Hydrate decomposition kinetic model establishment method
Through single-stage buck decomposition experiments and kinetic accelerator fitting based on Kim-Bishnoi model, a methane hydrate decomposition kinetic model was established, which solved the problem of insufficient model construction in the prior art and improved the prediction accuracy of methane hydrate decomposition time and gas yield.
Patent Information
- Application Number
- CN202510773680.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-11
- Publication Date
- 2025-09-02
Smart Images
Figure CN120581082A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of hydrate decomposition kinetics research, and in particular to a method for establishing a hydrate decomposition kinetics model. Background Art
[0002] Natural gas hydrates, commonly known as "solid gas" or "gas ice," are mostly formed in terrestrial permafrost zones and oceans. They are ice-like non-stoichiometric cage compounds formed by water molecules and natural gas molecules in a certain proportion under high pressure and low temperature conditions. Methane molecules account for a considerable proportion of the natural gas molecules that make up hydrates. Research and exploration of the decomposition laws of methane hydrates have a good reference value for the actual exploitation of natural gas hydrates. Compared with traditional petroleum energy, hydrates are particularly prominent in terms of rich reserves, wide distribution, and low pollution. Studying the decomposition characteristics of hydrates and achieving efficient hydrate exploitation are of great practical significance.
[0003] Currently, methods such as reducing pressure, thermal injection stimulation, injecting inhibitors, carbon dioxide gas replacement, and combined actions can achieve hydrate recovery. Their essence is to change the temperature, pressure, or chemical conditions of the hydrate, causing it to break away from the stable crystalline state and enter the unstable zone, thereby achieving the purpose of decomposition and gas production. Studies have also found that alcohols such as methanol and ethylene glycol, inorganic salts such as sodium chloride, and macromolecular polymers have a certain strengthening and promoting effect on the decomposition of methane hydrate. Indoor experiments can more accurately reflect the effect of kinetic promoters (due to their different effects on the hydrate formation and decomposition processes, they can also be called thermodynamic inhibitors during the hydrate formation process). Experiments on the decomposition of natural gas hydrates under reduced pressure and under the conditions of injecting promoters have been carried out. Relatively speaking, the currently known decomposition experiments of methane hydrates under reduced pressure under the action of kinetic promoters are relatively few, and the model construction work in this area has also been carried out relatively little. Therefore, the present invention proposes a method for establishing a hydrate decomposition kinetic model to address the problems existing in the prior art. Summary of the Invention
[0004] In response to the above problems, the present invention aims to propose a method for establishing a hydrate decomposition kinetic model. The method is based on the Kim-Bishnoi model and a single-stage decompression decomposition experiment of methane hydrate, ignoring the effects of heat and mass transfer during the decomposition of hydrates. The decomposition kinetic model of methane hydrate is derived, and the methane hydrate decomposition time t and the amount of methane molecules present in the methane hydrate at that time n are obtained. H relationship;
[0005] By optimizing the methane hydrate decomposition model, the optimal value of the hydrate particle size D0 was determined, and the relationship between the methane hydrate decomposition time t and the methane molecules n in the hydrate was improved. H The relationship between the content and the hydrate content has a certain reference significance for predicting the decomposition time of hydrate and the amount of methane gas produced by decomposition;
[0006] Based on the experimental results of methane hydrate decomposition in a kinetic accelerator (taking 20% ethylene glycol as an example), the established model was fitted and modified to determine the optimal value of the parameter B related to the type and mass concentration of the injected kinetic accelerator. This further improved the relationship between the decomposition time t of methane hydrate and the amount of methane molecules n present in the methane hydrate at that moment. H The relationship between the two is given, and a general method for establishing the decomposition model of hydrates under different types and concentrations of kinetic promoters and pressure reduction is given.
[0007] To achieve the purpose of the present invention, the present invention is implemented by the following technical solution: a method for establishing a hydrate decomposition kinetic model, comprising the following steps:
[0008] Step 1: Experimental design and data collection: Synthesize methane hydrate in a high-pressure reactor. Through conventional pressure reduction and injection of kinetic accelerator experiments, record pressure, temperature, and gas production data in real time, and calculate the corresponding relationship between the amount of undecomposed methane and time to provide a data basis for model construction.
