CN116070332B - Reservoir methane bubble emission modeling method, system, terminal and storage medium - Google Patents

Reservoir methane bubble emission modeling method, system, terminal and storage medium Download PDF

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CN116070332B
CN116070332B CN202310203327.8A CN202310203327A CN116070332B CN 116070332 B CN116070332 B CN 116070332B CN 202310203327 A CN202310203327 A CN 202310203327A CN 116070332 B CN116070332 B CN 116070332B
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methane
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bubble discharge
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CN116070332A (en
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杨英杰
马恩泽
梁修雨
赵鑫
刘进
张将伟
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Southwest University of Science and Technology
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Abstract

The invention relates to a modeling method, a modeling system, a modeling terminal and a storage medium for reservoir methane bubble emission, wherein the method comprises the following steps: constructing a reservoir methane bubble discharge model considering a deposition process, and describing a reservoir heat transfer process and a methane generation-migration-discharge process by using a classical partial differential equation module; describing a sediment deposition process by using a mobile grid module; introducing a water reservoir geometric model, and defining reservoir sediment-water body continuum heat transfer parameters, methane generation-migration-discharge parameters and deposition rate; setting the conditions of the model; meshing is carried out on the reservoir geometric model; calculating the methane bubble discharge flux of the reservoir; the dynamic numerical simulation is carried out on the bio-geochemical process of the reservoir methane bubble discharge, the influence of the reservoir sediment deposition process on methane generation and bubble discharge is considered, and the coupling equation of reactive diffusion and heat conduction is solved by finite element numerical values, so that the method can be well applied to estimation and prediction of the reservoir methane bubble discharge flux.

Description

Reservoir methane bubble emission modeling method, system, terminal and storage medium
Technical Field
The invention relates to the technical field of reservoir methane emission monitoring, in particular to a reservoir methane bubble emission modeling method, a system, a terminal and a storage medium.
Background
Methane is a powerful greenhouse gas, accounting for approximately one-fourth of the total contribution of greenhouse gases to global warming, and reservoirs are important sources of methane emissions. Methane in the reservoir is discharged into the atmosphere mainly through two forms of water surface diffusion and bubble discharge, wherein the bubble discharge is the most important discharge path and accounts for 70% of the total methane discharge amount in the reservoir on average. However, methane bubble emissions present a high degree of spatiotemporal heterogeneity and sporadic emissions processes, which present significant challenges for site monitoring and emissions estimation.
The existing reservoir methane emission model is an empirical model driven by observation data, the empirical model mainly reflects the correlation among physical quantities, lacks the internal connection among factors and the knowledge of the mechanism level of the whole process from generation to emission of methane, has great uncertainty in the prediction result, and needs a method capable of better estimating and predicting the reservoir methane emission flux.
Disclosure of Invention
The invention aims to solve the technical problems of the prior art, and provides a reservoir methane bubble discharge modeling method, a reservoir methane bubble discharge modeling system, a reservoir methane bubble discharge modeling terminal and a computer readable storage medium.
The technical scheme adopted for solving the technical problems is as follows:
a modeling method for reservoir methane bubble emission is constructed, which comprises the following steps:
constructing a reservoir methane bubble discharge model considering a deposition process, wherein the reservoir methane bubble discharge model comprises a heat transfer module, a methane generation-migration-discharge module and a sediment deposition module;
describing a reservoir heat transfer process and a methane generation-migration-discharge process by using a classical partial differential equation module;
describing a sediment deposition process by using a mobile grid module;
introducing a water reservoir geometric model, and defining reservoir sediment-water body continuum heat transfer parameters, methane generation-migration-discharge parameters and deposition rate;
setting boundary conditions and initial conditions of a reservoir methane bubble discharge model considering a deposition process;
meshing is carried out on the reservoir geometric model;
and calculating the methane bubble discharge flux of the reservoir.
The reservoir methane bubble discharge modeling method provided by the invention comprises a reservoir heat transfer process comprising a heat transfer process in a reservoir water body and a heat transfer process in reservoir sediments.
The invention relates to a modeling method for reservoir methane bubble discharge, wherein a heat transfer process in a reservoir water body is described by adopting a heat conduction equation:
Figure SMS_1
；
wherein:
Figure SMS_2
indicating the temperature of the water body>
Figure SMS_3
Representing the thermal diffusivity in a body of water, +.>
Figure SMS_4
Representing the elevation of the calculated point relative to the initial water-sediment interface, the initial water-sediment interface coordinates being 0,/and->
Figure SMS_5
Representing the simulation time.
