A method and system for calculating the effective stress around a three-hole, three-permeability well considering the sealing layer.

Abstract

This invention relates to a method and system for calculating the effective wellbore stress considering a three-pore, three-permeability sealing layer. The method includes: collecting reservoir core samples and obtaining the mechanical characteristics of the rock matrix through triaxial compression; collecting reservoir core samples and in-situ drilling fluid; firstly, obtaining the physicochemical parameters of the interaction between rock pores and drilling fluid through pressure transmission experiments; then, testing the physicochemical parameters of the interaction between rock fracture fluid and drilling fluid; finally, testing the physicochemical parameters of the effective sealing layer formed by the drilling fluid and rock; establishing a three-pore, three-permeability model considering the control equations of the rock matrix field, the rock fracture field, and the sealing layer field; and calculating the effective wellbore stress considering the three-pore, three-permeability sealing layer. This invention can effectively analyze the influence of fluid seepage and solute diffusion patterns within the drilling fluid sealing layer on the wellbore stress distribution, and can further combine strength criteria to calculate formation collapse pressure and fracture pressure, guiding drilling fluid density design.

Description

Technical Field

[0001] This invention relates to the field of oil and gas drilling engineering technology, and in particular to a method and system for calculating the effective stress around a well considering a three-hole, three-permeability sealing layer. Background Technology

[0002] As shale oil and gas exploration and development continues to advance into deeper and ultra-deep formations, the geological structures and lithologies encountered are complex, with well-developed microfractures, nanoscale fractures, and bedding. During drilling, drilling fluid and its filtrate can easily penetrate formation fractures and weak structural layers, altering the pore pressure of the shale, reducing its strength, and increasing formation collapse pressure, leading to wellbore instability and severely impacting the development process. For water-sensitive shale formations with well-developed fractures, ultra-low porosity and permeability, hardness and brittleness (fracture), and poor cementation, simply inhibiting hydration is insufficient to completely guarantee shale wellbore stability. Effective plugging is one of the key technologies for solving shale wellbore instability. Solid particles in the drilling fluid enter the rock pores to form bridging plugs, polymeric alcohols plug pores through the cloud point effect, and silicates and aluminates form precipitates to plug mudstone pore throats, forming a plugging layer that effectively slows down pressure transmission, reduces the increase in mudstone pore pressure, and lowers the risk of wellbore instability.

[0003] Wellbore stability research is currently a key focus in the oil and gas industry. Current research on plugging layers largely concentrates on the chemical aspects of plugging agent development and mechanism explanation. Common plugging agents include polymers, polyols, bituminous compounds, and nano-plugging agents. The plugging mechanisms include hydrogen bonding, surface adsorption blocking pores and throats, turbidity effects, flocculent precipitation at the filtrate front blocking pores or microfractures, high-temperature softening, and deformable physical plugging, ultimately hindering the entry of free water from the drilling fluid into the shale wellbore and maintaining wellbore stability. However, there is little research on the impact of plugging layers on the material transport patterns of fractured matrix-containing dual-pore, dual-permeability formations. Therefore, based on the dual-pore, dual-permeability theory, this paper introduces the influence of plugging layers on formation material transport patterns, establishes a three-pore, three-permeability model considering the plugging layer, and calculates the effective stress around the well. Clarifying the material transport patterns and effective stress distribution around the well in a three-pore, three-permeability model considering the plugging layer is beneficial for guiding the development and mechanism explanation of plugging agents, effectively reducing wellbore instability accidents during drilling. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention provides a method and system for calculating the effective stress around a three-hole, three-permeability well considering the sealing layer;

[0005] The technical solution of this invention is as follows:

[0006] A method for calculating the effective stress around a three-hole, three-permeable well considering the sealing layer includes:

[0007] Reservoir cores were collected, and the mechanical characteristics of the rock matrix were obtained through triaxial compression, including: core porosity, permeability, water content, compressive strength, Young's modulus, Poisson's ratio, internal friction angle, cohesion, and pore fluid activity.

[0008] Reservoir core samples and in-situ drilling fluid were collected. First, the physicochemical parameters of the interaction between rock pores and drilling fluid were obtained through pressure transmission experiments. Next, the physicochemical parameters of the interaction between rock fracture fluid and drilling fluid were tested. Finally, the physicochemical parameters of the effective sealing layer formed by the drilling fluid and rock were tested. The physicochemical parameters of the effective sealing layer formed by the drilling fluid and rock include: film efficiency, hydraulic conductivity, solute diffusion coefficient, thermal conductivity, pore fluid activity, and in-situ drilling fluid activity.

[0009] A three-pore, three-permeability model was established, considering the control equations of the rock matrix field, the rock fracture field, and the sealing layer field. The deformation equation of the shale skeleton and the physical property parameter equations under the action of the stress field and the deformation field of the microfracture porous medium were also established. Boundary conditions were set according to the actual drilling conditions, and the stress field, pore pressure field, thermal field, and chemical field were calculated using the finite element method.

[0010] Based on Biot's effective stress principle, and combined with the stress and pore pressure distribution calculated by the three-hole, three-permeability model considering the sealing layer, the effective stress around the well considering the three-hole, three-permeability model considering the sealing layer is calculated.

