Natural gas hydrate exploitation method for promoting carbon dioxide replacement by using organic matters

Abstract

The invention belongs to the field of natural gas exploitation, and discloses a natural gas hydrate exploitation method for promoting carbon dioxide replacement by using organic matters. Belongs to the technical field of natural gas hydrate exploitation. Comprising the following steps: firstly, introducing methane gas into a high-pressure reaction kettle filled with organic matter-containing sediments at low temperature, and quickly reacting to obtain a hydrate-containing sediment reservoir; and then carbon dioxide is injected for replacement mining. By adjusting the type and concentration of organic matters in sediments, organic matter injection is simulated to promote carbon dioxide replacement and exploitation of natural gas hydrates. The organic matters in the process can effectively improve the mining speed and efficiency. The method is easy to implement, capable of remarkably improving the replacement efficiency and suitable for large-scale exploitation of the natural gas hydrate. Meanwhile, organic matters in natural soil are used in the method, so that the method has the advantages of rich resources, low price, environmental protection and no pollution, and shows a good application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of natural gas hydrate exploitation, and in particular relates to a natural gas hydrate exploitation method utilizing organic matter to promote carbon dioxide replacement. Background Art

[0002] Natural gas hydrate (NGH), also known as combustible ice, is a crystalline compound formed by small guest molecules (mainly CH4) and water under low temperature and high pressure. Recently, large amounts of NGH have been discovered in marine sediments and permafrost areas. As a clean energy source, the extraction and utilization of natural gas is expected to reduce carbon emissions and global warming. By changing the stability conditions of hydrates, a variety of extraction methods have been explored, including decompression, thermal stimulation, injection of inhibitors, and CH4 / CO2 substitution. CH4 / CO2 substitution utilizes the huge carbon dioxide storage capacity of the seabed and has the advantage of almost no damage to the marine ecological environment. Therefore, it is considered a promising solution to multiple challenges such as energy shortages, the greenhouse effect, and geological risks associated with other extraction methods.

[0003] The spontaneity and feasibility of CH4 / CO2 replacement have been verified in thermodynamics and kinetics. In order to improve the CH4 recovery rate and CO2 sequestration rate, the combination of CH4 / CO2 replacement with other methods, such as decompression, intermittent heating, etc., has also been explored. The present study found that the actual CH4 / CO2 replacement is closely related to the properties of the water-containing sediments, and organic matter makes the process more complicated. The use of toxic and destructive additives is strictly prohibited in the marine geological environment, so some eco-friendly or natural additives need to be tested on a laboratory scale first. As mentioned earlier, organic matter has a significant promoting effect on the formation of hydrates, and its effect on CH4 / CO2 exchange is rarely reported in the current literature. Then injecting these organics is undoubtedly a good choice to help CH4 / CO2 exchange in the future.

[0004] Therefore, the present invention utilizes organic matter to promote carbon dioxide replacement to exploit natural gas hydrates. The effects of organic matter type and content are systematically studied. One of the goals of the present invention is to clarify the effects of organic matter on CH4 / CO2 replacement, and another goal is to screen some good natural additives to help gas exchange in the hydrate phase. The results of the invention will provide valuable insights for the actual exploitation of NGH using CH4 / CO2 replacement. Summary of the invention

[0005] The present invention provides the molecular structure of lignin, fulvic acid and humic acid, which are promoters of carbon dioxide replacement for natural gas hydrates. The structure is as follows: Lignin Fulvic acid Humic acid (R in the structural formula represents an alkyl group which has little effect on the properties of the molecule) Conventional natural gas extraction has problems such as high energy consumption, low efficiency, and environmental damage. The purpose of the present invention is to provide an efficient, safe, and pollution-free natural gas hydrate replacement extraction auxiliary agent. The effects of organic matter type (lignin, humic acid, fulvic acid) and content on carbon dioxide replacement extraction of natural gas hydrates were systematically studied. The results showed that organic matter significantly improved the CH4 / CO2 replacement. The CH4 recovery rate and CO2 sequestration rate of the sediment containing 1.0 wt% humic acid reached 51.07% and 30.66%, respectively, which were 64.69% and 43.00% higher than those of the system without organic matter. These findings help to better understand the CH4 / CO2 replacement in practical applications and provide valuable insights for the actual extraction of NGH using CH4 / CO2 replacement in the future.

