Deep coal-rock in-situ gas content and adsorption / free gas ratio calculation method and device

Abstract

The present application discloses a method and device for calculating in-situ gas content and adsorption / free gas ratio of deep coal and rock, which relates to the field of reservoir resource potential evaluation. It includes constructing an isotope fractionation model coupled with a dual-dispersed pore structure (matrix pores and kerogen pores) and multiple gas transport mechanisms (viscous flow, Knudsen diffusion, and surface diffusion), and solving it. The cumulative desorbed gas volume and the apparent isotope value of the produced gas obtained by the solution are fitted with the measured cumulative desorbed gas volume and the apparent isotope value of the produced gas to obtain the key parameters corresponding to the optimal fitting result. According to the production capacity evaluation 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. The present application calculates the in-situ gas content, in-situ adsorbed gas ratio, and in-situ free gas ratio of deep coal and rock based on an isotope fractionation model coupled with a dual-dispersed pore structure and multiple gas transport mechanisms, so as to predict the gas resource content of deep coal and rock.

Description

Technical Field

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

[0002] Compared with shallow coal reservoirs, deep coal reservoirs have higher in-situ 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 with different coal ranks decrease rapidly with the increase in effective stress. After exceeding a certain burial depth, the damage rate of coal rock permeability will reach the maximum. The maximum damage rate depths of low-rank and medium-high-rank coal rocks are approximately 500 m and 900 m respectively. Beyond this depth, coal reservoirs will become dense and low-permeability, and the effect of conventional reservoir stimulation measures is poor, which is a key factor restricting the efficient flow and rapid production increase of deep coalbed methane. The increase in the proportion of free gas in deep coalbed methane is beneficial to increasing the in-situ gas content of coal reservoirs and is also more likely to promote the rapid production stage dominated by free gas in the initial production stage, achieving the effect of improving recovery efficiency. At present, the overall research on deep coalbed methane is still in its initial stage. In particular, there is no clear understanding of the enrichment characteristics and flow laws of deep coalbed methane, lacking systematic and in-depth research work, and facing many challenges and problems. Among the many problems to be explored and solved, the following two issues have received special attention and emphasis: one is the restoration of in-situ gas content in deep coal reservoirs; the other is the determination of the adsorption gas / free gas ratio in deep coal reservoirs. These two issues are related to the evaluation of coalbed methane resource potential, the scientific calculation of (recoverable) reserves, and the screening of favorable target areas / horizons, and thus also determine the decision-making on the investment intensity of relevant targets and the exploration and development benefits.

[0003] For the evaluation of in-situ gas content of coal rock, the methods proposed and applied so far can be divided into direct methods and indirect methods. The direct method, also known as the core desorption method, can be divided into the pressure-maintained coring method and the 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 volume and the dissolved gas volume can be calculated through the gas state equation and the solubility equation. The key of the indirect method lies in the determination of the adsorbed gas volume. The isothermal adsorption method is the most commonly used method for testing the adsorbed gas content of rocks at present. The methods for determining the in-situ adsorption gas / free gas ratio of coal rock can also be divided into two categories: one is the direct method based on the on-site desorption process, and the other is the indirect method based on the gas occurrence state. There are certain deficiencies in the existing methods for evaluating the in-situ gas content of coal rock and the methods for determining the in-situ adsorption gas / free gas ratio of coal rock.

[0004] In recent years, researchers at home and abroad have carried out extensive research work in aspects such as on-site analysis, gas well production, laboratory simulation, molecular simulation, and numerical simulation, which have strongly confirmed that there is a significant isotope fractionation effect during the migration process of methane in tight rocks such as shale / coal rock. And this fractionation phenomenon is closely related to the in-situ gas content and the proportion of adsorbed gas in the rock. By establishing an isotope fractionation model to calibrate the degassing gas volume and isotopes, the in-situ gas content and the proportion of in-situ free / adsorbed gas can be determined simultaneously. This method has been popularized and applied in multiple shale gas blocks in China and achieved good evaluation results. Previous studies have also verified through pressure-maintained coring data that the accuracy of the CIF model (carbon isotope fractionation model) is better than that of other traditional methods. However, the existing isotope fractionation models are only applicable to homogeneous cases with relatively simple pore structures. Whether they are applicable to coal rocks with strong heterogeneity and mainly dual-porosity characteristics needs to be studied systematically. 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 the proportion of adsorbed / free gas in deep coal rock. By establishing an isotope fractionation model that couples a dual-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, the proportion of in-situ adsorbed gas, and the proportion of in-situ free gas in deep coal rock can be calculated, so as to predict the gas resource content of deep coal rock.

[0006] To achieve the above purpose, this application provides the following solutions:

[0007] In the first aspect, this application provides a method for calculating the in-situ gas content and the proportion of adsorbed / free gas in deep coal rock, including:

[0008] Obtain the rock physical property parameters of the coal rock, and construct a coal rock simulation geometric model based on the rock physical property parameters;

[0009] According to the coal rock simulation geometric model, construct an isotope fractionation model; the isotope fractionation model is 12 CH4 and 13Control equations for the mass transfer process of CH4 in a dual - pore structure; the dual - pore structure includes matrix pores and kerogen pores; a multi - gas transport mechanism considering the coupling of viscous flow, Knudsen diffusion, and surface diffusion is considered in the control equations; the isotope fractionation model is used to determine the production capacity evaluation parameters at any time according to the key parameters of coal - rock; the key parameters include the intrinsic permeability of matrix pores, the permeability of kerogen pores, Langmuir volume, Langmuir pressure, the initial average pore diameter of matrix pores, kerogen porosity, the ratio of apparent diffusion coefficients in matrix pores, the ratio of diffusion coefficients in kerogen pores, and the initial carbon isotope value; the production capacity evaluation parameters include the free state 12 CH4, the free state 13 CH4, the adsorbed state 12 CH4, the adsorbed state 13 CH4 and the dissolved gas in kerogen pores 12 CH4 and 13 CH4, the cumulative desorbed gas volume and the apparent isotope value of the produced gas;

[0010] 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 evaluation parameters at any time; the initial conditions are set according to the burial depth and pressure coefficient of the core of coal - rock; the boundary conditions are set according to atmospheric pressure, extraction time, initial core pressure, and mud density;

[0011] Obtain the measured cumulative desorbed gas volume and the apparent isotope value of the produced gas in the in - situ coalbed methane desorption experiment, and fit the measured cumulative desorbed gas volume and the apparent isotope value of the produced gas with the cumulative desorbed gas volume and the apparent isotope value of the produced gas obtained by 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;

[0012] Determine the in - situ gas content, in - situ adsorbed gas ratio, and in - situ free gas ratio according to the production capacity evaluation parameters at the initial time 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 evaluate the production capacity of coal - rock gas resources; the optimal key parameters are the key parameters corresponding to the optimal fitting result.

