A method for exploiting natural gas hydrate by using organic matter to promote carbon dioxide replacement

Abstract

The application belongs to the field of natural gas exploitation, and discloses a method for exploiting natural gas hydrate by using organic matter to promote carbon dioxide replacement. The method belongs to the technical field of natural gas hydrate exploitation and comprises the following steps: firstly, under low temperature, methane gas is introduced into a high-pressure reaction kettle filled with organic matter-containing sediment, and a hydrate-containing sediment reservoir is obtained after rapid reaction; then, carbon dioxide is injected to perform replacement exploitation. By adjusting the type and concentration of organic matter in the sediment, the replacement exploitation of natural gas hydrate by carbon dioxide is simulated by using organic matter. The organic matter in the process can effectively improve the exploitation speed and efficiency. The method is simple to implement, can significantly improve the replacement efficiency, and is suitable for large-scale exploitation of natural gas hydrate. Meanwhile, the method uses organic matter in natural soil, has the advantages of rich resources, low price, environmental protection and no pollution, and has good application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of natural gas hydrate exploitation, and particularly relates to a method for exploiting natural gas hydrate by using organic matter to promote carbon dioxide replacement. BACKGROUND

[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, a large amount of NGH has been found in marine sediments and permafrost regions. As a clean energy, exploitation and utilization of natural gas is expected to reduce carbon emissions and global warming. By changing the stability conditions of hydrates, people have explored various exploitation methods, including depressurization, thermal stimulation, injection of inhibitors and CH4 / CO2 replacement. CH4 / CO2 replacement takes advantage of the huge carbon dioxide sequestration capacity of the seabed, with almost no damage to the marine ecological environment. Therefore, it is considered as a promising solution to multiple challenges such as energy shortage, greenhouse effect and geological risks related to other exploitation 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, CH4 / CO2 replacement has also been combined with other methods, such as depressurization, intermittent heating, etc. The present application found that the actual CH4 / CO2 replacement is closely related to the properties of water-containing sediments, and organic matter makes this process more complicated. In the marine geological environment, the use of toxic and destructive additives is strictly prohibited, so some eco-friendly or natural additives need to be tested first at the laboratory scale. As mentioned earlier, organic matter has a significant promoting effect on the formation of hydrates, but its influence on CH4 / CO2 exchange is rarely reported in the current literature. Therefore, the injection of these organic matters is undoubtedly a good choice to help CH4 / CO2 exchange in the future.

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

[0005] The present application provides the molecular structures of lignin, fulvic acid and humic acid as promoters for natural gas hydrate carbon dioxide replacement exploitation, which are as follows:

[0006]

[0007] Lignin

[0008]

[0009] fulvic acid

[0010]

[0011] humic acid (R in the structural formula represents an alkyl group that has little effect on the properties of the molecule)

[0012] Traditional natural gas exploitation has problems such as high energy consumption, low efficiency, and environmental damage. The purpose of the present application is to provide a high-efficiency, safe, and pollution-free natural gas hydrate displacement exploitation auxiliary agent. The effects of organic matter types (lignin, humic acid, and fulvic acid) and contents on the displacement of natural gas hydrate by carbon dioxide were systematically studied. The results showed that organic matter significantly improved the CH4 / CO2 displacement. The CH4 recovery rate and CO2 storage rate of the sediment containing 1.0 wt% humic acid reached 51.07% and 30.66%, respectively, which were increased by 64.69% and 43.00%, respectively, compared with the system without organic matter. These findings help better understand the CH4 / CO2 displacement in practical applications and provide valuable insights for future practical exploitation of NGH using CH4 / CO2 displacement.

[0013] The method proposed in the present application is a natural gas hydrate exploitation method using organic matter to promote carbon dioxide displacement. The organic matter is one or more of lignin, fulvic acid, and humic acid, which can promote the displacement of natural gas hydrate by carbon dioxide. Specifically, the organic matter is introduced into the reservoir of natural gas hydrate, and the concentration of the organic matter in the reservoir is allowed to reach 1.0 wt%-10.0 wt% before carbon dioxide displacement.

