Acid flow simulation method and device considering wall filtration and non-uniform dissolution

Abstract

This application discloses a method and apparatus for simulating acid flow considering wall filtration loss and non-uniform dissolution, relating to the field of reservoir numerical simulation technology. A digital model incorporating fractures and porous media is established, with perforation inlets set and mesh generation performed. A VOF multiphase flow model is selected, and a viscous model is chosen according to preset rules to determine the flow behavior of the fluid phase in fractures and porous media. The porosity of the porous media and the viscous resistance of the fluid phase are set, and all meshes in the digital model are traversed to obtain the average volume fraction of acid in the computational domain. The viscous resistance of the acid is dynamically adjusted based on the average volume fraction to reflect the influence of acid concentration changes on the flow and dissolution behavior of acid in fractures and porous media in real time. Boundary conditions of the digital model are set, and digital model initialization, numerical simulation calculations, and post-processing are performed. This solves the problem of how to quantitatively analyze the distribution and changes of acid concentration and improve the efficiency and accuracy of the simulation.

Description

Technical Field

[0001] This application relates to the field of reservoir numerical simulation technology, and in particular to a method and apparatus for simulating acid flow that takes into account wall filtration loss and non-uniform dissolution. Background Technology

[0002] Carbonate reservoirs play a crucial role in global energy development due to their widespread distribution and vast reserves. However, their poor porosity and permeability, low pore-throat coordination, poor connectivity, and significant heterogeneity result in low oil and gas recovery rates. Acid fracturing has become a key method for improving carbonate reservoirs and enhancing production. Its principle is to use acid to dissolve the fracture walls, thereby increasing fracture conductivity. Currently, research on wall dissolution during acid fracturing primarily utilizes visual model experiments and computational fluid dynamics numerical simulations.

[0003] While visual model experiments are intuitive, they suffer from drawbacks such as long preparation periods, high costs, complex influencing factors, and low reproducibility of results. Furthermore, they lack quantitative analysis of acid concentration distribution and changes. Computational fluid dynamics numerical simulation methods can simulate chemical reactions, but they are computationally complex, computationally intensive, and time-consuming. They are also affected by complex geological features, leading to uncertainties in simulation results and failing to provide information on acid concentration distribution throughout the acid fracturing process.

[0004] Therefore, how to quantitatively analyze the distribution and changes of acid concentration, and improve the efficiency and accuracy of simulating non-uniform dissolution phenomena on crack walls, has become an urgent technical problem to be solved. Summary of the Invention

[0005] In this embodiment of the application, an acid flow simulation method that considers wall filtration and non-uniform erosion is provided, which solves the problem of how to quantitatively analyze the distribution and changes of acid concentration and improve the efficiency and accuracy of the simulation.

[0006] In a first aspect, embodiments of this application provide an acid flow simulation method considering wall filtration loss and non-uniform dissolution. The method includes: establishing a digital model encompassing cracks and porous media, setting perforation inlets, and meshing; based on the established digital model, selecting a VOF multiphase flow model, selecting a viscous model according to preset rules, and setting the physical properties of the fluid phases and the surface tension coefficients between fluid phases in the VOF multiphase flow model to determine the flow behavior of the fluid phases in cracks and porous media; wherein the fluid phases include acid and a pre-fluid, and the physical properties of the fluid phases include density and viscosity; for the porous media in the digital model, setting porosity and viscous resistance of the fluid phases, traversing all meshes in the digital model, and obtaining the average volume fraction of acid within the computational domain; wherein the computational 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 influence of acid concentration changes on the flow and dissolution behavior of acid in cracks and porous media; setting boundary conditions for the digital model, performing digital model initialization, numerical simulation calculations, and post-processing, aiming to simulate and analyze the non-uniform dissolution phenomenon of crack walls.

[0007] In one possible implementation, establishing a digital model including cracks and porous media, setting perforation inlets, and performing mesh generation includes: setting the porous media and cracks to be adjacent in the digital model, simplifying the cracks in the digital model to cracks of uniform width; performing mesh generation on the digital model, and determining the number of meshes required for the cracks and the number of meshes required for the porous media in the digital model; wherein, all meshes in the digital model are cubes; the formula for calculating the number of meshes required for the cracks in the digital model is: ;in, The number of meshes required for the crack is given by l, where l is the length of the digital model. The width of the crack. For the height of digital models, Let be 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, The required number of meshes for porous media. For the width of the digital model, denoted as the side length of the mesh in the porous medium.

[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 follows: ;in, Let Reynolds number be 1. The density of the acid solution. The viscosity of the acid solution. The injection rate of the acid solution. , To increase the acid injection rate, For the effective perforation height, , The diameter of the perforation hole. Number of perforations , The distance between the perforations. For the height of digital models, This refers to the phase angle.

