A method for predicting the rate of hydrate decomposition in a water-in-oil emulsion system

Abstract

The application relates to a method for predicting hydrate decomposition rate in a water-in-oil emulsion system. By measuring parameters such as temperature and pressure in the hydrate decomposition stage and bringing them into formula (1) to formula (3), the hydrate decomposition rate in the water-in-oil emulsion system can be effectively predicted. The method has important significance for the research and industrial popularization and application of hydrate solid storage, hydrate solid storage natural gas technology, refrigeration, chemical separation and hydrate freezing blockage risk control in oil and gas pipeline.

Description

Technical Field

[0001] This article relates to, but is not limited to, the field of hydrates, and in particular to, but is not limited to, a method for calculating the decomposition rate of hydrates in water-in-oil emulsion systems. Background Technology

[0002] Gas hydrates are crystalline substances similar to ice, primarily non-stoichiometric complexes formed by water and guest molecules (small molecule gases such as methane, ethane, propane, carbon dioxide, and hydrogen sulfide) under high pressure and low temperature conditions. Because the water molecules in hydrates mainly form cages through hydrogen bonding, they are also called cage-type hydrates. Hydrate technology has wide applications in CO2 separation and capture, seawater desalination, and hydrogen storage. However, as oil and gas development extends into the deep sea, the harsh environment of the high pressure and low temperature at the seabed provides a natural breeding ground for hydrate formation. Furthermore, seabed resource extraction often involves the multiphase transportation of oil, gas, and water. Crude oil and water easily form relatively stable oil-water emulsions, and these emulsions are more prone to hydrate formation during deep-sea oil and gas pipeline transportation. This significantly increases the viscosity of the liquid phase, increases pipeline pressure drop, and thus increases the risk of hydrate blockage during oil and gas transportation, posing a significant threat to the normal operation of oil and gas pipelines. Therefore, studying the decomposition laws of hydrates in water-in-oil emulsions and being able to quantitatively calculate them is of great significance for guiding the safe transportation of oil and gas pipelines.

[0003] Furthermore, understanding the decomposition patterns of hydrates in water-in-oil emulsion systems is of great significance for expanding the application fields of hydrate technology. For example, in natural gas storage, hydrate technology utilizes gaseous hydrates for storage. This method offers numerous advantages for natural gas storage and transportation, such as high energy density, simple refrigeration technology, stable performance, and safe storage. It also allows for the effective regasification of gaseous hydrates for secondary use. Therefore, research on hydrate decomposition patterns is a crucial foundation for deepening the application of hydrate technology in various fields. Summary of the Invention

[0004] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0005] This application provides a method and apparatus for calculating the decomposition rate of hydrates in water-in-oil emulsion systems. This method enables quantitative calculation of the decomposition rate of hydrates in water-in-oil emulsion systems and is of great significance for research and industrial application in areas such as solid-state storage of natural gas with hydrates, refrigeration, chemical separation, and risk control of hydrate freezing in oil and gas pipelines.

[0006] This application provides a method for predicting the decomposition rate of hydrates in a water-in-oil emulsion system. The water-in-oil emulsion system comprises alkanes, an oil phase, and an aqueous phase (the water-in-oil emulsion is formed by mixing alkanes, an oil phase, and an aqueous phase, and may also contain an oil phase and an aqueous phase that do not form a water-in-oil emulsion). The hydrates are alkane hydrates; the alkanes are selected from C1 to C4 alkanes.

[0007] Including the following methods:

[0008] 1) In a closed reaction vessel, the pressure is adjusted to control the formation of hydrates from the mixture including the water-in-oil emulsion (the oil phase and water phase can be first formed into a water-in-oil emulsion, and then alkane gas is introduced into the system to form hydrates). After that, the pressure is adjusted to the decomposition pressure to decompose the hydrates. The temperature and pressure in the reaction vessel at different times from the start of hydrate formation to the end of hydrate decomposition are measured.

