) in a through-type manner from the inside to the outside. A group of embedded spherical valves (52) is installed at the inner bottom of the through-type switchable cylindrical window (43), and a switch control valve rod (45) is connected to the embedded spherical valves (52) for controlling the opening and closing of the embedded spherical valves (52); The gas-liquid injection system consists of a high-purity methane high-pressure gas cylinder (64), a high-purity carbon dioxide high-pressure gas cylinder (65), a gas booster device (67), a transfer gas cylinder (68) during the injection process, a liquid container (70), a liquid injection pump (71), a gas-liquid flow T-shaped three-way joint (72), and a vacuum pump (73). The high-purity methane high-pressure gas cylinder (64) and the high-purity carbon dioxide high-pressure gas cylinder (65) are connected to the transfer gas cylinder (68) during the injection process through pipelines and the gas booster device (67), and then sent into the gas-liquid injection pipeline (17) of the axial head pressure application sub-module (3) through pipelines and the gas-liquid flow T-shaped three-way joint (72); the liquid container (70) is connected to the gas-liquid flow T-shaped three-way joint (72) through pipelines and the liquid injection pump (71); The gas-liquid recovery system includes an outlet pressure control valve (75), a primary gas-liquid separation tank (76), a secondary gas-liquid separation tank (77), a gas drying device (78), a gas mass flow controller and accumulator (79), a methane concentration sensor (80), a gas recovery gas cylinder (81), and a liquid recovery container (82). The outer end of the gas-liquid discharge pipeline (21) of the axial tail seal sub-module (4) is connected to the primary gas-liquid separation tank (76) through the outlet pressure control valve (75). The side line of the primary gas-liquid separation tank (76) is connected to the secondary gas-liquid separation tank (77) through a pipeline. The top of the primary gas-liquid separation tank (76) is connected to the gas recovery gas cylinder (81) through the gas drying device (78), the gas mass flow controller and accumulator (79), and the methane concentration sensor (80). The bottoms of the primary gas-liquid separation tank (76) and the secondary gas-liquid separation tank (77) are respectively connected to the liquid recovery container (82).

2. The reservoir pressure rebound simulation device in marine hydrate exploitation according to claim 1, wherein: The axial head pressure application sub-module (3) consists of an axial head steel seal cylinder base (10) and an axial head steel pressure application cylinder base (11). The annular space between the two is the axial pressure chamber (12). The axial head steel seal cylinder base (10) is embedded with an axial pressure injection head (13) and an axial pressure injection pipeline (14). The axial pressure injection head (13) is connected to the axial pressure injection device (16) through a stainless steel ventilation pipeline (15) for applying pressure to the axial pressure chamber (12). The axial head steel pressure application cylinder base (11) is embedded with a gas-liquid injection pipeline (17) for injecting gas and liquid into the core.

3. The reservoir pressure rebound simulation device for marine hydrate exploitation according to claim 2, characterized in that: The axial tail seal sub-module (4) consists of an axial tail steel seal cylinder base (19) and an axial tail steel fixed cylinder base (20). The axial tail steel fixed cylinder base (20) is embedded with a gas-liquid discharge pipeline (21) for discharging the gas and liquid generated after the hydrate decomposition in the core.

4. The reservoir pressure rebound simulation device in the exploitation of marine hydrates according to claim 3, characterized in that: The single-body pressing device consists of a cylindrical steel body sleeve (22), an embedded confining pressure injection / feedback probe (23), a segmented confining pressure chamber (24), a pressure application / feedback leather sleeve (25), and a core filling space (26) from the outside to the inside. The embedded confining pressure injection / feedback probe (23) is penetrated and embedded in the steel double-layer cooling cylinder (2) and the cylindrical steel body sleeve (22). The tail of each embedded confining pressure injection / feedback probe (23) corresponds to an independent segmented confining pressure chamber (24), and the head is connected with an independent probe pressure gauge (48) and an independent high-pressure ball valve (49). The embedded confining pressure injection / feedback probe (23) is divided into two groups of upper and lower parts, and is respectively connected in parallel to two confining pressure injection devices (50) through stainless steel ventilation pipelines (15). The pressure application / feedback leather sleeve (25) is located between the segmented confining pressure chamber (24) and the core filling space (26). The core filling space (26) is filled with the mixed material required for pressing the core or the finished pressed core.

