Phase equilibrium calculation method, device, electronic device and storage medium for fracture-cavity reservoir

Abstract

The present disclosure provides a method, device, electronic device, and storage medium for calculating the phase equilibrium of a fracture-cavity oil reservoir. The method includes determining the medium type of a target fracture-cavity oil reservoir; selecting a corresponding calculation method based on the medium type of the target fracture-cavity oil reservoir to calculate the oil-gas-water three-phase phase equilibrium in the target fracture-cavity oil reservoir; wherein, when the medium type of the target fracture-cavity oil reservoir is a dense medium, a continuous medium, or a discrete medium, a flash calculation method, a Gibbs free energy method, or a proxy model method are respectively selected to calculate the oil-gas-water three-phase phase equilibrium in the target fracture-cavity oil reservoir. This method adopts a phase equilibrium calculation method based on different medium types, overcoming the problems of large calculation errors and large computational complexity caused by selecting a single phase equilibrium calculation method without considering the medium type. It can effectively obtain the phase characteristics of fracture-cavity oil reservoirs of various medium types, better guide oilfield gas injection development, and has high practical value.

Description

Technical Field

[0001] The present disclosure relates to the field of oil exploration technology, and in particular to a method, device, electronic device and storage medium for calculating phase equilibrium in fracture-vuggy oil reservoirs. Background Art

[0002] Fracture-vuggy reservoirs have diverse media types (i.e., storage space types), strong reservoir heterogeneity, and unclear phase states after gas injection, which affects the effectiveness of subsequent gas injection development. In particular, miscibility is very likely to occur when carbon dioxide is injected. The oil-gas-water three-phase equilibrium problem is also an important issue that needs to be addressed in gas injection numerical simulation.

[0003] The current phase equilibrium calculation process of the reservoir system adopts a single calculation method without considering the medium type of the reservoir. Therefore, the traditional single phase equilibrium calculation method cannot be applied to fracture-cavity reservoirs with various medium types, which will cause large calculation errors and large calculation workload. Summary of the Invention

[0004] In response to the above problems, the present disclosure provides a method, device, electronic device and storage medium for calculating the phase equilibrium of fracture-vuggy oil reservoirs, which solves the problem of large calculation errors and large calculation amount caused by selecting a single phase equilibrium calculation method without considering the medium type in the phase equilibrium calculation process of fracture-vuggy oil reservoirs in the prior art.

[0005] In a first aspect, the present disclosure provides a method for calculating phase equilibrium in a fracture-vuggy reservoir, the method comprising:

[0006] Determine the medium type of the target fracture-vuggy reservoir;

[0007] According to the medium type of the target fracture-vuggy oil reservoir, a corresponding calculation method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy oil reservoir.

[0008] Wherein, when the medium type of the target fracture-vuggy oil reservoir is a tight medium, the calculation method is a flash evaporation calculation method;

[0009] When the medium type of the target fracture-vuggy reservoir is a continuous medium, the calculation method is the Gibbs free energy method;

[0010] When the medium type of the target fracture-vuggy reservoir is discrete medium, the calculation method is the proxy model method.

[0011] According to an embodiment of the present disclosure, optionally, in the above-mentioned fracture-vuggy oil reservoir phase equilibrium calculation method, when the medium type of the target fracture-vuggy oil reservoir is a tight medium, a flash evaporation calculation method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy oil reservoir, comprising the following steps:

[0012] According to the PR state equation, the calculation formula of the gas-liquid two-phase equilibrium constant of each component is obtained;

[0013] According to the calculation formula of the gas-liquid two-phase equilibrium constant of each component, the gas-liquid two-phase equilibrium constant of each component is calculated by the iteration method;

[0014] The oil-gas-water three-phase equilibrium constant of each component is calculated based on the gas-liquid two-phase equilibrium constant of each component, so as to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy reservoir.

[0015] According to an embodiment of the present disclosure, optionally, in the above-mentioned fracture-vuggy reservoir phase equilibrium calculation method, the PR state equation is:

[0016]

[0017] Wherein, P is the pressure of the target fracture-vuggy reservoir, T is the temperature of the target fracture-vuggy reservoir, R is the gas constant, V m is the residual molar volume of each component after adsorption, a and b are the process coefficients of the equation, and α(T) is a function of relative temperature and eccentricity factor.

[0018] According to an embodiment of the present disclosure, optionally, in the above-mentioned fracture-vuggy reservoir phase equilibrium calculation method, a calculation formula for the gas-liquid two-phase equilibrium constant of each component is obtained according to the PR state equation, comprising the following steps:

[0019] According to the PR state equation and the relationship between the residual molar volume and the compressibility factor of each component after adsorption, V m =ZRT / P, we get the following cubic equation for the compressibility factor:

[0020] Z 3 -(1-B)Z 2 +(A-2B-3B 2 )Z-(AB-B 2 -B 3 )=0

[0021] Where Z is the compression factor, A=aα(T)P / (R 2 T 2 ), B = bP / (RT);

[0022] Solving the cubic equation to obtain a solution, wherein the maximum value in the solution is the compressibility factor of the gas phase and the minimum value in the solution is the compressibility factor of the liquid phase;

[0023] According to the compressibility factor of the gas phase and the compressibility factor of the liquid phase, the fugacity coefficient of each component in the gas phase and liquid phase is calculated by the following formula:

[0024]

[0025]

[0026] in, is the fugacity coefficient of the i-th component in the gas phase, is the fugacity coefficient of component i in the liquid phase, b i is the b coefficient of the i-th component, Z V is the compressibility factor of the gas phase, Z L is the compressibility factor of the liquid phase, N C is the number of components, x j is the mole fraction of the jth component in the target fracture-vuggy reservoir, k ij is the combination coefficient of the i-th component and the j-th component, a i is the a coefficient of the i-th component, a j is the a coefficient of the jth component;

[0027] According to the fugacity coefficients of each component in the gas phase and liquid phase respectively, the gas-liquid two-phase equilibrium constant of each component is calculated by the following formula:

[0028]

[0029] in, is the gas-liquid two-phase equilibrium constant of the i-th component.

[0030] According to an embodiment of the present disclosure, optionally, in the above-mentioned fracture-vuggy reservoir phase equilibrium calculation method, when the medium type of the target fracture-vuggy reservoir is a continuous medium, the Gibbs free energy method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy reservoir, comprising the following steps:

[0031] According to the Gibbs free energy function of the target fracture-vuggy reservoir and its corresponding constraint conditions, a set of objective function equations is obtained;

[0032] Solving the objective function equations by an iterative method to obtain the mole fractions of each component in the oil phase, gas phase and water phase respectively;

[0033] The oil-gas-water three-phase equilibrium constant of each component is obtained according to the mole fraction of each component in the oil phase, gas phase and water phase, so as to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy reservoir.

[0034] According to an embodiment of the present disclosure, optionally, in the above-mentioned method for calculating phase equilibrium of fracture-vuggy reservoirs, the Gibbs free energy function is:

[0035]

[0036] Where G is Gibbs free energy, nik is the molar number of component i in phase k, μ ik is the chemical potential of the i-th component in the k-th phase, π is the total number of phases, N C is the number of components, and when the target fracture-vuggy reservoir is in equilibrium, the Gibbs free energy is minimum.

[0037] According to an embodiment of the present disclosure, optionally, in the above-mentioned fracture-vuggy reservoir phase equilibrium calculation method, the constraint conditions include:

[0038]

[0039]

[0040]

[0041] Among them, α k is the phase fraction of phase k, n t is the total number of moles in the target fracture-vuggy reservoir, α r is the phase fraction of the reference phase r phase, where the reference phase r phase is the oil phase or the water phase.

