Multi-factor synergistic shale gas apparent permeability prediction method coupled with molecular dynamics and related device
By coupling molecular dynamics methods to study the movement of gas molecules in nanopores and combining them with macroscopic calculations, the problem of pressure and temperature influence in shale gas reservoir permeability prediction was solved, achieving more accurate permeability prediction.
Patent Information
- Application Number
- CN202411762206.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-03
- Publication Date
- 2025-10-17
- Estimated Expiration
- 2044-12-03
AI Technical Summary
Existing technologies have difficulty accurately describing the nonlinear relationship between the apparent permeability and pressure of shale gas reservoirs. The temperature effect is not adequately considered, and there is a lack of micro-dynamic research, resulting in inaccurate permeability predictions.
By using the coupled molecular dynamics method and studying the motion trajectory and collision frequency of gas molecules in nanopores, combined with macroscopic calculations, a multi-factor synergistic shale gas apparent permeability prediction model is constructed, taking into account pressure sensitivity effects and temperature changes.
It significantly improves the accuracy of shale gas reservoir permeability prediction, adapts to complex reservoir conditions, and provides a more accurate permeability prediction tool through the combination of micro and macro.
Smart Images
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Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of petroleum engineering, and particularly relates to a multi-factor synergistic shale gas apparent permeability prediction method coupled with molecular dynamics and a related device. BACKGROUND
[0002] In the study of apparent permeability of shale gas reservoirs, the existing technology mainly faces the following technical problems: 1. Complexity of pore structure: The pore structure of shale gas reservoirs is complex and highly heterogeneous, which makes it difficult for traditional models to accurately capture the pressure sensitivity of permeability. The existing models fail to fully describe the nonlinear relationship between apparent permeability and pressure, and this pressure sensitivity effect is crucial for predicting reservoir characteristics. 2. Insufficient consideration of temperature effects: Although the Langmuir equation is used to describe the adsorption process of gas, it is not adaptable to temperature changes, resulting in a large deviation in the prediction of adsorption / desorption processes in actual applications. 3. Lack of micro-dynamics: The existing technology fails to fully combine micro-characterization and macro-computation. Through molecular dynamics methods, the motion trajectory and collision frequency of gas molecules in nanometer pores can be studied in detail, thereby obtaining key characteristic parameters. Combining these micro-characterization results with macro-computation can more comprehensively consider pressure sensitivity, temperature changes, and the motion characteristics of gas molecules in nanometer pores, and construct a more accurate permeability prediction model.
[0003] In order to more accurately predict the apparent permeability of shale gas reservoirs, it is urgent to develop a new model to combine micro-characterization and macro-computation, and thus more accurately predict permeability. SUMMARY
[0004] To solve the problems existing in the prior art, the purpose of the present application is to provide a multi-factor synergistic shale gas apparent permeability prediction method coupled with molecular dynamics and a related device. Through molecular dynamics methods, the motion trajectory and collision frequency of gas molecules in nanometer pores can be studied in detail, thereby obtaining key characteristic parameters. Combining these micro-characterization results with macro-computation can more comprehensively consider pressure sensitivity, temperature changes, and the motion characteristics of gas molecules in nanometer pores, and can more accurately predict permeability.
[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:
[0006] The multi-factor synergistic shale gas apparent permeability prediction method coupled with molecular dynamics comprises:
[0007] Obtaining initial parameters: The initial parameters include the pore radius , stress sensitivity coefficient of shale matrix , and effective stress received by shale matrix the partial pressure of the adsorbed molecules in the gas phase the diameter of the gas molecules and the mean free path of the gas molecules
[0008] the pore radius in the initial state the stress sensitivity coefficient of the shale matrix and the effective stress to which the shale matrix is subjected the effective pore radius under stress is calculated
[0009] the pore radius in the initial state and the effective stress to which the shale matrix is subjected the effective pore radius under stress is calculated
[0010] the effective pore radius under stress and the pore radius in the initial state the pore radius change due to the pressure sensitivity effect is calculated
[0011] the gas coverage is calculated using the Langmuir equation, the Arrhenius equation, and the partial pressure of the adsorbed molecules in the gas phase
[0012] the equivalent pore radius occupied by the adsorbed gas molecules is calculated using the diameter of the gas molecules and the gas coverage
[0013] the pore radius change considering the temperature effect is calculated using the equivalent pore radius occupied by the adsorbed gas molecules and the pore radius in the initial state
[0014] the equivalent pore radius considering the pressure sensitivity effect and the effect of temperature on the shale gas adsorption process is calculated using the pore radius in the initial state the pore radius change and the pore radius change
[0015] the Knudsen number considering the pressure sensitivity effect, the effect of temperature on the shale gas adsorption process, and the movement of gas molecules in nanopores is calculated using the equivalent pore radius and the mean free path of the gas molecules
[0016] Effective pore radius Pore radius in initial state Knudsen number Initial permeability of shale matrix The apparent permeability considering the pressure-sensitive effect, the influence of temperature on the shale gas adsorption process and the movement characteristics of gas molecules in nanopores .
