Method and device for simplifying numerical well testing geologic model of fractured-vuggy reservoir

Abstract

The invention discloses a method and a device for simplifying a numerical well testing geological model of a fracture-vug type oil and gas reservoir. The method comprises the steps that according to the radius of a karst cave in the fracture-vug type oil and gas reservoir and the distance between the karst cave and a test well, the bottom hole pressure derivative sinking amplitude caused by the karst cave is determined according to the corresponding relation between the bottom hole pressure derivative sinking amplitude caused by the karst cave and the corresponding relation between the karst cave radius and the distance between the karst cave and the test well; the sinking amplitude of the bottom hole pressure derivative is the sinking amplitude of the lowest point in a double logarithmic curve of the bottom hole pressure derivative and time relative to a set bottom hole pressure derivative baseline; and in the process of establishing the numerical well testing geologic model of the well testing, deleting the karst cave of which the sinking amplitude caused by the bottom hole pressure derivative is smaller than a set sinking amplitude threshold value. According to the method, the concept of the sinking amplitude of the bottom hole pressure derivative caused by the karst caves is innovatively defined, the karst caves are screened on the basis of the concept, and reasonable simplification of the numerical well testing geologic model of the fracture-vug type oil and gas reservoir is achieved.

Description

Technical Field

[0001] This invention relates to the field of oil and gas reservoir development technology, and in particular to a simplified method and apparatus for numerical well testing geological models of fractured-vuggy oil and gas reservoirs. Background Technology

[0002] The main reservoir spaces of fracture-vuggy carbonate oil and gas reservoirs include tectonic fractures caused by structural deformation and pores, cavities, and fractures formed by karstification. Among these, large cavities are the most important reservoir spaces, while fractures serve as both the primary reservoir spaces and the main flow channels. Due to the presence of fractures and karst caves, fracture-vuggy carbonate oil and gas reservoirs are highly heterogeneous, posing significant challenges to the description of their reservoir characteristics.

[0003] Well testing is a method that uses high-precision pressure gauges to measure the response of bottom-hole pressure to changes in bottom-hole flow rate, and then calculates formation properties based on seepage mechanics theory. The curves showing the relationship between bottom-hole pressure, pressure derivative, and time in well testing are important characteristic curves for identifying reservoir features and calculating reservoir parameters. These curves are influenced by reservoir properties. In fractured-vuggy carbonate oil and gas reservoirs, the presence of fractures and caverns results in complex characteristics on the well testing curves. Furthermore, the irregularity and large number of fractures and caverns limit the application of analytical methods in well testing interpretation of fractured-vuggy carbonate oil and gas reservoirs. Numerical well testing, on the other hand, uses numerical methods to solve well testing models. Compared to conventional analytical well testing, numerical well testing has the advantage of handling complex flows and complex reservoirs. For example, the equations of nonlinear seepage problems cannot be solved analytically and can only be solved using numerical well testing techniques. Conventional analytical well testing can only handle regular boundaries such as circles and rectangles, while numerical well testing can handle arbitrary irregular boundaries. The aforementioned advantages of numerical well testing make it particularly effective in interpreting well test data from fractured-vuggy carbonate oil and gas reservoirs. The basic idea behind numerical well test interpretation is to establish a geological model using information on caverns and fractures identified from geological and seismic data. This model explicitly represents fractures and caverns, then performs mesh generation and numerical solution calculations to interpret the test data. However, actual reservoirs often contain numerous fractures and caverns. Including all of these in the model would make modeling difficult and significantly increase the computational load. Therefore, simplifying the geological model for numerical well testing in fractured-vuggy carbonate oil and gas reservoirs is a crucial technical problem that urgently needs to be solved. Summary of the Invention

[0004] To enrich the process routes and increase the selection space, this invention provides a method and apparatus for simplifying the geological model of numerical well testing for fractured-vuggy oil and gas reservoirs. The method uses the concavity of the bottom hole pressure derivative as the basis for screening caverns, thereby achieving a reasonable simplification of the geological model of numerical well testing for fractured-vuggy oil and gas reservoirs.

[0005] In a first aspect, embodiments of the present invention provide a simplified method for numerical well testing geological models of fractured-vuggy oil and gas reservoirs, comprising:

[0006] Based on the radius of the cavern in the fractured-vuggy oil and gas reservoir and the distance between the cavern and the well test, the bottom pressure derivative depression caused by the cavern is determined by the pre-determined correspondence between the cavern radius and the distance between the cavern and the well test. The bottom pressure derivative depression is the depression of the lowest point in the double logarithmic curve of the bottom pressure derivative versus time relative to the set bottom pressure derivative baseline.

[0007] During the establishment of the numerical well test geological model for the well test, karst caves that cause a bottomhole pressure derivative concavity amplitude smaller than the set concavity amplitude threshold are deleted.

