Acid liquid flow simulation method and device considering wall surface filtration and non-uniform corrosion

Abstract

The invention discloses an acid liquid flow simulation method and device considering wall surface filtration and non-uniform corrosion, and relates to the technical field of oil reservoir numerical simulation. Establishing a digital model containing cracks and a porous medium, setting a perforation inlet, and carrying out grid division; selecting a VOF multiphase flow model, and selecting a viscous model according to a preset rule to determine a flow rule of a fluid phase in the fracture and the porous medium; the porosity of a porous medium and the viscous resistance of a fluid phase are set, all grids in the digital model are traversed, and the average volume fraction of the acid liquor in a computational domain is obtained; dynamically adjusting the viscous resistance of the acid liquor according to the average volume fraction so as to reflect the influence of the concentration change of the acid liquor on the flowing and corrosion behaviors of the acid liquor in the crack and the porous medium in real time; and setting boundary conditions of the digital model, and carrying out digital model initialization, numerical simulation calculation and post-processing. The problems of how to quantitatively analyze the concentration distribution and change of the acid liquor and how to improve the simulation efficiency and accuracy are solved.

Description

Technical Field

[0001] The present application relates to the technical field of oil reservoir numerical simulation, and in particular to a method and device for simulating acid flow taking into account wall filtration and non-uniform dissolution. Background Art

[0002] Carbonate oil and gas reservoirs play a crucial role in global energy development due to their widespread distribution and vast reserves. However, carbonate reservoirs suffer from poor porosity and permeability, low pore-throat compatibility, poor connectivity, and significant heterogeneity, resulting in low oil and gas recovery rates. Acid fracturing technology has become a key tool for improving carbonate reservoirs and increasing production. Its principle is to use acid to dissolve fracture walls and improve fracture conductivity. Currently, the main methods used to study wall corrosion during acid fracturing are visual physical modeling and computational fluid dynamics numerical simulation.

[0003] While visual modeling experiments are intuitive, they suffer from long preparation times, high costs, complex influencing factors, and low reproducibility of results. Furthermore, they lack quantitative analysis of the distribution and changes in acid concentration. Computational fluid dynamics (CFD) simulations, while capable of simulating chemical reactions, are complex, computationally intensive, and time-consuming. Furthermore, they are affected by complex geological features, leading to uncertainty in simulation results and failing to provide a complete picture of the acid concentration distribution throughout the fracturing process.

[0004] Therefore, how to quantitatively analyze the distribution and changes of acid concentration and improve the efficiency and accuracy of simulating the non-uniform dissolution phenomenon of crack walls has become a technical problem that needs to be solved urgently. Summary of the Invention

[0005] In the embodiments of the present application, by providing an acid flow simulation method that takes into account wall filtration and non-uniform dissolution, the problem of how to quantitatively analyze the distribution and changes of acid concentration and improve the efficiency and accuracy of the simulation is solved.

[0006] In a first aspect, an embodiment of the present application provides an acid flow simulation method that takes into account wall filtration and heterogeneous dissolution. The method includes: establishing a digital model including fractures and porous media, setting perforation inlets, and performing grid division; selecting a volume of fluid (VOF) multiphase flow model based on the established digital model, selecting a viscosity model according to preset rules, and setting the physical properties of the fluid phase and the surface tension coefficient between the fluid phases in the VOF multiphase flow model to determine the flow pattern of the fluid phase in the fractures and porous media; wherein the fluid phase includes acid and pre-fluid, and the physical properties of the fluid phase include density and viscosity; setting the porosity and viscous resistance of the fluid phase for the porous media in the digital model, traversing all grids in the digital model, and obtaining the average volume fraction of the acid in the calculation domain; wherein the calculation domain is the spatial range covered by the digital model; dynamically adjusting the viscous resistance of the acid based on the average volume fraction to reflect in real time the impact of changes in acid concentration on the flow and dissolution behavior of the acid in the fractures and porous media; setting boundary conditions for the digital model, initializing the digital model, performing numerical simulation calculations, and post-processing to simulate and analyze the heterogeneous dissolution phenomenon of the fracture wall.

[0007] In one possible implementation, establishing a digital model including fractures and porous media, setting perforation entrances, and performing meshing includes: assuming that the porous media and fractures in the digital model are adjacent, simplifying the fractures in the digital model into fractures with uniform widths; meshing the digital model, and determining the number of meshes required for the fractures and the number of meshes required for the porous media in the digital model; wherein the meshes in the digital model are all cubes; and the calculation formula for the number of meshes required for the fractures in the digital model is: ;in, is the number of grids required for the crack, l is the length of the digital model, is the width of the crack, is the height of the digital model, is the side length of the crack mesh; the calculation formula for the number of meshes required for the porous medium in the digital model is: ;in, is the number of grids required for porous media, is the width of the digital model, is the side length of the porous medium mesh.

[0008] In one possible implementation, the preset rules include: calculating the Reynolds number; determining whether the Reynolds number is greater than the critical Reynolds number; if the Reynolds number is greater than the critical Reynolds number, selecting the k-ε model as the viscous model; if the Reynolds number is less than or equal to the critical Reynolds number, selecting the laminar flow model as the viscous model.

[0009] In one possible implementation, the Reynolds number is calculated as: ;in, is the Reynolds number, is the density of the acid solution, is the viscosity of the acid solution, is the injection rate of the acid solution, , For acid injection displacement, is the effective perforation height, , is the perforation aperture, is the number of perforations, , is the perforation spacing, is the height of the digital model, is the phase angle.