[0042] According to an embodiment of the present disclosure, optionally, in the above-mentioned fracture-vuggy reservoir phase equilibrium calculation method, obtaining the objective function equation group according to the Gibbs free energy function of the target fracture-vuggy reservoir and its corresponding constraints includes the following steps:

[0043] According to the Gibbs free energy function and the constraints, the mole fraction of each component in each phase is calculated using the law of conservation of mass according to the following formula:

[0044]

[0045]

[0046] Among them, x ir is the mole fraction of the i-th component in the r-phase, x ik is the mole fraction of the i-th component in the k-phase, x i is the mole fraction of the i-th component in the target fracture-vuggy reservoir, is the kr two-phase equilibrium constant of component i, θ k is the phase stability variable of phase k, α j is the phase fraction of phase j, is the jr two-phase equilibrium constant of component i, θ j is the phase stability variable of phase j;

[0047] Substitute the mole fraction of each component in each phase into the calculation formula The first objective function is obtained as:

[0048]

[0049] Among them, E k is the first objective function;

[0050] According to the relationship between the phase fraction of each phase and the phase stability variable α k θ k =0, the second objective function is:

[0051]

[0052] Among them, F k is the second objective function;

[0053] According to the calculation formula of the mole fraction of each component in each phase, the third objective function is obtained as follows:

[0054]

[0055] Among them, D ik is the third objective function, and the first objective function, the second objective function and the third objective function constitute an objective function equation group.

[0056] According to an embodiment of the present disclosure, optionally, in the above-mentioned fracture-vuggy reservoir phase equilibrium calculation method, solving the objective function equation group by an iterative method to obtain the mole fraction of each component in the oil phase, gas phase and water phase, respectively, comprises the following steps:

[0057] Solving the objective function equations by an iterative method to obtain the mole fractions of each component in the other two phases except the reference phase;

[0058] According to the mole fractions of each component in the other two phases except the reference phase, the mole fraction of each component in the reference phase is calculated by the law of conservation of mass to obtain the mole fractions of each component in the oil phase, gas phase and water phase respectively.

[0059] According to an embodiment of the present disclosure, optionally, in the above-mentioned fracture-vuggy reservoir phase equilibrium calculation method, when the medium type of the target fracture-vuggy reservoir is a discrete medium, a proxy model method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy reservoir, comprising the following steps:

[0060] According to the approximate expression between input parameters and output results, the polynomial response model is established as follows:

[0061]

[0062] in, is the output result, m iis the first input parameter of the i-th order, n j is the jth second input parameter, b0, b i 、b ij is the coefficient to be determined, k is the number of the first input parameter and the second input parameter;

[0063] Training the polynomial response model using a plurality of sample points to determine estimated values ​​of each undetermined coefficient, thereby optimizing the polynomial response model;

[0064] The pressure of the target fracture-vuggy oil reservoir is input as a first input parameter, and the mole fraction of each component in the target fracture-vuggy oil reservoir is input as a second input parameter into the optimized polynomial response model to output the oil-gas-water three-phase equilibrium constant of each component, thereby calculating the oil-gas-water three-phase equilibrium in the target fracture-vuggy oil reservoir.

[0065] According to an embodiment of the present disclosure, optionally, in the above-mentioned fracture-vuggy reservoir phase equilibrium calculation method, the polynomial response model is trained using a plurality of sample points to determine estimated values ​​of each undetermined coefficient, thereby optimizing the polynomial response model, including the following steps:

[0066] Inputting the reservoir pressure corresponding to a plurality of sample points as a first input parameter and the mole fraction of each component in the reservoir as a second input parameter into the polynomial response model to obtain corresponding output results; wherein the output results include the oil-gas-water three-phase equilibrium constant of each component at the sample points;

[0067] The calculation formula to determine the error between the output result of a sample point and its actual value is:

[0068]

[0069] Among them, s is the error, y i is the actual value corresponding to the output result;

[0070] The error calculation formula between the output result and its corresponding actual value is subjected to regression analysis by the least square method to determine the estimated value of each undetermined coefficient, thereby optimizing the polynomial response model.

[0071] According to an embodiment of the present disclosure, optionally, in the above-mentioned fracture-vuggy reservoir phase equilibrium calculation method,

[0072] The dense medium includes a matrix;

[0073] The continuous medium includes small and medium-sized cracks and small and medium-sized dissolution pores;

[0074] The discrete media include large caves and large cracks.

[0075] In a second aspect, the present disclosure provides a phase equilibrium calculation device for a fracture-vuggy oil reservoir, the device comprising:

[0076] A medium type determination module is used to determine the medium type of the target fracture-vuggy reservoir;

[0077] a phase equilibrium calculation module, configured to select a corresponding calculation method according to the medium type of the target fracture-vuggy reservoir to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy reservoir;

[0078] When the medium type of the target fracture-cavity oil reservoir is a tight medium, the flash evaporation calculation method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-cavity oil reservoir;

[0079] When the medium type of the target fracture-cavity oil reservoir is a continuous medium, the Gibbs free energy method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-cavity oil reservoir;

[0080] When the medium type of the target fracture-vuggy oil reservoir is discrete medium, a proxy model method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy oil reservoir.

[0081] In a third aspect, the present disclosure provides an electronic device comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the method for calculating phase equilibrium of a fracture-cavity reservoir as described in any one of the first aspects is executed.

[0082] In a fourth aspect, the present disclosure provides a storage medium, wherein the computer program stored in the storage medium can be executed by one or more processors and can be used to implement the phase equilibrium calculation method for fracture-cavity reservoirs as described in any one of the first aspects.

[0083] Compared with the prior art, one or more embodiments of the above solutions may have the following advantages or beneficial effects:

[0084] The present disclosure provides a method, device, electronic device and storage medium for calculating phase equilibrium of a fracture-vuggy oil reservoir. The method includes determining the medium type of a target fracture-vuggy oil reservoir; selecting a corresponding calculation method to calculate the oil-gas-water three-phase phase equilibrium in the target fracture-vuggy oil reservoir according to the medium type of the target fracture-vuggy oil reservoir; wherein, when the medium type of the target fracture-vuggy oil reservoir is a dense medium, a flash evaporation calculation method is selected to calculate the oil-gas-water three-phase phase equilibrium in the target fracture-vuggy oil reservoir; when the medium type of the target fracture-vuggy oil reservoir is a continuous medium, a Gibbs free energy method is selected to calculate the oil-gas-water three-phase phase equilibrium in the target fracture-vuggy oil reservoir; when the medium type of the target fracture-vuggy oil reservoir is a discrete medium, a proxy model method is selected to calculate the oil-gas-water three-phase phase equilibrium in the target fracture-vuggy oil reservoir. This method, which employs a phase equilibrium calculation method tailored to each medium type, overcomes the existing problems of large calculation errors and heavy computational effort in fracture-vuggy reservoir phase equilibrium calculations, which arise from selecting a single phase equilibrium calculation method without considering the medium type. This method effectively captures the phase characteristics of fracture-vuggy reservoirs with various medium types, providing better guidance for oilfield gas injection development and possessing high practical value. This method can be applied to fracture-vuggy reservoir gas injection development, providing technical support for the optimization of injection-production well patterns, injection-production parameters, and the formulation of subsequent gas injection technology policies. BRIEF DESCRIPTION OF THE DRAWINGS