[0008] In some embodiments, the correspondence is pre-established in the following manner:

[0009] Establish a geological model that includes a circular cave and a well, with the well represented by a circular wellbore;

[0010] The radius of the karst cave and the distance between the well and the karst cave in the geological model were modified in turn. For each modified geological model, numerical well test simulation was carried out to obtain a set of data including the radius of the karst cave, the distance between the well and the karst cave, and the concavity of the bottom hole pressure derivative caused by the karst cave. The obtained data sets constituted a dataset.

[0011] Based on the dataset, a correlation was established between the bottom hole pressure derivative concavity amplitude, the radius of the karst cave, and the distance between the karst cave and the well test by fitting.

[0012] In some embodiments, the numerical well test simulation yields a set of data including the radius of the cavern, the distance between the well and the cavern, and the downward concavity of the bottomhole pressure derivative caused by the cavern, including:

[0013] The geological model is divided into grids to obtain a grid system;

[0014] Based on the single-phase seepage theory, a numerical well test model was established, which includes a single-phase seepage model of the karst region and a single-phase seepage model of the matrix region in the geological model.

[0015] The numerical well test model is discretized on the grid system to obtain a system of linear equations. The system of linear equations is solved to obtain the bottom hole pressure derivatives at different times.

[0016] Based on the bottom hole pressure derivative at different times, the relationship curve between the bottom hole pressure derivative and time is plotted in a double logarithmic coordinate system. Based on this curve, the extent of the bottom hole pressure derivative depression caused by the karst cave is determined.

[0017] In some embodiments, the step of meshing the geological model to obtain a mesh system includes:

[0018] Subtract the wellbore from the outer boundary of the geological model using Boolean operations. In the resulting geological model, the wellbore is the inner boundary, and the area outside the cave is the matrix region.

[0019] Discrete points are set on the inner boundary, outer boundary, and cave boundary, respectively;

[0020] By expanding outwards from discrete points on the boundary, the entire geological model's grid is obtained, and all grids form a grid system.

[0021] In some embodiments, establishing a numerical well test model based on single-phase seepage theory includes:

[0022] Based on the theory of single-phase seepage, the single-phase seepage model for the karst cave region in the geological model is established as follows:

[0023]

[0024] The single-phase flow model for the matrix region in the geological model is established as follows:

[0025]

[0026] Where, p 1D p is the dimensionless pressure of the matrix. 2D The dimensionless pressure in the karst cave; T D C is a dimensionless time; D S is the dimensionless wellbore storage coefficient; S is the skin coefficient; ω is the cavern storage ratio, defined as ω=(φc t )2 / (φc t )1, where φ is porosity, c t The comprehensive compressibility coefficient is given by subscripts 1 and 2, which represent the matrix region and the cavern region, respectively; M is the cavern mobility ratio, defined as M = (K / μ)² / (K / μ)¹, where K is the permeability and μ is the viscosity; x D =x / r w and y D =y / r w r w Let x be the radius of the wellbore, and y be the coordinates of the corresponding directions.

[0027] In some embodiments, it also includes:

[0028] The wellbore boundary conditions of the numerical well test model are determined to be fixed flow rate boundaries:

[0029]

[0030] The external boundary conditions of the numerical well test model are determined to be closed boundary conditions:

[0031]

[0032] Among them, L j Let be the length of the line segment between two adjacent discrete points on the inner boundary of the wellbore, j be the index of the inner boundary line segment, N be the number of the inner boundary line segments, and p be the length of the line segment between two adjacent discrete points on the inner boundary of the wellbore. wD Let Γ be the bottom hole pressure, n be the outward normal direction of the boundary, and Γ be the bottom hole pressure. i p represents the inner boundary. D For the dimensionless pressure at the boundary, Γ e Indicates the outer boundary.

[0033] In some embodiments, solving the linear equation system to obtain the bottom hole pressure derivative at different times includes:

[0034] Solve the system of linear equations to obtain the pressure values ​​at different times on the grid system;

[0035] The pressure at all points on the inner boundary of the wellbore is equal, and all of them are bottom hole pressure. The sequence of pressure and time change on the inner boundary of the wellbore is extracted to obtain the sequence of bottom hole pressure and time change. The derivative of bottom hole pressure at different times is calculated using the difference scheme.

[0036] In some embodiments, establishing the correspondence between the bottom hole pressure derivative concavity amplitude and the radius of the cavern and the distance between the cavern and the well test, based on the dataset, through fitting, includes:

[0037] Based on the dataset, the following relationship was established by fitting: the indentation amplitude of the bottom hole pressure derivative, the radius of the cavern, and the distance between the cavern and the well test.

[0038]

[0039] Among them, g max r represents the concavity of the bottom hole pressure derivative. v Let d be the radius of the karst cave, d1 be the distance between the karst cave and the test well, and D, B, F and E are constants obtained from the fitting.