The invention relates to a modeling method for reservoir methane bubble discharge, wherein a heat transfer process in reservoir sediment is described by adopting a heat conduction equation:
Figure SMS_6
；
wherein:
Figure SMS_7
indicating sediment temperature, +.>
Figure SMS_8
Indicating the thermal diffusivity in the deposit +.>
Figure SMS_9
Representing the elevation of the calculated point relative to the initial water-sediment interface, the initial water-sediment interface coordinates being 0,/and->
Figure SMS_10
Representing the simulation time.
The invention relates to a modeling method for reservoir methane bubble discharge, wherein the methane generation-migration-discharge process comprises a migration and oxidation process of methane in a reservoir water body and a migration and generation process of methane in reservoir sediments.
The invention relates to a reservoir methane bubble discharge modeling method, wherein the migration and oxidation process of methane in a reservoir water body is described by adopting a reactive diffusion equation:
Figure SMS_11
；
wherein:
Figure SMS_12
represents the concentration of dissolved methane in the water, +.>
Figure SMS_13
Representing the diffusion coefficient of methane in water body, < >>
Figure SMS_14
Represents the oxidation amount of methane.
The invention relates to a reservoir methane bubble discharge modeling method, wherein the oxidation amount of methane is expressed by using a Mies equation:
Figure SMS_15
；
wherein:
Figure SMS_16
indicates methane oxidation rate, +.>
Figure SMS_17
Represents the methane half-saturation constant, < >>
Figure SMS_18
Represents the half-saturation constant of oxygen,
Figure SMS_19
representing the concentration of dissolved oxygen in the body of water.
The invention relates to a reservoir methane bubble discharge modeling method, wherein the migration and generation processes of methane in reservoir sediments are described by adopting a reactive diffusion equation:
Figure SMS_20
；
wherein:
Figure SMS_21
representing sediment porosity, +.>
Figure SMS_22
Represents the methane concentration in the deposit, +.>
Figure SMS_23
Represents the diffusion coefficient of methane in the deposit, +.>
Figure SMS_24
Indicating methane production in the sediment, +.>
Figure SMS_25
Indicating the generation of methane bubbles in the deposit.
The invention relates to a reservoir methane bubble discharge modeling method, wherein, the generation item of methane
Figure SMS_26
Expressed using the following formula:
Figure SMS_27
；
wherein:
Figure SMS_28
representing the methanogenic factor, < >>
Figure SMS_29
Represents the organic carbon content of the deposit, +.>
Figure SMS_30
Represents the methane production rate decay factor,/-)>
Figure SMS_31
Indicates sediment deposition time, +.>
Figure SMS_32
Representing the temperature sensitivity coefficient of methanogen, < +.>
Figure SMS_33
Representing the methanogenic reference temperature.
The invention relates to a reservoir methane bubble discharge modeling method, wherein, the deposition time
Figure SMS_34
Expressed as:
Figure SMS_35
；
wherein:
Figure SMS_36
indicating the sediment deposition rate.
The invention relates to a reservoir methane bubble emission modeling method, wherein the generation term of methane bubbles
Figure SMS_37
Using a critical concentration model representation:
Figure SMS_38
；
wherein:
Figure SMS_39
represents bubble generation rate, +.>
Figure SMS_40
Representing a step function +.>
Figure SMS_41
Indicating the relative saturation of bubble generation, +.>
Figure SMS_42
Critical concentration of methane bubble generation.
The invention relates to a reservoir methane bubble discharge modeling method, wherein, critical concentration is as follows
Figure SMS_43
Expressed using the following formula:
Figure SMS_44
；
wherein:
Figure SMS_45
represents the water-gas phase Henry coefficient, +.>
Figure SMS_46
Represents atmospheric pressure, +.>
Figure SMS_47
Represents the density of water>
Figure SMS_48
Indicating the acceleration of gravity>
Figure SMS_49
Representing the depth of the water body>
Figure SMS_50
Indicating the nitrogen partial pressure.
The invention relates to a modeling method for reservoir methane bubble discharge, wherein the flux of reservoir methane bubble discharge is expressed as:
Figure SMS_51
；
wherein:
Figure SMS_52
represents the dissolution proportion of bubbles in the water body floating process,/->
Figure SMS_53
Indicating the bottom position of the methane-generating fraction of the sediment,/->
Figure SMS_54
Indicating the current position of the water-sediment interface, +.>
Figure SMS_55
Represents the molar mass of methane.
The invention relates to a reservoir methane bubble discharge modeling method, wherein the sediment deposition process is simulated as follows:
the reservoir sediment deposition process is described by using a moving grid method, and the moving rate of the grid nodes of the water-sediment interface is set as the reservoir sediment deposition rate
Figure SMS_56
。
According to the reservoir methane bubble discharge modeling method, a reservoir methane bubble discharge model taking a deposition process into consideration is constructed in COMSOL software; the classical partial differential equation module and the mobile mesh module are both derived from a COMSOL mathematical module.
