Fractured horizontal well numerical well test analysis method based on shale gas complex flow mechanism

Abstract

The invention relates to the technical field of shale gas reservoir production and development, in particular to a fractured horizontal well numerical well test analysis method based on a shale gas complex flow mechanism. The method comprises the steps that a shale reservoir matrix system gas phase seepage model is established; establishing gas phase and water phase seepage models of the shale reservoir fracture system; according to the seepage models of the matrix system and the crack system, establishing a gas-water two-phase seepage model of the shale gas reservoir; according to the method, a gas-water two-phase seepage model of a shale gas well is solved by utilizing a Galerkin meshless method, a meshless node system is constructed according to a proximity average method, COO tissue matrix compression and CSR format storage are adopted, and a result is brought into a PARDISO solver for solving so as to ensure the accuracy of the numerical well test analysis method. Compared with a calculation method in the prior art, the numerical well test analysis method for the shale gas reservoir fractured horizontal well is higher in accuracy of numerical well test analysis for the shale gas reservoir fractured horizontal well by the adoption of the numerical well test analysis method for the shale gas reservoir fractured horizontal well.

Description

Technical Field

[0001] The invention relates to the technical field of shale gas reservoir production and development, and in particular to a numerical well testing analysis method for a fractured horizontal well based on the complex flow mechanism of shale gas. Background Art

[0002] Shale reservoirs have a significant ultra-dense, ultra-low porosity, and ultra-low permeability nanoporous structure, and its pore-permeability structure is extremely complex. Therefore, its development requires large-scale sand fracturing and other means to transform the reservoir, so that the induced fractures formed after fracturing can communicate with the natural fractures of the reservoir, thereby forming a criss-crossing fracture grid to obtain effective production capacity. In addition, due to the desorption of matrix adsorbed gas in shale reservoirs and the mass transfer and diffusion mechanism in nanoscale reservoir pores, the fluid flow process is extremely complex. The mathematical model of seepage established by these complex factors is therefore very complex and often cannot be solved using conventional methods. Therefore, conventional well test analysis methods cannot be directly applied to the numerical interpretation of shale gas reservoirs. Through numerical solution methods, complex shale gas reservoir well test mathematical models can be directly solved to obtain more accurate shale reservoir parameters.

[0003] In the current numerical well testing research, the finite difference method and the finite element method are the most widely used numerical calculation methods. However, these methods are based on grids in numerical calculations, and the final calculation accuracy will be affected by the grid division. Grids that do not meet the regulations need to be rebuilt, and the grids need to be constantly re-divided when solving the problem of crack expansion, which greatly increases the amount of calculations. The processing process is also very complicated, resulting in the lack of accuracy in the existing numerical well testing analysis of shale gas reservoir fractured horizontal wells. Summary of the invention

[0004] The purpose of the present invention is to provide a numerical well testing analysis method for fractured horizontal wells based on the complex flow mechanism of shale gas, so as to solve the problem that the numerical calculation method used in the prior art for numerical well testing analysis of fractured horizontal wells in shale gas reservoirs has too much calculation amount, resulting in poor analysis accuracy.

[0005] To achieve the above object, the present invention provides a numerical well testing analysis method for a fractured horizontal well based on the complex flow mechanism of shale gas, and the numerical well testing analysis method for a fractured horizontal well based on the complex flow mechanism of shale gas comprises the following steps:

[0006] S1: Establish a gas phase seepage model for shale reservoir matrix system considering complex flow mechanisms;

[0007] S2: Establish a gas and water seepage model for shale reservoir fracture systems taking into account complex flow mechanisms;

[0008] S3: Based on the seepage models of the matrix system and fracture system, a gas-water two-phase seepage model of shale gas reservoirs is established;

[0009] S4: Use the Galerkin meshless method to solve the gas-water two-phase seepage model of shale gas wells and give the corresponding numerical integration method;

[0010] S5: Determine the support domain of the meshless method according to the neighbor averaging method, thereby constructing a meshless node system;

[0011] S6: According to the characteristics of the constructed gridless node system, the COO organization matrix is ​​compressed and stored in CSR format, and finally brought into the PARDISO solver for solving to ensure the accuracy of the numerical well test analysis method;

[0012] S7: Numerical well test analysis method for forming fractured horizontal wells in shale gas reservoirs by dividing different flow characteristic sections;

[0013] S8: Based on this method, the measured data of shale gas wells are fitted to obtain the typical curve of well test analysis of fractured horizontal wells in shale gas reservoirs.