[0010] In one possible implementation, the porosity and viscous resistance of the fluid phase are set for the porous media in the digital model, all grids in the digital model are traversed, and the average volume fraction of the acid liquid in the calculation domain is obtained. This includes: setting the porosity of the porous media region and the viscous resistance of the pre-fluid as constants; setting a custom function to traverse all grids in the digital model, accumulating the volume of the acid liquid and the volume of the grid to obtain the average volume fraction of the acid liquid in the calculation domain, and storing the sum in all variables; the calculation formula for the average volume fraction of the acid liquid in the calculation domain is: ;in, is the average volume fraction of acid in the calculation domain, For time The total volume of the acid in all grids in the digital model is is the total volume of all meshes in the digitized model.

[0011] In one possible implementation, the method of dynamically adjusting the viscous resistance of the acid fluid according to the average volume fraction to reflect in real time the effect of changes in acid concentration on the flow and dissolution behavior of the acid fluid in fractures and porous media includes: establishing a dynamic adjustment model to dynamically adjust the viscous resistance of the acid fluid according to the average volume fraction; the expression of the dynamic adjustment model is: ;in, is the viscous resistance of the current acid, is the viscous resistance of the initial acid solution, is the minimum viscous resistance after the acid is fully reacted.

[0012] In one possible implementation, the boundary conditions of the digital model are set, and the digital model is initialized, numerical simulation is calculated, and post-processed, including: the boundary conditions include the inlet conditions, outlet conditions, and wall conditions of the digital model; the setting of the inlet conditions includes setting the injection rate of the acid liquid and the acid liquid injection volume fraction; the setting of the outlet conditions includes setting the gauge pressure value of the outlet pressure to 0 and prohibiting backflow; the setting of the wall conditions includes setting the contact angle between the acid liquid and the pre-fluid at the wall surface; and the post-processing includes using post-processing software to analyze the simulation results after the numerical simulation calculation is completed.

[0013] In a second aspect, an embodiment of the present application provides an acid flow simulation device that takes into account wall filtration and non-uniform dissolution, the device comprising: a partitioning module for establishing a digital model including fractures and porous media, setting perforation entrances and performing grid division; a determination module for selecting a VOF multiphase flow model based on the established digital model, selecting a viscosity model according to preset rules, and setting the physical properties of the fluid phase and the surface tension coefficient between the fluid phases in the VOF multiphase flow model to determine the flow law of the fluid phase in the fracture and porous media; wherein the fluid phase comprises an acid solution and a pre-fluid, and the physical properties of the fluid phase comprise density and viscosity; The acquisition module is used to set the porosity and viscous resistance of the fluid phase for the porous media in the digital model, traverse all the grids in the digital model, and obtain the average volume fraction of the acid in the calculation domain; the calculation domain is the spatial range covered by the digital model; the adjustment module is used to dynamically adjust the viscous resistance of the acid according to the average volume fraction to reflect in real time the impact of changes in acid concentration on the flow and dissolution behavior of the acid in fractures and porous media; the setting module is used to set the boundary conditions of the digital model, perform digital model initialization, numerical simulation calculations and post-processing, aiming to simulate and analyze the non-uniform dissolution phenomenon of the fracture wall.

[0014] In the third aspect, an embodiment of the present application provides an acid flow simulation server that takes into account wall filtration and non-uniform dissolution, including a memory and a processor; the memory is used to store computer-executable instructions; the processor is used to execute the computer-executable instructions to implement the method described in the first aspect or any possible implementation method of the first aspect.

[0015] In a fourth aspect, an embodiment of the present application provides a computer-readable storage medium, which stores executable instructions. When a computer executes the executable instructions, it can implement the method described in the first aspect or any possible implementation method of the first aspect.

[0016] One or more technical solutions provided in the embodiments of this application have at least the following technical effects: The embodiments of this application provide an acid flow simulation method that considers wall filtration and heterogeneous dissolution. By establishing a digital model of fractures and porous media, applying a VOF multiphase flow model, and obtaining the average volume fraction of the acid within the computational domain, this method enables accurate quantitative analysis of the concentration distribution and changes of the acid in complex reservoir structures. The method can clearly present the acid concentration at different locations and time periods. The method of dynamically adjusting the viscous resistance of the acid based on the average volume fraction of the acid avoids the complex calculation process in traditional simulation methods and reduces the amount of computation and computation time of numerical simulations. Dynamically adjusting the viscous resistance of the acid to reflect the impact of changes in acid concentration on the flow and dissolution behavior of the acid in fractures and porous media in real time improves the consistency of the simulation results with actual conditions and enhances the credibility of the simulation results. This method solves the problem of how to quantitatively analyze the distribution and changes of acid concentration and improves the efficiency and accuracy of simulating heterogeneous dissolution phenomena on fracture walls. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments of the present application or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 A flowchart of an acid flow simulation method considering wall filtration and non-uniform dissolution provided in an embodiment of the present application; Figure 2 A schematic diagram of a digital model provided in an embodiment of the present application in which cracks in the digital model are not simplified into cracks of uniform width; Figure 3 A schematic diagram of a digital model in which cracks in a digital model are simplified into cracks with uniform widths, provided in an embodiment of the present application; Figure 4 A schematic diagram of the coupled zoning of wall dissolution and pipe seepage provided in an embodiment of the present application; Figure 5 A schematic diagram of a digital model constructed for an embodiment of the present application; Figure 6 A schematic diagram of the mesh division results provided in an embodiment of the present application; Figure 7 A schematic diagram of the boundary conditions of the digital model provided in an embodiment of the present application; Figure 8 A schematic diagram of initializing a digital model provided in an embodiment of the present application; Figure 9 The acid liquid finger-in flow diagram at 50s provided in the embodiment of the present application; Figure 10 This is the non-uniform dissolution diagram of the crack wall at 1000s provided in the embodiment of the present application; Figure 11 A comparison diagram of the non-uniform dissolution diagram at the crack entrance at different times provided in the embodiment of the present application; Figure 12 A comparison diagram of crack aperture diagrams at different times provided in the embodiments of the present application; Figure 13 A schematic diagram of an acid flow simulation device taking into account wall filtration and non-uniform dissolution provided in an embodiment of the present application; Figure 14 A schematic diagram of an acid flow simulation server that takes into account wall filtration and non-uniform dissolution provided in an embodiment of the present application. DETAILED DESCRIPTION

