A method and system for evaluating the longitudinal cross-layering capability of fractures in interbedded sandstone and mudstone.

Abstract

This invention discloses a method and system for evaluating the longitudinal penetration capability of fractures in sandstone-mudstone interbedded layers. The method includes: obtaining the thicknesses and minimum horizontal principal stresses of sandstone and mudstone at different layers within the interbedded layer based on the profile characteristics of the strata containing the interbedded rock formation and well logging data; establishing a longitudinal model of the sandstone-mudstone interbedded layer based on this data; conducting rock mechanics experiments on sandstone and mudstone cores from the strata containing the interbedded rock formation to obtain corresponding rock mechanics parameters; calculating the interfacial strength of the current sandstone-mudstone interbedded layer based on these parameters; and simulating the longitudinal penetration fractures of the interbedded rock formation based on the longitudinal model, rock mechanics parameters, interfacial strength, and relevant parameters affecting the longitudinal penetration characteristics of the fractures, thereby evaluating the longitudinal penetration capability of the sandstone-mudstone interbedded layer fractures. This invention can accurately evaluate the longitudinal penetration capability of fractures in sandstone-mudstone interbedded layers.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field production enhancement and transformation, and in particular relates to a method and system for evaluating the longitudinal cross-layering capacity of fractures in interbedded sandstone and mudstone. Background Technology

[0002] Currently, the upper and lower sub-sections of the fifth member of the Xinchang Xujiahe Formation are mainly composed of interbedded sandstone and mudstone, characterized by deep reservoir burial, large thickness of interbedded sandstone and mudstone, strong heterogeneity, local development of low-angle fractures, large difference in horizontal principal stress, and poor gas content.

[0003] In response to the characteristics of the five thick interbedded sandstone and mudstone formations in Xinchangxu, large-scale layered volumetric fracturing is primarily employed during vertical well development. This involves using high-volume, high-displacement, and low-viscosity, water-resistance-reducing fracturing systems. This achieves sufficient vertical stimulation of the sandstone-mudstone interbedded reservoir. However, in developing this invention, the inventors discovered that the overall stimulation effect of the interbedded reservoirs obtained using the aforementioned development method is inconsistent, and existing technologies lack an effective method for evaluating the adequacy of vertical stimulation of sandstone-mudstone interbedded reservoirs. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a method for evaluating the longitudinal penetration capability of fractures in interbedded sandstone and mudstone formations. The method includes: obtaining the thicknesses and minimum horizontal principal stresses of sandstone and mudstone at different layers within the interbedded sandstone and mudstone formation based on the profile characteristics of the strata containing the interbedded sandstone and mudstone, combined with well logging data; establishing a longitudinal model of the interbedded sandstone and mudstone formations based on this data; conducting rock mechanics experiments on sandstone and mudstone cores from the strata containing the interbedded sandstone and mudstone formations to obtain corresponding rock mechanics parameters; calculating the interfacial strength of the current interbedded sandstone and mudstone formations based on these parameters; and simulating the longitudinal penetration fractures of the interbedded sandstone and mudstone formations based on the longitudinal model, the rock mechanics parameters, the interfacial strength, and relevant parameters affecting the longitudinal penetration characteristics of the fractures, thereby evaluating the longitudinal penetration capability of the fractures in the interbedded sandstone and mudstone formations.

[0005] Preferably, a triaxial rock mechanics test method is used to obtain the first type of parameters in the rock mechanics parameters, which include Young's modulus and Poisson's ratio of mudstone, Young's modulus and Poisson's ratio of sandstone, and Young's modulus and Poisson's ratio of the sand-mud interface; a tensile strength test method is used to obtain the second type of parameters in the rock mechanics parameters, which include the tensile strength of mudstone, the tensile strength of sandstone, and the tensile strength of the sand-mud interface.