[0009] 2) The molar amount of gaseous alkanes in the reaction vessel at different times was obtained through phase equilibrium calculations;

[0010]

[0011] In the formula, n is the molar amount of gaseous alkanes; P is the pressure inside the reaction vessel, Pa; and V is the volume of the gas phase space inside the reaction vessel, m³. 3 Z is the compressibility factor of the alkane at temperature and pressure at time t, and R is the gas constant R = 8.314 J·mol⁻¹. -1 ·K -1 T is the temperature inside the reaction vessel, in K;

[0012] 3) Obtain the amount of alkane absorbed in the alkane hydrate;

[0013] n H,t =n0-n t ………………………………(2)

[0014] n0 is the amount of gas mixture in the gas phase space of the reaction vessel before the formation of alkane hydrates, in mol; t n represents the amount of gas mixture in the gas phase space of the reaction vessel at each time point from the end of the alkane hydrate formation stage to the time of complete decomposition of the alkane hydrate, expressed in mol. H,t The moles of alkanes in the alkane hydrate at each time point from the end of the alkane hydrate formation stage to the time of complete decomposition of the alkane hydrate, in mol;

[0015] 4) Substitute into formula (3) to calculate, and the hydrate decomposition rate of the water-in-oil emulsion system at time t can be obtained.

[0016]

[0017] In the formula, n H,t n represents the number of moles of alkanes in the hydrate at time t, in mol; H,t-1 t is the number of moles of alkane in the hydrate at time t-1, in mol; t is time, in s; e is the natural base; f is the fugacity of alkane at the corresponding temperature and pressure in the gas phase space, in MPa; f e ν is the gas-phase equilibrium fugacity under three-phase equilibrium conditions, in MPa;

[0018] The value of A is 5 × 10 -9 Up to 1×10 -6 The unit is mol·s -1 The value of B ranges from 550 to 900, and the unit is MPa. -1 ;

[0019] In one embodiment provided in this application, while adjusting the pressure to the initial pressure in step 1), the temperature of the reaction vessel is also adjusted (e.g., by a water bath). The adjusted temperature is the temperature of the system that can generate hydrates. The temperature measured in formula (1) is the temperature of the system. The temperature change trend (or specific value) of the system will change with the water bath temperature, but it will not be precisely controlled by the water bath temperature.

[0020] In the simulation method for the hydrate decomposition rate of the water-in-oil emulsion system provided in this application, the alkane is selected from any one or more of methane, ethane, and propane.

[0021] In the simulation method for the hydrate decomposition rate of the water-in-oil emulsion system provided in this application, the parameters A and B in formula (3) are obtained by the following method:

[0022] a) Determine the stirring rate of the reaction vessel, the initial pressure inside the reaction vessel, and the water content of the water-in-oil emulsion;

[0023] b) Add the water-in-oil emulsion system described in step 1) into the closed reaction vessel used to obtain parameters A and B to generate alkane hydrates;

[0024] c) Artificially set a decomposition pressure lower than the hydrate equilibrium pressure, and adjust the pressure inside the sealed, insulated reaction vessel used to obtain parameters A and B to the decomposition pressure, so that the alkane hydrate decomposes.

[0025] d) Obtain the number of moles of alkane in the hydrate at each moment under the decomposition pressure, and calculate the decomposition rate of the alkane hydrate at each moment; obtain the fugacity f of the alkane at the gas-space temperature and pressure, and the gas-phase equilibrium fugacity f under three-phase equilibrium conditions. e ;

[0026] e) Substitute the parameters obtained in step d) into formula (3) to obtain parameters A and B under the decomposition pressure;

[0027] In one embodiment provided in this application, the relationship between the equilibrium pressure of the hydrate, the decomposition pressure of the hydrate, and the initial pressure in step c) is as follows: decomposition pressure < equilibrium pressure < initial pressure. Based on this, parameters A and B can be used to calculate the decomposition rate at any decomposition pressure below the equilibrium pressure.

[0028] The equilibrium pressure can be calculated based on the Chen-Guo model, according to the following literature;

[0029] GJChen,TMGuo,A new approach to gas hydrate modeling,Chem.Eng.J.71(1998)145–151.

[0030] "Science and Technology of Gas Hydrates", Chen Guangjin, Sun Changyu, Ma Qinglan, 2nd Edition, pp. 50-55.