[0017] Effective pore radius under stress The calculation formula is as follows:
[0018]
[0019] wherein, Pore radius in initial state, unit: m ; Stress sensitivity coefficient of shale matrix, unit: MPa-1 ; Effective stress of shale matrix, unit: MPa ;
[0020] Pore radius change amount caused by pressure-sensitive effect The calculation formula is as follows:
[0021]
[0022] wherein, Effective pore radius under stress, unit: m .
[0023] Gas coverage degree The calculation formula is as follows:
[0024]
[0025] wherein, Gas coverage degree, A is a pre-exponential factor; Experimental activation energy, unit: J / mol ; Temperature, unit: K ; Molar gas constant, unit: J / mol·K ; Partial pressure of adsorbed molecules in gas phase; Correction parameter, wherein , Boltzmann constant, Planck constant.
[0026] Effective pore radius The calculation formula of the pore radius change amount considering the temperature effect is as follows:
[0027]
[0028] Wherein, is the gas molecule diameter, in ; is the gas coverage, taking
[0029] The calculation formula of the pore radius change amount considering the temperature effect is as follows:
[0030]
[0031] Wherein, is the pore radius in the initial state, in ; is the equivalent pore radius occupied by the adsorbed gas molecules, in .
[0032] The calculation formula of the equivalent pore radius considering the pressure-sensitive effect and the temperature effect on the shale gas adsorption process is as follows:
[0033]
[0034] Wherein, is the pore radius in the initial state, in : is the pore radius change amount caused by the pressure-sensitive effect, in ; is the pore radius change amount considering the temperature effect, in .
[0035] The calculation formula of the equivalent pore radius considering the pressure-sensitive effect, the temperature effect on the shale gas adsorption process and the motion of the gas molecules in the nanopore is as follows:
[0036] The calculation formula of the Knudsen number considering the pressure-sensitive effect, the temperature effect on the shale gas adsorption process and the motion of the gas molecules in the nanopore is as follows:
[0037]
[0038] Wherein, is the mean free path of gas molecules, in units of ; is the equivalent pore radius that takes into account the pressure sensitivity effect and the influence of temperature on the shale gas adsorption process, and the unit is .
[0039] Preferably, the apparent permeability is considered, which takes into account the pressure sensitivity effect, the influence of temperature on the shale gas adsorption process, and the movement characteristics of gas molecules in nanopores. The calculation formula is as follows:
[0040]
[0041] in, is the equivalent pore radius that takes into account the pressure sensitivity effect and the influence of temperature on the shale gas adsorption process, and the unit is ; is the pore radius in the initial state, in units of ; The Knudsen number takes into account the pressure sensitivity effect, the influence of temperature on the shale gas adsorption process, and the movement of gas molecules in nanopores; is the initial permeability of the shale matrix, in .
[0042] The present invention also provides a multi-factor synergistic shale gas apparent permeability prediction system coupled with molecular dynamics, which is used to implement the above prediction method. The system includes:
[0043] Parameter acquisition unit: used to obtain initial parameters: the initial parameters include the pore radius in the initial state , stress sensitivity coefficient of shale matrix , effective stress on shale matrix , partial pressure of adsorbed molecules in the gas phase , gas molecule diameter and the mean free path of gas molecules ;
[0044] The first calculation unit: used to use the pore radius in the initial state , stress sensitivity coefficient of shale matrix and the effective stress on the shale matrix , calculate the effective pore radius under stress ;
[0045] The second calculation unit is used to use the effective pore radius under stress and the pore radius in the initial state Calculate the change in pore radius caused by pressure sensitivity effect ;
[0046] Third calculation unit: for calculating the gas coverage degree by using the Langmuir equation, the Arrhenius equation, the partial pressure of the adsorbed gas molecules in the gas phase
[0047] Fourth calculation unit: for calculating the equivalent pore radius occupied by the adsorbed gas molecules by using the gas molecule diameter and the gas coverage degree
[0048] Fifth calculation unit: for calculating the pore radius change amount considering the temperature effect by using the equivalent pore radius occupied by the adsorbed gas molecules and the pore radius in the initial state
[0049] Sixth calculation unit: for calculating the equivalent pore radius considering the pressure-sensitive effect and the temperature effect on the shale gas adsorption process by using the pore radius in the initial state , the pore radius change amount and the pore radius change amount
[0050] Seventh calculation unit: for calculating the Knudsen number considering the pressure-sensitive effect, the temperature effect on the shale gas adsorption process and the motion of the gas molecules in the nanopore by using the equivalent pore radius and the average free path of the gas molecules
[0051] Eighth calculation unit: for calculating the apparent permeability considering the pressure-sensitive effect, the temperature effect on the shale gas adsorption process and the motion characteristics of the gas molecules in the nanopore by using the equivalent pore radius , the pore radius in the initial state , the Knudsen number and the initial permeability of the shale matrix .