[0019] The following will be combined with the accompanying drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0020] The following description of some of the technologies involved in the embodiments of this application is provided to facilitate understanding and should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications may be made to the embodiments described herein without departing from the scope and spirit of this application. Similarly, for the sake of clarity and conciseness, some descriptions of well-known functions and structures are omitted from the following description.

[0021] The present application provides an acid flow simulation method considering wall filtration and non-uniform dissolution, such as Figure 1 As shown, the method includes steps S101 to S105. Figure 1 This is only an execution sequence shown in the embodiment of the present application, and does not represent the only execution sequence of the acid flow simulation method considering wall loss and non-uniform dissolution. Figure 1 The steps shown may be performed in parallel or reversed.

[0022] S101: Create a digital model containing fractures and porous media, set perforation entrances, and perform meshing.

[0023] Establishing a digital model containing fractures and porous media, setting perforation entrances and performing meshing includes the following steps.

[0024] The porous medium and the cracks in the digital model are assumed to be adjacent, and the cracks in the digital model are simplified to cracks of uniform width. The digital model is meshed to determine the number of grids required for the cracks and the number of grids required for the porous medium. The grids in the digital model are all cubes.

[0025] Figure 2 A schematic diagram of a digital model provided in an embodiment of the present application in which cracks in the digital model are not simplified into cracks with uniform width. Figure 2 Where l is the length of the digital model, is the width of the crack, is the height of the digital model, is the width of the digital model. The blue arrow in the figure indicates the injection direction of the acid. The acid will be lost during the flow process, and the direction of acid loss is shown, that is, the acid penetrates into the crack wall and etches the crack wall. It should be noted that the width of the crack It is an idealized description of a regular geometric model, representing the aperture of a crack. Under actual working conditions, cracks often exhibit irregular shapes, and the crack width distribution along the wall has significant spatial non-uniformity. However, to simplify the model and reduce computational complexity, in this application, the cracks in the digital model are simplified to cracks of uniform width, and a regular rectangular parallelepiped geometry is used to represent the cracks. This simplified approach captures the main characteristics of dissolution while ensuring computational efficiency.

[0026] Figure 3 A schematic diagram of a digital model provided in an embodiment of the present application for simplifying cracks in a digital model into cracks with uniform width. Figure 3 The irregular fracture walls were simplified into uniform-width fractures, with the fracture zone, porous medium zone, fracture zone entrance and exit, and porous medium zone filtration outlet indicated. The simulation assumed that the acid was injected into the fracture at a uniform rate along the fracture entrance, ignoring changes in fracture length and height during the simulation. To further determine the number of meshes in the digital model and calculate the number of simulation iterations, the fracture-matrix interface within any digital model can be intercepted.

[0027] Figure 4 Schematic diagram of the coupled zoning of wall dissolution and pipe seepage provided in the embodiment of the present application. Figure 4 (a) in the figure is a schematic diagram of the partition in the initial state. Figure 4 (b) shows the zoning diagram after wall dissolution. A specific zoning method was used to address the coupled effects between wall dissolution and pipe flow, dividing the network into distinct permeability zones. The yellow grid represents the pipe flow zone, while the blue grid represents the seepage zone.

[0028] Figure 5 This is a schematic diagram of a digital model constructed for the embodiment of the present application. This application uses Workbench Design Modeler (a modeling software) to model and generate a digital model such as Figure 5 As shown, Figure 5 The green rectangle in the middle of (a) represents a crack, and the blue and gray rectangles on either side of the crack represent porous media. To distinguish different areas, Workbench Design Modeler automatically sets different colors for different areas. At the same time, to facilitate the display and observation of the crack area, the porous media is made transparent. Figure 5 Figure (b) shows the perforation entrances in the digital model. The red area represents the perforation entrances, the green area represents the fractures, and the blue and gray areas on either side of the fractures represent the porous medium. Five perforations were evenly spaced at the acid inlet. This even distribution of perforations helps improve the uniformity of the acid, allowing it to more easily penetrate all areas of the reservoir, thereby maximizing the acidizing effect and preventing excessive concentration of acid in certain localized areas, which can lead to uneven etching and unnecessary damage to the reservoir.

[0029] After the digital model is established, it needs to be discretized. The purpose of discretization is to ensure the accuracy and efficiency of numerical calculations. This application uses the mesh generator Meshing that comes with Fluent (a computational fluid dynamics software) to define the size of the mesh unit by adjusting the size according to the length, width and height parameters of the digital model. According to the shape of the digital model, select a suitable meshing method. The meshing methods include automatic methods Automatic, Tetrahedrons, Hex Dominant, Sweep, etc. Among them, the automatic method Automatic will automatically select the optimal mesh generation strategy based on the geometric features. It is suitable for simple geometric models with no special requirements for the mesh type. Therefore, this application uses the automatic method Automatic to divide the mesh. Figure 6 A schematic diagram of the grid division results provided in an embodiment of the present application. Figure 6 The blue and gray areas in the figure are porous media, and the green part in the middle is the crack. This grid division lays the foundation for subsequent numerical simulation calculations.