The reservoir methane bubble discharge modeling system is applied to the reservoir methane bubble discharge modeling method, and comprises a modeling module, a classical partial differential equation module, a mobile grid module, a data input module and a data processing module;
the modeling module is used for constructing a reservoir methane bubble discharge model considering a deposition process, and the reservoir methane bubble discharge model comprises a heat transfer module, a methane generation-migration-discharge module and a sediment deposition module;
the classical partial differential equation module is used for describing a reservoir heat transfer process and a methane generation-migration-discharge process;
the mobile grid module is used for describing a sediment deposition process;
the data input module is used for importing a reservoir geometric model, defining reservoir sediment-water continuum heat transfer parameters, methane generation-migration-discharge parameters and deposition rate, and setting boundary conditions and initial conditions of a reservoir methane bubble discharge model considering a deposition process;
and the data processing module is used for meshing the reservoir geometric model and calculating the methane bubble discharge flux of the reservoir.
A modeling terminal for methane bubble emission from a reservoir comprising a memory, a processor and a computer program stored in the memory and operable on the processor, wherein the processor, when executing the computer program, performs the steps of the method as described above.
A computer readable storage medium storing a computer program, wherein the computer program when executed by a processor implements the steps of the method as described above.
The invention has the beneficial effects that: by using the method, dynamic numerical simulation is carried out on the bio-geochemical process of reservoir methane bubble discharge, the influence of the reservoir sediment deposition process on methane generation and bubble discharge is considered in the model, the coupling equation of reactive diffusion and heat conduction is solved by finite element numerical values, and the reservoir methane bubble discharge flux is verified by experimental measurement, so that the verification result shows that the model can be well applied to estimation and prediction of reservoir methane bubble discharge flux.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the present invention will be further described with reference to the accompanying drawings and embodiments, in which the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained by those skilled in the art without inventive effort:
FIG. 1 is a flow chart of a modeling method for reservoir methane bubble emissions in accordance with a preferred embodiment of the present invention;
FIG. 2 is a diagram of a geometric model set up in the reservoir methane bubble emission modeling method COMSOL according to the preferred embodiment of the present invention;
FIG. 3 is a diagram of a model set up of reservoir methane bubble discharge taking into account the sedimentation process in the reservoir methane bubble discharge modeling method COMSOL according to the preferred embodiment of the present invention;
FIG. 4 is a graph showing the measured water temperature of the reservoir surface layer during a research period according to the modeling method for methane bubble discharge in a reservoir according to the preferred embodiment of the present invention;
FIG. 5 is a graph showing the variation of sediment-water interface temperature over a study period for a reservoir methane bubble discharge modeling method in accordance with a preferred embodiment of the present invention;
FIG. 6 is a graph showing the spatial distribution of sediment methane production rate over a study period for a reservoir methane bubble discharge modeling method in accordance with a preferred embodiment of the present invention;
FIG. 7 is a graph showing the spatial distribution of methane concentration in sediment pore water over a study period in a modeling method for reservoir methane bubble discharge in accordance with a preferred embodiment of the present invention;
FIG. 8 is a graph showing the spatial distribution of threshold methane bubble generation concentrations in reservoir methane bubble discharge modeling method deposits over a study period in accordance with a preferred embodiment of the present invention;
FIG. 9 is a graph showing the spatial distribution of sediment methane bubble generation rate over a study period for a reservoir methane bubble discharge modeling method in accordance with a preferred embodiment of the present invention;
FIG. 10 is a graph comparing simulation results and actual measurement results of reservoir methane bubble flux in a reservoir methane bubble discharge modeling method according to a preferred embodiment of the present invention;
FIG. 11 is a schematic block diagram of a reservoir methane bubble discharge modeling system in accordance with a preferred embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the following description will be made in detail with reference to the technical solutions in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by a person skilled in the art without any inventive effort, are intended to be within the scope of the present invention, based on the embodiments of the present invention.
The modeling method for reservoir methane bubble discharge according to the preferred embodiment of the invention is shown in fig. 1, and referring to fig. 2 to 10, the modeling method comprises the following steps:
s01: constructing a reservoir methane bubble discharge model considering a deposition process, wherein the reservoir methane bubble discharge model comprises a heat transfer module, a methane generation-migration-discharge module and a sediment deposition module;
s02: describing a reservoir heat transfer process and a methane generation-migration-discharge process by using a classical partial differential equation module;
s03: describing a sediment deposition process by using a mobile grid module;
s04: introducing a water reservoir geometric model, and defining reservoir sediment-water body continuum heat transfer parameters, methane generation-migration-discharge parameters and deposition rate;
s05: setting boundary conditions and initial conditions of a reservoir methane bubble discharge model considering a deposition process;
s06: meshing is carried out on the reservoir geometric model;
s07: calculating the methane bubble discharge flux of the reservoir;
by using the method, dynamic numerical simulation is carried out on the bio-geochemical process of reservoir methane bubble discharge, the influence of the reservoir sediment deposition process on methane generation and bubble discharge is considered in the model, the coupling equation of reactive diffusion and heat conduction is solved by finite element numerical values, and the reservoir methane bubble discharge flux is verified by experimental measurement, so that the verification result shows that the model can be well applied to estimation and prediction of reservoir methane bubble discharge flux.