[0052] The present application also provides an electronic device comprising:
[0053] one or more processors;
[0054] a storage device having one or more programs stored thereon;
[0055] The one or more programs, when executed by the one or more processors, cause the one or more processors to implement the method for predicting apparent permeability of shale gas by multi-factor synergistic coupled molecular dynamics as described above.
[0056] The application further provides a storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the method for predicting apparent permeability of shale gas by multi-factor synergistic coupled molecular dynamics as described above.
[0057] Compared with the prior art, the application has the following beneficial effects:
[0058] Improving prediction accuracy: The application significantly improves the prediction accuracy of apparent permeability of shale gas reservoirs by comprehensively considering the pressure sensitivity effect, temperature change and complex behavior of gas molecules in nanopores. This effect is achieved by constructing a multi-factor coupled calculation model, which can more accurately capture the dynamic changes of pore structure under different pressure and temperature conditions, and the flow behavior of gas in nanopores. Adapt to complex reservoir conditions: The model of the application can adapt to the complex temperature environment in the actual reservoir, and by introducing the temperature corrected adsorption equilibrium constant model, the permeability calculation can adapt to the temperature fluctuation in the reservoir, which is often ignored in the prior art. Combination of micro and macro: The application innovatively combines the molecular dynamics method, simulates the micro behavior of gas molecules in nanopores, and combines the micro insight with macro calculation, providing a more comprehensive and accurate apparent permeability prediction tool. DETAILED DESCRIPTION
[0059] To make the objects, technical solutions and advantages of the embodiments of the application clearer, the technical solutions in the embodiments of the application are described below clearly and completely. Obviously, the described embodiments are some of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.
[0060] The main idea of the method for predicting apparent permeability of shale gas by multi-factor synergistic coupled molecular dynamics of the application is as follows:
[0061] Firstly, the application establishes the relationship between the effective permeability and the initial permeability of shale matrix, introduces the stress sensitivity coefficient and the effective stress, and constructs a calculation framework to describe the nonlinear relationship between the permeability and the pressure change. This step provides basic pore structure parameters for subsequent temperature influence and molecular dynamics analysis.
[0062] On the basis of the first step, the present application further considers the influence of temperature on gas adsorption behavior, and develops a temperature-corrected adsorption equilibrium constant model by combining the Langmuir equation and the Arrhenius equation. This step ensures that the model can adapt to the complex temperature environment in the actual reservoir, and provides temperature-corrected parameters for the next step of molecular dynamics simulation.
[0063] On the basis of the first two steps, the present application uses the molecular dynamics method to study the motion trajectory and collision frequency of gas molecules in nanopores in detail through Newton's second law and the Lennard-Jone potential energy function. This step reveals the dynamic motion law of gas molecules in nanopores, and provides key data at the microscopic level for the final apparent permeability model.
[0064] Finally, the present application integrates the pressure-sensitive effect, temperature influence and motion characteristics of gas molecules in nanopores obtained in the above steps to construct a multi-factor coupled apparent permeability calculation model. This step combines microscopic insights with macroscopic calculations, significantly improves the prediction accuracy of the model for the motion of gas molecules in nanopores, and thus provides a comprehensive and accurate tool for predicting the apparent permeability of shale gas reservoirs.