[0011] According to a preferred embodiment of the present invention, the Biot effective stress principle is as follows:

[0012]

[0013] In the formula, For the effective stress tensor, p I p is the pore fluid pressure of the matrix. II For the fracture fluid pressure; α I α is the effective stress coefficient of the matrix; II δ is the effective stress coefficient of the crack. ij For Kronecker symbols.

[0014] According to a preferred embodiment of the present invention, the rock matrix field control equations include the rock matrix fluid mass balance equation, the rock matrix solute mass balance equation, the rock matrix state equation, the rock matrix temperature control equation, the rock matrix chemical field control equation, and the rock matrix pore pressure field control equation.

[0015] The mass balance equation for fluid in rock matrix is ​​shown below:

[0016]

[0017] Where: φ I ρ represents the porosity of the rock matrix. fLet be the fluid density, and t be the time. The solvent flow velocity in the rock matrix;

[0018] The mass balance equation for solute in the rock matrix is ​​shown below:

[0019]

[0020] Where: φ I ρ represents the porosity of the rock matrix. f Let ω be the fluid density, t be time, and ω be the mass fraction of the salt. This represents the mass flow rate of solute in the rock matrix.

[0021] The equation of state for the rock matrix is ​​shown below:

[0022]

[0023] In the formula: p I ρ is the pore pressure of the rock matrix, β is the compressibility coefficient of the fluid, p0 is the initial pressure, ρ0 is the fluid density at pressure p0, and ρ0 is the rock density.

[0024] The temperature control equation for the rock matrix is ​​shown below:

[0025]

[0026] Where: K eff Effective thermal diffusivity;

[0027] The governing equations for the chemical field of the rock matrix are shown below:

[0028]

[0029] In the formula: D0 is the diffusion velocity, I m For membrane efficiency, c I Solute concentration in the rock matrix.

[0030] The governing equations for the pore pressure field in the rock matrix are shown below:

[0031]

[0032] In the formula: k I Let μ be the rock matrix permeability, μ be the fluid viscosity, v be the dissociation constant, R be the gas constant, and K be the K value. T Thermal conductivity coefficient.

[0033] According to a preferred embodiment of the present invention, the rock fracture field control equations include the rock fracture fluid mass balance equation, the rock fracture solute mass balance equation, the rock fracture state equation, the rock fracture temperature control equation, the rock fracture chemical field control equation, and the rock fracture pore pressure field control equation.

[0034] The mass balance equation for fluid in rock fractures is shown below:

[0035]

[0036] Where: φ II ρ represents the porosity of rock fractures. f Let be the fluid density, and t be the time. The velocity of the solvent flow in the rock fracture is denoted as .

[0037] The mass balance equation for solute in rock fractures is shown below:

[0038]

[0039] Where: φ II ρ represents the porosity of rock fractures. f Let ω be the fluid density, t be time, and ω be the mass fraction of the salt. This represents the mass flow rate of solute in rock fractures.

[0040] The equation of state for rock fractures is shown below:

[0041]

[0042] In the formula: p II ρ is the pore pressure in the rock fracture, β is the compressibility coefficient of the fluid, p0 is the initial pressure, ρ0 is the fluid density at pressure p0, and ρ0 is the rock density.

[0043] The rock fracture temperature control equation is shown below:

[0044]

[0045] In the formula: K eff Effective thermal diffusivity;

[0046] The governing equations for the chemical field of rock fractures are shown below:

[0047]

[0048] In the formula: D0 is the diffusion velocity, I m For membrane efficiency, c II Solute concentration in rock fissures;

[0049] The governing equations for the pore pressure field in rock fractures are as follows:

[0050]

[0051] In the formula: k II Let μ be the rock fracture permeability, μ be the fluid viscosity, v be the dissociation constant, R be the gas constant, and K be the K value. T Thermal conductivity coefficient.

[0052] According to a preferred embodiment of the present invention, the field control equations of the sealing layer include the fluid mass balance equation of the sealing layer, the solute mass balance equation of the sealing layer, the chemical field control equation of the sealing layer, and the pore pressure field control equation of the sealing layer.

[0053] The fluid mass balance equation for the sealing layer is shown below:

[0054]

[0055] Where: φ III For the porosity of the sealing layer, J v III The solvent flow rate of the sealing layer;

[0056] The solute mass balance equation for the sealing layer is shown below:

[0057]

[0058] Where: φ III For the porosity of the sealing layer, This represents the mass flow rate of the solute in the sealing layer.

[0059] The governing equations for the chemical field of the sealing layer are shown below:

[0060]

[0061] In the formula: I represents the diffusion velocity of the sealing layer. m For membrane efficiency, c III Solute concentration in rock fissures;

[0062] The governing equations for the pore pressure field of the sealing layer are as follows:

[0063]

[0064] In the formula: k II Let μ be the permeability of the sealing layer, μ be the fluid viscosity, v be the dissociation constant, R be the gas constant, and K be the K value. T Thermal conductivity;

[0065] The three-pore, three-permeability model is a set of equations consisting of the control equations for the rock matrix field, the rock fracture field, and the sealing layer field.