[0040] In some embodiments, the set concave amplitude threshold is 0.1.

[0041] In some embodiments, the baseline for setting the bottomhole pressure derivative is the line in the coordinate system where the bottomhole pressure derivative of the double logarithmic curve is 0.5.

[0042] In some embodiments, the deflection of the bottomhole pressure derivative is determined by the following formula:

[0043]

[0044] Among them, g maxΔv represents the concavity of the bottomhole pressure derivative, and Δv is the distance between the lowest point of the double logarithmic curve of the bottomhole pressure derivative versus time and the set bottomhole pressure derivative baseline.

[0045] Secondly, embodiments of the present invention provide a simplified geological model device for numerical well testing of fractured-vuggy oil and gas reservoirs, comprising:

[0046] The bottom hole pressure derivative concavity determination module is used to determine the bottom hole pressure derivative concavity caused by the cavern based on the radius of the cavern and the distance between the cavern and the well test in the fractured-vuggy oil and gas reservoir. This is achieved by using a pre-determined correspondence between the bottom hole pressure derivative concavity caused by the cavern and the radius of the cavern and the distance between the cavern and the well test. The bottom hole pressure derivative concavity is the concavity of the lowest point in the double logarithmic curve of the bottom hole pressure derivative versus time relative to the set bottom hole pressure derivative baseline.

[0047] The geological model simplification module is used to delete cavities that cause the bottom hole pressure derivative to sink less than a set sinking threshold during the establishment of the numerical well test geological model of the well test.

[0048] Thirdly, embodiments of the present invention provide a computer storage medium storing computer-executable instructions, which, when executed by a processor, implement the above-mentioned simplified method for numerical well testing geological models of fractured-vuggy oil and gas reservoirs.

[0049] Fourthly, this disclosure provides a server, including: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the above-mentioned simplified method for numerical well testing geological models of fractured-vuggy oil and gas reservoirs.

[0050] The beneficial effects of the above-described technical solutions provided in the embodiments of the present invention include at least the following:

[0051] The simplified method for numerical well testing geological models of fractured-vuggy oil and gas reservoirs provided in this invention innovatively defines the concept of the downward concavity of the bottomhole pressure derivative caused by caverns. Using this as a standard for cavern screening, only two parameters—the size of the cavern and its distance from the wellbore—are needed to determine whether a cavern can be identified by the well test curve. During numerical well testing geological modeling, unidentifiable caverns are eliminated, thereby greatly simplifying the numerical well testing model, reducing the amount of grid space and computation, improving the efficiency of numerical well test interpretation, and reducing the ambiguity of well test interpretation.

[0052] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description, claims, and drawings.

[0053] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0054] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0055] Figure 1 This is a flowchart of the method for determining the concavity amplitude of the bottom pressure derivative caused by karst caves in Embodiment 1 of the present invention;

[0056] Figure 2 This is a schematic diagram of the geological model established in Embodiment 1 of the present invention;

[0057] Figure 3 for Figure 1 The detailed implementation flowchart of step S12 is shown below;

[0058] Figure 4 for Figure 1 The detailed implementation flowchart of step S14 is shown below;

[0059] Figure 5 This is the curve of bottom hole pressure versus bottom hole pressure derivative in a double logarithmic coordinate system in Embodiment 1 of the present invention;

[0060] Figure 6 This is a flowchart illustrating the specific implementation of the method for establishing the correspondence between the bottom pressure derivative concavity amplitude caused by the karst cave and the radius of the karst cave and the distance between the karst cave and the test well in Embodiment 2 of the present invention.

[0061] Figure 7 This is the curve showing the relationship between the concavity amplitude and the distance to the cave in Embodiment 2 of the present invention;

[0062] Figure 8 This is the curve showing the relationship between the concavity amplitude and the size of the cave in Embodiment 2 of the present invention;

[0063] Figure 9 This is a flowchart of the simplified geological model method for numerical well testing of fractured-vuggy oil and gas reservoirs in Embodiment 3 of the present invention;

[0064] Figure 10 This is a contour map of the concavity amplitude of the bottom hole pressure derivative in Embodiment 3 of the present invention;

[0065] Figure 11 This is a schematic diagram of the simplified geological model device for numerical well testing of fractured-vuggy oil and gas reservoirs in an embodiment of the present invention. Detailed Implementation

[0066] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0067] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0068] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0069] To address the problems of complex geological models, large grid size, low computational efficiency, and high ambiguity caused by multiple karst caves in numerical well testing of fractured-vuggy oil and gas reservoirs, this invention provides a method and apparatus for simplifying the geological model of numerical well testing for fractured-vuggy oil and gas reservoirs. The method uses the concavity of the bottomhole pressure derivative as the basis for karst cave selection, thereby achieving a reasonable simplification of the geological model of numerical well testing for fractured-vuggy oil and gas reservoirs.