[0030] Furthermore, the calculation formula for the number of grids required to digitize the cracks in the model is: .in, is the number of grids required for the crack, l is the length of the digital model, is the width of the crack, is the height of the digital model, is the side length of the crack mesh. The formula for calculating the number of meshes required for the porous medium in the digital model is: .in, is the number of grids required for porous media, is the width of the digital model, is the side length of the porous medium mesh.

[0031] Specifically, when dividing the mesh of cracks and porous media, different side lengths can be selected respectively. and , and allow , that is, the side length of the mesh of the fracture can be smaller than that of the mesh of the porous medium. This is because the fracture is usually a relatively narrow space with a small width. In order to more accurately capture the flow characteristics of the acid in the fracture, a smaller mesh side length is required. to divide the crack area.

[0032] S102: Based on the established digital model, a VOF multiphase flow model is selected. A viscosity model is selected according to preset rules. The physical properties of the fluid phase and the surface tension coefficient between the fluid phases in the VOF multiphase flow model are set to determine the flow patterns of the fluid phase in the fracture and porous media. The fluid phase includes the acid and the pre-pad fluid, and the physical properties of the fluid phase include density and viscosity.

[0033] Specifically, after importing the meshed digital model into Fluent, we selected a multiphase flow model. Taking into account the surface tension and viscous interaction requirements between the acid and prepad fluids, we chose the VOF multiphase flow model because it accurately captures the interface characteristics between the acid and prepad fluids and is suitable for simulating the fingering phenomenon and wall dissolution processes described in this application.

[0034] The preset rules include the following: Calculate the Reynolds number. Determine whether the Reynolds number is greater than the critical Reynolds number. If the Reynolds number is greater than the critical Reynolds number, select the k-ε model as the viscous model. If the Reynolds number is less than or equal to the critical Reynolds number, select the laminar flow model as the viscous model.

[0035] Specifically, the critical Reynolds number is .

[0036] The formula for calculating the Reynolds number is: .in, is the Reynolds number, is the density of the acid solution, is the viscosity of the acid solution, is the injection rate of the acid solution, , For acid injection displacement, is the effective perforation height, , is the perforation aperture, is the number of perforations, , is the perforation spacing, is the height of the digital model, is the phase angle.

[0037] Specifically, the perforation aperture Much smaller than the height of the digital model Acid injection displacement The unit is m 3 / min. Acid injection speed The unit is m / s. Since the acid mainly occurs in the crack area, the characteristic length is twice the width of the crack, that is, .Right now .in, is the characteristic length.

[0038] Furthermore, considering that the acid flow mainly occurs in the fracture area and has high viscosity, the calculated Reynolds number is usually much smaller than the critical Reynolds number, so the laminar flow model is selected as the viscosity model.

[0039] Specifically, the physical properties of the fluid phase are set in Fluent through Materials → Fluid → Create Materials. The surface tension coefficient between fluid phases is set in Fluent through Models → VOF → Phase Interaction → Surface Tension Coefficient.

[0040] S103: For the porous media in the digital model, set the porosity and viscous resistance of the fluid phase, traverse all grids in the digital model, and obtain the average volume fraction of the acid in the computational domain. The computational domain is the spatial range covered by the digital model.

[0041] For the porous media in the digital model, the porosity and the viscous resistance of the fluid phase are set, all the grids in the digital model are traversed, and the average volume fraction of the acid in the calculation domain is obtained, including the following.

[0042] The porosity of the porous media region and the viscous resistance of the pad fluid are set as constants.

[0043] Specifically, acid fracturing simulation involves complex chemical reactions, fluid flow, and dissolution processes. Setting the porosity and the viscous resistance of the pre-pad fluid as constants avoids introducing additional dynamic variables and improves computational efficiency.

[0044] Specifically, porosity is the ratio of the pore volume to the total volume of a porous medium and reflects the matrix's storage capacity. Porosity can be set in Fluent via: Setup → Cell Zone Conditions → Fluid → Porous Zone → Porosity. The viscous resistance of the prepad fluid reflects the ease with which the prepad fluid flows in the porous medium. This can be set in Fluent via: Setup → Cell Zone Conditions → Fluid → Phase → Porous Zone → Viscous Resistance.

[0045] Set a custom function to traverse all grids in the digital model, accumulate the volume of the acid and the volume of the grid to obtain the average volume fraction of the acid in the calculation domain, and store it in all variables.

[0046] The calculation formula for the average volume fraction of acid in the calculation domain is: .in, is the average volume fraction of acid in the calculation domain, For time The total volume of the acid in all grids in the digital model is is the total volume of all meshes in the digitized model.

[0047] Specifically, the acid concentration decreases during the reaction, causing changes in its viscosity and viscous drag. By calculating the average volume fraction of the acid within the computational domain, we can reflect the concentration distribution of the acid and dynamically adjust the viscous drag.

[0048] Specifically, the path to set up a custom function in Fluent is: User-Defined → Functions → Interpreted UDFs. The path to set up the viscous resistance of the acid in Fluent is: Setup → Cell Zone Conditions → Fluid → Phase → Porous Zone → Viscous Resistance → UDF.

[0049] It should be noted that the total volume of all grids in the digital model is Remains constant during the simulation.

