Numerical simulation method and system for carbonate rock acid fracturing crack corrosion form prediction

Abstract

The embodiment of the invention provides a numerical simulation method and system for carbonate rock acid fracturing fracture corrosion form prediction, and belongs to the field of acid fracturing reservoir transformation. The method comprises the following steps: S10) carrying out natural fracture generation in a geological model based on a statistical distribution model; s20) obtaining in-crack pressure and crack width distribution based on fluid-solid coupling, and obtaining a dynamic expansion form of the acid fracturing crack in the acid fracturing process; s30) judging whether the acid fracturing fracture is further expanded or not based on the dynamic expansion form of the acid fracturing fracture in the acid fracturing process and the critical expansion condition of the fracture tip, and determining the interaction between the natural fracture and the acid fracturing fracture through the Mohr-Coulomb criterion during further expansion to obtain the expansion path and form of the acid fracturing fracture; and (S40) in the fracturing process, the steps (S20)-(S30) are repeatedly executed, and the real-time acid fracturing crack extension path and form are obtained till fracturing is completed. According to the scheme, a more reliable theoretical basis is provided for design and optimization of the carbonate rock acid fracturing process.

Description

Technical Field

[0001] This invention relates to the field of acid fracturing reservoir stimulation, specifically to a numerical simulation method for predicting the dissolution morphology of acid fracturing fractures in carbonate rocks and a numerical simulation system for predicting the dissolution morphology of acid fracturing fractures in carbonate rocks. Background Technology

[0002] In the development of carbonate oil and gas reservoirs, acid fracturing is a commonly used production enhancement measure. It involves injecting acid at pressures higher than the rock fracture pressure, causing the fractures to expand under the influence of the acid, thereby increasing the permeability of oil and gas. However, carbonate reservoirs are often characterized by strong heterogeneity, low porosity, low permeability, and well-developed natural fractures, which poses significant challenges to the control and optimization of the acid fracturing process.

[0003] Currently, the main research methods for fracture propagation and dissolution morphology during acid fracturing of carbonate rocks, both domestically and internationally, are laboratory simulation and numerical simulation. Laboratory simulation relies on rock slab experiments, which, while allowing direct observation of fracture propagation, are limited by experimental conditions and cannot accurately reproduce the acid fracturing process under formation conditions. On the other hand, numerical simulation primarily uses two-dimensional fracture propagation models, such as the PKN and KGD models, to simulate fracture extension and dissolution during acid fracturing. These models can reflect fracture propagation trends to some extent, but due to the complex coupling process of fracture propagation and acid dissolution, existing models typically calculate these two processes step-by-step, lacking real-time coupled simulation capabilities. This makes it difficult to accurately predict fracture morphology during actual acid fracturing operations.

[0004] Existing numerical simulation methods typically do not adequately account for the random distribution of natural fractures and their interaction with hydraulic fractures. In actual construction, natural fractures can significantly alter the flow path and dissolution efficiency of acid, affecting the final morphology and conductivity of the acid-etched fractures. Therefore, existing numerical simulation methods still have limitations in predicting fracture propagation and dissolution morphology, making it difficult to provide effective guidance for acid fracturing design of carbonate rocks under complex geological conditions.

[0005] In summary, existing technologies lack real-time coupled calculations of crack propagation and acid dissolution processes, and do not adequately consider the interaction between natural and hydraulic cracks, thus limiting the accurate prediction and optimized design of carbonate rock acid fracturing processes. Summary of the Invention

[0006] The purpose of this invention is to provide a numerical simulation method and system for predicting the dissolution morphology of acid-pumped fractures in carbonate rocks, so as to at least solve the problems of existing technologies lacking real-time coupled calculation of fracture propagation and acid dissolution processes, and not fully considering the interaction between natural fractures and hydraulic fractures.

[0007] To achieve the above objectives, the first aspect of the present invention provides a numerical simulation method for predicting the dissolution morphology of acid-fracturing fractures in carbonate rocks, the method comprising: S10) Construct a geological model of the region to be calculated, and generate natural fractures in the geological model based on a statistical distribution model; S20) Based on fluid-structure interaction simulation of acid-firing fracture propagation process, the pressure and width distribution within the fracture are obtained, and the fracture width distribution is adjusted under the action of acid dissolution to obtain the dynamic propagation morphology of acid-firing fracture during acid-firing process; S30) Based on the dynamic propagation morphology of acid-pneumatic fractures during acid-pneumatic process and the critical propagation conditions at the fracture tip, it is determined whether the acid-pneumatic fractures will propagate further. When they propagate further, the interaction between the natural fractures and the acid-pneumatic fractures is determined by the Mohr-Coulomb criterion, and the propagation path and morphology of the acid-pneumatic fractures are obtained. S40) During the fracturing process, repeat steps S20)-S30) to obtain the real-time acid fracturing fracture propagation path and morphology until fracturing is completed.

[0008] Optionally, constructing the geological model of the area to be calculated includes: Collect geological data of the area to be calculated, and construct a three-dimensional geological model of the area based on the geological data; Mesh the 3D geological model to discretize a continuous geological region into multiple meshes; Based on the geological data corresponding to each grid, attributes are assigned to each grid cell to obtain a geological model of the area to be calculated.

[0009] Optionally, the generation of natural fractures in the geological model based on the statistical distribution model includes: The azimuth angle of the natural crack is generated based on the Fisher distribution, and the length of the corresponding natural crack is generated based on the normal distribution. Within the grid area of ​​the geological model, the starting points of natural fractures are randomly distributed, and corresponding natural fractures are generated based on the azimuth and length of the natural fractures.