The dynamic numerical simulation of the bio-geochemical process of reservoir methane bubble discharge can be carried out by adopting COMSOL Multiphysics software, the influence of the reservoir sediment deposition process on methane generation and bubble discharge is considered in a model, the coupling equation of reactive diffusion and heat conduction is solved by finite element numerical values, and the reservoir methane bubble discharge flux is verified by experimental determination.
Numerical simulation and experimental verification of reservoir methane bubble discharge considering sediment deposition process are as follows:
and (3) using COMSOL Multiphysics multi-physical field coupling simulation software as a platform to dynamically simulate the reservoir methane bubble discharge process considering the sediment deposition process, solving a coupling equation of reactive diffusion and heat conduction by finite element values, and verifying the reservoir methane bubble discharge flux by experimental determination.
The computer running the software is a DELL high-performance personal computer, and the processor is i7-8700, 3.2GHz six-core processor, 64G RAM and a Win10 bit operating system.
The model building steps are as follows:
selecting a physical field: the experiment selects three physical fields of a heat conduction equation and a convection dispersion equation in a module of a mathematical-classical partial differential equation and a moving grid in a module of a mathematical-deformed grid;
establishing a geometric model: one-dimensional sediment and water columns (straight line, initial length of sediment is 2 meters, initial length of methane part which can be generated by reaction is 0.1 meter, initial length of water column is 4 meters);
inputting physical and chemical parameters of methane and parameters related to methane generation and migration;
setting boundary conditions: the upper boundary water-atmosphere interface is a dirichlet boundary, the temperature of the surface water is higher, and the methane concentration is the background concentration of the atmospheric methane;
dividing grids: the grids are set to be extremely fine grids;
moving the grid setting: setting a prescribed speed of 0.29 m/year (namely sediment deposition speed) at the grid points of the sediment-water interface;
selecting a solver: selecting a MUMPS direct linear solver to solve the partial differential equation, wherein the relative tolerance is set to be 0.0001;
and outputting a calculation result.
The specific embodiments are as follows:
and constructing a reservoir water body methane generation and emission model considering the deposition rate in COMSOL software, wherein the model comprises a methane generation-migration-emission module, a heat transfer module and a sediment deposition module. The model construction comprises the following steps:
selecting a physical field: 1) Selecting a 'thermal equation' in a COMSOL 'mathematical' module- > 'classical partial differential equation' module to describe a heat transfer process in a reservoir; 2) A ' convection dispersion equation ' in a COMSOL ' math ' module ' - > ' classical partial differential equation ' module is selected to describe a methane generation-migration-discharge process in a reservoir; 3) Selecting a COMSOL (compact grid deformation) module- > "mobile grid" module to describe a sediment deposition process;
establishing a geometric model: establishing a vertical one-dimensional reservoir geometric model in COMSOL, wherein the model comprises a sediment layer and a water body layer;
parameter and variable definitions: defining parameters of heat conduction and methane physicochemical properties in a COMSOL "parameters" module; defining a temperature-controlled methane generation, migration and emission coefficient empirical model in a COMSOL variable module;
setting model boundary conditions: defining an upper boundary of the heat transfer module, namely a water-atmosphere interface boundary, as a dirichlet boundary, wherein the boundary temperature is the surface water temperature; defining the upper boundary of the methane migration and emission module as a dirichlet boundary, wherein the boundary methane concentration is the background concentration of atmospheric methane; the lower boundaries of the two modules, namely the bottom boundary of the deposition layer, are zero flux boundaries;
setting initial value conditions of a model: setting the initial temperature of the model as the annual average water temperature; setting the initial concentration of the model as the water dissolution concentration corresponding to the background concentration of the atmospheric methane;
dividing grids: according to the specific model size, the grid sizes of different areas are customized;
running the model and outputting a calculation result;
further, the equation for the heat transfer process and the methane generation-migration-discharge process is:
the heat transfer process in the reservoir can be described by the heat transfer equation:
a) The heat transfer process in a body of water in a reservoir is described using the heat transfer equation:
Figure SMS_57
(1)
wherein:
Figure SMS_58
the water temperature is represented by K; />
Figure SMS_59
The thermal diffusion coefficient in the water body is expressed in m2/s; />
Figure SMS_60
Representing the elevation of the calculated point relative to the initial water-sediment interface in m; the initial water-sediment interface coordinates were 0; />
Figure SMS_61
The simulation time is represented by s;
b) The heat transfer process in reservoir sediments is described using the heat transfer equation:
Figure SMS_62
(2)
wherein:
Figure SMS_63
the sediment temperature is expressed in K; />
Figure SMS_64
Representing the thermal diffusivity in the deposit in m2/s;
the methane production-migration-discharge process in reservoirs can be described by the reactive diffusion equation:
a) The methane migration process in a water body of a reservoir is described using the reactive diffusion equation:
Figure SMS_65
(3)
wherein:
Figure SMS_66
the concentration of dissolved methane in the water body is expressed in mol/L; />
Figure SMS_67
The diffusion coefficient of methane in the water body is expressed in m2/s; />
Figure SMS_68
Representation armorThe unit of the oxidation amount of the alkane is mol/L/s; the oxidation amount of methane can be expressed using the mie equation:
Figure SMS_69
(4)
wherein:
Figure SMS_70
represents the oxidation rate of methane, and the unit is mol/m3/s; />
Figure SMS_71
Represents the methane half-saturation constant, and the unit is mol/m3; />
Figure SMS_72
Represents the oxygen half saturation constant, and the unit is mol/m3; />
Figure SMS_73
The concentration of dissolved oxygen in the water body is expressed in mol/m < 3 >;
b) The methane generation-migration process in reservoir sediments is described using the reactive diffusion equation:
Figure SMS_74
(5)
wherein:
Figure SMS_75
representing sediment porosity; />
Figure SMS_76
Represents the methane concentration in the deposit in mol/L; />
Figure SMS_77
Represents the diffusion coefficient of methane in the sediment, and the unit is m2/s; />
Figure SMS_78
Represents the generation of methane in the deposit in mol/L/s; />
Figure SMS_79
The generation of methane bubbles in the deposit is expressed in mol/L/s. Wherein the production term of methane->
Figure SMS_80
Expressed using the following formula:
Figure SMS_81
(6)
wherein:
Figure SMS_82
representing the methane production coefficient, wherein the unit is 1/s; />
Figure SMS_83
Represents the organic carbon content in the sediment, mol/L3; />
Figure SMS_84
Representing the methane production rate decay factor; />
Figure SMS_85
Representing sediment deposition time s; />
Figure SMS_86
Representing the temperature sensitivity coefficient of methanogen; />
Figure SMS_87
The methanogenic reference temperature is expressed in K. In view of the present model describing sediment deposition process using a moving grid, deposition time +.>
Figure SMS_88
Expressed as:
Figure SMS_89
(7)
wherein:
Figure SMS_90
representing sediment deposition rate, m/s;
methane bubble generation term
Figure SMS_91
The critical concentration model representation may be used:
Figure SMS_92
(8)
wherein:
Figure SMS_93
the bubble generation rate is expressed as 1/s; />
Figure SMS_94
Representing a step function; />
Figure SMS_95
Representing the relative saturation of bubble generation; />
Figure SMS_96
The critical concentration of methane bubbles is given in mol/L. Critical concentration->
Figure SMS_97
Can be expressed as:
Figure SMS_98
(9)
wherein:
Figure SMS_99
represents the water-gas phase Henry coefficient, and the unit is mol/L/Pa; />
Figure SMS_100
The atmospheric pressure is expressed in Pa;
Figure SMS_101
represents the density of water in kg/m3; />
Figure SMS_102
The gravity acceleration is expressed in m/s2; />
Figure SMS_103
Representing the depth of a water body, wherein the unit is m;
Figure SMS_104
the partial pressure of nitrogen is expressed in Pa;
c) The methane bubble discharge flux of the reservoir is expressed as:
Figure SMS_105
(10)
wherein:
Figure SMS_106
the dissolution proportion of bubbles in the water body buoyancy process is represented; />
Figure SMS_107
Representing the position of the bottom of the sediment, wherein the unit is m; />
Figure SMS_108
Representing the current position of a water-sediment interface, wherein the unit is m; />
Figure SMS_109
Represents the molar mass of methane in g/mol;
the reservoir sediment deposition process is described by using a moving grid method, and the moving rate of the grid nodes of the water-sediment interface is set as the reservoir sediment deposition rate
Figure SMS_110
。
The actual verification is as follows:
taking the methane bubble discharge process of a certain reservoir on the Saar river in Germany as an example, the COMSOL software is utilized for numerical simulation, if the model can be matched with the actual observed methane bubble flux, the in-situ measurement can be avoided in the later period, and the model is directly used for prediction, so that time and labor are wasted, and cost and resources are avoided.