[0031] In the simulation method for the hydrate decomposition rate of the water-in-oil emulsion system provided in this application, when predicting the hydrate decomposition rate in the water-in-oil emulsion system:

[0032] The stirring rate of the reaction vessel is the same as the stirring rate used when obtaining parameters A and B;

[0033] In one embodiment provided in this application, the initial pressure inside the reaction vessel is the same as the initial pressure used when acquiring parameters A and B;

[0034] In one embodiment provided in this application, the water content of the water-in-oil emulsion in the water-in-oil emulsion system is the same as the water content of the water-in-oil emulsion in the water-in-oil emulsion system used when obtaining parameters A and B;

[0035] In one embodiment provided in this application, the gas phase composition used to obtain parameters A and B may be different from the gas phase composition used to calculate the hydrate decomposition rate of the water-in-oil emulsion system.

[0036] In the simulation method for the hydrate decomposition rate of the water-in-oil emulsion system provided in this application, the temperature and pressure in the reaction vessel are measured from the end of the hydrate formation to the end of the hydrate decomposition.

[0037] In one embodiment provided in this application, the compressibility factor of the alkane at a specific temperature and pressure in formula (1) is calculated using the SRK equation of state, etc.

[0038] SRK state equations:

[0039] Rewrite it in Z form and represent it using cubic state equations:

[0040] Z 3 -Z 2 +(ABB 2 Z-AB=0

[0041] in

[0042]

[0043]

[0044] Let: PP = -1 QQ = ABB 2 RR = -AB

[0045] For methane, the critical temperature Tc = 190.4 K; the critical pressure Pc = 4600 kPa; and the eccentricity factor w = 0.011. (If the gas is a mixture of various alkanes, the critical temperature, critical pressure, and eccentricity factor are calculated accordingly.) By obtaining the temperature P and pressure T at a specific moment, the compressibility factor Z can be obtained by solving the cubic equation of state.

[0046] The method for obtaining the fugacity corresponding to the gas phase space temperature and pressure in formula (3) is common knowledge in this field, and it is calculated through the following:

[0047] GJChen, TMGuo, A new approach to gas hydrate modeling, Chem.Eng.J.71(1998)145-151.

[0048] "Science and Technology of Gas Hydrates", Chen Guangjin, Sun Changyu, Ma Qinglan, 2nd Edition, pp. 50-55.

[0049] Among the parameters required for the above calculations, the temperature and pressure of the system need to be measured using relevant instruments; the fugacity of guest molecules under equilibrium pressure conditions corresponding to system temperature, the fugacity of guest molecules under system temperature and pressure conditions, and the equilibrium temperature corresponding to the system pressure can all be calculated using hydrate phase equilibrium theory. Using the parameters determined above, a calculation model for hydrate decomposition in a water-in-oil emulsion system can be obtained.

[0050] This application is mainly applied to technologies such as solid-state storage of natural gas using hydrates, refrigeration, chemical separation, and risk control of hydrate freezing in oil and gas pipelines.

[0051] The beneficial effects of this application include:

[0052] This calculation method can be used to calculate the hydrate decomposition rate in water-in-oil emulsion systems. When applied to natural gas storage and transportation, it can calculate the working time required for the decomposition of gas hydrates in water-in-oil emulsions, thus contributing to the commercialization of natural gas storage and transportation. Simultaneously, this method can effectively calculate the decomposition time and gas release rate of gas hydrates in subsea crude oil, gas, and water mixed-transport pipelines, also contributing to the safety assurance of hydrate flow in mixed-transport pipelines.

[0053] Other features and advantages of this application will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the application. Other advantages of this application may be realized and obtained by means of the methods described in the specification. Attached Figure Description

[0054] The accompanying drawings are used to provide an understanding of the technical solutions of this application and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of this application and do not constitute a limitation on the technical solutions of this application.

[0055] Figure 1 The results of the calculated values ​​and actual measured values ​​obtained by substituting the parameters A and B obtained under condition a into formula (3) are statistically analyzed, where the horizontal axis is time and the vertical axis is the amount of alkane gas in the hydrate.

[0056] Figure 2 The results of the calculated values ​​and actual measured values ​​obtained by substituting the parameters A and B obtained under condition a into formula (3) are statistically analyzed, where the horizontal axis is time and the vertical axis is the amount of alkane gas in the hydrate.

[0057] Figure 3 The results of the calculated values ​​and actual measured values ​​obtained by substituting the parameters A and B obtained under condition c into formula (3) are statistically analyzed, where the horizontal axis is time and the vertical axis is the amount of alkane gas in the hydrate.