[0014] Wherein, in step S1, the complex flow mechanism includes desorption mechanism, quasi-steady-state diffusion, non-steady-state diffusion and seepage mechanism.

[0015] Wherein, in step S1, the process of establishing the gas phase seepage model of the shale reservoir matrix system is as follows:

[0016] S11: Establish a shale gas isothermal adsorption model and obtain:

[0017]

[0018] Where: V is the adsorbed gas volume, unit is cm 3 / g; V L is the Langmuir volume in cm 3 / g;p L is the Langmuir pressure, in MPa;

[0019] S12: Establish a gas phase seepage model for the shale reservoir matrix system, and establish the formula as follows:

[0020]

[0021] The gas flow from the matrix to the fracture system is expressed as:

[0022]

[0023] The shape factor is expressed as:

[0024]

[0025] The matrix rock compressibility coefficient is expressed as:

[0026]

[0027] The formation gas compressibility factor is:

[0028]

[0029] Where: L x ,L y ,L z is the length of the matrix rock in the x, y, and z directions, in meters; α is the dimension factor, dimensionless; K m is the effective permeability of the matrix, in μm 2 ;μ mg is the matrix gas viscosity, in mPa·s; B g is the gas volume coefficient, in m 3 / m 3 ;P m is the matrix pore pressure, in MPa; φ m is the matrix porosity; P fg V is the gas phase pressure of the fracture system, in MPa; d is the matrix desorption per unit volume; V L is the Langmuir volume constant, in cm 3 / g;P L is the Langmuir pressure constant, in MPa; P0 is the original pore pressure of the matrix, in MPa.

[0030] Wherein, in step S2, the process of establishing the gas phase and water phase seepage model of the shale reservoir fracture system is as follows:

[0031] S21: Considering the influence of stress sensitivity, an exponential stress sensitivity correction fracture system permeability is established:

[0032]

[0033] in:

[0034]

[0035] Where: K0 is the initial permeability of the fracture system, in μm 2 ; C φ is the rock compression coefficient, in MPa -1 ; σ is the effective stress of rock, in MPa; A is the cross-sectional area through which the fluid flows, in m 2 ; N is the number of cracks; l is the length of the crack, in m; ξ is the effective width of the crack, in m;

[0036] S22: Establish a gas and water seepage model for a shale reservoir fracture system that takes into account complex flow mechanisms, and obtain:

[0037] Gas phase:

[0038]

[0039] Aqueous phase:

[0040]

[0041] Where: α is the dimension factor, dimensionless; B g , B w is the volume coefficient of gas and water in the fracture system, in m 3 / m 3 ;P fg , P fw is the pressure of gas phase and water phase in the fracture system, in MPa; q sg ,q sw is the wellbore production of gas and water in the fracture system, in kg / s; φ f is the porosity of the fracture system; S fg , S fw is the saturation of gas and water phases in the fracture system.

[0042] Wherein, in step S3, the process of establishing the gas-water two-phase seepage model of the shale gas well is as follows:

[0043] S31: In a period of time after the well is switched on and off, since the surface production affected by the wellbore reservoir is not equal to the bottom hole production, the numerical well test production model of the fractured horizontal well is derived, including the pressure drop production model of the fractured horizontal well and the pressure recovery production model of the fractured horizontal well, and the result is:

[0044] Fracturing horizontal well pressure drop production model:

[0045]

[0046] Fracturing horizontal well pressure recovery production model:

[0047]

[0048] in:

[0049]

[0050] Where: F lm,i is the well index; is the formation gas flow rate of the ith node in the mth fracture; C is the wellbore storage coefficient; f m,i is the production fraction of the i-th node in the m-th fracture; P fm,i is the formation pressure;