[0013] In a second aspect, the present application provides a device for calculating the in - situ gas content and adsorption / free gas ratio of deep coal - rock, including:

[0014] A simulation geometric model construction module, configured to obtain the petrophysical parameters of coal - rock and construct a coal - rock simulation geometric model according to the petrophysical parameters;

[0015] Isotope fractionation model construction module, which 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 The governing equation for the mass transfer process of CH4 in a bimodal pore structure; the bimodal pore structure includes matrix pores and kerogen pores; a multi-gas transport mechanism coupling viscous flow, Knudsen diffusion, and surface diffusion is considered in the governing equation; the isotope fractionation model is used to determine the production capacity evaluation parameters at any time according to the key parameters of the coal-rock; the key parameters include the intrinsic permeability of the matrix pores, the permeability of the kerogen pores, the Langmuir volume, the Langmuir pressure, the initial average pore diameter of the matrix pores, the kerogen porosity, the ratio of the apparent diffusion coefficient in the matrix pores, the ratio of the diffusion coefficient in the kerogen pores, and the initial carbon isotope value; the production capacity evaluation parameters include the free 12 CH4, free 13 CH4, adsorbed 12 CH4, adsorbed 13 CH4 and the dissolved gas in the kerogen pores 12 CH4 and 13 CH4, and the cumulative desorbed gas volume and the apparent isotope value of the produced gas;

[0016] Condition setting and solving module, which 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 evaluation 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, the lifting time, the initial pressure of the core, and the mud density;

[0017] Data fitting module, which is used to obtain the measured cumulative desorbed gas volume and the apparent isotope value of the produced gas in the in-situ coalbed methane desorption experiment, and fit the measured cumulative desorbed gas volume and the apparent isotope value of the produced gas with the cumulative desorbed gas volume and the apparent isotope value of the produced gas obtained by model solving to obtain the key parameters corresponding to the optimal fitting result; the optimal fitting result refers to the fitting result with the minimum fitting error;

[0018] Gas resource production capacity evaluation module, which 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 production 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 used to evaluate the production capacity of the coal-rock gas resources; the optimal key parameters are the key parameters corresponding to the optimal fitting result.

[0019] In a third aspect, the present application provides a computer device, including: a memory, a processor, and a computer program stored on the memory and executable on the processor, where the processor executes the computer program to implement the above-mentioned method for calculating in-situ gas content and adsorption / free gas ratio of deep coal and rock.

[0020] In a fourth aspect, the present application provides a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the above-mentioned method for calculating in-situ gas content and adsorption / free gas ratio of deep coal and rock is implemented.

[0021] According to the specific embodiments provided by the present application, the following technical effects are disclosed:

[0022] The present application provides a method and device for calculating in-situ gas content and adsorption / free gas ratio of deep coal and rock. By establishing an isotope fractionation model coupling a dual-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 desorbed gas volume and the apparent isotope value of the produced gas during the in-situ desorption process, and then invert and determine the key parameters close to the real core. Substituting these key parameters into the isotope fractionation model for forward calculation, the in-situ gas content, in-situ adsorbed gas ratio, and in-situ free gas ratio of deep coal and rock can be calculated, so as to predict the gas resource content of deep coal and rock. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0024] Figure 1 It is an application environment diagram of a method for calculating in-situ gas content and adsorption / free gas ratio of deep coal and rock in an embodiment of the present application;

[0025] Figure 2 It is a flowchart of a method for calculating in-situ gas content and adsorption / free gas ratio of deep coal and rock provided in an embodiment of the present application;

[0026] Figure 3 It is a functional module diagram of a device for calculating in-situ gas content and adsorption / free gas ratio of deep coal and rock provided in an embodiment of the present application;

[0027] Figure 4 It is a structural diagram of a computer device provided in an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0029] To make the above objects, features, and advantages of the present application more obvious and understandable, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0030] For the evaluation of in-situ gas content in coal and rock, the methods proposed and applied so far can be divided into direct methods and indirect methods. The direct method, also known as the core analysis method, can be divided into the pressure-maintaining coring method and the normal-pressure coring method. The pressure-maintaining coring method is a technical method that uses special pressure-maintaining coring tools to keep the core at the original formation pressure until it reaches the ground and then measures the gas content. This technology can minimize the loss of oil, gas, and other components in the core and is currently recognized as the most reliable method for determining gas content. However, on the one hand, due to the pressure-maintaining ability and engineering construction problems, it is difficult to reduce the gas loss to zero. On the other hand, the cost of pressure-maintaining coring is too high to be widely promoted. The normal-pressure coring method uses conventional coring tools without pressure-maintaining ability. After obtaining the core from the well, the core is segmented and placed in an analysis tank, and analyzed at normal pressure and a specific temperature until no gas is released from the core. The gas volume measured in this process is recorded as the analyzed gas volume. The gas that is difficult to spontaneously analyze at normal pressure and a specific temperature and needs to be released and measured by grinding and crushing, which remains in micropores or closed pores, is called the residual gas volume. The most critical problem of the normal-pressure coring method is that during the process of lifting the core in the wellbore and the ground exposure before sealing the tank, most of the gas escapes due to the decrease in environmental pressure and is not actually measured. This part of the gas is called the lost gas volume. For the lost gas volume in this process, the widely used recovery methods currently include the USBM method, polynomial fitting, Smith-Williams method, ACF method, and MCF method. These above methods have the following deficiencies: (1) They are more applicable to shallow coalbed methane with a short loss time and a low proportion of free gas, but there are significant errors when applied to deep shale gas with a long loss time and a high proportion of free gas. Therefore, their applicability and accuracy in deep coalbed methane are also questioned; (2) They only consider the concentration diffusion effect and do not consider the desorption effect of adsorbed gas and its coupling relationship with the diffusion effect, resulting in an insufficiently rigorous theoretical basis for this method and being unable to effectively evaluate the key parameter of the adsorbed gas / free gas ratio; (3) There are subjective errors in defining the zero point of the loss time as the time when the core is lifted to half of the well depth and the number of initial analysis data points participating in the fitting.