[0058] Figure 4 The results of the calculated and actual measured values ​​of the hydrate decomposition rate of the water-in-oil emulsion system obtained by fitting parameters A and B under condition c at a decomposition pressure of 3.3 MPa are statistically analyzed. The horizontal axis represents time, and the vertical axis represents the amount of alkane gas in the hydrate.

[0059] Figure 5 The results of the calculated and actual measured values ​​of the hydrate decomposition rate of the water-in-oil emulsion system obtained by fitting parameters A and B under condition a at a decomposition pressure of 3.3 MPa are statistically analyzed. The horizontal axis represents time, and the vertical axis represents the amount of alkane gas in the hydrate.

[0060] Figure 6The results are statistically analyzed for the calculated and actual measured values ​​of the hydrate decomposition rate of the water-in-oil emulsion system under a decomposition pressure of 3.0 MPa, with the horizontal axis representing time and the vertical axis representing the amount of alkane gas in the hydrate. Detailed Implementation

[0061] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application are described in detail below. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be arbitrarily combined with each other.

[0062] In this embodiment of the application, the experimental materials are as follows:

[0063] 0# diesel oil (as shown in Table 1) has a density of 819.9 kg / m³. 3 The viscosity was 2.69 mPa·s (20℃). The experimental water was deionized water prepared by an ELGA OPTION-S7 pure water system, with a density of 992.8 kg / m³. 3 The viscosity was 0.93 mPa·s (measured at 20℃).

[0064] The mixed gas used in the experiment (87 vol.% methane, 8 vol.% ethane, and 5 vol.% propane) was purchased from Beijing Antailong Gas Company.

[0065] The emulsifiers Span80 and Tween80 used in the experiment were purchased from Beijing Innocare Technology Co., Ltd.

[0066] Table 1 Components of 0# Diesel

[0067] carbon number mole fraction / % carbon number mole fraction / % C 10 ]]> 3.025 [C 19 ]]> 1.287 [C 11 ]]> 6.104 <![CDATA[C 20 ]]> 0.261 <![CDATA[C 12 ]]> 10.131 <![CDATA[C 21 ]]> 0.466 <![CDATA[C 14 ]]> 28.037 <![CDATA[C 22 ]]> 0.207 <![CDATA[C 15 ]]> 39.272 <![CDATA[C 23 ]]> 0.146 <![CDATA[C 16 ]]> 8.834 <![CDATA[C 24 ]]> 0.103 <![CDATA[C 17 ]]> 3.662 <![CDATA[C 25+ ]]> 0.233 <![CDATA[C 18 ]]> 0.644 - -

[0068] In this embodiment of the application, the experimental setup is as follows:

[0069] (1) High-pressure reactor system

[0070] The high-pressure reactor system consists of a high-pressure reactor, a temperature and pressure measurement system, a stirring system, a resistivity measurement system, a water bath constant temperature system, and a safety pressure relief system.

[0071] The high-pressure reactor is a fixed-volume reactor made of 316 stainless steel, with an effective volume of 548 mL. The temperature of the reactor is measured using a precision platinum resistance thermometer, with measuring points located at both the top and bottom of the reactor body. The measurement range is -20℃ to 100℃. The reactor can withstand a maximum pressure of 30 MPa.

[0072] The pressure is measured using an electric contact pressure gauge, with a pressure range of 0 to 20 MPa and an accuracy of 0.25%.

[0073] The stirring device on the reactor has a rotation speed range of 90 r / min to 1350 r / min, the stirrer blades adopt a stepless speed regulation method, and the blade installation height is adjustable;

[0074] The reactor uses an O-ring seal, which is easy and quick to disassemble and leak-free;

[0075] The water bath constant temperature system of this device adopts water jacket temperature control, and the constant temperature chamber uses a JULABO FP25-SL temperature controller with an accuracy of ±0.1℃.

[0076] The reactor is equipped with a safety valve with a set upper limit pressure of 30MPa. When the pressure inside the reactor exceeds 30MPa, the safety valve opens to relieve pressure and keep the pressure inside the reactor below the set pressure.

[0077] In addition, three circular transparent windows are installed on the reactor to observe the formation and decomposition of hydrates.