[0014] Further, the method includes the following steps: the effect of the organic matter on the displacement of natural gas hydrate by CO2 simulation method includes the following steps:

[0015] (1) Feeding: four kinds of 1250 mesh clay (montmorillonite, illite, kaolinite, and chlorite) and five kinds of silica sand (40-70 mesh, 70-120 mesh, 100-200 mesh, 325 mesh, and 600 mesh) are mixed uniformly at 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 are 45.91% and 6.767 μm, respectively. The initial liquid of the reaction system is 14 g of a solution containing 3.5 wt% NaCl and organic matter. The reaction system is configured, the above initial solution is introduced into the sediment (90 g) and mixed uniformly, and then the treated sediment is filled into the reaction kettle and compacted;

[0016] (2) Natural gas hydrate synthesis: The gas methane is introduced, the experimental pressure is 8.5 MPa, the experimental temperature is 274.15 K, and the sudden drop of the reactor pressure indicates that the hydrate begins to generate. When the reactor temperature and pressure remain constant for a long time (more than 5 hours), it is considered that the CH4 hydrate generation experiment is completed, and the hydrate saturation degree ranges from 20% to 60%;

[0017] (3) Carbon dioxide replacement: After the CH4 hydrate synthesis is completed, the experimental temperature is reduced to 268.15 K. At this temperature, the CH4 hydrate has the best self-preservation effect. After the reactor temperature is stabilized, the CH4 is released, and the pre-cooled CO2 is rapidly injected to the required value. Subsequently, the experimental temperature is increased to the expected value, and the replacement experiment is started. Then, the gas sample is collected from the reactor, and the content of each component in the gas sample after the reaction is completed is measured by a gas chromatograph. The CH4 replacement rate and the CO2 storage rate are calculated.

[0018] Preferably, the concentration of the organic matter in step (1) ranges from 1.0 wt% to 10.0 wt%.

[0019] Preferably, in the replacement process of the natural gas hydrate in step (3), the CO2 injection maintains the pressure of the reactor in the range of 2.5 MPa to 3.5 MPa, and the expected value of the experimental temperature increase ranges from 268.15 K to 277.15 K.

[0020] Preferably, the replacement time of the natural gas hydrate in step (3) ranges from 120 hours.

[0021] Preferably, the natural gas includes one or more than one of methane, ethane, and propane.

[0022] Compared with the traditional natural gas hydrate exploitation method, the present application has the following advantages:

[0023] (1) Carbon sequestration: The carbon dioxide replacement method is helpful for global carbon dioxide control. Compared with the traditional exploitation method, this method also has the advantages of maintaining the reservoir mechanical stability, reducing water and sand production, and reducing additional energy input.

[0024] (2) High replacement efficiency: The organic matter significantly improves the CH4 / CO2 replacement. The CH4 recovery rate and the CO2 storage rate of the sediment containing 1.0 wt% humic acid reach 51.07% and 30.66%, respectively, which are increased by 64.69% and 43.00%, respectively, compared with the system without organic matter. This provides a new idea for obtaining natural gas rich in CH4 in the future natural gas replacement.

[0025] (3) Environmentally friendly: The organic matter has a wide source and good biodegradability, has less impact on the environment, and meets the requirements of sustainable development.

[0026] (4) Simple operation: the method for replacing and exploiting natural gas hydrate by using carbon dioxide combined with organic matter is simple in operation, avoids complicated equipment and cumbersome operation process, is more suitable for industrial production, and has important practical significance for optimizing replacement and exploitation of natural gas hydrate. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a diagram of an experimental device.

[0028] Figure 2 is a diagram of a hydrate generation replacement process.

[0029] Figure 3 is a diagram of the influence of the presence of organic matter on CH4 replacement rate.

[0030] Figure 4 is a diagram of the influence of the presence of organic matter on CO2 storage rate. DETAILED DESCRIPTION

[0031] The technical solutions and implementation effects of the present application will be further described in detail below in combination with examples, but should not be understood as limiting the implementation scope of the present application.

[0032] In order to study the natural gas hydrate exploitation method provided by the present application for promoting carbon dioxide replacement by using organic matter, details are shown in Figure 1 .