[0006] Preferably, if both the sandstone core and the mudstone core belong to a first core layer with the same vertical depth as the interbedded rock to be analyzed, then the first type of parameters of the first core layer are used as the first type of parameters of the interbedded rock to be analyzed. If both the sandstone core and the mudstone core belong to a second core layer with a different vertical depth than the interbedded rock to be analyzed, then the confining pressure of the interbedded rock to be analyzed and the second core layer are obtained respectively, and the first type of parameters are fitted with the confining pressure to obtain the fitting coefficients between each sub-parameter of the first type of parameters of the second core layer and the confining pressure. Based on this, combined with the confining pressure of the interbedded rock to be analyzed, the first type of parameters of the interbedded rock to be analyzed are calculated.

[0007] Preferably, the ratios of the tensile strength of mudstone to that of sandstone, the ratio of the tensile strength of the sand-mud interface to that of sandstone, the ratio of the Young's modulus of mudstone to that of sandstone, and the ratio of the Young's modulus of the sand-mud interface to that of sandstone are calculated respectively, and the minimum ratio is taken as the interfacial strength of the current sand-mudstone interlayer.

[0008] Preferably, the relevant parameters include geostress parameters, formation property parameters, and construction parameters. Using the geostress parameters, a first longitudinal fracture propagation model is established to represent the stress field of sandstone or mudstone in the interbedded rocks to be analyzed; using the formation property parameters, a second longitudinal fracture propagation model is established to represent the matrix seepage of sandstone or mudstone in the interbedded rocks to be analyzed; and using the construction parameters, a third longitudinal fracture propagation model is established to represent the flow characteristics within the longitudinal fractures in the interbedded rocks to be analyzed.

[0009] Preferably, the first longitudinal crack propagation model is established using the following expression:

[0010]

[0011] Where x represents the crack propagation depth, z represents the crack propagation height, and σ x σ represents the normal stress in sandstone or mudstone along the x-direction. z τ represents the normal stress in sandstone or mudstone along the z-direction. xz τ represents the shear stress in sandstone or mudstone along the xz direction. zx B represents the shear stress in sandstone or mudstone along the zx direction. x B represents the rock mass force of sandstone or mudstone in the x-direction. z a represents the rock mass force of sandstone or mudstone in the z-direction. x a represents the acceleration of sandstone or mudstone in the x-direction. z ρ represents the acceleration of sandstone or mudstone in the z-direction, and ρ represents the density of sandstone or mudstone.

[0012] Preferably, the second longitudinal crack propagation model is established using the following expression:

[0013]

[0014] Where x represents the crack propagation depth, z represents the crack propagation height, and v x v represents the matrix seepage velocity of sandstone or mudstone in the x-direction. z φ represents the matrix seepage velocity of sandstone or mudstone in the z-direction, q represents the injection flow rate at the perforation point, φ represents the ratio of the pore volume of sandstone or mudstone to the corresponding volume of sandstone or mudstone, k represents the matrix permeability of sandstone or mudstone, μ represents the viscosity of fracturing fluid, H represents the vertical depth of sandstone or mudstone, g represents the gravitational acceleration, t represents the matrix seepage time, ρ represents the density of sandstone or mudstone, and p represents the fluid pressure in the fracture.

[0015] Preferably, the third longitudinal crack propagation model is established using the following expression:

[0016]

[0017] Where x represents the crack propagation depth, z represents the crack propagation height, and v Fz The velocity v represents the flow velocity within the longitudinal crack in the x-direction, q represents the injection flow rate at the perforation point, and v represents the flow rate within the crack. Fz φ represents the flow velocity within the longitudinal crack in the z-direction. F The ratio of fracture volume to sandstone or mudstone volume is given by: w, fracture width, n, indicator function, μ, fracturing fluid viscosity, H, vertical depth of sandstone or mudstone, g, gravitational acceleration, t, matrix seepage time, ρ, density of sandstone or mudstone, and p, fluid pressure in the fracture.

[0018] Preferably, the direction of the minimum horizontal principal stress is set as the transverse direction of the longitudinal model, and the transverse dimension of the longitudinal model is determined by extending equidistantly along the transverse direction with the perforation point as the center; the direction of the vertical stress of the interbedded rock to be analyzed is set as the longitudinal direction of the longitudinal model, and the longitudinal dimension of the longitudinal model is determined according to the thickness of the sandstone and mudstone of the interbedded rock to be analyzed.