[0078] The embodiments of this application include the following experimental steps:

[0079] 1.0) 1 wt.% of surfactant (with a mass ratio of Span80 and Tween80 of 4:1) was injected into the diesel fuel to obtain a mixture. The mixture was then stirred at 8000 rpm using an IKA T25 impeller, while 10 mL of deionized water was added to the mixture every 1 minute until all the required amount of deionized water was added. A water-in-oil emulsion was formed in the mixture. The water content of the water-in-oil emulsion was measured.

[0080] 1.1) Place 250 mL of the prepared mixture containing the water-in-oil emulsion into a high-pressure reactor with visibility. Tighten the reactor lid and all gas connection components. Turn on the data acquisition system, replace the air with the mixed gas, and check the airtightness of the device.

[0081] 1.2) Add the mixed gas to the reactor and bring the pressure inside the reactor to the experimental pressure (initial pressure). Set the rotation speed in the system to 300 rpm.

[0082] 1.3) Set the water bath temperature in the system to the target temperature of 279.15K.

[0083] 1.4) Set the system so that the hydrate formation process ends when the system pressure remains constant for 30 minutes.

[0084] 1.5) Set the following parameters in the system: decomposition pressure is 3.6 MPa, water bath temperature is 291.15 K, and decompose hydrates in the decomposition vessel.

[0085] 1.6) Set the following in the system: when the pressure in the gas collecting bottle remains constant, the hydrate decomposition process ends.

[0086] 2.1) Start the experiment by changing the temperature inside the reactor (by water bath) under the stirring speed, water content and initial pressure, so that alkane hydrates are generated in the mixture (containing water-in-oil emulsion). Then adjust the pressure inside the reaction vessel to the decomposition pressure so that the alkane hydrates are completely decomposed. Record the temperature, pressure inside the reaction vessel and the corresponding time throughout the process.

[0087] 2.2) Obtain the compressibility factor of the alkane at the stated time (at the pressure and temperature inside the reactor at that time), calculated using the SRK equation of state, etc.

[0088] SRK state equations:

[0089] Rewrite it in Z form and represent it using cubic state equations:

[0090] Z 3 -Z 2 +(ABB 2 Z-AB=0

[0091] in

[0092]

[0093]

[0094] Let: PP = -1 QQ = ABB 2 RR = -AB

[0095] Based on common knowledge in the field, the critical temperature, critical pressure, and eccentricity factor of the mixed gas phase of methane, ethane, and propane are calculated. Given the temperature P and pressure T at a specific moment, the compressibility factor Z of alkane hydrates in the water-in-oil emulsion at different times from formation to decomposition (or only the time from the end of alkane hydrate formation to the complete decomposition of alkane hydrates) can be obtained through the above cubic equation of state.

[0096] 2.3) Substitute the compressibility factor Z, temperature and pressure at different times from the end of the formation of alkane hydrate in the water-in-oil emulsion obtained in 2.2) into formula (1), and calculate the phase equilibrium using formula (1) to obtain the molar amount of gaseous alkanes in the reaction vessel at different times from the end of the formation of alkane hydrate in the water-in-oil emulsion to the complete decomposition.

[0097]

[0098] In the formula, n is the molar amount of gaseous alkanes; P is the pressure of the reactor (Pa); and V is the volume of the gas phase space in the reactor (m³). 3 Z is the compressibility factor of the alkane at temperature and pressure at time t, and R is the gas constant R = 8.314 J·mol⁻¹. -1 ·K -1 T is the temperature of the reactor, in K.

[0099] 3) Obtain the amount of alkane absorbed in the alkane hydrate.

[0100] n H,t =n0-n t ………………………………(2)

[0101] n0 is the amount of gas mixture in the gas phase space of the reactor before alkane hydrates are formed, in mol; n t n represents the amount of gas mixture in the gas phase space of the reactor at each time point from the end of the alkane hydrate formation stage to the complete decomposition of the alkane hydrate, expressed in mol. H,t The moles of alkanes in the alkane hydrate at each time point from the end of the alkane hydrate formation stage to the time of complete decomposition of the alkane hydrate, in mol;

[0102] 4.1) The fugacity f of alkanes under the gas phase space temperature and pressure in formula (3), and the gas phase equilibrium fugacity f under three-phase equilibrium conditions. e The method for obtaining this is common knowledge in the field and can be calculated using the following literature:

[0103] GJChen,TMGuo,A new approach to gas hydrate modeling,Chem.Eng.J.71(1998)145–151.