[0006] The method proposed by the present invention is a method for exploiting natural gas hydrates by using organic matter to promote carbon dioxide replacement. The organic matter is one or more of lignin, fulvic acid and humic acid, and the organic matter can promote carbon dioxide replacement for exploiting natural gas hydrates. Specifically, the organic matter is introduced into the reservoir of natural gas hydrates, and carbon dioxide replacement is performed after the concentration of the organic matter in the reservoir reaches 1.0 wt%-10.0 wt%.

[0007] Further, the method comprises the following steps: The method for simulating the effect of organic matter on CO2 displacement of natural gas hydrate comprises the following steps: (1) Adding materials: Four 1250 mesh clays (montmorillonite, illite, kaolinite and chlorite) and five silica sands (40-70 mesh, 70-120 mesh, 100-200 mesh, 325 mesh and 600 mesh) were mixed evenly in a certain mass ratio (1.5:0.9:0.3:0.3:1:1:2:1:1). The porosity and average particle size of the mixed minerals were 45.91% and 6.767 μm, respectively. The initial liquid of the reaction system was 14 g of a solution containing 3.5 wt% NaCl and organic matter. The reaction system was configured, and the above initial solution was introduced into the sediment (90 g) and mixed evenly, and then the treated sediment was filled into the reactor and compacted; (2) Natural gas hydrate synthesis: methane gas was introduced, the experimental pressure was 8.5 MPa, and the experimental temperature was 274.15 K. The sudden drop in reactor pressure indicated that hydrates began to form. When the reactor temperature and pressure remained constant for a long time (more than 5 hours), the CH4 hydrate formation experiment was considered to be completed, and the hydrate saturation range was 20%-60%; (3) Carbon dioxide replacement: After the synthesis of CH4 hydrate is completed, the experimental temperature is reduced to 268.15 K. At this temperature, CH4 hydrate has the best self-preservation effect. After the reactor temperature stabilizes, CH4 is released and pre-cooled CO2 is quickly injected to the required value. Subsequently, the experimental temperature is raised to the expected value and the replacement experiment is started. Then, a gas sample is collected from the reactor, and the gas sample after the reaction is completed is measured by gas chromatography to determine the content of each component, and the CH4 replacement rate and CO2 storage rate are calculated.

[0008] Preferably, the concentration of organic matter in step (1) is in the range of 1.0 wt% to 10.0 wt%.

[0009] Preferably, during the replacement of natural gas hydrate in step (3), CO2 is injected to maintain the pressure of the reactor in the range of 2.5 MPa-3.5 MPa, and the expected value of the experimental temperature rise is 268.15 K-277.15 K.

[0010] Preferably, the replacement time of natural gas hydrate in step (3) is in the range of 120 hours.

[0011] Preferably, the natural gas includes one or more of methane, ethane and propane.

[0012] Compared with the traditional natural gas hydrate development method, the present invention has the following advantages: (1) Carbon sequestration: The carbon dioxide replacement method helps to control carbon dioxide globally. Compared with traditional mining methods, this method also has the advantages of maintaining reservoir mechanical stability, reducing water and sand production, and reducing additional energy input.

[0013] (2) High replacement efficiency: Organic matter significantly improves the replacement of CH4 / CO2. The CH4 recovery rate and CO2 sequestration rate of the sediment containing 1.0 wt% humic acid reached 51.07% and 30.66%, respectively, which were 64.69% and 43.00% higher than those of the system without organic matter. This provides a new idea for obtaining CH4-rich natural gas in natural gas replacement in the future.