[0010] Optionally, the step of simulating the propagation process of acid-pneumatic fractures based on fluid-structure interaction to obtain the pressure and width distribution within the fracture includes: executing an acid flow equilibrium model within the fracture based on the initial fracture width distribution to obtain the corresponding flow pressure; using the fluid pressure as input to the displacement discontinuity equation to obtain the fracture width distribution under coupled solid deformation; using the fracture width distribution as input to the acid flow equilibrium model within the fracture; iterating the acid flow equilibrium model and the acid flow equilibrium model within the fracture using the Newton-Raphson method until the difference between the fracture width distributions obtained from two consecutive iterations is less than a first preset difference threshold, and the corresponding fracture width distribution is taken as the hydraulic fracture width at that moment, and the corresponding pressure is taken as the fluid pressure within the fracture.

[0011] Optionally, the acid flow equilibrium model within the crevice is:

[0012]

[0013] in, This refers to the width of the acid-poured crack. This refers to the filtration rate; This refers to the volumetric flow rate within the slit; Let K be the injection flow rate of the k-crack. Let k be the coordinates of the injection point in the crack; μ is the dynamic viscosity of the liquid.

[0014] Optionally, the displacement discontinuity model is:

[0015] in, The fluid pressure inside the seam; The pressure of the fluid inside the gap is N; N is the total number of elements. This refers to the width of the acid-poured crack. It is an integral function.

[0016] Optionally, the integration function is:

[0017] in, To a rectangular unit (such as) Figure 1 Source The distance, m; For spatial points With the source The distance is expressed as: .

[0018] Optionally, adjusting the fracture width distribution under acid dissolution to obtain the dynamic propagation morphology of the acid-pneumatic fracture during the acid-pneumatic process includes: executing an acid concentration distribution model based on the fracture width distribution to obtain the concentration within the fracture, and executing a fracture width change model caused by acid dissolution of the fracture surface based on the concentration within the fracture to obtain the corresponding dissolution fracture width; executing an acid flow equilibrium model within the fracture based on the dissolution fracture width to obtain the pressure within the fracture corresponding to the dissolution fracture width; executing a displacement discontinuity equation based on the dissolution fracture width to obtain a new pressure within the fracture, and using the Newton-Raphson iteration method to iterate the generation process of the pressure within the fracture until the difference between the pressures within the fracture obtained from two consecutive iterations is not greater than a second difference threshold, thereby obtaining the fracture width distribution under the coupled flow-solid deformation-chemical reaction condition, and using the corresponding fracture width as the dynamic propagation morphology of the acid-pneumatic fracture during the acid-pneumatic process.

[0019] Optionally, the acid concentration distribution model is:

[0020] in, Crack point ( Pressure at point ) Formation pressure; For matrix permeability; The apparent viscosity of the fluid; The thickness of the rock slab.

[0021] Optionally, the model for the change in crack width caused by acid etching is as follows:

[0022] in, The solubility of acids; Porosity; This is the coefficient of the reaction between the filtered acid and the crack wall; For the thickness of the filter band; The density of the acid solution; This represents the density of the rock.

[0023] Optionally, the determination of whether the acid-poured fracture should further propagate based on the dynamic propagation morphology of the fracture during the acid-pouring process and the critical propagation conditions at the fracture tip includes: The corresponding critical expansion joint width is calculated based on the critical expansion joint width calculation model. The relationship between the crack tip mesh width and the critical propagation width in the dynamic propagation morphology of acid-poured cracks during the acid-pouring process is used to determine whether the acid-poured cracks will propagate further; among which, If the width of the grid at the crack tip is greater than the critical expansion crack width, the acid fracturing crack is determined to have expanded further; conversely, if the width of the grid at the crack tip is not greater than the critical expansion crack width, the acid fracturing crack is determined not to have expanded further.

[0024] Optionally, the critical expansion seam width calculation model is as follows:

[0025] Where w is the critical expansion slit width; This is a scaling factor. Dimensionless spatial coordinates represent a certain location; Parameters are preset under specific conditions; Coefficients related to crack propagation conditions; It is the deformation factor.

[0026] Optionally, determining the interaction between natural fractures and acid-fracturing fractures using the Mohr-Coulomb criterion to obtain the propagation path and morphology of the acid-fracturing fractures includes: The shear stress, frictional resistance, and cohesion of acid-fracturing cracks in natural fractures are determined based on the Mohr-Coulomb criterion. If the shear stress on a natural crack is greater than the sum of the frictional resistance and the cohesion of the crack, it is determined that the acid-poured crack extends along the natural crack. Conversely, if the shear stress on a natural crack is not greater than the sum of the frictional resistance and the cohesion of the natural crack, it is determined that the acid-poured crack has penetrated the natural crack. The determination result is used as the propagation path of the acid-pneumatic fracture, and the dynamic propagation morphology of the acid-pneumatic fracture during the acid-pneumatic process is used as the morphology of the acid-pneumatic fracture.

[0027] A second aspect of this invention provides a numerical simulation system for predicting the dissolution morphology of acid-pneumatic fractures in carbonate rocks. The system includes: a model building unit for constructing a geological model of the area to be calculated and generating natural fractures in the geological model based on a statistical distribution model; a simulation unit for simulating the propagation process of acid-pneumatic fractures based on fluid-structure interaction, obtaining the pressure and width distribution within the fracture, and adjusting the width distribution under acid dissolution to obtain the dynamic propagation morphology of the acid-pneumatic fractures during the acid-pneumatic process; a fracture propagation unit for determining whether the acid-pneumatic fractures should further propagate based on the dynamic propagation morphology of the acid-pneumatic fractures during the acid-pneumatic process and the critical propagation conditions at the fracture tip, and determining the interaction between the natural fractures and the acid-pneumatic fractures when further propagation occurs, thereby obtaining the propagation path and morphology of the acid-pneumatic fractures; and a looping unit for repeatedly obtaining the real-time propagation path and morphology of the acid-pneumatic fractures during the fracturing process until fracturing is completed.

[0028] A third aspect of the present invention provides a computer-readable storage medium storing instructions that, when executed on a computer, cause the computer to perform the above-described numerical simulation method for predicting the dissolution morphology of acid-pressure fractures in carbonate rocks.