[0066] According to a preferred embodiment of the present invention, the deformation equation of the shale skeleton is established, including: the continuity equation of the rock skeleton, the equilibrium equation of the rock skeleton, the effective stress equation, the geometric equation, and the constitutive equation;

[0067] The continuity equation for the rock skeleton is shown below:

[0068]

[0069] Where: ε v For volumetric strain;

[0070] The equilibrium equations for the rock skeleton are shown below:

[0071] σ ij,j T +f i =0 (19)

[0072] Where: σ ij,j T For each stress component of the formation, f i For physical loads;

[0073] The geometric equations are as follows:

[0074]

[0075] In the formula: u i,j u j,i For displacement components;

[0076] The constitutive equation is shown below:

[0077]

[0078] In the formula: G is the rock shear modulus, and λ is the Lame-Changshu rock mass.

[0079] According to a preferred embodiment of the present invention, physical property parameter equations under the action of stress field and deformation field of microcracked porous medium are established, including the established porosity equation, permeability equation, and pore compressibility coefficient equation.

[0080] The porosity equation is as follows:

[0081]

[0082] The permeability equation is as follows:

[0083]

[0084] The equation for the pore compressibility coefficient is shown below:

[0085]

[0086] In the formula: φ is the porosity after deformation, φ o Porosity under original conditions, k is the permeability after deformation, k0 is the permeability under original conditions, C φ Δε is the pore compressibility coefficient, Δε is the matrix shrinkage deformation rate, and ΔP is the formation pressure change.

[0087] According to a preferred embodiment of the present invention, in conjunction with the setting of boundary conditions, specifically including setting the initial and boundary conditions of shale skeleton deformation, the initial and boundary conditions of multi-component seepage in the three-pore three-permeability model, and the initial reservoir temperature conditions, the formation pore pressure field and stress field are calculated using the finite element method, and the wellbore stress is calculated by simultaneously applying the Biot effective stress principle. The Biot effective stress principle is as follows:

[0088]

[0089] In the formula, To obtain the effective stress tensor, we need to consider the effective stress around the three-hole, three-permeability well in the sealing layer. I p is the pore fluid pressure of the matrix. II For the fracture fluid pressure; α I α is the effective stress coefficient of the matrix; II δ is the effective stress coefficient of the crack. ij Kronecker symbol.

[0090] A computer device includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the steps of a method for calculating the effective stress around a three-hole, three-permeable well considering a sealing layer.

[0091] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of a method for calculating the effective stress around a three-hole, three-permeable well considering a sealing layer.

[0092] A system for calculating the effective stress around a three-hole, three-permeability well considering the sealing layer, comprising:

[0093] The rock matrix mechanical characteristic parameter acquisition module is configured to: collect reservoir cores and obtain rock matrix mechanical characteristic parameters through triaxial compression, including: core porosity, permeability, water content, compressive strength, Young's modulus, Poisson's ratio, internal friction angle, cohesion, and pore fluid activity;

[0094] The reservoir core and in-situ drilling fluid acquisition module is configured to: first, obtain the physicochemical parameters of the interaction between rock pores and drilling fluid through pressure transmission experiments; then, test the physicochemical parameters of the interaction between rock fracture fluid and drilling fluid; and finally, test the physicochemical parameters of the effective sealing layer formed by the drilling fluid and rock. The physicochemical parameters of the effective sealing layer formed by the drilling fluid and rock include: film efficiency, hydraulic conductivity, solute diffusion coefficient, thermal conductivity, pore fluid activity, and in-situ drilling fluid activity.

[0095] The module for establishing the three-pore, three-permeability model is configured to: establish a three-pore, three-permeability model considering the control equations of the rock matrix field, the rock fracture field, and the sealing layer field; establish the deformation equation of the shale skeleton and the physical property parameter equations under the action of the stress field and the deformation field of the microfracture porous medium; set boundary conditions according to the actual drilling conditions; and use the finite element method to calculate the stress field, pore pressure field, thermal field, and chemical field.

[0096] The module for calculating the effective stress around a well with a three-hole, three-seepage well considering the plugging layer is configured to: calculate the effective stress around a well with a three-hole, three-seepage well considering the plugging layer based on the Biot effective stress principle and the stress and pore pressure distribution calculated by the three-hole, three-seepage model considering the plugging layer.

[0097] The beneficial effects of this invention are as follows:

[0098] 1. Establishing a model that considers the material transport law of the three pores and three seepages in the plugging layer and the effective stress around the well can effectively analyze the influence of fluid seepage and solute diffusion law in the drilling fluid plugging layer on the stress distribution law around the well. It can further calculate the formation collapse pressure and fracture pressure in conjunction with the strength criterion, and guide the design of drilling fluid density.

[0099] 2. It can effectively evaluate the sealing effect of drilling fluid on formation. Using key parameters such as fluid seepage, solute diffusion, porosity and permeability as evaluation indicators, it can effectively guide the development of drilling fluid plugging agents and inhibitors and the optimization of drilling fluid formulation. Attached Figure Description

[0100] Figure 1 This is a cloud map showing the pressure distribution in a three-pore, three-permeability pore.

[0101] Figure 2 This is a cloud map showing the pressure distribution in a dual-pore, dual-permeability pore.

[0102] Figure 3 This is a cloud map showing the solute distribution in a three-pore, three-permeability configuration.

[0103] Figure 4 This is a cloud map showing the solute distribution in a dual-pore, dual-permeation configuration. Detailed Implementation

[0104] The present invention will be further defined below with reference to the accompanying drawings and embodiments, but is not limited thereto.