5. The reservoir pressure rebound simulation device for marine hydrate exploitation according to claim 4, characterized in that: The single-body pressing device has five sections. The segmented confining pressure chamber (24) of each section of the single-body pressing device is evenly divided into 3 small sections axially. Each small-section confining pressure chamber is evenly divided into 4 sections in the tangential cross-section with the radii at the positions of 45°, 135°, 225°, and 315° of the circumference as the midlines. Each section of the confining pressure chamber is separated by a confining pressure annulus separating steel plate (51); there are 12 segmented confining pressure chambers in each section of the single-body pressing device, and there are 60 segmented confining pressure chambers (24) in the entire multi-section continuous high-pressure reaction pressing module (1), and their quantities and positions exactly correspond to the embedded confining pressure injection / feedback probes (23).

6. The reservoir pressure rebound simulation device for marine hydrate exploitation according to claim 5, characterized in that: The steel cylinder set consists of 4 solid cylinders made of stainless steel, namely the first steel cylinder (85), the second steel cylinder (86), the third steel cylinder (87), and the fourth steel cylinder (88), with lengths of 1600mm, 1200mm, 800mm, and 400mm respectively, diameters of 200mm, and pressure resistance ranges of 0 to 40 MPa. They are respectively used as the extended sections of the axial head steel pressing cylinder seat (11) during the process of five-section segmented core pressing in the first single-body pressing device (31), the second single-body pressing device (30), the third single-body pressing device (29), and the fourth single-body pressing device (28) to conduct axial pressure to the core pressing material.

7. The experimental method of the reservoir pressure rebound simulation device in marine hydrate exploitation according to claim 6, characterized in that: An integrated pressing method is used to prepare five sections of cores with different porosities connected end to end and an experimental method, including the following process: First, cores with non-uniform porosity distribution are prepared by an integrated pressing method in the multi-section continuous high-pressure reaction pressing module (1), mainly including the following steps: a1. Check and confirm that all high-pressure ball valves (49) and the ball valves (74) of the injection and recovery system are all closed. Check and confirm that the right end of the multi-section continuous high-pressure reaction pressing module (1) is completely sealed by the axial tail sealing sub-module (4); remove the axial head pressing sub-module (3), and pull the tail ends of the pluggable steel temperature probes (46) in the second single-body pressing device (30) to the fifth single-body pressing device (27) to the inner wall of the pressure application / feedback leather sleeve (25) at the lower end of the core filling space (26) to ensure the tightness of the core filling space (26) in the second single-body pressing device (30) to the fifth single-body pressing device (27); insert the first steel cylinder (85) to the left boundary of the core filling space (26) of the first single-body pressing device (31), and at the same time open the through-switchable cylindrical window (43) at the top of the first single-body pressing device (31), and pour the quartz mortar liquid and clay mixture material with the first ratio through the top window. Among them, the mass ratio of quartz sand to clay is 5:5, and the water-cement ratio is 0.5; then close the top window and let the mixture stand for a period of time; a2. Open the through-type switchable cylindrical window (43) at the top of the second monomer holding device (30), quickly draw the first steel cylinder (85) to the left boundary of the core filling space (26) of the second monomer holding device (30), and at the same time quickly pour the quartz mortar liquid and clay mixture with the second ratio through the top window. Among them, the mass ratio of quartz sand to clay is 5:5, and the water-cement ratio is 0.

9. Insert the pluggable steel temperature probe (46) of the second monomer holding device (30) to the initial position, then close the top window, and let the mixture stand for a period of time; a3. Open the through-type switchable cylindrical window (43) at the top of the third monomer holding device (29), quickly draw the first steel cylinder (85) to the left boundary of the core filling space (26) of the third monomer holding device (29), and at the same time quickly pour the quartz mortar liquid and clay mixture with the third ratio through the top window. Among them, the mass ratio of quartz sand to clay is 6:4, and the water-cement ratio is 1. Insert the pluggable steel temperature probe (46) of the third monomer holding device (29) to the initial position, then close the top window, and let the mixture stand for a period of time; a4. Open the through-type switchable cylindrical window (43) at the top of the fourth monomer holding device (28), quickly draw the first steel cylinder (85) to the left boundary of the core filling space (26) of the fourth monomer holding device (28), and at the same time quickly pour the quartz mortar liquid and clay mixture with the fourth ratio through the top window. Among them, the mass ratio of quartz sand to clay is 7:3, and the water-cement ratio is 1.