[0029] A fourth aspect of the present invention provides an electronic device, the electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the numerical simulation method for predicting the dissolution morphology of acid-pressure fractures in carbonate rocks as described above.

[0030] The fifth aspect of the present invention provides a computer program product, including a computer program that, when executed by a processor, implements a numerical simulation method for predicting the dissolution morphology of acid-pressure fractures in carbonate rocks as described above.

[0031] Through the above technical solution, this invention constructs a geological model and randomly generates natural fractures within the model to accurately reflect the fracture distribution under actual geological conditions. Then, fluid-structure interaction is used to simulate the propagation process of acid-fracturing fractures, dynamically adjusting fracture width and pressure distribution to achieve dynamic prediction of fracture propagation under acid dissolution. Based on the critical conditions at the fracture tip, it determines whether the acid-fracturing fracture will continue to propagate, and the Mohr-Coulomb criterion is used to determine the interaction between natural fractures and acid-fracturing fractures, thereby accurately simulating the propagation path and morphology of acid-fracturing fractures. By repeatedly executing the propagation and judgment steps, the state of fracture propagation is updated in real time, providing accurate predictions of fracture propagation and dissolution morphology during acid fracturing, offering a more reliable theoretical basis for the design and optimization of carbonate rock acid fracturing processes.

[0032] Other features and advantages of the embodiments of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0033] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a flowchart of the steps of a numerical simulation method for predicting the dissolution morphology of acid-fracturing fractures in carbonate rocks, provided by one embodiment of the present invention. Figure 2 This is a schematic diagram of rectangular cell data provided in one embodiment of the present invention; Figure 3 This is a schematic diagram of crack propagation and dissolution morphology provided in one embodiment of the present invention; Figure 4 This is a system structure diagram of a numerical simulation system for predicting the dissolution morphology of acid-pressure fractures in carbonate rocks, provided by one embodiment of the present invention. Detailed Implementation

[0034] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0035] Figure 1 This is a flowchart of a numerical simulation method for predicting the dissolution morphology of acid-fracturing fractures in carbonate rocks, provided by one embodiment of the present invention. Figure 1 As shown, this invention provides a numerical simulation method for predicting the dissolution morphology of acid-fracturing fractures in carbonate rocks, the method comprising: Step S10: Construct a geological model of the region to be calculated, and generate natural fractures in the geological model based on a statistical distribution model.

[0036] Specifically, the construction of the geological model of the region to be calculated includes: collecting geological data of the region to be calculated, and constructing a three-dimensional geological model of the region to be calculated based on the geological data; performing mesh generation on the three-dimensional geological model to discretize the continuous geological region into multiple meshes; and assigning attributes to each mesh unit based on the geological data corresponding to each mesh to obtain the geological model of the region to be calculated.

[0037] In this embodiment of the invention, detailed geological data of the area to be calculated is collected. This data typically includes parameters such as rock type, porosity, permeability, bedding, fault distribution, and the development of natural fractures, which can be obtained through methods such as drilling, seismic exploration, and core analysis. This data provides fundamental support for subsequent model construction. Based on the collected data, a three-dimensional geological model of the area to be calculated is established. Professional modeling software (such as Petrel or GOCAD) is used to visualize the spatial location, structural characteristics, and physical properties of each stratum in three dimensions, making the model as close as possible to the actual geological conditions.

[0038] Furthermore, after establishing a preliminary 3D geological model, the model is meshed, discretizing the continuous geological region into multiple mesh units. The fineness of the mesh is usually adjusted according to the required computational accuracy and available computational resources. Numerical methods such as the finite element method and finite difference method are used to divide the 3D model into multiple small units to facilitate independent calculation and solution of each region in the numerical simulation. A finer mesh can capture more subtle geological changes and provide higher simulation accuracy, but it also increases the computational burden. Based on the geological data corresponding to each mesh, each mesh unit is assigned corresponding physical properties. For example, parameters such as porosity, permeability, rock density, and elastic modulus are interpolated or averaged according to the original geological data, so that each mesh unit has geological characteristics that conform to the actual strata. By assigning properties, the mesh units can more accurately represent different regions in actual geology.

[0039] Based on the present invention, accurate initial and boundary conditions can be provided for subsequent acid fracturing fracture propagation and dissolution simulation, making the simulation closer to the actual geological environment, ensuring more accurate prediction of fracture propagation and dissolution morphology during acid fracturing, and providing reliable technical support for the design and optimization of acid fracturing process.

[0040] Specifically, the generation of natural fractures in the geological model based on the statistical distribution model includes: generating the azimuth angle of the natural fractures based on the Fisher distribution and generating the length of the corresponding natural fractures based on the normal distribution; randomly distributing the starting points of natural fractures within the grid area of ​​the geological model and generating the corresponding natural fractures based on the azimuth angle and length of the natural fractures.

[0041] In this embodiment of the invention, the azimuth angle of natural fractures is generated using the Fisher distribution. The Fisher distribution is a statistical model suitable for describing directional data and can be used to simulate the directionality of natural fractures in geological environments. This method can derive the azimuth angle distribution characteristics of fractures based on statistical data, thereby realistically reproducing the azimuth characteristics of natural fractures under actual geological conditions.

[0042] Next, the lengths of corresponding natural cracks are generated based on a normal distribution. The lengths of natural cracks vary considerably under different geological conditions, and the normal distribution can be used to simulate the randomness and variability of these lengths. By setting the mean and standard deviation of the crack lengths, a series of natural cracks with different lengths but conforming to geological patterns can be obtained, making the crack generation process more representative and realistic.

[0043] In one possible implementation, the azimuth (β) and length (l) of the natural crack can be described by Fisher distribution and normal distribution, with the generation rule being:

[0044] In the formula, γ represents the angle between the natural fracture zone and the horizontal wellbore (°); R is a random number between 0 and 1. This is the deviation coefficient; The average length of a natural crack, in meters; Let m be the standard deviation of length. 2 .

