Method and device for calculating in-situ gas content and adsorption / free gas ratio of deep coal rock

Abstract

The invention discloses a deep coal rock in-situ gas content and adsorption / free gas proportion calculation method and device, and relates to the field of reservoir resource potential evaluation.The deep coal rock in-situ gas content and adsorption / free gas proportion calculation method comprises the steps that an isotope fractionation model coupled with a double-dispersion pore structure (matrix pores and kerogen pores) and a multi-gas transmission mechanism (viscous flow, Knudsen diffusion and surface diffusion) is constructed; the accumulated analytic gas quantity and the apparent isotope value of the produced gas obtained through solving are fitted with the actually measured accumulated analytic gas quantity and the apparent isotope value of the produced gas, and key parameters corresponding to the optimal fitting result are obtained; and determining the in-situ gas content, the in-situ adsorption gas proportion and the in-situ free gas proportion according to the productivity evaluation parameters at the initial moment corresponding to the optimal key parameters. According to the method, the in-situ gas content, the in-situ adsorbed gas proportion and the in-situ free gas proportion of the deep coal rock are calculated on the basis of an isotope fractionation model coupled with a double-dispersion pore structure and a multi-gas transmission mechanism, so that the gas resource content of the deep coal rock is predicted.

Description

Technical Field

[0001] The present application relates to the field of reservoir resource potential evaluation, and in particular to a method and device for calculating the in-situ gas content and adsorbed / free gas ratio of deep coal rocks. Background Art

[0002] Compared with shallow coal reservoirs, deep coal reservoirs have higher ground stress, formation fluid pressure and formation temperature conditions. The increase in formation pressure controls the physical properties of coal reservoirs: the porosity and permeability of coal reservoirs of different coal ranks decrease rapidly with the increase of effective stress. The permeability damage rate of coal rocks will reach the maximum after exceeding a specific burial depth. The maximum damage rate depths of low-rank coal and medium-high-rank coal rocks are about 500m and 900m respectively. Beyond this depth, the coal reservoir will become dense and low-permeable, and the effect of conventional reservoir transformation methods is poor. This is a key factor restricting the efficient flow and rapid production of deep coalbed methane. The increase in the proportion of free gas in deep coalbed methane is conducive to increasing the in-situ gas content of coal reservoirs, and it is also easier to promote the rapid production stage dominated by free gas in the early stage of production, so as to achieve the effect of improving the recovery rate. At present, the overall research on deep coalbed methane is still in its initial stage, especially for the enrichment characteristics and flow laws of deep coalbed methane, there is no clear understanding, lack of systematic and in-depth research work, and faces many challenges and difficulties. Among the many problems to be explored and solved, the following two have received special attention and importance: one is the recovery of the in-situ gas content of deep coal reservoirs; the other is the determination of the ratio of adsorbed gas to free gas in deep coal reservoirs. These two problems are related to the evaluation of coalbed methane resource potential, scientific calculation of (recoverable) reserves, and screening of favorable target areas / layers, and therefore also determine the decision-making on the investment intensity of the relevant targets and the benefits of exploration and development.

[0003] The methods proposed and applied so far for the evaluation of the in-situ gas content of coal and rock can be divided into direct method and indirect method. The direct method is also called core analysis method, which can be divided into pressure coring method and normal pressure coring method. The indirect method divides the total gas content into free gas, adsorbed gas and (a small amount of) dissolved gas according to the gas occurrence state. Among them, the free gas content and the dissolved gas content can be calculated by the gas state equation and the solubility equation. The key to the indirect method is the determination of the adsorbed gas content. Isothermal adsorption method is currently the most commonly used method for testing the adsorbed gas content of rocks. The method for determining the ratio of adsorbed gas / free gas in situ of coal and rock can also be divided into two categories: one is a direct method based on the on-site analysis process, and the other is an indirect method based on the gas occurrence state. There are certain shortcomings in the existing methods for evaluating the in-situ gas content of coal and rock and determining the ratio of adsorbed gas / free gas in situ of coal and rock.

[0004] In recent years, domestic and foreign researchers have conducted field analysis, gas well production, indoor simulation, molecular simulation and numerical simulation and other research work, which have strongly confirmed that there is a significant isotope fractionation effect in the migration process of methane in dense rocks such as shale / coal. And this fractionation phenomenon is closely related to the in-situ gas content and adsorbed gas ratio of the rock. By establishing an isotope fractionation model to calibrate the degassed gas volume and isotopes, the in-situ gas content and the in-situ free / adsorbed gas ratio can be determined simultaneously. This method has been promoted and applied in many shale gas blocks in China and has achieved good evaluation results. Previous researchers have also verified that the accuracy of the CIF model (carbon isotope fractionation model) is better than other traditional methods through pressure-maintained coring data. However, the existing isotope fractionation model is only applicable to homogeneous and relatively simple pore structures. Whether it is applicable to coal rocks with strong heterogeneity and pore structures mainly showing double pore characteristics still requires systematic research. Summary of the invention

[0005] The purpose of this application is to provide a method and device for calculating the in-situ gas content and adsorbed / free gas ratio of deep coal rocks. By establishing an isotope fractionation model that couples a double-dispersed pore structure (including matrix pores and kerogen pores) and multiple gas transport mechanisms (viscous flow, Knudsen diffusion and surface diffusion), the in-situ gas content, in-situ adsorbed gas ratio and in-situ free gas ratio of deep coal rocks can be calculated, thereby predicting the gas resource content of deep coal rocks.