1. Insert the pluggable steel temperature probe (46) of the fourth monomer holding device (28) to the initial position, then close the top window, and let the mixture stand for a period of time; a5. Open the through-type switchable cylindrical window (43) at the top of the fifth monomer holding device (27), quickly draw the first steel cylinder (85) to the left boundary of the core filling space (26) of the fifth monomer holding device (27), and at the same time quickly pour the quartz mortar liquid and clay mixture with the fifth ratio through the top window. Among them, the mass ratio of quartz sand to clay is 8:2, and the water-cement ratio is 1.

2. Insert the pluggable steel temperature probe (46) of the fifth monomer holding device (27) to the initial position, close the top window, and let the mixture stand for a period of time; Then quickly draw out the first steel cylinder (85), quickly assemble and seal the axial head pressure sub-module (3) at the left end of the multi-stage continuous high-pressure reaction holding module (1), and apply a pressure of 10 MPa to both the axial pressure chamber (12) and the segmented confining pressure chamber (24) at the same time, and continuously press the mixture in the core filling space (26) of the 5-stage monomer holding device for 8 hours, so as to form a core in the shape of an integrated long horizontal cylinder with 5 significantly different porosities in the multi-stage continuous high-pressure reaction holding module (1), and the porosity unevenly distributed in the core decreases gradually from left to right; Secondly, the generation of hydrates in a continuous one-piece long rock core with significant differences in porosity in multiple sections includes the following steps: b1. Release the pressure in the axial pressure chamber (12) and the segmented confining pressure chamber (24) to 0 MPa, and use a vacuum pump (73) to pump the pressure in the core filling space (26) and the transfer gas cylinder (68) during the injection process to -0.1 MPa; b2. Close all the ball valves (74) on the liquid injection line side of the gas-liquid flow T-shaped tee (72), and use a high-purity methane high-pressure gas cylinder (64) and a gas booster device (67) to make the pressure of methane gas in the transfer gas cylinder (68) during the injection process reach 10 MPa; then use the pressure difference between the transfer gas cylinder (68) and the core filling space (26) during the injection process to inject methane into the core, and stop injecting methane when the pressure in the segmented confining pressure chamber (24) reaches 8 MPa; b3. Close all the ball valves (74) on the gas injection line side of the gas-liquid flow T-shaped tee (72), use a liquid injection pump (71) to inject pure water into the core filling space (26), stop injecting pure water when the pressure in the segmented confining pressure chamber (24) reaches 10 MPa, and close all the ball valves (74) on the liquid injection line side of the gas-liquid flow T-shaped tee (72); b4. Let the core stand for 1 hour to ensure that the pure water in the core is saturated with methane, repeat step b2, inject a small amount of methane into the core again, and make the pressure in the segmented confining pressure chamber (24) stable at 10 MPa, and then close all the ball valves (74) on the liquid injection line side of the gas-liquid flow T-shaped tee (72); b5. Turn on the refrigerating water bath circulation machine (56), set the target water bath temperature to 1°C, and make the coolant continuously cool down and circulate in the water bath annulus (7) in the steel double-layer cooling cylinder (2); continuously monitor the temperature of the temperature monitoring points on the pluggable steel temperature probe (46) in the core filling space (26). A sudden increase in a certain temperature indicates the generation of hydrates in that sub-region of the core; b6. After the temperatures of all the temperature monitoring points have all shown an upward trend, continue to maintain the target water bath temperature of 1°C and let the coolant circulate for 30 minutes to ensure that the hydrates generated in the continuous one-piece long rock core with significant differences in porosity in multiple sections are annealed and enter a stable state; Finally, the decomposition of hydrates in a continuous one-piece long rock core with significant differences in porosity in multiple sections, that is, the simulation of the hydrate pressure reduction production process, includes the following steps: c1. Check and ensure that all spherical valves (74) of the gas-liquid recovery system are closed. Then open the spherical valve (74) between the gas-liquid discharge pipeline (21) and the first-stage gas-liquid separation tank (76). During the process of the pressure reduction in the core, hydrates gradually start to decompose into methane gas and water, and migrate non-uniformly in the pores of the integral long core towards one end of the gas-liquid discharge pipeline (21). After passing through the outlet pressure control valve (75), it flows into the first-stage gas-liquid separation tank (76). The data acquisition system is used to record in real time the temperature and pressure changes in the core sub-regions that can be monitored within the multi-stage continuous high-pressure reaction holding module (1), and monitor the regions where the pressure rebound phenomenon occurs in the core during the hydrate decomposition process and the variation law of the pressure rebound. c2. When the pressure in the first-stage gas-liquid separation tank (76) reaches stability, open the spherical valve (74) between the first-stage gas-liquid separation tank (76) and the second-stage gas-liquid separation tank (77). c3. When the pressure in the second-stage gas-liquid separation tank (77) reaches stability, sequentially open all the spherical valves (74) at the rear ends of the first-stage gas-liquid separation tank (76) and the second-stage gas-liquid separation tank (77). Methane gas flows into the gas recovery gas cylinder (81) through the gas drying device (78), the gas mass flow controller and accumulator (79), and the methane concentration sensor (80). c4. When the pressure in the gas recovery gas cylinder (81) reaches stability, inject carbon dioxide gas into the core filling space (26) through the gas-liquid injection system, so that all the remaining methane gas in the core and the two gas-liquid separation tanks flows into the gas recovery gas cylinder (81). When the methane concentration sensor (80) monitors that the methane concentration is 0, close the spherical valve (74) at the front end of the gas recovery gas cylinder (81), close the spherical valve (74) at the rear end of the high-purity carbon dioxide high-pressure gas cylinder (65), open the discharge valves at the lower ends of the first-stage gas-liquid separation tank (76) and the second-stage gas-liquid separation tank (77), discharge the carbon dioxide gas outdoors, and discharge the water into the liquid recovery container (82).