[0105] Example 1

[0106] A method for calculating the effective stress around a three-hole, three-permeable well considering the sealing layer includes:

[0107] Reservoir cores were collected, and the mechanical characteristics of the rock matrix were obtained through triaxial compression, including: core porosity, permeability, water content, compressive strength, Young's modulus, Poisson's ratio, internal friction angle, cohesion, and pore fluid activity.

[0108] In addition to the parameters mentioned above, other parameters can be tested, such as the strength of the weak surface of the rock and the rock grain size distribution. Parameters such as core porosity, permeability, water content, compressive strength, Young's modulus, Poisson's ratio, internal friction angle, cohesion, and pore fluid activity are readily available testing instruments. For example, porosity can be measured using a porosity testing instrument (PoroPDP-200 overburden porosity and permeability measuring instrument); permeability can be measured using a permeability testing instrument (PoroPDP-200 overburden porosity and permeability measuring instrument); and water content can be measured using the drying and weighing method (first weigh the core rock mass as m1, then dry the core and measure its mass as m). 0 The water content is (m1-m0) / m0*100%); compressive strength, Young's modulus, Poisson's ratio, internal friction angle, and cohesion are directly measured using rock mechanics measuring instruments (RTR-2000 high temperature and high pressure rock comprehensive testing system); pore fluid activity is measured using activity testing instruments (HD-6 type water activity measuring instrument).

[0109] Reservoir core samples and in-situ drilling fluid were collected. First, the physicochemical parameters of the interaction between rock pores and drilling fluid were obtained through pressure transmission experiments. Next, the physicochemical parameters of the interaction between rock fracture fluid and drilling fluid were tested. Finally, the physicochemical parameters of the effective sealing layer formed by the drilling fluid and rock were tested. The physicochemical parameters of the effective sealing layer formed by the drilling fluid and rock include: film efficiency, hydraulic conductivity, solute diffusion coefficient, thermal conductivity, pore fluid activity, and in-situ drilling fluid activity.

[0110] Membrane efficiency, hydraulic conductivity, solute diffusion coefficient, and thermal conductivity are parameters that can be obtained by testing with a pressure transmission experimental instrument (SHM-3 type high temperature and high pressure wellbore stability simulation experimental device); pore fluid activity and on-site drilling fluid activity can be obtained by testing with an activity tester (HD-6 type water activity meter).

[0111] A three-pore, three-permeability model was established, considering the control equations of the rock matrix field, the rock fracture field, and the sealing layer field. The deformation equation of the shale skeleton and the physical property parameter equations under the action of the stress field and the deformation field of the microfracture porous medium were also established. Boundary conditions were set according to the actual drilling conditions, and the stress field, pore pressure field, thermal field, and chemical field were calculated using the finite element method.

[0112] Based on Biot's effective stress principle, and combined with the stress and pore pressure distribution calculated by the three-hole, three-permeability model considering the sealing layer, the effective stress around the well considering the three-hole, three-permeability model considering the sealing layer is calculated.

[0113] Example 2

[0114] The difference between the method for calculating the effective stress around a three-hole, three-permeability well considering the sealing layer described in Example 1 and the method described in Example 1 is as follows:

[0115] The effective stress principle of Biot is:

[0116]

[0117] In the formula, For the effective stress tensor, p I p is the pore fluid pressure of the matrix. II For the fracture fluid pressure; α I α is the effective stress coefficient of the matrix; II δ is the effective stress coefficient of the crack. ij For Kronecker symbols.

[0118] The governing equations of the rock matrix field include the rock matrix fluid mass balance equation, the rock matrix solute mass balance equation, the rock matrix state equation, the rock matrix temperature control equation, the rock matrix chemical field control equation, and the rock matrix pore pressure field control equation.

[0119] The mass balance equation for fluid in rock matrix is ​​shown below:

[0120]

[0121] Where: φ I ρ represents the porosity of the rock matrix. f Let be the fluid density, and t be the time. The solvent flow velocity in the rock matrix;

[0122] The mass balance equation for solute in the rock matrix is ​​shown below:

[0123]

[0124] Where: φ I ρ represents the porosity of the rock matrix. f Let ω be the fluid density, t be time, and ω be the mass fraction of the salt. This represents the mass flow rate of solute in the rock matrix.

[0125] The equation of state for the rock matrix is ​​shown below:

[0126] Assuming that the density of the solute fluid in the rock matrix is ​​a function of pressure and depends only on pressure, neglecting the effects of temperature and mass fraction on the liquid density, the equation of state is given by the following:

[0127]

[0128] In the formula: p I ρ is the pore pressure of the rock matrix, β is the compressibility coefficient of the fluid, p0 is the initial pressure, ρ0 is the fluid density at pressure p0, and ρ0 is the rock density.

[0129] The temperature control equation for the rock matrix is ​​shown below:

[0130] Since shale has very low permeability, fluid convective heat transfer can be neglected, and its temperature control equation can be expressed as:

[0131]

[0132] In the formula: K eff Effective thermal diffusivity;

[0133] The governing equations for the chemical field of the rock matrix are shown below:

[0134] During drilling, a chemical potential difference exists between the drilling fluid and the shale pore fluid, generating chemical potential energy that drives the fluid to enter and exit the formation. The governing equations for this chemical field are as follows:

[0135]

[0136] In the formula: D0 is the diffusion velocity, I m For membrane efficiency, c I Solute concentration in the rock matrix.