[0006] To achieve the above objectives, this application provides the following solutions: In a first aspect, the present application provides a method for calculating the in-situ gas content and adsorbed / free gas ratio of deep coal rocks, comprising: Obtaining rock physical property parameters of coal and rock, and constructing a coal and rock simulation geometric model according to the rock physical property parameters; According to the coal-rock simulation geometric model, an isotope fractionation model is constructed; the isotope fractionation model is: 12 CH 4 and 13 CH 4 Control equations for mass transfer in bidisperse pore structures; bidisperse pore structures include matrix pores and kerogen pores; multi-gas transport mechanisms that couple viscous flow, Knudsen diffusion, and surface diffusion are considered in the control equations; the isotope fractionation model is used to determine the productivity evaluation parameters at any time based on the key parameters of coal rock; the key parameters include intrinsic permeability of matrix pores, permeability of kerogen pores, Langmuir volume, Langmuir pressure, initial average pore size of matrix pores, kerogen porosity, apparent diffusion coefficient ratio in matrix pores, diffusion coefficient ratio in kerogen pores, and initial carbon isotope value; the productivity evaluation parameters include free carbon in matrix pores12 CH 4 , free state 13 CH 4 , adsorption state 12 CH 4 , adsorption state 13 CH 4 and kerogen pore solution gas 12 CH 4 and 13 CH 4 The cumulative analyzed gas volume and apparent isotope value of produced gas; The initial conditions and boundary conditions of the isotope fractionation model are set, and under the constraints of the initial conditions and the boundary conditions, the isotope fractionation model is solved to calculate the production capacity assessment parameters at any time; the initial conditions are set according to the burial depth and pressure coefficient of the core of the coal rock; the boundary conditions are set according to the atmospheric pressure, core extraction time, initial core pressure and mud density; Obtain the cumulative analytical gas volume and the apparent isotope value of the produced gas measured in the field analytical experiment of coalbed methane, and fit the measured cumulative analytical gas volume and the apparent isotope value of the produced gas with the cumulative analytical gas volume and the apparent isotope value of the produced gas obtained by solving the model to obtain the key parameters corresponding to the optimal fitting result; the optimal fitting result refers to the fitting result with the smallest fitting error; According to the production capacity assessment parameters at the initial moment corresponding to the optimal key parameters, the in-situ gas content, the in-situ adsorbed gas ratio and the in-situ free gas ratio are determined; the in-situ gas content, the in-situ adsorbed gas ratio and the in-situ free gas ratio are used to assess the production capacity of coal rock gas resources; the optimal key parameters are the key parameters corresponding to the optimal fitting results.

[0007] In a second aspect, the present application provides a device for calculating the in-situ gas content and adsorbed / free gas ratio of deep coal rocks, comprising: A simulation geometry model building module is used to obtain rock physical property parameters of coal and rock, and to build a coal and rock simulation geometry model according to the rock physical property parameters; The isotope fractionation model construction module is used to construct an isotope fractionation model according to the coal rock simulation geometric model; the isotope fractionation model is 12 CH 4 and 13 CH 4Control equations for mass transfer in bidisperse pore structures; bidisperse pore structures include matrix pores and kerogen pores; multi-gas transport mechanisms that couple viscous flow, Knudsen diffusion, and surface diffusion are considered in the control equations; the isotope fractionation model is used to determine the productivity evaluation parameters at any time based on the key parameters of coal rock; the key parameters include intrinsic permeability of matrix pores, permeability of kerogen pores, Langmuir volume, Langmuir pressure, initial average pore size of matrix pores, kerogen porosity, apparent diffusion coefficient ratio in matrix pores, diffusion coefficient ratio in kerogen pores, and initial carbon isotope value; the productivity evaluation parameters include free carbon in matrix pores 12 CH 4 , free state 13 CH 4 , adsorption state 12 CH 4 , adsorption state 13 CH 4 and kerogen pore solution gas 12 CH 4 and 13 CH 4 The cumulative analyzed gas volume and apparent isotope value of produced gas; The condition setting and solving module is used to set the initial conditions and boundary conditions of the isotope fractionation model, and solve the isotope fractionation model under the constraints of the initial conditions and the boundary conditions to calculate the production capacity assessment parameters at any time; the initial conditions are set according to the burial depth and pressure coefficient of the coal core; the boundary conditions are set according to the atmospheric pressure, core extraction time, core initial pressure and mud density; The data fitting module is used to obtain the cumulative analytical gas volume and the apparent isotope value of the produced gas measured in the field analysis experiment of coalbed methane, and fit the measured cumulative analytical gas volume and the apparent isotope value of the produced gas with the cumulative analytical gas volume and the apparent isotope value of the produced gas obtained by the model solution to obtain the key parameters corresponding to the optimal fitting result; the optimal fitting result refers to the fitting result with the smallest fitting error; The gas resource capacity assessment module is used to determine the in-situ gas content, the in-situ adsorbed gas ratio and the in-situ free gas ratio according to the capacity assessment parameters at the initial moment corresponding to the optimal key parameters; the in-situ gas content, the in-situ adsorbed gas ratio and the in-situ free gas ratio are used to assess the capacity of coal gas resources; the optimal key parameters are the key parameters corresponding to the optimal fitting results.

[0008] In the third aspect, the present application provides a computer device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the above-mentioned method for calculating the in-situ gas content and adsorbed / free gas ratio of deep coal rocks.

[0009] In a fourth aspect, the present application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the above-mentioned method for calculating the in-situ gas content and adsorbed / free gas ratio of deep coal rocks.

[0010] According to the specific embodiments provided in this application, this application discloses the following technical effects: The present application provides a method and device for calculating the in-situ gas content and adsorbed / free gas ratio of deep coal rocks. By establishing an isotope fractionation model that couples a double-dispersed pore structure (including matrix pores and kerogen pores) and multiple gas transport mechanisms (viscous flow, Knudsen diffusion, and surface diffusion), it is possible to simultaneously fit the cumulative analyzed gas volume and the apparent isotope value of the produced gas during the field analysis process, and then invert and determine key parameters close to the real core. These key parameters are substituted into the isotope fractionation model to forward calculate the in-situ gas content, in-situ adsorbed gas ratio, and in-situ free gas ratio of deep coal rocks, thereby predicting the gas resource content of deep coal rocks. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0012] Figure 1 This is an application environment diagram of a method for calculating the in-situ gas content and adsorbed / free gas ratio of deep coal rock in one embodiment of the present application; Figure 2 A schematic flow chart of a method for calculating the in-situ gas content and adsorbed / free gas ratio of deep coal rock provided in one embodiment of the present application; Figure 3 A schematic diagram of functional modules of a device for calculating the in-situ gas content and adsorbed / free gas ratio of deep coal rock provided in one embodiment of the present application; Figure 4 A schematic diagram of the structure of a computer device provided in one embodiment of the present application. DETAILED DESCRIPTION

