Application of phase change materials and methods to eliminate wall effects in physical simulation of hydrate extraction

Abstract

The present invention provides an application of phase change material and a method for eliminating wall effects during a physical simulation of hydrate extraction. The application is the application of phase change material as a reagent for eliminating wall effects during a physical simulation. The method comprises: filling a certain volume of water-saturated sediment layer in a high-pressure autoclave for physical simulation of hydrate extraction, leaving a certain amount of residual space at the top of the autoclave; vacuuming to remove gas in the autoclave; injecting phase change material from the top of the autoclave until the pressure in the autoclave reaches a certain pressure and then stopping; opening a drain valve at the bottom of the autoclave and continuing to inject phase change material from the top of the autoclave to displace a certain amount of pore water in the sediment layer so that the phase change material penetrates a certain depth into the sediment layer; closing the injection valve at the top of the autoclave and injecting water from the bottom of the autoclave until the pressure in the autoclave reaches the formation simulation pressure corresponding to the physical simulation of hydrate extraction and then stopping injection; maintaining the autoclave pressure at the formation simulation pressure corresponding to the physical simulation of hydrate extraction, cooling the autoclave to below the phase change temperature of the phase change material so that the phase change material undergoes a phase change and becomes a solid.

Description

Technical Field

[0001] The present invention belongs to the technical field of natural gas hydrate exploitation, and relates to the application of phase change materials as reagents for eliminating wall effects in a physical simulation process and a method for eliminating wall effects in a physical simulation process of hydrate exploitation. Background Art

[0002] Natural gas hydrates are ice-like substances formed by natural gas and water under certain conditions of high pressure and low temperature. They are primarily found in deep-sea sediments or terrestrial permafrost. They are characterized by large reserves, shallow burial depths, and cleanliness. It is estimated that the methane reserves contained in natural gas hydrates are twice the current global reserves of natural gas, coal, and oil, and their total organic carbon content is as high as 10 trillion tons, making them an important alternative energy source.

[0003] Unlike traditional oil and gas reservoirs, natural gas hydrates are mostly found in seafloor sediments. These reservoirs typically lack stable overburden or confining rock formations, and their permeability varies significantly with the geological environment, making them extremely complex and unstable. Some hydrate reservoirs are also characterized by shallow depths, diverse types, complex hydrate formation processes, and complex hydrate decomposition and migration mechanisms. This creates significant uncertainty in hydrate drilling and production, making efficient extraction a significant challenge.

[0004] To guide the optimization of existing hydrate extraction processes and develop new, more efficient and safer extraction technologies, it is urgently necessary to conduct physical simulation experiments under laboratory conditions that are comparable to real-world extraction processes. Hydrate research has been conducted for decades, and a solid foundation has been established in physical simulation research, both in terms of experimental simulation equipment and data monitoring. Despite numerous remarkable achievements in physical simulation experiments and the technical support provided for numerous offshore field extractions, the wall effect observed in current laboratory-based physical simulation experiments remains difficult to eliminate, which can compromise the reliability of the data obtained. Wall effect refers to the influence of the walls of various hydrate high-pressure reactors. This effect primarily refers to the significant differences in the spatial structure near the wall compared to the rest of the reactor, resulting in significant differences in the flow, mass transfer, and heat transfer conditions at the wall compared to those in the main flow stream. When the reactor simulator is limited in size, wall effect can significantly impact the mass transfer, heat transfer, and reaction patterns observed in laboratory-based physical simulation experiments of hydrate extraction. In hydrate simulation experiments, since the sediment samples are mostly composed of quartz sand, the sand layer may experience a certain degree of sedimentation during water saturation or hydrate decomposition. This will lead to large void spaces above the kettle and a significant wall effect. Furthermore, in hydrate production experiments, the gas and liquid produced by decomposition will tend to migrate to the void spaces above the kettle, which will seriously interfere with the observed mass and heat transfer patterns.