[0070] Example 1

[0071] Embodiment 1 of the present invention provides a method for determining the concavity amplitude of the bottom pressure derivative caused by karst caves, the process of which is as follows: Figure 1 As shown, it includes the following steps:

[0072] Step S11: Create a geological model that includes a circular cave and a well.

[0073] See the geological model established. Figure 2 As shown, the specific process may include: drawing the outer boundary 3 of the geological model, which is circular; drawing the wellbore 1 inside the circular outer boundary 3, i.e., using the circular wellbore to represent a single well; and drawing the karst cave 2 inside the circular outer boundary 3, which is circular with a radius of r. v The distance between it and wellbore 1 is d1.

[0074] Step S12: Grid the geological model to obtain a grid system.

[0075] For details, see Figure 3 As shown, it includes the following steps:

[0076] Step S121: Subtract the wellbore from the outer boundary of the geological model using Boolean operation. In the resulting geological model, the wellbore is the inner boundary, and the area outside the cave is the matrix area.

[0077] Step S122: Set discrete points on the inner boundary, outer boundary, and cave boundary respectively.

[0078] For example, the radius of the outer boundary of the geological model can be set to 10000, the radius of the wellbore to 1, the radius of the karst cave to 20, and the distance between the karst cave and the wellbore to 10. Using the above settings as an example, the number of discrete points on the inner boundary can be 10, the number of discrete points on the karst cave boundary can be 20, and the spacing between discrete points on the outer boundary can be 10.

[0079] Step S123: Expand outwards sequentially from the discrete points on the boundary to obtain the grid of the entire geological model. All grids form a grid system.

[0080] Step S13: Based on the single-phase flow theory, establish a numerical well test model, including the single-phase flow model of the karst region and the single-phase flow model of the matrix region in the geological model.

[0081] Based on the theory of single-phase seepage, the single-phase seepage model for the karst cave region in the geological model is established as follows:

[0082]

[0083] The single-phase flow model for the matrix region in the geological model is established as follows:

[0084]

[0085] In equations (1) and (2), p 1D p is the dimensionless pressure of the matrix. 2D The dimensionless pressure in the karst cave; T D C is a dimensionless time; D S is the dimensionless wellbore storage coefficient; S is the skin coefficient; ω is the cavern storage ratio, defined as ω=(φc t )2 / (φc t )1, where φ is porosity, c t The comprehensive compressibility coefficient is given by subscripts 1 and 2, which represent the matrix region and the cavern region, respectively; M is the cavern mobility ratio, defined as M = (K / μ)² / (K / μ)¹, where K is the permeability and μ is the viscosity; x D =x / r w and yD =y / r w r w Let x be the radius of the wellbore, and y be the coordinates of the corresponding directions.

[0086] It can be seen that the established single-phase seepage equations (models) for the karst cave region and the matrix region have the same equation form, but the specific parameters such as permeability, porosity, and compressibility are different, and the seepage equations are in dimensionless form.

[0087] Boundary conditions for the numerical well test model are proposed for the inner boundary of the wellbore and the outer boundary of the model:

[0088] The boundary condition inside the wellbore is a constant flow rate boundary condition:

[0089]

[0090] The model's outer boundary conditions are closed boundary conditions:

[0091]

[0092] In equations (3) and (4), L j Let be the length of the line segment between two adjacent discrete points on the inner boundary of the wellbore, j be the index of the inner boundary line segment, N be the number of the inner boundary line segments, and p be the length of the line segment between two adjacent discrete points on the inner boundary of the wellbore. wD Let Γ be the bottom hole pressure, n be the outward normal direction of the boundary, and Γ be the bottom hole pressure. i p represents the inner boundary. D For the dimensionless pressure at the boundary, Γ e Indicates the outer boundary.

[0093] Step S14: Discretize the numerical well test model on the grid system to obtain a system of linear equations, solve the system of linear equations, and obtain the bottom hole pressure derivatives at different times.

[0094] For details, see Figure 4 As shown, it includes the following steps:

[0095] Step S141: Set the permeability of the karst cave to a maximum value, and discretize the seepage equation on the grid system using the finite element method to obtain a linear equation system.

[0096] The permeability of the karst cave is set to a maximum value, i.e., M = 10000.

[0097] A triangular three-node element is used, with linear interpolation function. The Galerkin weighted residual method is employed, and the weight function is set to the element interpolation function, i.e.:

[0098] N i =a i +b i x+c i y (5)

[0099] The weak-form unit integral equation within the matrix region is:

[0100]

[0101] The unit pressure is:

[0102]

[0103] in Given the pressure values ​​at the element nodes, the discretized finite element equations for the matrix region are as follows:

[0104]

[0105] The equations for the cavern region and the matrix region have the same form, and their weak-form unit integral equations are as follows:

[0106]

[0107] The right-hand side terms of equations (7) and (8) represent the flow rates at the element boundaries. Multiplying equation (9) by M and then superimposing it with equation (7) eliminates the right-hand side terms. Therefore, the finite element equation for the karst region is:

[0108]

[0109] In equation (10), A is the area of ​​the triangle.