[0010] In one possible implementation, for the porous medium in the digital model, setting the porosity and viscous resistance of the fluid phase, traversing all grids in the digital model, and obtaining the average volume fraction of acid in the computational domain includes: setting the porosity of the porous medium region and the viscous resistance of the pretreatment liquid as constants; setting a custom function to traverse all grids in the digital model, accumulating the volume of acid and the volume of the grids to obtain the average volume fraction of acid in the computational domain, and storing it in all variables; the formula for calculating the average volume fraction of acid in the computational domain is: ;in, This represents the average volume fraction of the acid solution within the computational domain. For time At that time, the total volume of acid in all grids of the digital model, This represents the total volume of all grids in the digital model.

[0011] In one possible implementation, the step of dynamically adjusting the viscous resistance of the acid solution based on the average volume fraction to reflect the influence of acid concentration changes on the flow and dissolution behavior of the acid solution in cracks and porous media in real time includes: establishing a dynamic adjustment model to dynamically adjust the viscous resistance of the acid solution based on the average volume fraction; the expression of the dynamic adjustment model is: ;in, The viscous resistance of the current acid solution, The initial viscous resistance of the acid solution. This represents the assumed minimum viscous resistance after the acid has fully reacted.

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

[0013] Secondly, embodiments of this application provide an acid flow simulation device considering wall filtration loss and non-uniform corrosion. The device includes: a meshing module for establishing a digital model containing cracks and porous media, setting perforation inlets, and performing mesh generation; and a determination module for selecting a VOF multiphase flow model based on the established digital model, selecting a viscous model according to preset rules, and setting the physical properties of the fluid phases and the surface tension coefficients between fluid phases in the VOF multiphase flow model to determine the flow characteristics of the fluid phases in cracks and porous media. The fluid phases include acid and a pre-fluid, and the physical properties of the fluid phases include density and viscosity. The acquisition module is used to set the porosity and viscous resistance of the fluid phase for porous media in the digital model, traverse all grids in the digital model, and obtain the average volume fraction of acid in the computational domain; where the computational 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, so as to reflect the influence of changes in acid concentration on the flow and dissolution behavior of acid in cracks and porous media in real time. The setting module is used to set the boundary conditions of the digital model, perform digital model initialization, numerical simulation calculation and post-processing, aiming to simulate and analyze the non-uniform dissolution phenomenon of crack walls.

[0014] Thirdly, embodiments of this application provide an acid flow simulation server that considers wall filtration and non-uniform corrosion, 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 of the first aspect.

[0015] Fourthly, embodiments of this application provide a computer-readable storage medium storing executable instructions, which, when executed by a computer, enable the method described in the first aspect or any possible implementation thereof.

[0016] The one or more technical solutions provided in this application embodiment have at least the following technical effects: This application embodiment provides an acid flow simulation method considering wall filtration loss and non-uniform dissolution. By establishing a digital model including fractures and porous media, and using the VOF multiphase flow model, combined with the acquisition of the average volume fraction of acid in the computational domain, it achieves accurate quantitative analysis of the concentration distribution and changes of acid in complex reservoir structures. It can clearly present the acid concentration at different locations and time periods. The method of dynamically adjusting the viscous resistance of acid based on the average volume fraction of acid avoids the complex calculation process in traditional simulation methods, reducing the computational load and time of numerical simulation. Dynamically adjusting the viscous resistance of acid to reflect the influence of acid concentration changes on the flow and dissolution behavior of acid in fractures and porous media in real time improves the consistency between simulation results and actual conditions, and enhances the reliability of simulation results. It solves the problem of how to quantitatively analyze the distribution and changes of acid concentration and improve the efficiency and accuracy of simulating non-uniform dissolution phenomena on fracture walls. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments of this application or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A flowchart of an acid flow simulation method considering wall filtration loss and non-uniform corrosion is provided for embodiments of this application;

[0019] Figure 2 A schematic diagram of a digital model provided in this application embodiment that does not simplify the cracks in the digital model into cracks of uniform width;

[0020] Figure 3 A schematic diagram of a digital model that simplifies cracks in a digital model into cracks of uniform width, provided for embodiments of this application;

[0021] Figure 4 This is a schematic diagram of the coupling zone between wall dissolution and pipe seepage provided in an embodiment of this application;

[0022] Figure 5 A schematic diagram of a digital model constructed for an embodiment of this application;

[0023] Figure 6 This is a schematic diagram of the mesh division result provided in an embodiment of this application;

[0024] Figure 7A schematic diagram of the boundary conditions of the digital model provided in the embodiments of this application;

[0025] Figure 8 This is a schematic diagram illustrating the initialization of a digital model as provided in an embodiment of this application.

[0026] Figure 9 A flow pattern of acid fingering at 50 s is provided for an embodiment of this application.

[0027] Figure 10 This application provides a non-uniform dissolution map of the crack wall at 1000s for an embodiment of the present application.

[0028] Figure 11 A comparison diagram of non-uniform dissolution at the crack entrance at different times provided in the embodiments of this application;

[0029] Figure 12 A comparison diagram of crack aperture at different times provided in the embodiments of this application;

[0030] Figure 13 A schematic diagram of an acid flow simulation device considering wall filtration loss and non-uniform corrosion provided in an embodiment of this application;

[0031] Figure 14 This is a schematic diagram of an acid flow simulation server that considers wall filtration loss and non-uniform dissolution, provided as an embodiment of this application. Detailed Implementation

[0032] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0033] The following description of some technologies involved in the embodiments of this application is provided to aid understanding and should be considered merely exemplary. Therefore, those skilled in the art should recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this application. Similarly, for clarity and brevity, some descriptions of well-known functions and structures are omitted in the following description.