[0065] Embodiment
[0066] This embodiment aims at the complexity and heterogeneity of the pore structure of shale reservoirs, and constructs a shale gas reservoir pore radius change calculation model considering the pressure-sensitive effect, by setting the relationship between the effective permeability and the initial permeability of the shale matrix, and the relationship between the porosity and the pore radius, to obtain the pore radius change under different pressure conditions;
[0067] In shale gas reservoirs, the change of permeability is significantly affected by effective stress, showing an exponential relationship. To accurately describe this relationship, the relationship between the effective permeability of the shale matrix and the initial permeability is set as follows:
[0068]
[0069] The above formula: is the initial permeability of the shale matrix, with the unit of ;
[0070] is the stress-sensitive coefficient of the shale matrix, with the unit of ;
[0071] is the effective stress of the shale matrix, with the unit of ;
[0072] The effective permeability of shale matrix is ;
[0073] To study the permeability change of shale reservoir under different pressure conditions more accurately, the complex pore structure is simplified as a nanotube bundle model. In this model, the initial porosity of shale is represented as:
[0074]
[0075] The above formula: The initial porosity of shale is taken as ;
[0076] The number of nanotubes on the cross-sectional area of the core is
[0077] The pore radius in the initial state is ;
[0078] The length of the nanotube bundle is ;
[0079] The cross-sectional area of the nanotube is ;
[0080] After considering the pressure-sensitive effect, the relationship between the effective porosity of shale and the effective pore radius is
[0081] The above formula: The effective porosity of shale is taken as
[0082]
[0083] The number of nanotubes on the cross-sectional area of the core is
[0084] The effective pore radius under stress is ;
[0085] The length of the nanotube bundle is ;
[0086] The cross-sectional area of the nanotube is ;
[0087] According to the Hagen-Poiseuille theorem, the relationship between the pore radius and the absolute permeability is:
[0088]
[0089] The above formula: is the initial porosity of shale, and the unit is ;
[0090] is the pore radius in the initial state, and the unit is ;
[0091] N is the number of nanotubes on the cross-sectional area of the core;
[0092] is the cross-sectional area of the nanotube, and the unit is ;
[0093] The permeability after considering the pressure-sensitive effect can be expressed as:
[0094]
[0095] The above formula: is the initial porosity of shale, and the unit is ;
[0096] is the pore radius in the initial state, and the unit is ;
[0097] is the effective pore radius under stress, and the unit is ;
[0098] N is the number of nanotubes on the cross-sectional area of the core;
[0099] is the cross-sectional area of the nanotube, and the unit is ;
[0100] Therefore, the calculation formula of the effective pore radius under stress is:
[0101]
[0102] The above formula: is the effective pore radius under stress, and the unit is ;
[0103] is the pore radius in the initial state, and the unit is ;
[0104] is the stress-sensitive coefficient of shale matrix, and the unit is ;
[0105] is the effective stress on shale matrix, with unit of ;
[0106] Therefore, the change of pore radius caused by pressure-sensitive effect is :
[0107]
[0108] The above formula is the change of pore radius caused by pressure-sensitive effect, with unit of ;
[0109] is the effective pore radius under stress, with unit of ;
[0110] is the pore radius in initial state, with unit of ;
[0111] is the stress-sensitive coefficient of shale matrix, with unit of ;
[0112] is the effective stress on shale matrix, with unit of ;
[0113] Based on the influence of temperature on gas adsorption behavior, the temperature corrected adsorption equilibrium constant model is used to quantitatively analyze the influence of temperature on shale gas adsorption equilibrium constant, and to calculate the change of pore radius considering the influence of temperature.
[0114] In shale gas reservoir, temperature has a significant influence on gas adsorption behavior, especially in the process of adsorption / desorption. To quantitatively analyze the influence of temperature on shale gas adsorption equilibrium constant, we based on Langmuir equation and introduced Arrhenius equation for correction. The specific process is as follows:
[0115] First, Langmuir equation is used to describe the adsorption process of gas, and its expression is:
[0116]
[0117] The above formula is the adsorption volume, with unit of ;
[0118] is the Langmuir pressure, with unit of ;
[0119] is the Langmuir volume, with units of ;
[0120] is the partial pressure of the adsorbing molecule in the gas phase;
[0121] gas coverage is given by the expression:
[0122]
[0123] the above equation: is the gas coverage, taken as
[0124] is the adsorption equilibrium constant;
[0125] is the partial pressure of the adsorbing molecule in the gas phase;
[0126] Since the temperature is constantly changing during the adsorption / desorption process, we introduce the Arrhenius equation to reflect the influence of temperature on the adsorption equilibrium constant based on the Langmuir equation. The basic form of the Arrhenius equation is:
[0127]
[0128] the above equation: A is the pre-exponential factor;
[0129] is the experimental activation energy, with units of ;
[0130] is the temperature, with units of ;
[0131] is the molar gas constant, with units of ;
[0132] In order to expand the scope of application of the Arrhenius equation, a correction parameter is introduced, where , is the Boltzmann constant ( ), is the Planck constant ( )
[0133] Therefore, the gas coverage can be expressed as:
[0134]
[0135] The above formula: is the gas coverage, taken as
[0136] A is the pre-exponential factor;
[0137] Ea is the experimental activation energy, with the unit of ;
[0138] T is the temperature, with the unit of ;
[0139] R is the molar gas constant, ;
[0140] P is the partial pressure of the adsorbed molecules in the gas phase;
[0141] The effective pore radius considering the temperature effect is :
[0142]
[0143] The above formula: is the effective pore radius considering the temperature effect, with the unit of ;
[0144] D is the diameter of the gas molecules, with the unit of ;
[0145] The gas coverage is taken as
[0146] The change amount of the pore radius considering the temperature effect is
[0147]
[0148] The above formula: is the change amount of the pore radius considering the temperature effect, with the unit of ;
[0149] r0 is the pore radius in the initial state, with the unit of ;
[0150] r is the equivalent pore radius occupied by the adsorbed gas molecules, with the unit of ;
[0151] Molecular dynamics methods are used to study the microscopic behavior of gas molecules in nanopores. Newton's second law and the Lennard-Jone potential energy function are used to describe the interaction forces between molecules and between molecules and the tube wall. The free path and Knudsen number of gas molecules are calculated to quantify the motion characteristics of gas molecules in nanopores.