[0110] Equations (8) and (10) are assembled into a global linear equation system according to the unit boundaries.

[0111] Step S142: Handle the inner and outer boundary conditions in the linear equation system.

[0112] The boundary conditions inside the wellbore are:

[0113]

[0114] The pressure at all points on the wellbore boundary is equal, and is always the bottom hole pressure:

[0115]

[0116] When dealing with linear equation systems, p w D As a new unknown, (11) is placed as a linear equation system in the last column of the overall linear equation system to obtain the final linear equation system.

[0117] Step S143: Solve the linear equations using an iterative or direct method to obtain the pressure values ​​at different times on the grid system.

[0118] Step S144: The pressure at each point on the inner boundary of the wellbore is equal, and all of them are bottom hole pressure. Extract the sequence of pressure and time changes on the inner boundary of the wellbore to obtain the sequence of bottom hole pressure and time changes. Use the difference scheme to calculate the bottom hole pressure derivative at different times.

[0119]

[0120] Step S15: Based on the bottom hole pressure derivative at different times, plot the relationship curve between the bottom hole pressure derivative and time in a double logarithmic coordinate system, and determine the extent of the bottom hole pressure derivative depression caused by the karst cave.

[0121] The bottomhole pressure derivative concavity is defined as the concavity of the lowest point in the double logarithmic curve of the bottomhole pressure derivative versus time relative to a set bottomhole pressure derivative baseline.

[0122] Furthermore, if the baseline of the bottom hole pressure derivative is set to the line in the coordinate system where the double logarithmic curve is located, where the bottom hole pressure derivative is 0.5, then the downward concavity of the bottom hole pressure derivative is determined by the following formula (14):

[0123]

[0124] In equation (14), g max Δv represents the concavity of the bottomhole pressure derivative, and Δv is the distance between the lowest point of the double logarithmic curve of the bottomhole pressure derivative versus time and the set bottomhole pressure derivative baseline.

[0125] by Figure 5 For example, Figure 5 Curve 4 is a double logarithmic curve of bottom hole pressure versus time, curve 5 is a double logarithmic curve of bottom hole pressure derivative versus time, and curve 6 is the baseline with bottom hole pressure derivative of 0.5.

[0126] Example 2

[0127] Embodiment 2 of the present invention provides a detailed implementation process for establishing the correspondence between the bottom-hole pressure derivative concavity amplitude caused by karst caves and the radius of the karst caves and the distance between the karst caves and the well test. See [link to implementation details]. Figure 6 As shown, it includes the following steps:

[0128] Step S61: Establish a geological model containing a circular cave and a well, with the well represented by a circular wellbore.

[0129] Step S62: Modify the radius of the cave and the distance between the well and the cave in the geological model in turn. For each modified geological model, conduct numerical well test simulation to obtain a set of data including the radius of the cave, the distance between the well and the cave, and the downward concavity of the bottom pressure derivative caused by the cave. The obtained sets of data constitute a dataset.

[0130] The establishment of the geological model in step S61 and the determination of the concavity of the bottom hole pressure derivative caused by the karst cave in step S62 are described in Example 1 and will not be repeated here.

[0131] Step S63: Based on the dataset, establish the correspondence between the bottom hole pressure derivative concavity amplitude, the radius of the karst cave, and the distance between the karst cave and the well test by fitting.

[0132] By changing the distance d1 between the cavern and the shaft to 50, 100, 200, 300, 500, 800, 1000, 1500, 2000, and 3000, we obtain g for different d1 values. max ,like Figure 7 As shown;

[0133] Change the size of the cave r v Given values ​​of 100, 200, 300, 400, 600, 800, 1000, 1500, 2000, 3000, 5000, 6000, 8000, 9000, and 10000 respectively, different values ​​of r are obtained. v g max ,like Figure 8 As shown;

[0134] Fitted concave amplitude g max With d1 and r v The data was used to obtain the fitting equation.

[0135] according to Figure 7 and Figure 8 The calculated results show that the curve shape is close to logarithmic, therefore the following logarithmic relationship is used to fit the data:

[0136]

[0137] Among them, g max r represents the concavity of the bottom hole pressure derivative. v Let d be the radius of the cave, d1 be the distance between the cave and the test well, and D, B, F, and E be undetermined constant coefficients. Figure 7 , Figure 8 The data were fitted nonlinearly, and the fitting results were: D = -0.052587, B = 0.002707, F = -0002244, E = 0.93371879.