[0137] The governing equations for the pore pressure field in the rock matrix are shown below:

[0138]

[0139] In the formula: k I Let μ be the rock matrix permeability, μ be the fluid viscosity, v be the dissociation constant, R be the gas constant, and K be the K value. T Thermal conductivity coefficient.

[0140] The governing equations of rock fracture fields include the rock fracture fluid mass balance equation, the rock fracture solute mass balance equation, the rock fracture state equation, the rock fracture temperature control equation, the rock fracture chemical field control equation, and the rock fracture pore pressure field control equation.

[0141] The mass balance equation for fluid in rock fractures is shown below:

[0142]

[0143] Where: φ II ρ represents the porosity of rock fractures. f Let be the fluid density, and t be the time. The velocity of the solvent flow in the rock fracture is denoted as .

[0144] The mass balance equation for solute in rock fractures is shown below:

[0145]

[0146] Where: φ IIρ represents the porosity of rock fractures. f Let ω be the fluid density, t be time, and ω be the mass fraction of the salt. This represents the mass flow rate of solute in rock fractures.

[0147] The equation of state for rock fractures is shown below:

[0148] Assuming the density of the solute fluid in the rock fracture is a function of pressure and depends only on pressure, neglecting the effects of temperature and mass fraction on the liquid density, the equation of state is given by the following:

[0149]

[0150] In the formula: p II ρ is the pore pressure in the rock fracture, β is the compressibility coefficient of the fluid, p0 is the initial pressure, ρ0 is the fluid density at pressure p0, and ρ0 is the rock density.

[0151] The rock fracture temperature control equation is shown below:

[0152] Since shale has very low permeability, fluid convective heat transfer can be neglected, and its temperature control equation can be expressed as:

[0153]

[0154] Where: K eff Effective thermal diffusivity;

[0155] The governing equations for the chemical field of rock fractures are shown below:

[0156] During drilling, a chemical potential difference exists between the drilling fluid and the shale pore fluid, generating chemical potential energy that drives the fluid to enter and exit the formation. The governing equations for this chemical field are as follows:

[0157]

[0158] In the formula: D0 is the diffusion velocity, I m For membrane efficiency, c II Solute concentration in rock fissures;

[0159] The governing equations for the pore pressure field in rock fractures are as follows:

[0160]

[0161] In the formula: k II Let μ be the rock fracture permeability, μ be the fluid viscosity, v be the dissociation constant, R be the gas constant, and K be the K value. T Thermal conductivity coefficient.

[0162] The controlling equations of the sealing layer field include the sealing layer fluid mass balance equation, the sealing layer solute mass balance equation, the sealing layer chemical field controlling equation, and the sealing layer pore pressure field controlling equation.

[0163] The fluid mass balance equation for the sealing layer is shown below:

[0164]

[0165] Where: φ III For the porosity of the sealing layer, The solvent flow rate of the sealing layer;

[0166] The solute mass balance equation for the sealing layer is shown below:

[0167]

[0168] Where: φ III For the porosity of the sealing layer, This represents the mass flow rate of the solute in the sealing layer.

[0169] The governing equations for the chemical field of the sealing layer are shown below:

[0170]

[0171] In the formula: I represents the diffusion velocity of the sealing layer. m For membrane efficiency, c III Solute concentration in rock fissures;

[0172] The governing equations for the pore pressure field of the sealing layer are as follows:

[0173]

[0174] In the formula: k II Let μ be the permeability of the sealing layer, μ be the fluid viscosity, v be the dissociation constant, R be the gas constant, and K be the K value. T Thermal conductivity;

[0175] The three-pore, three-permeability model represents the porosity and permeability of the rock matrix, the porosity and permeability of the rock fractures, and the porosity and permeability of the sealing layer, respectively. The three-pore, three-permeability model is a set of equations consisting of the rock matrix field control equation, the rock fracture field control equation, and the sealing layer field control equation.

[0176] Establish the deformation equations for the shale skeleton, including: the continuity equation of the rock skeleton, the equilibrium equation of the rock skeleton, the effective stress equation, the geometric equation, and the constitutive equation;

[0177] The continuity equation for the rock skeleton is shown below:

[0178]

[0179] Where: ε v For volumetric strain;

[0180] The equilibrium equations for the rock skeleton are shown below:

[0181] When the surrounding rock of a shale formation well is subjected to external forces and the stress of the surrounding rock is in equilibrium, a stress state analysis is performed using a small element, and the tensor form is expressed as follows:

[0182] σ ij,j T +f i =0 (19)

[0183] In the formula: σ ij,j T For each stress component of the formation, f i For physical loads;

[0184] The geometric equations are as follows:

[0185] The degree of formation deformation is characterized by strain. According to the basic principle of small deformation in solid mechanics, strain and displacement are related, and the differential relationship between the strain components and the displacement components satisfies the deformation geometry equation:

[0186]

[0187] In the formula: u i,j u j,i For displacement components;

[0188] The constitutive equation is shown below:

[0189] For linear elastic deformation problems, there is a linear relationship between stress and strain. The strain components and stress components obey the generalized Hooke's law, and the constitutive equation is expressed as follows:

[0190]

[0191] In the formula: G is the rock shear modulus, and λ is the Lame-Changshu rock mass.

[0192] Equations for physical property parameters under the action of stress field and deformation field of microcracked porous media were established, including the established porosity equation, permeability equation, and pore compressibility coefficient equation.