[0045] After generating the azimuth and length, the origins of natural fractures are randomly distributed within the grid area of ​​the geological model. This randomness in the fracture origins better simulates the distribution of fractures in nature, avoiding overly regular or concentrated distributions in the model. Based on the generated azimuth and length, natural fractures are drawn starting from each origin, forming a fracture network that conforms to actual geological characteristics.

[0046] Based on the present invention, the distribution of natural fractures in actual formations can be accurately reflected, providing more accurate initial conditions for subsequent acid fracturing fracture propagation simulation. In acid fracturing fracture propagation simulation, the presence of natural fractures affects the flow path of the acid and the direction of fracture propagation, thus impacting the effectiveness of acid fracturing operations. Therefore, by using statistically distributed natural fractures, the interaction between natural and hydraulic fractures during acid fracturing can be better simulated, providing reliable numerical model support for acid fracturing process design and improving the accuracy and reliability of the simulation.

[0047] Step S20: Based on fluid-structure interaction simulation of acid-firing fracture propagation process, obtain the internal pressure and fracture width distribution, and adjust the fracture width distribution under acid dissolution to obtain the dynamic propagation morphology of acid-firing fracture during acid-firing process.

[0048] Specifically, the step of simulating the propagation process of acid-pneumatic fractures based on fluid-structure interaction to obtain the pressure and width distribution within the fracture includes: executing an acid flow equilibrium model within the fracture based on the initial fracture width distribution to obtain the corresponding flow pressure; using the fluid pressure as input to the displacement discontinuity equation to obtain the fracture width distribution under coupled solid deformation; using the fracture width distribution as input to the acid flow equilibrium model within the fracture; iterating the acid flow equilibrium model and the acid flow equilibrium model within the fracture using the Newton-Raphson method until the difference between the fracture width distributions obtained from two consecutive iterations is less than a first preset difference threshold, and the corresponding fracture width distribution is taken as the hydraulic fracture width at that moment, and the corresponding pressure is taken as the fluid pressure within the fracture.

[0049] In this embodiment of the invention, based on the initial fracture width distribution of the acid-pumped fracture, an acid flow equilibrium model is executed within the fracture to calculate the flow pressure of the fluid within the fracture. During acid fracturing, the flow pressure of the fluid within the fracture changes continuously as the fracture expands; therefore, it is necessary to accurately solve the flow equilibrium equation within the fracture to reflect the flow characteristics of the fluid under different fracture width conditions. This flow equilibrium model uses Poiseuille's laminar flow equation to calculate the flow pressure within the fracture, thereby obtaining the fluid pressure distribution under the initial state.

[0050] Furthermore, a displacement discontinuity model based on flow pressure is used to calculate the fracture width distribution under coupled solid deformation. Acid flow within the fracture exerts pressure on the rock strata, causing deformation. The displacement discontinuity model simulates the width variation of the fracture under external pressure, yielding the fracture width distribution under coupled solid deformation. This step achieves fluid-structure interaction calculations by coupling the mechanical deformation of the fracture with fluid flow, thus obtaining a fracture morphology closer to actual formation conditions.

[0051] Furthermore, after obtaining the crack width distribution under coupled solid deformation, it is necessary to determine whether the difference between this distribution and the initial crack width distribution satisfies the convergence condition, i.e., whether it is less than a first preset difference threshold. If the difference is not less than the preset threshold, it indicates that the crack morphology has not yet stabilized. In this case, the crack width distribution under coupled solid deformation is used as the new initial crack width distribution, and the acid flow equilibrium model within the crack is re-executed. This process iterates multiple times, gradually adjusting the crack width distribution until the crack width distribution and fluid pressure reach equilibrium.

[0052] Furthermore, the iteration process ends when the difference between the fracture width distribution under coupled solid deformation and the initial fracture width distribution is less than a preset difference threshold. The fracture width distribution obtained at this point can be considered as the fracture width distribution under steady-state conditions, and the flow pressure corresponding to this distribution is the determined intra-fracture pressure. This fluid-structure interaction iterative solution method ensures accurate calculation of fracture morphology and intra-fracture pressure during acid fracturing, making the simulation results more consistent with actual formation conditions.

[0053] Based on the scheme of this invention, the fluid-structure interaction simulation method effectively combines the interaction between fluid flow and rock deformation, and can more accurately simulate the fracture propagation behavior during acid fracturing. Secondly, through iterative convergence calculation, it ensures that the fracture morphology and pressure distribution reach an equilibrium state at each time step, thereby improving the accuracy of the simulation. Finally, the obtained intra-fracture pressure and fracture width distribution provide key parameter references for acid fracturing design and provide a theoretical basis for optimizing the acid fracturing process of carbonate reservoirs.

[0054] Specifically, the acid flow equilibrium model within the crevice is as follows:

[0055]

[0056] in, This refers to the width of the acid-poured crack. This refers to the filtration rate; This refers to the volumetric flow rate within the slit; Let K be the injection flow rate of the k-crack. Let k be the coordinates of the injection point in the crack; μ is the dynamic viscosity of the liquid.

[0057] like Figure 2 Based on the Crouch 3D boundary element method, for a planar 3D crack, the two shear displacement discontinuities of the crack element are zero, and only the normal displacement discontinuity exists; the width of each rectangular element is constant. According to the superposition principle, the displacement discontinuity equation corresponding to the crack width under pressure for each rectangular element is further obtained from the geometric and physical equations:

[0058] in, The fluid pressure inside the seam; The pressure of the fluid inside the gap is N; N is the total number of elements. This refers to the width of the acid-poured crack. It is an integral function.

[0059] The integral function is:

[0060] in, To a rectangular unit (such as) Figure 1 Source The distance, m; For spatial points With the source The distance is expressed as: .