[0013] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0014] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0015] The methods proposed and applied so far for the evaluation of the in-situ gas content of coal and rock can be divided into direct method and indirect method. The direct method is also called core analysis method, which can be divided into pressure-maintaining coring method and normal pressure coring method. The pressure-maintaining coring method is a technical method that uses special pressure-maintaining coring drill tools to maintain the original formation pressure of the core until it reaches the ground and then measures the gas content. This technology can minimize the loss of oil and gas components in the core and is currently recognized as the most reliable method for determining gas content. However, on the one hand, due to pressure-maintaining capacity and engineering construction problems, pressure-maintaining coring is also difficult to reduce the gas loss to zero. On the other hand, the cost of pressure-maintaining coring is too high and it is difficult to promote and use on a large scale. The normal pressure coring method uses conventional coring tools that do not have pressure-maintaining capacity. After drilling to obtain the core, the core is divided into sections and placed in an analysis tank. The core is analyzed at normal pressure and a specific temperature until there is basically no gas precipitated from the core. The gas volume measured in this process is recorded as the analyzed gas volume. The gas remaining in the micropores or closed pores is difficult to spontaneously analyze under normal pressure and specific temperature, and needs to be released and measured by grinding and crushing. This part of the gas is called residual gas volume. The most critical problem of the normal pressure coring method is that during the lifting of the core in the wellbore and the exposure to the ground before sealing, most of the gas escapes due to the reduction of environmental pressure and is not actually measured. This part of the gas is called lost gas volume. For the lost gas volume in this process, the widely used recovery methods include USBM method, polynomial fitting, Smith-Williams method, ACF method and MCF method. The above methods have the following shortcomings: (1) They are more suitable for shallow coalbed methane with a short loss time and a low free gas ratio, but there are significant errors when applied to deep shale gas with a long loss time and a high free gas ratio. Therefore, their applicability and accuracy in deep coalbed methane are also questioned; (2) They only consider the concentration diffusion effect, but do not consider the desorption effect of adsorbed gas and its coupling relationship with the diffusion effect, resulting in the lack of rigor in the theoretical basis of this method and the inability to effectively evaluate the key parameter of the adsorbed gas / free gas ratio; (3) The zero point of the loss time is defined as the time from core lifting to half the well depth, and there are subjective errors in the number of initial analytical data points involved in the fitting.

[0016] The indirect method divides the total gas content into free gas, adsorbed gas and (a small amount of) dissolved gas according to the gas occurrence state. The free gas content and dissolved gas content can be calculated by the gas state equation and the solubility equation. The key to the indirect method is the determination of the adsorbed gas content. The isothermal adsorption method is currently the most commonly used method to test the adsorbed gas content of rocks. However, the difficulty of this method lies in how the isothermal adsorption experimental device simulates the real in-situ formation conditions, especially the temperature, pressure, water content and microscopic distribution conditions of the formation.

[0017] The methods for determining the ratio of in-situ adsorbed gas to free gas in coal can also be divided into two categories: one is a direct method based on the on-site analysis process, and the other is an indirect method based on the gas occurrence state. δ 13 C 1 The monotonic change law of the value is to convert the first-order analytical gas and the third-order analytical gas δ 13 C 1 The values ​​are used as the isotopic compositions of free gas end members and adsorbed gas end members, respectively. The contribution ratio of each end member in the second-order analyzed gas can be determined through the binary mixing model, and then the adsorbed gas / free gas ratio in the total gas content can be determined. The principle and operation of this method are relatively simple, but there may be the following problems: ① The loss gas volume is a key intermediate parameter involved in the calculation of the adsorbed gas / free gas ratio, but there is still no recognized accurate method for the accurate recovery of the loss gas content, and the accuracy of the adsorbed gas / free gas ratio calculated by this method is also questionable; ② The numerical simulation calculation results of the shale gas analysis process show that there is no ideal end member gas in the complete analysis process, the adsorbed gas ratio in the loss gas and the first-order analyzed gas cannot be ignored, and the free gas in the second-order and third-order analyzed gas also has a large contribution.

[0018] The indirect method mainly combines isothermal adsorption experiments with other methods, such as isothermal adsorption experiments combined with gas state equations, or isothermal adsorption experiments combined with nuclear magnetic resonance technology. The former uses different theoretical equations to characterize gases in different states of occurrence, such as isothermal adsorption experiments combined with adsorption theoretical equations to evaluate the amount of adsorbed gas in rocks, and gas state equations combined with reservoir parameters (such as pressure, temperature and effective porosity, etc.) to evaluate the free gas content. The latter is to conduct real-time monitoring of nuclear magnetic resonance in isothermal adsorption experiments, and use the advantages of nuclear magnetic resonance T2 spectrum in quantitative identification of the response characteristics of gas content and distribution in different states of occurrence, set T2 cutoff values ​​to divide the T2 spectrum ranges to which free gas and adsorbed gas belong, and quantitatively calculate the adsorbed gas / free gas content and ratio in rocks by integrating the spectrum peak area within a specific range. The key to this method lies in the accuracy of the T2 cutoff value division. However, the existing methods for evaluating the in-situ gas content of coal rocks and determining the in-situ adsorbed gas / free gas ratio of coal rocks have certain shortcomings.

[0019] In addition, by establishing an isotope fractionation model to calibrate the degassed gas volume and isotopes, the in-situ gas content and the in-situ free / adsorbed gas ratio can be determined simultaneously. However, the existing isotope fractionation model is only applicable to homogeneous conditions with relatively simple pore structures. Whether it is applicable to coal rocks with strong heterogeneity and pore structures mainly showing dual-porosity characteristics still requires systematic research.

[0020] In this regard, the present application provides a method for calculating the in-situ gas content and adsorbed / free gas ratio of deep coal rock, which can be applied to Figure 1 In the application environment shown. Among them, the terminal communicates with the server through the network. The data storage system can store the data that the server needs to process. The data storage system can be set up separately, integrated on the server, or placed on the cloud or other servers. The terminal can send construction parameters (including core lifting time, ground exposure time, drilling fluid density and drilling fluid temperature), reservoir parameters (including reservoir burial depth and pressure coefficient) and rock physical parameters (core radius, core length, core quality and gas porosity) to the server. After the server receives the parameters required by the isotope fractionation model, it constructs a coal-rock simulation geometric model and an isotope fractionation model to evaluate the production capacity of coal-rock gas resources. Specifically, the server constructs a coal-rock simulation geometric model according to the rock physical parameters; constructs an isotope fractionation model according to the coal-rock simulation geometric model; the isotope fractionation model is 12 CH 4 and 13 CH 4 Control equations for the mass transfer process in a bidispersed pore structure; the bidispersed pore structure includes matrix pores and kerogen pores; the multi-gas transport mechanism of viscous flow, Knudsen diffusion and surface diffusion coupling is considered in the control equation; the initial conditions and boundary conditions of the isotope fractionation model are set, and the isotope fractionation model is solved under the constraints of the initial conditions and the boundary conditions to calculate the capacity evaluation parameters at any time; the cumulative desorbed gas volume and the apparent isotope value of the produced gas measured in the field analysis experiment of coalbed methane are obtained, and the measured cumulative desorbed gas volume and the apparent isotope value of the produced gas are fitted with the cumulative desorbed gas volume and the apparent isotope value of the produced gas obtained by the model solution to obtain the key parameters corresponding to the optimal fitting result; according to the capacity evaluation parameters at the initial moment corresponding to the optimal key parameters, the in-situ gas content, the in-situ adsorbed gas ratio and the in-situ free gas ratio are determined. The server can feed back the obtained in-situ gas content, in-situ adsorbed gas ratio and in-situ free gas ratio to the terminal. In addition, in some embodiments, the method for calculating the in-situ gas content and the adsorbed / free gas ratio of deep coal rock can also be implemented independently by a server or a terminal. For example, the in-situ gas content and the adsorbed / free gas ratio can be directly calculated by the terminal, or the server can obtain relevant parameters from the data storage system and calculate the in-situ gas content and the adsorbed / free gas ratio.