[0050] S104: Dynamically adjust the viscous resistance of the acid according to the average volume fraction to reflect in real time the impact of changes in acid concentration on the flow and dissolution behavior of the acid in fractures and porous media.

[0051] The viscous resistance of the acid fluid is dynamically adjusted according to the average volume fraction to reflect in real time the impact of changes in acid concentration on the flow and dissolution behavior of the acid fluid in fractures and porous media, including the following.

[0052] A dynamic adjustment model is established to dynamically adjust the viscous resistance of the acid according to the average volume fraction.

[0053] The expression of the dynamic adjustment model is: .in, is the viscous resistance of the current acid, is the viscous resistance of the initial acid solution, is the minimum viscous resistance after the acid is fully reacted.

[0054] Specifically, when the concentration of the acid solution is high ( When it is close to 1), the viscous resistance of the acid is close to the initial value When the acid concentration decreases ( decreases), the viscous resistance of the acid gradually decreases and the interaction between the molecules of the reaction acid weakens.

[0055] Specifically, the viscous resistance of the acid can also be called the inverse absolute permeability. Since the viscous resistance in Fluent mainly describes the resistance characteristics of the porous medium, the calculation formula for the minimum viscous resistance after the acid is fully reacted is as follows: .in, is the permeability. After the acid solution fully reacts, the matrix permeability increases. Taking dolomite matrix as an example, the permeability range is to When the matrix permeability is , the minimum viscous resistance after the acid is fully reacted is .

[0056] Furthermore, the above process can be implemented through a user-defined function (UDF), including the DEFINE_EXECUTE_AT_END (excecute_at_end) function, which is used to execute at the end of each time step to calculate the average volume fraction of the acid solution. By traversing all the grids, traversing all the grids in the digital model, accumulating the volume of the acid and the volume of the grid, calculate It also includes the DEFINE_PROFILE(vis_res,thread,position) function, which is executed when the boundary conditions of the digital model are updated at each time step to dynamically adjust the viscous resistance of the acid. and dynamically adjust the model to calculate and update the viscous resistance of the acid.

[0057] S105: Setting boundary conditions of the digital model, performing digital model initialization, numerical simulation calculation and post-processing.

[0058] Set the boundary conditions of the digital model, perform digital model initialization, numerical simulation calculation and post-processing, including the following contents.

[0059] Boundary conditions include inlet conditions, outlet conditions and wall conditions of the digital model.

[0060] The setting of inlet conditions includes setting the injection rate of the acid solution and the acid solution injection volume fraction.

[0061] Specifically, the acid injection rate is set in Fluent via Setup → Boundary Conditions → Inlet. The acid injection volume fraction is set in Fluent via Setup → Boundary Conditions → Inlet → Phase. The acid volume fraction is set based on the ratio of acid to pre-pad fluid. If no ratio is specified, the default acid injection volume fraction is set to 1.

[0062] The outlet condition settings include setting the gauge pressure value of the outlet pressure to 0 and prohibiting backflow.

[0063] Specifically, the outlet condition is set in Fluent via Setup → Boundary Conditions → Outlet → Gauge Pressure. Setting the gauge pressure value of the outlet pressure to 0 indicates that the outlet is connected to the ambient atmospheric pressure. Disabling backflow prevents the fluid phase from flowing back into the computational domain from the outlet.

[0064] The setting of the wall condition includes setting the contact angle between the acid solution and the pre-fluid at the wall.

[0065] Specifically, the path to set the wall condition in Fluent is Setup→Boundary Conditions→Wall→Wall Adhesion→Contact Angles. Set the contact angle between the acid solution and the pre-fluid at the wall. , the wettability of the reaction fluid phase on the wall. If there is no experimental data, it can be set to the default value of 165°.

[0066] Digital model initialization and numerical simulation calculations include the following contents.

[0067] Set the solution method, the setting path is: Solution→Methods, and select SIMPLE as the solution method.

[0068] Set the spatial discretization method. The setting path is: Solution→Methods. Select Second Ordre Upwind as the spatial discretization method.

[0069] Set the sub-relaxation factor in the solution control. The setting path is: Solution→Controls. Here, the pressure, density, and momentum parameters are set to make the calculation easier to converge.

[0070] Set the absolute standard for the convergence condition in the residual monitor. The setting path is: Solution→Monitors→Residual.

[0071] Set up solution data export, for example exporting Volume fraction (sy) as CDAT for CFD-Post&EnSight (cdat) file.

[0072] Set the number of calculation steps and time step.

[0073] Determine whether the calculation results converge.

[0074] Specifically, Fluent calculates the mass conservation equation and momentum conservation equation in the model and automatically monitors the residual value of each equation. When the residual value drops to the specified residual threshold, it indicates that the calculation has converged. The residual threshold is usually to .

[0075] Post-processing involves using post-processing software to analyze the simulation results after the numerical simulation calculation is completed.

[0076] Specifically, during the simulation process, the accuracy of the model can be verified by monitoring simulation results, such as flow field distribution, pressure distribution, and temperature distribution. If the simulation results do not match the actual situation, the model parameters can be adjusted and the simulation can be rerun. The simulation results should show non-uniform dissolution of the fracture wall. If non-uniform dissolution occurs or even no dissolution occurs, the simulation results are considered unrealistic and the model needs to be adjusted and re-simulated.

[0077] Specifically, the post-processing software can be CFD Post. To import the cdat file for the final time step, go to File → Load Results File → cdat file. To set the transparency of the digitized model, go to Render → Transparency. To set the resolution, go to Insert Volume → Volume Rendering → Resolution.