[0009] Step 2: Build a basic model. Based on the Kim-Bishnoi kinetic equation, establish a decomposition rate equation. Combined with the expressions of hydrate particle surface area, decomposition rate constant, and real-time pressure, derive an analytical solution to the relationship, covering the boundary conditions of complete and partial decomposition.
[0010] Step 3: Decomposition promotion correction: introduce the correction factor B into the decomposition rate constant, determine the quantitative relationship between B and the type and concentration of the promoter through experimental data fitting, establish a correction model, and quantify the enhancement effect of the promoter on the decomposition rate;
[0011] Step 4: Model verification: Analyze the sensitivity of the pressure reduction gradient and accelerator concentration based on the modified model and select the optimal mining parameters.
[0012] A further improvement is that the decomposition experiment of methane hydrate under normal depressurization conditions in step 1 includes the following steps:
[0013] S1: Clean the autoclave. Repeat the autoclave with distilled water for 3 times to remove any remaining chemical reagents from the previous experiment.
[0014] S2: Displacement gas: Use high-purity methane gas sample to repeatedly displace the air in the high-pressure reactor twice to ensure that the composition of the gas in the reactor is the same as the prepared gas to the greatest extent possible;
[0015] S3: Inject water to cool down. Pour 160 mL of distilled water into the autoclave and adjust the temperature to 4°C using a constant temperature water bath.
[0016] S4: Injecting high-purity methane gas; injecting high-purity methane gas into the reactor. After the pressure in the reactor reaches 15 MPa, stop injecting methane gas and turn on the stirring device. Set the stirring rate to 200 r / min to accelerate the formation of methane hydrate in the reactor. When the pressure in the reactor remains stable (observe for 2 hours), it means that no new hydrate is generated.
[0017] S5: Depressurization. When the reactor pressure remains constant (higher than the equilibrium pressure of the hydrate at that temperature), a depressurization mining simulation experiment can be carried out. Before the experiment, the temperature and pressure data at a certain moment are recorded, and the simulated mining pressure is set. When no more gas is produced, the hydrate decomposition reaction is considered to be complete.
[0018] S6: Data Collection. The temperature and pressure changes in the reactor during the entire experiment are fully recorded using the data collection system. After the experiment is completed, the data is saved and the reactor is cleaned.
[0019] A further improvement is that the methane hydrate decomposition experiment under the condition of injecting a kinetic promoter in step 1 includes the following steps:
[0020] S1: Clean the autoclave. Repeat the autoclave with distilled water for 3 times to remove any remaining chemical reagents from the previous experiment.
[0021] S2: Displacement gas: Use high-purity methane gas sample to repeatedly displace the air in the high-pressure reactor twice to ensure that the composition of the gas in the reactor is the same as the prepared gas to the greatest extent possible;
[0022] S3: Inject water to cool down. Pour 160 mL of distilled water into the autoclave and adjust the temperature to 4°C using a constant temperature water bath.
[0023] S4: Injecting high-purity methane gas; injecting high-purity methane gas into the reactor. After the pressure in the reactor reaches 15 MPa, stop injecting methane gas and turn on the stirring device. Set the stirring rate to 200 r / min to accelerate the formation of methane hydrate in the reactor. When the pressure in the reactor remains stable (observe for 2 hours), it means that no new hydrate is generated.
[0024] S5: Pressure reduction and injection. After the hydrate is completely formed, the pressure in the reactor is reduced to the specified simulated production pressure. The prepared decomposition agent solution is injected into the high-pressure reactor through a horizontal flow pump at an injection rate of 8 mL·min-1 until no more gas is produced. The hydrate decomposition reaction is considered to be complete.
[0025] S6: Data collection. The changes in temperature and pressure in the reactor during the entire experiment are fully recorded using the data collection system. After the experiment is completed, the data is saved and the reactor is cleaned.
[0026] A further improvement is that the methane amount calculation formula in step 1 is:
[0027]
[0028] Where q is the volume of methane gas produced, n G is the number of moles of methane gas produced, n G / n0 is the ratio of the amount of methane molecules decomposed to the amount of methane molecules in the initial hydrate.
[0029] A further improvement is that the chemical expressions of the formation and decomposition processes of methane hydrate in step 2 are:
[0030]
[0031] Where n is the water index of the hydrate. In the decomposition experiment, it is assumed that the hydrates generated in the high-pressure reactor are all SI type, so the value of n is 5.75.