[0193] The porosity equation is as follows:

[0194]

[0195] The permeability equation is as follows:

[0196]

[0197] The equation for the pore compressibility coefficient is shown below:

[0198]

[0199] In the formula: φ is the porosity after deformation, φ o Porosity under original conditions, k is the permeability after deformation, k0 is the permeability under original conditions, C φ Δε is the pore compressibility coefficient, Δε is the matrix shrinkage deformation rate, and ΔP is the formation pressure change.

[0200] Boundary conditions are set based on actual drilling conditions, and the stress field, pore pressure field, thermal field, and chemical field are calculated using the finite element method.

[0201] Stress field, pore pressure field, thermodynamic field, and chemical field can be solved using COMSOL finite element software. The specific solution steps are as follows:

[0202] 1) Establish a physical model, which simply means establishing a geometric model that needs to be solved, such as a square research region, a circular research region, etc.

[0203] 2) Use COMSOL finite element software. This software has many interfaces, such as the stress field interface for solid mechanics, the pore pressure field interface for Darcy's law, the thermal field interface for solid heat transfer, and the chemical field interface for rare matter transport. After selecting these interfaces, fill in the parameters required by the governing equations into the corresponding interfaces in sequence.

[0204] 3) Set boundary conditions, such as setting roller support, stress boundary conditions, and displacement boundary conditions for stress fields; setting pressure boundary conditions for pore pressure fields; setting temperature boundary conditions for thermal fields; and setting solute concentration boundary conditions for chemical fields.

[0205] 4) Set initial conditions. Each physics interface has an initial conditions node. You can directly input the parameters.

[0206] 5) Divide the grid;

[0207] 6) Click "Calculate" to get the calculation result.

[0208] Based on the defined boundary conditions, specifically including setting the initial and boundary conditions for shale skeleton deformation, the initial and boundary conditions for multi-component seepage in the three-pore, three-permeability model, and the initial reservoir temperature, the finite element method is used to calculate the formation pore pressure field and stress field. The Biot effective stress principle is then applied to calculate the wellbore stress. The Biot effective stress principle is as follows:

[0209]

[0210] In the formula, To obtain the effective stress tensor, we need to consider the effective stress around the three-hole, three-permeability well in the sealing layer.I p is the pore fluid pressure of the matrix. II For the fracture fluid pressure; α I α is the effective stress coefficient of the matrix; II δ is the effective stress coefficient of the crack. ij Kronecker symbol.

[0211] The values ​​and units of each parameter are shown in Table 1:

[0212] Table 1

[0213]

[0214] Figure 1 This is a cloud map showing the pressure distribution in a three-pore, three-permeability pore. Figure 2 A cloud map showing the pressure distribution in a dual-pore, dual-permeability pore; compared to... Figure 1 and Figure 2 The results showed that: Figure 1 The pressure around the wellbore is significantly less than Figure 2 The presence of the plugging layer slows down the transmission of pressure around the wellbore, thereby increasing the effective stress in the formation and effectively improving wellbore stability.

[0215] Figure 3 This is a cloud map showing the solute distribution in a three-pore, three-permeability configuration. Figure 4 A solute distribution cloud map of a dual-pore, dual-permeation system; comparison Figure 3 and Figure 4 The results showed that the presence of the plugging layer slowed down the diffusion of drilling fluid solutes into the formation. On the one hand, it reduced the pollution of the formation by drilling fluid filtrate. On the other hand, the concentration gradient between the plugging layer and the drilling fluid solutes was small, which reduced the potential energy of drilling fluid solutes transferred into the formation.

[0216] Example 3

[0217] A computer device includes a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the steps of the method for calculating the effective stress around a three-hole, three-permeable well considering a sealing layer, as described in Embodiment 1 or 2.

[0218] Example 4

[0219] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method for calculating the effective stress around a three-hole, three-permeable well considering a sealing layer, as described in Embodiment 1 or 2.

[0220] Example 5

[0221] A system for calculating the effective stress around a three-hole, three-permeability well considering the sealing layer, comprising:

[0222] The rock matrix mechanical characteristic parameter acquisition module is configured to: collect reservoir cores and obtain rock matrix mechanical characteristic parameters through triaxial compression, including: core porosity, permeability, water content, compressive strength, Young's modulus, Poisson's ratio, internal friction angle, cohesion, and pore fluid activity;

[0223] The reservoir core and in-situ drilling fluid acquisition module is configured to: first, obtain the physicochemical parameters of the interaction between rock pores and drilling fluid through pressure transmission experiments; then, test the physicochemical parameters of the interaction between rock fracture fluid and drilling fluid; and finally, test the physicochemical parameters of the effective sealing layer formed by the drilling fluid and rock. The physicochemical parameters of the effective sealing layer formed by the drilling fluid and rock include: film efficiency, hydraulic conductivity, solute diffusion coefficient, thermal conductivity, pore fluid activity, and in-situ drilling fluid activity.

[0224] The module for establishing the three-pore, three-permeability model is configured to: establish a three-pore, three-permeability model considering the control equations of the rock matrix field, the rock fracture field, and the sealing layer field; establish the deformation equation of the shale skeleton and the physical property parameter equations under the action of the stress field and the deformation field of the microfracture porous medium; set boundary conditions according to the actual drilling conditions; and use the finite element method to calculate the stress field, pore pressure field, thermal field, and chemical field.