[0034] This application provides an acid flow simulation method that considers wall filtration loss and non-uniform dissolution, such as... Figure 1 As shown, the method includes steps S101 to S105. Wherein, Figure 1This is merely one execution order shown in the embodiments of this application and does not represent the only execution order for an acid flow simulation method that considers wall filtration and non-uniform dissolution. Where the final result can be achieved, Figure 1 The steps shown can be performed in parallel or in reverse order.

[0035] S101: Establish a digital model containing cracks and porous media, set perforation inlets, and perform mesh generation.

[0036] A digital model containing cracks and porous media is established, perforation inlets are set, and mesh generation is performed, including the following steps.

[0037] In the digital model, the porous medium and cracks are assumed to be adjacent, and the cracks in the digital model are simplified to cracks of uniform width. The digital model is then meshed to determine the required number of meshes for the cracks and the porous medium. The meshes in the digital model are all cubes.

[0038] Figure 2 This is a schematic diagram of a digital model provided in an embodiment of this application that does not simplify the cracks in the digital model to cracks of uniform width. Figure 2 In this context, l represents the length of the digital model. The width of the crack. For the height of digital models, This represents the width of the digital model. The blue arrows in the diagram indicate the direction of acid injection. Acid leaching occurs during flow, and the diagram shows the direction of leaching, where the acid penetrates the crack wall and etches it. The width of the crack needs further explanation. This is an idealized description of a regular geometric model, representing the crack opening. In actual working conditions, cracks often exhibit irregular shapes, and their width distribution along the wall surface shows significant spatial non-uniformity. However, to simplify the model and reduce computational complexity, this application simplifies the cracks in the digital model to uniformly wide cracks and uses a regular cuboid geometry to represent them. This simplification method captures the main characteristics of dissolution while ensuring computational efficiency.

[0039] Figure 3 This is a schematic diagram of a digital model that simplifies cracks in a digital model into cracks of uniform width, as provided in an embodiment of this application. Figure 3The irregular crack walls were simplified into uniformly wide cracks, and the crack zone, porous media zone, inlet and outlet of the crack zone, and filtration outlet of the porous media zone were marked. During the simulation, it was assumed that acid was injected into the crack at a uniform velocity along the crack opening, and changes in crack length and height during the simulation were not considered. To further determine the number of meshes in the digital model and the number of simulation iterations, any crack-matrix section of the digital model could be extracted.

[0040] Figure 4 This is a schematic diagram of the coupling zone between wall dissolution and pipe seepage provided in an embodiment of this application. Figure 4 (a) in the diagram is a partition diagram in the initial state. Figure 4 (b) in the diagram shows the zoning after wall erosion. To address the coupling effect between wall erosion and pipe flow seepage, a specific zoning method was used to divide the network into different permeability zones. The yellow grid areas represent pipe flow zones, and the blue grid areas represent seepage zones.

[0041] Figure 5 This is a schematic diagram of a digital model constructed for an embodiment of this application. This application uses WorkbenchDesign Modeler (a modeling software) to perform modeling, generating a digital model as shown below. Figure 5 As shown, Figure 5 In (a), the green cuboid in the middle represents the crack, and the blue and gray cuboids on both sides of the crack represent the porous medium. To distinguish different areas, Workbench Design Modeler automatically sets different areas to different colors. At the same time, to facilitate the display and observation of the crack area, the porous medium is made transparent. Figure 5 Figure (b) shows a schematic diagram of the perforation inlet in the digital model. The red area represents the perforation inlet, the green area represents the fracture, and the blue and gray areas on either side of the fracture represent the porous medium. Five perforations are uniformly distributed at the acid inlet in this application. This uniform distribution of perforations helps improve the uniformity of the acid solution, making it easier for the acid to penetrate all areas of the reservoir, thereby maximizing the acidizing effect and preventing excessive concentration of acid in certain localized areas, which could lead to uneven etching and unnecessary damage to the reservoir.

[0042] After establishing the digital model, it needs to be discretized. The purpose of discretization is to ensure the accuracy and efficiency of numerical calculations. This application uses the Meshing mesh generator built into Fluent (a computational fluid dynamics software). Based on the length, width, and height parameters of the digital model, the size of the mesh cells is defined by adjusting the dimensions. According to the shape of the digital model, an appropriate mesh generation method is selected. Mesh generation methods include Automatic, Tetrahedrons, HexDominant, and Sweep. Among them, the Automatic method automatically selects the optimal mesh generation strategy based on geometric features, which is suitable for simple geometric models without special requirements on mesh type. Therefore, this application uses the Automatic method for mesh generation. Figure 6 This is a schematic diagram of the mesh division result provided in an embodiment of this application. Figure 6 The blue and gray areas represent porous media, while the green area in the middle represents cracks. This grid division lays the foundation for subsequent numerical simulation calculations.