[0005] In summary, it is of great practical significance to effectively eliminate the wall effect in hydrate mining simulation experiments conducted under laboratory conditions. The objective existence of the wall effect has become a bottleneck restricting the acquisition of high-field reduction experimental data and urgently needs to be resolved. Summary of the Invention

[0006] In view of the problems that arise in conducting hydrate mining model experiments under the above-mentioned existing laboratory conditions, in order to solve the problems caused by the wall effect in the model experiments, the present invention provides the following technical solutions.

[0007] The present invention provides application of phase change material as a reagent for eliminating wall effect in a physical simulation process.

[0008] According to the above application, preferably, the phase change material is a liquid-solid phase change material, which is solid under the temperature and pressure conditions corresponding to the physical simulation process and does not react with the fluid involved in the physical simulation process and is insoluble in the liquid phase fluid involved in the physical simulation process.

[0009] According to the above application, preferably, the physical simulation is a physical simulation of hydrate extraction; more preferably, the phase change material is a phase change material of an alkane and / or alcohol mixture that does not react with methane and is insoluble in water;

[0010] Wherein, the phase change temperature of the phase change material is preferably 10°C-30°C;

[0011] The density of the phase change material is preferably lower than that of water.

[0012] The present invention also provides a method for eliminating the wall effect in the physical simulation process of hydrate extraction, wherein the method is performed before the physical simulation process of hydrate extraction, and specifically comprises:

[0013] Sediment layer filling step: filling a certain volume of water-saturated sediment layer into the hydrate mining physical simulation autoclave, leaving a certain amount of residual space on the upper part of the hydrate mining physical simulation autoclave without filling;

[0014] Autoclave vacuuming step: after completing the sediment layer filling step, the hydrate mining physical simulation autoclave is vacuumed to remove the gas in the hydrate mining physical simulation autoclave;

[0015] Phase change material injection step: after completing the autoclave vacuuming step, injecting phase change material from the upper part of the hydrate mining physical simulation autoclave until the pressure in the hydrate mining physical simulation autoclave reaches a certain pressure and then stopping the injection; opening the drain valve at the bottom of the hydrate mining physical simulation autoclave and continuing to inject phase change material from the upper part of the hydrate mining physical simulation autoclave to displace a certain amount of pore water in the sediment layer so that the phase change material penetrates a certain depth into the sediment layer;

[0016] Pressurization step: After the phase change material injection step is completed, the upper injection valve of the hydrate production physical simulation autoclave is closed, and water is injected from the lower part of the hydrate production physical simulation autoclave until the pressure in the hydrate production physical simulation autoclave reaches the formation simulation pressure corresponding to the hydrate production physical simulation, and then the injection is stopped;

[0017] Injecting water from the bottom rather than from the top can effectively prevent the phase change material from being carried by the injected water to the area of ​​the sediment layer that does not contain phase change material;

[0018] Phase change material phase change step: After completing the pressurization step, the hydrate extraction physical simulation autoclave is cooled to below the phase change temperature of the phase change material to cause the phase change material to undergo a phase change into a solid state; wherein, the pressure of the hydrate extraction physical simulation autoclave is maintained at the formation simulation pressure corresponding to the hydrate extraction physical simulation.

[0019] After the phase change step of the phase change material is completed, the subsequent hydrate mining physical simulation process can be carried out.

[0020] According to the above method for eliminating the wall effect in the physical simulation process of hydrate mining, preferably, the composition of the water-saturated sediment layer includes deionized water, 3.35% wt salt solution, clay and quartz sand particles (preferably with a mesh size of 40-300 mesh).

[0021] According to the above-mentioned method for eliminating the wall effect in the process of physical simulation of hydrate extraction, preferably, the remaining space left on the top of the hydrate extraction physical simulation autoclave that is not filled accounts for 5%-10% of the effective volume of the hydrate extraction physical simulation autoclave, that is, the volume of the water-saturated sediment layer in the hydrate extraction physical simulation autoclave accounts for 90%-95% of the effective volume of the hydrate extraction physical simulation autoclave.

