A reservoir pressure rebound simulation device and experimental method for marine hydrate production

Abstract

The present invention relates to the field of safe exploitation of natural gas hydrates, and in particular to a reservoir pressure rebound simulation device and experimental method for marine hydrate exploitation. Its technical solution includes a multi-stage continuous high-pressure reaction pressure holding 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 cylindrical set. The multi-stage continuous high-pressure reaction pressure holding module is composed of five sections of single-body pressure holding devices connected end to end, and is equipped with a total of 60 pressure and temperature monitoring sub-areas in the axial and tangential directions. It can prepare cores through two methods: one-piece pressing and five-stage pressing, and conduct in-situ reservoir pressure rebound phenomenon simulation experiments. It solves the problem that traditional devices can only simulate discontinuous, fixed-porosity reservoirs and have low internal temperature and pressure monitoring accuracy. It has important theoretical and practical significance for reservoir stability control, mining strategies, and reservoir transformation plan optimization during hydrate exploitation.

Description

Technical Field

[0001] The present invention relates to the field of safe exploitation of natural gas hydrates, and in particular to a reservoir pressure rebound simulation device and an experimental method for offshore hydrate exploitation. Background Art

[0002] In the process of offshore natural gas hydrate extraction, the depressurization method is currently the preferred method in pilot production projects both domestically and internationally due to its simplicity, cost-effectiveness, and lack of additional energy input. It also holds the most promise for the future. With depressurization, the hydrate phase equilibrium is disrupted, and the hydrates within the reservoir medium begin to decompose into natural gas and water, which accumulate and migrate within the reservoir pores. However, this process can cause localized pore pressure rebound within the hydrate reservoir, making wellbore pressure control difficult, severely impacting extraction efficiency and strategies, and even triggering marine geological hazards such as rupture of shallow overlying strata.

[0003] During the extraction of natural gas hydrates in offshore areas, the driving force for gas and water migration in the reservoir mainly comes from the continuous in-situ accumulation of hydrate decomposition products, which leads to an increase in the local pore pressure of the reservoir. Only when the pore pressure reaches a certain value do the decomposition products begin to migrate to the adjacent pores in the direction of the extraction well. In other words, the pore pressure represents the pressure head in the local area, and the change in pore pressure can reflect the accumulation of decomposition products in the in-situ pores and the process of migration to 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 force consumed by gas and water migration, gas and water will migrate to adjacent pores; when the sensible heat in the local area of the reservoir is rapidly consumed and cannot be replenished in time, the hydrate decomposition rate decreases rapidly. Once the increase in the local pore pressure potential energy is less than the driving force required for gas and water migration, the local pore pressure rebound phenomenon will occur.

[0004] Accurately describing the heat transfer and migration of gas and water within reservoirs with heterogeneous porosity distribution during hydrate decomposition will facilitate the development of safe and efficient natural gas hydrate recovery methods. The phenomenon of pore pressure rebound in localized reservoirs has been confirmed by numerical experiments and laboratory hydrate decomposition experiments. When local pressure exceeds the reservoir shear stress, layered fractures and even outbursts (in shallow hydrate reservoirs) can occur in these areas, which is extremely detrimental to reservoir stability. However, current research focuses on efficiently recovering natural gas from reservoirs, while analysis of localized pore pressure changes during hydrate decomposition is relatively scarce. This results in a lack of clarity regarding the strong coupling of the reservoir's thermal, fluid, solidification, and chemical multi-physics fields during hydrate recovery. Furthermore, there is a lack of experimental equipment specifically focused on the occurrence and prevention of localized pore pressure rebound in reservoirs. At the same time, the current existing hydrate reservoir mining simulation device can only realize the compression and testing of a single section of fixed porosity core, and cannot realize 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] In summary, during hydrate depressurization, the causes and patterns of pore pressure rebound in localized reservoirs remain unclear, prevention methods are lacking, and the relationship between pore pressure rebound and overlying shallow strata fractures is unclear, severely impacting the optimization of depressurization strategies, reservoir reconstruction plans, and implementation plans. Therefore, an experimental device is urgently needed that can achieve integrated core compression and testing of multiple sections with significantly different porosities, as well as precise monitoring of multi-dimensional temperature and pressure within the core, to effectively simulate and deeply explore the pore pressure rebound phenomenon in reservoirs. Summary of the Invention

[0006] The purpose of the present invention is to address the above-mentioned defects of the existing technology and provide a reservoir pressure rebound simulation device and experimental method in marine hydrate exploitation. It can prepare long horizontal cylindrical rock cores with a high degree of integration, continuity, and significant porosity differences in multiple sections, and conduct in situ hydrate formation and decomposition experiments in the rock cores, thereby studying the pore pressure rebound mechanism of the hydrate reservoir.

[0007] The present invention relates to a reservoir pressure rebound simulation device for marine hydrate production, the technical solution of which is as follows: comprising a low-temperature control module, a data acquisition module, a multi-stage continuous high-pressure reaction pressure holding module, a top window module, a gas-liquid injection system, a gas-liquid recovery system, and a steel cylinder set, wherein the steel cylinder set is made of multiple solid stainless steel cylinders;

[0008] The exterior of the multi-stage continuous high-pressure reaction holding module is composed of a steel double-layer cooling cylinder, an axial head pressure submodule, and an axial tail sealing submodule; the interior of the multi-stage continuous high-pressure reaction holding module is composed of multiple sections of monomer holding devices connected end to end; the steel double-layer cooling cylinder is a double-layer structure, and a water bath annulus is embedded between the outer wall and the inner wall of the cooling cylinder for circulating coolant; a coolant inlet is embedded on the upper side of the cooling cylinder in the axial head direction, and a coolant outlet is embedded on the lower side of the cooling cylinder in the axial tail direction. More than one set of monomer holding devices is installed in the inner cavity of the steel double-layer cooling cylinder, and the axial head pressure submodule is installed at one end of the steel double-layer cooling cylinder, and the axial tail sealing submodule is installed at the other end;

[0009] The top window module consists of a through-type switchable cylindrical window and a switch control valve stem. The through-type switchable cylindrical window is embedded from the inside to the outside in the pressure application / feedback leather sleeve, the segmented confining pressure chamber, the cylindrical steel body sleeve and the steel double-layer cooling cylinder. A set of embedded ball valves is installed at the bottom of the inner side of the through-type switchable cylindrical window. The embedded ball valve is connected to the switch control valve stem for controlling the opening and closing of the embedded ball valve.

[0010] 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, a gas cylinder for transferring gas during injection, a liquid container, a liquid injection pump, a gas-liquid flow T-joint, 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 gas cylinder for transferring gas during injection via pipelines and the gas booster, and then fed into the gas-liquid injection pipeline of the axial head pressure submodule via pipelines and the gas-liquid flow T-joint; the liquid container is connected to the gas-liquid flow T-joint via pipelines and the liquid injection pump.

[0011] 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 cylinder, and a liquid recovery container. The outer end of the gas-liquid discharge pipeline of the axial tail sealing submodule 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 cylinder through the gas drying device, the gas mass flow controller and the accumulator and the methane concentration sensor, and the bottoms of the primary gas-liquid separation tank and the secondary gas-liquid separation tank are respectively connected to the liquid recovery container.

[0012] Preferably, the above-mentioned axial head pressure submodule is composed of an axial head steel sealing cylinder seat and an axial head steel pressure cylinder seat. The annular space between the two is an axial pressure cavity. 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 the axial pressure injection device through a stainless steel ventilation pipeline, which is used to apply pressure to the axial pressure cavity; the axial head steel pressure cylinder seat is embedded with a gas-liquid injection pipeline, which is used to inject gas and liquid into the core.

[0013] Preferably, the above-mentioned axial tail sealing submodule consists of an axial tail steel sealing cylinder seat and an axial tail steel fixed cylinder seat. The axial tail steel fixed cylinder seat is embedded with a gas-liquid discharge pipeline for discharging the gas and liquid produced after the decomposition of hydrates in the core.

[0014] Preferably, the above-mentioned single-body holding device is composed of a cylindrical steel body sleeve, an embedded confining pressure injection / feedback probe, a segmented confining pressure cavity, a pressure application / feedback sleeve and a core filling space from the outside to the inside;

[0015] The embedded confining pressure injection / feedback probe is embedded in a through-type manner within a double-layer steel cooling cylinder and a cylindrical steel body sleeve. The tail of each embedded confining pressure injection / feedback probe corresponds to an independent segmented confining pressure cavity, and the head is connected to 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, which are connected in parallel to the two confining pressure injection devices via stainless steel ventilation pipelines.