[0043] Furthermore, the formula for calculating the number of meshes required for cracks in the digital model is as follows: .in, The number of meshes required for the crack is given by l, where l is the length of the digital model. The width of the crack. For the height of digital models, Let be the side length of the crack mesh. The formula for calculating the required number of meshes for porous media in a digital model is: .in, The required number of meshes for porous media. For the width of the digital model, denoted as the side length of the mesh in the porous medium.

[0044] Specifically, when meshing cracked and porous media, different side lengths can be selected respectively. and and allow This means that the side length of the crack mesh can be smaller than that of the porous medium mesh. This is because cracks typically have relatively narrow spaces with small widths. To more accurately capture the flow characteristics of acid within cracks, a smaller mesh side length is required. To delineate the crack area.

[0045] S102: Based on the established digital model, the VOF multiphase flow model is selected, and a viscous model is chosen according to preset rules. The physical properties of the fluid phases and the surface tension coefficients between fluid phases in the VOF multiphase flow model are then set to determine the flow characteristics of the fluid phases in cracked and porous media. The fluid phases include acid and pre-fluid, and the physical properties of the fluid phases include density and viscosity.

[0046] Specifically, after importing the meshed digital model into Fluent, a multiphase flow model was selected. Considering the surface tension and viscous force interaction requirements between the acid and the pre-fluid, the VOF multiphase flow model was chosen because it can accurately capture the interface characteristics of the acid and the pre-fluid, making it suitable for simulating the fingering phenomenon and wall dissolution process in this application.

[0047] The preset rules include the following: Calculate the Reynolds number. Determine if 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.

[0048] Specifically, the critical Reynolds number is .

[0049] The formula for calculating the Reynolds number is: .in, Let Reynolds number be 1. The density of the acid solution. The viscosity of the acid solution. The injection rate of the acid solution. , To increase the acid injection rate, For the effective perforation height, , The diameter of the perforation hole. Number of perforations , The distance between the perforations. For the height of digital models, This refers to the phase angle.

[0050] Specifically, perforation aperture Much smaller than the height of a digital model Acid injection displacement The unit is m 3 / min. Acid injection rate. The unit is m / s. Given that the acid mainly occurs in the fracture region, the characteristic length is taken as twice the width of the fracture. .Right now .in, The characteristic length is denoted as .

[0051] Furthermore, given that acid flow mainly occurs in the crack region and has a high viscosity, the calculated Reynolds number is usually much smaller than the critical Reynolds number. Therefore, the laminar flow model is chosen as the viscous model.

[0052] Specifically, the path to set the physical properties of the fluid phase in Fluent is: Materials → Fluid → CreatMaterials. The path to set the surface tension coefficient between fluid phases in Fluent is: Models → VOF → Phase Interaction → Surface Tension Coefficient.

[0053] S103: For 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 acid in the computational domain. The computational domain is the spatial extent covered by the digital model.

[0054] For porous media in the digital model, 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 acid in the computational domain, including the following.

[0055] The porosity of the porous media region and the viscous resistance of the pre-fluid are set as constants.

[0056] Specifically, acid fracturing simulations involve complex chemical reactions, fluid flows, and dissolution processes. By setting porosity and the viscous resistance of the pretreatment fluid as constants, additional dynamic variables can be avoided, thus improving computational efficiency.

[0057] Specifically, porosity is the ratio of pore volume to total volume in a porous medium, reflecting the matrix's storage capacity. The porosity setting path in Fluent is: Setup → Cell Zone Conditions → Fluid → Porous Zone → Porosity. The viscous resistance of the pre-fluid reflects the ease with which the pre-fluid flows in the porous medium. The viscous resistance setting path in Fluent is: Setup → Cell Zone Conditions → Fluid → Phase → Porous Zone → Viscous Resistance.

[0058] Set a custom function to iterate through all the grids in the digital model, sum the volume of the acid solution and the volume of the grids to obtain the average volume fraction of the acid solution in the computational domain, and store it in all variables.

[0059] The formula for calculating the average volume fraction of acid within the computational domain is as follows: .in, This represents the average volume fraction of the acid solution within the computational domain. For time At that time, the total volume of acid in all grids of the digital model, This represents the total volume of all grids in the digital model.

[0060] Specifically, the concentration of the acid decreases during the reaction, leading to changes in the acid's viscosity and viscous resistance. By calculating the average volume fraction of the acid within the computational domain, the concentration distribution of the acid can be reflected, thereby allowing for dynamic adjustment of the acid's viscous resistance.

[0061] Specifically, the path to set custom functions in Fluent is: User-Defined → Functions → Interpreted UDFs, which reads the custom function. The path to set the viscous resistance of acid in Fluent is: Setup → Cell Zone Conditions → Fluid → Phase → Porous Zone → Viscous Resistance → UDF.

[0062] It should be noted that the total volume of all grids in the digital model It remains unchanged during the simulation.