[0019] On the other hand, the present invention also provides a system for evaluating the longitudinal penetration capability of fractures in sandstone-mudstone interbedded layers. The system includes the following modules: a model building module, used to obtain the thicknesses of sandstone and mudstone at different layers within the sandstone-mudstone interbedded layer and the minimum horizontal principal stress based on the profile characteristics of the strata where the interbedded rock formation is located, combined with well logging data; and to establish a longitudinal model of the sandstone-mudstone interbedded layer; a parameter calculation module, used to conduct rock mechanics experiments on sandstone and mudstone cores of the strata where the interbedded rock formation is located, obtain corresponding rock mechanics parameters, and calculate the interfacial strength of the current sandstone-mudstone interbedded layer based on the rock mechanics parameters; and a penetration capability evaluation module, used to simulate the longitudinal penetration fractures of the sandstone-mudstone interbedded layer based on the longitudinal model, the rock mechanics parameters, and the interfacial strength, combined with relevant parameters affecting the longitudinal penetration characteristics of the fractures in the sandstone-mudstone interbedded layer, thereby evaluating the longitudinal penetration capability of the fractures in the sandstone-mudstone interbedded layer.

[0020] Compared with the prior art, one or more embodiments of the above solutions may have the following advantages or beneficial effects:

[0021] This invention proposes a method for evaluating the longitudinal penetration capability of fractures in interbedded sandstone and mudstone. The method first establishes a physical model of the interbedded rock formation based on its thickness and minimum horizontal principal stress. Next, multiple longitudinal fracture propagation models are established using geostress parameters, formation properties, and construction parameters. Then, each longitudinal fracture propagation model is used to obtain characteristic information (stress field characteristics, matrix seepage characteristics, and fracturing fluid flow characteristics within the longitudinal fractures) that influences the formation of longitudinal penetration fractures, resulting in a physical model of the interbedded rock formation that considers these characteristics. Finally, the current physical model is combined with the rock mechanics parameters of the sandstone, mudstone, and sand-mudstone interfaces within the interbedded rock formation, as well as the interface strength of the sandstone-mudstone interbedded rock formation obtained from the rock mechanics parameters, to simulate the morphology, trajectory, and other characteristics of the longitudinal penetration fractures. Therefore, this invention evaluates the longitudinal penetration capability of fractures in interbedded sandstone and mudstone based on the intuitive longitudinal penetration effect of the fractures, thus obtaining accurate and reliable evaluation results.

[0022] Other features and advantages of the invention will be set forth in the description which follows, 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 description, claims, and drawings. Attached Figure Description

[0023] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0024] Figure 1 This is a step diagram illustrating a method for evaluating the longitudinal cross-layer capability of interbedded sandstone and mudstone fractures according to an embodiment of this application.

[0025] Figure 2 This is an example diagram of a longitudinal model of interbedded sandstone and mudstone, used in an embodiment of this application for evaluating the longitudinal cross-layering capability of fractures in interbedded sandstone and mudstone.

[0026] Figure 3 This is a schematic diagram showing the fitting relationship of relevant parameters in the method for evaluating the longitudinal cross-layering ability of interbedded sandstone and mudstone fractures according to an embodiment of this application.

[0027] Figure 4 This is a schematic diagram of the longitudinal penetration effect of fractures in a method for evaluating the longitudinal penetration capability of interbedded sandstone and mudstone, according to an embodiment of this application.

[0028] Figure 5 This is a block diagram of a system for evaluating the longitudinal cross-layering capability of fractures in interbedded sandstone and mudstone, according to an embodiment of this application. Detailed Implementation

[0029] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings and examples, so that the process of how the present invention uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly. It should be noted that, as long as there is no conflict, the various embodiments and features in the various embodiments of the present invention can be combined with each other, and the resulting technical solutions are all within the protection scope of the present invention.

[0030] Furthermore, the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0031] Currently, the upper and lower sub-sections of the fifth member of the Xinchang Xujiahe Formation are mainly composed of interbedded sandstone and mudstone, characterized by deep reservoir burial, large thickness of interbedded sandstone and mudstone, strong heterogeneity, local development of low-angle fractures, large difference in horizontal principal stress, and poor gas content.