1. Model arrangement
Fig. 2 shows the simulated geometric model, consisting essentially of 2 parts, sediment ((1) and (2)) and body of water ((3)). Wherein the sediment section comprises a non-methane producing fraction ((1)) and a methane producing fraction ((2)). (4) Representing sediment-water interface, the grid points are arranged as a moving grid, with a prescribed velocity of 0.29 m/year, representing sediment deposition processes. Fig. 3 shows the setting of the parameters of the model and the physical field control equations. Fig. 4 shows the surface water temperature observations over the year of the target reservoir as temperature boundary conditions for the input model.
2. Simulation results
Fig. 5 shows the variation of the temperature of the sediment-water interface with the deposition time, the abscissa indicates the temperature of the sediment-water interface, the ordinate indicates the elevation of the sediment-water interface, and the gradual variation of the color of the points on the curve from dark blue to dark red indicates the increase of the deposition time. As shown in fig. 5, it can be seen that as the deposition time increases, the sediment-water interface height Cheng Zhujian rises with the sediment deposition process. At the same time, as the deposition time increases, the interface temperature shows a significant tendency to change seasonally.
Fig. 6 shows the change in the spatial distribution of the methane production rate in the deposit at different times, the abscissa indicates the methane production rate of the deposit, the ordinate indicates the deposit thickness relative to the initial time of simulation, and the gradual change in the curve color from dark blue to dark red indicates the change in the spatial distribution of the methane production rate with increasing deposit time. As shown in fig. 6, it can be seen that as the deposition time increases, the thickness of the deposit increases and the range of deposits capable of producing methane increases. For all moments, the methane production rate always reaches a maximum at the top of the deposit, and then drops rapidly with the depth of deposit; the methane production rate at the top of the deposit at different times has a high correlation with the deposit temperature at the corresponding times (fig. 5).
Fig. 7 shows the change in the spatial distribution of the methane concentration in the pore water of the sediment at different moments, the abscissa represents the methane concentration in the pore water of the sediment, the ordinate represents the deposition thickness relative to the initial moment of simulation, and the gradual change of the curve color from dark blue to dark red represents the change of the spatial distribution of the methane concentration in the pore water with the increase of the deposition time. As shown in fig. 7, it was found that for any one deposition timing, a steep increase in the methane concentration in the deposit occurred at the deposit surface layer, after which no significant change in the methane concentration occurred with increasing depth of deposition. Comparing fig. 5 and 7, it can be seen that the sediment methane concentration is significantly affected by the sediment temperature change, and decreases with increasing sediment temperature.
Fig. 8 shows the spatial distribution of the threshold concentration required for methane bubble generation in the deposit at different times, the abscissa represents the threshold concentration required for methane bubble generation in the deposit, the ordinate represents the deposition thickness relative to the initial time of simulation, and the gradual change of the curve color from dark blue to dark red represents the change of the spatial distribution of the threshold concentration required for methane bubble generation in the deposit with increasing deposition time. Comparing fig. 5 and 7, it can be seen that the sediment methane concentration is significantly affected by the sediment temperature change, and that the threshold concentration required for sediment methane bubble generation decreases with increasing sediment temperature.
Fig. 9 shows the change in the spatial distribution of the generation rate of methane bubbles in the deposit at different times, the abscissa represents the generation rate of methane bubbles in the deposit, the ordinate represents the deposition thickness at the initial time of simulation, and the gradual change in the color of the curve from dark blue to dark red represents the change in the spatial distribution of the generation rate of methane bubbles in the deposit with the increase in the deposition time. Comparing fig. 5 and 7, it can be seen that the sediment methane bubble generation rate significantly varies with the sediment temperature, and increases with the sediment temperature.
Fig. 10 shows a comparison of reservoir methane bubble flux (green solid line) and site monitoring results (green dot) for model simulation. As shown in FIG. 10, the simulation results can be well fit with the observation results in general, which shows that the model can be well applied to estimating and predicting the methane bubble discharge flux of the reservoir
The modeling system for reservoir methane bubble discharge is applied to the modeling method for reservoir methane bubble discharge, and as shown in FIG. 11, the modeling system comprises a modeling module 1, a classical partial differential equation module 2, a mobile grid module 3, a data input module 4 and a data processing module 5;
the modeling module 1 is used for constructing a reservoir methane bubble discharge model considering a deposition process, wherein the reservoir methane bubble discharge model comprises a heat transfer module, a methane generation-migration-discharge module and a sediment deposition module;
a classical partial differential equation module 2 for describing a reservoir heat transfer process and a methane generation-migration-discharge process;
a mobile grid module 3 for describing the sediment deposition process;
the data input module 4 is used for importing a reservoir geometric model, defining reservoir sediment-water continuum heat transfer parameters, methane generation-migration-discharge parameters and deposition rate, and setting boundary conditions and initial conditions of a reservoir methane bubble discharge model considering a deposition process;
the data processing module 5 is used for meshing the reservoir geometric model and calculating the methane bubble discharge flux of the reservoir;
the dynamic numerical simulation is carried out on the bio-geochemical process of reservoir methane bubble discharge, the influence of the reservoir sediment deposition process on methane generation and bubble discharge is considered in the model, the coupling equation of reactive diffusion and heat conduction is solved by finite element numerical values, the reservoir methane bubble discharge flux is verified through experimental measurement, and the verification result shows that the model can be well applied to estimation and prediction of the reservoir methane bubble discharge flux.