[0032] A further improvement is that the Kim-Bishnoi kinetic equation in step 2 is:
[0033]
[0034] Where n H is the amount of methane molecules in the hydrate at time t, in mol, t is the reaction time, in s, dn H / dt is the decomposition rate of hydrate, in mol / s, K d is the decomposition rate constant of water and matter, in mol / (m 2 ·Pa·s). A s is the total surface area of hydrate particles, in m 2 ,,P e is the three-phase equilibrium pressure of hydrate, in MPa, P (t) is the pressure in the reactor at time t, in MPa.
[0035] A further improvement is that the modified hydrate decomposition intrinsic rate constant in step 4 is
[0036]
[0037] A further improvement is that the modified hydrate decomposition rate constant in step 4 is
[0038] Where R is the ideal gas constant, 8.314 J / (mol·K), T is the temperature in the reactor during the experiment, in K, and ΔE is the activation energy for the decomposition of methane hydrate, in J / mol.
[0039] The present invention has the following beneficial effects: Based on the Kim-Bishnoi model and a single-stage decompression decomposition experiment of methane hydrate, the present invention neglects the influence of heat transfer and mass transfer during the decomposition of hydrate by decompression, derives a decomposition kinetic model of methane hydrate, and obtains the relationship between the methane hydrate decomposition time t and the amount of methane molecules nH present in the methane hydrate at that time;
[0040] By optimizing the methane hydrate decomposition model, the optimal value of the hydrate particle size D0 was determined, and the relationship between the methane hydrate decomposition time t and the methane molecules n in the hydrate was improved. H The relationship between the content and the hydrate content has a certain reference significance for predicting the decomposition time of hydrate and the amount of methane gas produced by decomposition;
[0041] Based on the experimental results of methane hydrate decomposition in a kinetic accelerator (taking 20% ethylene glycol as an example), the established model was fitted and modified to determine the optimal value of the parameter B related to the type and mass concentration of the injected kinetic accelerator. This further improved the relationship between the decomposition time t of methane hydrate and the amount of methane molecules n present in the methane hydrate at that moment. H The relationship between the two is given, and a general method for establishing the decomposition model of hydrates under different types and concentrations of kinetic promoters and pressure reduction is given. BRIEF DESCRIPTION OF THE DRAWINGS
[0042] Figure 1 is a flow chart of the steps of the present invention;
[0043] Figure 2 This is a flow chart of the experimental steps for decomposing methane hydrate under normal depressurization conditions in Example 1 of the present invention;
[0044] Figure 3 This is a flow chart of the experimental steps for decomposing methane hydrate under the condition of injecting a kinetic promoter in Example 2 of the present invention. DETAILED DESCRIPTION
[0045] In order to deepen the understanding of the present invention, the present invention will be further described in detail below with reference to the examples. The examples are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.
[0046] Example 1
[0047] according to Figure 1 、 Figure 2 As shown, this embodiment provides a method for establishing a hydrate decomposition kinetic model, comprising the following steps:
[0048] Step 1: Experimental design and data collection: synthesize methane hydrate or gas hydrates such as carbon dioxide in a high-pressure reactor. Through ordinary pressure reduction and injection of kinetic promoters, record the pressure, temperature and gas production data in real time, calculate the corresponding relationship between the amount of undecomposed methane and time, and provide a data basis for model construction; by precisely controlling the temperature, pressure and kinetic promoter injection conditions in the high-pressure reactor, simulate the pressure reduction decomposition environment of the real hydrate reservoir, and obtain the decomposition time (t) and the amount of undecomposed methane (n H )’s dynamic relationship data;
[0049] The decomposition experiment of methane hydrate under normal depressurization conditions includes the following steps:
[0050] S1: Clean the autoclave. Repeat the autoclave with distilled water for 3 times to remove any remaining chemical reagents from the previous experiment.
[0051] S2: Displacement gas: Use high-purity methane gas sample to repeatedly displace the air in the high-pressure reactor twice to ensure that the composition of the gas in the reactor is the same as the prepared gas to the greatest extent possible;
[0052] S3: Inject water to cool down. Pour 160 mL of distilled water into the autoclave and adjust the temperature to 4°C using a constant temperature water bath.