[0051] S32: The gas phase continuity equation established in the matrix system and the gas and water continuity equations established in the fracture system are combined to obtain the basic seepage equation of shale gas considering the complex flow mechanism:

[0052]

[0053] S33: Before numerically simulating and solving the basic seepage equation of shale gas, the initial conditions and boundary conditions need to be defined. The solution conditions of the model include the boundary conditions and initial conditions of the fracture and matrix system. The initial conditions need to give the pressure and saturation parameter distribution at the initial time. Assuming that the initial pressure of the fracture and matrix system is the same, the initial pressure condition is:

[0054]

[0055] S34: Since the research object is a closed unit, the outer boundary of the mathematical model is closed, and the inner boundary is a constant bottom hole pressure production, so the inner boundary condition of the model is:

[0056] P fg (x,y,t)=P wf (t)

[0057] The outer boundary conditions are:

[0058]

[0059] Among them, in step S4, the corresponding equation is first discretized before solving by using the numerical solution method of implicit pressure and explicit saturation alternately:

[0060] EFGM numerical model of gas phase flow equation of matrix system:

[0061]

[0062] EFGM numerical model of gas phase flow equation in fracture system:

[0063]

[0064] EFGM numerical model of water phase flow equation in fracture system:

[0065]

[0066] Since the above EFGM numerical model has an integral function, it is necessary to give an integral method to solve the numerical model:

[0067]

[0068] Where: n cis the number of background units; G is the integrand; Ω k is the domain of the kth background unit.

[0069] Among them, in step S5, when constructing the gridless node system, the complex seepage characteristics near the fractured horizontal well are considered, and the size of the support domain of the gridless method is determined by the neighboring average method. The calculation formula is:

[0070]

[0071] Where: A ns is the sum of the areas of all triangular units in the neighborhood; n Ans is the number of field nodes; d c is the average spacing of field nodes;

[0072] The node encryption method based on integral grid isoparametric transformation is used to encrypt the fractures of the horizontal well, and the density of the transition zone between the encrypted zone and the non-encrypted zone is increased. The encryption formula is:

[0073]

[0074] Where: x i ,y i is the global coordinate of the i-th corner point of the triangle unit; L i,k is the i-th local coordinate of the k-th newly added node;

[0075] Based on the generation and encryption method of meshless nodes and background meshes studied above, the node arrangement and background mesh generation program is compiled and displayed through Matlab language to complete the construction of meshless node system.

[0076] Among them, in step S6, the specific steps for solving the problem of complex calculation of the node system constructed by the Galerkin meshless method are:

[0077] The stiffness matrix of the large-scale, symmetrical and sparse numerical well test linear equations for fractured horizontal wells in shale gas reservoirs is constructed, and the stiffness matrix is ​​assembled using the COO compression storage strategy.

[0078] Use CSR format to store and solve the system of linear equations;

[0079] Based on the node system matrix in CSR storage format, the converted numerical well testing global weak meshless method CSR format system equations are brought into the PARDISO solver for solution.

[0080] The invention discloses a numerical well test analysis method for fractured horizontal wells based on the complex flow mechanism of shale gas, establishes a gas phase seepage model of a shale reservoir matrix system considering complex flow mechanisms such as desorption mechanism, diffusion mechanism and seepage mechanism; establishes gas phase and water phase seepage models of a shale reservoir fracture system considering complex flow mechanisms; establishes a gas-water two-phase seepage model of a shale gas reservoir according to the seepage models of the matrix system and the fracture system; solves the gas-water two-phase seepage model of a shale gas well by using the Galerkin gridless method and gives a corresponding numerical integration method; determines the support domain of the gridless method according to the neighboring average method, designs a set of node arrangement and encryption methods considering the complex seepage characteristics of fractured horizontal wells, and generates gridless method nodes and background A gridless node system is constructed by forming a scene grid. According to the characteristics of the constructed gridless node system, the system is compressed by COO organization matrix and stored in CSR format. Finally, the system is brought into PARDISO solver for solving to ensure the accuracy of the numerical well test analysis method. Different flow characteristic sections are divided to form a numerical well test analysis method for fractured horizontal wells in shale gas reservoirs. Based on this method, the measured data of shale gas wells are fitted to obtain typical curves of well test analysis for fractured horizontal wells in shale gas reservoirs. A set of typical numerical well test analysis methods for fractured horizontal wells in shale gas reservoirs suitable for actual mines is formed. Compared with the calculation method in the prior art, the accuracy of numerical well test analysis for fractured horizontal wells in shale gas reservoirs using the above method is higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0082] Figure 1 It is a flow chart of the steps of the numerical well testing analysis method for fractured horizontal wells based on the complex flow mechanism of shale gas of the present invention.