[0225] The module for calculating the effective stress around a well with a three-hole, three-seepage well considering the plugging layer is configured to: calculate the effective stress around a well with a three-hole, three-seepage well considering the plugging layer based on the Biot effective stress principle and the stress and pore pressure distribution calculated by the three-hole, three-seepage model considering the plugging layer.

Claims

1. A method for calculating the effective stress around a three-hole, three-permeability well considering a sealing layer, characterized in that, include: Reservoir cores were collected, and the mechanical characteristics of the rock matrix were obtained through triaxial compression, including: core porosity, permeability, water content, compressive strength, Young's modulus, Poisson's ratio, internal friction angle, cohesion, and pore fluid activity. Reservoir core samples and in-situ drilling fluid were collected. First, the physicochemical parameters of the interaction between rock pores and drilling fluid were obtained through pressure transmission experiments. Next, the physicochemical parameters of the interaction between rock fracture fluid and drilling fluid were tested. Finally, the physicochemical parameters of the effective sealing layer formed by the drilling fluid and rock were tested. The physicochemical parameters of the effective sealing layer formed by the drilling fluid and rock include: film efficiency, hydraulic conductivity, solute diffusion coefficient, thermal conductivity, pore fluid activity, and in-situ drilling fluid activity. A three-pore, three-permeability model was established, considering the control equations of the rock matrix control field, the rock fracture field control equation, and the sealing layer field control equation. The deformation equation of the shale skeleton and the physical property parameter equations under the action of the stress field and the deformation field of the microfracture porous medium were also established. Boundary conditions were set according to the actual drilling conditions, and the stress field, pore pressure field, thermal field, and chemical field were calculated using the finite element method. The governing equations for the rock matrix control field include the rock matrix fluid mass balance equation, rock matrix solute mass balance equation, rock matrix state equation, rock matrix temperature control equation, rock matrix chemical field control equation, and rock matrix pore pressure field control equation; the governing equations for the rock fracture field include the rock fracture fluid mass balance equation, rock fracture solute mass balance equation, rock fracture state equation, rock fracture temperature control equation, rock fracture chemical field control equation, and rock fracture pore pressure field control equation; the governing equations for the sealing layer field include the sealing layer fluid mass balance equation, sealing layer solute mass balance equation, sealing layer chemical field control equation, and sealing layer pore pressure field control equation; the three-pore three-permeability model is a set of equations composed of the rock matrix control field governing equation, the rock fracture field governing equation, and the sealing layer field governing equation; Based on the Biot effective stress principle, and combined with the stress and pore pressure distribution calculated by the three-hole three-permeability model considering the plugging layer, the effective stress around the well considering the three-hole three-permeability model is calculated. The effective stress principle of Biot is: In the formula, For the effective stress tensor, p I p is the pore fluid pressure of the matrix. II For the fracture fluid pressure; α I α is the effective stress coefficient of the matrix; II δ is the effective stress coefficient of the crack. ij For Kronecker symbols.

2. The method for calculating the effective stress around a three-hole, three-permeability well considering the sealing layer as described in claim 1, characterized in that, The mass balance equation for fluid in rock matrix is ​​shown below: Where: φ I ρ represents the porosity of the rock matrix. f Let be the fluid density, and t be the time. The solvent flow velocity in the rock matrix; The mass balance equation for solute in the rock matrix is ​​shown below: Where: φ I ρ represents the porosity of the rock matrix. f Let ω be the fluid density, t be time, and ω be the mass fraction of the salt. This represents the mass flow rate of solute in the rock matrix. The equation of state for the rock matrix is ​​shown below: In the formula: p I ρ is the pore pressure of the rock matrix, β is the compressibility coefficient of the fluid, p0 is the initial pressure, ρ0 is the fluid density at pressure p0, and ρ0 is the rock density. The temperature control equation for the rock matrix is ​​shown below: In the formula: K eff Effective thermal diffusivity; The governing equations for the chemical field of the rock matrix are shown below: In the formula: D0 is the diffusion velocity, I m For membrane efficiency, c I Rock matrix solute concentration; The governing equations for the pore pressure field in the rock matrix are shown below: In the formula: k I Let μ be the rock matrix permeability, μ be the fluid viscosity, v be the dissociation constant, R be the gas constant, and K be the K value. T Thermal conductivity coefficient.

3. The method for calculating the effective stress around a three-hole, three-permeability well considering the sealing layer as described in claim 1, characterized in that, The mass balance equation for fluid in rock fractures is shown below: Where: φ II ρ represents the porosity of rock fractures. f Let be the fluid density, and t be the time. The solvent flow velocity in the rock fracture; The mass balance equation for solute in rock fractures is shown below: Where: φ II ρ represents the porosity of rock fractures. f Let ω be the fluid density, t be time, and ω be the mass fraction of the salt. The mass flow rate of solute in rock fractures; The equation of state for rock fractures is shown below: In the formula: p II ρ is the pore pressure in the rock fracture, β is the compressibility coefficient of the fluid, p0 is the initial pressure, ρ0 is the fluid density at pressure p0, and ρ0 is the rock density. The rock fracture temperature control equation is shown below: Where: K eff Effective thermal diffusivity; The governing equations for the chemical field of rock fractures are shown below: In the formula: D0 is the diffusion velocity, I m For membrane efficiency, c II Solute concentration in rock fissures; The governing equations for the pore pressure field in rock fractures are as follows: In the formula: k II Let μ be the rock fracture permeability, μ be the fluid viscosity, v be the dissociation constant, R be the gas constant, and K be the K value. T Thermal conductivity coefficient.