[0063] S104: The viscosity resistance of the acid solution is dynamically adjusted 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 solution in cracks and porous media.

[0064] The viscosity resistance of the acid solution is dynamically adjusted 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 solution in cracks and porous media, including the following.

[0065] A dynamic adjustment model was established to dynamically adjust the viscous resistance of the acid solution based on the average volume fraction.

[0066] The expression for the dynamically adjusted model is: .in, The viscous resistance of the current acid solution, The initial viscous resistance of the acid solution. This represents the assumed minimum viscous resistance after the acid has fully reacted.

[0067] Specifically, when the concentration of the acid solution is high ( When approaching 1), the viscous resistance of the acid solution is close to its initial value. When the concentration of the acid solution decreases ( When the viscosity of the acid decreases, the viscous resistance of the acid gradually decreases, and the interaction between the reacting acid molecules weakens.

[0068] Specifically, the viscous resistance of the acid solution can also be called the reverse absolute permeability. Since the viscous resistance in Fluent mainly describes the resistance characteristics of porous media, the formula for calculating the minimum viscous resistance after the acid solution has fully reacted is as follows: .in, This refers to permeability. The matrix permeability increases after the acid has fully reacted. Taking dolomite matrix as an example, the permeability range is... to When the matrix permeability is The assumed minimum viscous resistance after the acid has fully reacted is .

[0069] Furthermore, the above process can be implemented using user-defined functions (UDFs). This includes the `DEFINE_EXECUTE_AT_END(excecute_at_end)` function, which is executed at the end of each time step to calculate the average volume fraction of the acid solution. By traversing all grids in the digital model, and summing the volumes of the acid and the grids, the calculation is performed. It also includes the `DEFINE_PROFILE(vis_res,thread,position)` function, which is executed at each time step when the boundary conditions of the digitized model are updated, dynamically adjusting the viscous drag of the acid solution based on the average volume fraction of the acid solution in the current mesh. And a dynamic adjustment model is used to calculate and update the viscous resistance of the acid solution.

[0070] S105: Set the boundary conditions for the digital model, perform digital model initialization, numerical simulation calculations, and post-processing.

[0071] Setting boundary conditions for the digital model, performing digital model initialization, numerical simulation calculations, and post-processing, including the following:

[0072] Boundary conditions include the entry conditions, exit conditions, and wall conditions of the digital model.

[0073] Setting the inlet conditions includes setting the acid injection rate and the acid injection volume fraction.

[0074] Specifically, the acid injection rate can be set in Fluent via: Setup→BoundaryConditions→Inlet. The acid injection volume fraction can be set in Fluent via: Setup→BoundaryConditions→Inlet→Phase. The acid volume fraction is set according to the ratio of acid to pretreatment solution. If no ratio is specified, the default acid injection volume fraction is 1.

[0075] The outlet conditions are set by setting the gauge pressure of the outlet pressure to 0 and prohibiting backflow.

[0076] Specifically, the outlet conditions are set in Fluent via the following path: Setup → Boundary Conditions → Outlet → Gauge Pressure. Set the outlet gauge pressure to 0. This indicates that the outlet is connected to the external atmospheric pressure. Disabling backflow prevents the fluid phase from flowing back from the outlet into the computational domain.

[0077] Setting the wall conditions includes setting the contact angle between the acid and the pretreatment solution at the wall.

[0078] Specifically, the path to set wall conditions in Fluent is Setup→Boundary Conditions→Wall→Wall Adhesion→Contact Angles. This sets the contact angle between the acid and the pretreatment solution at the wall. This indicates the wettability of the reaction fluid phase on the wall surface. If no experimental data is available, the default value of 165° can be used.

[0079] Digital model initialization and numerical simulation calculations, including the following.

[0080] To set the solution method, go to Solution → Methods and select SIMPLE.

[0081] To set the spatial discretization method, go to Solution → Methods and select Second Ordre Upwind.

[0082] Configure the sub-relaxation factor in the solution controls via the path: Solution → Controls. Here, you can set the pressure, density, and momentum parameters to make the calculation converge more easily.

[0083] To set the absolute criteria for convergence in the residual monitor, the path is: Solution→Monitors→Residual.

[0084] Configure solution data export, such as exporting a CDAT for CFD-Post&EnSight (cdat) file of volume fraction (sy).

[0085] Set the number of calculation steps and the time step.

[0086] Determine whether the calculation results converge.

[0087] Specifically, Fluent calculates the mass and momentum conservation equations in the model and automatically monitors the residual values ​​of each equation. The calculation converges when the residual value drops to a specified residual threshold, which is typically [value missing]. to .

[0088] Post-processing includes using post-processing software to analyze the simulation results after the numerical simulation calculations are completed.

[0089] 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 reality, the model parameters can be adjusted and the simulation can be rerun. The simulation results should show non-uniform dissolution phenomena on the crack walls. If no non-uniform dissolution or even no dissolution phenomenon occurs, the simulation results are considered unrealistic, and the model needs to be adjusted and the simulation repeated.