[0083] Figure 2 It is the background grid of the gridless global weak method of the present invention.

[0084] Figure 3 This is the method for determining the support domain of the present invention.

[0085] Figure 4 It is a double logarithmic curve comparison diagram of the numerical solution of the meshless method simulator of the present invention and the Zerzar analytical solution.

[0086] Figure 5 This is the flow stage of the well test curve of the shale gas reservoir fractured horizontal well of the present invention.

[0087] Figure 6It is the influence of Langmuir volume and Langmuir pressure on the typical curve of numerical well testing in the parameter sensitivity analysis of the present invention. DETAILED DESCRIPTION

[0088] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0089] See also Figures 1 to 6 The present invention provides a numerical well testing analysis method for a fractured horizontal well based on the complex flow mechanism of shale gas. The numerical well testing analysis method for a fractured horizontal well based on the complex flow mechanism of shale gas comprises the following steps:

[0090] S1: Establish a gas phase seepage model for shale reservoir matrix system considering complex flow mechanisms;

[0091] S2: Establish a gas and water seepage model for shale reservoir fracture systems taking into account complex flow mechanisms;

[0092] S3: Based on the seepage models of the matrix system and fracture system, a gas-water two-phase seepage model of shale gas reservoirs is established;

[0093] S4: Use the Galerkin meshless method to solve the gas-water two-phase seepage model of shale gas wells and give the corresponding numerical integration method;

[0094] S5: Determine the support domain of the meshless method according to the neighbor averaging method, thereby constructing a meshless node system;

[0095] S6: According to the characteristics of the constructed gridless node system, the COO organization matrix is ​​compressed and stored in CSR format, and finally brought into the PARDISO solver for solving to ensure the accuracy of the numerical well test analysis method;

[0096] S7: Numerical well test analysis method for forming fractured horizontal wells in shale gas reservoirs by dividing different flow characteristic sections;

[0097] S8: Based on this method, the measured data of shale gas wells are fitted to obtain the typical curve of well test analysis of fractured horizontal wells in shale gas reservoirs.

[0098] In this embodiment, a gas phase seepage model of a shale reservoir matrix system is established considering complex flow mechanisms such as desorption mechanism, diffusion mechanism and seepage mechanism; a gas phase and water phase seepage model of a shale reservoir fracture system is established considering complex flow mechanisms; a gas-water two-phase seepage model of a shale gas reservoir is established based on the seepage models of the matrix system and the fracture system; the gas-water two-phase seepage model of a shale gas well is solved using the Galerkin meshless method and a corresponding numerical integration method is given; the meshless method support domain is determined based on the neighbor averaging method, and a set of node arrangement and encryption methods considering the complex seepage characteristics of fractured horizontal wells are designed, as well as meshless method nodes and background grids are generated, thereby constructing a meshless node point system; according to the characteristics of the constructed gridless node system, the COO organization matrix is ​​compressed and stored in CSR format, and finally brought into the PARDISO solver for solving to ensure the accuracy of the numerical well testing analysis method, and different flow characteristic sections are divided to form a numerical well testing analysis method for fractured horizontal wells in shale gas reservoirs. Based on this method, the measured data of shale gas wells are fitted to obtain typical curves of well testing analysis for fractured horizontal wells in shale gas reservoirs, forming a set of typical numerical well testing analysis methods for fractured horizontal wells in shale gas reservoirs suitable for actual mines. Compared with the calculation method in the prior art, the above method has higher accuracy in numerical well testing analysis of fractured horizontal wells in shale gas reservoirs.

[0099] Wherein, in step S1, the complex flow mechanism includes special mechanisms such as desorption mechanism, quasi-steady-state diffusion, non-steady-state diffusion and seepage mechanism.