[0032] In response to the characteristics of the five thick interbedded sandstone and mudstone formations in Xinchangxu, large-scale layered volumetric fracturing is primarily employed during vertical well development. This involves using high-volume, high-displacement, and low-viscosity, water-resistance-reducing fracturing systems. This achieves sufficient vertical stimulation of the sandstone-mudstone interbedded reservoir. However, in developing this invention, the inventors discovered that the overall stimulation effect of the interbedded reservoirs obtained using the aforementioned development method is inconsistent, and existing technologies lack an effective method for evaluating the adequacy of vertical stimulation of sandstone-mudstone interbedded reservoirs.

[0033] Example 1

[0034] Figure 1 This is a step diagram illustrating a method for evaluating the longitudinal cross-layering capability of fractures in interbedded sandstone and mudstone according to an embodiment of this application. See below for reference. Figure 1 This will explain each step of the method.

[0035] like Figure 1 As shown, in step S110, based on the profile characteristics of the strata where the interbedded rocks to be analyzed are located, and combined with well logging data, the thicknesses of sandstone and mudstone at different layers within the interbedded rocks to be analyzed, as well as the minimum horizontal principal stress, are obtained. Based on this, a vertical model of the sandstone-mudstone interbedded rocks is established. Specifically, firstly, the geological distribution characteristics of the strata where the interbedded rocks to be analyzed are obtained, resulting in a geological profile map of the strata. Then, the profile characteristics of the interbedded rock region to be analyzed are obtained using the geological profile map. Analysis of the profile characteristics of the interbedded rocks to be analyzed reveals that the superposition of multiple layers forms the current interbedded rocks to be analyzed. Each layer contains sandstone and mudstone layers, and sandstone and mudstone layers at different layers are alternately arranged in the current interbedded rock region. Therefore, this invention, based on the aforementioned profile characteristics of the interbedded rocks to be analyzed, and combined with well logging data, obtains the thickness of all sandstone layers and the thickness of mudstone layers forming the current interbedded rocks to be analyzed. Subsequently, based on well logging data, the magnitude and direction of the minimum horizontal principal stresses in the corresponding sandstone and mudstone layers of the current interbedded rock are determined. Based on this, a physical model is established to simulate the longitudinal cross-layering capability of the fractures in the current sandstone-mudstone interbedded rock, namely: the longitudinal model of the sandstone-mudstone interbedded rock.

[0036] Figure 2 This is an example diagram of a longitudinal model of interbedded sandstone and mudstone, used in an embodiment of this application for evaluating the longitudinal cross-layering capability of fractures in interbedded sandstone and mudstone. Next, referring to... Figure 2 This paper will provide a detailed explanation of the process of establishing a longitudinal model of interbedded sandstone and mudstone.

[0037] Specifically, in this embodiment, based on the direction of the minimum horizontal principal stress of the sandstone and mudstone layers constituting the current interbedded rock layers obtained in step S110, the horizontal direction parallel to the minimum horizontal principal stress is set as the transverse direction of the current sandstone-mudstone interbedded longitudinal model. Next, the perforation point is taken as the center of the transverse direction of the sandstone-mudstone interbedded longitudinal model, and further extended equidistantly along the transverse direction with the perforation point as the center. The transverse dimensions of the sandstone-mudstone interbedded longitudinal model are determined based on the extension distance. In this embodiment, a clustered perforation technique is used for construction. According to the clustered design scheme corresponding to the current perforation technique, the transverse propagation characteristics of the interbedded fractures corresponding to the current clustered design scheme are determined. Then, the corresponding extension distance is determined based on the transverse propagation characteristics, and the transverse dimensions of the sandstone-mudstone interbedded longitudinal model are obtained using the extension distance. It should be noted that in this embodiment, the extension distance is determined based on the clustered design scheme (number of clusters, cluster spacing, etc.) corresponding to the current perforation technique. Those skilled in the art can set the extension distance according to the actual construction operation.