[0022] According to the above-mentioned method for eliminating the wall effect in the physical simulation process of hydrate extraction, preferably, the phase change material is a liquid-solid phase change material, which is solid under the temperature and pressure conditions corresponding to the physical simulation process and does not react with the fluid involved in the physical simulation process and is insoluble in the liquid phase fluid involved in the physical simulation process; more preferably, the phase change material is a phase change material of an alkane and / or alcohol mixture that does not react with methane and is insoluble in water;

[0023] Wherein, the phase change temperature of the phase change material is preferably 10°C-30°C;

[0024] Among them, the density of the phase change material is preferably less than that of water; the properties of the phase change material being less than that of water and being insoluble in water ensure that the injected phase change material can complete the filling of the upper part of the hydrate mining physical simulation autoclave without applying external force. The property of the phase change material not reacting with methane also indicates that it can be applied to most hydrate mining physical simulation experiments.

[0025] According to the above-mentioned method for eliminating the wall effect in the physical simulation process of hydrate extraction, preferably, in the phase change material injection step, the pressure at which the injection is stopped during the injection of the phase change material from the upper part of the hydrate extraction physical simulation autoclave to the pressure in the hydrate extraction physical simulation autoclave rising to a certain pressure is such that the injected phase change material can fill the remaining space on the upper part of the hydrate extraction physical simulation autoclave without immersing into the lower sediment layer, for example, 0.01MPa-0.1MPa.

[0026] According to the above-mentioned method for eliminating the wall effect during the physical simulation of hydrate extraction, preferably, in the phase change material injection step, the depth of the phase change material immersed in the sediment layer is 1%-5% of the height of the inner cavity of the autoclave of the physical simulation of hydrate extraction; the depth of the phase change material immersed in the sediment layer can be monitored by back calculation through the volume of the displaced water and the porosity of the sediment layer.

[0027] According to the above-mentioned method for eliminating the wall effect in the physical simulation process of hydrate extraction, preferably, in the pressurization step, water is injected from the lower part of the high-pressure autoclave of the physical simulation of hydrate extraction to 5MPa-40MPa. This pressure range can basically cover all the pressure conditions of the formations where hydrates are stored in real land or sea areas.

[0028] According to the above method for eliminating the wall effect in the physical simulation process of hydrate production, preferably, in the phase change step of the phase change material, the pressure of the autoclave of the physical simulation of hydrate production is maintained by the following method:

[0029] Setting the pressure parameters of the tracking pump and connecting the tracking pump to the lower part of the high-pressure autoclave for hydrate extraction physical simulation; wherein the pressure parameters of the tracking pump are set to the formation simulation pressure corresponding to the hydrate extraction physical simulation;

[0030] This method can effectively ensure that the pressure of the autoclave in the hydrate mining physical simulation during the phase change process of the phase change material always remains the same as the pressure conditions in the subsequent hydrate mining physical simulation process, and can to a certain extent avoid the risk of affecting the mechanical strength of the phase change material after it becomes solid due to changes in pressure conditions.

[0031] According to the above method for eliminating the wall effect in the physical simulation process of hydrate extraction, preferably, in the phase change step of the phase change material, the hydrate extraction physical simulation autoclave is cooled to 3°C-5°C below the phase change temperature of the phase change material to ensure absolute solidification of the phase change material.

[0032] The technical solution provided by this invention is based on the liquid-solid properties of phase change materials (PCMs) within a specific temperature range. By placing a certain amount of PCM on top of a high-pressure autoclave for physical simulation of hydrate extraction, the influence of wall effects on the variation of field parameters during the hydrate simulation process is eliminated. This allows for the completion of physical simulation experiments with a high degree of fidelity under laboratory conditions, providing relevant theoretical and technical support for the commercialization of hydrate extraction. Compared with existing technologies, the technical solution provided by this invention has the following beneficial effects:

[0033] (1) The technical solution provided by the present invention effectively eliminates the wall effect that occurs in laboratory-based hydrate simulation experiments by filling the top of a certain amount of phase change material in the autoclave used in the hydrate extraction simulation. This reduces the impact of the wall effect on heat transfer, mass transfer, and reaction processes in the actual hydrate extraction simulation experiments. The use of phase change material ensures that gas-liquid flow occurs within the sedimentary layer, increasing the similarity and comparability between the simulation experiments and the actual extraction process.