[0053] S4: Injecting high-purity methane gas; injecting high-purity methane gas into the reactor. After the pressure in the reactor reaches 15 MPa, stop injecting methane gas and turn on the stirring device. Set the stirring rate to 200 r / min to accelerate the formation of methane hydrate in the reactor. When the pressure in the reactor remains stable (observe for 2 hours), it means that no new hydrate is generated.
[0054] S5: Depressurization. When the reactor pressure remains constant (higher than the equilibrium pressure of the hydrate at that temperature), a depressurization mining simulation experiment can be carried out. Before the experiment, the temperature and pressure data at a certain moment are recorded, and the simulated mining pressure is set. When no more gas is produced, the hydrate decomposition reaction is considered to be complete.
[0055] S6: Data Collection. The temperature and pressure changes in the reactor during the entire experiment are fully recorded using a data collection system. After the experiment is completed, the data is saved and the reactor is cleaned.
[0056] Using a hydrate formation and decomposition experimental device, the decomposition process of methane hydrate under the action of a kinetic promoter (taking 20% ethylene glycol solution as an example) was studied. By analyzing the effect of whether or not the kinetic promoter solution was injected on the decomposition rate of methane hydrate under decompression, the decomposition mechanism of methane hydrate under the action of a hydrate kinetic promoter was revealed.
[0057] The formula for calculating the amount of methane is:
[0058]
[0059] Where q is the volume of methane gas produced, n G is the number of moles of methane gas produced, n G / n0 is the ratio of the amount of methane molecules decomposed to the amount of methane molecules in the initial hydrate;
[0060] The reactor volume is 200 mL, the pressure sensor accuracy is ±0.01 MPa, and the temperature control method is PID temperature control.
[0061] Step 2: Build a basic model. Based on the Kim-Bishnoi kinetic equation, establish a decomposition rate equation. Combined with the expressions of hydrate particle surface area, decomposition rate constant, and real-time pressure, derive an analytical solution to the relationship, covering the boundary conditions of complete and partial decomposition.
[0062] The chemical expressions of the formation and decomposition processes of methane hydrate are:
[0063]
[0064] Where n is the water index of the hydrate. In the decomposition experiment, it is assumed that the hydrates generated in the high-pressure reactor are all SI type, so the value of n is 5.75;
[0065] The Kim-Bishnoi kinetic equation is:
[0066]
[0067] Where n H is the amount of methane molecules in the hydrate at time t, in mol, t is the reaction time, in s, dn H / dt is the decomposition rate of hydrate, in mol / s, K d is the decomposition rate constant of water and matter, in mol / (m 2·Pa·s). As is the total surface area of hydrate particles, in m 2 , P e is the three-phase equilibrium pressure of hydrate, in MPa, P (t) is the pressure in the reactor at time t, in MPa, and is expressed by P (t) The expression correlates the gas production and the pressure change in the kettle in real time, enhancing the model's adaptability to actual working conditions;
[0068] Step 3: Decomposition promotion correction: The least squares method is used to calculate the time error between the experimental data and the model prediction, and the hydrate particle size is optimized in the range of 5-11 μm to determine the optimal value. Based on the particle size optimization result D0, a correction factor B is introduced into the decomposition rate constant. The quantitative relationship between B and the type and concentration of the accelerator is determined by fitting the experimental data. A correction model is established to quantify the enhancing effect of the accelerator on the decomposition rate.
[0069] The revised model is
[0070] K=K0*(1+B*C)
[0071] B is the accelerator enhancement coefficient and C is the concentration.
[0072] Key parameters such as hydrate particle size (D0) and activation energy (ΔE) are incorporated into the equation to provide an interface for subsequent optimization. H When / n0 takes a fixed value, the time corresponding to the experimental data and the predicted data is t Sn and t Mn The error S is expressed as:
[0073]
[0074] The error S is calculated for different values of hydrate particle size D0, and the results are shown in Table 1;
[0075] Table 1 Error S under different values of D0
[0076]
[0077] The corrected intrinsic rate constant for hydrate decomposition is
[0078]
[0079] The corrected hydrate decomposition rate constant is
[0080]
[0081] Where R is the ideal gas constant, 8.314 J / (mol·K), T is the temperature in the reactor during the experiment, in K, and ΔE is the activation energy for the decomposition of methane hydrate, in J / mol.