[0100] Wherein, in step S1, the process of establishing the gas phase seepage model of the shale reservoir matrix system is as follows:

[0101] S11: Establish a shale gas isothermal adsorption model and obtain:

[0102]

[0103] Where: V is the adsorbed gas volume, unit is cm 3 / g; V L is the Langmuir volume in cm 3 / g;p L is the Langmuir pressure, in MPa;

[0104] S12: Establish a gas phase seepage model for the shale reservoir matrix system, and establish the formula as follows:

[0105]

[0106] The gas flow from the matrix to the fracture system is expressed as:

[0107]

[0108] The shape factor is expressed as:

[0109]

[0110] The matrix rock compressibility coefficient is expressed as:

[0111]

[0112] The formation gas compressibility factor is:

[0113]

[0114] Where: L x ,L y ,L z is the length of the matrix rock in the x, y, and z directions, in meters; α is the dimension factor, dimensionless; K m is the effective permeability of the matrix, in μm 2 ;μ mg is the matrix gas viscosity, in mPa·s; B g is the gas volume coefficient, in m 3 / m 3 ;P m is the matrix pore pressure, in MPa; φ m is the matrix porosity; P fg V is the gas phase pressure of the fracture system, in MPa; d is the matrix desorption per unit volume; V L is the Langmuir volume constant, in cm 3 / g;P L is the Langmuir pressure constant, in MPa; P0 is the original pore pressure of the matrix, in MPa.

[0115] Wherein, in step S2, the process of establishing the gas phase and water phase seepage model of the shale reservoir fracture system is as follows:

[0116] S21: Considering the influence of stress sensitivity, an exponential stress sensitivity correction fracture system permeability is established:

[0117]

[0118] in:

[0119]

[0120] Where: K0 is the initial permeability of the fracture system, in μm 2 ; C φ is the rock compression coefficient, in MPa -1; σ is the effective stress of rock, in MPa; A is the cross-sectional area through which the fluid flows, in m 2 ; N is the number of cracks; l is the length of the crack, in m; ξ is the effective width of the crack, in m;

[0121] S22: Establish a gas and water seepage model for a shale reservoir fracture system that takes into account complex flow mechanisms, and obtain:

[0122] Gas phase:

[0123]

[0124] Aqueous phase:

[0125]

[0126] Where: α is the dimension factor, dimensionless; B g , B w is the volume coefficient of gas and water in the fracture system, in m 3 / m 3 ;P fg , P fw is the pressure of gas phase and water phase in the fracture system, in MPa; q sg ,q sw is the wellbore production of gas and water in the fracture system, in kg / s; φ f is the porosity of the fracture system; S fg , S fw is the saturation of gas and water phases in the fracture system.

[0127] Wherein, in step S3, the process of establishing the gas-water two-phase seepage model of the shale gas well is as follows:

[0128] S31: In a period of time after the well is switched on and off, since the surface production affected by the wellbore reservoir is not equal to the bottom hole production, the numerical well test production model of the fractured horizontal well is derived, including the pressure drop production model of the fractured horizontal well and the pressure recovery production model of the fractured horizontal well, and the result is:

[0129] Fracturing horizontal well pressure drop production model:

[0130]

[0131] Fracturing horizontal well pressure recovery production model:

[0132]

[0133] in:

[0134]

[0135] Where: F lm,iis the well index; is the formation gas flow rate of the ith node in the mth fracture; C is the wellbore storage coefficient; f m,i is the production fraction of the i-th node in the m-th fracture; P fm,i is the formation pressure;

[0136] S32: The gas phase continuity equation established in the matrix system and the gas and water continuity equations established in the fracture system are combined to obtain the basic seepage equation of shale gas considering the complex flow mechanism:

[0137]

[0138] S33: Before numerically simulating and solving the basic seepage equation of shale gas, the initial conditions and boundary conditions need to be defined. The solution conditions of the model include the boundary conditions and initial conditions of the fracture and matrix system. The initial conditions need to give the pressure and saturation parameter distribution at the initial time. Assuming that the initial pressure of the fracture and matrix system is the same, the initial pressure condition is:

[0139]

[0140] S34: Since the research object is a closed unit, the outer boundary of the mathematical model is closed, and the inner boundary is a constant bottom hole pressure production, so the inner boundary condition of the model is:

[0141] P fg (x,y,t)=P wf (t)

[0142] The outer boundary conditions are:

[0143]

[0144] Among them, in step S4, the corresponding equation is first discretized before solving by using the numerical solution method of implicit pressure and explicit saturation alternately:

[0145] EFGM numerical model of gas phase flow equation of matrix system:

[0146]

[0147] EFGM numerical model of gas phase flow equation in fracture system:

[0148]

[0149] EFGM numerical model of water phase flow equation in fracture system:

[0150]

[0151] Since the above EFGM numerical model has an integral function, it is necessary to give an integral method to solve the numerical model:

[0152]

[0153] Where: n c is the number of background units; G is the integrand; Ω k is the domain of the kth background unit.

[0154] Among them, in step S5, when constructing the gridless node system, the complex seepage characteristics near the fractured horizontal well are considered, and the size of the support domain of the gridless method is determined by the neighboring average method. The calculation formula is:

[0155]

[0156] Where: A ns is the sum of the areas of all triangular elements in the neighborhood; is the number of field nodes; d c is the average spacing of field nodes;

[0157] The node encryption method based on integral grid isoparametric transformation is used to encrypt the fractures of the horizontal well, and the density of the transition zone between the encrypted zone and the non-encrypted zone is increased. The encryption formula is:

[0158]

[0159] Where: x i ,y i is the global coordinate of the i-th corner point of the triangle unit; L i,k is the i-th local coordinate of the k-th newly added node;

[0160] Based on the generation and encryption method of meshless nodes and background meshes studied above, the node arrangement and background mesh generation program is compiled and displayed through Matlab language to complete the construction of meshless node system.

[0161] Among them, in step S6, the specific steps for solving the problem of complex calculation of the node system constructed by the Galerkin meshless method are:

[0162] The stiffness matrix of the large-scale, symmetrical and sparse numerical well test linear equations for shale gas reservoir fracture horizontal wells is constructed. When the COO format assembles the matrix of the global weak meshless method, only the upper triangular matrix needs to be considered. Therefore, the COO compression storage strategy is used to assemble the stiffness matrix.

[0163] After that, the equations are stored. The equations stored in CSR format require 30% less memory than those stored in COO format during the solution process. Therefore, CSR format is used to store and solve the linear equations of the system.

[0164] Based on the node system matrix in CSR storage format, the converted numerical well testing global weak meshless method CSR format system equations are brought into the PARDISO solver for solution.

[0165] In this embodiment, according to a typical shale gas well fracturing parameters, reservoir parameters, node parameters and coring data, the basic simulation parameters shown in the following table are set:

[0166]

[0167]

[0168] First, it is necessary to verify the correctness of the numerical well test curve calculated by the global weak gridless method, that is, to obtain the numerical well test curve of the fractured horizontal well in the shale gas reservoir by calculating the reservoir parameters and fracturing parameter values, and divide the corresponding flow stages. Combined with the simplified model and the basic parameters of the simulation calculation, the numerical solution calculated by the gridless method simulator is compared with the Zerzar analytical solution for verification.

[0169] Based on the numerical solution of the gridless simulator obtained after verification, the measured pressure data of shale gas wells were analyzed and fitted. Combined with the discrete mathematical model of fractured horizontal well EFGM derived by the Galerkin gridless method and the well test analysis theory of fractured horizontal wells in shale gas reservoirs, the typical curve of fractured horizontal well test analysis in shale gas reservoirs was obtained by simulation calculation using the gridless simulator. Through comprehensive analysis of the curves, the skin coefficient is 0.878, and there is slight contamination at the bottom of the well. In the shale reservoir, the permeability of the fracture system is 0.00175mD, and the permeability of the matrix system is 2.75×10 -6 mD, indicating that the shale reservoir is a low-permeability reservoir; the number of fracturing stages is 32, and the half-length of each fracturing stage is 37.7 meters, which can effectively connect the fracture system near the wellbore area; the Langmuir volume is 0.013m 3 / kg, the Langmuir pressure is 7MPa, which reflects the influence of matrix adsorption and desorption in shale gas reservoirs; the extrapolated formation pressure is 56.72MPa, which reflects the current formation energy.