[0016] The pressure applying / feedback sleeve is located between the segmented confining pressure cavity and the core filling space, and the core filling space is filled with mixed materials required for pressing the core or the finished pressed core.

[0017] Preferably, the above-mentioned single pressing device is provided with five sections, and the segmented confining pressure chamber of each single pressing device is divided into three small sections in the axial direction, and each small confining pressure chamber is divided into four sections on the tangential section with the radius at the circumferential positions of 45°, 135°, 225° and 315° as the center line, and each confining pressure chamber is separated by a confining pressure annulus partition steel plate; there are a total of 12 segmented confining pressure chambers in each single pressing device, and a total of 60 segmented confining pressure chambers in the entire multi-section continuous high-pressure reaction pressing module, and their number and position are completely corresponding to the embedded confining pressure injection / feedback probe.

[0018] Preferably, the above-mentioned steel cylinder set consists of four 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 1600mm, 1200mm, 800mm and 400mm respectively, a diameter of 200mm, and a pressure resistance range of 0 to 40MPa. They are respectively used as extensions of the axial head steel pressure cylinder seat during the five-step core pressing process 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 transmit axial pressure to the core pressing material.

[0019] 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, which includes the following process:

[0020] First, a core with non-uniform porosity distribution is prepared by an integrated pressing method in a multi-stage continuous high-pressure reaction holding module, which mainly includes the following steps:

[0021] a1. Check and confirm that all high-pressure ball valves and ball valves of the injection and recovery systems are fully closed. Check and confirm that the right end of the multi-stage continuous high-pressure reaction holding module is completely sealed by the axial tail sealing submodule. Remove the axial head pressure submodule and pull the tail end of the pluggable steel temperature probe in the second to fifth single-body holding devices to the inner wall of the pressure application / feedback sleeve at the lower end of the core filling space to ensure the sealing of the core filling space in the second to fifth single-body holding devices. Insert the first steel cylinder into the left boundary of the core filling space of the first single-body holding device. Simultaneously, open the through-type switchable cylindrical window at the top of the first single-body holding device and pour the first ratio of quartz sand mortar and clay mixture through the top window, where the mass ratio of quartz sand to clay is 5:5 and the water-binder ratio is 0.5. Then close the top window and let the mixture stand for a while.

[0022] a2. Open the through-type switchable cylindrical window at the top of the second single-body holding device, quickly pull the first steel cylinder to the left boundary of the core filling space of the second single-body holding device, and simultaneously quickly pour the second ratio of quartz sand mortar and clay mixture through the top window, wherein the mass ratio of quartz sand to clay is 5:5 and the water-binder ratio is 0.9. Insert the pluggable steel temperature probe of the second single-body holding device to the initial position, then close the top window and let the mixture stand for a while;

[0023] a3. Open the through-type switchable cylindrical window at the top of the third unit holding device, quickly pull the first steel cylinder to the left boundary of the core filling space of the third unit holding device, and simultaneously quickly pour the third ratio of quartz sand mortar and clay mixture through the top window, where the quartz sand and clay mass ratio is 6:4 and the water-binder ratio is 1. Insert the pluggable steel temperature probe of the third unit holding device to the initial position, then close the top window and let the mixture stand for a while.

[0024] a4. Open the through-type switchable cylindrical window at the top of the fourth single-body holding device, quickly pull the first steel cylinder to the left boundary of the core filling space of the fourth single-body holding device, and simultaneously quickly pour the fourth ratio of quartz sand mortar and clay mixture through the top window, wherein the mass ratio of quartz sand to clay is 7:3 and the water-binder ratio is 1.1. Insert the pluggable steel temperature probe of the fourth single-body holding device to the initial position, then close the top window and let the mixture stand for a while;

[0025] a5. Open the through-type switchable cylindrical window at the top of the fifth single-body holding device, quickly pull the first steel cylinder to the left boundary of the core filling space of the fifth single-body holding device, and simultaneously quickly pour the fifth ratio of quartz sand mortar and clay mixture through the top window, where the mass ratio of quartz sand to clay is 8:2 and the water-binder ratio is 1.2. Insert the pluggable steel temperature probe of the fifth single-body holding device to the initial position, close the top window, and let the mixture stand for a while. The first steel cylinder was then quickly withdrawn, and the axial head pressure submodule was quickly assembled and sealed to the left end of the multi-stage continuous high-pressure reaction holding module. A pressure of 10 MPa was simultaneously applied to the axial pressure chamber and the segmented confining pressure chamber. The mixed material in the core-filled space of the five-stage single-stage holding device was continuously pressed for 8 hours. This resulted in the formation of a single-piece long horizontal cylindrical core with five sections of significantly different porosities within the multi-stage continuous high-pressure reaction holding module. The non-uniformly distributed porosity within the core decreased segment by segment from left to right.

[0026] Secondly, the generation of hydrates in a continuous, integrated long core with multiple sections of significantly different porosities involves the following steps:

[0027] b1. Unload the pressure in the axial pressure chamber and the segmented confining pressure chamber to 0 MPa, use a vacuum pump to fill the core into the space, and pump the pressure in the transfer cylinder to -0.1 MPa during the injection process;

[0028] b2. Close all ball valves on the injection line side of the gas-liquid flow T-junction. Use a high-purity methane high-pressure cylinder and a gas booster to ensure that the methane gas pressure in the cylinder reaches 10 MPa during the injection process. Then, use the pressure difference between the cylinder and the core filling space to inject methane into the core. Stop methane injection when the pressure in the segmented confining pressure chamber reaches 8 MPa.

[0029] b3. Close all ball valves on the gas-liquid T-type three-way gas injection line, and use a liquid injection pump to inject pure water into the core filling space. When the pressure in the segmented confining pressure chamber reaches 10 MPa, stop injecting pure water and close all ball valves on the gas-liquid T-type three-way liquid injection line;

[0030] b4. Allow the core to stand for 1 hour to ensure that the pure water in the core is saturated with methane. Repeat step b2 and inject a small amount of methane into the core again to stabilize the pressure in the segmented confining pressure chamber at 10 MPa. Then close all ball valves on the T-shaped three-way injection line for gas-liquid flow.

[0031] b5. Start the refrigerated water bath circulator and set the target water bath temperature to 1°C. Allow the coolant to cool continuously and circulate within the water bath annulus within the steel double-layer cooling cylinder. Monitor the temperature of the temperature monitoring points on the removable steel temperature probe within the core filling space in real time. A sudden increase in temperature indicates the formation of hydrates in that core sub-region.

[0032] b6. When the temperatures at all temperature monitoring points have shown an upward trend, continue to maintain the water bath target temperature of 1°C and circulate the coolant for 30 minutes to ensure that the hydrate formation in the long, one-piece core with multiple sections of significantly different porosities is annealed and enters a stable state;

[0033] Finally, the decomposition of hydrates in a continuous, integrated long core with multiple sections of significantly different porosities, i.e., the simulation of hydrate depressurization production, includes the following steps:

[0034] c1. Check and ensure that all ball valves in the gas-liquid recovery system are closed. Then, open the ball valve between the gas-liquid discharge pipeline and the primary gas-liquid separation tank. As the pressure in the core decreases, the hydrate gradually decomposes into methane gas and water. The hydrate migrates through the unevenly distributed pores in the long, integrated core toward one end of the gas-liquid discharge pipeline, passes through the outlet pressure control valve, and flows into the primary gas-liquid separation tank. The data acquisition system records in real time the temperature and pressure changes in the core sub-areas that can be monitored in the multi-stage continuous high-pressure reaction and holding module. The areas where pressure rebound occurs in the core during hydrate decomposition and the pattern of pressure rebound changes are monitored.

[0035] c2. When the pressure in the primary gas-liquid separation tank reaches a stable level, open the ball valve between the primary gas-liquid separation tank and the secondary gas-liquid separation tank;

[0036] c3. When the pressure in the secondary gas-liquid separator reaches a stable level, all ball valves at the rear ends of the primary and secondary gas-liquid separators are opened in sequence. The methane gas flows into the gas recovery cylinder through the gas drying device, gas mass flow controller and accumulator, and methane concentration sensor.