[0085] Hereinafter, the present disclosure will be described in more detail based on embodiments and with reference to the accompanying drawings:

[0086] Figure 1 A schematic flow chart of a phase equilibrium calculation method for a fracture-vuggy reservoir provided in an embodiment of the present disclosure;

[0087] Figure 2 A schematic diagram of a curve showing the change in the mole fraction of N2 in the oil phase versus pressure in a certain fracture-cavity oil reservoir T well provided in an embodiment of the present disclosure;

[0088] Figure 3 A schematic diagram of a curve showing the change in mole fraction of C1 in the oil phase versus pressure in a certain fracture-cavity oil reservoir T well provided in an embodiment of the present disclosure;

[0089] Figure 4 The heavy component C in the oil phase of a certain fracture-cavity oil reservoir T well provided in the embodiment of the present disclosure is 11+ Schematic diagram of the curve of the mole fraction of versus pressure;

[0090] Figure 5 A schematic diagram of a curve showing changes in crude oil density versus pressure in a certain fracture-cavity oil reservoir, well T, provided in an embodiment of the present disclosure;

[0091] Figure 6A schematic diagram of a curve showing changes in crude oil viscosity versus pressure for a certain fracture-cavity oil reservoir, well T, provided in an embodiment of the present disclosure;

[0092] Figure 7 A schematic diagram of a curve showing changes in interfacial tension versus pressure for a certain fracture-vuggy oil reservoir, well T, provided in an embodiment of the present disclosure;

[0093] Figure 8 A schematic diagram of a curve showing changes in the mole fractions of N2 and C1 in the gas phase versus the mole fraction of injected N2 in a certain fracture-cavity oil reservoir T well provided by an embodiment of the present disclosure;

[0094] Figure 9 A schematic structural diagram of a phase equilibrium calculation device for a fracture-cavity oil reservoir provided in an embodiment of the present disclosure;

[0095] In the drawings, like components are given like reference numerals, and the drawings are not drawn to scale. DETAILED DESCRIPTION

[0096] The following will describe the implementation methods of the present disclosure in detail with reference to the accompanying drawings and examples, so that the implementation process of how the present disclosure applies technical means to solve technical problems and achieve corresponding technical effects can be fully understood and implemented accordingly. The embodiments of the present disclosure and the various features therein can be combined with each other as long as they do not conflict with each other, and the resulting technical solutions are all within the scope of protection of the present disclosure.

[0097] Meanwhile, in the following description, for the purpose of explanation, numerous specific details are set forth to provide a thorough understanding of the embodiments of the present invention. However, it will be apparent to those skilled in the art that the present invention may be implemented without the specific details herein or the specific manner described.

[0098] Example 1

[0099] Figure 1 This is a flow chart of a phase equilibrium calculation method for a fracture-cavity reservoir provided by an embodiment of the present disclosure. Figure 1 This embodiment provides a method for calculating phase equilibrium in a fracture-vuggy reservoir, including:

[0100] Step S101: Determine the medium type of the target fracture-vuggy reservoir.

[0101] Fracture-vuggy reservoirs are a special type of reservoir characterized by diverse medium types (i.e., reservoir space types), large scale variations, highly discrete distribution, diverse fracture-vuggy combination connectivity patterns, and coexistence of multiple flow patterns.

[0102] The main media types of fracture-vuggy reservoirs include matrix, small and medium-scale fractures, small and medium-scale dissolution pores, discrete large fractures, and large caves. Among them, the matrix is ​​a dense medium, small and medium-scale fractures and small and medium-scale dissolution pores are continuous media, and large fractures and large caves are discrete media.

[0103] Step S102: selecting a corresponding calculation method according to the medium type of the target fracture-vuggy oil reservoir to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy oil reservoir;

[0104] When the medium type of the target fracture-cavity oil reservoir is a tight medium, the flash evaporation calculation method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-cavity oil reservoir;

[0105] When the medium type of the target fracture-cavity oil reservoir is a continuous medium, the Gibbs free energy method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-cavity oil reservoir;

[0106] When the medium type of the target fracture-vuggy oil reservoir is discrete medium, a proxy model method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy oil reservoir.

[0107] The three calculation methods are explained below.

[0108] The first calculation method, when the medium type of the target fracture-vuggy oil reservoir is a tight medium, selects a flash evaporation calculation method to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy oil reservoir, comprising the following steps:

[0109] (1) Calculate the initial value of the gas-liquid equilibrium constant of each component using the Wilson equation based on the critical capillary pressure of each component;

[0110] (2) According to the PR state equation, the calculation formula of the gas-liquid two-phase equilibrium constant of each component is obtained;

[0111] (3) Calculate the gas-liquid two-phase equilibrium constant of each component by an iterative method according to the calculation formula of the gas-liquid two-phase equilibrium constant of each component;

[0112] (4) Calculating the oil-gas-water three-phase equilibrium constant of each component based on the gas-liquid two-phase equilibrium constant of each component to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy reservoir.

[0113] Specifically, the matrix permeability and porosity of fracture-vuggy reservoirs are low. After the injection of gases such as carbon dioxide, adsorption will occur, which will affect the accuracy of phase equilibrium calculations. Therefore, the amount of gas adsorbed per unit mass of matrix is ​​q = V / m, with the unit being m 3 / g, from which the residual molar volume V of each component after adsorption can be calculated m .

[0114] Then, by inputting temperature, pressure and critical properties of components, the initial equilibrium constant value of each component is estimated by Wilson equation, which is calculated as follows:

[0115]

[0116] in, is the initial value of the gas-liquid two-phase equilibrium constant of the i-th component, P ci is the critical capillary pressure of the i-th component, P is the pressure of the target fracture-vuggy reservoir, ω i is the eccentricity factor of the i-th component, T ci is the critical temperature of the i-th component, and T is the temperature of the target fracture-vuggy reservoir.

[0117] The pressure P of the target fracture-vuggy oil reservoir is related to the porosity. The smaller the porosity, the lower the pressure P of the target fracture-vuggy oil reservoir.

[0118] The PR state equation is:

[0119]

[0120] Wherein, P is the pressure of the target fracture-cavity reservoir, R is the gas constant, T is the temperature of the target fracture-cavity reservoir, V m is the residual molar volume of each component after adsorption, a and b are the process coefficients of the equation, and α(T) is a function of relative temperature and eccentricity factor. m It is also related to the porosity. The smaller the porosity, the stronger the gas adsorption. m Therefore, in this embodiment, the PR state equation comprehensively considers capillary pressure, adsorption and pore effect.

[0121] Specifically, in the above PR equation,

[0122]

[0123]

[0124] Where ω is the eccentricity factor, T r is the comparison temperature, N C is the number of components, x i is the mole fraction of the i-th component, x j is the mole fraction of the jth component in the target fracture-vuggy reservoir, k ij is the combination coefficient of the i-th component and the j-th component, a i is the a coefficient of the i-th component, aj is the a coefficient of the jth component, b i is the a coefficient of the i-th component.

[0125] According to the PR state equation and the relationship between molar volume and compressibility factor V m =ZRT / P, which is V m =ZRT / P into the PR equation, replacing V m , we get the following cubic equation for the compression factor:

[0126] Z 3 -(1-B)Z 2 +(A-2B-3B 2 )Z-(AB-B 2 -B 3 )=0

[0127] Where Z is the compression factor, A=aα(T)P / (R 2 T 2 ), B = bP / (RT);

[0128] Solve the cubic equation to obtain the solution, wherein the maximum value in the solution is the compressibility factor Z of the gas phase V The minimum value in the solution of the equation is the compressibility factor Z of the liquid phase L .