[0014] (3) Environmentally friendly: Organic matter has a wide range of sources and good biodegradability, has little impact on the environment, and meets the requirements of sustainable development.

[0015] (4) Easy to operate: The method of the present invention for the replacement of natural gas hydrates with carbon dioxide combined with organic matter is easy to operate, avoids complex equipment and cumbersome operating procedures, is more suitable for industrial production, and has important practical significance for optimizing the replacement of natural gas hydrates. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1Figure 2 shows the experimental setup.

[0017] Figure 2 Generate a displacement process diagram for the hydrate.

[0018] Figure 3 This is a diagram showing the effect of organic matter presence on CH4 replacement rate.

[0019] Figure 4 This is a diagram showing the effect of organic matter presence on CO2 storage efficiency. Specific implementation plan

[0020] The technical scheme and implementation effects of the present invention are further described in detail below in conjunction with the embodiments, but they should not be construed as limiting the scope of implementation of the present invention.

[0021] In order to study the present invention, a method for exploiting natural gas hydrates by using organic matter to promote carbon dioxide replacement is provided. Figure 1 .

[0022] In order to study the method of the present invention for the replacement of marine natural gas hydrates with organic carbon dioxide, the implementation equipment used is a high-pressure reactor and a supporting system. The simulation device for the influence of the organic properties corresponding to the method on the replacement of natural gas hydrates with CO2 includes: a high-pressure reactor, a constant temperature water bath, a temperature and pressure data monitoring and acquisition system, and a gas chromatograph. The high-pressure reactor is the core component of this device. It is made of 316L stainless steel, with a maximum pressure of 32.0 MPa and an effective volume of 205.0 mL. The pressure and temperature sensors are placed on the top of the reactor. The temperature sensor used in the experiment is a Pt100 precision platinum resistor with a measurement range of 263.15~373.15 K and an uncertainty of ±0.1K. The pressure sensor has a measurement range of 0.0~25.0MPa and an uncertainty of ±0.05 MPa. Each sensor has been calibrated before the experiment. A constant temperature water bath (model DC-2006, temperature control range -20~100℃, total power 2 kW, external circulation pump flow rate 8.0 L / min, temperature control accuracy ±0.05℃) is connected to the interlayer outside the reactor to control the temperature of the reactor. The coolant used in the experiment is a mixed liquid of ethylene glycol and water (volume ratio 1:2). The equilibrium reactor is used to store and precool the gas. Its main material is 316L stainless steel, the maximum pressure is 32.0MPa, and the effective volume is 1000.0 mL. The data acquisition system is mainly composed of a temperature module, a pressure module, a transformer, and an MCGS data collection system installed on a computer. It can monitor and save the temperature and pressure data in the reactor in real time. The data acquisition system automatically collects temperature and pressure data every 1 s. The gas chromatograph used in the experiment is GC-950, which can be used to determine the content of CH4 and CO2 in the gas phase during the reaction process. The detectors are flame ionization detector (FID) and thermal conductivity detector (TCD), and the carrier gas is argon (Ar, 99.999 mol%). The high-pressure reactor used is a commonly used device for studying hydrate technology, see Figure 1 .

[0023] Before the reaction begins, the entire experimental system is cleaned with deionized water. After vacuum drying, the prepared organic matter-containing sediment is filled and placed in the reactor. The constant temperature water bath temperature is set to the required experimental temperature. After the system temperature stabilizes for 2 hours, the experimental gas (methane) is introduced to replace the air in the reactor 3-4 times. The experimental gas of a certain pressure (less than the equilibrium pressure of hydrate formation at this temperature, the equilibrium pressure of hydrate is calculated using the Chen-Guo hydrate model) is introduced to achieve equilibrium. Then the experimental gas is introduced from the equilibrium reactor to raise the system pressure to the test pressure, and the inlet valve is closed. As the reaction proceeds, the gas is continuously consumed, and the relevant data in the reactor are obtained through the pressure and temperature measuring instruments. Subsequently, when the reactor pressure remains constant for 5 hours, the CH4 hydrate synthesis ends, and the experimental temperature drops to 268.15 K. At this temperature, CH4 hydrate has the best self-preservation effect. After the reactor temperature stabilizes, CH4 is released, and pre-cooled CO2 is quickly injected to the required value. Then the experimental temperature is raised to the target value and the replacement is started. Parallel samples are extracted at regular intervals, and the gas after the reaction is completed is measured by gas chromatography to determine the content of each component therein.