[0033] In order to study the method for replacing and exploiting marine natural gas hydrate by carbon dioxide provided with organic matter, the high-pressure reaction kettle and the matching system are adopted, and the simulation device for the influence of the corresponding organic matter on the CO2 replacement natural gas hydrate includes: a high-pressure reaction kettle, a constant temperature water bath, a temperature and pressure data monitoring and acquisition system and a gas chromatograph. The high-pressure reaction kettle is the core component of the device, the material thereof is 316L stainless steel, the maximum pressure bearing pressure is 32.0 MPa, the effective volume is 205.0 mL, the pressure and temperature sensors are arranged on the top of the reaction kettle, the temperature sensor used in the experiment is a Pt100 type precision platinum resistance, the measurement range is 263.15-373.15 K, and the uncertainty is ±0.1 K. The measurement range of the pressure sensor is 0.0-25.0 MPa, and the uncertainty is ±0.05 MPa, and each sensor has been corrected before the experiment. The constant temperature water bath (model DC-2006, temperature control range is -20-100 DEG C, total power is 2 kW, the flow of the outer circulating pump is 8.0 L / min, and the temperature control accuracy is ±0.05 DEG C) is connected with the interlayer outside the reaction kettle and is used to control the temperature of the reaction kettle, the cooling liquid used in the experiment is a mixed liquid of ethylene glycol and water (the volume ratio is 1:2). The balance kettle is used for storing and precooling gas, the main material thereof is 316L stainless steel, the maximum pressure bearing pressure is 32.0 MPa, and the effective volume is 1000.0 mL. The data acquisition system mainly includes a temperature module, a pressure module, a transformer and a MCGS data collection system installed on a computer, can monitor and save the temperature and pressure data in the reaction kettle in real time, and the data acquisition system automatically collects temperature and pressure data every 1 s. The gas chromatograph used in the experiment is a GC-950, which can be used to determine the CH4 and CO2 content in the gas phase in the reaction process. The detector is a flame ionization detector (FID) and a thermal conductivity detector (TCD), and the carrier gas is argon (Ar, 99.999 mol %). The high-pressure reaction kettle used is a commonly used device for studying hydrate technology, and is seen in Figure 1 .

[0034] Before the reaction, the whole experimental system was cleaned with deionized water, and after vacuum drying, the prepared sediment containing organic matter was filled into the reactor, and the constant temperature water bath was set to the required temperature of the experiment. When the system temperature was stable for 2 hours, the experimental gas (methane) was introduced to displace the air in the reactor for 3-4 times. The experimental gas was introduced into the reactor to reach equilibrium at a certain pressure (less than the hydrate formation equilibrium pressure at this temperature, and the hydrate equilibrium pressure was calculated by the Chen-Guo hydrate model). Then the experimental gas was introduced from the equilibrium reactor to increase the system pressure to the test pressure, and the gas valve was closed as the reaction proceeded. The relevant data in the reactor were obtained by pressure and temperature measuring instruments. Subsequently, when the reactor pressure remained constant for 5 hours, the CH4 hydrate synthesis was completed, and the experimental temperature was reduced to 268.15 K, at which the CH4 hydrate had the best self-preservation effect. After the reactor temperature stabilized, the CH4 was released, and the pre-cooled CO2 was quickly injected to the required value. Then the test temperature was increased to the target value, and the displacement was started. The parallel samples were taken every certain time, and the gas components after the reaction were measured by gas chromatography.

[0035] Comparative Example 1

[0036] Charging: Four kinds of 1250 mesh clay (montmorillonite, illite, kaolinite and chlorite) and five kinds of silica sand (40-70 mesh, 70-120 mesh, 100-200 mesh, 325 mesh and 600 mesh) were mixed 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. The reaction system was prepared, the above initial solution was introduced into the sediment (90 g) and mixed uniformly, and then the treated sediment was filled into the reactor and compacted;

[0037] Natural gas hydrate synthesis: methane gas was introduced, the experimental pressure was 8.5 MPa, the experimental temperature was 274.15 K, and the sudden drop of the reactor pressure indicated that the hydrate began to form. When the reactor temperature and pressure remained constant for a long time (more than 5 hours), it was considered that the CH4 hydrate formation experiment was completed, and the hydrate saturation was 54.37%, and the amount of methane hydrate was calculated to be 0.11693 mol;

[0038] Carbon dioxide replacement: After the synthesis of CH4 hydrate was completed, the temperature of the experiment was reduced to 268.15 K, at which temperature CH4 hydrate has the best self-preservation effect. After the temperature of the reactor was stabilized, CH4 was released, and pre-cooled CO2 was rapidly injected to 3 MP. Subsequently, the temperature of the experiment was increased to 277.15 K, and the replacement experiment was started. 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), gas samples were collected from the reactor, and the contents of the components in the gas samples after the reaction were measured by a gas chromatograph, and the CH4 replacement rate and the 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.