[0138] Example 3

[0139] Embodiment 3 of the present invention provides a simplified method for numerical well testing geological models of fractured-vuggy oil and gas reservoirs, the process of which is as follows: Figure 9 As shown, it includes the following steps:

[0140] Step S91: Based on the radius of the cavern in the fractured-vuggy oil and gas reservoir and the distance between the cavern and the well test, determine the extent of the bottom hole pressure derivative concavity caused by the cavern through the pre-determined correspondence between the cavern radius and the distance between the cavern and the well test.

[0141] The above correspondence was established in advance using the method described in Example 2.

[0142] Step S92: During the establishment of the numerical well test geological model, delete the karst caves that cause the bottom hole pressure derivative to sink less than the set sinking threshold.

[0143] The threshold for the concave amplitude can be set to 0.1.

[0144] Drawing g max Regarding r v The contour plots of d1 and d1, and with g max Using 0.1 as the boundary, the contour lines are divided into two regions. max The threshold criterion of 0.1 refers to Gringarten's definition of a new investigation radius, which considers a cavity to be identifiable when the maximum depression on the pressure derivative curve caused by cavitation exceeds 10%; otherwise, the cavity cannot be identified on the well test curve. See [link to relevant documentation]. Figure 10 As shown.

[0145] Based on Gringarten's definition of the investigation radius, the limit of the downward concavity of the pressure derivative curve caused by karst caves on the well test curve was determined, so that the properties of the karst caves themselves can be used to determine whether they can have a sufficient impact on the well test pressure derivative curve.

[0146] The simplified geological model method for numerical well testing of fractured-vuggy oil and gas reservoirs provided in Embodiment 3 of this invention innovatively defines the concept of the downward concavity of the bottomhole pressure derivative caused by caverns. Using this as a standard for cavern screening, it is possible to determine whether a cavern can be identified by the well test curve using only two parameters: the size of the cavern and its distance from the wellbore. During numerical well testing geological modeling, unidentifiable caverns are eliminated, thereby greatly simplifying the numerical well testing model, reducing the amount of grid and computation, improving the efficiency of numerical well test interpretation, and reducing the ambiguity of well test interpretation.

[0147] Based on the inventive concept of this invention, embodiments of this invention also provide a simplified device for numerical well testing geological models of fractured-vuggy oil and gas reservoirs, the structure of which is as follows: Figure 11 As shown, it includes:

[0148] The bottom hole pressure derivative concavity determination module 111 is used to determine the bottom hole pressure derivative concavity caused by the cavern based on the radius of the cavern and the distance between the cavern and the well test in the fractured-vuggy oil and gas reservoir, through a pre-determined correspondence between the bottom hole pressure derivative concavity caused by the cavern and the radius of the cavern and the distance between the cavern and the well test. The bottom hole pressure derivative concavity is the concavity of the lowest point in the double logarithmic curve of the bottom hole pressure derivative versus time relative to the set bottom hole pressure derivative baseline.

[0149] The geological model simplification module 112 is used to delete karst caves that cause the bottom hole pressure derivative to sink less than a set sinking threshold during the establishment of the numerical well test geological model of the well test.

[0150] Regarding the apparatus in the above embodiments, the specific manner in which each module performs its operation has been described in detail in the embodiments related to the method, and will not be elaborated upon here.

[0151] Based on the inventive concept of the present invention, the embodiments of the present invention also provide a computer storage medium, wherein the computer storage medium stores computer-executable instructions, and when the computer-executable instructions are executed by a processor, the above-mentioned simplified method for numerical well testing geological models of fractured-vuggy oil and gas reservoirs is implemented.

[0152] Based on the inventive concept of this invention, this embodiment of the invention also provides a server, including: a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it implements the above-mentioned simplified method for numerical well testing geological models of fractured-vuggy oil and gas reservoirs.

[0153] Unless otherwise specifically stated, terms such as processing, calculation, operation, determination, display, etc., may refer to the actions and / or processes of one or more processing or computing systems or similar devices that represent the manipulation and conversion of data representing physical (e.g., electronic) quantities within the registers or memory of the processing system into other data similarly representing physical quantities within the memory, registers, or other such information storage, transmission, or display devices of the processing system. Information and signals can be represented using any of a variety of different techniques and methods. For example, data, instructions, commands, information, signals, bits, symbols, and chips mentioned throughout the above description can be represented by voltage, current, electromagnetic waves, magnetic fields or particles, light fields or particles, or any combination thereof.

[0154] It should be understood that the specific order or hierarchy of steps in the disclosed process is an example of an exemplary method. Based on design preferences, it should be understood that the specific order or hierarchy of steps in the process may be rearranged without departing from the scope of this disclosure. The appended method claims provide elements of various steps in an exemplary order and are not intended to limit the scope to the specific order or hierarchy described.