[0104] "Science and Technology of Gas Hydrates", Chen Guangjin, Sun Changyu, Ma Qinglan, 2nd Edition, pp. 50-55.

[0105] 4.2) Determine parameters A and B for the stirring speed, the moisture content, and the initial pressure:

[0106] The method for obtaining the hydrate decomposition rate in this step includes the following steps:

[0107] Under the stirring speed, water content of the water-in-oil emulsion, and initial pressure determined in 1.0) and 1.2) above, an alkane hydrate decomposition experiment was conducted (the composition of the alkane, oil phase, and water phase is the same as above). That is, the mixture in step 1.0) was added to the closed reaction vessel used to obtain parameters A and B to generate alkane hydrate.

[0108] A decomposition pressure (set to 3.6 MPa) lower than the initial pressure is artificially set, and the pressure inside the sealed, insulated reaction vessel used to obtain parameters A and B is adjusted to the decomposition pressure, so that the alkane hydrate decomposes.

[0109] The number of moles of alkane in the hydrate at each moment under the decomposition pressure is obtained, and the decomposition rate of the alkane hydrate at each moment is calculated; the fugacity f of the alkane at the gas-space temperature and pressure, and the gas-phase equilibrium fugacity f under three-phase equilibrium conditions are obtained. e ;

[0110] Substitute the obtained parameters into formula (3) and use the least squares method to fit and obtain parameters A and B under the decomposition pressure.

[0111] The pressure for the hydrate decomposition experiment can be randomly set (e.g., a decomposition pressure of 3.6 MPa), and parameters A and B are obtained based on this. The obtained parameters A and B can be directly used to predict the decomposition rate at different decomposition pressures.

[0112] For example, the parameters A and B obtained by fitting under different stirring speeds, moisture contents, and initial pressures are shown in Table 2. Figures 1 to 3 As shown ( Figure 1 This is a statistical graph of the simulated and experimental values ​​corresponding to number 'a'. Figure 2 The graph shows the simulated and experimental values ​​corresponding to number b. Figure 3 (Statistical graph of simulated and experimental values ​​corresponding to number c).

[0113] from Figure 1 As can be seen, the error between the experimental values ​​and the calculated values ​​of parameters A and B obtained based on the simulation is 12.1%.

[0114] from Figure 2 As can be seen, the error between the experimental values ​​and the calculated values ​​of parameters A and B obtained based on the simulation is 12.3%.

[0115] from Figure 3 As can be seen, the error between the experimental values ​​and the calculated values ​​of parameters A and B obtained from the simulation is 10.9%.

[0116] Table 2: Parameters A and B at specific stirring speeds, moisture contents, and initial pressures.

[0117]

[0118] 4.3) Set parameters A, B, f, and f e Substituting into formula (3), the hydrate decomposition rate of the water-in-oil emulsion system at time t can be obtained:

[0119]

[0120] In the formula, n H,t n represents the number of moles of alkanes in the hydrate at the current moment, in mol; H,t-1 t is the number of moles of alkane in the hydrate at the previous moment, in mol; t is time, in s; e is the natural base; f is the fugacity at the corresponding temperature and pressure in the gas phase space, in MPa; f e ν is the gas-phase equilibrium fugacity under three-phase equilibrium conditions, in MPa;

[0121] Three sets of predictions were performed under the conditions shown in Table 3 (with varying decomposition pressures) to predict the decomposition rate of hydrates in the water-in-oil emulsion system. The prediction results are as follows: Figures 4 to 6 As shown, Figure 4 The figure shows a summary of the decomposition rate under condition 1 obtained by the calculation method provided in this application and the experimental results. It can be seen from the figure that the error between the experimental value and the calculated value is 11.4%. Figure 5 The figure shows a summary of the decomposition rate under condition No. 2 obtained by the calculation method provided in this application and the experimental results. It can be seen from the figure that the error between the experimental value and the calculated value is 27.6%. Figure 6 The figure shows a summary of the decomposition rate under condition No. 3 obtained by the calculation method provided in this application and the experimental results. It can be seen from the figure that the error between the experimental value and the calculated value is 27.6%.