[0039] Example one

[0040] Charging: Four kinds of 1250 mesh clay (montmorillonite, illite, kaolinite and chlorite) and five kinds of silica sand (40-70 mesh, 70-120 mesh, 100-200 mesh, 325 mesh and 600 mesh) were mixed uniformly 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, the above initial solution was introduced into the sediment (90 g) and mixed uniformly, and then the treated sediment was filled into the reaction kettle and compacted;

[0041] Natural gas hydrate synthesis: methane gas was introduced, the experimental pressure was 8.5 MPa, the experimental temperature was 274.15 K, and the sudden drop of the pressure of the reactor indicated that the hydrate began to generate. When the temperature and pressure of the reactor remained constant for a long time (more than 5 hours), it was considered that the CH4 hydrate generation experiment was completed, the hydrate saturation was 53.71%, and the amount of methane hydrate was calculated to be 0.11552 mol;

[0042] Carbon dioxide replacement: After the synthesis of CH4 hydrate was completed, the temperature of the experiment was reduced to 268.15 K, at which temperature CH4 hydrate has the best self-preservation effect. After the temperature of the reactor was stabilized, CH4 was released, and pre-cooled CO2 was rapidly injected to 3 MP. Subsequently, the temperature of the experiment was increased to 277.15 K, and the replacement experiment was started. 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), gas samples were collected from the reactor, and the contents of the components in the gas sample after the reaction were measured by a gas chromatograph, and the CH4 replacement rate and the CO2 storage rate were calculated. The final CH4 replacement rate and the CO2 storage rate were 37.31% and 24.90%, respectively, as shown in Table 1. Compared with Comparative Example 1, the replacement speed was faster, and the CH4 replacement rate and the CO2 storage rate were increased by 20.32% and 16.14%, respectively. The relevant data are shown in Table 1 and FIG. 1. Figure 3 and Figure 4

[0043] Example Two

[0044] Charging: Four kinds of 1250 mesh clay (montmorillonite, illite, kaolinite and chlorite) and five kinds of silica sand (40-70 mesh, 70-120 mesh, 100-200 mesh, 325 mesh and 600 mesh) were mixed uniformly 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, the above initial solution was introduced into the sediment (90 g) and mixed uniformly, and then the treated sediment was filled into the reaction kettle and compacted;

[0045] Natural gas hydrate synthesis: methane was introduced, the experimental pressure was 8.5 MPa, the experimental temperature was 274.15 K, and the sudden drop of the pressure of the reactor indicated that the hydrate began to generate. When the temperature and pressure of the reactor remained constant for a long time (more than 5 hours), it was considered that the CH4 hydrate generation experiment was completed, the hydrate saturation was 53.57%, and the amount of methane hydrate was calculated to be 0.11523 mol;

[0046] ​Carbon dioxide replacement: After the synthesis of CH4 hydrate was completed, the temperature of the experiment was reduced to 268.15 K, at which temperature CH4 hydrate has the best self-preservation effect. After the temperature of the reactor was stabilized, CH4 was released, and pre-cooled CO2 was rapidly injected to 3 MP. Subsequently, the temperature of the experiment was increased to 277.15 K, and the replacement experiment was started. 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), gas samples were collected from the reactor, and the contents of the components in the gas sample after the reaction were measured by a gas chromatograph, and the CH4 replacement rate and the CO2 storage rate were calculated. The final CH4 replacement rate and the CO2 storage rate were 40.48% and 27.74%, respectively, as shown in Table 1. Compared with Comparative Example 1, the replacement speed was faster, and the CH4 replacement rate and the CO2 storage rate were increased by 30.54% and 29.38%, respectively. The relevant data are shown in Table 1 and FIG. 1. Figure 3 and Figure 4

[0047] Example Three

[0048] Charging: Four kinds of 1250 mesh clay (montmorillonite, illite, kaolinite and chlorite) and five kinds of silica sand (40-70 mesh, 70-120 mesh, 100-200 mesh, 325 mesh and 600 mesh) were mixed uniformly 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, the above initial solution was introduced into the sediment (90 g) and mixed uniformly, and then the treated sediment was filled into the reaction kettle and compacted;