[0021] The terminal may be, but is not limited to, various desktop computers, laptops, smart phones, tablet computers, IoT devices, and portable wearable devices. The server may be implemented as an independent server or a server cluster consisting of multiple servers, or may be a cloud server.

[0022] In an exemplary embodiment, Figure 2 As shown, a method for calculating the in-situ gas content and adsorption / free gas ratio of deep coal rock is provided. The method is executed by a computer device, and can be executed by a computer device such as a terminal or a server alone, or by a terminal and a server together. In the embodiment of the present application, the method is applied to Figure 1 The server in is taken as an example to illustrate, including the following steps 101 to 105.

[0023] Step 101, obtaining rock physical property parameters of coal rock, and constructing a coal rock simulation geometric model according to the rock physical property parameters, and performing meshing.

[0024] Step 102: construct an isotope fractionation model based on the coal-rock simulation geometric model; the isotope fractionation model is 12 CH 4 and 13 CH 4 Control equations for mass transfer in bidisperse pore structures; bidisperse pore structures include matrix pores and kerogen pores; multi-gas transport mechanisms that couple viscous flow, Knudsen diffusion, and surface diffusion are considered in the control equations; the isotope fractionation model is used to determine the productivity evaluation parameters at any time based on the key parameters of coal rock; the key parameters include intrinsic permeability of matrix pores, permeability of kerogen pores, Langmuir volume, Langmuir pressure, initial average pore size of matrix pores, kerogen porosity, apparent diffusion coefficient ratio in matrix pores, diffusion coefficient ratio in kerogen pores, and initial carbon isotope value; the productivity evaluation parameters include free carbon in matrix pores 12 CH 4 , free state 13 CH 4 , adsorption state 12 CH 4 , adsorption state 13 CH 4 and kerogen pore solution gas 12 CH 4 and 13 CH 4 The cumulative analyzed gas volume and apparent isotope value of produced gas.

[0025] Step 103, setting the initial conditions and boundary conditions of the isotope fractionation model, and solving the isotope fractionation model under the constraints of the initial conditions and the boundary conditions, and calculating the production capacity assessment parameters at any time; the initial conditions are set according to the burial depth and pressure coefficient of the coal core; the boundary conditions are set according to the atmospheric pressure, core extraction time, core initial pressure and mud density.

[0026] Step 104, obtain the cumulative analyzed gas volume and the apparent isotope value of the produced gas measured in the coalbed methane field analysis experiment, and fit the measured cumulative analyzed gas volume and the apparent isotope value of the produced gas with the cumulative analyzed gas volume and the apparent isotope value of the produced gas obtained by solving the model to obtain the key parameters corresponding to the optimal fitting result; the optimal fitting result refers to the fitting result with the smallest fitting error.

[0027] Step 105, determine the in-situ gas content, in-situ adsorbed gas ratio and in-situ free gas ratio according to the capacity assessment parameters at the initial moment corresponding to the optimal key parameters; the in-situ gas content, in-situ adsorbed gas ratio and in-situ free gas ratio are used to assess the capacity of coal rock gas resources; the optimal key parameters are the key parameters corresponding to the optimal fitting results.

[0028] Implementing the above steps 101 to 105 provides a method for determining the in-situ gas content and adsorbed gas / free gas ratio of deep coal rocks based on isotope fractionation. By establishing an isotope fractionation model that couples a double-dispersed pore structure (matrix pores and kerogen pores) and multiple gas transport mechanisms (viscous flow, Knudsen diffusion, and surface diffusion), it is possible to simultaneously fit the cumulative analyzed gas volume and the isotope values ​​of the produced gas during the field analysis process, and then inversely determine the key unknown parameters of the model. These key unknown parameters are substituted into the isotope fractionation model to forward calculate the in-situ gas content, in-situ adsorbed gas ratio, and in-situ free gas ratio of deep coal rocks, thereby predicting the gas resource content of deep coal rocks.

[0029] In another exemplary embodiment of the present application, in step 102, establishing 12 CH 4 and 13 CH 4 Partial differential equations for mass transfer in a bidispersed pore structure. As an example, the specific formula of the partial differential equations is as follows (1).

[0030] (1).

[0031] In the formula, B 1 , B 2 , C 1 and C 2 They are respectively expressed as the following formula (2).

[0032] (2).

[0033] In the formula, P m , , P k and They are 12 CH 4 The gas pressure in the matrix pores, 13 CH 4 The gas pressure in the matrix pores, 12 CH 4 Gas pressure in the kerogen pores, 13 CH 4 Gas pressure in kerogen pores; D m_app and They are 12 CH 4 and 13 CH 4 The apparent diffusion coefficient of D k and They are 12 CH 4 and 13 CH 4 apparent diffusion coefficient in kerogen pores; ; represents the viscosity of the kerogen pores; k k represents the kerogen pore permeability; is the effective porosity of the matrix pores; is the initial gas-containing porosity of matrix pores; is the porosity of kerogen pores; c is the mass balance ratio parameter, ,in, is the apparent density of coal rock, V L is the Langmuir volume of coal rock, Z m is the gas compressibility factor of the matrix pores, R is the ideal gas constant, T To resolve the temperature, V std is the standard molar volume constant of the gas; and They are 12 CH 4 and 13 CH 4 The Langmuir constant is, =exp( A / T 2 - B / T ),in A =95.17K 2 , B =0.125K). represents the gradient; t represents the time t.

[0034] In the partial differential equation group of formula (1), considering the influence of the adsorption layer on the average pore size and porosity of the matrix pores and the real gas effect (the viscosity, compressibility factor and density of the gas are affected by temperature and pressure), the influence of the adsorption layer on the average pore size and porosity of the matrix pores can be expressed as the following formula (3) and the following formula (4).

[0035] (3).

[0036] (4).

[0037] In the formula, is the average pore size of the matrix pores; r 0 is the initial average pore size of the matrix pores not affected by the adsorption layer; d m is the diameter of the methane molecule, methane is taken as 0.38 nm; is the initial porosity of the matrix pores not affected by the adsorption layer; express 12 CH 4 coverage rate; express 13 CH 4 coverage.

[0038] The effect of temperature and pressure on the gas density in matrix pores and kerogen pores can be expressed as follows (5).

[0039] (5).

[0040] in, represents the gas density of the matrix pores; represents the gas density of the kerogen pores; represents the gas compressibility factor of the kerogen pores; M is the relative molecular mass of the gas.