[0024] Comparative Example 1 Adding materials: Four 1250 mesh clays (montmorillonite, illite, kaolinite and chlorite) and five silica sands (40-70 mesh, 70-120 mesh, 100-200 mesh, 325 mesh and 600 mesh) were mixed evenly in a certain mass ratio (1.5:0.9:0.3:0.3:1:1:2:1:1). The initial liquid of the reaction system was 14 g of 3.5 wt% NaCl solution. The reaction system was configured, and the above initial solution was introduced into the sediment (90 g) and mixed evenly, and then the treated sediment was filled into the reactor and compacted; Natural gas hydrate synthesis: gas methane was introduced, the experimental pressure was 8.5 MPa, the experimental temperature was 274.15 K, and the sudden drop in reactor pressure indicated that hydrates began to form. When the reactor temperature and pressure remained constant for a long time (more than 5 hours), the CH4 hydrate formation experiment was considered to be completed, and its hydrate saturation was 54.37%. The amount of methane hydrate was calculated to be 0.11693 mol; Carbon dioxide replacement: After the synthesis of CH4 hydrate was completed, the experimental temperature dropped to 268.15 K, at which temperature CH4 hydrate has the best self-preservation effect. After the reactor temperature stabilized, CH4 was released and pre-cooled CO2 was quickly injected to 3 MP. Subsequently, the experimental temperature was raised to 277.15 K and the replacement experiment began. Gas samples were collected from the reactor at different time points (0 h, 1 h, 2 h, 4 h, 8 h, 12 h, 24 h, 48 h, 72 h, 96 h, 120 h), and the gas samples after the reaction were measured by gas chromatograph to determine the content of each component, and the CH4 replacement rate and CO2 storage rate were calculated. The final CH4 replacement rate and CO2 storage rate were 31.01% and 21.44%, respectively, as shown in Table 1.

[0025] Embodiment 1 Adding materials: Four 1250 mesh clays (montmorillonite, illite, kaolinite and chlorite) and five silica sands (40-70 mesh, 70-120 mesh, 100-200 mesh, 325 mesh and 600 mesh) were mixed evenly in a certain mass ratio (1.5:0.9:0.3:0.3:1:1:2:1:1). The initial liquid of the reaction system was 14 g of a solution containing 3.5 wt% NaCl and 1.0 wt% lignin. The reaction system was configured, and the above initial solution was introduced into the sediment (90 g) and mixed evenly, and then the treated sediment was filled into the reactor and compacted; Natural gas hydrate synthesis: gas methane was introduced, the experimental pressure was 8.5 MPa, the experimental temperature was 274.15 K, and the sudden drop in reactor pressure indicated that hydrates began to form. When the reactor temperature and pressure remained constant for a long time (more than 5 hours), the CH4 hydrate formation experiment was considered to be completed, and its hydrate saturation was 53.71%. The amount of methane hydrate was calculated to be 0.11552 mol; Carbon dioxide replacement: After the synthesis of CH4 hydrate is completed, the experimental temperature drops to 268.15 K. At this temperature, CH4 hydrate has the best self-preservation effect. After the reactor temperature stabilizes, CH4 is released, and pre-cooled CO2 is quickly injected to 3 MP. Subsequently, the experimental temperature is raised to 277.15 K, and the replacement experiment is started. Gas samples are collected from the reactor at different time points (0 h, 1 h, 2 h, 4 h, 8 h, 12 h, 24 h, 48 h, 72 h, 96 h, 120 h), and the gas samples after the reaction are completed are measured by gas chromatograph to measure the content of each component, and the CH4 replacement rate and CO2 storage rate are calculated. The final CH4 replacement rate and CO2 storage rate are 37.31% and 24.90%, respectively, as shown in Table 1. Compared with comparative example 1, the replacement speed is faster, and the CH4 replacement rate and CO2 storage rate are increased by 20.32% and 16.14%, respectively. Relevant data are shown in Table 1. Figure 3 and Figure 4 shown.