[0049] Natural gas hydrate synthesis: methane was introduced, the experimental pressure was 8.5 MPa, the experimental temperature was 274.15 K, and the sudden drop of the pressure of the reactor indicated that the hydrate began to generate. When the temperature and pressure of the reactor remained constant for a long time (more than 5 hours), it was considered that the CH4 hydrate generation experiment was completed, the hydrate saturation was 52.69%, and the amount of methane hydrate was calculated to be 0.10924 mol;

[0050] ​Carbon dioxide replacement: After the synthesis of CH4 hydrate was completed, the temperature of the experiment was reduced to 268.15 K, at which temperature CH4 hydrate has the best self-preservation effect. After the temperature of the reactor was stabilized, CH4 was released, and pre-cooled CO2 was rapidly injected to 3 MP. Subsequently, the temperature of the experiment was increased to 277.15 K, and the replacement experiment was started. 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), gas samples were collected from the reactor, and the contents of the components in the gas sample after the reaction were measured by a gas chromatograph, and the CH4 replacement rate and the CO2 storage rate were calculated. The final CH4 replacement rate and the CO2 storage rate were 51.07% and 30.66%, respectively, as shown in Table 1. Compared with Comparative Example 1, the replacement speed was faster, and the CH4 replacement rate and the CO2 storage rate were increased by 64.69% and 43.00%, respectively. The relevant data are shown in Table 1 and FIG. 1. Figure 3 and Figure 4

[0051] Example Four

[0052] Charging: Four kinds of 1250 mesh clay (montmorillonite, illite, kaolinite and chlorite) and five kinds of silica sand (40-70 mesh, 70-120 mesh, 100-200 mesh, 325 mesh and 600 mesh) were mixed uniformly 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, the above-mentioned initial solution was introduced into the sediment (90 g) and mixed uniformly, and then the treated sediment was filled into the reaction kettle and compacted;

[0053] Natural gas hydrate synthesis: methane was introduced, the experimental pressure was 8.5 MPa, the experimental temperature was 274.15 K, and the sudden drop of the pressure of the reactor indicated that the hydrate began to generate. When the temperature and pressure of the reactor remained constant for a long time (more than 5 hours), it was considered that the CH4 hydrate generation experiment was completed, the hydrate saturation was 52.35%, and the amount of methane hydrate was calculated to be 0.11261 mol;

[0054] ​Carbon dioxide replacement: After the synthesis of CH4 hydrate was completed, the temperature of the experiment was reduced to 268.15 K, at which temperature CH4 hydrate has the best self-preservation effect. After the temperature of the reactor was stabilized, CH4 was released, and pre-cooled CO2 was rapidly injected to 3 MP. Subsequently, the temperature of the experiment was increased to 277.15 K, and the replacement experiment was started. 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), gas samples were collected from the reactor, and the contents of the components in the gas sample after the reaction were measured by a gas chromatograph, and the CH4 replacement rate and the CO2 storage rate were calculated. The final CH4 replacement rate and the CO2 storage rate were 49.45% and 29.36%, respectively, as shown in Table 1. Compared with Comparative Example 1, the replacement speed was faster, and the CH4 replacement rate and the CO2 storage rate were increased by 59.46% and 36.94%, respectively. The relevant data are shown in Table 1 and FIG. 1. Figure 3 and Figure 4

[0055] Example Five

[0056] Charging: Four kinds of 1250 mesh clay (montmorillonite, illite, kaolinite and chlorite) and five kinds of silica sand (40-70 mesh, 70-120 mesh, 100-200 mesh, 325 mesh and 600 mesh) were mixed uniformly 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, the above initial solution was introduced into the sediment (90 g) and mixed uniformly, and then the treated sediment was filled into the reaction kettle and compacted;

[0057] Natural gas hydrate synthesis: methane was introduced, the experimental pressure was 8.5 MPa, the experimental temperature was 274.15 K, and the sudden drop of the pressure of the reactor indicated that the hydrate began to generate. When the temperature and pressure of the reactor remained constant for a long time (more than 5 hours), it was considered that the CH4 hydrate generation experiment was completed, the hydrate saturation was 53.11%, and the amount of methane hydrate was calculated to be 0.11425 mol;