[0031] 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 volume and dissolved gas volume can be calculated through the gas state equation and solubility equation. The key of the indirect method lies in the determination of the adsorbed gas volume. The isothermal adsorption method is the most commonly used method for testing the adsorbed gas content in rocks at present. However, the difficulty of this method lies in how to simulate the real in-situ formation conditions in the isothermal adsorption experiment device, especially the formation temperature, pressure, water content, and microscopic distribution conditions of water.

[0032] The methods for determining the in-situ adsorbed gas / free gas ratio of coal and rock can also be divided into two categories: one is the direct method based on the on-site desorption process, and the other is the indirect method based on the gas occurrence state. The direct method mainly determines the in-situ adsorbed gas / free gas ratio according to the δ 13 monotonic change law of the C1 value, taking the C1 values of the first-order desorbed gas and the third-order desorbed gas as the isotope compositions of the free gas end member and the adsorbed gas end member respectively. Through the binary mixing model, the contribution ratio of each end member in the second-order desorbed gas can be determined, 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 lost gas volume is a key intermediate parameter for calculating the adsorbed gas / free gas ratio, but there is still no generally recognized accurate method for accurately recovering the lost gas content, and the accuracy of the adsorbed gas / free gas ratio calculated therefrom is also questionable; ② The numerical simulation calculation results of the shale gas desorption process show that there is no ideal end member gas in the complete desorption process, and the adsorbed gas ratio in the lost gas and the first-order desorbed gas cannot be ignored, and the free gas in the second-order and third-order desorbed gas also makes a greater contribution. δ 13 The indirect method mainly combines the isothermal adsorption experiment with other methods, such as the isothermal adsorption experiment combined with the gas state equation, or the isothermal adsorption experiment combined with nuclear magnetic resonance technology. The former uses different theoretical equations to characterize gases in different occurrence states. For example, the isothermal adsorption experiment combined with the adsorption theory equation is used to evaluate the adsorbed gas volume of rocks, and the gas state equation combined with reservoir parameters (such as pressure, temperature, and effective porosity, etc.) is used to evaluate the free gas content. The latter is to carry out real-time nuclear magnetic resonance monitoring of the isothermal adsorption experiment, utilize the quantitative recognition advantage of the response characteristics of the nuclear magnetic resonance T2 spectrum to the gas content and distribution in different occurrence states, set the T2 cut-off value to divide the T2 spectrum range belonging to the free gas and the adsorbed gas, and quantitatively calculate the adsorbed gas / free gas content and ratio in the rock by integrating the peak area within a specific range. The key of this method lies in the accuracy of the T2 cut-off value division. However, there are certain deficiencies in the existing evaluation methods for the in-situ gas content of coal and rock and the methods for determining the in-situ adsorbed gas / free gas ratio of coal and rock.

[0033]

[0034] ​In addition, by establishing an isotope fractionation model to calibrate the degassing gas volume and isotopes, it is possible to simultaneously determine the in-situ gas content and the in-situ free / adsorbed gas ratio. However, the existing isotope fractionation models are only applicable to homogeneous cases with relatively simple pore structures. Whether they are applicable to coal rocks with strong heterogeneity and mainly dual-porosity characteristics still requires systematic research work.

[0035] In response to this, the embodiments of the present application provide a method for calculating the in-situ gas content and the adsorbed / free gas ratio of deep coal rocks, which can be applied to the application environment as Figure 1 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 separately, integrated on the server, placed in the cloud or on other servers. The terminal can send construction parameters (including lifting time, ground exposure time, drilling fluid density, and drilling fluid temperature), reservoir parameters (including reservoir burial depth and pressure coefficient), and rock physical property parameters (core radius, core length, core mass, and gas-bearing porosity) to the server. After receiving the parameters required by the isotope fractionation model, the server constructs a coal rock simulation geometric model and an isotope fractionation model to evaluate the coal rock gas resource production capacity. Specifically, the server constructs a coal rock simulation geometric model according to the rock physical property parameters; constructs an isotope fractionation model according to the coal rock simulation geometric model; the isotope fractionation model is 12 the control equation for the mass transfer process of 13 CH4 and

[0036] CH4 in the dual-dispersed pore structure; the dual-dispersed pore structure includes matrix pores and kerogen pores; in the control equation, a multi-gas transport mechanism coupling viscous flow, Knudsen diffusion, and surface diffusion is considered; 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 evaluation parameters at any time; the measured cumulative desorbed gas volume and the apparent isotope value of the produced gas in the in-situ coalbed methane desorption experiment 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 model solving to obtain the key parameters corresponding to the optimal fitting result; according to the production 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 feedback 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 rocks can also be implemented by the server or the terminal alone. 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.Among them, the terminal can be, but is not limited to, various desktop computers, laptop computers, smart phones, tablet computers, Internet of Things devices, and portable wearable devices. The server can be implemented by an independent server or a server cluster composed of multiple servers, and can also be a cloud server.

[0037] In an exemplary embodiment, as Figure 2 shown, a method for calculating the in-situ gas content and the ratio of adsorbed / free gas in deep coal and rock is provided. This method is executed by a computer device, and specifically can be executed alone by a computer device such as a terminal or a server, or can be jointly executed by a terminal and a server. In the embodiments of the present application, taking this method applied to Figure 1 the server in

[0038] Step 101: Obtain the rock physical property parameters of the coal and rock, construct a coal and rock simulation geometric model according to the rock physical property parameters, and perform mesh division.