[0037] c4. When the pressure in the gas recovery cylinder stabilizes, inject carbon dioxide gas into the core filling space through the gas-liquid injection system, so that the remaining methane gas in the core and the two gas-liquid separation tanks all flow into the gas recovery cylinder; when the methane concentration sensor detects that the methane concentration is 0, close the ball valve at the front end of the gas recovery cylinder, close the ball valve at the rear end of the high-purity carbon dioxide high-pressure cylinder, open the discharge valves at the lower ends of the first-level gas-liquid separation tank and the second-level gas-liquid separation tank, discharge the carbon dioxide gas to the outside, and discharge the water into the liquid recovery container.

[0038] Preferably, the present invention adopts a five-stage method to prepare five sections of cores with different porosities connected end to end, and the experimental method includes the following process:

[0039] First, a core with non-uniform porosity distribution was prepared by five-stage pressing in a multi-stage continuous high-pressure reaction holding module. This pressing method achieves non-uniform porosity distribution within a large core section by precisely controlling the ratio of mixed materials and the pressing time of the small core sections. It is suitable for experiments requiring large porosity differences and mainly includes the following steps:

[0040] S1. Check and confirm that all high-pressure ball valves and ball valves of the injection and recovery systems are closed, check and confirm that the right end of the multi-stage continuous high-pressure reaction pressure holding module is completely sealed by the axial tail sealing submodule; remove the axial head pressure submodule, pull the tail end of the pluggable steel temperature probe from the second to the fifth monomer pressure holding device 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 pressure holding device, and put the axial head pressure submodule in the multi-stage continuous The left end of the high-pressure reaction holding module was quickly assembled and sealed. The through-type switchable cylindrical window at the top of the first single holding device was opened, and a fixed ratio of quartz sand mortar and clay was poured through the top window. The mass ratio of quartz sand to clay was 8:2, and the water-binder ratio was 1.2. The top window was then closed, and the removable steel temperature probe of the first single holding device was inserted into the initial position. A pressure of 10 MPa was simultaneously applied to the axial pressure chamber and the segmented confining pressure chamber. The mixed material in the core filling space of the first single holding device was continuously pressed for 1 hour.

[0041] S2. Unload the pressure in the axial pressure chamber and the segmented confining pressure chamber to 0 MPa, remove the axial head pressure submodule, extract the first steel cylinder and insert the second steel cylinder into the left boundary of the core filling space of the second single pressing device, and quickly assemble and seal the axial head pressure submodule; open the through-type switchable cylindrical window at the top of the second single pressing device, and pour the quartz mortar and clay mixture in the same proportion as in step S1 through the top window; then close the top window, insert the removable steel temperature probe of the second single pressing device into the initial position, apply a pressure of 10 MPa to the axial pressure chamber and the segmented confining pressure chamber at the same time, and press the mixed material in the second single pressing device and the formed core in the first single pressing device for 1 hour;

[0042] S3, unloading the pressure in the axial pressure chamber and the segmented confining pressure chamber to 0 MPa, removing the axial head pressure submodule, extracting the second steel cylinder and inserting the third steel cylinder into the left boundary of the core filling space of the third single-body pressing device, quickly assembling and sealing the axial head pressure submodule; opening the through-type switchable cylindrical window at the top of the third single-body pressing device, and pouring the quartz mortar and clay mixture in the same proportion as in step S1 through the top window; then closing the top window, inserting the removable steel temperature probe of the third single-body pressing device to the initial position, applying a pressure of 10 MPa to the axial pressure chamber and the segmented confining pressure chamber at the same time, and pressing the mixed material in the third single-body pressing device and the formed cores in the first single-body pressing device and the second single-body pressing device for 1 hour;

[0043] S4, unloading the pressure in the axial pressure chamber and the segmented confining pressure chamber to 0 MPa, removing the axial head pressure submodule, extracting the third steel cylinder and inserting the fourth steel cylinder into the left boundary of the core filling space of the fourth single pressing device, quickly assembling and sealing the axial head pressure submodule; opening the through-type switchable cylindrical window at the top of the fourth single pressing device, pouring the quartz mortar and clay mixture in the same proportion as in step S1 through the top window; then closing the top window, inserting the removable steel temperature probe of the fourth single pressing device into the initial position, applying a pressure of 10 MPa to the axial pressure chamber and the segmented confining pressure chamber at the same time, and simultaneously pressing the mixed material in the fourth single pressing device and the formed cores in the first, second and third single pressing devices for 1 hour;

[0044] S5, unload the pressure in the axial pressure chamber and the segmented confining pressure chamber to 0MPa, remove the axial head pressure submodule, pull out the fourth steel cylinder, quickly assemble and seal the axial head pressure submodule; open the through-type switchable cylindrical window at the top of the fifth single pressing device, and pour the quartz mortar and clay mixed material with the same proportion as in step S1 through the top window; then close the top window, insert the pluggable steel temperature probe of the fifth single pressing device to the initial position, apply a pressure of 10MPa to the axial pressure chamber and the segmented confining pressure chamber at the same time, and press the fifth single The mixed material in the single pressing device and the formed cores in the first, second, third and fourth single pressing devices are pressed for 4 hours; after the pressing is completed, an integrated long horizontal cylindrical core with 5 sections of significantly different porosities is formed in the multi-stage continuous high-pressure reaction pressing module. The ratio of the mixed materials used to press each small section of the core is exactly the same, but the pressing time of the 5 small sections of the core are 4, 5, 6, 7 and 8 hours from left to right, respectively. Therefore, the non-uniformly distributed porosity in the integrated long horizontal cylindrical core decreases step by step from left to right.

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0046] (1) The present invention provides a top window module, which is composed of a through-type switchable cylindrical window and a switch control valve stem at the top of the single pressing device. In the process of pressing a large section of core with uneven porosity distribution, it provides conditions for injecting mixed materials with different proportions into the single pressing device at different positions;

[0047] (2) The present invention sets up a multi-section continuous high-pressure reaction holding module composed of five sections of single-body holding devices connected end to end. A removable steel temperature probe is set at the bottom of each section of the single-body holding device. Combined with the top window module, the steel cylinder set and the experimental method provided by the present invention, a long horizontal cylindrical rock core with a high degree of integration, continuity and significant porosity difference in multiple sections can be prepared by two methods of one-piece pressing and five-stage pressing. In addition, the free combination of small sections of rock cores with different porosities can be controlled, which provides conditions for the long-distance continuous migration of fluids after hydrate decomposition in porous media with non-uniform porosity distribution and complex and variable porosity, and can realize effective simulation of reservoir pressure rebound phenomenon during hydrate extraction;

[0048] (3) The present invention innovatively sets up 12 segmented confining pressure chambers, 12 embedded confining pressure injection / feedback probes, and 6 removable steel temperature probes in each section of the single-body holding device. The temperature and pressure of the entire core in the multi-section continuous high-pressure reaction holding module in a total of 60 fan-shaped columnar sub-areas in the axial and tangential dimensions can be independently monitored, which can achieve precise monitoring of the specific location of the pressure rebound phenomenon and the pressure fluctuation changes in the integrated long horizontal cylindrical core with significantly different porosities in multiple sections. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a schematic diagram of the overall system of the present invention;

[0050] Figure 2 This is a front structural diagram of the multi-stage continuous high-pressure reaction holding module mentioned in the present invention;

[0051] Figure 3 It is a structural diagram of the steel cylinder set mentioned in the present invention;

[0052] Figure 4 It is a structural schematic diagram of the steel double-layer cooling cylinder of the present invention;

[0053] Figure 5 This is a schematic diagram of the exploded structure of the axial head pressure submodule, the 5-stage single-body pressing device, and the axial tail sealing submodule installed in the steel double-layer cooling cylinder;

[0054] Figure 6 It is a cross-sectional schematic diagram of a multi-stage continuous high-pressure reaction holding module of the present invention;

[0055] Figure 7 It is a schematic diagram of the curve of the core pore pressure rebound phenomenon occurring in the multi-stage continuous high-pressure reaction holding module during the experimental process of simulating hydrate depressurization mining of the present invention;