A modeling terminal for methane bubble emission from a reservoir comprising a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor performs the steps of the method as described above when the computer program is executed.
A computer readable storage medium storing a computer program, wherein the computer program when executed by a processor implements the steps of the method as described above.
It will be understood that modifications and variations will be apparent to those skilled in the art from the foregoing description, and it is intended that all such modifications and variations be included within the scope of the following claims.

Claims (18)

1. The modeling method for methane bubble discharge of the reservoir is characterized by comprising the following steps of:
constructing a reservoir methane bubble discharge model considering a deposition process, wherein the reservoir methane bubble discharge model comprises a heat transfer module, a methane generation-migration-discharge module and a sediment deposition module;
describing a reservoir heat transfer process and a methane generation-migration-discharge process by using a classical partial differential equation module; the heat transfer process is described by using a heat conduction equation, and the methane generation-migration-discharge process comprises a migration and oxidation process of methane in a reservoir water body and a migration and generation process of methane in reservoir sediments, and is described by using a reactive diffusion equation;
describing a sediment deposition process by using a mobile grid module;
introducing a water reservoir geometric model, and defining reservoir sediment-water body continuum heat transfer parameters, methane generation-migration-discharge parameters and deposition rate;
setting boundary conditions and initial conditions of a reservoir methane bubble discharge model considering a deposition process;
meshing is carried out on the reservoir geometric model;
and calculating the methane bubble discharge flux of the reservoir.
2. The modeling method of reservoir methane bubble discharge of claim 1, wherein the reservoir heat transfer process comprises a heat transfer process in a body of water of the reservoir and a heat transfer process in a deposit of the reservoir.
3. The modeling method of reservoir methane bubble discharge according to claim 2, wherein the heat transfer process in the body of water of the reservoir is described by using a heat transfer equation:
Figure QLYQS_1
；
wherein:
Figure QLYQS_2
indicating the temperature of the water body>
Figure QLYQS_3
Representing the thermal diffusivity in a body of water, +.>
Figure QLYQS_4
Representing the elevation of the calculated point relative to the initial water-sediment interface, the initial water-sediment interface coordinates being 0,/and->
Figure QLYQS_5
Representing the simulation time.
4. The modeling method of reservoir methane bubble discharge according to claim 2, wherein the heat transfer process in the reservoir deposit is described by a heat transfer equation:
Figure QLYQS_6
；
wherein:
Figure QLYQS_7
indicating sediment temperature, +.>
Figure QLYQS_8
Indicating the thermal diffusivity in the deposit +.>
Figure QLYQS_9
Representing the elevation of the calculated point relative to the initial water-sediment interface, the initial water-sediment interface coordinates being 0,/and->
Figure QLYQS_10
Representing the simulation time.
5. The modeling method of methane bubble discharge in a reservoir according to any one of claims 1-4, wherein the methane generation-migration-discharge process includes a process of migration and oxidation of methane in a body of water in the reservoir and a process of migration and production of methane in a sediment in the reservoir.
6. The modeling method for methane bubble discharge in a reservoir according to claim 5, wherein the migration and oxidation process of methane in the water body of the reservoir is described by a reactive diffusion equation:
Figure QLYQS_11
；
wherein:
Figure QLYQS_12
represents the concentration of dissolved methane in the water, +.>
Figure QLYQS_13
Representing the diffusion coefficient of methane in water body, < >>
Figure QLYQS_14
Represents the oxidation amount of methane.
7. The modeling method for methane bubble discharge in a reservoir of claim 6, wherein the oxidation amount of methane is expressed using a mie equation:
Figure QLYQS_15
；
wherein:
Figure QLYQS_16
indicates methane oxidation rate, +.>
Figure QLYQS_17
Represents the methane half-saturation constant, < >>
Figure QLYQS_18
Represents the oxygen half saturation constant, < >>
Figure QLYQS_19
Representing the concentration of dissolved oxygen in the body of water.