[0041] The effect of temperature and pressure on the gas compressibility factor in matrix pores and kerogen pores can be expressed as follows (6).

[0042] (6).

[0043] In the formula, represents the gas compressibility factor of the matrix pores; Represents the gas compressibility factor of the kerogen pores.

[0044] (7).

[0045] The effect of temperature and pressure on the viscosity in matrix pores and kerogen pores can be expressed as follows (8).

[0046] (8).

[0047] In the formula, represents the viscosity of the matrix pores; represents the viscosity of the kerogen pores; M is the relative molecular mass of the gas, methane is taken as 16kg / mol.

[0048] In this application, in the partial differential equation system of formula (1), the multi-gas transport mechanism of viscous flow, Knudsen diffusion and surface diffusion coupling is considered, as shown in the following formula (9).

[0049] (9).

[0050] Among them, the apparent diffusion coefficient of equation (1) is D m_app Reflects viscous flow.

[0051] In the formula, K n_real is the Knudsen number of the real gas, which can be expressed as ; k v is the intrinsic permeability of the matrix pores; P L is the Langmuir pressure of coal rock; is the tortuosity of the matrix pores; D s is the surface diffusion coefficient, which can be expressed as the following formula (10).

[0052] (10).

[0053] In the formula, κ It is the ratio of the blocking rate constant to the forward transmission rate constant, and is usually taken as 0.5 in coal rock; D s0 is the surface diffusion coefficient when the gas coverage is 0, which can be expressed as the following formula (11).

[0054] (11).

[0055] In the formula, Δ H is the isothermal adsorption heat when the gas coverage is 0.

[0056] The control equation corresponding to the isotope fractionation model is mainly formula (1). Formulas (2) to (11) are mainly calculation formulas for the parameter variables in formula (1).

[0057] In another exemplary embodiment of the present application, in step 103, the initial conditions of the isotope fractionation model are set: after the control equation corresponding to the isotope fractionation model is established, the initial conditions are set according to the reservoir parameters (including the burial depth and pressure coefficient of the core), specifically as shown in the following formula (12).

[0058] (12).

[0059] In the formula, P 0 is the initial reservoir pressure of the core, which can be calculated by multiplying the pressure coefficient by the burial depth; for 12 CH 4 and 13 CH 4 The ratio of the amounts of initial substances; δ 0 is the initial carbon isotope value of methane; R st is the carbon isotope atomic ratio of the PDB standard sample, and its value is 0.0112372. The “x, y, z” in represents any position in the coal-rock simulation geometric model; The “0” in represents the initial time (t=0).

[0060] In another exemplary embodiment of the present application, in step 103, the boundary conditions of the isotope fractionation model are set as follows: the time when the core starts to lose gas during the core extraction process is determined based on the mud density and the initial pressure of the core, and other surfaces are insulated except for the connection surface between the desorption tank and the pipeline for exhausting gas. The boundary conditions of the isotope fractionation model can be set as the following formula (13).

[0061] (13).

[0062] In the formula, It is the connection surface between the analytical tank and the exhaust gas pipeline in the coal-rock simulation geometric model; It represents the top end surface of the core in the coal-rock simulation geometric model, excluding the connection surface with the pipeline for exhausting gas; This is the bottom end face of the core in the coal rock simulation geometric model. This is the side view of the core in the coal rock simulation geometric model. is the radius of the exhaust pipe; is the radius of the core; H is the height of the core; express 12 CH 4 and 13 CH 4 The ratio of the amount of a substance; P b ( t) is the boundary pressure, which can be expressed as the following formula.

[0063] .

[0064] In the formula, P atm is atmospheric pressure, t coring To remind time, t loss is the time when gas loss starts. The time when gas loss starts can be calculated from the initial core pressure, mud density and core lifting time, as shown in the following formula (14).

[0065] (14).

[0066] In the formula, Indicates mud pressure.

[0067] In another exemplary embodiment of the present application, the established coal-rock simulation geometric model, partial differential equations, initial conditions and boundary conditions are imported into mathematical computing software (such as MATLAB or COMSOL), and the dependent variable of the equations can be solved ( P m , , P k and ) changes with time and space, that is, the pressure field distribution inside the core is obtained. By volume integrating the pressure field obtained, the free state in the matrix pores at any time can be calculated. 12 CH 4 , free state 13 CH 4 , adsorption state 12 CH 4 , adsorption state 13 CH 4 and kerogen pore solution gas 12 CH 4 and 13 CH 4 The cumulative analyzed gas volume.

[0068] Optionally, the specific formula of the volume integration method is the following formula (15).

[0069] (15).

[0070] In the formula, , , and , respectively t 0 ~ t i Matrix pore free state12 CH 4 , free state 13 CH 4 , adsorption state 12 CH 4 and adsorption state 13 CH 4 The cumulative amount of gas analyzed, and They are t 0 ~ t i Kerogen pores during the time period 12 CH 4 and 13 CH 4 The cumulative amount of gas analyzed; V is the apparent density of coal rock; L is the Langmuir volume of coal rock; is the porosity of kerogen pores; t 0 is the initial moment; t i express t i time; is the rock quality; is the molar volume of the gas, which is 22.4 L / mol.

[0071] According to the above solution of methane in different states of existence, that is, the free state in the matrix pores 12 CH 4 , free state 13 CH 4 , adsorption state 12 CH 4 , adsorption state 13 CH 4 and kerogen pore solution gas 12 CH 4 and 13 CH 4 The total cumulative desorbed gas volume and apparent isotope value can be further calculated as shown in the following formula (16).

[0072] (16).

[0073] In the formula, Indicates the total cumulative analyzed gas volume; represents the apparent isotope value.

[0074] Based on the above content, in step 103, under the constraints of the initial conditions and the boundary conditions, the isotope fractionation model is solved to calculate the production capacity assessment parameters at any time, specifically including: (1) Randomly determine several numerical combinations corresponding to the key parameters within the valid numerical range of the key parameters.

[0075] (2) Under the constraints of the initial conditions and the boundary conditions, each of the numerical combinations is substituted into the isotope fractionation model to obtain the production capacity assessment parameters corresponding to each numerical combination at any time.

[0076] Each key parameter (including matrix pore intrinsic permeability, kerogen pore permeability, Langmuir volume, Langmuir pressure, initial average pore diameter of matrix pores, kerogen porosity, apparent diffusion coefficient ratio in matrix pores, diffusion coefficient ratio in kerogen pores and initial carbon isotope value) has a corresponding range of values. A value is selected within each range of values. After all key parameters are selected, a value combination is formed. Under this value combination, the corresponding capacity evaluation parameter (free state in matrix pores) can be calculated. 12 CH 4 , free state 13 CH 4 , adsorption state 12 CH 4 , adsorption state 13 CH 4 and kerogen pore solution gas 12 CH 4 and 13 CH 4 The cumulative analyzed gas volume and apparent isotope value of the produced gas are then fitted and compared with the measured production capacity assessment parameters under each value combination to obtain the case with the smallest fitting error, and the optimal key parameters can be further obtained.