[0056] In the figure above: 1-Multi-stage continuous high-pressure reaction holding module, 2-Steel double-layer cooling cylinder, 3-Axial head pressure submodule, 4-Axial tail sealing submodule, 5-Cooling cylinder outer wall, 6-Cooling cylinder inner wall, 7-Water bath annulus, 8-Cooling liquid inlet, 9-Cooling liquid outlet, 10-Axial head steel sealing cylinder seat, 11-Axial head steel pressure 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 fixed 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 single-unit pressing and holding device, 28-fourth single-unit pressing and holding device, 29-third single-unit pressing and holding device, 30-second single-unit pressing and holding device, 31-first single-unit pressing and holding device, 32-first cylindrical steel body sleeve axial small section, 33-second cylindrical steel body sleeve axial small section, 34-third cylindrical steel body sleeve axial small section;

[0057] 43-through-type switchable cylindrical window, 44-valve stem top wrench, 45-switch control valve stem, 46-pluggable steel temperature probe, 47-temperature gauge, 48-probe pressure gauge, 49-high-pressure ball valve, 50-confining pressure injection device, 51-confining pressure annulus separation steel plate, 52-embedded ball valve, 53-first steel temperature probe monitoring point, 54-second steel temperature probe monitoring point, 55-data transmission line, 56-refrigeration water bath circulation machine, 57-coolant input pipeline, 58-coolant discharge pipeline, 59-gas-liquid injection system internal pressure gauge, 60-gas-liquid recovery system internal pressure gauge, 61-electronic scale, 62-data acquisition module, 63-computer, 64-high-purity methane high-pressure gas Bottle, 65-high-purity carbon dioxide high-pressure gas cylinder, 66-pressure reducing valve, 67-gas booster, 68-injection process transfer cylinder, 69-process control valve, 70-liquid container, 71-liquid injection pump, 72-gas-liquid flow T-type tee, 73-vacuum pump, 74-ball 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. DETAILED DESCRIPTION

[0058] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0059] Example 1, with reference to Figure 1-Figure 7 The present invention relates to a reservoir pressure rebound simulation device for marine hydrate production, the technical solution of which is as follows: comprising a low-temperature control module, a data acquisition module, a multi-stage continuous high-pressure reaction pressure holding module 1, a top window module, a gas-liquid injection system, a gas-liquid recovery system, and a steel cylinder set, wherein the steel cylinder set is made of multiple solid stainless steel cylinders;

[0060] The exterior of the multi-stage continuous high-pressure reaction holding module 1 is composed of a steel double-layer cooling cylinder 2, an axial head pressure submodule 3, and an axial tail sealing submodule 4; the interior of the multi-stage continuous high-pressure reaction holding module 1 is composed of multiple sections of monomer holding 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 of the cooling cylinder and the inner wall 6 of the cooling cylinder for circulating coolant; a coolant inlet 8 is embedded on the upper side of the cooling cylinder in the axial head direction, and a coolant outlet 9 is embedded on the lower side of the cooling cylinder in the axial tail direction. More than one set of monomer holding devices is installed in the inner cavity of the steel double-layer cooling cylinder 2, and the axial head pressure submodule 3 is installed at one end of the steel double-layer cooling cylinder 2 through a sealing bolt 18, and the axial tail sealing submodule 4 is installed at the other end through a sealing bolt 18;

[0061] 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 from the inside to the outside in the pressure application / feedback leather sleeve 25, the segmented confining pressure chamber 24, the cylindrical steel body sleeve 22 and the steel double-layer cooling cylinder 2. A set of embedded ball valves 52 are installed at the bottom of the inner side of the through-type switchable cylindrical window 43. The switch control valve stem 45 is connected to the embedded ball valve 52. The top of the switch control valve stem 45 is installed with a valve stem top wrench 44 for controlling the opening and closing of the embedded ball valve 52.

[0062] 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, a gas cylinder 68 for rotating during injection, a liquid container 70, a liquid injection pump 71, a gas-liquid flow T-type 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 gas cylinder 68 for rotating during injection through a pipeline and the gas booster 67, and then fed into the gas-liquid injection pipeline 17 of the axial head pressure submodule 3 through a pipeline and a gas-liquid flow T-type tee 72; the liquid container 70 is connected to the gas-liquid flow T-type tee 72 through a pipeline and a liquid injection pump 71;

[0063] 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 injection process transfer cylinder 68 by the gas booster 67. Subsequently, under the action of the pressure differential, the gas is injected into the core through the process control valve 69, the gas-liquid flow T-type tee 72, and the gas-liquid injection pipeline 17. During the injection process, the transfer cylinder 68 is used to control the pressure and composition of the injected gas. The pumping pressure of the gas booster 67 is adjustable from 0 to 20 MPa, and the flow rate 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 injected into the core through the liquid injection pump 71, the gas-liquid flow T-type tee 72, and the gas-liquid injection pipeline 17. The operating 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 before the experiment begins and in the transfer cylinder 68 during the injection process. The operating pressure is -0.2 to 0.5 MPa.

[0064] 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 cylinder 81, and a liquid recovery container 82. The outer end of the gas-liquid discharge pipeline 21 of the axial tail sealing submodule 4 is connected to the primary gas-liquid separation tank 76 through the outlet pressure control valve 75, and 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 net 84. The top of the primary gas-liquid separation tank 76 is connected to the gas recovery 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.

[0065] Reference Figure 2 and Figure 5 The axial head pressure submodule 3 mentioned in the present invention is composed of an axial head steel sealing cylinder seat 10 and an axial head steel pressure cylinder seat 11. The annular space between the two is an axial pressure cavity 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, which is used to apply pressure to the axial pressure cavity 12; the axial head steel pressure cylinder seat 11 is embedded with a gas-liquid injection pipeline 17, which is used to inject gas and liquid into the core.

[0066] The above-mentioned axial tail sealing submodule 4 consists 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 decomposition of hydrates in the core.

[0067] The above-mentioned single-body holding device is composed of a cylindrical steel body sleeve 22, an embedded confining pressure injection / feedback probe 23, a segmented confining pressure cavity 24, a pressure application / feedback leather sleeve 25 and a core filling space 26 from the outside to the inside.

[0068] The embedded confining pressure injection / feedback probes 23 are 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 to an independent probe pressure gauge 48 and an independent high-pressure ball valve 49. The embedded confining pressure injection / feedback probes 23 are divided into two groups, the upper half and the lower half, which are connected in parallel to two confining pressure injection devices 50 through stainless steel ventilation lines 15.

[0069] The pressure applying / feedback 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 mixed materials required for core pressing or finished pressed cores.

[0070] Reference Figure 5 and Figure 6 The single-body pressing device mentioned in the present invention is provided with five sections. The segmented confining pressure chamber 24 of each single-body pressing device is evenly divided into three small sections in the axial direction, namely: the first cylindrical steel body sleeve axial small section 32, the second cylindrical steel body sleeve axial small section 33, and the third cylindrical steel body sleeve axial small section 34. Each small confining pressure chamber is evenly divided into four sections on the tangential section with the radius at the circumferential positions of 45°, 135°, 225° and 315° as the center line. Each confining pressure chamber is separated by a confining pressure annulus partition steel plate 51; there are a total of 12 segmented confining pressure chambers in each single-body pressing device, and a total of 60 segmented confining pressure chambers 24 in the entire multi-stage continuous high-pressure reaction pressing module 1, and their number and position are completely corresponding to the embedded confining pressure injection / feedback probe 23.

[0071] Six pluggable steel temperature probes 46 are embedded in the bottom of each cylindrical steel body sleeve 22. The head of each pluggable steel temperature probe 46 is connected to an independent temperature meter 47. At the same time, each pluggable steel temperature probe 46 is provided with two temperature monitoring points, specifically a first steel temperature probe monitoring point 53 and a second steel temperature probe monitoring point 54, which are used to monitor the temperature inside different sub-areas of the core.

[0072] Reference Figure 3The steel cylinder set mentioned in the present invention is composed of four 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, and a diameter of 200 mm. The pressure range is 0 to 40 MPa, and they are used as extensions of the axial head steel pressure cylinder seat 11 during the five-step core pressing process 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, respectively, to transmit axial pressure to the core pressing material.