[0034] (2) The technical solution provided by the present invention ensures that the phase change material completely fills the remaining space reserved above the reactor by controlling the stopping pressure of the primary injection of the phase change material. In addition, by controlling the volume of the displacement water during the secondary injection of the phase change material, it is also ensured that the injected phase change material is immersed into the sediment layer to a certain depth. This avoids the formation of new voids due to volume shrinkage of the phase change material during the phase change process, thus avoiding the occurrence of the new wall effect.

[0035] (3) For the hydrate mining physical simulation autoclave where sand filling operation is difficult or difficult to fill, the use of phase change materials can effectively reduce the impact of filling blind areas on the physical simulation experiment.

[0036] (4) Physical simulation of hydrate mining The autoclave is usually made of stainless steel, and the heat exchange rate between it and the environment is relatively fast. Filling the upper space of the autoclave with phase change material can reduce the heat transfer rate between the sediment layer and the environment while eliminating the wall effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the process for eliminating wall effects in the physical simulation of hydrate production.

[0038] Figure 2 Schematic diagram of the device used in the physical simulation experiment of hydrate mining in Example 1.

[0039] Figure 3A This is a diagram of the fluid flow trend during the hydrate production simulation after using the method to eliminate the wall effect during the hydrate production physical simulation process.

[0040] Figure 3BThe fluid flow trend diagram during the hydrate production simulation is directly performed without using the method of eliminating the wall effect during the physical simulation of hydrate production.

[0041] Figure 4 This is a graph showing the change in bottom pressure difference over time during the hydrate production simulation process of Examples 1 to 3 and Comparative Examples 1 to 3. DETAILED DESCRIPTION

[0042] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] A specific embodiment of the present invention provides the use of phase change materials as agents for eliminating wall effects in a physical simulation process.

[0044] Furthermore, the phase change material is a liquid-solid phase change material, which is solid under the temperature and pressure conditions corresponding to the physical simulation process and does not react with the fluid involved in the physical simulation process and is insoluble in the liquid phase fluid involved in the physical simulation process.

[0045] Furthermore, the physical simulation is a physical simulation of hydrate mining;

[0046] Furthermore, the phase change material is a phase change material of a mixture of alkanes and / or alcohols that does not react with methane and is insoluble in water;

[0047] Furthermore, the phase change temperature of the phase change material is 10°C-30°C;

[0048] Furthermore, the density of the phase change material is less than that of water.

[0049] A specific embodiment of the present invention provides a method for eliminating wall effects during a physical simulation process of hydrate extraction. The method is performed before the physical simulation process of hydrate extraction and specifically includes:

[0050] Sediment layer filling step: fill a certain volume of water-saturated sediment layer in the hydrate mining physical simulation autoclave, and leave a certain amount of residual space on the top of the hydrate mining physical simulation autoclave without filling (such as Figure 1 (as described in A);

[0051] Autoclave vacuuming step: after completing the sediment layer filling step, the hydrate mining physical simulation autoclave is vacuumed to remove the gas in the hydrate mining physical simulation autoclave;

[0052] Phase change material injection step: After completing the autoclave vacuuming step, inject phase change material from the upper part of the hydrate mining physical simulation autoclave until the pressure in the hydrate mining physical simulation autoclave rises to a certain pressure and then stop the injection (such as Figure 1 B); open the drain valve at the bottom of the hydrate production physical simulation autoclave and continue to inject phase change material from the top of the hydrate production physical simulation autoclave to displace a certain amount of pore water in the sediment layer so that the phase change material is immersed in a certain depth of the sediment layer (such as Figure 1 (as described in C);

[0053] Pressurization step: After the phase change material injection step is completed, the upper injection valve of the hydrate production physical simulation autoclave is closed, and water is injected from the lower part of the hydrate production physical simulation autoclave until the pressure in the hydrate production physical simulation autoclave reaches the formation simulation pressure corresponding to the hydrate production physical simulation, and then the injection is stopped;

[0054] Phase change material phase change step: After the pressure increase step is completed, the temperature of the hydrate mining physical simulation autoclave is lowered to below the phase change temperature of the phase change material to make the phase change material undergo a phase change into a solid state (such as Figure 1 D); wherein, the pressure of the autoclave for hydrate production physical simulation is maintained at the formation simulation pressure corresponding to the hydrate production physical simulation.