[0129] According to the compressibility factor of the gas phase and the compressibility factor of the liquid phase, the fugacity coefficient of each component in the gas phase and liquid phase is calculated by the following formula:

[0130]

[0131]

[0132] in, is the fugacity coefficient of the i-th component in the gas phase, is the fugacity coefficient of component i in the liquid phase, b i is the b coefficient of the i-th component, Z V is the compressibility factor of the gas phase, Z L is the compressibility factor of the liquid phase, N C is the number of components, x j is the mole fraction of the jth component in the target fracture-vuggy reservoir, k ij is the combination coefficient of the i-th component and the j-th component, a i is the a coefficient of the i-th component, a j is the a coefficient of the jth component.

[0133] According to the fugacity coefficients of each component in the gas phase and liquid phase respectively, the gas-liquid two-phase equilibrium constant of each component is calculated by the following formula:

[0134]

[0135] in, is the gas-liquid two-phase equilibrium constant of the i-th component.

[0136] Then, according to the calculation formula of the gas-liquid two-phase equilibrium constant of each component, the gas-liquid two-phase equilibrium constant of each component is calculated by an iterative method.

[0137] Since the compositional changes occur between the gas and oil phases, the volume of water remains constant, and the solubility of each component in water remains unchanged, the mole fraction of each component in water can be calculated. Based on the gas-liquid equilibrium constant for each component, the mole fraction of each component in the gas and liquid phases can be calculated. Since the liquid phase consists of both water and oil, and the mole fraction of each component in water is known, the mole fraction of each component in the oil phase can be calculated, thereby obtaining the mole fractions of each component in the oil, gas, and water phases. Based on the mole fractions of each component in the gas and oil phases, the mole fraction of each component in the oil-gas phase can be calculated. By calculating the ratio of the mole fraction of each component in the oil-gas phase to the mole fraction in the water phase, the oil-gas-water three-phase equilibrium constant can be obtained. Parameters such as density and viscosity can then be calculated based on the equilibrium constant.

[0138] The second calculation method, when the medium type of the target fracture-vuggy reservoir is a continuous medium, selects the Gibbs free energy method to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy reservoir, including the following steps:

[0139] (1) obtaining a set of objective function equations based on the Gibbs free energy function of the target fracture-vuggy reservoir and its corresponding constraints;

[0140] (2) solving the objective function equations by an iterative method to obtain the mole fractions of each component in the oil phase, gas phase, and water phase, respectively;

[0141] (3) According to the mole fractions of each component in the oil phase, gas phase and water phase, the oil-gas-water three-phase equilibrium constant of each component is obtained to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy reservoir.

[0142] Small-scale fractures and dissolution pores in fracture-vuggy reservoirs can be ignored in the calculation due to their weak adsorption. Taking into account the characteristics of this type of medium, the Gibbs free energy minimization method is used to transform the multiphase and multicomponent phase equilibrium calculation into a mathematical optimization problem for minimizing the Gibbs free energy of the mixture system.

[0143] The Gibbs free energy minimization method is based on the thermodynamic theory of phase equilibrium, which states that a multiphase, multicomponent mixture in a stable state under certain temperature and pressure conditions must satisfy the minimum Gibbs free energy requirement. Phase equilibrium calculations are primarily performed by solving nonlinear equations and directly optimizing the Gibbs free energy. According to the second law of thermodynamics, minimizing the Gibbs free energy is a necessary and sufficient condition for a system to reach equilibrium.

[0144] Since the chemical potentials at equilibrium are equal, a set of nonlinear equations can be established to determine the components of each phase.

[0145] Specifically, to calculate the thermodynamic equilibrium of a closed system, when all phases in the system are known, the minimum Gibbs free energy of the system needs to meet three basic conditions: ① The temperature of all phases in the system is equal; ② The pressure of all phases in the system is equal; ③ The fugacity of any component in each phase of the system is equal.

[0146] For the target fracture-vuggy reservoir, the Gibbs free energy function is:

[0147]

[0148] Where G is Gibbs free energy, n ik is the molar number of component i in phase k, μ ik is the chemical potential of the i-th component in the k-th phase, π is the total number of phases, N C is the number of components.

[0149] Assuming that phase r is the reference phase and that the reference phase must exist when the reservoir system is in equilibrium, we have:

[0150]

[0151] Among them, μ ir is the chemical potential of the i-th component in the reference phase r, in J / mol.

[0152] In this embodiment, the r phase is an oil phase or a water phase, and there are two phases in addition to the r phase.

[0153] Then we can get the following three constraints:

[0154]

[0155]

[0156]

[0157] Among them, α k is the phase fraction of phase k, n ik is the molar number of component i in phase k, n tis the total number of moles in the target fracture-vuggy reservoir, α r is the phase fraction of the reference phase r, π is the total number of phases, N C is the number of components.

[0158] According to the above constraints, the Lagrangian function is introduced to calculate the minimum value of Gibbs free energy by calculating the minimum value of the Lagrangian function. The calculation formula of the Lagrangian function is as follows:

[0159]

[0160] Among them, G * is the Lagrangian function, λ k is the Lagrange multiplier, and when the Lagrange multiplier λ k When =0, the Lagrangian function is minimum.

[0161] In order to get G * The extreme point (minimum value) of

[0162] Therefore, according to the calculation formula of the Lagrangian function, we can get:

[0163]

[0164] Among them, f ik and f ir are the fugacity of the i-th component in phase k and phase r respectively; for all components in phase k, λ k The values ​​of are the same, and through λ k The stability of the phases in the system can be determined.

[0165] When the system is in equilibrium, the Gibbs free energy is minimum. At this time, it should satisfy:

[0166]

[0167] Because α k Greater than 0, all, only in λ k = 0, the Gibbs free energy of the system is minimum, so we can get: k λ k =0.

[0168] Then the phase stability constant is introduced to reflect the stability of the system. The calculation formula of the phase stability constant is as follows:

[0169] θ k =ln(f ik / f ir )

[0170] Where, is θ k is the phase stability constant of the k-phase.

[0171] The relationship between the fugacity coefficient, fugacity and equilibrium constant is as follows:

[0172]

[0173] in, is the kr two-phase equilibrium constant of component i, and are the fugacity coefficients of group i in phase k and phase r, respectively, and x ir and x ik are the mole fractions of the i-th component in the k-phase and r-phase, respectively.

[0174] According to the above formula, we can get: So we can get: k θ k =0.

[0175] The following calculation formula can be obtained from the law of conservation of mass:

[0176]

[0177] Among them, x i is the mole fraction of the i-th component in the target fracture-vuggy reservoir.

[0178] The mole fraction of each component in each phase can be calculated according to the following formula:

[0179]

[0180]

[0181] Among them, x ir is the mole fraction of the i-th component in the r-phase, x ik is the mole fraction of the i-th component in the k-phase, x i is the total mole fraction of the i-th component in the target fracture-vuggy reservoir, is the kr two-phase equilibrium constant of component i, θ k is the phase stability variable of phase k, α j is the phase fraction of phase j, is the jr two-phase equilibrium constant of component i, θ j is the phase stability variable of phase j.