[0038] Next, based on the profile characteristics of the interbedded rock layers to be analyzed and combined with well logging data, the direction of the vertical stress in the current interbedded rock layers to be analyzed is determined, and the direction of the vertical stress is set as the longitudinal direction of the current sandstone-mudstone interbedded vertical model. Then, the thicknesses of all sandstone layers and mudstone layers forming the current interbedded rock layers to be analyzed, obtained in step S110, are directly superimposed, or the thickness ratio of all sandstone layers and mudstone layers is calculated based on well logging data, and the thicknesses of the sandstone and mudstone layers in the interbedded rock layers to be analyzed are restored according to the thickness ratio, and then the restored thicknesses are superimposed. It should be noted that, due to the complex distribution of interbedded rock layers, in this embodiment, according to the cluster design scheme corresponding to the current perforation technology, the longitudinal propagation characteristics of the interbedded fractures corresponding to the current cluster design scheme are determined, and then the longitudinal dimensions of the sandstone-mudstone interbedded vertical model are determined based on the longitudinal propagation characteristics.

[0039] Further, in step S120, rock mechanics experiments are conducted on sandstone and mudstone cores from the strata containing the interbedded rocks to be analyzed, and the corresponding rock mechanics parameters are obtained. Specifically, firstly, sandstone and mudstone cores are selected from the strata containing the interbedded rocks to be analyzed, and rock mechanics experiments are conducted using the selected cores. Then, based on the rock mechanics experiments, Young's modulus, Poisson's ratio, and tensile strength data are obtained for each sandstone, mudstone, and sand-mud interface in the interbedded rocks to be analyzed. The average Young's modulus, average Poisson's ratio, and average tensile strength of the sandstone, mudstone, and sand-mud interface are then used as the rock mechanics parameters of the sandstone, mudstone, and sand-mud interface of the current interbedded rocks to be analyzed.

[0040] In this embodiment, the rock mechanics parameters include a first type of parameter and a second type of parameter. Specifically, the first type of parameter is obtained using a triaxial rock mechanics test method, wherein the first type of parameter includes Young's modulus and Poisson's ratio of mudstone, Young's modulus and Poisson's ratio of sandstone, and Young's modulus and Poisson's ratio of the sand-mud interface. The second type of parameter is obtained using a tensile strength test method, wherein the second type of parameter includes the tensile strength of mudstone, the tensile strength of sandstone, and the tensile strength of the sand-mud interface.

[0041] When collecting sandstone and mudstone cores from the strata containing the interbedded rocks to be analyzed, a core sampling method can be used, where cores are taken within the interbedded rocks to be analyzed. If the aforementioned core sampling method is inconvenient to implement, a core sampling method can also be used, where cores are taken from other interbedded rocks within the strata containing the interbedded rocks to be analyzed.

[0042] Next, we will explain in detail the methods for obtaining the first type of parameters for the two different core-taking methods.

[0043] In one embodiment of this application, if both the sandstone core and the mudstone core belong to a first core layer with the same vertical depth as the interbedded rock to be analyzed, then the first type of parameters of the first core layer are used as the first type of parameters of the interbedded rock to be analyzed. Specifically, in the current stratum, the first core layer has the same vertical depth as the current interbedded rock to be analyzed; that is, the first core layer is located within the current interbedded rock to be analyzed. Specifically, the sandstone core and mudstone core used for rock mechanics experiments are both taken from the sandstone or mudstone layer of the current interbedded rock to be analyzed. Thus, the first type of parameters obtained using the sandstone core and mudstone core from the first core layer can be used as the first type of parameters of the current interbedded rock to be analyzed.