[0082] The particle swarm optimization algorithm was used to optimize D0. The objective function was the root mean square error (RMSE < 5%) between the experimental data and the simulation results. The optimization range of D0 was 20-100 μm, preferably 50 μm. The parameter B was related to the type of kinetic promoter: tetrahydrofuran (B = 0.15-0.25) and SDS surfactant (B = 0.30-0.45).
[0083] Step 4: Model verification. Based on the particle size optimization results of Step 3, a decomposition promoter correction term was further introduced. The sensitivity of the pressure reduction gradient to the promoter concentration was analyzed based on the modified model, and the optimal mining parameters were selected. After optimization, D0 = 50 μm, which reduced the model prediction error (S) from 320.6 in the traditional model to 36.0, a decrease of 88.7%. The optimized D0 reflects the microstructural characteristics of actual hydrate particles (such as the particle size distribution in porous media), improving the explanatory power of the model.
[0084] Example 2
[0085] according to Figure 1 、 Figure 3 As shown, this embodiment provides a method for establishing a hydrate decomposition kinetic model, comprising the following steps:
[0086] Step 1: Experimental design and data collection. Methane hydrate or carbon dioxide hydrate is synthesized in a high-pressure reactor. Through ordinary pressure reduction and injection of kinetic promoters, the pressure, temperature and gas production data are recorded in real time. The corresponding relationship between the amount of undecomposed methane and time is calculated to provide a data basis for model construction. By precisely controlling the temperature, pressure and kinetic promoter injection conditions in the high-pressure reactor at 4°C and 15MPa, the pressure reduction decomposition environment of the real hydrate reservoir is simulated to obtain the decomposition time (t) and the amount of undecomposed methane (n H )’s dynamic relationship data;
[0087] The methane hydrate decomposition experiment under the conditions of injection of kinetic accelerators includes the following steps:
[0088] S1: Clean the autoclave. Repeat the autoclave with distilled water for 3 times to remove any remaining chemical reagents from the previous experiment.
[0089] S2: Displacement gas: Use high-purity methane gas sample to repeatedly displace the air in the high-pressure reactor twice to ensure that the composition of the gas in the reactor is the same as the prepared gas to the greatest extent possible;
[0090] S3: Inject water to cool down. Pour 160 mL of distilled water into the autoclave and adjust the temperature to 4°C using a constant temperature water bath.
[0091] S4: Injecting high-purity methane gas; injecting high-purity methane gas into the reactor. After the pressure in the reactor reaches 15 MPa, stop injecting methane gas and turn on the stirring device. Set the stirring rate to 200 r / min to accelerate the formation of methane hydrate in the reactor. When the pressure in the reactor remains stable (observe for 2 hours), it means that no new hydrate is generated.
[0092] S5: Pressure reduction and injection. After the hydrate is completely formed, the pressure in the reactor is reduced to the specified simulated production pressure. The prepared decomposition agent solution is injected into the high-pressure reactor through a horizontal flow pump at an injection rate of 8 mL·min-1 until no more gas is produced. The hydrate decomposition reaction is considered to be complete.
[0093] S6: Data collection: The temperature and pressure changes in the reactor during the entire experiment are fully recorded using a data collection system. After the experiment is completed, the data is saved and the reactor is cleaned.
[0094] Using a hydrate formation and decomposition experimental device, the decomposition process of methane hydrate under the action of a kinetic promoter (taking 20% ethylene glycol solution as an example) was studied. By analyzing the effect of whether or not the kinetic promoter solution was injected on the decomposition rate of methane hydrate under decompression, the decomposition mechanism of methane hydrate under the action of a hydrate kinetic promoter was revealed.
[0095] After the injection of the kinetic promoter (taking 20% ethylene glycol as an example), the decomposition curve has good consistency. The injection of the kinetic promoter has a certain promoting effect on the decomposition of hydrates, revealing the law that the promoter enhances the decomposition rate.
[0096] The formula for calculating the amount of methane is:
[0097]
[0098] Where q is the volume of methane gas produced, n G is the number of moles of methane gas produced, n G / n0 is the ratio of the amount of methane molecules decomposed to the amount of methane molecules in the initial hydrate.
[0099] Step 2: Build a basic model. Based on the Kim-Bishnoi kinetic equation, establish a decomposition rate equation. Combined with the expressions of hydrate particle surface area, decomposition rate constant, and real-time pressure, derive an analytical solution to the relationship, covering the boundary conditions of complete and partial decomposition.