[0182] Substitute the mole fraction of each component in each phase into the calculation formula The first objective function is obtained as:

[0183]

[0184] Among them, E k is the first objective function;

[0185] According to the relationship between the phase fraction of each phase and the phase stability variable α k θ k =0, the second objective function is:

[0186]

[0187] Among them, F k is the second objective function;

[0188] According to the calculation formula of the mole fraction of each component in each phase, the third objective function is obtained as follows:

[0189]

[0190] Among them, D ik is the third objective function;

[0191] The first objective function, the second objective function and the third objective function constitute an objective function equation group.

[0192] Therefore, the problem of finding the minimum value of the Lagrangian function is transformed into solving the objective function equation group.

[0193] When the temperature and pressure of the target fracture-vuggy reservoir remain unchanged, the Newton-Raphson iteration method is used to solve the objective function equation group as follows:

[0194]

[0195] Where i = 1,…,N C -1;k=1,2,…,π;k≠r;Δα k , Δθ k and Δx ik They are the main variables α k ,θ k and x ik The increment vector of ; p is the number of Newton-Raphson iteration steps.

[0196] The solution of the objective function equation group is the molar fraction x of each component in the other two phases except the reference phase. ik Then, according to the law of conservation of mass, the molar fraction x of each component in the reference phase can be calculated. ir , thus obtaining the mole fraction of each component in the oil phase, gas phase and water phase, and thus calculating the oil-gas-water three-phase equilibrium constant of each component.

[0197] It should be noted that the initial value of the above iterative method can also be obtained using the Wilson equation, and in addition to the Newton-Raphson iterative method, methods such as the successive iteration method, the accelerated iteration method, and the Powel method can also be used to solve the objective function equation group.

[0198] The Gibbs free energy method has wide adaptability, stable calculation and good convergence, and is suitable for the calculation of phase equilibrium of continuous medium multiphase systems in fracture-vuggy reservoirs.

[0199] The third calculation method is to select a proxy model method to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy oil reservoir when the medium type of the target fracture-vuggy oil reservoir is a discrete medium.

[0200] Fracture-vuggy reservoirs are large in scale and less affected by the medium. To improve the calculation speed without compromising the accuracy of phase equilibrium calculations, a phase equilibrium calculation method based on a surrogate model is proposed. Common surrogate models include the polynomial response model, radial basis function model, and kriging model. The polynomial response model (RSM) is a surrogate model that uses mathematical functions to fit the relationship between design variables and output results. It is widely used due to its simple structure, ease of implementation, fast fitting speed, and high solution efficiency. Therefore, the surrogate model used in this embodiment is the polynomial response model (RSM).

[0201] The third method specifically includes the following steps:

[0202] (1) Based on the approximate expression between input parameters and output results, the polynomial response model is established as follows:

[0203]

[0204] in, is the output result, m i is the first input parameter of the i-th order, n j is the jth second input parameter, b0, b i 、b ij is the coefficient to be determined, k is the number of the first input parameter and the second input parameter;

[0205] (2) The polynomial response model is trained using a number of sample points to determine estimated values ​​of each undetermined coefficient, thereby optimizing the polynomial response model.

[0206] The specific training process is as follows:

[0207] Inputting the reservoir pressure corresponding to a plurality of sample points as a first input parameter and the mole fraction of each component in the reservoir as a second input parameter into the polynomial response model, and obtaining corresponding output results; wherein the output results include the oil-gas-water three-phase equilibrium constant of each component at the sample points, the viscosity and density of the reservoir;

[0208] The calculation formula to determine the error between the output result of the sample point and its corresponding actual value is:

[0209]

[0210] Where s is the error, y i is the actual value corresponding to the output result;

[0211] The least square method is used to perform regression analysis on the above error calculation formula to determine the various unknown coefficients (b0, b i ,b ij ) to optimize the polynomial response model.

[0212] (3) The pressure data of the target fracture-cavity oil reservoir is input as the first input parameter and the mole fraction of each component in the target fracture-cavity oil reservoir is input as the second input parameter into the optimized polynomial response model to output data such as the equilibrium constant of each component, the density or viscosity of crude oil, etc., so as to calculate the oil-gas-water three-phase equilibrium in the target fracture-cavity oil reservoir.

[0213] Of course, during the training process, the input parameters of the sample points are the mole fraction data, pressure data or temperature data of each component obtained through a large number of experiments, and the actual value of the output result is the actual measured value of the corresponding oil-gas-water three-phase equilibrium constant, reservoir density or viscosity and other parameters. In order to obtain the most accurate unknown coefficients (b0, b i ,b ij ), so that the optimized polynomial response model is closer to the actual situation.

[0214] In this way, the optimized polynomial response model can directly output data such as the oil-gas-water three-phase equilibrium constant of each component in the target fracture-vuggy reservoir, the density or viscosity of the reservoir, etc. This method is easy to implement, has a fast fitting speed, high solution efficiency, and is direct and effective.

[0215] The present disclosure provides a method for calculating phase equilibrium of a fracture-vuggy oil reservoir, the method comprising determining a medium type of a target fracture-vuggy oil reservoir; selecting a corresponding calculation method according to the medium type of the target fracture-vuggy oil reservoir to calculate the oil-gas-water three-phase phase equilibrium in the target fracture-vuggy oil reservoir; wherein, when the medium type of the target fracture-vuggy oil reservoir is a tight medium, a flash evaporation calculation method is selected to calculate the oil-gas-water three-phase phase equilibrium in the target fracture-vuggy oil reservoir; when the medium type of the target fracture-vuggy oil reservoir is a continuous medium, a Gibbs free energy method is selected to calculate the oil-gas-water three-phase phase equilibrium in the target fracture-vuggy oil reservoir; and when the medium type of the target fracture-vuggy oil reservoir is a discrete medium, a proxy model method is selected to calculate the oil-gas-water three-phase phase equilibrium in the target fracture-vuggy oil reservoir. This method, which employs a phase equilibrium calculation method tailored to each medium type, overcomes the existing problems of large calculation errors and heavy computational effort in fracture-vuggy reservoir phase equilibrium calculations, which arise from selecting a single phase equilibrium calculation method without considering the medium type. This method effectively captures the phase characteristics of fracture-vuggy reservoirs with various medium types, providing better guidance for oilfield gas injection development and possessing high practical value. This method can be applied to fracture-vuggy reservoir gas injection development, providing technical support for the optimization of injection-production well patterns, injection-production parameters, and the formulation of subsequent gas injection technology policies.

[0216] Example 2

[0217] Based on the first embodiment, this embodiment illustrates the method described in the first embodiment through a specific implementation case.

[0218] This embodiment is based on a fracture-cavity oil reservoir T well to illustrate the method described in the first embodiment.

[0219] Well T in a fracture-vuggy reservoir is primarily characterized by large-scale karst fractures. Therefore, a surrogate model approach was employed to calculate phase equilibrium for this reservoir. First, a multi-similar model was trained using a number of sample points to determine the estimated values ​​of each undetermined coefficient. This optimized polynomial response model was then optimized. Then, the optimized polynomial response model was input with pressure and component mole fraction data for five gas injection scenarios to determine the oil-gas-water three-phase equilibrium constants for each component in each scenario, as well as the reservoir density and viscosity. Table 1 shows the crude oil composition statistics for Well T.