[0039] Step 102: Construct an isotope fractionation model according to the coal and rock simulation geometric model; the isotope fractionation model is 12 the governing equations for the mass transfer process of 13 CH4 and 12 CH4 in a bimodal pore structure; the bimodal pore structure includes matrix pores and kerogen pores; in the governing equations, a multi-gas transport mechanism coupling viscous flow, Knudsen diffusion, and surface diffusion is considered; the isotope fractionation model is used to determine the production capacity evaluation parameters at any time according to the key parameters of the coal and rock; the key parameters include the intrinsic permeability of the matrix pores, the permeability of the kerogen pores, the Langmuir volume, the Langmuir pressure, the initial average pore diameter of the matrix pores, the kerogen porosity, the apparent diffusion coefficient ratio in the matrix pores, the diffusion coefficient ratio in the kerogen pores, and the initial carbon isotope value; the production capacity evaluation parameters include the free state of 13 CH4 in the matrix pores, the free state of 12 CH4, the adsorbed state of 13 CH4, the adsorbed state of 12 CH4, and the cumulative desorbed gas volume and the apparent isotope value of the produced gas of 13 CH4 in the dissolved gas in the kerogen pores.

[0040] Step 103: 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 evaluation parameters at any time; the initial conditions are set according to the burial depth and pressure coefficient of the core of the coal and rock; the boundary conditions are set according to the atmospheric pressure, the lifting time, the initial pressure of the core, and the mud density.

[0041] Step 104: Obtain the measured cumulative desorbed gas volume and the apparent isotope value of the produced gas in the in-situ coalbed methane desorption experiment, and fit the measured cumulative desorbed gas volume and the apparent isotope value of the produced gas with the cumulative desorbed gas volume and the apparent isotope value of the produced gas obtained by model solution to obtain the key parameters corresponding to the optimal fitting result; the optimal fitting result refers to the fitting result with the minimum fitting error.

[0042] Step 105: Determine the in-situ gas content, the proportion of in-situ adsorbed gas, and the proportion of in-situ free gas according to the productivity evaluation parameters at the initial moment corresponding to the optimal key parameters; the in-situ gas content, the proportion of in-situ adsorbed gas, and the proportion of in-situ free gas are used to evaluate the productivity of coalbed methane resources; the optimal key parameters are the key parameters corresponding to the optimal fitting result.

[0043] Implementing the above Steps 101 to 105 provides a method for determining the in-situ gas content and the proportion of adsorbed gas / free gas in deep coal rock based on isotope fractionation. By establishing an isotope fractionation model coupled with a dual-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 desorbed gas volume and the isotope value of the produced gas during the in-situ desorption process, and then inversely determine the key undetermined parameters of the model. Substitute these key undetermined parameters into the isotope fractionation model for forward calculation to obtain the in-situ gas content, the proportion of in-situ adsorbed gas, and the proportion of in-situ free gas in deep coal rock, so as to predict the gas resource content of deep coal rock.

[0044] In another exemplary embodiment of the present application, in Step 102, establish 12 CH4 and 13 the partial differential equations for the mass transfer process of CH4 in the dual-dispersed pore structure. As an example, the specific formula of the partial differential equations is as follows in Equation (1).

[0045] (1).

[0046] In the formula, B 1, B 2, C 1 and C 2 are respectively expressed as the following Equation (2).

[0047] (2).

[0048] In the formula, P m 、 、 P k and are respectively 12 the gas pressure of CH4 in the matrix pores, 13 the gas pressure of CH4 in the matrix pores, 12Gas pressure of CH4 in kerogen pores, 13 Gas pressure of CH4 in kerogen pores; D m_app and are respectively 12 CH4 and 13 the apparent diffusion coefficient of CH4; D k and are respectively 12 CH4 and 13 the apparent diffusion coefficient of CH4 in kerogen pores; ; represents the viscosity of kerogen pores; k k represents the permeability of kerogen pores; is the effective porosity of matrix pores; is the initial gas-bearing porosity of matrix pores; is the porosity of kerogen pores; c is the mass balance ratio parameter, , where is the apparent density of coal rock, V L is the Langmuir volume of coal rock, Z m is the gas compressibility factor of matrix pores, R is the ideal gas constant, T is the desorption temperature, V std is the molar volume constant of gas under standard conditions; and are respectively 12 CH4 and 13 the Langmuir constant of CH4, where =exp( A / T 2 - B / T ), where A =95.17K 2 , B =0.125K). represents the gradient; t represents the time at t.

[0049] In the system of partial differential equations of formula (1), considering the influence of the adsorption layer on the average pore size and porosity of matrix pores and the real gas effect (the viscosity, compressibility factor and density of gas are affected by temperature and pressure), the influence of the adsorption layer on the average pore size and porosity of matrix pores can be expressed as the following formula (3) and the following formula (4).

[0050] (3).

[0051] (4).

[0052] In the formula, is the average pore diameter of the matrix pores; r 0 is the initial average pore diameter of the matrix pores not affected by the adsorption layer; d m is the diameter of the methane molecule, and methane is taken as 0.38 nm; is the initial porosity of the matrix pores not affected by the adsorption layer; represents 12 the coverage rate of CH4; represents 13 the coverage rate of CH4.

[0053] The influence of temperature and pressure on the gas density in the matrix pores and kerogen pores can be expressed by the following formula (5).

[0054] (5).

[0055] Among them, 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.

[0056] The influence of temperature and pressure on the gas compressibility factor in the matrix pores and kerogen pores can be expressed by the following formula (6).

[0057] (6).

[0058] In the formula, represents the gas compressibility factor of the matrix pores; represents the gas compressibility factor of the kerogen pores.

[0059] (7).

[0060] The influence of temperature and pressure on the viscosity in the matrix pores and kerogen pores can be expressed by the following formula (8).

[0061] (8).

[0062] 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, and methane is taken as 16 kg / mol.

[0063] In this application, in the partial differential equations of formula (1), a multi-gas transport mechanism considering the coupling of viscous flow, Knudsen diffusion, and surface diffusion is considered, as shown in the following formula (9).

[0064] (9).