[0055] Furthermore, the water-saturated sediment layer comprises deionized water, 3.35% wt salt solution, clay and quartz sand particles (preferably with a mesh size of 40-300 meshes).

[0056] Furthermore, the remaining unfilled space on the top of the hydrate mining physical simulation autoclave accounts for 5%-10% of the effective volume of the hydrate mining physical simulation autoclave, that is, the volume of the water-saturated sediment layer in the hydrate mining physical simulation autoclave accounts for 90%-95% of the effective volume of the hydrate mining physical simulation autoclave.

[0057] Furthermore, the phase change material is a liquid-solid phase change material, which is in a solid state under the temperature and pressure conditions corresponding to the physical simulation process and does not react with the fluid involved in the physical simulation process and is insoluble in the liquid phase fluid involved in the physical simulation process;

[0058] Furthermore, the phase change material is a phase change material of an alkane and / or alcohol mixture that does not react with methane and is insoluble in water;

[0059] Furthermore, the phase change temperature of the phase change material is preferably 10°C-30°C;

[0060] Furthermore, the density of the phase change material is preferably less than that of water;

[0061] For example, the phase change material is composed of n-dodecane, n-tetradecane, n-docosane and n-tetracosane, with a phase change temperature of 16°C and a density of 0.731 g / cm 3 .

[0062] Furthermore, in the phase change material injection step, the pressure at which the injection is stopped during the process of injecting the phase change material from the upper part of the hydrate mining physical simulation autoclave to the pressure inside the hydrate mining physical simulation autoclave rising to a certain pressure is such that the injected phase change material can fill the remaining space on the upper part of the hydrate mining physical simulation autoclave without seeping into the lower sediment layer, for example, 0.01 MPa-0.1 MPa.

[0063] Furthermore, in the phase change material injection step, the depth of the phase change material immersed in the sediment layer is 1%-5% of the height of the inner cavity of the high-pressure autoclave for physical simulation of hydrate mining; the depth of the phase change material immersed in the sediment layer can be monitored by back calculation through the volume of the displaced water and the porosity of the sediment layer.

[0064] Furthermore, in the pressure-increasing step, water is injected from the lower part of the high-pressure autoclave of the hydrate production physical simulation to 5MPa-40MPa. This pressure range can basically cover all the pressure conditions of the hydrate storage formations in real land or sea areas.

[0065] Furthermore, in the phase change step of the phase change material, the pressure of the autoclave for hydrate mining physical simulation is maintained by the following means:

[0066] The tracking pump pressure parameters are set and the tracking pump is connected to the lower part of the high-pressure autoclave for hydrate production physical simulation; wherein the tracking pump pressure parameters are set to the formation simulation pressure corresponding to the hydrate production physical simulation.

[0067] Furthermore, in the phase change step of the phase change material, the temperature of the hydrate mining physical simulation autoclave is lowered to 3°C-5°C below the phase change temperature of the phase change material to ensure absolute solidification of the phase change material.

[0068] Example 1

[0069] This embodiment provides a physical simulation experiment of hydrate mining, using Figure 2 The device shown is carried out.

[0070] The device comprises: a circulating water bath, a chiller connected to the circulating water bath, a hydrate mining physical simulation autoclave arranged inside the circulating water bath, a PLC pneumatic regulating valve arranged on a production channel connected to the inlet of a production well of the hydrate mining physical simulation autoclave, a mass balance arranged at the outlet of the production channel connected to the inlet of the production well of the hydrate mining physical simulation autoclave, a diaphragm metering pump connected to the injection channel at the top of the hydrate mining physical simulation autoclave, and a data acquisition system connected to the pressure measuring point at the bottom of the hydrate mining physical simulation autoclave; a water flow channel is arranged at the bottom of the hydrate mining physical simulation autoclave, and a drain valve is arranged on the water flow channel; and an injection valve is arranged on the injection channel at the top of the hydrate mining physical simulation autoclave.