[0220] Table 1

[0221] Components Mole fraction (%) Components Mole fraction (%) <![CDATA[C1]]> 33.11 <![CDATA[C7]]> 1.68 <![CDATA[C2]]> 4.63 <![CDATA[C8]]> 1.98 <![CDATA[C3]]> 2.78 <![CDATA[C9]]> 1.66 <![CDATA[iC4]]> 0.75 <![CDATA[C 10 ]]> 1.50 <![CDATA[nC4]]> 1.50 <![CDATA[C 11+ ]]> 44.62 <![CDATA[iC5]]> 0.68 <![CDATA[CO2]]> 1.06 <![CDATA[nC5]]> 0.95 <![CDATA[N2]]> 1.73 <![CDATA[nC6]]> 1.37

[0222] The reservoir temperature is 128.7℃. The changes of N2, C1 and C in the oil phase were studied. 11+The change of the mole fraction of N2 in the oil phase with pressure is shown in the figure. Figure 2 As shown in the figure, under the same pressure, the mole fraction of N2 in the oil phase decreases with the decrease of N2 content in the injected gas, and the effect of C1 in the injected gas on the N2 content in the oil phase is more obvious than that of CO2. That is, relative to the same proportion of CO2, C1 reduces the mole fraction of N2 in the oil phase more.

[0223] The curve of the change of the mole fraction of C1 in the oil phase with pressure is as follows: Figure 3 As shown in the figure, at the same pressure, when the injected gas composition is 80% N2 and 20% Cl, the Cl content in the oil phase is the highest. When the injected gas is a mixture of N2 and CO2, an increase in the CO2 content (10% → 20%) increases the Cl content in the oil phase. For the injection of 80% N2 and 20% Cl, the system achieves miscibility when the pressure reaches 67 MPa, with all components dissolved in the oil phase.

[0224] Heavy component C in the oil phase 11+ The curve of the mole fraction of Figure 4 As shown in the figure, due to the extraction effect of gas injection, the heavy component C in crude oil 11+ The content of C 11+ The content decreased most significantly.

[0225] The density of crude oil at a temperature of 128.7°C and a pressure of 57 MPa (0.8185 g / cm 3 ) and viscosity value (0.1699cP) as the benchmark values, the density and viscosity changes of the five gas injection schemes were compared, and the results were as follows: Figure 5 and Figure 6 The results show that under the same pressure, the density of crude oil decreases most significantly when 100% N2 or a mixture of N2 and C1 is injected, and the viscosity reduction effect of the mixture of N2 and C1 is better than that of the mixture of N2 and CO2, but the difference is not significant.

[0226] The curves of interfacial tension changing with pressure for the five gas injection schemes are shown in Figure 2. Figure 7 As shown, it can be seen that both C1 and CO2 in the injected gas will reduce the minimum miscibility pressure (MMP, that is, the pressure value corresponding to the interfacial tension of 0) of the reservoir system; when the injected gas is all N2, the MMP is about 65MPa; when the injected gas is a mixture of 90% N2 and 10% C1, the MMP is about 60.3MPa; when the injected gas is 80% N2 and 20% C1, the MMP is about 55.6MPa.

[0227] Furthermore, when the injected gas is a mixture of 90% N2 and 10% CO2, the MMP is approximately 57.8 MPa; when it is 80% N2 and 20% CO2, the MMP is approximately 52.5 MPa. Compared to C1, the MMP decreases more significantly when CO2 is mixed with N2. Therefore, during actual N2 injection in oil reservoirs, CO2 can be mixed into the injected gas to reduce interfacial tension, thereby achieving miscibility in the system more quickly.

[0228] For the fluid in well T, under the conditions of reservoir temperature of 128.7℃ and pressure of 57MPa, the variation curve of the mole fraction of N2 and C1 in the gas phase with the mole fraction of N2 injected into the reservoir is as follows: Figure 8 As shown, it can be seen that when enough N2 is injected, the mole fraction of N2 in the gas phase gradually increases, while the mole fraction of C1 gradually decreases.

[0229] Under conditions of a reservoir temperature of 128.7°C and a pressure of 57 MPa, the mole fractions of the various components in the reservoir fluid at equilibrium were calculated as a function of the N2 mole fraction in the reservoir. Table 2 shows the variation in the mole fractions of the gas and liquid phases of Well T as a function of the N2 mole fraction in the reservoir.

[0230] Table 2

[0231]

[0232]

[0233] From the results in Table 2, it can be seen that with the increase of N2 mole fraction in the reservoir, the C1 content in the liquid phase gradually decreases, and C 11+ The content increased slightly.

[0234] Then, the surrogate model method was used to calculate the oil-gas-water three-phase equilibrium constants of each component as a function of the N2 mole fraction in the reservoir. Table 3 shows the statistical table of the oil-gas-water three-phase equilibrium constants of each component of crude oil from Well T as a function of the N2 mole fraction in the reservoir.

[0235] Table 3

[0236]

[0237]

[0238] As can be seen from Table 3, the change in N2 mole fraction has little effect on the oil-gas-water three-phase equilibrium constant of each component. Under different N2 mole fractions, the oil-gas-water three-phase equilibrium constant of the same component is slightly different.

[0239] To investigate the effects of changes in injected gas composition on the oil-gas-water equilibrium constants of each component, we statistically analyzed the variations of the oil-gas-water equilibrium constants for each component with the CO2 mole fraction and the C1 mole fraction in the injected gas at a reservoir temperature of 128.7°C and a pressure of 57 MPa. Table 4 shows the variations of the oil-gas-water equilibrium constants for each component with the CO2 mole fraction in the injected gas, and Table 5 shows the variations of the oil-gas-water equilibrium constants for each component with the C1 mole fraction in the injected gas.

[0240] Table 4

[0241]

[0242] Table 5

[0243]

[0244] Tables 4 and 5 show that as the N₂ content in the injected gas decreases and the CO₂ and Cl contents increase, the oil-gas-water three-phase equilibrium constants of the hydrocarbon components change minimally. Therefore, the calculation results reveal the phase characteristics of Well T, guide the formulation of the gas injection plan, and improve injection efficiency.

[0245] It can be seen that the phase equilibrium calculation method provided in this disclosure can be used for gas injection development in fracture-cavity oil reservoirs, and provides technical support for the optimization of injection-production well patterns, injection-production parameters, and the formulation of subsequent gas injection technology policies.

[0246] Example 3

[0247] Figure 9 This is a schematic diagram of a phase equilibrium calculation device for a fracture-cavity reservoir provided by an embodiment of the present disclosure. Figure 9 This embodiment provides a phase equilibrium calculation device 100 for a fracture-vuggy oil reservoir, including a medium type determination module 101 and a phase equilibrium calculation module 102 .

[0248] The medium type determination module 101 is used to determine the medium type of the target fracture-vuggy reservoir;

[0249] Phase equilibrium calculation module 102, for selecting a corresponding calculation method according to the medium type of the target fracture-vuggy reservoir to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy reservoir;

[0250] When the medium type of the target fracture-cavity oil reservoir is a tight medium, the flash evaporation calculation method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-cavity oil reservoir;

[0251] When the medium type of the target fracture-cavity oil reservoir is a continuous medium, the Gibbs free energy method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-cavity oil reservoir;

[0252] When the medium type of the target fracture-vuggy oil reservoir is discrete medium, a proxy model method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy oil reservoir.

[0253] The medium type determination module 101 determines the medium type of the target fracture-vuggy oil reservoir; the phase equilibrium calculation module 102 selects a corresponding calculation method according to the medium type of the target fracture-vuggy oil reservoir to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy oil reservoir.

[0254] The specific embodiment of the method for calculating the phase equilibrium of a fracture-vuggy reservoir based on the above modules has been described in detail in the first embodiment and will not be repeated here.