8. The modeling method of reservoir methane bubble discharge according to claim 5, wherein the migration and generation process of methane in reservoir sediment is described by a reactive diffusion equation:
Figure QLYQS_20
；
wherein:
Figure QLYQS_21
representing sediment porosity, +.>
Figure QLYQS_22
Represents the methane concentration in the deposit, +.>
Figure QLYQS_23
Represents the diffusion coefficient of methane in the deposit, +.>
Figure QLYQS_24
Indicating methane production in the sediment, +.>
Figure QLYQS_25
Indicating the generation of methane bubbles in the deposit.
9. The modeling method of reservoir methane bubble discharge according to claim 8, wherein the term of methane generation
Figure QLYQS_26
Expressed using the following formula:
Figure QLYQS_27
；
wherein:
Figure QLYQS_28
representing the methanogenic factor, < >>
Figure QLYQS_29
Represents the organic carbon content of the deposit, +.>
Figure QLYQS_30
Representing the methane production rate decay factor,
Figure QLYQS_31
indicates sediment deposition time, +.>
Figure QLYQS_32
Representing the temperature sensitivity coefficient of methanogen, < +.>
Figure QLYQS_33
Representing the methanogenic reference temperature.
10. The modeling method of reservoir methane bubble discharge according to claim 9, wherein the deposition time
Figure QLYQS_34
Expressed as:
Figure QLYQS_35
；
wherein:
Figure QLYQS_36
indicating the sediment deposition rate.
11. The modeling method for methane bubble discharge in reservoir of claim 8, wherein the term for generating methane bubbles
Figure QLYQS_37
Using a critical concentration model representation:
Figure QLYQS_38
；
wherein:
Figure QLYQS_39
represents bubble generation rate, +.>
Figure QLYQS_40
Representing a step function +.>
Figure QLYQS_41
Indicating the relative saturation of bubble generation, +.>
Figure QLYQS_42
Critical concentration of methane bubble generation.
12. The modeling method of reservoir methane bubble discharge in accordance with claim 11, wherein the critical concentration
Figure QLYQS_43
Expressed using the following formula:
Figure QLYQS_44
；
wherein:
Figure QLYQS_45
represents the water-gas phase Henry coefficient, +.>
Figure QLYQS_46
Represents atmospheric pressure, +.>
Figure QLYQS_47
Represents the density of water>
Figure QLYQS_48
Representing gravitational acceleration，/>
Figure QLYQS_49
Representing the depth of the water body>
Figure QLYQS_50
Indicating the nitrogen partial pressure.
13. The modeling method of reservoir methane bubble discharge according to any one of claims 1 to 4 and 6 to 12, wherein the reservoir methane bubble discharge flux is expressed as:
Figure QLYQS_51
；
wherein:
Figure QLYQS_52
represents the dissolution proportion of bubbles in the water body floating process,/->
Figure QLYQS_53
Indicating the bottom position of the methane-generating fraction of the sediment,/->
Figure QLYQS_54
Indicating the generation of methane bubbles in the deposit, +.>
Figure QLYQS_55
Indicating the current position of the water-sediment interface, +.>
Figure QLYQS_56
Represents the molar mass of methane.
14. The modeling method for methane bubble discharge in a reservoir according to any one of claims 1-4 and 6-12, wherein the sediment deposition process is simulated as follows:
the reservoir sediment deposition process is described by using a moving grid method, and the moving rate of the grid nodes of the water-sediment interface is set as the reservoir sedimentDeposition rate
Figure QLYQS_57
。
15. The modeling method of reservoir methane bubble discharge according to any one of claims 1-4, 6-12, wherein a reservoir methane bubble discharge model taking into account a deposition process is built in COMSOL software; the classical partial differential equation module and the mobile mesh module are both derived from a COMSOL mathematical module.
16. A reservoir methane bubble discharge modeling system applied to the reservoir methane bubble discharge modeling method as claimed in any one of claims 1 to 15, which is characterized by comprising a modeling module, a classical partial differential equation module, a mobile grid module, a data input module and a data processing module;
the modeling module is used for constructing a reservoir methane bubble discharge model considering a deposition process, and the reservoir methane bubble discharge model comprises a heat transfer module, a methane generation-migration-discharge module and a sediment deposition module;
the classical partial differential equation module is used for describing a reservoir heat transfer process and a methane generation-migration-discharge process;
the mobile grid module is used for describing a sediment deposition process;
the data input module is used for importing a reservoir geometric model, defining reservoir sediment-water continuum heat transfer parameters, methane generation-migration-discharge parameters and deposition rate, and setting boundary conditions and initial conditions of a reservoir methane bubble discharge model considering a deposition process;
and the data processing module is used for meshing the reservoir geometric model and calculating the methane bubble discharge flux of the reservoir.
17. A reservoir methane bubble discharge modeling terminal comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, performs the steps of the method of any one of claims 1 to 15.
18. A computer readable storage medium storing a computer program, characterized in that the computer program when executed by a processor implements the steps of the method according to any one of claims 1 to 15.
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