[0077] In another exemplary embodiment of the present application, in step 104, a specific coal rock sample is selected, a coalbed methane field analysis experiment is carried out, the gas in the analysis process is collected with a salt water bottle (the salt water bottle is kept upside down), and the cumulative amount of analyzed gas in the analysis process is recorded. The collected field analyzed gas is tested for methane carbon isotope to obtain isotope value data of the analyzed gas, thereby obtaining the cumulative analyzed gas volume and the apparent isotope value of the produced gas measured in the coalbed methane field analysis experiment.

[0078] The cumulative gas volume and apparent isotope values ​​calculated theoretically based on formulas (15) and (16) were compared with the measured cumulative gas volume and isotope values ​​of the produced gas obtained by isotope testing. The error function was established using the least squares method. The minimum value of the error function was obtained using the BOBYQA algorithm of COMSOL software, and the optimal key parameters in the isotope fractionation model were obtained, including the matrix pore intrinsic permeability ( k v ), kerogen pore permeability ( kk )、Langmuir volume( V L )、Langmuir pressure( P L ), initial average pore size of matrix pores ( r 0 ), kerogen porosity ( ), the apparent diffusion coefficient ratio in the matrix pores ( ), the diffusion coefficient ratio in the kerogen pores ( ), initial carbon isotope value ( δ 0 The parameters determined in the model are the core radius ( r )、Core height( H ), initial gas-bearing porosity of matrix pores ( ), the ratio of the blocking rate constant to the forward transmission rate constant ( κ =0.5), isothermal adsorption heat when the gas coverage is 0 (Δ H= 28kJ / mol), matrix pore tortuosity ( =1.05).

[0079] In another exemplary embodiment of the present application, in step 105, the obtained optimal key parameters are substituted into formula (1) to formula (11), and the internal pressure field distribution close to the real core at any time can be obtained by forward calculation based on the established coal-rock simulation geometric model, partial differential equations, initial conditions and boundary conditions. The in-situ gas content, in-situ adsorbed gas ratio and in-situ free gas ratio can be obtained by simply integrating the pressure field at the initial time, as shown in the following formulas (17) and (18).

[0080] (17).

[0081] (18).

[0082] In the formula, GIP content is the in-situ gas content; FGR is the in-situ free gas ratio; AGR is the in-situ adsorbed gas ratio; , , and , respectively Matrix pore free state 12 CH 4 , free state 13 CH 4 , adsorption state 12 CH 4 and adsorption state 13 CH 4 The cumulative gas volume; and Kerogen pores 12 CH 4 and 13 CH 4 The cumulative gas volume; Indicates the initial moment. Since no analysis has been performed at the initial moment, there is no cumulative analysis volume at the initial moment, which is called cumulative volume.

[0083] Based on the above, in step 105, the in-situ gas content, the in-situ adsorbed gas ratio and the in-situ free gas ratio are determined according to the capacity evaluation parameters at the initial moment corresponding to the optimal key parameters, specifically including: (1) The optimal key parameters are introduced into the isotope fractionation model to obtain the pressure field distribution inside the core corresponding to the optimal key parameters.

[0084] (2) Perform volume integration on the pressure field distribution at the initial moment to obtain the free state in the matrix pores at the initial moment 12 CH 4 , free state 13 CH 4 , adsorption state 12 CH 4 , adsorption state 13 CH 4 and kerogen pore solution gas 12 CH 4 and 13 CH 4 The gas content.

[0085] (3) According to the free state in the matrix pores at the initial moment 12 CH 4 , free state 13 CH 4 , adsorption state 12 CH 4 , adsorption state 13 CH 4 and kerogen pore solution gas 12 CH 4 and 13 CH 4 The in-situ gas content, in-situ free gas ratio and in-situ adsorbed gas ratio are calculated based on the accumulated gas volume.

[0086] The present application also provides an application scenario, which applies the above-mentioned method for calculating the in-situ gas content and adsorption / free gas ratio of deep coal rocks. Specifically: the method for calculating the in-situ gas content and adsorption / free gas ratio of deep coal rocks provided in this embodiment can be applied in the scenario of capacity assessment of deep coal rock gas resources. The scenario of capacity assessment of deep coal rock gas resources includes a data acquisition link, which is used to obtain relevant parameters for capacity assessment; a capacity assessment link, which is used to calculate the in-situ gas content and adsorption / free gas ratio based on the acquired relevant parameters for capacity assessment to realize the capacity assessment of deep coal rock gas resources; and a result display link, which is used to display the results of capacity assessment. The method for calculating the in-situ gas content and adsorption / free gas ratio of deep coal rocks provided in this embodiment belongs to the capacity assessment link.

[0087] Based on the same inventive concept, the embodiment of the present application also provides a deep coal rock in-situ gas content and adsorption / free gas ratio calculation device for realizing the deep coal rock in-situ gas content and adsorption / free gas ratio calculation method involved in the above. The implementation scheme for solving the problem provided by the device is similar to the implementation scheme recorded in the above method, so the specific limitations in one or more deep coal rock in-situ gas content and adsorption / free gas ratio calculation device embodiments provided below can refer to the limitations of the deep coal rock in-situ gas content and adsorption / free gas ratio calculation method in the above text, and will not be repeated here.

[0088] In an exemplary embodiment, Figure 3 As shown, a device for calculating the in-situ gas content and adsorption / free gas ratio of deep coal rock is provided, comprising: The simulation geometric model building module M1 is used to obtain rock physical property parameters of coal rock and build a coal rock simulation geometric model according to the rock physical property parameters.

[0089] The isotope fractionation model construction module M2 is used to construct an isotope fractionation model according to the coal rock simulation geometric model; the isotope fractionation model is 12 CH 4 and 13 CH 4 Control equations for mass transfer in bidisperse pore structures; bidisperse pore structures include matrix pores and kerogen pores; multi-gas transport mechanisms that couple viscous flow, Knudsen diffusion, and surface diffusion are considered in the control equations; the isotope fractionation model is used to determine the productivity evaluation parameters at any time based on the key parameters of coal rock; the key parameters include intrinsic permeability of matrix pores, permeability of kerogen pores, Langmuir volume, Langmuir pressure, initial average pore size of matrix pores, kerogen porosity, apparent diffusion coefficient ratio in matrix pores, diffusion coefficient ratio in kerogen pores, and initial carbon isotope value; the productivity evaluation parameters include free carbon in matrix pores 12 CH 4 , free state13 CH 4 , adsorption state 12 CH 4 , adsorption state 13 CH 4 and kerogen pore solution gas 12 CH 4 and 13 CH 4 The cumulative analyzed gas volume and apparent isotope value of produced gas.