[0255] Example 4

[0256] An embodiment of the present application provides an electronic device, which may be a mobile phone, computer, or tablet computer, including a memory and a processor. The memory stores a computer program, which, when executed by the processor, implements the fracture-vuggy reservoir phase equilibrium calculation method described in Example 1. It is understood that the electronic device may also include a multimedia component, an input / output (I / O) interface, and a communication component.

[0257] The processor is used to execute all or part of the steps in the fracture-vuggy reservoir phase equilibrium calculation method as described in Example 1. The memory is used to store various types of data, such as instructions for any application or method in the electronic device, as well as data related to the application.

[0258] The processor can be an application specific integrated circuit (ASIC), a digital signal processor (DSP), a digital signal processing device (DSPD), a programmable logic device (PLD), a field programmable gate array (FPGA), a controller, a microcontroller, a microprocessor, or other electronic components, and is used to execute the phase equilibrium calculation method for the fracture-cavity reservoir in the above-mentioned embodiment 1.

[0259] The memory can be implemented by any type of volatile or non-volatile memory device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic memory, flash memory, magnetic disk or optical disk.

[0260] Example 5

[0261] This embodiment further provides a computer-readable storage medium, such as a flash memory, a hard disk, a multimedia card, a card-type memory (e.g., an SD or DX memory), a random access memory (RAM), a static random access memory (SRAM), a read-only memory (ROM), an electrically erasable programmable read-only memory (EEPROM), a programmable read-only memory (PROM), a magnetic memory, a magnetic disk, an optical disk, a server, an App store, etc., on which a computer program is stored. When the computer program is executed by a processor, the following method steps can be implemented:

[0262] Step S101: determining the medium type of the target fracture-vuggy reservoir;

[0263] Step S102: selecting a corresponding calculation method according to the medium type of the target fracture-vuggy oil reservoir to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy oil reservoir;

[0264] When the medium type of the target fracture-cavity oil reservoir is a tight medium, the flash evaporation calculation method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-cavity oil reservoir;

[0265] When the medium type of the target fracture-cavity oil reservoir is a continuous medium, the Gibbs free energy method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-cavity oil reservoir;

[0266] When the medium type of the target fracture-vuggy oil reservoir is discrete medium, a proxy model method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy oil reservoir.

[0267] The specific implementation process of the above method steps can be found in Example 1, and this embodiment will not be repeated here.

[0268] In summary, the present disclosure provides a method, device, electronic device and storage medium for calculating the phase equilibrium of a fracture-vuggy oil reservoir. The method includes determining the medium type of a target fracture-vuggy oil reservoir; according to the medium type of the target fracture-vuggy oil reservoir, selecting a corresponding calculation method to calculate the oil-gas-water three-phase phase equilibrium in the target fracture-vuggy oil reservoir; wherein, when the medium type of the target fracture-vuggy oil reservoir is a dense medium, the flash evaporation calculation method is selected to calculate the oil-gas-water three-phase phase equilibrium in the target fracture-vuggy oil reservoir; when the medium type of the target fracture-vuggy oil reservoir is a continuous medium, the Gibbs free energy method is selected to calculate the oil-gas-water three-phase phase equilibrium in the target fracture-vuggy oil reservoir; when the medium type of the target fracture-vuggy oil reservoir is a discrete medium, the proxy model method is selected to calculate the oil-gas-water three-phase phase equilibrium in the target fracture-vuggy oil reservoir. This method, which employs a phase equilibrium calculation method tailored to each medium type, overcomes the existing problems of large calculation errors and heavy computational effort in fracture-vuggy reservoir phase equilibrium calculations, which arise from selecting a single phase equilibrium calculation method without considering the medium type. This method effectively captures the phase characteristics of fracture-vuggy reservoirs with various medium types, providing better guidance for oilfield gas injection development and possessing high practical value. This method can be applied to fracture-vuggy reservoir gas injection development, providing technical support for the optimization of injection-production well patterns, injection-production parameters, and the formulation of subsequent gas injection technology policies.

[0269] In the several embodiments provided in the present disclosure, it should be understood that the disclosed methods can also be implemented in other ways. The above-described method embodiments are merely illustrative.

[0270] It should be noted that, in this document, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus comprising the element.

[0271] Although the embodiments disclosed in this disclosure are as described above, the contents described are merely embodiments adopted to facilitate understanding of the disclosure and are not intended to limit the disclosure. Any person skilled in the art of the disclosure may make any modifications and changes in the form and details of the implementation without departing from the spirit and scope of the disclosure. However, the scope of patent protection of the disclosure shall still be based on the scope defined by the attached claims.

Claims

1. A method for calculating phase equilibrium of fracture-vuggy reservoirs, characterized in that: The method comprises: Determine the medium type of the target fracture-vuggy reservoir; According to the medium type of the target fracture-cavity oil reservoir, a corresponding calculation method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-cavity oil reservoir; When the medium type of the target fracture-cavity oil reservoir is a tight medium, the flash evaporation calculation method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-cavity oil reservoir; When the medium type of the target fracture-cavity oil reservoir is a continuous medium, the Gibbs free energy method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-cavity oil reservoir; When the medium type of the target fracture-cavity oil reservoir is discrete medium, a proxy model method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-cavity oil reservoir; When the medium type of the target fracture-vuggy oil reservoir is a tight medium, a flash evaporation calculation method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy oil reservoir, including the following steps: According to the PR state equation, the calculation formula of the gas-liquid two-phase equilibrium constant of each component is obtained; According to the calculation formula of the gas-liquid two-phase equilibrium constant of each component, the gas-liquid two-phase equilibrium constant of each component is calculated by the iteration method; Calculating the oil-gas-water three-phase equilibrium constant of each component based on the gas-liquid two-phase equilibrium constant of each component to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy reservoir; The PR state equation is: Wherein, P is the pressure of the target fracture-vuggy reservoir, T is the temperature of the target fracture-vuggy reservoir, R is the gas constant, is the residual molar volume of each component after adsorption, a and b are the process coefficients of the equation, is a function of relative temperature and eccentricity factor; According to the PR state equation, the calculation formula of the gas-liquid two-phase equilibrium constant of each component is obtained, which includes the following steps: According to the PR state equation and the relationship between the residual molar volume and the compressibility factor of each component after adsorption , we get the following cubic equation for the compression factor: Where Z is the compression factor, , ; Solving the cubic equation to obtain a solution, wherein the maximum value in the solution is the compressibility factor of the gas phase and the minimum value in the solution is the compressibility factor of the liquid phase; According to the compressibility factor of the gas phase and the compressibility factor of the liquid phase, the fugacity coefficient of each component in the gas phase and liquid phase is calculated by the following formula: in, is the fugacity coefficient of the i-th component in the gas phase, is the fugacity coefficient of the i-th component in the liquid phase, is the b coefficient of the i-th component, is the compressibility factor of the gas phase, is the compressibility factor of the liquid phase, is the number of components, is the mole fraction of the jth component in the target fracture-vuggy reservoir, is the combination coefficient of the i-th component and the j-th component, is the a coefficient of the i-th component, is the a coefficient of the jth component; According to the fugacity coefficients of each component in the gas phase and liquid phase respectively, the gas-liquid two-phase equilibrium constant of each component is calculated by the following formula: in, is the gas-liquid two-phase equilibrium constant of the i-th component.

2. The method according to claim 1, characterized in that When the medium type of the target fracture-vuggy oil reservoir is a continuous medium, the Gibbs free energy method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy oil reservoir, including the following steps: According to the Gibbs free energy function of the target fracture-vuggy reservoir and its corresponding constraint conditions, a set of objective function equations is obtained; Solving the objective function equations by an iterative method to obtain the mole fractions of each component in the oil phase, gas phase and water phase respectively; The oil-gas-water three-phase equilibrium constant of each component is obtained according to the mole fraction of each component in the oil phase, gas phase and water phase, so as to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy reservoir.