[0058] ​Carbon dioxide replacement: After the synthesis of CH4 hydrate was completed, the temperature of the experiment was reduced to 268.15 K, at which temperature CH4 hydrate has the best self-preservation effect. After the temperature of the reactor was stabilized, CH4 was released, and pre-cooled CO2 was rapidly injected to 3 MP. Subsequently, the temperature of the experiment was increased to 277.15 K, and the replacement experiment was started. 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), gas samples were collected from the reactor, and the content of each component in the gas sample after the reaction was completed was measured by a gas chromatograph, and the CH4 replacement rate and the CO2 storage rate were calculated. The final CH4 replacement rate and CO2 storage rate were 48.45% and 28.71%, respectively, as shown in Table 1. Compared with Comparative Example 1, the replacement speed was faster, and the CH4 replacement rate and the CO2 storage rate were increased by 56.24% and 33.91%, respectively. The relevant data are shown in Figure 3 and Figure 4

[0059] Table 1 Replacement rate and storage rate under different conditions

[0060]

[0061] The above only describes the preferred embodiments of the present application, and any equivalent changes and modifications made within the scope of the patent application of the present application shall be included in the scope of the present application.​

Claims

1. A method for exploiting natural gas hydrate by using organic matter to promote carbon dioxide replacement, characterized in that, The organic matter is one or more of lignin, fulvic acid and humic acid, and the organic matter can promote the replacement of natural gas hydrate by carbon dioxide; The method for promoting the replacement of natural gas hydrate by carbon dioxide by using organic matter comprises the following steps: (1) adding: four kinds of 1250 mesh clay and five kinds of silica sand are mixed uniformly according to a mass ratio of 1.5:0.9:0.3:0.3:1:1:2:1:1, the porosity and the average particle size of the mixed minerals are 45.91% and 6.767 μm respectively, the initial liquid of the reaction system is 14 g of a solution containing 3.5 wt% NaCl and organic matter, the reaction system is configured, the initial solution is introduced into 90 g of the mixed minerals and mixed uniformly, and then the treated sediment is filled into a reaction kettle and compacted; (2) synthesizing natural gas hydrate: methane gas is introduced, the experimental pressure is 8.5 MPa, the experimental temperature is 274.15 K, the sudden drop of the pressure of the reactor indicates that the hydrate starts to generate, when the temperature and the pressure of the reactor remain constant for a long time, it is considered that the CH4 hydrate generation experiment is completed, and the hydrate saturation degree ranges from 20% to 60%; (3) replacing carbon dioxide: after the CH4 hydrate synthesis is completed, the experimental temperature is reduced to 268.15 K, at the temperature, the CH4 hydrate has the best self-preservation effect; after the temperature of the reactor is stabilized, CH4 is released, and pre-cooled CO2 is rapidly injected to a required value, then the experimental temperature is increased to an expected value, the replacement experiment is started, then gas samples are collected from the reactor, the content of each component in the gas sample after the reaction is measured by using a gas chromatograph, and the CH4 replacement rate and the CO2 storage rate are calculated. The four kinds of 1250 mesh clay are montmorillonite, illite, kaolinite and chlorite respectively, and the five kinds of silica sand are 40-70 mesh, 70-120 mesh, 100-200 mesh, 325 mesh and 600 mesh respectively.

2. The method for natural gas hydrate production by using organic matter to promote carbon dioxide replacement according to claim 1, characterized in that, The organic matter is introduced into the reservoir of natural gas hydrate, and the concentration of the organic matter in the reservoir reaches 1.0 wt%-10.0 wt% before the replacement of carbon dioxide.

3. The method for natural gas hydrate production with organic matter promoting carbon dioxide replacement according to claim 1, characterized in that, In the replacement process of the natural gas hydrate in step (3), the pressure of the reaction kettle is maintained in the range from 2.5 MPa to 3.5 MPa by injecting CO2, and the expected value of the experimental temperature increase is from 268.15 K to 277.15 K.

4. The method for natural gas hydrate production with organic matter promoting carbon dioxide replacement according to claim 1, characterized in that, The concentration range of the organic matter in step (1) is 1.0 wt%-10.0 wt%.

5. The method for natural gas hydrate production with organic matter promoting carbon dioxide replacement according to claim 1, characterized in that, The replacement time of the natural gas hydrate in step (3) is 120 hours.

6. The method for natural gas hydrate production with organic matter promoting carbon dioxide replacement according to claim 1, characterized in that, The natural gas comprises one or more of methane, ethane and propane.

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