[0044] In another embodiment of this application, if both sandstone and mudstone cores belong to a second core layer with a different vertical depth than the interbedded rock to be analyzed, that is, in the current formation, the second core layer has a different vertical depth than the current interbedded rock to be analyzed. In this case, the second core layer no longer belongs to the current interbedded rock to be analyzed, but is located in other interbedded layers of the current formation. That is, the sandstone and mudstone cores used for rock mechanics experiments are both taken from sandstone or mudstone layers of other interbedded layers. In this case, it is first necessary to use the corresponding first-type parameters obtained from the sandstone and mudstone cores of the second core layer. Then, using well logging data, the formation confining pressure of the second core layer is calculated. Next, for the second core layer, each sub-parameter in the first-type parameters (Young's modulus of mudstone, Poisson's ratio of mudstone, Young's modulus of sandstone, Poisson's ratio of sandstone, Young's modulus of sandstone-mudstone interface, and Poisson's ratio of sandstone-mudstone interface) is fitted with the formation confining pressure corresponding to the second core layer to obtain the following results: Figure 3 The fitting relationship shown ( Figure 3This is a schematic diagram illustrating the fitting relationship of relevant parameters in the method for evaluating the longitudinal cross-layer capability of fractures in interbedded sandstone and mudstone according to an embodiment of this application. Further, based on the aforementioned fitting relationship, for the second core layer, the fitting coefficients between the corresponding sub-parameters of the first type of parameters and the formation confining pressure are obtained. Finally, using well logging data, the formation confining pressure of the current interbedded rock layer to be analyzed is calculated, and the formation confining pressure of the current interbedded rock layer to be analyzed is combined with the fitting coefficients of the second core layer to obtain the first type of parameters of the current interbedded rock layer to be analyzed.

[0045] It should be noted that, in the embodiments of this application, the method for obtaining the second type of parameters of the interbedded rocks to be analyzed is similar to the method for obtaining the first type of parameters, so it will not be described again here.

[0046] Furthermore, after obtaining the rock mechanical parameters (first-type parameters and second-type parameters) of the interbedded rocks to be analyzed, the ratios of the tensile strength of mudstone to sandstone, the ratio of the tensile strength of the sand-mudstone interface to sandstone, the ratio of the Young's modulus of mudstone to sandstone, and the ratio of the Young's modulus of the sand-mudstone interface to sandstone are calculated. Then, based on the calculation results of these ratios, the interfacial strength of the current sand-mudstone interbedded rock is obtained.

[0047] Furthermore, when calculating the interfacial strength of the current sandstone-mudstone interbedded layer, the results of the aforementioned ratio calculations are compared, and the smallest ratio data is extracted and used as the interfacial strength of the current sandstone-mudstone interbedded layer.

[0048] In step S130, based on the longitudinal model of the sandstone-mudstone interbedded layer, rock mechanics parameters, and interface strength, combined with relevant parameters affecting the longitudinal penetration characteristics of the sandstone-mudstone interbedded layer fractures, longitudinal penetration fractures of the interbedded rock layer to be analyzed are simulated, thereby evaluating the longitudinal penetration capability of the sandstone-mudstone interbedded layer fractures. Specifically, in this embodiment, using parameters belonging to the characteristics of the interbedded rock layer to be analyzed (rock mechanics parameters and sandstone-mudstone interbedded layer interface strength obtained in step S120), combined with relevant parameters affecting the longitudinal penetration characteristics of the sandstone-mudstone interbedded layer fractures (e.g., fracture trajectory, fracture morphology, fracture depth, etc.), simulated longitudinal fractures penetrating the interbedded rock layer to be analyzed are formed in the longitudinal model of the sandstone-mudstone interbedded layer established in step S110. Thus, the simulated longitudinal fractures in the longitudinal model of the sandstone-mudstone interbedded layer are used to visually reflect the longitudinal penetration effect of the fractures in the interbedded rock layer to be analyzed, thereby evaluating the longitudinal penetration capability of the fractures in the interbedded rock layer to be analyzed.

[0049] In actual construction, the relevant parameters affecting the longitudinal cross-layer characteristics of fractures in interbedded sandstone and mudstone include geostress parameters, formation physical property parameters, and construction parameters. Accordingly, this application incorporates characteristic information that influences the formation of longitudinal cross-layer fractures (stress field characteristics, matrix seepage characteristics, and fracturing fluid flow characteristics within the longitudinal fracture) into the physical model of the interbedded rock layers to be analyzed. This allows the current physical model to accurately simulate the morphology, trajectory, and other characteristics of longitudinal cross-layer fractures, thereby accurately evaluating the cross-layer capability of the longitudinal fractures.