[0170] What is disclosed above is only a preferred embodiment of the present invention, and it certainly cannot be used to limit the scope of rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiment and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A numerical well test analysis method for fractured horizontal wells based on the complex flow mechanism of shale gas, characterized in that: The steps include: S1: Establish a gas phase seepage model for shale reservoir matrix system considering complex flow mechanisms; S2: Establish a gas and water seepage model for shale reservoir fracture systems that takes into account complex flow mechanisms; S3: Based on the seepage models of the matrix system and fracture system, a gas-water two-phase seepage model of shale gas reservoirs is established; S4: Use the Galerkin meshless method to solve the gas-water two-phase seepage model of shale gas wells and give the corresponding numerical integration method; S5: Determine the support domain of the meshless method according to the neighbor averaging method, thereby constructing a meshless node system; S6: According to the characteristics of the constructed gridless node system, the COO organization matrix is ​​compressed and stored in CSR format, and finally brought into the PARDISO solver for solving to ensure the accuracy of the numerical well test analysis method; S7: Numerical well test analysis method for forming fractured horizontal wells in shale gas reservoirs by dividing different flow characteristic sections; S8: Based on this method, the measured data of shale gas wells are fitted to obtain the typical curve of well test analysis of fractured horizontal wells in shale gas reservoirs.

2. The method for numerical well testing analysis of fractured horizontal wells based on complex flow mechanism of shale gas according to claim 1, characterized in that: In step S1, the complex flow mechanism includes desorption mechanism, quasi-steady-state diffusion, unsteady-state diffusion and percolation mechanism.

3. The method for numerical well testing analysis of fractured horizontal wells based on complex flow mechanism of shale gas according to claim 2, characterized in that: In step S1, the process of establishing the gas phase seepage model of the shale reservoir matrix system is as follows: S11: Establish a shale gas isothermal adsorption model and obtain: Where: V is the adsorbed gas volume, unit is cm 3 / g; V L is the Langmuir volume in cm 3 / g;p L is the Langmuir pressure, in MPa; S12: Establish a gas phase seepage model for the shale reservoir matrix system, and establish the formula as follows: The gas flow from the matrix to the fracture system is expressed as: The shape factor is expressed as: The matrix rock compressibility coefficient is expressed as: The formation gas compressibility factor is: Where: L x ,L y ,L z is the length of the matrix rock in the x, y, and z directions, in meters; α is the dimension factor, dimensionless; K m is the effective permeability of the matrix, in μm 2 ; μ mg is the matrix gas viscosity, in mPa·s; B g is the gas volume coefficient, in m 3 / m 3 ; P m is the matrix pore pressure, in MPa; φ m is the matrix porosity; P fg V is the gas phase pressure of the fracture system, in MPa; d is the matrix desorption per unit volume; V L is the Langmuir volume constant, in cm 3 / g;P L is the Langmuir pressure constant, in MPa; P0 is the original pore pressure of the matrix, in MPa.

4. The method for numerical well testing analysis of fractured horizontal wells based on complex flow mechanism of shale gas according to claim 3, characterized in that: In step S2, the process of establishing the gas phase and water phase seepage model of the shale reservoir fracture system is as follows: S21: Considering the influence of stress sensitivity, an exponential stress sensitivity correction fracture system permeability is established: in: Where: K0 is the initial permeability of the fracture system, in μm 2 ; C φ is the rock compression coefficient, in MPa -1 ; σ is the effective stress of rock, in MPa; A is the cross-sectional area through which the fluid flows, in m 2 ; N is the number of cracks; l is the length of the crack, in m; ξ is the effective width of the crack, in m; S22: Establish a gas and water seepage model for a shale reservoir fracture system that takes into account complex flow mechanisms, and obtain: Gas phase: Aqueous phase: Where: α is the dimension factor, dimensionless; B g , B w is the volume coefficient of gas and water in the fracture system, in m 3 / m 3 ;P fg , P fw is the pressure of gas phase and water phase in the fracture system, in MPa; q sg ,q sw is the wellbore production of gas and water in the fracture system, in kg / s; φ f is the porosity of the fracture system; S fg , S fw is the saturation of gas and water phases in the fracture system.