[0073] In addition, the low-temperature control module mentioned in the present invention is composed of a refrigerated water bath circulation machine 56, a coolant input pipeline 57, and a coolant discharge pipeline 58. The refrigerated water bath circulation machine 56 can cool the antifreeze coolant inside it, and successively pump the coolant into the water bath annulus 7 in the steel double-layer cooling cylinder 2 through the coolant input pipeline 57 and the coolant input port 8. The coolant flows toward the coolant discharge port 9 inside the annulus under the influence of its own gravity and the pumping power of the refrigerated water bath circulation machine, and flows back to the refrigerated water bath circulation machine 56 through the coolant discharge pipeline 58. The temperature control range of the refrigerated water bath circulation machine 56 is -20°C to 50°C.

[0074] The data acquisition module mentioned in the present invention consists of four pressure gauges 59 within the gas-liquid injection system, 60 probe pressure gauges 48 for the embedded confining pressure injection / feedback probes 23, five pressure gauges 60 within the gas-liquid recovery system, temperature gauges 47 for 30 removable steel temperature probes 46, three electronic scales 61, data transmission lines 55, a data acquisition module 62, and a computer 63. All pressure gauges and temperature gauges are connected to the data acquisition module 62 via the data transmission lines 55. The computer 63 records and stores the temperature and pressure data monitored in real time by the acquisition module, with the data recording interval ranging from 1 to 10 seconds.

[0075] In addition, refer to Figure 7 , which is a curve diagram of the core pore pressure rebound phenomenon that occurs in the multi-stage continuous high-pressure reaction holding module during the experimental process of simulating hydrate depressurization extraction in the present invention. It can be used to obtain the local pore pressure rebound phenomenon of the core of the fourth and fifth single-unit holding devices; and further, research on methods for preventing and controlling reservoir pressure rebound can be carried out.

[0076] In addition, the experimental method of the reservoir pressure rebound simulation device in offshore hydrate exploitation mentioned in the present invention is mainly divided into three experimental stages: core preparation stage, hydrate generation stage and hydrate decomposition stage. In the core preparation stage, five sections of cores with different porosities connected end to end are prepared by one-piece pressing or five-stage pressing methods, and then hydrate generation and decomposition experiments are carried out, thereby realizing the simulation and prevention of the pore pressure rebound phenomenon in the reservoir with non-uniform porosity distribution during hydrate exploitation. Experimental research.

[0077] The present invention adopts an integrated pressing method to prepare five sections of cores with different porosities connected end to end, and the experimental method includes the following process:

[0078] First, a core with non-uniform porosity distribution is prepared by an integrated pressing method in a multi-stage continuous high-pressure reaction holding module 1, which mainly includes the following steps:

[0079] a1. 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 sealing submodule 4. Remove the axial head pressure submodule 3. Pull the tail end of the pluggable steel temperature probe 46 in the second single-unit holding device 30 to the fifth single-unit holding 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 that the second single-unit holding device 30 To ensure the sealing of the core filling space 26 in the fifth single pressing device 27; insert the first steel cylinder 85 into the left boundary of the core filling space 26 of the first single pressing device 31, and at the same time open the through-type switchable cylindrical window 43 at the top of the first single pressing device 31, and pour the first ratio of quartz sand mortar and clay mixture through the top window, wherein the mass ratio of quartz sand to clay is 5:5 and the water-binder ratio is 0.5; then close the top window and let the mixture stand for a period of time;

[0080] a2. Open the through-type switchable cylindrical window 43 at the top of the second single-body holding device 30, quickly pull the first steel cylinder 85 to the left boundary of the core filling space 26 of the second single-body holding device 30, and simultaneously quickly pour the second ratio of quartz sand mortar and clay mixture through the top window, wherein the mass ratio of quartz sand to clay is 5:5 and the water-binder ratio is 0.9. Insert the pluggable steel temperature probe 46 of the second single-body holding device 30 to the initial position, then close the top window, and let the mixture stand for a while;

[0081] a3. Open the through-type switchable cylindrical window 43 at the top of the third single-body holding device 29, quickly pull the first steel cylinder 85 to the left boundary of the core filling space 26 of the third single-body holding device 29, and simultaneously quickly pour the third ratio of quartz sand mortar and clay mixture through the top window, wherein the mass ratio of quartz sand to clay is 6:4 and the water-binder ratio is 1. Insert the pluggable steel temperature probe 46 of the third single-body holding device 29 to the initial position, then close the top window and let the mixture stand for a while;

[0082] a4. Open the through-type switchable cylindrical window 43 at the top of the fourth single-body holding device 28, quickly pull the first steel cylinder 85 to the left boundary of the core filling space 26 of the fourth single-body holding device 28, and simultaneously quickly pour the fourth ratio of quartz sand mortar and clay mixture through the top window, wherein the mass ratio of quartz sand to clay is 7:3 and the water-binder ratio is 1.1. Insert the pluggable steel temperature probe 46 of the fourth single-body holding device 28 to the initial position, then close the top window and let the mixture stand for a while;

[0083] a5. Open the through-type switchable cylindrical window 43 at the top of the fifth single-body holding device 27, quickly pull the first steel cylinder 85 to the left boundary of the core filling space 26 of the fifth single-body holding device 27, and simultaneously quickly pour the fifth ratio of quartz sand mortar and clay mixture through the top window, wherein the mass ratio of quartz sand to clay is 8:2 and the water-binder ratio is 1.2. Insert the pluggable steel temperature probe 46 of the fifth single-body holding device 27 to the initial position, close the top window, and let the mixture stand for a while. Then, the first steel cylinder 85 was quickly withdrawn, and the axial head pressure submodule 3 was quickly assembled and sealed on the left end of the multi-stage continuous high-pressure reaction holding module 1. A pressure of 10 MPa was simultaneously applied to the axial pressure chamber 12 and the segmented confining pressure chamber 24. The mixed material in the core-filling space 26 of the five-stage single-unit holding device was continuously pressed for 8 hours, so that a single-piece long horizontal cylindrical core with five sections of significantly different porosities was formed in the multi-stage continuous high-pressure reaction holding module 1. The non-uniformly distributed porosity in the core decreased step by step from left to right.

[0084] Secondly, the generation of hydrates in a continuous, integrated long core with multiple sections of significantly different porosities involves the following steps:

[0085] b1. Unload 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 fill the core into the space 26 and reduce the pressure in the transfer cylinder 68 to -0.1 MPa during the injection process;

[0086] b2. Close all ball valves 74 on the liquid injection line side of the gas-liquid flow T-joint 72. Utilize the high-purity methane high-pressure cylinder 64 and the gas booster 67 to raise the methane gas pressure in the transfer cylinder 68 to 10 MPa during the injection process. Then, utilize the pressure difference between the transfer cylinder 68 and the core filling space 26 during the injection process to inject methane into the core. Stop methane injection when the pressure in the segmented confining pressure chamber 24 reaches 8 MPa.

[0087] b3. Close all ball valves 74 on the gas injection line side of the gas-liquid flow T-shaped tee 72, and use the liquid injection pump 71 to inject pure water into the core filling space 26. When the pressure in the segmented confining pressure chamber 24 reaches 10 MPa, stop injecting pure water and close all ball valves 74 on the liquid injection line side of the gas-liquid flow T-shaped tee 72;

[0088] b4. Allow the core to stand for 1 hour to ensure that the pure water in the core is saturated with methane. Repeat step b2 and inject a small amount of methane into the core again to stabilize the pressure in the segmented confining pressure chamber 24 at 10 MPa. Then close all ball valves 74 on the injection line of the gas-liquid flow T-type tee 72.

[0089] b5. Turn on the refrigerated water bath circulator 56 and set the target water bath temperature to 1° C., allowing the coolant to cool continuously and circulate in the water bath annulus 7 within the steel double-layer cooling cylinder 2; monitor the temperature of the temperature monitoring points on the removable steel temperature probe 46 within the core filling space 26 in real time. A sudden increase in temperature indicates the formation of hydrates in that core sub-region;

[0090] b6. When the temperatures at all temperature monitoring points have shown an upward trend, continue to maintain the water bath target temperature of 1°C and circulate the coolant for 30 minutes to ensure that the hydrate formation in the long, one-piece core with multiple sections of significantly different porosities is annealed and enters a stable state;

[0091] Finally, the decomposition of hydrates in a continuous, integrated long core with multiple sections of significantly different porosities, i.e., the simulation of hydrate depressurization production, includes the following steps:

[0092] c1. Check and ensure that all ball valves 74 of the gas-liquid recovery system are closed. Then, open the ball valve 74 between the gas-liquid discharge pipeline 21 and the primary gas-liquid separation tank 76. As the pressure in the core decreases, the hydrate gradually decomposes into methane gas and water. The hydrate migrates through the unevenly distributed pores in the integrated long core toward one end of the gas-liquid discharge pipeline 21, passes through the outlet pressure control valve 75, and flows into the primary gas-liquid separation tank 76. The data acquisition system records in real time the temperature and pressure changes in the core sub-areas that can be monitored in the multi-stage continuous high-pressure reaction holding module 1, and monitors the areas in the core where pressure rebound occurs and the changing patterns of the pressure rebound during hydrate decomposition.