[0152] When using molecular dynamics to study the behavior of gas molecules in nanotubes, the motion of gas molecules is described by Newton's second law, which has the basic form:
[0153]
[0154] The above formula: For gas molecules The mass of ;
[0155] For gas molecules The acceleration, in units of ;
[0156] For gas molecules The position vector of ;
[0157] To act on molecules The net force on ;
[0158] The interaction forces between molecules and between molecules and the tube wall can be described by the Lennard-Jone potential energy function:
[0159]
[0160] The above formula: is the distance between the gas molecules and the tube wall surface, in units of ;
[0161] is the potential energy depth, in units of ;
[0162] is the distance scale, with units of ;
[0163] Acts on molecules The combined force molecule The combined force It can be obtained from the gradient of the potential energy:
[0164]
[0165] The above equation: is the resultant force acting on the molecule , in units of ;
[0166] is the gradient of the potential energy with respect to the intermolecular distance , in units of ;
[0167] is the distance between the gas molecule and the surface of the tube wall, in units of ;
[0168] is the depth of the potential well, in units of ;
[0169] is the distance scale, in units of ;
[0170] According to Newton's second law, the acceleration of the molecule can be written as the time derivative of the velocity:
[0171]
[0172] The above equation: is the acceleration of the gas molecule at time , in units of ;
[0173] The above equation: is the velocity of the gas molecule at time , in units of ;
[0174] The velocity is the time derivative of the position:
[0175]
[0176] The above equation: is the velocity of the gas molecule at time , in units of ;
[0177] The above equation: is the position of the gas molecule at time , in units of ;
[0178] By substituting the expression for the acceleration into the time variation of the velocity, the variation of the velocity with time can be obtained:
[0179]
[0180] The above equation: is the velocity of the gas molecule at time , in units of ; ;
[0181] The above equation: is the velocity of the gas molecule at time , in units of ;
[0182] The above equation: is the acceleration of the gas molecule at time , in units of ;
[0183] The above equation: is the time step, in units of ;
[0184] By integrating the position over time, we get the change in position over time:
[0185]
[0186] The above equation: is the position of the molecule at time , in units of ;
[0187] The above equation: is the position of the gas molecule at time , in units of ;
[0188] The above equation: is the time step, in units of ;
[0189] In the case where the time step is very small, we can integrate the velocity to get:
[0190]
[0191] The above equation: is the position of the molecule at time , in units of ;
[0192] The above equation: is the position of the gas molecule at time , in units of ;
[0193] is the time ; ;
[0194] is the time ; ;
[0195] is the time step ;
[0196] Collision detection (including intermolecular collision detection and molecule-wall collision detection) is performed, in which intermolecular collision detection is calculating the distance between each pair of gas molecules within each time step. When the distance between two molecules is less than , (when the distance between two molecules is less than , the repulsive force between the two molecules is very strong, indicating that their electron clouds have come very close and have produced a substantial collision), it can be considered that a collision has occurred; molecule-wall collision detection is detecting the distance between a gas molecule and the wall of the hole to determine whether a collision has occurred, if the distance is less than , it is considered that a collision has occurred. For the periodic boundary condition, when a molecule crosses the boundary, it will be mapped back into the box, which can also be considered as a collision.