[0065] Among them, the apparent diffusion coefficient of equation (1) D m_app reflects viscous flow.

[0066] 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 the 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).

[0067] (10).

[0068] In the formula,[[]] κ is the ratio of the blocking rate constant to the forward transport rate constant, and the common value in coal rock is 0.5; D s0 is the surface diffusion coefficient when the gas coverage is 0, which can be expressed as the following formula (11).

[0069] (11).

[0070] In the formula, Δ H is the isosteric heat of adsorption when the gas coverage is 0.

[0071] The control equation corresponding to the isotope fractionation model is mainly formula (1), and formulas (2) to (11) are mainly the calculation formulas of the various parameter variables in formula (1).

[0072] In another exemplary embodiment of this application, in step 103, the setting of the initial conditions of the isotope fractionation model: after establishing the control equation corresponding to the isotope fractionation model, set the initial conditions according to the reservoir parameters (including the burial depth and pressure coefficient of the core), specifically as the following formula (12).

[0073] (12).

[0074] 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; is 12 the molar ratio of CH4 and 13 the initial molar 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, with a value of 0.0112372. "x, y, z" in represents any position in the coal rock simulation geometric model; "0" in represents the initial moment (t = 0).

[0075] In another exemplary embodiment of the present application, in step 103, the setting of the boundary conditions of the isotope fractionation model: Determine the time when the core starts to lose gas during the core lifting process according to the mud density and the initial pressure of the core. Except for the connection surface between the analytical tank and the gas discharge pipeline, set other surfaces to be insulated. The boundary conditions of the isotope fractionation model can be set as the following formula (13).

[0076] (13).

[0077] In the formula, is the connection surface between the analytical tank and the gas discharge pipeline in the coal rock simulation geometric model; represents the top end face of the core in the coal rock simulation geometric model except for the connection surface with the gas discharge pipeline; is the bottom end face of the core in the coal rock simulation geometric model. is the side surface of the core in the coal rock simulation geometric model. is the radius of the gas discharge pipeline; is the radius of the core; H is the height of the core; represents 12 the molar ratio of CH4 and 13 the molar amount of CH4; P b ( t ) is the boundary pressure, which can be expressed as the following formula.

[0078] .

[0079] In the formula, P atm is the atmospheric pressure, t coring is the core lifting time, t loss is the time when the core starts to lose gas. The time when the core starts to lose gas can be calculated from the initial pressure of the core, the mud density, and the core lifting time, as shown in the following formula (14).

[0080] (14).

[0081] In the formula, represents the mud pressure.

[0082] 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 a mathematical calculation software (such as MATLAB or COMSOL), and the dependent variables of the equations ( P m , , P k and ) can be solved for their variations with time and space, that is, the pressure field distribution inside the core is obtained. By performing a volume integral on the solved pressure field, the cumulative desorbed gas volumes of free 12 CH4, free 13 CH4, adsorbed 12 CH4, adsorbed 13 CH4, and the 12 CH4 and 13 CH4 in the kerogen pore dissolved gas in the matrix pores at any moment can be calculated.

[0083] Optionally, the specific formula of the volume integral method is the following formula (15).

[0084] (15).

[0085] In the formula, , , and are respectively the cumulative desorbed gas volumes of free t 0 to t i in the matrix pores for free 12 CH4, free 13 CH4, adsorbed 12 CH4, and adsorbed 13 CH4 during the time period, and are respectively the cumulative desorbed gas volumes of t 0 to t i in the kerogen pores for 12 CH4 and 13 CH4 during the time period; is the apparent density of the coal-rock; V L is the Langmuir volume of the coal-rock; is the porosity of the kerogen pores; t 0 is the initial moment; t i represents t i moment; is the rock mass; is the molar volume of gas, which is 22.4 L / mol.

[0086] According to the methane in different occurrence states solved above, that is, the free state in matrix pores 12 CH4, free state 13 CH4, adsorbed state 12 CH4, adsorbed state 13 CH4 and the dissolved gas in kerogen pores 12 CH4 and 13 The cumulative desorbed gas volume of CH4, and further the total cumulative desorbed gas volume and the apparent isotope value can be calculated, as shown in the following formula (16).

[0087] (16).

[0088] In the formula, represents the total cumulative desorbed gas volume; represents the apparent isotope value.

[0089] Based on the above, 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 evaluation parameters at any time, specifically including:

[0090] (1) Randomly determine several numerical combinations corresponding to the key parameters within the effective numerical range of the key parameters.

[0091] (2) Under the constraints of the initial conditions and the boundary conditions, substitute each numerical combination into the isotope fractionation model to obtain the production capacity evaluation parameters at any time corresponding to each numerical combination.

[0092] Each key parameter (including the intrinsic permeability of matrix pores, the permeability of kerogen pores, Langmuir volume, Langmuir pressure, the initial average pore diameter of matrix pores, kerogen porosity, the ratio of apparent diffusion coefficients in matrix pores, the ratio of diffusion coefficients in kerogen pores, and the initial carbon isotope value) has a corresponding value range. Select a value within its respective value range, and after all key parameters are valued, they form a numerical combination. Under this numerical combination, the corresponding production capacity evaluation parameters (the free state of CH4 in matrix pores 12 CH4, free state 13 CH4, adsorbed state 12 CH4, adsorbed state 13 CH4 and the dissolved gas in kerogen pores 12 CH4 and 13The cumulative desorbed gas volume of CH4 and the apparent isotope value of the produced gas), and subsequently, the productivity evaluation parameters under each numerical combination are fitted and compared with the measured values to obtain the case with the smallest fitting error, and then the optimal key parameters can be further obtained.

[0093] In another exemplary embodiment of the present application, in step 104, specific coal rock samples are selected to conduct in-situ desorption experiments of coalbed methane. The gas during the desorption process is collected with a saline bottle (the saline bottle is kept with gas and water inverted), and the cumulative desorbed gas volume during the desorption process is recorded. The methane carbon isotope of the collected in-situ desorbed gas is tested to obtain the isotope value data of the desorbed gas, so as to obtain the measured cumulative desorbed gas volume and the apparent isotope value of the produced gas in the in-situ desorption experiment of coalbed methane.