[0090] Specifically, the post-processing software can be CFD Post. The path to import the cdat file from the last time step is: File → Load Results File → cdat file. The path to set the transparency of the digitized model is: Render → Transparency. The path to set the resolution is: Insert Volum → Volum Rendering → Resolution.

[0091] The following example illustrates the above content of this application. Of course, other examples are also possible, and this application is not limited to this example.

[0092] Figure 5 A digital model was used to simulate the flow and dissolution process of acid in fractures and porous media. An inlet with five perforations was selected to simulate the multi-perforation injection scenario in actual acid fracturing operations. Complex surface morphology of the fractures (such as the roughness of natural fractures) was omitted to simplify calculations and highlight the main physical processes. The digital model is 150m long, 30m high, and 30.01m wide. The width of the fracture is 0.01m. The side length of the fracture mesh is 0.01m (consistent with the fracture width). The side length of the porous media mesh is 0.05m. Based on the calculation formulas for the number of meshes required for the fractures and porous media in the digital model, the total number of meshes was calculated to be 1.54 million. The total number of meshes is the sum of the number of meshes required for the fractures and the number of meshes required for the porous media. The meshing results are as follows: Figure 6 As shown, the crack mesh is dense, while the porous medium mesh is sparse.

[0093] Figure 7A schematic diagram of the boundary conditions of the digital model provided in an embodiment of this application. Figure 7 As you can see, a blue arrow at the inlet indicates the injection of acid. The inlet condition should be set to the acid injection rate. At the same time, the physical properties of the acid solution need to be specified, and the density of the acid solution is... The viscosity of the acid solution is In fluid phase simulation, parameters such as the volume fraction of the acid solution also need to be set. The Reynolds number calculated using the Reynolds number formula is 12.1, which is much smaller than... Furthermore, the acid flow rate in this application is low, the viscosity is high, and the acid fingering phenomenon is present. Therefore, this application selects the laminar flow model as the viscous model. Figure 7 A red arrow at the outlet indicates fluid loss. The outlet condition is typically set to static pressure; for example, setting the gauge pressure to 0 indicates the outlet is connected to atmospheric pressure. Simultaneously, to prevent fluid from flowing back into the computational domain from the outlet, a backflow prevention condition needs to be set. The wall condition is set to a 165° contact angle between the acid and the pre-fluid at the wall.

[0094] Acid fingering refers to the irregular, finger-like advance of acid at its front end when flowing through porous media or cracks due to the viscosity difference between the acid and the precursor fluid. Fingering can still occur in laminar flow models, affecting acid distribution and dissolution. Numerical simulations require appropriate multiphase flow models (such as the VOF multiphase flow model) to capture the acid-precursor interface and accurately simulate fingering and its impact on wall dissolution.

[0095] Figure 8 This is a schematic diagram illustrating the initialization of a digital model as provided in an embodiment of this application. Figure 8 In this context, Sy represents acid solution, Sy.Volume Fraction represents the volume fraction of acid solution, and Volume Rendering 1 represents volume rendering. Figure 8 The figure shows the volume fraction of acid under initial conditions. It can be seen from the figure that the inlet is filled with acid under initial conditions.

[0096] Figure 9 The diagram shows the acid fingering flow pattern at 50 seconds, as provided in this embodiment of the application. At 50 seconds, a clear fingering phenomenon can be observed, with the inlet width increasing compared to the initial value. This indicates that the acid has etched the inlet within 50 seconds.

[0097] Figure 10This image shows the non-uniform etching of the crack wall at 1000 s, provided for an embodiment of this application. It clearly shows significant non-uniform etching at the crack entrance. With continuous acid injection, distinct etching paths formed along the entrances of the five perforations. These paths extended along the crack and gradually evolved into five irregular etching channels.

[0098] Figure 11 A comparison diagram of non-uniform dissolution at the crack entrance at different times, provided for embodiments of this application. Figure 11 (a) in the figure is a diagram of non-uniform dissolution at the crack entrance at 200s. Figure 11 Figure (b) shows the non-uniform dissolution at the crack inlet at 1000 s. As can be seen from the figure, the dissolution at the crack inlet gradually intensifies and exhibits significant non-uniformity over time. The overall width of the crack inlet increases significantly, especially at the locations corresponding to the five clusters of inlets, where dissolution is more intense, forming obvious localized expansion areas. The figure at 200 s shows that the non-uniform dissolution at the inlet is already taking shape, exhibiting early characteristics of the five clusters of etching paths. At 1000 s, the dissolution at the five clusters of inlets further develops, with the etching paths becoming wider and more irregular, indicating a significant increase in acid flow and dissolution rate in these areas.

[0099] It should be noted that all entrances in this application are entrances to perforations.

[0100] Figure 12 A comparison diagram of crack opening at different times provided in the embodiments of this application. Figure 12 (a) in the diagram shows the crack opening at 200s. Figure 12 (b) shows the crack aperture at 1000 s. The crack aperture at 200 s indicates that the increase in crack aperture is mainly concentrated near the entrance, reflecting the spatial limitation of the initial etching. At 1000 s, the crack aperture increases significantly and shows a trend of extension along the crack depth. Simultaneously, the crack wall aperture exhibits a non-uniform expansion trend starting from the entrance. Therefore, it can be concluded that the extension of the etching path is not limited to the entrance but extends into the crack interior, forming a complex channel structure.