[0122] Table 3: Experimental conditions and parameters

[0123]

Claims

1. A method for predicting the decomposition rate of hydrates in a water-in-oil emulsion system, wherein the water-in-oil emulsion system comprises a water-in-oil emulsion formed by mixing an alkane, an oil phase, and an aqueous phase, and the hydrate is an alkane hydrate; wherein the alkane is selected from C1 to C4 alkanes; Including the following methods: 1) In a closed reaction vessel, the mixture including the water-in-oil emulsion is controlled to generate hydrate by adjusting the pressure, and then the pressure is adjusted to the decomposition pressure to decompose the hydrate. The temperature and pressure in the reaction vessel at different times from the start of hydrate formation to the end of hydrate decomposition are measured. 2) The molar amount of gaseous alkanes in the reaction vessel at different times was obtained through phase equilibrium calculations; …………………………………（1） In the formula, n is the molar amount of gaseous alkanes; P is the pressure inside the reaction vessel, Pa; and V is the volume of the gas phase space inside the reaction vessel, m³. 3 Z is the compressibility factor of the alkane at temperature and pressure at time t, and R is the gas constant R = 8.314 J·mol⁻¹. -1 ·K -1 T is the temperature inside the reaction vessel, in K; 3) Obtain the amount of alkane absorbed in the alkane hydrate; ………………………………（2） n 0 represents the amount of gas mixture in the gas phase space of the reaction vessel before alkane hydrates are formed, in mol; n t The amount of gas mixture in the gas phase space of the reaction vessel at each time from the end of the alkane hydrate formation stage to the time of complete decomposition of the alkane hydrate, in mol; n H,t The moles of alkanes in the alkane hydrate at each time point from the end of the alkane hydrate formation stage to the time of complete decomposition of the alkane hydrate, in mol; 4) Substitute into formula (3) to calculate, and the hydrate decomposition rate of the water-in-oil emulsion system at time t can be obtained. : ……………………（3） In the formula, n H,t Let be the number of moles of alkane in the hydrate at time t, in mol; n H , t-1 The moles of alkanes in the hydrate at time t-1, in mol; t For time, s ; e The base is the natural number; f ν represents the fugacity of alkanes at the corresponding temperature and pressure in the gas phase space, in MPa; f e ν is the gas-phase equilibrium fugacity under three-phase equilibrium conditions, in MPa; The value of A is 5 × 10 -9 Up to 1×10 -6 The unit is mol·s -1 The value of B ranges from 550 to 900, and the unit is MPa. -1 ; The parameters A and B in formula (3) are obtained through the following method: a) Determine the stirring rate of the reaction vessel, the initial pressure inside the reaction vessel, and the water content of the water-in-oil emulsion; b) Add the water-in-oil emulsion system described in step 1) into the closed reaction vessel used to obtain parameters A and B to generate alkane hydrates; c) Artificially set a decomposition pressure lower than the hydrate equilibrium pressure, and adjust the pressure inside the sealed, insulated reaction vessel used to obtain parameters A and B to the decomposition pressure, so that the alkane hydrate decomposes. d) Obtain the number of moles of alkanes in the hydrate at each moment under the decomposition pressure, and calculate the decomposition rate of the alkane hydrate at each moment; obtain the fugacity of the alkanes at the corresponding gas phase space temperature and pressure. f and gas-phase equilibrium fugacity under three-phase equilibrium conditions f e ; e) Substitute the parameters obtained in step d) into formula (3) to obtain parameters A and B under the decomposition pressure; In predicting the hydrate decomposition rate in the water-in-oil emulsion system: The stirring rate of the reaction vessel is the same as the stirring rate used when obtaining parameters A and B; The initial pressure inside the reaction vessel is the same as the initial pressure used to obtain parameters A and B; The water content of the water-in-oil emulsion in the water-in-oil emulsion system is the same as the water content of the water-in-oil emulsion used when obtaining parameters A and B.

2. The prediction method according to claim 1, wherein, In step 1), the temperature and pressure in the reaction vessel are measured at different times from the end of the hydrate formation to the end of the hydrate decomposition.

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