[0155] In the detailed description above, various features are combined together in a single embodiment to simplify this disclosure. This approach to disclosure should not be construed as reflecting an intention that embodiments of the claimed subject matter require more features than those stated in each claim. Rather, as reflected in the appended claims, the invention is presented with fewer features than all of the features in a single disclosed embodiment. Therefore, the appended claims are hereby clearly incorporated into the detailed description, wherein each claim stands alone as a preferred embodiment of the invention.

[0156] Those skilled in the art will also understand that the various illustrative logic blocks, modules, circuits, and algorithm steps described in conjunction with the embodiments herein can be implemented as electronic hardware, computer software, or a combination thereof. To clearly illustrate the interchangeability between hardware and software, the various illustrative components, blocks, modules, circuits, and steps described above are generally described in terms of their functionality. Whether such functionality is implemented as hardware or software depends on the specific application and the design constraints imposed on the overall system. Those skilled in the art can implement the described functionality in alternative ways for each specific application; however, such implementation decisions should not be construed as departing from the scope of this disclosure.

[0157] The steps of the methods or algorithms described in conjunction with the embodiments herein can be directly embodied in hardware, software modules executed by a processor, or a combination thereof. The software modules can reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disks, removable disks, CD-ROMs, or any other form of storage medium well known in the art. An exemplary storage medium is connected to the processor, enabling the processor to read information from and write information to the storage medium. Of course, the storage medium can also be a component of the processor. The processor and storage medium can reside in an ASIC. The ASIC can reside in a user terminal. Alternatively, the processor and storage medium can exist as discrete components in the user terminal.

[0158] For software implementation, the techniques described in this application can be implemented using modules (e.g., procedures, functions, etc.) that perform the functions described in this application. This software code can be stored in memory units and executed by a processor. The memory units can be implemented within the processor or outside the processor; in the latter case, they are communicatively coupled to the processor via various means, as is well known in the art.

[0159] The foregoing description includes examples of one or more embodiments. It is certainly impossible to describe all possible combinations of components or methods in order to describe the above embodiments, but those skilled in the art will recognize that further combinations and arrangements of the various embodiments are possible. Therefore, the embodiments described herein are intended to cover all such changes, modifications, and variations that fall within the scope of the appended claims. Furthermore, the term "comprising" as used in the specification or claims is interpreted in a manner similar to the term "including," as interpreted when used as a conjunction in the claims. Additionally, the use of any term "or" in the specification of the claims is intended to mean "non-exclusive or."

Claims

1. A simplified method for numerical well testing geological models of fractured-vuggy oil and gas reservoirs, characterized in that, include: Based on the radius of the cavern in the fractured-vuggy oil and gas reservoir and the distance between the cavern and the well test, the bottom pressure derivative depression caused by the cavern is determined by the pre-determined correspondence between the cavern radius and the distance between the cavern and the well test. The bottom pressure derivative depression is the depression of the lowest point in the double logarithmic curve of the bottom pressure derivative versus time relative to the set bottom pressure derivative baseline. During the establishment of the numerical well test geological model for the well test, karst caves that cause a bottomhole pressure derivative concavity amplitude smaller than the set concavity amplitude threshold are deleted.

2. The method as described in claim 1, characterized in that, The correspondence is established in advance in the following manner: Establish a geological model that includes a circular cave and a well, with the well represented by a circular wellbore; The radius of the karst cave and the distance between the well and the karst cave in the geological model were modified in turn. For each modified geological model, numerical well test simulation was carried out to obtain a set of data including the radius of the karst cave, the distance between the well and the karst cave, and the concavity of the bottom hole pressure derivative caused by the karst cave. The obtained data sets constituted a dataset. Based on the dataset, a correlation was established between the bottom hole pressure derivative concavity amplitude, the radius of the karst cave, and the distance between the karst cave and the well test by fitting.

3. The method as described in claim 2, characterized in that, The numerical well test simulation yielded a set of data including the radius of the cave, the distance between the well and the cave, and the downward concavity of the bottomhole pressure derivative caused by the cave, including: The geological model is divided into grids to obtain a grid system; Based on the single-phase seepage theory, a numerical well test model was established, which includes a single-phase seepage model of the karst region and a single-phase seepage model of the matrix region in the geological model. The numerical well test model is discretized on the grid system to obtain a system of linear equations. The system of linear equations is solved to obtain the bottom hole pressure derivatives at different times. Based on the bottom hole pressure derivative at different times, the relationship curve between the bottom hole pressure derivative and time is plotted in a double logarithmic coordinate system. Based on this curve, the extent of the bottom hole pressure derivative depression caused by the karst cave is determined.

4. The method as described in claim 3, characterized in that, The process of dividing the geological model into grids to obtain a grid system includes: Subtract the wellbore from the outer boundary of the geological model using Boolean operations. In the resulting geological model, the wellbore is the inner boundary, and the area outside the cave is the matrix region. Discrete points are set on the inner boundary, outer boundary, and cave boundary, respectively; By expanding outwards from discrete points on the boundary, the entire geological model's grid is obtained, and all grids form a grid system.