[0197] The calculation of the free path is based on the displacement of the molecule before and after each collision. When a collision is detected, the position of the gas molecule is recorded, which can be considered as the position of the molecule before the collision. In the next time step, when a new collision occurs, a new position is recorded, which can be considered as the position of the molecule after the collision. By calculating the change in position of the gas molecule before and after the collision, the free path of the molecule can be obtained, and the formula is:
[0198]
[0199] The above formula: is the free path of the gas molecule ;
[0200] is the position of the gas molecule after the collision, with the unit of ;
[0201] is the position of the gas molecule before the collision, with the unit of ;
[0202] Calculation of the mean free path of the molecules:
[0203]
[0204] The above formula: is the mean free path of the gas molecules, with the unit of ;
[0205] is the number of all collision events;
[0206] is the free path of the gas molecules , with the unit of ;
[0207] is the Knudsen number considering the pressure-sensitive effect, the influence of temperature on the shale gas adsorption process and the movement of gas molecules in nanopores, which can be expressed as:
[0208]
[0209] wherein is the equivalent pore radius considering the pressure-sensitive effect and the influence of temperature on the shale gas adsorption process, , with the unit of .
[0210] The apparent permeability model is constructed by comprehensively considering the pressure-sensitive effect, the influence of temperature and the movement characteristics of gas molecules in nanopores, a multi-factor coupled apparent permeability calculation model is established by integrating the pressure-sensitive effect, the influence of temperature on the shale gas adsorption process and the movement characteristics of gas molecules in nanopores, and the apparent permeability of the shale gas reservoir is predicted through the model.
[0211] In order to comprehensively consider the pressure-sensitive effect, the influence of temperature on the shale gas adsorption process and the influence of the movement characteristics of gas molecules in nanopores on the apparent permeability of shale, the present application provides a multi-factor coupled apparent permeability model. The model integrates the pressure-sensitive effect, the influence of temperature on the shale gas adsorption process and the movement characteristics of gas molecules in nanopores, and the specific steps are as follows:
[0212] The apparent permeability calculation formula is:
[0213]
[0214] The above formula: is the correction factor caused by the slip flow;
[0215] is the initial permeability of shale matrix, unit is ;
[0216] where the sparse coefficient
[0217] Therefore, the apparent permeability model considering the pressure-sensitive effect, the influence of temperature on shale gas adsorption process and the movement characteristics of gas molecules in nanopores can be expressed as:
[0218]
[0219] The above formula: is the equivalent pore radius considering the pressure-sensitive effect and the influence of temperature on shale gas adsorption process, unit is ;
[0220] is the pore radius in the initial state, unit is ;
[0221] is the Knudsen number considering the pressure-sensitive effect, the influence of temperature on shale gas adsorption process and the movement of gas molecules in nanopores;
[0222] is the initial permeability of shale matrix, unit is ;
[0223] As can be seen from the above scheme, the method of the present application comprehensively considers the pressure sensitivity, temperature change and the complex behavior of gas molecules in nanopores, and through the use of molecular dynamics method, the micro-dynamics of gas molecules in nanopores is deeply explored, and the prediction accuracy of the model for gas transmission characteristics is significantly improved.
[0224] As can be seen from the above scheme, the present application overcomes the following defects or deficiencies in the prior art:
[0225] a. In view of the problem that the existing model fails to fully describe the nonlinear relationship between apparent permeability and pressure, and fails to accurately capture the pressure sensitivity of permeability, the present application constructs a calculation framework that can accurately capture the nonlinear change of porosity and apparent permeability under different pressure conditions.
[0226] b. In view of the problem that the existing technology does not adequately consider the influence of temperature on gas adsorption behavior, the present application ingeniously combines the Langmuir equation and the Arrhenius equation, and develops a temperature-corrected adsorption equilibrium constant model to accurately characterize the temperature effect in the adsorption / desorption process.
[0227] c. To address the lack of in-depth research on the microscopic behavior of gas molecules in nanopores in existing technologies, this paper uses molecular dynamics methods to deeply explore the microscopic behavior of gas molecules in nanopores. By calculating the Knudsen number, this paper combines microscopic insights with macroscopic calculations, thereby significantly improving the model's prediction accuracy for the movement of gas molecules in nanopores.
[0228] The present invention also provides a multi-factor synergistic shale gas apparent permeability prediction system coupled with molecular dynamics, which is used to implement the above prediction method. The system includes:
[0229] Parameter acquisition unit: used to obtain initial parameters: the initial parameters include the pore radius in the initial state , stress sensitivity coefficient of shale matrix , effective stress on shale matrix , partial pressure of adsorbed molecules in the gas phase , gas molecule diameter and the mean free path of gas molecules ;
[0230] The first calculation unit: used to use the pore radius in the initial state , stress sensitivity coefficient of shale matrix and the effective stress on the shale matrix , calculate the effective pore radius under stress ;
[0231] The second calculation unit is used to use the effective pore radius under stress and the pore radius in the initial state Calculate the change in pore radius caused by pressure sensitivity effect ;
[0232] The third calculation unit is used to use the Langmuir equation, Arrhenius equation, and the partial pressure of adsorbed molecules in the gas phase. Calculating gas coverage ;
[0233] The fourth calculation unit: used to use the diameter of gas molecules and gas coverage Calculate the equivalent pore radius occupied by adsorbed gas molecules ;
[0234] The fifth calculation unit: used to use the equivalent pore radius occupied by adsorbed gas molecules and the pore radius in the initial state Calculate the change in pore radius considering temperature effects ;
[0235] The sixth calculation unit is configured to calculate the equivalent pore radius by using the pore radius in the initial state , the pore radius change amount , and the pore radius change amount The calculation considers the pressure-sensitive effect, the influence of temperature on the shale gas adsorption process, and the equivalent pore radius .