4. The method for calculating the effective stress around a three-hole, three-permeability well considering the sealing layer as described in claim 1, characterized in that, The fluid mass balance equation for the sealing layer is shown below: Where: φ III For the porosity of the sealing layer, The solvent flow rate of the sealing layer; The solute mass balance equation for the sealing layer is shown below: Where: φ III For the porosity of the sealing layer, This represents the mass flow rate of the solute in the sealing layer. The governing equations for the chemical field of the sealing layer are shown below: In the formula: I represents the diffusion velocity of the sealing layer. m For membrane efficiency, c III Solute concentration in rock fissures; The governing equations for the pore pressure field of the sealing layer are as follows: In the formula: k II Let μ be the permeability of the sealing layer, μ be the fluid viscosity, v be the dissociation constant, R be the gas constant, and K be the K value. T Thermal conductivity coefficient.

5. The method for calculating the effective stress around a three-hole, three-permeability well considering the sealing layer as described in claim 1, characterized in that, Establish the deformation equations for the shale skeleton, including: the continuity equation of the rock skeleton, the equilibrium equation of the rock skeleton, the effective stress equation, the geometric equation, and the constitutive equation; The continuity equation for the rock skeleton is shown below: Where: ε v For volumetric strain; The equilibrium equations for the rock skeleton are shown below: s ij,j T +f i =0 (19) In the formula: σ ij,j T For each stress component of the formation, f i For physical loads; The geometric equations are as follows: In the formula: u i,j u j,i For displacement components; The constitutive equation is shown below: In the formula: G is the rock shear modulus, and λ is the Lame-Changshu rock mass.

6. The method for calculating the effective stress around a three-hole, three-permeability well considering the sealing layer according to claim 1, characterized in that, Equations for physical property parameters under the action of stress field and deformation field of microcracked porous media were established, including the established porosity equation, permeability equation, and pore compressibility coefficient equation. The porosity equation is as follows: The permeability equation is as follows: The equation for the pore compressibility coefficient is shown below: In the formula: φ is the porosity after deformation, φ o Porosity under original conditions, k is the permeability after deformation, k0 is the permeability under original conditions, C φ Δε is the pore compressibility coefficient, Δε is the matrix shrinkage deformation rate, and ΔP is the formation pressure change. Based on the defined boundary conditions, specifically including setting the initial and boundary conditions for shale skeleton deformation, the initial and boundary conditions for multi-component seepage in the three-pore, three-permeability model, and the initial reservoir temperature, the finite element method is used to calculate the formation pore pressure field and stress field. The Biot effective stress principle is then applied to calculate the wellbore stress. The Biot effective stress principle is as follows: In the formula, To obtain the effective stress tensor, we need to consider the effective stress around the three-hole, three-permeability well in the sealing layer. I p is the pore fluid pressure of the matrix. II For the fracture fluid pressure; α I α is the effective stress coefficient of the matrix; II δ is the effective stress coefficient of the crack. ij Kronecker symbol.

7. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method for calculating the effective stress around a three-hole, three-permeable well considering the sealing layer as described in any one of claims 1-6.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the method for calculating the effective stress around a three-hole, three-permeable well considering the sealing layer as described in any one of claims 1-6.

9. A system for calculating the effective stress around a three-hole, three-permeable well considering a sealing layer, used to implement the method for calculating the effective stress around a three-hole, three-permeable well considering a sealing layer as described in claim 1 of any one of claims 1-6, characterized in that, include: The rock matrix mechanical characteristic parameter acquisition module is configured to: collect reservoir cores and obtain rock matrix mechanical characteristic parameters through triaxial compression, including: core porosity, permeability, water content, compressive strength, Young's modulus, Poisson's ratio, internal friction angle, cohesion, and pore fluid activity; The reservoir core and in-situ drilling fluid acquisition module is configured to: first, obtain the physicochemical parameters of the interaction between rock pores and drilling fluid through pressure transmission experiments; then, test the physicochemical parameters of the interaction between rock fracture fluid and drilling fluid; and finally, test the physicochemical parameters of the effective sealing layer formed by the drilling fluid and rock. The physicochemical parameters of the effective sealing layer formed by the drilling fluid and rock include: film efficiency, hydraulic conductivity, solute diffusion coefficient, thermal conductivity, pore fluid activity, and in-situ drilling fluid activity. The module for establishing the three-pore, three-permeability model is configured to: establish a three-pore, three-permeability model considering the control equations of the rock matrix control field, the rock fracture field control equation, and the control equation of the sealing layer field; establish the shale skeleton deformation equation and the physical property parameter equations under the action of the stress field and the deformation field of the microfracture porous medium; set boundary conditions according to the actual drilling conditions; and use the finite element method to calculate the stress field, pore pressure field, thermal field, and chemical field. The module for calculating the effective stress around a well with a three-hole, three-seepage well considering the plugging layer is configured to: calculate the effective stress around a well with a three-hole, three-seepage well considering the plugging layer based on the Biot effective stress principle and the stress and pore pressure distribution calculated by the three-hole, three-seepage model considering the plugging layer.

Images