[0093] c2. When the pressure in the primary gas-liquid separation tank 76 reaches a stable level, open the ball valve 74 between the primary gas-liquid separation tank 76 and the secondary gas-liquid separation tank 77;

[0094] c3. When the pressure in the secondary gas-liquid separator 77 reaches a stable level, all ball valves 74 at the rear ends of the primary gas-liquid separator 76 and the secondary gas-liquid separator 77 are opened in sequence. The methane gas flows into the gas recovery cylinder 81 through the gas drying device 78, the gas mass flow controller and accumulator 79, and the methane concentration sensor 80.

[0095] c4. After the pressure in the gas recovery cylinder 81 stabilizes, carbon dioxide gas is injected 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 cylinder 81; when the methane concentration sensor 80 detects that the methane concentration is 0, the ball valve 74 at the front end of the gas recovery cylinder 81 is closed, the ball valve 74 at the rear end of the high-purity carbon dioxide high-pressure cylinder 65 is closed, and the discharge valves at the lower ends of the first gas-liquid separation tank 76 and the second gas-liquid separation tank 77 are opened to discharge the carbon dioxide gas to the outside and the water to the liquid recovery container 82.

[0096] Example 2, the experimental method of the reservoir pressure rebound simulation device in marine hydrate production mentioned in the present invention is different from that of Example 1 in that:

[0097] This embodiment adopts a five-stage method to prepare five sections of core with different porosities connected end to end, and the experimental method includes the following process:

[0098] First, a core with non-uniform porosity distribution was prepared by five segmented pressing steps in a multi-stage continuous high-pressure reaction holding module 1. This pressing method achieves non-uniform porosity distribution within a large core segment by precisely controlling the ratio of mixed materials used to press the small core segments and the pressing time of the small core segments. It is suitable for experiments requiring large porosity differences and mainly includes the following steps:

[0099] 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 sealing submodule 4. Remove the axial head pressure submodule 3. Pull the tail end of the pluggable steel temperature probe 46 in the second monomer holding device 30 to the fifth monomer holding device 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. The left end of the continuous high-pressure reaction holding module 1 is quickly assembled and sealed; the through-type switchable cylindrical window 43 at the top of the first single-body holding device 31 is opened, and a fixed ratio of quartz sand mortar and clay mixed material is poured through the top window, wherein the mass ratio of quartz sand to clay is 8:2 and the water-binder ratio is 1.2; then the top window is closed, and the pluggable steel temperature probe 46 of the first single-body holding device 31 is inserted into the initial position. A pressure of 10 MPa is simultaneously applied to the axial pressure chamber 12 and the segmented confining pressure chamber 24, and the mixed material in the core filling space 26 of the first single-body holding device 31 is continuously pressed for 1 hour;

[0100] S2, unloading the pressure in the axial pressure chamber 12 and the segmented confining pressure chamber 24 to 0 MPa, removing the axial head pressure submodule 3, extracting the first steel cylinder 85 and inserting the second steel cylinder 86 into the left boundary of the core filling space 26 of the second single pressing device 30, quickly assembling and sealing the axial head pressure submodule 3; opening the through-type switchable cylindrical window 43 at the top of the second single pressing device 30, and pouring the quartz mortar and clay mixed material with the same proportion as in step S1 through the top window; then closing the top window, inserting the removable steel temperature probe 46 of the second single pressing device 30 to the initial position, applying a pressure of 10 MPa to the axial pressure chamber 12 and the segmented confining pressure chamber 24 at the same time, and pressing the mixed material in the second single pressing device 30 and the formed core in the first single pressing device 31 for 1 hour;

[0101] S3, unloading the pressure in the axial pressure chamber 12 and the segmented confining pressure chamber 24 to 0 MPa, removing the axial head pressure submodule 3, extracting the second steel cylinder 86 and inserting the third steel cylinder 87 into the left boundary of the core filling space 26 of the third single pressing device 29, quickly assembling and sealing the axial head pressure submodule 3; opening the through-type switchable cylindrical window 43 at the top of the third single pressing device 29, and pouring the quartz mortar and clay mixed material with the same proportion as in step S1 through the top window; then closing the top window, inserting the removable steel temperature probe 46 of the third single pressing device 29 to the initial position, applying a pressure of 10 MPa to the axial pressure chamber 12 and the segmented confining pressure chamber 24 at the same time, and pressing the mixed material in the third single pressing device 29 and the formed core in the first single pressing device 31 and the second single pressing device 30 for 1 hour;

[0102] S4, unloading the pressure in the axial pressure chamber 12 and the segmented confining pressure chamber 24 to 0 MPa, removing the axial head pressure submodule 3, extracting the third steel cylinder 87 and inserting the fourth steel cylinder 88 into the left boundary of the core filling space 26 of the fourth single pressing device 28, quickly assembling and sealing the axial head pressure submodule 3; opening the through-type switchable cylindrical window 43 at the top of the fourth single pressing device 28, and pouring the quartz mortar and clay mixed material with the same proportion as in step S1 through the top window; then closing the top window, inserting the removable steel temperature probe 46 of the fourth single pressing device 28 to the initial position, applying a pressure of 10 MPa to the axial pressure chamber 12 and the segmented confining pressure chamber 24 at the same time, and pressing the mixed material in the fourth single pressing device 28 and the formed cores in the first single pressing device 31, the second single pressing device 30 and the third single pressing device 29 for 1 hour;

[0103] S5, unload the pressure in the axial pressure chamber 12 and the segmented confining pressure chamber 24 to 0 MPa, remove the axial head pressure submodule 3, pull out the fourth steel cylinder 88, quickly assemble and seal the axial head pressure submodule 3; open the through-type switchable cylindrical window 43 at the top of the fifth single-body pressing device 27, and pour the quartz mortar and clay mixed material with the same proportion 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, and apply a pressure of 10 MPa to the axial pressure chamber 12 and the segmented confining pressure chamber 24 at the same time, and press The mixed material in the fifth single pressing device 27 and the formed cores 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 are pressed for 4 hours; after the pressing is completed, an integrated long horizontal cylindrical core with 5 sections of significantly different porosities is formed in the multi-stage continuous high-pressure reaction pressing module 1. The ratio of the mixed materials used to press each small section of the core is exactly the same, but the pressing time of the 5 small sections of the core is 4, 5, 6, 7 and 8 hours from left to right, respectively. Therefore, the non-uniformly distributed porosity in the integrated long horizontal cylindrical core decreases step by step from left to right.