[0078] An embodiment is listed below to further illustrate the above content of the present application. Of course, other embodiments are also possible, and the present application is not limited to this embodiment.

[0079] Figure 5 The digital model is used to simulate the flow and dissolution process of acid in fractures and porous media. An inlet with 5 clusters of perforations was selected to simulate the multi-cluster perforation injection scenario in actual acid fracturing operations. The complex morphology of the fracture surface (such as the roughness of natural fractures) was omitted to simplify the calculation and highlight the main physical processes. The length of the digital model is 150m, the height is 30m, and the width is 30.01m. Among them, the width of the fracture is 0.01m. The side length of the fracture grid is 0.01m (consistent with the fracture width). The side length of the porous medium grid is 0.05m. According to the calculation formula for the number of grids required for the fracture in the digital model and the calculation formula for the number of grids required for the porous medium in the digital model, the total number of grids is 1.54 million. Among them, the total number of grids is the sum of the number of grids required for the fracture and the number of grids required for the porous medium. The division results are as follows Figure 6 As shown, the mesh of the fracture is dense and the mesh of the porous medium is sparse.

[0080] Figure 7 Schematic diagram of the boundary conditions of the digital model provided in the embodiment of the present application. Figure 7 You can see the blue arrow at the inlet indicating the injection of acid. The inlet condition should be set to the injection rate of the acid , and the physical properties of the acid need to be specified. The density of the acid is The viscosity of the acid is In the fluid phase simulation, it is also necessary to set parameters such as the volume fraction of the acid solution. According to the Reynolds number formula, the Reynolds number is 12.1, which is much smaller than , and the acid liquid of this application has a low flow rate, a high viscosity, and is accompanied by the fingering phenomenon of the acid liquid. Therefore, this application selects the laminar flow model as the viscosity model. Figure 7 The red arrow at the outlet indicates fluid loss. The outlet condition is typically set to a static pressure outlet. For example, setting the gauge pressure value of the outlet to 0 indicates that the outlet is connected to the ambient atmospheric pressure. Furthermore, a no-backflow condition is required to prevent fluid from flowing back into the computational domain from the outlet. The wall condition sets the contact angle between the acid and the prepad at the wall to 165°.

[0081] Fingering of acid refers to the irregular, finger-like advance of the acid front as it flows through porous media or fractures due to the viscosity difference between the acid and the pad fluid. Fingering can still occur in laminar flow models, affecting the acid distribution and dissolution effects. Numerical simulations require an appropriate multiphase flow model (such as the VOF multiphase flow model) to capture the interface between the acid and pad fluid and accurately simulate fingering and its impact on wall dissolution.

[0082] Figure 8 A schematic diagram of initializing a digital model provided in an embodiment of the present application. Figure 8 Sy is the acid liquid, Sy.Volume Fraction is the volume fraction of the acid liquid, and Volume Rendering 1 is volume rendering. Figure 8 It is the volume fraction cloud diagram of the acid liquid under the initial conditions. It can be seen from the figure that the inlet is full of acid liquid under the initial conditions.

[0083] Figure 9 The example of the present application provides a flow diagram of acid fingering at 50 seconds. At 50 seconds, it can be seen that the acid shows obvious fingering phenomenon, and the inlet width is wider than the initial width. This phenomenon indicates that the acid has etched the inlet within 50 seconds.

[0084] Figure 10 This is an image of the non-uniform corrosion of the fracture wall at 1000 s, provided in this example. The image clearly shows significant non-uniform etching at the fracture entrance. With continued acid injection, distinct etching paths formed along the entrances of the five clusters of perforations. These paths extended along the fracture and gradually evolved into five irregular etching channels.

[0085] Figure 11 This is a comparison diagram of the non-uniform dissolution diagram at the crack entrance at different times provided in the examples of this application. Figure 11 (a) in the figure is the non-uniform dissolution diagram at the crack entrance at 200s. Figure 11 Figure (b) shows the heterogeneous dissolution at the crack entrance at 1000 s. As can be seen from the figure, dissolution at the crack entrance gradually intensified over time and exhibited significant heterogeneity. The overall width of the crack entrance increased significantly, especially at the locations corresponding to the five cluster entrances, where dissolution became more intense, forming a distinct localized expansion area. The 200 s figure shows that heterogeneous dissolution at the entrance has begun to take shape, showing the early characteristics of the five cluster etching paths. At 1000 s, dissolution at the five cluster entrances further developed, and the etching paths became wider and more irregular, indicating that the flow and dissolution rate of the acid in these areas have significantly increased.

[0086] It should be noted that the entrances in this application are all entrances of perforations.

[0087] Figure 12 This is a comparison diagram of the crack aperture diagrams at different times provided in the embodiments of this application. Figure 12 (a) in the figure is the crack opening diagram at 200s. Figure 12 Figure (b) shows the crack aperture at 1000 s. The crack aperture at 200 s shows that the increase in crack aperture is primarily concentrated near the entrance, demonstrating the spatial limitations of the initial etching. However, at 1000 s, the crack aperture increases significantly, extending along the crack depth. Furthermore, the crack wall aperture exhibits an uneven expansion from the entrance. This indicates that the expansion of the etching path is not limited to the entrance but also extends into the crack interior, forming a complex channel structure.

[0088] The embodiment of the present application also provides an acid flow simulation device 1300 that takes into account wall filtration and non-uniform dissolution, such as Figure 13 As shown, the device includes: a division module 1301 , a determination module 1302 , an acquisition module 1303 , an adjustment module 1304 and a setting module 1305 .