8. The experimental method of the reservoir pressure rebound simulation device in marine hydrate exploitation according to claim 6, characterized in that: Adopt a five-stage segmented method to prepare five sections of cores with different porosities connected end to end and an experimental method, including the following process: First, prepare a core with non-uniformly distributed porosity in the multi-stage continuous high-pressure reaction holding module (1) by a five-stage segmented pressing method. This pressing method realizes the non-uniform distribution of porosity in the large-section core by precisely controlling two factors: the mixing material ratio of the small-section core pressing and the small-section core pressing time, and is suitable for experiments that require a large porosity difference condition. It mainly includes the following steps: S1. Check and confirm that all high-pressure ball valves (49) and ball valves (74) of the injection and recovery system are fully closed. Check and confirm that the right end of the multi-stage continuous high-pressure reaction holding module (1) is completely sealed by the axial tail seal sub-module (4). Remove the axial head pressure application sub-module (3). Pull the tail end of the pluggable steel temperature probe (46) in the second to fifth monomer holding devices (30 - 27) to the inner wall of the pressure application / feedback leather sleeve (25) at the lower end of the core filling space (26). Insert the first steel cylinder (85) into the left boundary of the core filling space (26) of the first monomer holding device (31). Quickly assemble and seal the axial head pressure application sub-module (3) at the left end of the multi-stage continuous high-pressure reaction holding module (1). Open the through-switchable cylindrical window (43) at the top of the first monomer holding device (31), and pour in a fixed ratio of quartz mortar liquid and clay mixture through the top window. Among them, the mass ratio of quartz sand to clay is 8:2, and the water-binder ratio is 1.