[0104] The above descriptions are merely some preferred embodiments of the present invention. Anyone skilled in the art may be able to modify the above-described technical solutions or convert them into equivalent technical solutions. Therefore, any corresponding simple modifications or equivalent transformations based on the technical solutions of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A reservoir pressure rebound simulation device for marine hydrate production, comprising a low-temperature control module and a data acquisition module, characterized by: 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, wherein the steel cylinder set is made of a plurality of solid cylinders made of stainless steel; The multi-stage continuous high-pressure reaction holding module (1) is externally composed of a steel double-layer cooling cylinder (2), an axial head pressure submodule (3), and an axial tail sealing submodule (4); the multi-stage continuous high-pressure reaction holding module (1) is internally composed of a multi-stage monomer holding device 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) of the cooling cylinder and the inner wall (6) of the cooling cylinder for circulating the cooling liquid; a cooling liquid inlet (8) is embedded above the cooling cylinder side in the axial head direction, and a cooling liquid outlet (9) is embedded below the cooling cylinder side in the axial tail direction; the inner cavity of the steel double-layer cooling cylinder (2) is installed with one or more monomer holding devices, the axial head pressure submodule (3) is installed at one end of the steel double-layer cooling cylinder (2), and the axial tail sealing submodule (4) is installed at the other end; The top window module is composed of a through-type switchable cylindrical window (43) and a switch control valve stem (45), wherein the through-type switchable cylindrical window (43) is embedded in the pressure application / feedback leather sleeve (25), the segmented confining pressure cavity (24), the cylindrical steel body sleeve (22) and the steel double-layer cooling cylinder (2) from the inside to the outside, and a group of embedded ball valves (52) are installed at the bottom of the inner side of the through-type switchable cylindrical window (43), and the embedded ball valve (52) is connected to the switch control valve stem (45) for controlling the opening and closing of the embedded ball valve (52); The gas-liquid injection system is composed of a high-purity methane high-pressure gas cylinder (64), a high-purity carbon dioxide high-pressure gas cylinder (65), a gas booster (67), a gas cylinder for rotating during injection (68), a liquid container (70), a liquid injection pump (71), a gas-liquid flow T-type 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 gas cylinder for rotating during injection (68) through a pipeline and the gas booster (67), and then sent to the gas-liquid injection pipeline (17) of the axial head pressure submodule (3) through a pipeline and the gas-liquid flow T-type tee (72); the liquid container (70) is connected to the gas-liquid flow T-type tee (72) through a pipeline and the liquid injection pump (71); The gas-liquid recovery system comprises 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 an accumulator (79), a methane concentration sensor (80), a gas recovery cylinder (81), and a liquid recovery container (82). The outer end of the gas-liquid discharge pipeline (21) of the axial tail sealing submodule (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 cylinder (81) through the gas drying device (78), the gas mass flow controller and an accumulator (79) and the methane concentration sensor (80), and 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 for marine hydrate production according to claim 1 is characterized by: The axial head pressure submodule (3) is composed of an axial head steel sealing cylinder seat (10) and an axial head steel pressure cylinder seat (11), and the annular space between the two is an axial pressure cavity (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) and is used to apply pressure to the axial pressure cavity (12); the axial head steel pressure cylinder seat (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 production according to claim 2 is characterized by: The axial tail sealing submodule (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 gas and liquid generated after hydrate decomposition in the core.

4. The reservoir pressure rebound simulation device for marine hydrate production according to claim 3 is characterized by: The single-body pressure holding device is composed of a cylindrical steel body sleeve (22), an embedded confining pressure injection / feedback probe (23), a segmented confining pressure cavity (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 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 cavity (24), and the head is connected to 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, which are respectively connected in parallel to the two confining pressure injection devices (50) through the stainless steel ventilation pipeline (15); The pressure application / feedback 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.

5. The reservoir pressure rebound simulation device for marine hydrate production according to claim 4 is characterized by: The single-body pressure holding device is provided with five sections, and the segmented confining pressure chamber (24) of each single-body pressure holding device is evenly divided into three small sections in the axial direction, and each small confining pressure chamber is evenly divided into four sections on the tangential section with the radius at the positions of 45°, 135°, 225° and 315° of the circumference as the center line, and each confining pressure chamber is separated by a confining pressure annulus partition steel plate (51); each single-body pressure holding device has a total of 12 segmented confining pressure chambers, and the entire multi-section continuous high-pressure reaction pressure holding module (1) has a total of 60 segmented confining pressure chambers (24), and their number and position are completely corresponding to the embedded confining pressure injection / feedback probe (23).

6. The reservoir pressure rebound simulation device for marine hydrate production according to claim 5 is characterized by: The steel cylinder set consists of four solid cylinders made of stainless steel, namely a first steel cylinder (85), a second steel cylinder (86), a third steel cylinder (87), and a fourth steel cylinder (88), with lengths of 1600 mm, 1200 mm, 800 mm, and 400 mm, respectively, a diameter of 200 mm, and a pressure resistance range of 0 to 40 MPa. The steel cylinder set is used as an extension of the axial head steel pressure cylinder seat (11) during the five-step core pressing process 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), respectively, to transmit axial pressure to the core pressing material.

7. The experimental method of the reservoir pressure rebound simulation device in marine hydrate production according to claim 6 is characterized by: An integrated pressing method was used to prepare five core sections with different porosities connected end to end, and the experimental method included the following steps: First, a core with non-uniform porosity distribution is prepared by an integrated pressing method in a multi-stage continuous high-pressure reaction holding module (1), which mainly includes the following steps: a1. Check and confirm that all high-pressure ball valves (49) and ball valves (74) of the injection and recovery systems are fully closed, and check and confirm that the right end of the multi-stage continuous high-pressure reaction pressure holding module (1) is completely sealed by the axial tail sealing submodule (4); remove the axial head pressure submodule (3), and pull the tail end of the pluggable steel temperature probe (46) in the second monomer pressure holding device (30) to the fifth monomer pressure holding device (27) to the inner wall of the pressure application / feedback sleeve (25) at the lower end of the core filling space (26) to ensure that the second monomer pressure holding device (30) to the sealing of the core filling space (26) in the fifth monomer holding device (27); insert the first steel cylinder (85) into the left boundary of the core filling space (26) of the first monomer holding device (31), and at the same time open the through-type switchable cylindrical window (43) at the top of the first monomer holding device (31), and pour the first ratio of quartz sand mortar and clay mixed material through the top window, wherein the mass ratio of quartz sand to clay is 5:5 and the water-binder ratio is 0.5; then close the top window and let the mixed material stand for a period of time; a2. Open the through-type switchable cylindrical window (43) at the top of the second single-body pressing device (30), quickly pull the first steel cylinder (85) to the left boundary of the core filling space (26) of the second single-body pressing device (30), and at the same time quickly pour the second ratio of quartz sand mortar and clay mixed material through the top window, wherein the mass ratio of quartz sand to clay is 5:5 and the water-binder ratio is 0.9, insert the pluggable steel temperature probe (46) of the second single-body pressing device (30) to the initial position, then close the top window, and let the mixed material 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 pull the first steel cylinder (85) to the left boundary of the core filling space (26) of the third monomer holding device (29), and quickly pour the third ratio of quartz sand mortar and clay mixed material through the top window, wherein the mass ratio of quartz sand to clay is 6:4 and the water-binder 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 mixed material 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 pull the first steel cylinder (85) to the left boundary of the core filling space (26) of the fourth monomer holding device (28), and quickly pour the fourth ratio of quartz sand mortar and clay mixed material through the top window, wherein the mass ratio of quartz sand to clay is 7:3 and the water-binder 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 mixed material stand for a period of time; a5. Open the through-type switchable cylindrical window (43) at the top of the fifth single-body pressing device (27), quickly pull the first steel cylinder (85) to the left boundary of the core filling space (26) of the fifth single-body pressing device (27), and quickly pour the fifth ratio of quartz sand mortar and clay mixed material through the top window, wherein the mass ratio of quartz sand to clay is 8:2 and the water-binder ratio is 1.