[0026] Embodiment 2 Adding materials: Four 1250 mesh clays (montmorillonite, illite, kaolinite and chlorite) and five silica sands (40-70 mesh, 70-120 mesh, 100-200 mesh, 325 mesh and 600 mesh) were mixed evenly in a certain mass ratio (1.5:0.9:0.3:0.3:1:1:2:1:1). The initial liquid of the reaction system was 14 g of a solution containing 3.5 wt% NaCl and 1.0 wt% fulvic acid. The reaction system was configured, and the above initial solution was introduced into the sediment (90 g) and mixed evenly, and then the treated sediment was filled into the reactor and compacted; Natural gas hydrate synthesis: gas methane was introduced, the experimental pressure was 8.5 MPa, the experimental temperature was 274.15 K, and the sudden drop in reactor pressure indicated that hydrates began to form. When the reactor temperature and pressure remained constant for a long time (more than 5 hours), the CH4 hydrate formation experiment was considered to be completed, and its hydrate saturation was 53.57%. The amount of methane hydrate was calculated to be 0.11523 mol; Carbon dioxide replacement: After the synthesis of CH4 hydrate is completed, the experimental temperature drops to 268.15 K. At this temperature, CH4 hydrate has the best self-preservation effect. After the reactor temperature stabilizes, CH4 is released, and pre-cooled CO2 is quickly injected to 3 MP. Subsequently, the experimental temperature is raised to 277.15 K, and the replacement experiment is started. Gas samples are collected from the reactor at different time points (0 h, 1 h, 2 h, 4 h, 8 h, 12 h, 24 h, 48 h, 72 h, 96 h, 120 h), and the gas samples after the reaction are completed are measured by gas chromatograph to measure the content of each component, and the CH4 replacement rate and CO2 storage rate are calculated. The final CH4 replacement rate and CO2 storage rate are 40.48% and 27.74%, respectively, as shown in Table 1. Compared with comparative example 1, the replacement speed is faster, and the CH4 replacement rate and CO2 storage rate are increased by 30.54% and 29.38%, respectively. Relevant data are as follows Figure 3 and Figure 4 shown.

[0027] Embodiment 3 Adding materials: Four 1250 mesh clays (montmorillonite, illite, kaolinite and chlorite) and five silica sands (40-70 mesh, 70-120 mesh, 100-200 mesh, 325 mesh and 600 mesh) were mixed evenly in a certain mass ratio (1.5:0.9:0.3:0.3:1:1:2:1:1). The initial liquid of the reaction system was 14 g of a solution containing 3.5 wt% NaCl and 1.0 wt% humic acid. The reaction system was configured, and the above initial solution was introduced into the sediment (90 g) and mixed evenly, and then the treated sediment was filled into the reactor and compacted; Natural gas hydrate synthesis: gas methane was introduced, the experimental pressure was 8.5 MPa, the experimental temperature was 274.15 K, and the sudden drop in reactor pressure indicated that hydrates began to form. When the reactor temperature and pressure remained constant for a long time (more than 5 hours), the CH4 hydrate formation experiment was considered to be completed, and its hydrate saturation was 52.69%. The amount of methane hydrate was calculated to be 0.10924 mol; Carbon dioxide replacement: After the synthesis of CH4 hydrate is completed, the experimental temperature drops to 268.15 K. At this temperature, CH4 hydrate has the best self-preservation effect. After the reactor temperature stabilizes, CH4 is released, and pre-cooled CO2 is quickly injected to 3 MP. Subsequently, the experimental temperature is raised to 277.15 K, and the replacement experiment is started. Gas samples are collected from the reactor at different time points (0 h, 1 h, 2 h, 4 h, 8 h, 12 h, 24 h, 48 h, 72 h, 96 h, 120 h), and the gas samples after the reaction are completed are measured by gas chromatograph to measure the content of each component, and the CH4 replacement rate and CO2 storage rate are calculated. The final CH4 replacement rate and CO2 storage rate are 51.07% and 30.66%, respectively, as shown in Table 1. Compared with comparative example 1, the replacement speed is faster, and the CH4 replacement rate and CO2 storage rate are increased by 64.69% and 43.00%, respectively. Relevant data are as follows Figure 3 and Figure 4 shown.