3. The method according to claim 2, characterized in that The Gibbs free energy function is: Where G is the Gibbs free energy, is the molar number of component i in phase k, is the chemical potential of the i-th component in the k-th phase, π is the total number of phases, is the number of components, and when the target fracture-vuggy reservoir is in equilibrium, the Gibbs free energy is minimum.

4. The method according to claim 3, characterized in that The constraints include: in, is the phase fraction of phase k, is the total number of moles in the target fracture-vuggy reservoir, is the phase fraction of the reference phase r phase, where the reference phase r phase is the oil phase or the water phase.

5. The method according to claim 4, characterized in that According to the Gibbs free energy function of the target fracture-vuggy reservoir and its corresponding constraints, the objective function equation group is obtained, which includes the following steps: According to the Gibbs free energy function and the constraints, the mole fraction of each component in each phase is calculated using the law of conservation of mass according to the following formula: in, is the mole fraction of the i-th component in the r-phase, is the mole fraction of the i-th component in the k-phase, is the mole fraction of the i-th component in the target fracture-vuggy reservoir, is the kr two-phase equilibrium constant of component i, is the phase stability variable of phase k, is the phase fraction of phase j, is the jr two-phase equilibrium constant of component i, is the phase stability variable of phase j; Substitute the mole fraction of each component in each phase into the calculation formula 1, the first objective function is: in, is the first objective function; According to the relationship between the phase fraction of each phase and the phase stability variable , the second objective function is: in, is the second objective function; According to the calculation formula of the mole fraction of each component in each phase, the third objective function is obtained as follows: in, is the third objective function, and the first objective function, the second objective function and the third objective function constitute an objective function equation group.

6. The method according to claim 5, characterized in that Solving the objective function equations by an iterative method to obtain the mole fractions of each component in the oil phase, gas phase, and water phase, respectively, comprises the following steps: Solving the objective function equations by an iterative method to obtain the mole fractions of each component in the other two phases except the reference phase; According to the mole fractions of each component in the other two phases except the reference phase, the mole fraction of each component in the reference phase is calculated by the law of conservation of mass to obtain the mole fractions of each component in the oil phase, gas phase and water phase respectively.

7. The method according to claim 1, characterized in that When the medium type of the target fracture-vuggy oil reservoir is a discrete medium, a proxy model method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy oil reservoir, including the following steps: According to the approximate expression between input parameters and output results, the polynomial response model is established as follows: in, To output the result, is the first input parameter of i, is the jth second input parameter, 、 、 is the coefficient to be determined, k is the number of the first input parameter and the second input parameter; Training the polynomial response model using a plurality of sample points to determine estimated values ​​of each undetermined coefficient, thereby optimizing the polynomial response model; The pressure of the target fracture-vuggy oil reservoir is input as a first input parameter, and the mole fraction of each component in the target fracture-vuggy oil reservoir is input as a second input parameter into the optimized polynomial response model to output the oil-gas-water three-phase equilibrium constant of each component, thereby calculating the oil-gas-water three-phase equilibrium in the target fracture-vuggy oil reservoir.

8. The method according to claim 7, characterized in that The polynomial response model is trained using a plurality of sample points to determine estimated values ​​of various undetermined coefficients, thereby optimizing the polynomial response model, including the following steps: Inputting the reservoir pressure corresponding to a plurality of sample points as a first input parameter and the mole fraction of each component in the reservoir as a second input parameter into the polynomial response model to obtain corresponding output results; wherein the output results include the oil-gas-water three-phase equilibrium constant of each component at the sample points; The calculation formula for determining the error between the output result and its corresponding actual value is: Where s is the error, is the actual value corresponding to the output result; The error calculation formula between the output result and its corresponding actual value is subjected to regression analysis by the least square method to determine the estimated value of each undetermined coefficient, thereby optimizing the polynomial response model.

9. The method according to claim 1, characterized in that The dense medium includes a matrix; The continuous medium includes small and medium-sized cracks and small and medium-sized dissolution pores; The discrete media include large caves and large cracks.

10. A phase equilibrium calculation device for a fracture-cavity oil reservoir, characterized in that: The device comprises: A medium type determination module is used to determine the medium type of the target fracture-vuggy reservoir; a phase equilibrium calculation module, configured to select a corresponding calculation method according to the medium type of the target fracture-vuggy reservoir to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy reservoir; When the medium type of the target fracture-cavity oil reservoir is a tight medium, the flash evaporation calculation method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-cavity oil reservoir; When the medium type of the target fracture-cavity oil reservoir is a continuous medium, the Gibbs free energy method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-cavity oil reservoir; When the medium type of the target fracture-cavity oil reservoir is discrete medium, a proxy model method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-cavity oil reservoir; When the medium type of the target fracture-vuggy oil reservoir is a tight medium, a flash evaporation calculation method is selected to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy oil reservoir, including the following steps: According to the PR state equation, the calculation formula of the gas-liquid two-phase equilibrium constant of each component is obtained; According to the calculation formula of the gas-liquid two-phase equilibrium constant of each component, the gas-liquid two-phase equilibrium constant of each component is calculated by the iteration method; Calculating the oil-gas-water three-phase equilibrium constant of each component based on the gas-liquid two-phase equilibrium constant of each component to calculate the oil-gas-water three-phase equilibrium in the target fracture-vuggy reservoir; The PR state equation is: Wherein, P is the pressure of the target fracture-vuggy reservoir, T is the temperature of the target fracture-vuggy reservoir, R is the gas constant, is the residual molar volume of each component after adsorption, a and b are the process coefficients of the equation, is a function of relative temperature and eccentricity factor; According to the PR state equation, the calculation formula of the gas-liquid two-phase equilibrium constant of each component is obtained, which includes the following steps: According to the PR state equation and the relationship between the residual molar volume and the compressibility factor of each component after adsorption , we get the following cubic equation for the compression factor: Where Z is the compression factor, , ; Solving the cubic equation to obtain a solution, wherein the maximum value in the solution is the compressibility factor of the gas phase and the minimum value in the solution is the compressibility factor of the liquid phase; According to the compressibility factor of the gas phase and the compressibility factor of the liquid phase, the fugacity coefficient of each component in the gas phase and liquid phase is calculated by the following formula: in, is the fugacity coefficient of the i-th component in the gas phase, is the fugacity coefficient of the i-th component in the liquid phase, is the b coefficient of the i-th component, is the compressibility factor of the gas phase, is the compressibility factor of the liquid phase, is the number of components, is the mole fraction of the jth component in the target fracture-vuggy reservoir, is the combination coefficient of the i-th component and the j-th component, is the a coefficient of the i-th component, is the a coefficient of the jth component; According to the fugacity coefficients of each component in the gas phase and liquid phase respectively, the gas-liquid two-phase equilibrium constant of each component is calculated by the following formula: in, is the gas-liquid two-phase equilibrium constant of the i-th component.

11. An electronic device, characterized in that: The method comprises a memory and a processor, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, the method for calculating phase equilibrium of a fracture-cavity oil reservoir according to any one of claims 1 to 9 is executed.

12. A storage medium, characterized in that: The computer program stored in the storage medium can be executed by one or more processors and can be used to implement the phase equilibrium calculation method for fracture-cavity oil reservoirs as claimed in any one of claims 1 to 9.

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