5. The method as described in claim 3, characterized in that, The numerical well test model established based on single-phase seepage theory includes: Based on the theory of single-phase seepage, the single-phase seepage model for the karst cave region in the geological model is established as follows: The single-phase flow model for the matrix region in the geological model is established as follows: In equations (1) and (2), p 1D p is the dimensionless pressure of the matrix. 2D The dimensionless pressure in the karst cave; T D C is a dimensionless time; D S is the dimensionless wellbore storage coefficient; S is the skin coefficient; ω is the cavern storage ratio, defined as ω=(φc t )2 / (φc t )1, where φ is porosity, c t The comprehensive compressibility coefficient is given by subscripts 1 and 2, which represent the matrix region and the cavern region, respectively; M is the cavern mobility ratio, defined as M = (K / μ)² / (K / μ)¹, where K is the permeability and μ is the viscosity; x D =x / r w and y D =y / r w r w Let x be the radius of the wellbore, and y be the coordinates of the corresponding directions.

6. The method as described in claim 5, characterized in that, Also includes: The wellbore boundary conditions of the numerical well test model are determined to be fixed flow rate boundaries: The external boundary conditions of the numerical well test model are determined to be closed boundary conditions: In equations (3) and (4), L j Let be the length of the line segment between two adjacent discrete points on the inner boundary of the wellbore, j be the index of the inner boundary line segment, N be the number of the inner boundary line segments, and p be the length of the line segment between two adjacent discrete points on the inner boundary of the wellbore. wD Let Γ be the bottom hole pressure, n be the outward normal direction of the boundary, and Γ be the bottom hole pressure. i p represents the inner boundary. D For the dimensionless pressure at the boundary, Γ e Indicates the outer boundary.

7. The method as described in claim 6, characterized in that, Solving the linear equation system yields the bottom hole pressure derivatives at different times, including: Solve the system of linear equations to obtain the pressure values ​​at different times on the grid system; The pressure at all points on the inner boundary of the wellbore is equal, and all of them are bottom hole pressure. The sequence of pressure and time change on the inner boundary of the wellbore is extracted to obtain the sequence of bottom hole pressure and time change. The derivative of bottom hole pressure at different times is calculated using the difference scheme.

8. The method as described in claim 3, characterized in that, Based on the dataset, the method of establishing the correspondence between the bottom hole pressure derivative concavity amplitude and the radius of the cavern and the distance between the cavern and the well test is performed by fitting, including: Based on the dataset, the following relationship was established by fitting: the indentation amplitude of the bottom hole pressure derivative, the radius of the cavern, and the distance between the cavern and the well test. In equation (5), g max r represents the concavity of the bottom hole pressure derivative. v Let d be the radius of the karst cave, d1 be the distance between the karst cave and the test well, and D, B, F and E are constants obtained from the fitting.

9. The method as described in claim 1, characterized in that, The set concave amplitude threshold is 0.

1.

10. The method as described in claim 1, characterized in that, The baseline for the bottom hole pressure derivative is the line in the coordinate system where the double logarithmic curve is located, where the bottom hole pressure derivative is 0.

5.

11. The method as described in claim 10, characterized in that, The deflection of the bottomhole pressure derivative is determined by the following formula (6): In equation (6), g max Δv represents the concavity of the bottomhole pressure derivative, and Δv is the distance between the lowest point of the double logarithmic curve of the bottomhole pressure derivative versus time and the set bottomhole pressure derivative baseline.

12. A simplified device for numerical well testing geological model of fractured-vuggy oil and gas reservoirs, characterized in that, include: The bottom hole pressure derivative concavity determination module is used to determine the bottom hole pressure derivative concavity caused by the cavern based on the radius of the cavern and the distance between the cavern and the well test in the fractured-vuggy oil and gas reservoir. This is achieved by using a pre-determined correspondence between the bottom hole pressure derivative concavity caused by the cavern and the radius of the cavern and the distance between the cavern and the well test. The bottom hole pressure derivative concavity is the concavity of the lowest point in the double logarithmic curve of the bottom hole pressure derivative versus time relative to the set bottom hole pressure derivative baseline. The geological model simplification module is used to delete cavities that cause the bottom hole pressure derivative to sink less than a set sinking threshold during the establishment of the numerical well test geological model of the well test.

13. A computer storage medium, characterized in that, The computer storage medium stores computer-executable instructions, which, when executed by a processor, implement the simplified method for numerical well testing geological models of fractured-vuggy oil and gas reservoirs as described in any one of claims 1 to 11.

14. A server, characterized in that, include: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the program, implements the simplified method for numerical well testing geological models of fractured-vuggy oil and gas reservoirs as described in any one of claims 1 to 11.

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