[0101] This application also provides an acid flow simulation device 1300 that considers wall filtration loss and non-uniform corrosion, 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.

[0102] The meshing module 1301 is used to create a digital model containing cracks and porous media, set perforation inlets, and perform mesh generation.

[0103] The determination module 1302 is used to select a VOF multiphase flow model based on the established digital model, select a viscous model according to preset rules, and set the physical properties of the fluid phases and the surface tension coefficients between the fluid phases in the VOF multiphase flow model, in order to determine the flow law of the fluid phases in cracks and porous media. The fluid phases include acid and pre-fluid, and the physical properties of the fluid phases include density and viscosity.

[0104] 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 acid in the computational domain. The computational domain is the spatial extent covered by the digital model.

[0105] The adjustment module 1304 is used to dynamically adjust the viscosity resistance of the acid solution according to the average volume fraction, so as to reflect in real time the influence of changes in acid concentration on the flow and dissolution behavior of the acid solution in cracks and porous media.

[0106] 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 on the crack wall.

[0107] Some modules in the apparatus described in this application can be described in the general context of computer-executable instructions that are executed by a computer, such as program modules. Generally, program modules include routines, programs, objects, components, data structures, classes, etc., that perform a specific task or implement a specific abstract data type. This application can also be practiced in distributed computing environments where tasks are performed by remote processing devices connected via a communication network. In distributed computing environments, program modules can reside in local and remote computer storage media, including storage devices.

[0108] The apparatus or module described in the above embodiments can be implemented by a computer chip or physical entity, or by a product with a certain function. For ease of description, the above apparatus is described by dividing it into various modules according to their functions. When implementing the embodiments of this application, the functions of each module can be implemented in one or more 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.

[0109] The methods, apparatus, or modules described in this application can be implemented in a computer-readable program code manner. The controller can be implemented in any suitable manner, for example, as 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, application-specific integrated circuits (ASICs), programmable logic controllers, and embedded microcontrollers. Examples of controllers include, but are not limited to, the following microcontrollers: ARC 625D, Atmel AT91SAM, Microchip PIC18F26K20, and Silicon Labs C8051F320. A memory controller can also be implemented as part of the control logic of a memory. Those skilled in the art will also recognize that, in addition to implementing the controller in purely computer-readable program code manner, the same functionality can be achieved by logically programming the method steps to make the controller take the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, such a controller can be considered a hardware component, and the means included within it for implementing various functions can also be considered as structures within the hardware component. Alternatively, the device used to implement various functions can be viewed as either a software module that implements the method or a structure within a hardware component.

[0110] like Figure 14 As shown, this application embodiment also provides an acid flow simulation server that considers wall filtration loss and non-uniform corrosion, 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 considering wall filtration loss and non-uniform corrosion described above in this application embodiment.

[0111] This application also provides a computer-readable storage medium storing executable instructions. When a computer executes the executable instructions, it can implement the acid flow simulation method considering wall filtration and non-uniform corrosion described above in this application.

[0112] As can be seen from the above description of the embodiments, those skilled in the art can clearly understand that this application can be implemented by means of software plus necessary hardware. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product, or it can be embodied in the process of data migration. The computer software product can be stored in a storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, mobile terminal, server, or network device, etc.) to execute the methods described in the embodiments of this application.

[0113] The various embodiments described in this specification are presented in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on its differences from other embodiments. All or part of this application can be used in numerous general-purpose or special-purpose computer system environments or configurations.

[0114] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A method for simulating acid flow considering wall filtration loss and non-uniform dissolution, characterized in that, include: A digital model incorporating cracks and porous media was established, perforation inlets were set, and mesh generation was performed. Based on the established digital model, the VOF multiphase flow model was selected, the viscosity model was selected according to the preset rules, and the physical properties of the fluid phase and the surface tension coefficient between the fluid phases in the VOF multiphase flow model were set to determine the flow law of the fluid phase in cracks and porous media; wherein, the fluid phase includes acid and pre-fluid, and the physical properties of the fluid phase include density and viscosity. For porous media in the digital model, 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 acid in the computational domain; where the computational domain is the spatial range covered by the digital model. The viscosity resistance of the acid solution is dynamically adjusted 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 solution in cracks and porous media. The boundary conditions of the digital model are set, and the digital model is initialized, numerical simulation calculations are performed, and post-processing is carried out, with the aim of simulating and analyzing the non-uniform dissolution phenomenon on the crack wall. The process of establishing a digital model containing fractures and porous media, setting perforation inlets, and meshing includes: defining the porous media and fractures as adjacent in the digital model; simplifying the fractures in the digital model to uniform width; meshing the digital model; and determining the required number of meshes for the fractures and porous media in the digital model. The meshes in the digital model are all cubes. The formula for calculating the required number of meshes for the fractures in the digital model is as follows: ;in, The number of meshes required for the crack is given by l, where l is the length of the digital model. The width of the crack. For the height of digital models, Let be 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, The required number of meshes for porous media. For the width of the digital model, Let be the side length of the mesh in the porous medium; The method of dynamically adjusting the viscous resistance of the acid solution based on the average volume fraction to reflect the influence of acid concentration changes on the flow and dissolution behavior of the acid solution in cracks and porous media includes: establishing a dynamic adjustment model to dynamically adjust the viscous resistance of the acid solution based on the average volume fraction; the expression of the dynamic adjustment model is: ;in, The viscous resistance of the current acid solution, The initial viscous resistance of the acid solution. This represents the assumed minimum viscous resistance after the acid has fully reacted.