[0061] Substitute the pressure P0 into the above model to obtain the gap width W1. If W1-W0 is less than the specified error value ε, the iteration ends. Otherwise, substitute W1 into the flow equation and repeat the above iteration steps until Wn-Wn-1 is less than or equal to the specified error value ε0. This gives the gap width Wt=t0 and the fluid pressure Pt=t0 in the gap corresponding to the mesh element under fluid-structure interaction conditions.

[0062] Furthermore, the step of adjusting the fracture width distribution under acid dissolution to obtain the dynamic propagation morphology of acid-pneumatic fractures during acid fracturing includes: executing an acid concentration distribution model based on the fracture width distribution to obtain the concentration within the fracture, and executing a fracture width change model caused by acid dissolution of the fracture surface based on the concentration within the fracture to obtain the corresponding dissolution fracture width; executing an acid flow equilibrium model within the fracture based on the dissolution fracture width to obtain the intra-fracture pressure corresponding to the dissolution fracture width; executing a displacement discontinuity equation based on the dissolution fracture width to obtain a new intra-fracture pressure, and using the Newton-Raphson iteration method to iteratively iterate the generation process of intra-fracture pressure until the difference between the intra-fracture pressures obtained from two consecutive iterations is not greater than a second difference threshold, thereby obtaining the fracture width distribution under coupled flow-solid deformation-chemical reaction conditions, and using the corresponding fracture width as the dynamic propagation morphology of acid-pneumatic fractures during acid fracturing.

[0063] In this embodiment of the invention, based on the current crack width distribution, an acid concentration distribution model is executed to calculate the acid concentration within the crack. The concentration distribution of the acid within the crack directly affects the dissolution rate; therefore, the acid concentration distribution model can determine the concentration changes of the acid at different locations on the crack wall, thereby reflecting the diffusion characteristics of the acid within the crack. This step, by calculating the concentration field within the crack, provides fundamental data for the subsequent acid dissolution process.

[0064] Furthermore, after obtaining the acid concentration within the crack, a model is executed based on this concentration distribution to calculate the crack width change caused by acid dissolution of the crack surface, thus obtaining the corresponding dissolution crack width. The dissolution effect of the acid gradually expands the crack width, causing the crack to form a non-uniform dissolution morphology. This step, through the dissolution model, links the acid concentration with the crack width change, thereby determining the crack expansion morphology under the action of acid, such as... Figure 3 This provides a model for crack propagation and dissolution.

[0065] Furthermore, based on the fracture width, an acid flow equilibrium model within the fracture is executed to calculate the intra-fracture pressure corresponding to that width. As the fracture dissolves and expands, the increase in fracture width will alter the flow resistance and pressure distribution of the fluid within the fracture. Therefore, it is necessary to recalculate the flow equilibrium model to obtain the intra-fracture pressure under the current fracture width conditions. This step reflects the impact of acid dissolution on the fluid flow characteristics within the fracture and is crucial for achieving fluid-solidification coupling.

[0066] Furthermore, when the difference between the intra-crack pressure corresponding to the dissolution crack width and the intra-crack pressure obtained from the fluid-structure interaction simulation of acid fracturing crack propagation exceeds a second preset difference threshold, it indicates that the current intra-crack pressure has not reached equilibrium. In this case, the displacement discontinuity model is re-executed based on the intra-crack pressure corresponding to the dissolution crack width to calculate the crack width distribution under coupled solid deformation. This step couples the fluid pressure within the crack with the solid deformation of the rock to more accurately reflect the influence of acid dissolution on crack propagation. Fluid-structure interaction calculations are performed based on the crack width distribution under coupled solid deformation to obtain the crack width corresponding to each grid cell under fluid-structure interaction conditions, and this is used as the dynamic propagation morphology of the acid fracturing crack during the acid fracturing process. This dynamic iterative calculation method allows for real-time updates of the crack propagation morphology under acid dissolution.

[0067] Based on the scheme of this invention, the combination of dissolution model and fluid-structure interaction enables simultaneous simulation of acid dissolution and fracture propagation, making the changes in fracture morphology more closely resemble actual formation conditions. Secondly, by dynamically adjusting the acid concentration and flow pressure within the fracture, it ensures that realistic fluid pressure distribution and fracture morphology are obtained at each time step, significantly improving the accuracy of the simulation. Finally, this technology can accurately predict the dynamic propagation of acid fracturing fractures in complex formation environments, providing reliable data support for the design and optimization of acid fracturing processes, and contributing to improved stimulation effects in carbonate reservoirs.

[0068] Specifically, the acid concentration distribution model is as follows:

[0069] in, Crack point ( Pressure at point ) Formation pressure; For matrix permeability; The apparent viscosity of the fluid; The thickness of the rock slab.

[0070] Furthermore, the model for the change in crack width caused by acid etching is as follows:

[0071] in, The solubility of acids; Porosity; This is the coefficient of the reaction between the filtered acid and the crack wall; For the thickness of the filter band; The density of the acid solution; This represents the density of the rock.

[0072] Step S30: Based on the dynamic propagation morphology of the acid-pneumatic fracture during the acid-pneumatic process and the critical propagation conditions at the fracture tip, determine whether the acid-pneumatic fracture will propagate further. If it propagates further, determine the interaction between the natural fracture and the acid-pneumatic fracture using the Mohr-Coulomb criterion to obtain the propagation path and morphology of the acid-pneumatic fracture.

[0073] Specifically, the method of determining whether an acid-poured fracture should further extend based on the dynamic propagation morphology of the fracture during acid pressing and the critical propagation condition at the fracture tip includes: calculating the corresponding critical propagation fracture width based on a critical propagation fracture width calculation model; determining whether the acid-poured fracture should further extend by comparing the size relationship between the fracture tip mesh width corresponding to the dynamic propagation morphology of the acid-poured fracture during acid pressing and the critical propagation fracture width; wherein, if the fracture tip mesh width is greater than the critical propagation fracture width, it is determined that the acid-poured fracture has further extended; conversely, if the fracture tip mesh width is not greater than the critical propagation fracture width, it is determined that the acid-poured fracture has not further extended.