[0089] The partitioning module 1301 is used to establish a digital model including fractures and porous media, set perforation entrances and perform grid partitioning.

[0090] Determination module 1302 is configured to select a VOF multiphase flow model based on the established digital model, select a viscosity model according to preset rules, and set the physical properties of the fluid phase and the surface tension coefficient between the fluid phases in the VOF multiphase flow model to determine the flow pattern of the fluid phase in the fracture and porous media. The fluid phase includes the acid solution and the pre-pad solution, and the physical properties of the fluid phase include density and viscosity.

[0091] The acquisition module 1303 is used to set the porosity and viscous resistance of the fluid phase for the porous medium in the digital model, traverse all grids in the digital model, and obtain the average volume fraction of the acid solution within the computational domain. The computational domain is the spatial range covered by the digital model.

[0092] The adjustment module 1304 is used to dynamically adjust the viscous resistance of the acid solution according to the average volume fraction, so as to reflect in real time the impact of the change in acid solution concentration on the flow and dissolution behavior of the acid solution in fractures and porous media.

[0093] The setting module 1305 is used to set the boundary conditions of the digital model, perform digital model initialization, numerical simulation calculation and post-processing, and aims to simulate and analyze the non-uniform dissolution phenomenon of the crack wall.

[0094] Some modules in the apparatus described herein may be described in the general context of computer-executable instructions executed by a computer, such as program modules. Generally, program modules include routines, programs, objects, components, data structures, classes, etc. that perform specific tasks or implement specific abstract data types. The present application may also be practiced in distributed computing environments where tasks are performed by remote processing devices connected via a communications network. In a distributed computing environment, program modules may be located in local and remote computer storage media, including storage devices.

[0095] The devices or modules described in the above application embodiments can be implemented by computer chips or physical devices, or by products with certain functions. For ease of description, the above devices are described separately by function in various modules. When implementing the embodiments of this application, the functions of each module can be implemented in the same or multiple software and / or hardware. Of course, a module that implements a certain function can also be implemented by combining multiple sub-modules or sub-units.

[0096] The methods, devices, or modules described herein can be implemented in the form of computer-readable program code. The controller can be implemented in any suitable manner. For example, the controller can take the form of a microprocessor or processor and a computer-readable medium storing computer-readable program code (e.g., software or firmware) executable by the (micro)processor, logic gates, switches, an application-specific integrated circuit (ASIC), a programmable logic controller, and an embedded microcontroller. Examples of controllers include, but are not limited to, the following microcontrollers: ARC 625D, Atmel AT91SAM, Microchip PIC18F26K20, and Silicone Labs C8051F320. The memory controller can also be implemented as part of the control logic of the memory. Those skilled in the art will also appreciate that, in addition to implementing the controller in the form of pure computer-readable program code, the controller can also be implemented in the form of logic gates, switches, an application-specific integrated circuit, a programmable logic controller, an embedded microcontroller, etc. by logically programming the method steps. Therefore, such a controller can be considered a hardware component, and the devices included therein for implementing various functions can also be considered as structures within the hardware component. Or even, the means for implementing various functions may be considered to be both a software module for implementing the method and a structure within a hardware component.

[0097] like Figure 14As shown, an embodiment of the present application also provides an acid flow simulation server that takes into account wall filtration and non-uniform dissolution, including a memory 1401 and a processor 1402; the memory 1401 is used to store computer-executable instructions; the processor 1402 is used to execute computer-executable instructions to implement the acid flow simulation method that takes into account wall filtration and non-uniform dissolution described above in the embodiment of the present application.

[0098] An embodiment of the present application also provides a computer-readable storage medium, which stores executable instructions. When a computer executes the executable instructions, it can implement the acid flow simulation method considering wall filtration and non-uniform dissolution described above in the embodiment of the present application.

[0099] Through the description of the above implementation methods, it can be seen that those skilled in the art can clearly understand that the present application can be implemented by means of software plus necessary hardware. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, can be embodied in the form of a software product, or can be embodied through the implementation process of data migration. The computer software product can be stored in a storage medium, such as ROM / RAM, a magnetic disk, an optical disk, etc., and includes a number of instructions for enabling a computer device (which can be a personal computer, a mobile terminal, a server, or a network device, etc.) to execute the method described in the embodiments of the present application.

[0100] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to in detail. Each embodiment focuses on the differences from other embodiments. All or part of this application can be used in many general or special computer system environments or configurations.

[0101] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit the present application. Although the present application has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions described in the aforementioned embodiments can still be modified, or some or all of the technical features therein can be replaced by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present application.

Claims

1. A method for simulating acid flow considering wall loss and non-uniform dissolution, characterized in that: include: Establish a digital model including fractures and porous media, set perforation entrances and perform meshing; Based on the established digital model, the VOF multiphase flow model is selected. A viscosity model is selected according to preset rules. The physical properties of the fluid phase and the surface tension coefficient between the fluid phases in the VOF multiphase flow model are set to determine the flow patterns of the fluid phase in fractures and porous media. The fluid phase includes acid and pre-pad fluid, and the physical properties of the fluid phase include density and viscosity. For the porous media in the digital model, the porosity and viscous resistance of the fluid phase are set, and all grids in the digital model are traversed to obtain the average volume fraction of the acid in the computational domain. The computational domain is the spatial range covered by the digital model. Dynamically adjust the viscous resistance of the acid according to the average volume fraction to reflect in real time the impact of changes in acid concentration on the flow and dissolution behavior of the acid in fractures and porous media; The boundary conditions of the digital model are set, and the digital model initialization, numerical simulation calculation and post-processing are carried out to simulate and analyze the non-uniform dissolution phenomenon of the crack wall.