[0071] Specifically include:

[0072] 1. Before the physical simulation process of hydrate extraction, a pretreatment method for eliminating the wall effect in the physical simulation process of hydrate extraction is used, which includes the following steps:

[0073] 1.1. Sediment layer filling step: Fill a certain volume of water-saturated sediment layer into the hydrate mining physical simulation autoclave, leaving a certain amount of residual space on the top of the hydrate mining physical simulation autoclave without filling (such as Figure 1 (as described in A);

[0074] The water-saturated sediment layer comprises deionized water, 3.35%wt salt solution, clay and quartz sand particles with a mesh size of 200 meshes;

[0075] Among them, the porosity of the sedimentary layer is 30.8%;

[0076] The remaining unfilled space on the upper part of the hydrate production physical simulation autoclave accounts for 5% of the effective volume of the hydrate production physical simulation autoclave, that is, the volume of the water-saturated sediment layer in the hydrate production physical simulation autoclave accounts for 95% of the effective volume of the hydrate production physical simulation autoclave;

[0077] 1.2. Autoclave Vacuuming Step: After the sedimentation layer filling step is completed, the device sealing test and the hydrate extraction physical simulation autoclave are vacuumed to ensure the overall airtightness of the device and remove the gas in the hydrate extraction physical simulation autoclave to ensure that the subsequently injected phase change material can fully occupy the unfilled space above the hydrate extraction physical simulation autoclave;

[0078] 1.3. Phase change material injection step: After the autoclave vacuuming step is completed, the phase change material is injected from the top until the pressure in the hydrate extraction physical simulation autoclave reaches 0.01 MPa. The injection is then stopped. The drain valve at the bottom of the hydrate extraction physical simulation autoclave is opened and the phase change material is continuously injected from the top of the autoclave to displace a certain amount of pore water in the sediment layer so that the phase change material is immersed in the sediment layer to a certain depth (the depth is 5% of the reactor cavity height).

[0079] 1.4. Pressure Boosting Step: After the phase change material injection step is completed, the injection valve on the upper part of the hydrate production physical simulation autoclave is closed, and water is injected from the lower part of the hydrate production physical simulation autoclave until the pressure in the hydrate production physical simulation autoclave reaches the formation simulation pressure corresponding to the hydrate production physical simulation. Then, the injection is stopped;

[0080] 1.5. Phase change material phase change step: After the pressurization step is completed, the pressure parameter of a tracking pump connected to a water flow channel provided at the bottom of the hydrate extraction physical simulation autoclave is set to the formation simulation pressure corresponding to the hydrate extraction physical simulation, and the hydrate extraction physical simulation autoclave is cooled to 3°C below the phase change temperature of the phase change material to cause the phase change material to undergo a phase change and become a solid state;

[0081] The phase change material used in this embodiment is a mixture phase change material composed of n-dodecane, n-tetradecane, n-docosane and n-tetracosane provided by Shanghai Lingbo Environmental Protection Technology Co., Ltd., with a density of 0.731 g / cm 3 , the phase transition temperature is 16℃.

[0082] 2. After step 1, perform a physical simulation process of hydrate extraction;

[0083] The fluid generation process (hydrate decomposition will produce fluid) occurring during hydrate reservoir production is simulated by replenishing water through the injection channel above the hydrate production autoclave in the physical simulation. The fluid production rate is adjusted by controlling the opening of a PLC pneumatic control valve on the production channel connected to the inlet of the production well of the hydrate production autoclave. In this embodiment, the opening is controlled to 5%. While the water replenishment rate is constant, the pressure value at the pressure measuring point below the hydrate production autoclave is recorded in real time.

[0084] The pressure difference between P4 and P1 at the bottom of the autoclave in the physical simulation of hydrate production can be found in Figure 4 .

[0085] Example 2

[0086] This embodiment provides a physical simulation experiment for hydrate production. The only difference from Example 1 is that in step 2, the opening of the PLC pneumatic regulating valve on the production channel connected to the inlet of the production well of the hydrate production physical simulation autoclave is controlled to 45%.