[0094] Compare the cumulative desorbed gas volume and the apparent isotope value calculated theoretically based on formulas (15) and (16) with the measured cumulative desorbed gas volume and the isotope value of the produced gas obtained by isotope testing. Use the least squares method to establish an error function, and find the minimum value of the error function through the BOBYQA algorithm of COMSOL software, and then obtain the optimal key parameters in the isotope fractionation model, including the intrinsic permeability of the matrix pores ( k v ), the permeability of the kerogen pores ( k k ), the Langmuir volume ( V L ), the Langmuir pressure ( P L ), the initial average pore diameter of the matrix pores ( r 0), the porosity of the kerogen pores ( ), the ratio of the apparent diffusion coefficient in the matrix pores ( ), the ratio of the diffusion coefficient in the kerogen pores ( ), the initial carbon isotope value ( δ 0). The parameters determined in the model are the core radius ( r ), the core height ( H ), the initial gas-bearing porosity of the matrix pores ( ), the ratio of the blocking rate constant to the forward transport rate constant ( κ = 0.5), the isosteric heat of adsorption when the gas coverage is 0 (Δ H= 28 kJ / mol), the tortuosity of the matrix pores ( = 1.05).

[0095] In another exemplary embodiment of the present application, in step 105, the obtained optimal key parameters are substituted into formulas (1) to (11), and based on the established coal-rock simulation geometric model, partial differential equations, initial conditions, and boundary conditions, the internal pressure field distribution close to the real core at any time can be obtained through forward calculation. By simply integrating the pressure field at the initial time, the in-situ gas content, in-situ adsorbed gas ratio, and in-situ free gas ratio can be obtained, as shown in the following formulas (17) and (18).

[0096] (17).

[0097] (18).

[0098] 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 、are respectively the cumulative gas volumes of free-state 12 CH4, free-state 13 CH4, adsorbed-state 12 CH4, and adsorbed-state 13 CH4 in the matrix pores during the and time periods; the cumulative gas volumes of 12 CH4 and 13 CH4 in the kerogen pores are respectively; represents the initial time. Since there is no desorption at the initial time, there is no cumulative desorbed gas volume at the initial time, which is called the cumulative gas volume.

[0099] Based on the above, in step 105, according to the production capacity evaluation parameters at the initial time corresponding to the optimal key parameters, determining the in-situ gas content, in-situ adsorbed gas ratio, and in-situ free gas ratio specifically includes:

[0100] (1) Substitute the optimal key parameters into the isotope fractionation model to obtain the pressure field distribution inside the core corresponding to the optimal key parameters.

[0101] (2) Perform volume integration on the pressure field distribution at the initial time to obtain the gas contents of free-state 12 CH4, free-state 13 CH4, adsorbed-state 12 CH4, adsorbed-state 13 CH4, and dissolved gas of 12 CH4 and 13 CH4 in the matrix pores at the initial time.

[0102] (3) Calculate the in-situ gas content, in-situ free gas ratio, and in-situ adsorbed gas ratio based on the cumulative gas volumes of free CH4, free CH4, adsorbed CH4, adsorbed CH4, CH4 in kerogen pore dissolved gas, CH4, and CH4 in the matrix pores at the initial moment. 12 CH4, free 13 CH4, adsorbed 12 CH4, adsorbed 13 CH4 and dissolved gas in kerogen pores 12 CH4 and 13 CH4 to calculate the in-situ gas content, in-situ free gas ratio, and in-situ adsorbed gas ratio.

[0103] The present application also provides an application scenario that applies the above-mentioned calculation method for in-situ gas content and adsorption / free gas ratio of deep coal and rock. Specifically: The calculation method for in-situ gas content and adsorption / free gas ratio of deep coal and rock provided in this embodiment can be applied in the scenario of evaluating the productivity of deep coal and rock gas resources. The scenario of evaluating the productivity of deep coal and rock gas resources includes a data acquisition link for obtaining relevant parameters for productivity evaluation; a productivity evaluation link for calculating the in-situ gas content and adsorption / free gas ratio based on the obtained relevant parameters for productivity evaluation to achieve the evaluation of the productivity of deep coal and rock gas resources; and a result display link for displaying the productivity evaluation results. The calculation method for in-situ gas content and adsorption / free gas ratio of deep coal and rock provided in this embodiment belongs to the productivity evaluation link.

[0104] Based on the same inventive concept, the embodiments of the present application also provide a device for calculating the in-situ gas content and adsorption / free gas ratio of deep coal and rock for implementing the above-mentioned calculation method for in-situ gas content and adsorption / free gas ratio of deep coal and rock. The solution provided by this device to solve the problem is similar to the solution described in the above method. Therefore, the specific limitations in one or more embodiments of the device for calculating the in-situ gas content and adsorption / free gas ratio of deep coal and rock provided below can refer to the limitations on the calculation method for in-situ gas content and adsorption / free gas ratio of deep coal and rock in the above text, and will not be repeated here.

[0105] In an exemplary embodiment, as Figure 3 shown, a device for calculating the in-situ gas content and adsorption / free gas ratio of deep coal and rock is provided, including:

[0106] A simulation geometric model construction module M1 for obtaining the rock physical property parameters of coal and rock and constructing a simulation geometric model of coal and rock according to the rock physical property parameters.