5. The method for numerical well testing analysis of fractured horizontal wells based on complex flow mechanism of shale gas according to claim 4, characterized in that: In step S3, the process of establishing the gas-water two-phase seepage model of the shale gas well is as follows: S31: In a period of time after the well is switched on and off, since the surface production affected by the wellbore reservoir is not equal to the bottom hole production, the numerical well test production model of the fractured horizontal well is derived, including the pressure drop production model of the fractured horizontal well and the pressure recovery production model of the fractured horizontal well, and the result is: Fracturing horizontal well pressure drop production model: Fracturing horizontal well pressure recovery production model: in: Where: F lm,i is the well index; is the formation gas flow rate of the ith node in the mth fracture; C is the wellbore storage coefficient; f m,i is the production fraction of the i-th node in the m-th fracture; P fm,i is the formation pressure; S32: The gas phase continuity equation established in the matrix system and the gas and water continuity equations established in the fracture system are combined to obtain the basic seepage equation of shale gas considering the complex flow mechanism: S33: Before numerically simulating and solving the basic seepage equation of shale gas, the initial conditions and boundary conditions need to be defined. The solution conditions of the model include the boundary conditions and initial conditions of the fracture and matrix system. The initial conditions need to give the pressure and saturation parameter distribution at the initial time. Assuming that the initial pressure of the fracture and matrix system is the same, the initial pressure condition is: S34: Since the research object is a closed unit, the outer boundary of the mathematical model is closed, and the inner boundary is a constant bottom hole pressure production, so the inner boundary condition of the model is: P fg (x,y,t)=P wf (t) The outer boundary conditions are:

6. The method for numerical well testing analysis of fractured horizontal wells based on complex shale gas flow mechanism according to claim 5, characterized in that: In step S4, the corresponding equation is discretized before solving by using the numerical solution method of alternating implicit pressure and explicit saturation: EFGM numerical model of gas phase flow equation of matrix system: EFGM numerical model of gas phase flow equation in fracture system: EFGM numerical model of water phase flow equation in fracture system: Since the above EFGM numerical model has an integral function, it is necessary to give an integral method to solve the numerical model: Where: n c is the number of background units; G is the integrand; Ω k is the domain of the kth background unit.

7. The method for numerical well testing analysis of fractured horizontal wells based on complex flow mechanism of shale gas according to claim 6, characterized in that: In step S5, when constructing the gridless node system, the complex seepage characteristics near the fractured horizontal well are considered, and the size of the support domain of the gridless method is determined by the neighboring average method. The calculation formula is: Where: A ns is the sum of the areas of all triangular elements in the neighborhood; is the number of field nodes; d c is the average spacing of field nodes; The node encryption method based on integral grid isoparametric transformation is used to encrypt the fractures of the horizontal well, and the density of the transition zone between the encrypted zone and the non-encrypted zone is increased. The encryption formula is: Where: x i ,y i is the global coordinate of the i-th corner point of the triangle unit; L i,k is the i-th local coordinate of the k-th newly added node; Based on the generation and encryption method of meshless nodes and background meshes studied above, the node arrangement and background mesh generation program is compiled and displayed through Matlab language to complete the construction of meshless node system.

8. The method for numerical well testing analysis of fractured horizontal wells based on complex shale gas flow mechanism according to claim 7, characterized in that: In step S6, the specific steps to solve the problem of complex calculation of the node system constructed by the Galerkin meshless method are: The stiffness matrix of the large-scale, symmetrical and sparse numerical well test linear equations for fractured horizontal wells in shale gas reservoirs is constructed, and the stiffness matrix is ​​assembled using the COO compression storage strategy. Use CSR format to store and solve the system of linear equations; Based on the node system matrix in CSR storage format, the converted numerical well testing global weak meshless method CSR format system equations are brought into the PARDISO solver for solution.

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