[0074] In this embodiment of the invention, the critical propagation fracture width is calculated using a critical propagation fracture width calculation model. The critical propagation fracture width refers to the minimum fracture width required for the fracture tip to continue propagating under specific geological and mechanical conditions. This critical value is typically calculated based on a comprehensive analysis of factors such as the mechanical properties of the formation rocks and the surrounding stress field, ensuring that the simulation of acid fracturing fracture propagation conforms to actual formation conditions.

[0075] Furthermore, after obtaining the critical propagation width, the current width of the crack tip mesh during acid fracturing is compared with this critical value to determine whether the conditions for continued propagation are met. Specifically, if the crack tip mesh width is greater than the critical propagation width, the crack tip is considered to have the conditions for further propagation, and the acid fracturing crack will continue to propagate in that direction; conversely, if the crack tip mesh width is not greater than the critical propagation width, it indicates that the current stress and crack width at the crack tip are insufficient to support its continued propagation, and the propagation of the acid fracturing crack will stop.

[0076] Based on the present invention, the propagation state of fractures during acid fracturing can be determined in real time, and the propagation path and morphology of acid-fracturing fractures can be precisely controlled by combining the dynamic morphology of the fracture tip. The ability to dynamically determine the propagation state of fractures based on the actual conditions at the fracture tip effectively avoids over- or under-propagation, improving the accuracy of acid fracturing fracture propagation simulation. Ultimately, the obtained fracture propagation morphology better conforms to the actual mechanical behavior of formations, providing scientific theoretical support for acid fracturing design of carbonate reservoirs, helping to optimize fracture morphology and improve the modification effect of acid fracturing processes.

[0077] Specifically, the calculation model for the critical expansion seam width is as follows:

[0078] Where w is the critical expansion slit width; This is a scaling factor. Dimensionless spatial coordinates represent a certain location; Parameters are preset under specific conditions; Coefficients related to crack propagation conditions; It is the deformation factor.

[0079] Specifically, determining the interaction between natural fractures and acid-poured fractures using the Mohr-Coulomb criterion to obtain the propagation path and morphology of the acid-poured fractures includes: determining the shear stress, frictional resistance, and cohesion of the acid-poured fractures based on the Mohr-Coulomb criterion; if the shear stress of the natural fracture is greater than the sum of the frictional resistance and cohesion of the natural fracture, the acid-poured fracture is determined to propagate along the natural fracture; conversely, if the shear stress of the natural fracture is not greater than the sum of the frictional resistance and cohesion of the natural fracture, the acid-poured fracture is determined to pass through the natural fracture; the determination result is used as the propagation path of the acid-poured fracture, and the dynamic propagation morphology of the acid-poured fracture during the acid-poured process is used as the morphology of the acid-poured fracture.

[0080] In this embodiment of the invention, the shear stress, frictional resistance, and cohesion of the acid-fracturing fracture are determined based on the Mohr-Coulomb criterion. The Mohr-Coulomb criterion is a widely used failure criterion in rock mechanics; it assesses the shear stress, frictional resistance, and cohesion of the rock to determine whether it will slide or fracture. During acid fracturing, these mechanical parameters play a crucial role in determining the fracture propagation path when hydraulic fractures encounter natural fractures.

[0081] Furthermore, after obtaining these mechanical parameters, it is determined whether the shear stress of the natural crack is greater than the sum of its frictional resistance and crack cohesion. Specifically, if the shear stress on the natural crack exceeds the sum of frictional resistance and cohesion, it indicates that the natural crack is prone to shear slip at that location, and the acid fracturing crack will extend along the direction of the natural crack. In this case, the natural crack becomes the extension path of the acid fracturing crack, which is conducive to the further extension of the crack in the weak area of ​​the natural crack, thus improving the conductivity of the acid fracturing operation.

[0082] Conversely, if the shear stress of a natural fracture does not exceed the sum of its frictional resistance and cohesion, the natural fracture will not slip, and the acid fracturing fracture will choose to extend through the natural fracture at that location. This means that the acid fracturing fracture spontaneously opens new paths in the formation, rather than extending along the natural fracture. In this way, new fracture propagation paths can be achieved in areas of higher stress, thereby increasing the coverage of the fracture network.

[0083] Based on the scheme of this invention, the influence of natural fractures on acid fracturing fractures is accurately simulated using the Mohr-Coulomb criterion, which can more realistically reflect the fracture propagation behavior under actual formation conditions. Secondly, this method can dynamically adjust the propagation path of acid fracturing fractures, enabling the fracture network to achieve better conductivity in areas with well-developed natural fractures, thereby enhancing reservoir permeability. Finally, by rationally controlling the fracture propagation path, acid fracturing construction design can be optimized, improving the stimulation effect of carbonate reservoirs and providing a more efficient solution for oil and gas field development.

[0084] Step S40: During the fracturing process, repeat steps S20-S30 to obtain the real-time acid fracturing fracture propagation path and morphology until fracturing is completed.

[0085] In this embodiment of the invention, step S20 involves simulating the propagation process of acid-pumped fractures based on fluid-structure interaction. This is achieved by solving the coupling equations of fluid pressure, fracture width, and solid deformation to dynamically obtain the fracture propagation state and pressure distribution within the fracture. Step S30 further determines whether the fracture tip has reached the critical condition for propagation, thus determining whether the fracture should continue to propagate. The Mohr-Coulomb criterion is used to simulate the interaction between natural fractures and acid-pumped fractures, thereby determining the fracture propagation path and morphology. Through the cyclic execution of these two steps, the simulation can capture the dynamic propagation of the fracture and the acid dissolution process in real time, allowing the fracture to continuously adjust its propagation direction and morphology during acid fracturing.