[0087] The pressure difference between P4 and P1 at the bottom of the autoclave in the physical simulation of hydrate production can be found in Figure 4 .

[0088] Example 3

[0089] This embodiment provides a physical simulation experiment for hydrate production. The only difference from Example 1 is that in step 2, the opening of the PLC pneumatic regulating valve on the production channel connected to the inlet of the production well of the hydrate production physical simulation autoclave is controlled to 75%.

[0090] The pressure difference between P4 and P1 at the bottom of the autoclave in the physical simulation of hydrate production can be found in Figure 4 .

[0091] Comparative Example 1

[0092] This comparative example provides a physical simulation experiment for hydrate mining, which differs from Example 1 only in that step 2 is performed directly without performing step 1.

[0093] The pressure difference between P4 and P1 at the bottom of the autoclave in the physical simulation of hydrate production can be found in Figure 4 .

[0094] Comparative Example 2

[0095] This comparative example provides a physical simulation experiment for hydrate mining, which differs from Example 2 only in that step 2 is performed directly without performing step 1.

[0096] The pressure difference between P4 and P1 at the bottom of the autoclave in the physical simulation of hydrate production can be found in Figure 4 .

[0097] Comparative Example 3

[0098] This comparative example provides a physical simulation experiment of hydrate mining, which differs from Example 3 only in that step 2 is performed directly without performing step 1.

[0099] The pressure difference between P4 and P1 at the bottom of the autoclave in the physical simulation of hydrate production can be found in Figure 4 .

[0100] See also Figure 4 It is easy to see that the presence of solid phase change materials forces the fluid to migrate from the sedimentary layer to the production well (e.g. Figure 3AAs shown, the pressure difference at the bottom of the autoclave in the hydrate production physical simulation is proportional to the valve opening of the PLC pneumatic control valve. Under the condition of a constant water replenishment rate, the far well end (position P4) exhibited similar pressures during the hydrate production physical simulation processes of Examples 1, 2, and 3. However, the pressure at the near well end (position P1) was significantly affected by the valve opening of the PLC pneumatic control valve due to its proximity to the production well. The larger the valve opening, the faster the fluid discharge rate, the lower the pressure at the near well end, and the greater the pressure difference (P4-P1) at the bottom of the autoclave in the hydrate production physical simulation. This proves that the use of phase change materials ensures the effective migration of fluids in the reservoir.

[0101] For physical simulation experiments on hydrate production without using phase change materials (see Figure 4 ), due to the lack of phase change materials, a certain amount of voids appeared in the upper part of the hydrate production physical simulation autoclave. The existence of voids in the upper part of the hydrate production physical simulation autoclave resulted in a fluid migration resistance weakening zone in the upper part of the hydrate production physical simulation autoclave compared to the lower sedimentary layer. In this case, the fluid supplied from the far well end will tend to migrate from the void zone in the upper part of the hydrate production physical simulation autoclave to the near well end (e.g. Figure 3B As shown), this makes the pressure difference at the bottom of the autoclave in the hydrate production physical simulation smaller than that in the hydrate production physical simulation experiment with the presence of phase change materials. Figure 4 It can be seen that Comparative Examples 1, 2, and 3 show that the pressure difference at the bottom of the hydrate production physical simulation autoclave (P4-P1) is inversely proportional to the valve opening of the PLC pneumatic control valve. When the remote water supply rate is constant, the larger the valve opening of the PLC pneumatic control valve, the faster the fluid discharge rate, the lower the pressure above the hydrate production physical simulation autoclave, and the remote supply fluid will tend to migrate from the upper part of the hydrate production physical simulation autoclave, which leads to a smaller pressure difference at the bottom of the hydrate production physical simulation autoclave. However, when the valve opening of the PLC pneumatic control valve is small, the fluid discharge rate is slow, and part of the remote supply fluid will migrate from the reservoir, which causes the bottom of the hydrate production physical simulation autoclave to show a certain pressure difference. This series of experiments proves that the larger the valve opening of the PLC pneumatic control valve, the greater the negative impact of the voids above the hydrate production physical simulation autoclave on the experimental results.