2. The acid flow simulation method considering wall loss and non-uniform dissolution according to claim 1 is characterized in that: The process of establishing a digital model including fractures and porous media, setting perforation entrances and performing meshing comprises: The porous medium and the cracks in the digital model are assumed to be adjacent, and the cracks in the digital model are simplified to cracks with uniform width; Meshing the digital model to determine the number of meshes required for the cracks and the number of meshes required for the porous medium in the digital model; wherein the meshes divided in the digital model are all cubes; The formula for calculating the number of meshes required to digitize the cracks in the model is: ;in, is the number of grids required for the crack, l is the length of the digital model, is the width of the crack, is the height of the digital model, is the side length of the crack mesh; The formula for calculating the number of meshes required to digitize the porous media in the model is: ;in, is the number of grids required for porous media, is the width of the digital model, is the side length of the porous medium mesh.

3. The acid flow simulation method considering wall loss and non-uniform dissolution according to claim 2 is characterized in that: The preset rules include: Calculate the Reynolds number; Determine whether the Reynolds number is greater than the critical Reynolds number; If the Reynolds number is greater than the critical Reynolds number, the k-ε model is selected as the viscosity model; If the Reynolds number is less than or equal to the critical Reynolds number, the laminar flow model is selected as the viscosity model.

4. The acid flow simulation method considering wall loss and non-uniform dissolution according to claim 3 is characterized in that: The formula for calculating the Reynolds number is: ;in, is the Reynolds number, is the density of the acid solution, is the viscosity of the acid solution, is the injection rate of the acid, , For acid injection displacement, is the effective perforation height, , is the perforation aperture, is the number of perforations, , is the perforation spacing, is the height of the digital model, is the phase angle.

5. The acid flow simulation method considering wall filtration and non-uniform dissolution according to claim 4 is characterized in that: The method includes setting the porosity and the viscous resistance of the fluid phase for the porous medium in the digital model, traversing all the grids in the digital model, and obtaining the average volume fraction of the acid in the calculation domain, including: The porosity of the porous medium region and the viscous resistance of the pre-fluid are set as constants; Set up a custom function to traverse all grids in the digital model, accumulate the volume of the acid and the volume of the grid to obtain the average volume fraction of the acid in the calculation domain, and store it in all variables; The calculation formula for the average volume fraction of acid in the calculation domain is: ;in, is the average volume fraction of acid in the calculation domain, For time The total volume of the acid in all grids in the digital model is is the total volume of all meshes in the digitized model.

6. The acid flow simulation method considering wall filtration and non-uniform dissolution according to claim 5 is characterized in that: The dynamic adjustment of the viscous resistance of the acid fluid according to the average volume fraction to reflect in real time the effect of changes in acid fluid concentration on the flow and dissolution behavior of the acid fluid in fractures and porous media includes: A dynamic adjustment model is established to dynamically adjust the viscous resistance of the acid according to the average volume fraction; The expression of the dynamic adjustment model is: ;in, is the viscous resistance of the current acid, is the viscous resistance of the initial acid solution, is the minimum viscous resistance after the acid is fully reacted.

7. The acid flow simulation method considering wall filtration and non-uniform dissolution according to claim 6 is characterized in that: The setting of the boundary conditions of the digital model, performing digital model initialization, numerical simulation calculation and post-processing includes: Boundary conditions include inlet conditions, outlet conditions and wall conditions of the digital model; The setting of inlet conditions includes setting the injection rate of acid solution and the injection volume fraction of acid solution; The setting of outlet conditions includes setting the gauge pressure value of outlet pressure to 0 and prohibiting backflow; The setting of the wall surface conditions includes setting the contact angle between the acid solution and the pre-fluid at the wall surface; Post-processing involves using post-processing software to analyze the simulation results after the numerical simulation calculation is completed.

8. An acid flow simulation device considering wall loss and non-uniform dissolution, characterized in that: include: The partitioning module is used to establish a digital model containing fractures and porous media, set perforation entrances and perform meshing; A determination module is used to select a VOF multiphase flow model based on the established digital model, select a viscosity model according to preset rules, and set the physical properties of the fluid phase and the surface tension coefficient between the fluid phases in the VOF multiphase flow model to determine the flow pattern of the fluid phase in the fracture and porous media; wherein the fluid phase includes acid and pre-pad fluid, and the physical properties of the fluid phase include density and viscosity; An acquisition module is used to set the porosity and viscous resistance of the fluid phase for the porous media in the digital model, traverse all grids in the digital model, and obtain the average volume fraction of the acid in the computational domain; the computational domain is the spatial range covered by the digital model; An adjustment module is used to dynamically adjust the viscous resistance of the acid according to the average volume fraction to reflect in real time the impact of changes in acid concentration on the flow and dissolution behavior of the acid in fractures and porous media; The setting module is used to set the boundary conditions of the digital model, perform digital model initialization, numerical simulation calculation and post-processing, and aims to simulate and analyze the non-uniform dissolution phenomenon of the crack wall.

9. An acid flow simulation server considering wall filtration and non-uniform dissolution, characterized in that: including memory and processor; The memory is used to store computer-executable instructions; The processor is configured to execute the computer-executable instructions to implement the method according to any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that The computer-readable storage medium stores executable instructions, and when a computer executes the executable instructions, the method according to any one of claims 1 to 7 can be implemented.

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