2. Then close the top window, insert the pluggable steel temperature probe (46) of the first monomer holding device (31) to the initial position, and apply a pressure of 10 MPa to both the axial pressure chamber (12) and the segmented confining pressure chamber (24) simultaneously, and continuously press the mixture in the core filling space (26) of the first monomer holding device (31) for 1 hour. S2. Release the pressure in the axial pressure chamber (12) and the segmented confining pressure chamber (24) to 0 MPa. Remove the axial head pressure application sub-module (3), pull out the first steel cylinder (85) and insert the second steel cylinder (86) into the left boundary of the core filling space (26) of the second monomer holding device (30). Quickly assemble and seal the axial head pressure application sub-module (3). Open the through-switchable cylindrical window (43) at the top of the second monomer holding device (30), and pour in the same ratio of quartz mortar liquid and clay mixture as in step S1 through the top window. Then close the top window, insert the pluggable steel temperature probe (46) of the second monomer holding device (30) to the initial position, apply a pressure of 10 MPa to both the axial pressure chamber (12) and the segmented confining pressure chamber (24) simultaneously, and press the mixture in the second monomer holding device (30) and the formed core in the first monomer holding device (31) simultaneously for 1 hour. S3. Release the pressures in the axial compression chamber (12) and the segmented confining pressure chamber (24) to 0 MPa, remove the axial head pressing sub-module (3), extract the second steel cylinder (86) and insert the third steel cylinder (87) at the left boundary of the core filling space (26) of the third single-body holding device (29). Quickly assemble and seal the axial head pressing sub-module (3). Open the through-type switchable cylindrical window (43) at the top of the third single-body holding device (29), and pour in the quartz mortar liquid and clay mixture with the same ratio as in step S1 through the top window. Then close the top window, insert the pluggable steel temperature probe (46) of the third single-body holding device (29) to the initial position, apply a pressure of 10 MPa to both the axial compression chamber (12) and the segmented confining pressure chamber (24), and simultaneously press the mixture in the third single-body holding device (29) and the formed cores in the first single-body holding device (31), the second single-body holding device (30) for 1 hour. S4. Release the pressures in the axial compression chamber (12) and the segmented confining pressure chamber (24) to 0 MPa, remove the axial head pressing sub-module (3), extract the third steel cylinder (87) and insert the fourth steel cylinder (88) at the left boundary of the core filling space (26) of the fourth single-body holding device (28). Quickly assemble and seal the axial head pressing sub-module (3). Open the through-type switchable cylindrical window (43) at the top of the fourth single-body holding device (28), and pour in the quartz mortar liquid and clay mixture with the same ratio as in step S1 through the top window. Then close the top window, insert the pluggable steel temperature probe (46) of the fourth single-body holding device (28) to the initial position, apply a pressure of 10 MPa to both the axial compression chamber (12) and the segmented confining pressure chamber (24), and simultaneously press the mixture in the fourth single-body holding device (28) and the formed cores in the first single-body holding device (31), the second single-body holding device (30), and the third single-body holding device (29) for 1 hour. S5. Release the pressure in the axial compression chamber (12) and the segmented confining pressure chamber (24) to 0 MPa, remove the axial head pressing sub-module (3), extract the fourth steel cylinder (88), quickly assemble and seal the axial head pressing sub-module (3); open the through-switchable cylindrical window (43) at the top of the fifth single-body pressing device (27), and pour the quartz mortar liquid and clay mixture with the same ratio as in step S1 through the top window; then close the top window, insert the pluggable steel temperature probe (46) of the fifth single-body pressing device (27) to the initial position, apply a pressure of 10 MPa to both the axial compression chamber (12) and the segmented confining pressure chamber (24), and simultaneously press the mixture in the fifth single-body pressing device (27) and the formed rock cores in the first single-body pressing device (31), the second single-body pressing device (30), the third single-body pressing device (29) and the fourth single-body pressing device (28) for 4 hours; after the pressing is completed, a rock core in the shape of an integral long horizontal cylinder with 5 significantly different porosities is formed in the multi-stage continuous high-pressure reaction pressing module (1). The mixture ratio used for pressing each small section of the rock core is exactly the same, but the pressing time for the 5 small sections of the rock core is 4, 5, 6, 7, and 8 hours from left to right respectively. Therefore, the non-uniformly distributed porosity in the integral long horizontal cylinder-shaped rock core decreases gradually from left to right in each section.

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