[0107] An isotope fractionation model construction module M2 for constructing an isotope fractionation model according to the simulation geometric model of coal and rock; the isotope fractionation model is for 12 CH4 and 13Control equations for the mass transfer process of CH4 in a dual - pore structure; the dual - pore structure includes matrix pores and kerogen pores; a multi - gas transport mechanism considering the coupling of viscous flow, Knudsen diffusion, and surface diffusion is considered in the control equations; the isotope fractionation model is used to determine the productivity evaluation parameters at any time according to the key parameters of coal - rock; the key parameters include the intrinsic permeability of matrix pores, the permeability of kerogen pores, Langmuir volume, Langmuir pressure, the initial average pore diameter of matrix pores, kerogen porosity, the ratio of apparent diffusion coefficients in matrix pores, the ratio of diffusion coefficients in kerogen pores, and the initial carbon isotope value; the productivity evaluation parameters include the free state of CH4 in matrix pores 12 CH4, the free state of 13 CH4, the adsorbed state of 12 CH4, the adsorbed state of 13 CH4 and the dissolved gas in kerogen pores 12 CH4 and 13 CH4, and the cumulative desorbed gas volume and the apparent isotope value of the produced gas

[0108] 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 productivity evaluation parameters at any time; the initial conditions are set according to the burial depth and pressure coefficient of the core of coal - rock; the boundary conditions are set according to the atmospheric pressure, lifting time, initial core pressure, and mud density

[0109] The data - fitting module M4 is used to obtain the measured cumulative desorbed gas volume and the apparent isotope value of the produced gas in the in - situ coalbed methane desorption experiment, and fit the measured cumulative desorbed gas volume and the apparent isotope value of the produced gas with the cumulative desorbed gas volume and the apparent isotope value of the produced gas obtained by model solving to obtain the key parameters corresponding to the optimal fitting result; the optimal fitting result refers to the fitting result with the minimum fitting error

[0110] The gas - resource productivity evaluation 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 productivity evaluation 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 evaluate the productivity of coal - rock gas resources; the optimal key parameters are the key parameters corresponding to the optimal fitting result

[0111] In an exemplary embodiment, a computer device is provided. The computer device can be a server or a terminal, and its internal structure diagram can be as Figure 4As shown in the figure. The computer device includes a processor, a memory, an input / output interface (Input / Output, abbreviated 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 external devices. 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, it implements a method for calculating the in-situ gas content and adsorption / free gas ratio of deep coal and rock.

[0112] Those skilled in the art can understand that Figure 4 The structure shown in the figure is only a block diagram of some structures related to the solution of this application, and does not constitute a limitation on the computer device to which the solution of this application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine some components, or have a different component arrangement. In an exemplary embodiment, a computer device is provided, including a memory and a processor. A computer program is stored in the memory. When the processor executes the computer program, the steps in the above method embodiments are implemented.

[0113] In an exemplary embodiment, a computer-readable storage medium is provided, storing a computer program. When the computer program is executed by the processor, the steps in the above method embodiments are implemented.

[0114] 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 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 need to comply with relevant regulations.

[0115] Those of ordinary skill in the art can understand that all or part of the processes of implementing the methods in the above embodiments can be completed by instructing relevant hardware through a computer program. 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 methods. Among them, any reference to a memory, database, or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memories. Non-volatile memories can include read-only memory (ROM), magnetic tapes, floppy disks, flash memories, optical memories, high-density embedded non-volatile memories, resistive random access memories (ReRAM), magnetoresistive random access memories (MRAM), ferroelectric random access memories (FRAM), phase change memories (PCM), graphene memories, etc. Volatile memories can include random access memory (RAM) or external cache memories, etc. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0116] The databases involved in the embodiments provided in the present application can include at least one of relational databases and non-relational databases. Non-relational databases can include distributed databases based on blockchain, etc., without limitation. The processors involved in the embodiments provided in the present application can be general-purpose processors, central processors, graphics processors, digital signal processors, programmable logics, data processing logics based on quantum computing, etc., without limitation.

[0117] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, 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, it should be considered as the scope described in this specification.

[0118] Specific examples are used in this article to elaborate on the principles and implementation manners of the present application. The description of the above embodiments is only used to help understand the method and its core idea of the present application; at the same time, for those of ordinary skill in the art, according to the idea of the present application, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A method for calculating in-situ gas content and adsorption / free gas ratio in deep coal and rock, characterized in that The calculation method for in-situ gas content and adsorption / free gas ratio of deep coal and rock includes: Obtain the rock physical property parameters of the coal and rock, and construct a coal and rock simulation geometric model based on the rock physical property parameters; Construct an isotope fractionation model according to the coal-rock simulation geometric model; the isotope fractionation model is 12 CH4 and 13 The governing equation for the mass transfer process of CH4 in a dual-porosity structure; the dual-porosity structure includes matrix pores and kerogen pores; a multi-gas transport mechanism coupling viscous flow, Knudsen diffusion, and surface diffusion is considered in the governing equation; the isotope fractionation model is used to determine the productivity evaluation parameters at any time according to the key parameters of the coal-rock; the key parameters include the intrinsic permeability of the matrix pores, the permeability of the kerogen pores, the Langmuir volume, the Langmuir pressure, the initial average pore diameter of the matrix pores, the kerogen porosity, the ratio of the apparent diffusion coefficients in the matrix pores, the ratio of the diffusion coefficients in the kerogen pores, and the initial carbon isotope value; the productivity evaluation parameters include the free state of 12 CH4, the free state of 13 CH4, the adsorbed state of 12 CH4, the adsorbed state of 13 CH4 and the dissolved gas in the kerogen pores 12 CH4 and 13 The cumulative desorbed gas volume of CH4 and the apparent isotope value of the produced gas; 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 evaluation parameters at any time; the initial conditions are set according to the burial depth and pressure coefficient of the core of the coal and rock; the boundary conditions are set according to the atmospheric pressure, lifting time, initial core pressure, and mud density; Obtain the measured cumulative desorbed gas volume and the apparent isotope value of the produced gas in the on-site desorption experiment of coalbed methane, and fit the measured cumulative desorbed gas volume and the apparent isotope value of the produced gas with the cumulative desorbed gas volume and the apparent isotope value of the produced gas obtained by 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; Determine the in-situ gas content, in-situ adsorbed gas ratio, and in-situ free gas ratio according to the production capacity evaluation parameters at the initial time 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 evaluate the production capacity of coal and rock gas resources; the optimal key parameters are the key parameters corresponding to the optimal fitting result.

2. The in-situ gas content and adsorption / free gas ratio calculation method for deep coal and rock according to claim 1, characterized in that The expression of the isotope fractionation model is: ； Among them, ; ； Wherein, P m , , P k and are respectively 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 are respectively 12 the apparent diffusion coefficient of CH4 and 13 CH4 in the matrix pores; D k and are respectively 12 the apparent diffusion coefficient of CH4 and 13 CH4 in the 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 are respectively 12 the Langmuir constant of CH4 and 13 CH4; is the initial gas-bearing porosity of the 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 diameter of the matrix pores; R is the ideal gas constant; T is the desorption temperature; r 0 is the initial average pore diameter of the matrix pores not affected by the adsorbed layer; M is the relative molecular mass of the gas; P L is the Langmuir pressure of the coal rock; represents the gradient; t represents the time t.