[0028] Embodiment 4 Adding materials: Four 1250 mesh clays (montmorillonite, illite, kaolinite and chlorite) and five silica sands (40-70 mesh, 70-120 mesh, 100-200 mesh, 325 mesh and 600 mesh) were mixed evenly in a certain mass ratio (1.5:0.9:0.3:0.3:1:1:2:1:1). The initial liquid of the reaction system was 14 g of a solution containing 3.5 wt% NaCl and 5.0 wt% humic acid. The reaction system was configured, and the above initial solution was introduced into the sediment (90 g) and mixed evenly, and then the treated sediment was filled into the reactor and compacted; Natural gas hydrate synthesis: gas methane was introduced, the experimental pressure was 8.5 MPa, the experimental temperature was 274.15 K, and the sudden drop in reactor pressure indicated that hydrates began to form. When the reactor temperature and pressure remained constant for a long time (more than 5 hours), the CH4 hydrate formation experiment was considered to be completed, and its hydrate saturation was 52.35%. The amount of methane hydrate was calculated to be 0.11261 mol; Carbon dioxide replacement: After the synthesis of CH4 hydrate is completed, the experimental temperature drops to 268.15 K. At this temperature, CH4 hydrate has the best self-preservation effect. After the reactor temperature stabilizes, CH4 is released, and pre-cooled CO2 is quickly injected to 3 MP. Subsequently, the experimental temperature is raised to 277.15 K, and the replacement experiment is started. Gas samples are collected from the reactor at different time points (0 h, 1 h, 2 h, 4 h, 8 h, 12 h, 24 h, 48 h, 72 h, 96 h, 120 h), and the gas samples after the reaction are completed are measured by gas chromatograph to measure the content of each component, and the CH4 replacement rate and CO2 storage rate are calculated. The final CH4 replacement rate and CO2 storage rate are 49.45% and 29.36%, respectively, as shown in Table 1. Compared with comparative example 1, the replacement speed is faster, and the CH4 replacement rate and CO2 storage rate are increased by 59.46% and 36.94%, respectively. Relevant data are as follows Figure 3 and Figure 4 shown.

[0029] Embodiment 5 Adding materials: Four 1250 mesh clays (montmorillonite, illite, kaolinite and chlorite) and five silica sands (40-70 mesh, 70-120 mesh, 100-200 mesh, 325 mesh and 600 mesh) were mixed evenly in a certain mass ratio (1.5:0.9:0.3:0.3:1:1:2:1:1). The initial liquid of the reaction system was 14 g of a solution containing 3.5 wt% NaCl and 10.0 wt% humic acid. The reaction system was configured, and the above initial solution was introduced into the sediment (90 g) and mixed evenly, and then the treated sediment was filled into the reactor and compacted; Natural gas hydrate synthesis: gas methane was introduced, the experimental pressure was 8.5 MPa, the experimental temperature was 274.15 K, and the sudden drop in reactor pressure indicated that hydrates began to form. When the reactor temperature and pressure remained constant for a long time (more than 5 hours), the CH4 hydrate formation experiment was considered to be completed, and its hydrate saturation was 53.11%. The amount of methane hydrate was calculated to be 0.11425 mol; Carbon dioxide replacement: After the synthesis of CH4 hydrate is completed, the experimental temperature drops to 268.15 K. At this temperature, CH4 hydrate has the best self-preservation effect. After the reactor temperature stabilizes, CH4 is released, and pre-cooled CO2 is quickly injected to 3 MP. Subsequently, the experimental temperature is raised to 277.15 K, and the replacement experiment is started. Gas samples are collected from the reactor at different time points (0 h, 1 h, 2 h, 4 h, 8 h, 12 h, 24 h, 48 h, 72 h, 96 h, 120 h), and the gas samples after the reaction are completed are measured by gas chromatograph to measure the content of each component, and the CH4 replacement rate and CO2 storage rate are calculated. The final CH4 replacement rate and CO2 storage rate are 48.45% and 28.71%, respectively, as shown in Table 1. Compared with comparative example 1, the replacement speed is faster, and the CH4 replacement rate and CO2 storage rate are increased by 56.24% and 33.91%, respectively. Relevant data are as follows Figure 3 and Figure 4 shown.