[0100] The chemical expressions of the formation and decomposition processes of methane hydrate are:
[0101]
[0102] Where n is the water index of the hydrate. In the decomposition experiment, it is assumed that the hydrates generated in the high-pressure reactor are all SI type, so the value of n is 5.75;
[0103] The Kim-Bishnoi kinetic equation is:
[0104]
[0105] Where n H is the amount of methane molecules in the hydrate at time t, in mol, t is the reaction time, in s, dn H / dt is the decomposition rate of hydrate, in mol / s, K d is the decomposition rate constant of water and matter, in mol / (m 2 ·Pa·s). As is the total surface area of hydrate particles, in m2, Pe is the three-phase equilibrium pressure of hydrate, in MPa, P (t) is the pressure in the reactor at time t, in MPa, and is expressed by P (t) The expression correlates the gas production and the pressure change in the kettle in real time, enhancing the adaptability of the model to actual working conditions.
[0106] Step 3: Decomposition promotion correction: The least squares method is used to calculate the time error between the experimental data and the model prediction, and the hydrate particle size is optimized in the range of 5-11 μm to determine the optimal value. Based on the particle size optimization result D0, a correction factor B is introduced into the decomposition rate constant. The quantitative relationship between B and the type and concentration of the accelerator is determined by fitting the experimental data. A correction model is established to quantify the enhancing effect of the accelerator on the decomposition rate.
[0107] The revised model is
[0108] K=K0*(1+B*C)
[0109] B is the accelerator enhancement coefficient, and C is the concentration;
[0110] Key parameters such as hydrate particle size (D0) and activation energy (ΔE) are incorporated into the equation to provide an interface for subsequent optimization. H When / n0 takes a fixed value, the time corresponding to the experimental data and the predicted data is t Sn and t Mn The error S is expressed as:
[0111]
[0112] The error S is calculated for different values of hydrate particle size D0, and the results are shown in Table 1;
[0113] Table 1 Error S under different values of D0
[0114]
[0115] The corrected intrinsic rate constant for hydrate decomposition is
[0116]
[0117] The corrected hydrate decomposition rate constant is
[0118]
[0119] Where R is the ideal gas constant, 8.314 J / (mol·K), T is the temperature in the reactor during the experiment, in K, and ΔE is the activation energy for the decomposition of methane hydrate, in J / mol.
[0120] Step 4: Model verification. Based on the modified model, the sensitivity of the pressure reduction gradient to the accelerator concentration was analyzed and the optimal mining parameters were selected. After optimization, D0 = 9.38 μm, which reduced the model prediction error (S) from 320.6 in the traditional model to 36.0, a decrease of 88.7%. The optimized D0 reflects the microstructural characteristics of actual hydrate particles (such as the particle size distribution in porous media), improving the explanatory power of the model.
[0121] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.
Claims
1. A method for establishing a hydrate decomposition kinetic model, comprising the following steps: Step 1: Experimental design and data collection: Synthesize methane hydrate in a high-pressure reactor. Through conventional pressure reduction and injection of kinetic accelerator experiments, record pressure, temperature, and gas production data in real time, and calculate the corresponding relationship between the amount of undecomposed methane and time to provide a data basis for model construction. Step 2: Build a basic model. Based on the Kim-Bishnoi kinetic equation, establish a decomposition rate equation. Combined with the expressions of hydrate particle surface area, decomposition rate constant, and real-time pressure, derive an analytical solution to the relationship, covering the boundary conditions of complete and partial decomposition. Step 3: Decomposition promotion correction: introduce the correction factor B into the decomposition rate constant, determine the quantitative relationship between B and the type and concentration of the promoter through experimental data fitting, establish a correction model, and quantify the enhancement effect of the promoter on the decomposition rate; Step 4: Model verification: Analyze the sensitivity of the pressure reduction gradient and accelerator concentration based on the modified model and select the optimal mining parameters.