[0086] In each iteration, the morphology of acid-fracturing fractures is influenced by the combined effects of acid dissolution, formation stress distribution, and natural fracture structure, thus continuously updating in a dynamic process. This allows acid-fracturing fractures to not only extend into more complex geometries but also form more efficient flow channels within the formation, enhancing oil and gas permeability. By repeatedly executing steps S20-S30, the complete fracture propagation path and morphology throughout the fracturing process are ultimately obtained, providing dynamic and accurate model support for acid fracturing operations.

[0087] Based on the scheme of this invention, by updating the propagation path and morphology of acid fracturing fractures in real time, the simulation results can more closely approximate the acid fracturing behavior in actual formations, providing high-precision guidance for the construction process. Secondly, the iterative calculation method ensures the adaptability of fracture propagation, meaning that the acid fracturing fractures can adjust their paths according to real-time formation and fluid conditions, thereby achieving better stimulation effects in complex carbonate reservoirs. Finally, this real-time coupled calculation not only optimizes fracture propagation paths and improves the production enhancement effect of acid fracturing, but also provides more practical data support for subsequent oil and gas field development.

[0088] Figure 4 This is a system structure diagram of a numerical simulation system for predicting the dissolution morphology of acid-fracturing fractures in carbonate rocks, provided in one embodiment of the present invention. Figure 4 As shown, this invention provides a numerical simulation system for predicting the dissolution morphology of acid-pumped fractures in carbonate rocks. The system includes: a model building unit for constructing a geological model of the area to be calculated and generating natural fractures in the geological model based on a statistical distribution model; a simulation unit for simulating the propagation process of acid-pumped fractures based on fluid-structure interaction, obtaining the pressure and width distribution within the fracture, and adjusting the width distribution under acid dissolution to obtain the dynamic propagation morphology of the acid-pumped fractures during the acid-pumping process; a fracture propagation unit for determining whether the acid-pumped fractures should further propagate based on the dynamic propagation morphology of the acid-pumped fractures during the acid-pumping process and the critical propagation conditions at the fracture tip, and determining the interaction between the natural fractures and the acid-pumped fractures when further propagation occurs, thereby obtaining the propagation path and morphology of the acid-pumped fractures; and a looping unit for repeatedly obtaining the real-time propagation path and morphology of the acid-pumped fractures during the fracturing process until fracturing is completed. A third aspect of the present invention provides a computer-readable storage medium storing instructions that, when executed on a computer, cause the computer to perform the above-described numerical simulation method for predicting the dissolution morphology of acid-pressure fractures in carbonate rocks.

[0089] A fourth aspect of the present invention provides an electronic device, the electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the numerical simulation method for predicting the dissolution morphology of acid-pressure fractures in carbonate rocks as described above.

[0090] The fifth aspect of the present invention provides a computer program product, including a computer program that, when executed by a processor, implements a numerical simulation method for predicting the dissolution morphology of acid-pressure fractures in carbonate rocks as described above.

[0091] Those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware. This program is stored in a storage medium and includes several instructions to cause a microcontroller, chip, or processor to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as a USB flash drive, a portable hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0092] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details described above. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention. It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the embodiments of the present invention will not further describe the various possible combinations.

[0093] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the embodiments of the present invention, they should also be regarded as the content disclosed by the embodiments of the present invention.

Claims

1. A numerical simulation method for predicting the dissolution morphology of acid-fracturing fractures in carbonate rocks, characterized in that, The method includes: S10) Construct a geological model of the region to be calculated, and generate natural fractures in the geological model based on a statistical distribution model; S20) Based on fluid-structure interaction simulation of acid-firing fracture propagation process, the pressure and width distribution within the fracture are obtained, and the fracture width distribution is adjusted under the action of acid dissolution to obtain the dynamic propagation morphology of acid-firing fracture during acid-firing process; S30) Based on the dynamic propagation morphology of acid-pneumatic fractures during acid-pneumatic process and the critical propagation conditions at the fracture tip, it is determined whether the acid-pneumatic fractures will propagate further. When they propagate further, the interaction between the natural fractures and the acid-pneumatic fractures is determined by the Mohr-Coulomb criterion, and the propagation path and morphology of the acid-pneumatic fractures are obtained. S40) During the fracturing process, repeat steps S20)-S30) to obtain the real-time acid fracturing fracture propagation path and morphology until fracturing is completed.

2. The method according to claim 1, characterized in that, The construction of the geological model of the region to be calculated includes: Collect geological data of the area to be calculated, and construct a three-dimensional geological model of the area based on the geological data; Mesh the 3D geological model to discretize a continuous geological region into multiple meshes; Based on the geological data corresponding to each grid, attributes are assigned to each grid cell to obtain a geological model of the area to be calculated.

3. The method according to claim 1, characterized in that, The generation of natural fractures in the geological model based on the statistical distribution model includes: The azimuth angle of the natural crack is generated based on the Fisher distribution, and the length of the corresponding natural crack is generated based on the normal distribution. Within the grid area of ​​the geological model, the starting points of natural fractures are randomly distributed, and corresponding natural fractures are generated based on the azimuth and length of the natural fractures.

4. The method according to claim 1, characterized in that, The method for simulating the propagation process of acid-pneumatic fractures based on fluid-structure interaction to obtain the intra-fracture pressure and fracture width distribution includes: Based on the initial fracture width distribution of the acid-pumped fracture, an acid flow equilibrium model within the fracture is executed to obtain the corresponding flow pressure. By using the fluid pressure as input to the displacement discontinuity equation, the slit width distribution under coupled solid deformation is obtained; The crack width distribution is used as the input of the acid flow equilibrium model within the crack; the acid flow equilibrium model within the crack and the acid flow equilibrium model are iterated using the Newton-Raphson method until the difference between the crack width distributions obtained from the two iterations is less than a first preset difference threshold. The crack width distribution obtained is taken as the hydraulic crack width at that moment, and the pressure obtained is taken as the fluid pressure within the crack.