[0030] Table 1 Replacement rate and storage rate under different conditions The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for exploiting natural gas hydrate by promoting carbon dioxide replacement using organic matter, characterized in that: The organic matter is one or more of lignin, fulvic acid and humic acid, and the organic matter can promote the carbon dioxide replacement and exploitation of natural gas hydrates.

2. The method according to claim 1, characterized in that Organic matter is introduced into the natural gas hydrate reservoir, and carbon dioxide is then introduced to replace the organic matter until the concentration of the organic matter in the reservoir reaches 1.0 wt%-10.0 wt%.

3. The method according to claim 1, characterized in that The steps include: (1) Adding materials: Four 1250 mesh clays and five silica sands were mixed evenly in a mass ratio of 1.5:0.9:0.3:0.3:1:1:2:1:

1. The porosity and average particle size of the mixed minerals were 45.91% and 6.767 μm, respectively. The initial liquid of the reaction system was 14 g of a solution containing 3.5 wt% NaCl and organic matter. The reaction system was prepared by introducing the initial solution into 90 g of the mixed minerals and mixing them evenly. Then, the treated sediment was filled into the reactor and compacted. (2) Natural gas hydrate synthesis: methane gas was introduced, the experimental pressure was 8.5 MPa, and the experimental temperature was 274.15 K. The sudden drop in reactor pressure indicated that hydrates began to form. When the reactor temperature and pressure remained constant for a long time, the CH4 hydrate formation experiment was considered to be completed. The hydrate saturation range was 20%-60%; (3) Carbon dioxide replacement: After the synthesis of CH4 hydrate is completed, the experimental temperature is reduced to 268.15 K. At this temperature, CH4 hydrate has the best self-preservation effect. After the reactor temperature stabilizes, CH4 is released and pre-cooled CO2 is quickly injected to the required value. Subsequently, the experimental temperature is raised to the expected value and the replacement experiment is started. Gas samples are then collected from the reactor. The gas samples after the reaction are completed are measured by gas chromatograph to determine the content of each component, and the CH4 replacement rate and CO2 storage rate are calculated.

4. The method according to claim 3, characterized in that The four 1250 mesh clays are montmorillonite, illite, kaolinite and chlorite, and the five silica sands are 40-70 mesh, 70-120 mesh, 100-200 mesh, 325 mesh and 600 mesh. The organic matter is one or more of lignin, fulvic acid and humic acid.

5. The method according to claim 3, characterized in that: During the replacement of natural gas hydrate in step (3), CO2 is injected to maintain the pressure of the reactor in the range of 2.5 MPa-3.5 MPa. The expected value of the experimental temperature rise is 268.15K-277.15K.

6. The method according to claim 3, characterized in that The concentration range of organic matter in step (1) is 1.0 wt%-10.0 wt%.

7. The method according to claim 3, characterized in that The replacement time of natural gas hydrate in step (3) is in the range of 120 hours.

8. The method according to claim 3, characterized in that The natural gas includes one or more of methane, ethane and propane.

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