[0102] The comparison between the embodiment and the comparative example proves that the use of phase change material can ensure the effective migration of fluid in the sedimentary layer, and effectively reduce the negative impact of the wall effect on the physical model data under laboratory conditions.

[0103] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for eliminating wall effects in a physical simulation process of hydrate extraction, wherein: This method is carried out before the physical simulation process of hydrate production, and specifically includes: Sediment layer filling step: filling a certain volume of water-saturated sediment layer into the hydrate mining physical simulation autoclave, leaving a certain amount of residual space on the upper part of the hydrate mining physical simulation autoclave without filling; Autoclave vacuuming step: after completing the sediment layer filling step, the hydrate mining physical simulation autoclave is vacuumed to remove the gas in the hydrate mining physical simulation autoclave; Phase change material injection step: after completing the autoclave vacuuming step, injecting phase change material from the upper part of the hydrate mining physical simulation autoclave until the pressure in the hydrate mining physical simulation autoclave reaches a certain pressure and then stopping the injection; opening the drain valve at the bottom of the hydrate mining physical simulation autoclave and continuing to inject phase change material from the upper part of the hydrate mining physical simulation autoclave to displace a certain amount of pore water in the sediment layer so that the phase change material penetrates a certain depth into the sediment layer; Pressurization step: After the phase change material injection step is completed, the upper injection valve of the hydrate production physical simulation autoclave is closed, and water is injected from the lower part of the hydrate production physical simulation autoclave until the pressure in the hydrate production physical simulation autoclave reaches the formation simulation pressure corresponding to the hydrate production physical simulation, and then the injection is stopped; Phase change material phase change step: After completing the pressurization step, the hydrate extraction physical simulation autoclave is cooled to below the phase change temperature of the phase change material to cause the phase change material to undergo a phase change into a solid state; wherein, the pressure of the hydrate extraction physical simulation autoclave is maintained at the formation simulation pressure corresponding to the hydrate extraction physical simulation.

2. The method according to claim 1, wherein The remaining space on the upper part of the hydrate production physical simulation autoclave that is not filled accounts for 5%-10% of the effective volume of the hydrate production physical simulation autoclave.

3. The method according to claim 1, wherein The phase change material is a liquid-solid phase change material, which is in solid state under the temperature and pressure conditions corresponding to the physical simulation process and does not react with the fluid involved in the physical simulation process and is insoluble in the liquid phase fluid involved in the physical simulation process.

4. The method according to claim 3, wherein the phase change material is a phase change material of an alkane and / or alcohol mixture that does not react with methane and is insoluble in water. The method according to claim 4 , wherein the phase change temperature of the phase change material is 10° C. to 30° C. The method according to claim 4 , wherein the density of the phase change material is less than that of water.

7. The method according to claim 1, wherein In the phase change material injection step, the phase change material is injected from the upper part of the hydrate mining physical simulation autoclave until the pressure in the hydrate mining physical simulation autoclave is raised to a certain pressure and the injection is stopped. The pressure at which the injection is stopped can ensure that the injected phase change material can fill the remaining space on the upper part of the hydrate mining physical simulation autoclave without seeping into the lower sediment layer.

8. The method according to claim 1, wherein In the phase change material injection step, the depth of the phase change material immersed in the sediment layer is 1%-5% of the height of the inner cavity of the hydrate mining physical simulation autoclave.

9. The method according to claim 1, wherein During the phase change step of the phase change material, the pressure of the autoclave for hydrate production physical simulation is maintained by the following means: The tracking pump pressure parameters are set and the tracking pump is connected to the lower part of the high-pressure autoclave for hydrate production physical simulation; wherein the tracking pump pressure parameters are set to the formation simulation pressure corresponding to the hydrate production physical simulation.

10. The method according to claim 1, wherein In the phase change step of the phase change material, the high-pressure autoclave for hydrate mining physical simulation is cooled to 3°C-5°C below the phase change temperature of the phase change material.

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