[0090] The condition setting and solving module M3 is used to set the initial conditions and boundary conditions of the isotope fractionation model, and solve the isotope fractionation model under the constraints of the initial conditions and the boundary conditions to calculate the production capacity assessment parameters at any time; the initial conditions are set according to the burial depth and pressure coefficient of the coal core; the boundary conditions are set according to the atmospheric pressure, core extraction time, core initial pressure and mud density.

[0091] The data fitting module M4 is used to obtain the cumulative analyzed gas volume and the apparent isotope value of the produced gas measured in the coalbed methane field analysis experiment, and to fit the measured cumulative analyzed gas volume and the apparent isotope value of the produced gas with the cumulative analyzed gas volume and the apparent isotope value of the produced gas obtained by solving the model to obtain the key parameters corresponding to the optimal fitting result; the optimal fitting result refers to the fitting result with the smallest fitting error.

[0092] The gas resource capacity assessment module M5 is used to determine the in-situ gas content, in-situ adsorbed gas ratio and in-situ free gas ratio according to the capacity assessment parameters at the initial moment corresponding to the optimal key parameters; the in-situ gas content, in-situ adsorbed gas ratio and in-situ free gas ratio are used to assess the capacity of coal rock gas resources; the optimal key parameters are the key parameters corresponding to the optimal fitting results.

[0093] In an exemplary embodiment, a computer device is provided. The computer device may be a server or a terminal. The internal structure diagram thereof may be as follows: Figure 4As shown. The computer device includes a processor, a memory, an input / output interface (Input / Output, referred to as I / O) and a communication interface. Among them, the processor, the memory and the input / output interface are connected through a system bus, and the communication interface is connected to the system bus through the input / output interface. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store in-situ gas content and adsorption / free gas ratio calculation data. The input / output interface of the computer device is used to exchange information between the processor and an external device. The communication interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, a method for calculating the in-situ gas content and adsorption / free gas ratio of deep coal and rock is realized.

[0094] Those skilled in the art will understand that Figure 4 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components. In an exemplary embodiment, a computer device is provided, including a memory and a processor, wherein a computer program is stored in the memory, and the processor implements the steps in the above-mentioned method embodiments when executing the computer program.

[0095] In an exemplary embodiment, a computer-readable storage medium is provided, storing a computer program, and when the computer program is executed by a processor, the steps in the above method embodiments are implemented.

[0096] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of relevant data must comply with relevant regulations.

[0097] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM may be in various forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM).

[0098] The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. The non-relational database may include a distributed database based on blockchain, etc., but is not limited thereto. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but is not limited thereto.

[0099] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0100] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A method for calculating the in-situ gas content and adsorbed / free gas ratio of deep coal rock, characterized in that: The method for calculating the in-situ gas content of deep coal and rock and the ratio of adsorbed gas to free gas includes: Obtaining rock physical property parameters of coal rock, and constructing a coal rock simulation geometric model according to the rock physical property parameters; According to the coal-rock simulation geometric model, an isotope fractionation model is constructed; the isotope fractionation model is: 12 CH4 and 13 Control equation of CH4 mass transfer process in bidispersed pore structure; bidispersed pore structure includes matrix pores and kerogen pores; multi-gas transport mechanism of viscous flow, Knudsen diffusion and surface diffusion coupling is considered in the control equation; the isotope fractionation model is used to determine the capacity evaluation parameters at any time according to the key parameters of coal rock; the key parameters include matrix pore intrinsic permeability, kerogen pore permeability, Langmuir volume, Langmuir pressure, initial average pore size of matrix pores, kerogen porosity, apparent diffusion coefficient ratio in matrix pores, diffusion coefficient ratio in kerogen pores and initial carbon isotope value; the capacity evaluation parameters include free carbon in matrix pores 12 CH4, free state 13 CH4, adsorption 12 CH4, adsorption 13 CH4 and kerogen pore solution gas 12 CH4 and 13 The cumulative amount of CH4 analyzed and the apparent isotopic value of the produced gas; The initial conditions and boundary conditions of the isotope fractionation model are set, and under the constraints of the initial conditions and the boundary conditions, the isotope fractionation model is solved to calculate the production capacity assessment parameters at any time; the initial conditions are set according to the burial depth and pressure coefficient of the core of the coal rock; the boundary conditions are set according to the atmospheric pressure, core extraction time, initial core pressure and mud density; Obtain the cumulative analytical gas volume and the apparent isotope value of the produced gas measured in the field analytical experiment of coalbed methane, and fit the measured cumulative analytical gas volume and the apparent isotope value of the produced gas with the cumulative analytical gas volume and the apparent isotope value of the produced gas obtained by solving the model to obtain the key parameters corresponding to the optimal fitting result; the optimal fitting result refers to the fitting result with the smallest fitting error; According to the production capacity assessment parameters at the initial moment corresponding to the optimal key parameters, the in-situ gas content, the in-situ adsorbed gas ratio and the in-situ free gas ratio are determined; the in-situ gas content, the in-situ adsorbed gas ratio and the in-situ free gas ratio are used to assess the production capacity of coal rock gas resources; the optimal key parameters are the key parameters corresponding to the optimal fitting results.

2. The method for calculating the in-situ gas content and adsorbed / free gas ratio of deep coal rock according to claim 1, characterized in that: The expression of the isotope fractionation model is: ； in, ; ； In the formula, P m , , P k and They are 12 The gas pressure of CH4 in the matrix pores, 13 The gas pressure of CH4 in the matrix pores, 12 The gas pressure of CH4 in the kerogen pores, 13 The gas pressure of CH4 in the kerogen pores; D m_app and They are 12 CH4 and 13 The apparent diffusion coefficient of CH4 in the matrix pores; D k and They are 12 CH4 and 13 The apparent diffusion coefficient of CH4 in kerogen pores; is the effective porosity of the matrix pores, is the porosity of the kerogen pores, c is the mass balance ratio parameter; and They are 12 CH4 and 13 Langmuir constant of CH4; is the initial gas-containing porosity of matrix pores; is the gas density in the matrix pores; is the viscosity in the matrix pores; K n_real is the Knudsen number of the real gas; k v is the intrinsic permeability of the matrix pores; is the tortuosity of the matrix pores; D s is the surface diffusion coefficient; is the average pore size of the matrix pores; R is the ideal gas constant; T is the analytical temperature; r 0 is the initial average pore size of the matrix pores not affected by the adsorption layer; M is the relative molecular mass of the gas; P L is the Langmuir pressure of coal rock; represents the gradient; t represents the time t.