3. The in-situ gas content and adsorption / free gas ratio calculation method for deep coal and 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 are respectively 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; is 12 the initial molar ratio of CH4 and 13 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 "0" in represents any position in the coal-rock simulation geometric model; represents the initial moment.

4. The in-situ gas content and adsorption / free gas ratio calculation method for deep coal and rock according to claim 3, characterized in that, The boundary conditions of the isotope fractionation model are: ； In the formula, is the connection surface between the analysis tank and the pipeline for the discharged gas in the coal and rock simulation geometric model; represents the top end face of the core in the coal and rock simulation geometric model except for the connection surface with the pipeline for the discharged gas; is the bottom end face of the core in the coal and rock simulation geometric model; is the side surface of the core in the coal and rock simulation geometric model; is the boundary pressure; is the radius of the pipeline for the discharged gas; is the radius of the core; H is the height of the core; represents 12 CH4 and 13 the molar ratio of CH4 and CH4.

5. The in-situ gas content and adsorption / free gas ratio calculation method for deep coal and rock according to claim 1, characterized in that Under the constraints of the initial conditions and the boundary conditions, solve the isotope fractionation model to calculate the production capacity evaluation parameters at any time, specifically including: Randomly determine several numerical combinations corresponding to the key parameters within the effective numerical range corresponding to the key parameters; Under the constraints of the initial conditions and the boundary conditions, substitute each numerical combination into the isotope fractionation model to obtain the production capacity evaluation parameters at any time corresponding to each numerical combination.

6. The method for calculating the in-situ gas content and the adsorbed / free gas ratio of deep coal and rock according to claim 1, characterized in that Determine the in-situ gas content, in-situ adsorbed gas ratio, and in-situ free gas ratio according to the production capacity evaluation parameters at the initial time corresponding to the optimal key parameters, specifically including: Substitute the optimal key parameters into the isotope fractionation model to obtain the pressure field distribution inside the core corresponding to the optimal key parameters; Perform a volume integral on the pressure field distribution at the initial moment to obtain the free state in the matrix pores at the initial moment 12 CH4 in the free state 13 CH4 in the adsorbed state 12 CH4 in the adsorbed state 13 CH4 and the dissolved gas in the kerogen pores 12 CH4 and 13 the gas content of CH4; According to the free state in the matrix pores at the initial moment 12 CH4 in the free state 13 CH4 in the adsorbed state 12 CH4 in the adsorbed state 13 CH4 and the dissolved gas in the kerogen pores 12 CH4 and 13 The cumulative gas volume of CH4 is used to calculate the in-situ gas content, the in-situ free gas ratio, and the in-situ adsorbed gas ratio.

7. The method for calculating the in-situ gas content and the adsorbed / free gas ratio of deep coal and rock according to claim 6, wherein 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 adsorbed gas ratio is: ； In the formula, GIP content is the in-situ gas content; FGR is the proportion of in-situ free gas; AGR is the proportion of in-situ adsorbed gas; , , and are respectively the cumulative gas volumes of free 12 CH4, free 13 CH4, adsorbed 12 CH4, and adsorbed 13 CH4 in the matrix pores during the and are respectively the cumulative gas volumes of 12 CH4 and 13 CH4 in the kerogen pores during the represents the initial moment.

8. A device for calculating the in-situ gas content and the proportion of adsorbed / free gas in deep coal and rock, characterized in that Including: A simulation geometric model construction module, which is used to obtain the rock physical property parameters of the coal and rock, and construct a coal and rock simulation geometric model based on the rock physical property parameters; Isotope fractionation model construction module, which 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 The control equation for the mass transfer process of CH4 in the double-dispersed pore structure; the double-dispersed pore structure includes matrix pores and kerogen pores; the multi-gas transport mechanism coupling viscous flow, Knudsen diffusion and surface diffusion is considered in the control equation; the isotope fractionation model is used to determine the production capacity evaluation parameters at any time according to the key parameters of coal-rock; the key parameters include the intrinsic permeability of matrix pores, the permeability of kerogen pores, Langmuir volume, Langmuir pressure, the initial average pore diameter of matrix pores, kerogen porosity, the apparent diffusion coefficient ratio in matrix pores, the diffusion coefficient ratio in kerogen pores and the initial carbon isotope value; the production capacity evaluation parameters include the free state of 12 CH4, free state 13 CH4, adsorbed state 12 CH4, adsorbed state 13 CH4 and the dissolved gas in kerogen pores 12 CH4 and 13 The cumulative desorbed gas volume of CH4 and the apparent isotope value of the produced gas; A condition setting and solving module, which 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 evaluation parameters at any time; the initial conditions are set according to the burial depth and pressure coefficient of the core of the coal and rock; the boundary conditions are set according to the atmospheric pressure, lifting time, initial core pressure, and mud density; A data fitting module, which is used to obtain the measured cumulative desorbed gas volume and the apparent isotope value of the produced gas in the in-situ desorption experiment of coalbed methane, and fit the measured cumulative desorbed gas volume and the apparent isotope value of the produced gas with the cumulative desorbed gas volume and the apparent isotope value of the produced gas obtained by model solving, so as 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. A gas resource production capacity evaluation module, which is used to determine the in-situ gas content, the proportion of in-situ adsorbed gas and the proportion of in-situ free gas according to the production capacity evaluation parameters at the initial moment corresponding to the optimal key parameters; the in-situ gas content, the proportion of in-situ adsorbed gas and the proportion of in-situ free gas are used to evaluate the production capacity of coalbed methane resources; the optimal key parameters are the key parameters corresponding to the optimal fitting result.

9. A computer device, comprising: A memory, a processor, and a computer program stored on 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 the adsorbed / free gas ratio of deep coal and rock as described in any one of claims 1-7.

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

Images