[0236] The seventh calculation unit is configured to calculate the Knudsen number by using the equivalent pore radius , and the average free path of gas molecules The calculation considers the pressure-sensitive effect, the influence of temperature on the shale gas adsorption process, and the movement of gas molecules in the nanopore .
[0237] The eighth calculation unit is configured to calculate the apparent permeability by using the equivalent pore radius , the pore radius in the initial state , the Knudsen number , and the initial permeability of the shale matrix The calculation considers the pressure-sensitive effect, the influence of temperature on the shale gas adsorption process, and the movement characteristics of gas molecules in the nanopore .
[0238] The embodiments of the present application also provide a corresponding electronic device and a computer readable storage medium, which are used to implement the scheme provided by the embodiments of the present application.
[0239] The device includes a memory and a processor, the memory is used to store instructions or codes, and the processor is used to execute the instructions or codes to enable the device to perform the multi-factor collaborative shale gas apparent permeability prediction method of coupled molecular dynamics described in any embodiment of the present application.
[0240] The storage medium stores a computer program, and when the computer program is executed by the processor, the multi-factor collaborative shale gas apparent permeability prediction method of coupled molecular dynamics described in any embodiment of the present application is realized.
[0241] Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should belong to the scope of protection of the present application.
[0242] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application but not to limit it. Although the present application has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that the specific embodiments of the present application can be modified or replaced equivalently without departing from the spirit and scope of the present application, and any modification or equivalent replacement without departing from the spirit and scope of the present application should be covered in the protection scope of the claims of the present application.
Claims
1. A multi-factor synergistic shale gas apparent permeability prediction method coupled with molecular dynamics, characterized by: include: Obtaining initial parameters: The initial parameters include pore radius, stress sensitivity coefficient of shale matrix, effective stress on shale matrix, partial pressure of adsorbed molecules in gas phase, gas molecule diameter and gas molecule mean free path in the initial state; The effective pore radius under stress is calculated using the pore radius in the initial state, the stress sensitivity coefficient of the shale matrix and the effective stress of the shale matrix. The calculation formula is as follows: in, is the pore radius in the initial state, in units of ; is the stress sensitivity coefficient of the shale matrix, in units of ; is the effective stress on the shale matrix, in units of ; Change in pore radius caused by pressure sensitivity effect The calculation formula is as follows: in, is the effective pore radius under stress, in units of ; The change in pore radius caused by the pressure sensitivity effect is calculated using the effective pore radius under stress and the pore radius in the initial state. Calculate gas coverage using the Langmuir equation, Arrhenius equation, and the partial pressure of adsorbed molecules in the gas phase; Gas coverage The calculation formula is as follows: in, is the gas coverage, taken as %; A is the pre-exponential factor; is the experimental activation energy, in units of ; is the temperature in units of ; is the molar gas constant, in units of ; is the partial pressure of adsorbed molecules in the gas phase; is the correction parameter, where , is the Boltzmann constant, is Planck's constant; The equivalent pore radius occupied by adsorbed gas molecules is calculated using the gas molecule diameter and gas coverage; the equivalent pore radius The calculation formula is as follows: in, is the gas molecule diameter, in units of ; is the gas coverage, which is %; Change in pore radius considering temperature effect The calculation formula is as follows: in, is the pore radius in the initial state, in units of ; is the equivalent pore radius occupied by adsorbed gas molecules, in units of ; The change in pore radius considering the temperature effect is calculated using the equivalent pore radius occupied by adsorbed gas molecules and the pore radius in the initial state. The pore radius, pore radius change and pore radius change under the initial state are used to calculate the equivalent pore radius considering the pressure sensitivity effect and the influence of temperature on the shale gas adsorption process; the equivalent pore radius considering the pressure sensitivity effect and the influence of temperature on the shale gas adsorption process The calculation formula is as follows: in, is the pore radius in the initial state, in units of : is the change in pore radius caused by the pressure sensitivity effect, in units of ; is the change in pore radius considering the temperature effect, in units of ; The equivalent pore radius and the mean free path of gas molecules were used to calculate the Knudsen number, taking into account the pressure sensitivity effect, the influence of temperature on the shale gas adsorption process, and the movement of gas molecules in nanopores. The apparent permeability is calculated using the equivalent pore radius, the pore radius at the initial state, the Knudsen number, and the initial permeability of the shale matrix, taking into account the pressure sensitivity effect, the influence of temperature on the shale gas adsorption process, and the movement characteristics of gas molecules in nanopores.