2. Insert the pluggable steel temperature probe (46) of the fifth single-body pressing device (27) to the initial position, close the top window, and let the mixed material stand for a period of time. ; Then, the first steel cylinder (85) is quickly pulled out, and the axial head pressure submodule (3) is quickly assembled and sealed at the left end of the multi-stage continuous high-pressure reaction holding module (1). A pressure of 10 MPa is simultaneously applied to the axial pressure chamber (12) and the segmented confining pressure chamber (24), and the mixed material in the core filling space (26) of the five-stage single-body pressure holding device is continuously pressed for 8 hours, so that a core with an integrated long horizontal cylindrical shape having five sections of significantly different porosities is formed in the multi-stage continuous high-pressure reaction holding module (1), and the non-uniformly distributed porosity in the core decreases from left to right. Secondly, the generation of hydrates in a continuous, integrated long core with multiple sections of significantly different porosities involves the following steps: b1. Unloading the pressure in the axial pressure chamber (12) and the segmented confining pressure chamber (24) to 0 MPa, using a vacuum pump (73) to fill the core into the space (26) and to pump the pressure in the gas cylinder (68) to -0.1 MPa during the injection process; b2. Close all ball valves (74) on the injection line side of the gas-liquid flow T-joint (72), and use the high-purity methane high-pressure gas cylinder (64) and the gas booster (67) to make the methane gas pressure in the rotating gas cylinder (68) reach 10 MPa during the injection process; then, use the pressure difference between the rotating 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 ball valves (74) on the gas-liquid flow T-type tee (72) on the gas injection line side, use the liquid injection pump (71) to inject pure water into the core filling space (26), and stop injecting pure water when the pressure in the segmented confining pressure chamber (24) reaches 10 MPa, and close all ball valves (74) on the liquid injection line side of the gas-liquid flow T-type tee (72); b4. Allow the core to stand for 1 hour to ensure that the pure water in the core is saturated with methane. Repeat step b2 and inject a small amount of methane into the core again to stabilize the pressure in the segmented confining pressure chamber (24) at 10 MPa. Then close all ball valves (74) on the injection line side of the gas-liquid flow T-type three-way (72); b5. Turn on the refrigerated water bath circulation machine (56), set the water bath target temperature to 1°C, and allow the coolant to continue to cool and circulate in the water bath annulus (7) within the steel double-layer cooling cylinder (2); monitor the temperature of the temperature monitoring point on the pluggable steel temperature probe (46) within the core filling space (26) in real time. A sudden increase in a certain temperature indicates the formation of hydrates in the core sub-region; b6. When the temperatures at all temperature monitoring points have shown an upward trend, continue to maintain the water bath target temperature of 1°C and circulate the coolant for 30 minutes to ensure that the hydrate formation in the long, one-piece core with multiple sections of significantly different porosities is annealed and enters a stable state; Finally, the decomposition of hydrates in a continuous, integrated long core with multiple sections of significantly different porosities, i.e., the simulation of hydrate depressurization production, includes the following steps: c1. Check and ensure that the ball valves (74) of the gas-liquid recovery system are all closed, and then open the ball valve (74) between the gas-liquid discharge pipeline (21) and the primary gas-liquid separation tank (76). The hydrate gradually begins to decompose into methane gas and water during the process of reducing the pressure in the core, and migrates to one end of the gas-liquid discharge pipeline (21) through the non-uniformly distributed pores in the integrated long core, and flows into the primary gas-liquid separation tank (76) after passing through the outlet pressure control valve (75); the temperature and pressure changes in the core sub-area that can be monitored in the multi-stage continuous high-pressure reaction pressure holding module (1) are recorded in real time by the data acquisition system, and the area where the pressure rebound phenomenon occurs in the core during the hydrate decomposition process and the change law of the pressure rebound are monitored; c2. When the pressure in the primary gas-liquid separation tank (76) reaches stability, the ball valve (74) between the primary gas-liquid separation tank (76) and the secondary gas-liquid separation tank (77) is opened; c3. When the pressure in the secondary gas-liquid separation tank (77) reaches stability, all ball valves (74) at the rear ends of the primary gas-liquid separation tank (76) and the secondary gas-liquid separation tank (77) are opened in sequence, and the methane gas flows into the gas recovery 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 cylinder (81) is stabilized, carbon dioxide gas is injected 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 cylinder (81); when the methane concentration sensor (80) detects that the methane concentration is 0, the ball valve (74) at the front end of the gas recovery cylinder (81) is closed, the ball valve (74) at the rear end of the high-purity carbon dioxide high-pressure cylinder (65) is closed, and the discharge valves at the lower ends of the first gas-liquid separation tank (76) and the second gas-liquid separation tank (77) are opened to discharge the carbon dioxide gas to the outside and the water is discharged into the liquid recovery container (82).

8. The experimental method of the reservoir pressure rebound simulation device in marine hydrate production according to claim 6 is characterized by: The five-stage preparation method and experimental method of five sections of core with different porosities connected end to end include the following process: First, a core with non-uniform porosity distribution is prepared by five-stage pressing in a multi-stage continuous high-pressure reaction holding module (1). This pressing method achieves non-uniform porosity distribution in a large section of core by precisely controlling the ratio of mixed materials for pressing the small section of core and the pressing time of the small section of core. It is suitable for experiments that require a large porosity difference. 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 completely closed, check and confirm that the right end of the multi-stage continuous high-pressure reaction pressure holding module (1) is completely sealed by the axial tail sealing submodule (4); remove the axial head pressure submodule (3), pull the tail end of the pluggable steel temperature probe (46) in the second monomer pressure holding device (30) to the fifth monomer pressure holding device (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 pressure holding device (31), and insert the axial head pressure submodule ( 3) Quickly assemble and seal the left end of the multi-stage continuous high-pressure reaction holding module (1); open the through-type switchable cylindrical window (43) at the top of the first monomer holding device (31), and pour a fixed ratio of quartz sand mortar and clay mixed material through the top window, wherein 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, apply a pressure of 10 MPa to the axial pressure chamber (12) and the segmented confining pressure chamber (24) at the same time, and continuously press the mixed material in the core filling space (26) of the first monomer holding device (31) for 1 hour; S2. Unload the pressure in the axial pressure chamber (12) and the segmented confining pressure chamber (24) to 0 MPa, remove the axial head pressure submodule (3), extract 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 single-body pressure holding device (30), quickly assemble and seal the axial head pressure submodule (3); open the through-type switchable cylindrical window (43) at the top of the second single-body pressure holding device (30), and then remove the axial head pressure submodule (3). ), pouring a quartz mortar and clay mixture of the same proportion as in step S1 through the top window; then closing the top window, inserting the removable steel temperature probe (46) of the second monomer pressing device (30) to the initial position, applying a pressure of 10 MPa to the axial pressure chamber (12) and the segmented confining pressure chamber (24) at the same time, and pressing the mixed material in the second monomer pressing device (30) and the formed core in the first monomer pressing device (31) for 1 hour; S3. Unload the pressure in the axial pressure chamber (12) and the segmented confining pressure chamber (24) to 0 MPa, remove the axial head pressure submodule (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 pressure holding device (29), quickly assemble and seal the axial head pressure submodule (3); open the through-type switchable cylindrical window (43) at the top of the third single-body pressure holding device (29), and A quartz mortar and clay mixture having the same proportion as in step S1 is poured into the window; the top window is then closed, and the removable steel temperature probe (46) of the third monomer pressing device (29) is inserted into the initial position, and a pressure of 10 MPa is simultaneously applied to the axial pressure chamber (12) and the segmented confining pressure chamber (24), while pressing the mixed material in the third monomer pressing device (29) and the formed core in the first monomer pressing device (31) and the second monomer pressing device (30) for 1 hour; S4. Unload the pressure in the axial pressure chamber (12) and the segmented confining pressure chamber (24) to 0 MPa, remove the axial head pressure submodule (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 pressing device (28), quickly assemble and seal the axial head pressure submodule (3); open the through-type switchable cylindrical window (43) at the top of the fourth single pressing device (28), and pour the same as in step S4 through the top window. A quartz mortar and clay mixture of the same proportion as in S1 is prepared; the top window is then closed, the removable steel temperature probe (46) of the fourth single-body pressing device (28) is inserted into the initial position, and a pressure of 10 MPa is simultaneously applied to the axial pressure chamber (12) and the segmented confining pressure chamber (24), while pressing the mixed material in the fourth single-body pressing device (28) and the formed cores in the first single-body pressing device (31), the second single-body pressing device (30) and the third single-body pressing device (29) for 1 hour; S5. Unload the pressure in the axial pressure chamber (12) and the segmented confining pressure chamber (24) to 0 MPa, remove the axial head pressure submodule (3), extract the fourth steel cylinder (88), and quickly assemble and seal the axial head pressure submodule (3); open the through-type switchable cylindrical window (43) at the top of the fifth single-body pressing device (27), and pour the quartz mortar and clay mixed material with the same proportion as in step S1 through the top window; then close the top window, insert the removable steel temperature probe (46) of the fifth single-body pressing device (27) to the initial position, and simultaneously apply a pressure of 10 MPa to the axial pressure chamber (12) and the segmented confining pressure chamber (24). The mixed material in the fifth single pressing device (27) and the formed 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) are pressed simultaneously for 4 hours; after the pressing is completed, a core having a shape of an integrated long horizontal cylindrical body with five sections of significantly different porosities is formed in the multi-stage continuous high-pressure reaction pressing module (1). The mixed material ratio used for pressing each section of the core is exactly the same, but the pressing time of the five sections of the core is 4, 5, 6, 7 and 8 hours from left to right, respectively. Therefore, the non-uniformly distributed porosity in the core having the shape of an integrated long horizontal cylindrical body decreases from left to right.

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