5. The method according to claim 4, characterized in that, The equilibrium model for acid flow within the crevice is as follows: in, This refers to the width of the acid-poured crack. This refers to the filtration rate; The volumetric flow rate within the slit; Let K be the injection flow rate of the crack. Let the coordinates of the injection point for crack k be given. μ represents the dynamic viscosity of the liquid.

6. The method according to claim 4, characterized in that, The displacement discontinuity model is as follows: in, The fluid pressure inside the seam; The fluid pressure inside the seam; N is the total number of units; This refers to the width of the acid-poured crack. It is an integral function.

7. The method according to claim 6, characterized in that, The integral function is: in, To reach the source point of the rectangular cell (as shown in Figure 1) The distance, m; For spatial points With the source The distance is expressed as: 。 8. The method according to claim 1, characterized in that, The method of adjusting the crack width distribution under acid dissolution to obtain the dynamic propagation morphology of acid-poured cracks during acid fracturing includes: Based on the crack width distribution, an acid concentration distribution model is executed to obtain the concentration within the crack. Based on the concentration within the crack, a crack width change model caused by acid dissolution of the crack surface is executed to obtain the corresponding dissolution crack width. Based on the width of the dissolution fracture, an acid flow balance model is executed within the fracture to obtain the pressure within the fracture corresponding to the width of the dissolution fracture. Based on the aforementioned dissolution fracture width, the displacement discontinuity equation is executed to obtain a new fracture pressure. The generation process of the fracture pressure is iterated cyclically using the Newton-Raphson iteration method until the difference between the fracture pressures obtained from two consecutive iterations is no greater than the second difference threshold. The fracture width distribution under the coupled flow-solid deformation-chemical reaction condition is then obtained, and the corresponding fracture width is taken as the dynamic expansion morphology of the acid-fusing fracture during the acid-fusing process.

9. The method according to claim 8, characterized in that, The acid concentration distribution model is as follows: in, Crack point ( Pressure at point ) Formation pressure; For matrix permeability; The apparent viscosity of the fluid; The thickness of the rock slab.

10. The method according to claim 8, characterized in that, The model for the change in crack width caused by acid etching is as follows: in, The solubility of acids; Porosity; This is the coefficient of the reaction between the filtered acid and the crack wall; The thickness of the filtration band; The density of the acid solution; This represents the density of the rock.

11. The method according to claim 1, characterized in that, The method for determining whether an acid-poured fracture should further propagate based on its dynamic propagation morphology and critical propagation conditions at the fracture tip during acid fracturing includes: The corresponding critical expansion joint width is calculated based on the critical expansion joint width calculation model. The relationship between the crack tip mesh width and the critical propagation width in the dynamic propagation morphology of acid-poured cracks during the acid-pouring process is used to determine whether the acid-poured cracks will propagate further; among which, If the width of the grid at the crack tip is greater than the critical expansion crack width, the acid fracturing crack is determined to have expanded further; conversely, if the width of the grid at the crack tip is not greater than the critical expansion crack width, the acid fracturing crack is determined not to have expanded further.

12. The method according to claim 11, characterized in that, The calculation model for the critical expansion gap width is as follows: Where w is the critical expansion slit width; This is the scaling factor. Dimensionless spatial coordinates represent a certain location; Parameters are preset under specific conditions; Coefficients related to crack propagation conditions; It is the deformation factor.

13. The method according to claim 1, characterized in that, The method of determining the interaction between natural fractures and acid-fracturing fractures using the Mohr-Coulomb criterion to obtain the propagation path and morphology of acid-fracturing fractures includes: The shear stress, frictional resistance, and cohesion of acid-fracturing cracks in natural fractures are determined based on the Mohr-Coulomb criterion. If the shear stress on a natural crack is greater than the sum of the frictional resistance and the cohesion of the crack, it is determined that the acid-poured crack extends along the natural crack. Conversely, if the shear stress on a natural crack is not greater than the sum of the frictional resistance and the cohesion of the natural crack, it is determined that the acid-poured crack has penetrated the natural crack. The determination result is used as the propagation path of the acid-pneumatic fracture, and the dynamic propagation morphology of the acid-pneumatic fracture during the acid-pneumatic process is used as the morphology of the acid-pneumatic fracture.

14. A numerical simulation system for predicting the dissolution morphology of acid-fracturing fractures in carbonate rocks, characterized in that, The system includes: The model building unit is used to build a geological model of the area to be calculated and to generate natural fractures in the geological model based on a statistical distribution model. The simulation unit is used to simulate the propagation process of acid-pneumatic fractures based on fluid-structure interaction, obtain the pressure and width distribution within the fracture, and adjust the width distribution under the action of acid dissolution to obtain the dynamic propagation morphology of acid-pneumatic fractures during the acid-pneumatic process. The crack propagation unit is used to determine whether the acid-pneumatic crack will propagate further based on the dynamic propagation morphology of the acid-pneumatic crack during the acid-pneumatic process and the critical propagation conditions at the crack tip. When it propagates further, the interaction between the natural crack and the acid-pneumatic crack is determined by the Mohr-Coulomb criterion to obtain the propagation path and morphology of the acid-pneumatic crack. The cyclic unit is used to repeatedly obtain the real-time acid fracturing fracture propagation path and morphology during the fracturing process until fracturing is completed.

15. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores instructions that, when executed on a computer, cause the computer to perform the numerical simulation method for predicting the dissolution morphology of acid-fracturing fractures in carbonate rocks as described in any one of claims 1-13.

16. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the numerical simulation method for predicting the dissolution morphology of acid-pressure fractures in carbonate rocks as described in any one of claims 1-13.

17. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by the processor, it implements the numerical simulation method for predicting the dissolution morphology of acid-fracturing fractures in carbonate rocks according to any one of claims 1-13.

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