2. The acid flow simulation method considering wall filtration loss and non-uniform dissolution according to claim 1, 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 chosen as the viscous model; If the Reynolds number is less than or equal to the critical Reynolds number, the laminar flow model is selected as the viscous model.

3. The acid flow simulation method considering wall filtration loss and non-uniform dissolution according to claim 2, characterized in that, The formula for calculating the Reynolds number is: ;in, The Reynolds number is... The density of the acid solution. The viscosity of the acid solution. The injection rate of the acid solution. , To adjust the acid injection rate, For the effective perforation height, , The diameter of the perforation hole. Number of perforations , The distance between the perforations. For the height of digital models, This refers to the phase angle.

4. The acid flow simulation method considering wall filtration loss and non-uniform corrosion according to claim 3, characterized in that, For porous media in the digital model, 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 acid in the computational domain, including: The porosity of the porous media region and the viscous resistance of the pre-fluid are set as constants; Set a custom function to traverse all grids in the digital model, accumulate the volume of acid and the volume of the grids to obtain the average volume fraction of acid in the computational domain, and store it in all variables; The formula for calculating the average volume fraction of acid within the computational domain is as follows: ;in, This represents the average volume fraction of the acid solution within the computational domain. For time At that time, the total volume of acid in all grids of the digital model, This represents the total volume of all grids in the digital model.

5. The acid flow simulation method considering wall filtration loss and non-uniform corrosion according to claim 4, characterized in that, The process of setting boundary conditions for the digital model, initializing the digital model, performing numerical simulation calculations, and post-processing includes: Boundary conditions include the entry conditions, exit conditions, and wall conditions of the digital model; Setting the inlet conditions includes setting the acid injection rate and the acid injection volume fraction; The outlet conditions are set by setting the gauge pressure of the outlet pressure to 0 and prohibiting backflow; Setting the wall conditions includes setting the contact angle between the acid and the pretreatment solution at the wall surface; Post-processing includes using post-processing software to analyze the simulation results after the numerical simulation calculations are completed.

6. An acid flow simulation device considering wall filtration loss and non-uniform dissolution, characterized in that, include: The meshing module is used to create a digital model containing cracks and porous media, set perforation inlets, and perform mesh generation. The determination module is used to select the VOF multiphase flow model based on the established digital model, select the 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 law of the fluid phase in cracks and porous media; wherein, the fluid phase includes acid and pre-fluid, and the physical properties of the fluid phase include density and viscosity. The acquisition module is used to set the porosity and viscous resistance of the fluid phase for porous media in the digital model, traverse all grids in the digital model, and obtain the average volume fraction of acid in the computational domain; where the computational domain is the spatial range covered by the digital model. The adjustment module is used to dynamically adjust the viscosity resistance of the acid solution based on the average volume fraction, so as to reflect in real time the influence of changes in acid concentration on the flow and dissolution behavior of the acid solution in cracks and porous media. The configuration 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 on the crack wall. The process of establishing a digital model containing fractures and porous media, setting perforation inlets, and meshing includes: defining the porous media and fractures as adjacent in the digital model; simplifying the fractures in the digital model to uniform width; meshing the digital model; and determining the required number of meshes for the fractures and porous media in the digital model. The meshes in the digital model are all cubes. The formula for calculating the required number of meshes for the fractures in the digital model is as follows: ;in, The number of meshes required for the crack is given by l, where l is the length of the digital model. The width of the crack. For the height of digital models, Let be 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, The required number of meshes for porous media. For the width of the digital model, Let be the side length of the mesh in the porous medium; The method of dynamically adjusting the viscous resistance of the acid solution based on the average volume fraction to reflect the influence of acid concentration changes on the flow and dissolution behavior of the acid solution in cracks and porous media includes: establishing a dynamic adjustment model to dynamically adjust the viscous resistance of the acid solution based on the average volume fraction; the expression of the dynamic adjustment model is: ;in, The viscous resistance of the current acid solution, The initial viscous resistance of the acid solution. This represents the assumed minimum viscous resistance after the acid has fully reacted.

7. A server for simulating acid flow considering wall filtration loss 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 1-5.

8. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores executable instructions, which, when executed by a computer, enable the implementation of the method as described in any one of claims 1-5.

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