2. The method for establishing a hydrate decomposition kinetic model according to claim 1, wherein: Decomposition experiment of methane hydrate under normal pressure reduction conditions in step 1 The following steps are involved: S1: Clean the autoclave. Repeat the autoclave with distilled water for 3 times to remove any remaining chemical reagents from the previous experiment. S2: Displacement gas: Use high-purity methane gas sample to repeatedly displace the air in the high-pressure reactor twice to ensure that the composition of the gas in the reactor is the same as the prepared gas to the greatest extent possible; S3: Inject water to cool down. Pour 160 mL of distilled water into the autoclave and adjust the temperature to 4°C using a constant temperature water bath. S4: Injecting high-purity methane gas; injecting high-purity methane gas into the reactor. After the pressure in the reactor reaches 15 MPa, stop injecting methane gas and turn on the stirring device. Set the stirring rate to 200 r / min to accelerate the formation of methane hydrate in the reactor. When the pressure in the reactor remains stable (observe for 2 hours), it means that no new hydrate is generated. S5: Depressurization. When the reactor pressure remains constant (higher than the equilibrium pressure of the hydrate at that temperature), a depressurization mining simulation experiment can be carried out. Before the experiment, the temperature and pressure data at a certain moment are recorded, and the simulated mining pressure is set. When no more gas is produced, the hydrate decomposition reaction is considered to be complete. S6: Data Collection. The temperature and pressure changes in the reactor during the entire experiment are fully recorded using the data collection system. After the experiment is completed, the data is saved and the reactor is cleaned.
3. The method for establishing a hydrate decomposition kinetic model according to claim 1, wherein: Decomposition experiment of methane hydrate under the condition of injecting kinetic promoter in step 1 The following steps are involved: S1: Clean the autoclave. Repeat the autoclave with distilled water for 3 times to remove any remaining chemical reagents from the previous experiment. S2: Displacement gas: Use high-purity methane gas sample to repeatedly displace the air in the high-pressure reactor twice to ensure that the composition of the gas in the reactor is the same as the prepared gas to the greatest extent possible; S3: Inject water to cool down. Pour 160 mL of distilled water into the autoclave and adjust the temperature to 4°C using a constant temperature water bath. S4: Injecting high-purity methane gas; injecting high-purity methane gas into the reactor. After the pressure in the reactor reaches 15 MPa, stop injecting methane gas and turn on the stirring device. Set the stirring rate to 200 r / min to accelerate the formation of methane hydrate in the reactor. When the pressure in the reactor remains stable (observe for 2 hours), it means that no new hydrate is generated. S5: Pressure reduction and injection. After the hydrate is completely formed, the pressure in the reactor is reduced to the specified simulated production pressure. The prepared decomposition agent solution is injected into the high-pressure reactor through a horizontal flow pump at an injection rate of 8 mL·min-1 until no more gas is produced. The hydrate decomposition reaction is considered to be complete. S6: Data collection. The changes in temperature and pressure in the reactor during the entire experiment are fully recorded using the data collection system. After the experiment is completed, the data is saved and the reactor is cleaned.
4. The method for establishing a hydrate decomposition kinetic model according to claim 1, wherein: The methane amount calculation formula in step 1 is: Where q is the volume of methane gas produced, n G is the number of moles of methane gas produced, n G / n0 is the ratio of the amount of methane molecules decomposed to the amount of methane molecules in the initial hydrate.
5. The method for establishing a hydrate decomposition kinetic model according to claim 1, wherein: The chemical expressions of the formation and decomposition processes of methane hydrate in step 2 are: Where n is the water index of the hydrate. In the decomposition experiment, it is assumed that the hydrates generated in the high-pressure reactor are all SI type, so the value of n is 5.
75.
6. The method for establishing a hydrate decomposition kinetic model according to claim 1, wherein: The Kim-Bishnoi kinetic equation in step 2 is: Where n H is the amount of methane molecules in the hydrate at time t, in mol, t is the reaction time, in s, dn H / dt is the decomposition rate of hydrate, in mol / s, K d is the decomposition rate constant of water and matter, in mol / (m 2 ·Pa·s). A s is the total surface area of hydrate particles, in m 2 ,,P e is the three-phase equilibrium pressure of hydrate, in MPa, P (t) is the pressure in the reactor at time t, in MPa.
7. The method for establishing a hydrate decomposition kinetic model according to claim 1, wherein: The corrected hydrate decomposition intrinsic rate constant in step 4 is:
8. The method for establishing a hydrate decomposition kinetic model according to claim 1, wherein: The corrected hydrate decomposition rate constant in step 4 is: Where R is the ideal gas constant, 8.314 J / (mol·K), T is the temperature in the reactor during the experiment, in K, and ΔE is the activation energy for the decomposition of methane hydrate, in J / mol.