2. The multi-factor synergistic shale gas apparent permeability prediction method based on coupled molecular dynamics according to claim 1 is characterized in that: The molecular dynamics method is used to study the microscopic behavior of gas molecules in nanopores. The interaction forces between molecules and between molecules and the tube wall are described by Newton's second law and the Lennard-Jone potential energy function. The mean free path of gas molecules and the Knudsen number that takes into account the pressure sensitivity effect, the influence of temperature on the shale gas adsorption process, and the movement of gas molecules in nanopores are calculated.
3. The multi-factor synergistic shale gas apparent permeability prediction method based on coupled molecular dynamics according to claim 1 is characterized in that: The Knudsen number of the shale gas adsorption process and the movement of gas molecules in nanopores are considered. The calculation formula is as follows: in, is the mean free path of gas molecules, in units of ; is the equivalent pore radius that takes into account the pressure sensitivity effect and the influence of temperature on the shale gas adsorption process, and the unit is .
4. The multi-factor synergistic shale gas apparent permeability prediction method coupled with molecular dynamics according to claim 1 is characterized in that: The apparent permeability takes into account the pressure sensitivity effect, the influence of temperature on the shale gas adsorption process, and the movement characteristics of gas molecules in nanopores. The calculation formula is as follows: in, is the equivalent pore radius that takes into account the pressure sensitivity effect and the influence of temperature on the shale gas adsorption process, and the unit is ; is the pore radius in the initial state, in units of ; The Knudsen number takes into account the pressure sensitivity effect, the influence of temperature on the shale gas adsorption process, and the movement of gas molecules in nanopores; is the initial permeability of the shale matrix, in .
5. A multi-factor synergistic shale gas apparent permeability prediction system coupled with molecular dynamics, used to implement the multi-factor synergistic shale gas apparent permeability prediction method coupled with molecular dynamics according to any one of claims 1 to 4, characterized in that: include: Parameter acquisition unit: used to acquire initial parameters: the initial parameters include pore radius, stress sensitivity coefficient of shale matrix, effective stress on shale matrix, partial pressure of adsorbed molecules in gas phase, gas molecule diameter and gas molecule mean free path in initial state; The first calculation unit is used to calculate the effective pore radius under stress using the pore radius in the initial state, the stress sensitivity coefficient of the shale matrix, and the effective stress on the shale matrix; The second calculation unit is used to calculate the pore radius change caused by the pressure sensitivity effect using the effective pore radius under stress and the pore radius in the initial state; The third calculation unit is used to calculate the gas coverage using the Langmuir equation, the Arrhenius equation, and the partial pressure of adsorbed molecules in the gas phase; The fourth calculation unit is used to calculate the equivalent pore radius occupied by the adsorbed gas molecules using the gas molecule diameter and gas coverage; The fifth calculation unit is used to calculate the pore radius change taking into account the temperature effect by using the equivalent pore radius occupied by the adsorbed gas molecules and the pore radius in the initial state; The sixth calculation unit is used to calculate the equivalent pore radius taking into account the pressure sensitivity effect and the influence of temperature on the shale gas adsorption process by using the pore radius, pore radius change and pore radius change in the initial state; The seventh calculation unit is used to calculate the Knudsen number by using the equivalent pore radius and the mean free path of gas molecules, taking into account the pressure sensitivity effect, the influence of temperature on the shale gas adsorption process, and the movement of gas molecules in nanopores; The eighth calculation unit is used to calculate the apparent permeability taking into account the pressure sensitivity effect, the influence of temperature on the shale gas adsorption process, and the movement characteristics of gas molecules in nanopores using the equivalent pore radius, the pore radius at the initial state, the Knudsen number, and the initial permeability of the shale matrix.
6. An electronic device, characterized in that: include: one or more processors; a storage device having one or more programs stored thereon; When the one or more programs are executed by the one or more processors, the one or more processors implement the multi-factor synergistic shale gas apparent permeability prediction method based on coupled molecular dynamics as described in any one of claims 1 to 4.
7. A storage medium, characterized in that: A computer program is stored thereon, wherein when the computer program is executed by a processor, the multi-factor synergistic shale gas apparent permeability prediction method based on coupled molecular dynamics as claimed in any one of claims 1 to 4 is implemented.