3. The method for calculating the in-situ gas content and adsorbed / free gas ratio of deep coal rock according to claim 1, characterized in that: The initial conditions of the isotope fractionation model are: ； In the formula, P m , , P k and They are 12 The gas pressure of CH4 in the matrix pores, 13 The gas pressure of CH4 in the matrix pores, 12 The gas pressure of CH4 in the kerogen pores, 13 The gas pressure of CH4 in the kerogen pores; P 0 is the initial reservoir pressure of the core; for 12 CH4 and 13 The ratio of the initial amount of CH4; δ 0 is the initial carbon isotope value of methane; R st is the carbon isotope atomic ratio of the PDB standard sample; "x, y, z" in the figure represents any position in the coal-rock simulation geometric model; The "0" in represents the initial time.

4. The method for calculating the in-situ gas content and adsorbed / free gas ratio of deep coal rock according to claim 3, characterized in that: The boundary conditions of the isotope fractionation model are: ； In the formula, It is the connection surface between the analytical tank and the exhaust gas pipeline in the coal-rock simulation geometric model; It represents the top end surface of the core in the coal-rock simulation geometric model, excluding the connection surface with the pipeline for exhausting gas; It is the bottom end face of the core in the coal-rock simulation geometric model; It is the side of the core in the coal-rock simulation geometric model; is the boundary pressure; is the radius of the exhaust pipe; is the radius of the core; H is the height of the core; express 12 CH4 and 13 CH4, the ratio of the amount of substance.

5. The method for calculating the in-situ gas content and adsorbed / free gas ratio of deep coal rock according to claim 1, characterized in that: Under the constraints of the initial conditions and the boundary conditions, the isotope fractionation model is solved to calculate the production capacity assessment parameters at any time, specifically including: Randomly determine a number of value combinations corresponding to the key parameters within the valid value range corresponding to the key parameters; Under the constraints of the initial conditions and the boundary conditions, each of the numerical combinations is substituted into the isotope fractionation model to obtain the production capacity assessment parameter corresponding to each numerical combination at any time.

6. The method for calculating the in-situ gas content and adsorbed / free gas ratio of deep coal rock according to claim 1, characterized in that: According to the capacity assessment parameters at the initial moment corresponding to the optimal key parameters, the in-situ gas content, in-situ adsorbed gas ratio and in-situ free gas ratio are determined, including: Bringing the optimal key parameters into the isotope fractionation model to obtain the pressure field distribution inside the core corresponding to the optimal key parameters; The pressure field distribution at the initial moment is volume integrated to obtain the free state in the matrix pores at the initial moment. 12 CH4, free state 13 CH4, adsorption 12 CH4, adsorption 13 CH4 and kerogen pore solution gas 12 CH4 and 13 CH4 content; According to the free state in the matrix pores at the initial moment 12 CH4, free state 13 CH4, adsorption 12 CH4, adsorption 13 CH4 and kerogen pore solution gas 12 CH4 and 13 The accumulated gas volume of CH4 is used to calculate the in-situ gas content, in-situ free gas ratio and in-situ adsorbed gas ratio.

7. The method for calculating the in-situ gas content and adsorbed / free gas ratio of deep coal rock according to claim 6, characterized in that: The expression of the in-situ gas content is: ； The expression of the in-situ free gas ratio is: ； The expression of the in-situ adsorption gas ratio is: ； In the formula, GIP content is the in-situ gas content; FGR is the in-situ free gas ratio; AGR is the in-situ adsorbed gas ratio; , , and , respectively Matrix pore free state 12 CH4, free state 13 CH4, adsorption 12 CH4 and adsorption 13 The cumulative amount of CH4; and They are Kerogen pores during the time period 12 CH4 and 13 The cumulative amount of CH4; Indicates the initial time.

8. A device for calculating the in-situ gas content and adsorbed / free gas ratio of deep coal rock, characterized in that: include: A simulation geometry model building module, used to obtain rock physical property parameters of coal and rock, and to build a coal and rock simulation geometry model according to the rock physical property parameters; The isotope fractionation model construction module is used to construct an isotope fractionation model according to the coal rock simulation geometric model; the isotope fractionation model is 12 CH4 and 13 Control equation of CH4 mass transfer process in bidispersed pore structure; bidispersed pore structure includes matrix pores and kerogen pores; multi-gas transport mechanism of viscous flow, Knudsen diffusion and surface diffusion coupling is considered in the control equation; the isotope fractionation model is used to determine the capacity evaluation parameters at any time according to the key parameters of coal rock; the key parameters include matrix pore intrinsic permeability, kerogen pore permeability, Langmuir volume, Langmuir pressure, initial average pore size of matrix pores, kerogen porosity, apparent diffusion coefficient ratio in matrix pores, diffusion coefficient ratio in kerogen pores and initial carbon isotope value; the capacity evaluation parameters include free carbon in matrix pores 12 CH4, free state 13 CH4, adsorption 12 CH4, adsorption 13 CH4 and kerogen pore solution gas 12 CH4 and 13 The cumulative amount of CH4 analyzed and the apparent isotopic value of the produced gas; The condition setting and solving module is used to set the initial conditions and boundary conditions of the isotope fractionation model, and solve the isotope fractionation model under the constraints of the initial conditions and the boundary conditions to calculate the production capacity assessment parameters at any time; the initial conditions are set according to the burial depth and pressure coefficient of the coal core; the boundary conditions are set according to the atmospheric pressure, core extraction time, core initial pressure and mud density; The data fitting module is used to obtain the cumulative analytical gas volume and the apparent isotope value of the produced gas measured in the field analysis experiment of coalbed methane, and fit the measured cumulative analytical gas volume and the apparent isotope value of the produced gas with the cumulative analytical gas volume and the apparent isotope value of the produced gas obtained by the model solution to obtain the key parameters corresponding to the optimal fitting result; the optimal fitting result refers to the fitting result with the smallest fitting error; The gas resource capacity assessment module is used to determine the in-situ gas content, the in-situ adsorbed gas ratio and the in-situ free gas ratio according to the capacity assessment parameters at the initial moment corresponding to the optimal key parameters; the in-situ gas content, the in-situ adsorbed gas ratio and the in-situ free gas ratio are used to assess the capacity of coal gas resources; the optimal key parameters are the key parameters corresponding to the optimal fitting results.

9. A computer device comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the method for calculating the in-situ gas content and adsorbed / free gas ratio of deep coal rock as described in any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, it implements the method for calculating the in-situ gas content and adsorbed / free gas ratio of deep coal rock as described in any one of claims 1-7.

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