[0050] Next, the acquisition of characteristic information that affects the formation of longitudinal cross-layer fractures in the embodiments of this application will be described in detail. Specifically, using geostress parameters, a first longitudinal fracture propagation model is established to represent the stress field of sandstone or mudstone in the interbedded rock layers to be analyzed, so as to combine the stress field of sandstone or mudstone in the interbedded rock layers to be analyzed with the longitudinal model of sandstone-mudstone interbedded rock layers, thereby obtaining a longitudinal model of sandstone-mudstone interbedded rock layers that takes into account the stress field. Using porosity and permeability in the formation physical properties, a second longitudinal fracture propagation model is established to represent the seepage of sandstone or mudstone matrix in the interbedded rock layers to be analyzed, so as to combine the seepage state of sandstone or mudstone matrix in the interbedded rock layers to be analyzed with the longitudinal model of sandstone-mudstone interbedded rock layers, thereby obtaining a longitudinal model of sandstone-mudstone interbedded rock layers that takes into account the seepage state of sandstone or mudstone matrix. Using fracturing fluid viscosity, discharge rate, and volume from the construction parameters, a third longitudinal fracture propagation model was established to represent the flow characteristics within longitudinal fractures in the interbedded rock layers to be analyzed. This model combines the fracturing fluid flow state within the longitudinal fractures of the interbedded rock layers with the longitudinal model of the sandstone-mudstone interbedded rock layers, resulting in a longitudinal model of the sandstone-mudstone interbedded rock layers that considers the flow state of the fracturing fluid within the fractures. Based on this, the longitudinal cross-layer fractures of the current sandstone-mudstone interbedded rock layers were simulated using the corresponding longitudinal models of each longitudinal fracture propagation model. The number of interfaces crossed by the longitudinal fractures in the corresponding sandstone-mudstone interbedded rock layers was recorded, and the cross-layer results for each longitudinal fracture propagation model were integrated. Finally, the longitudinal cross-layer effect of the fractures in the interbedded rock layers to be analyzed was evaluated based on the number of interfaces crossed. Figure 4 ( Figure 4 This is a schematic diagram of the longitudinal penetration effect of fractures in a method for evaluating the longitudinal penetration capability of interbedded sandstone and mudstone, as described in an embodiment of this application.

[0051] In this embodiment, the first longitudinal crack propagation model is established using the following expression:

[0052]

[0053] Where x represents the crack propagation depth, z represents the crack propagation height, and σ x σ represents the normal stress in sandstone or mudstone along the x-direction. zτ represents the normal stress in sandstone or mudstone along the z-direction. zx τ represents the shear stress in sandstone or mudstone along the xz direction. zx B represents the shear stress in sandstone or mudstone along the zx direction. x B represents the rock mass force of sandstone or mudstone in the x-direction. z a represents the rock mass force of sandstone or mudstone in the z-direction. x a represents the acceleration of sandstone or mudstone in the x-direction. z ρ represents the acceleration of sandstone or mudstone in the z-direction, and ρ represents the density of sandstone or mudstone.

[0054] In this embodiment, the second longitudinal crack propagation model is established using the following expression:

[0055]

[0056] Among them, v x v represents the matrix seepage velocity of sandstone or mudstone in the x-direction. z φ represents the matrix seepage velocity of sandstone or mudstone in the z-direction, q represents the injection flow rate at the perforation point, φ represents the ratio of the pore volume of sandstone or mudstone to the corresponding volume of sandstone or mudstone, k represents the matrix permeability of sandstone or mudstone, μ represents the viscosity of fracturing fluid, H represents the vertical depth of sandstone or mudstone, g represents the gravitational acceleration, t represents the matrix seepage time, and p represents the fluid pressure in the fracture.

[0057] In this embodiment of the application, the third longitudinal crack propagation model is established using the following expression:

[0058]

[0059] Among them, v Fx v represents the flow velocity within the longitudinal crack in the x-direction. Fz φ represents the flow velocity within the longitudinal crack in the z-direction. F The ratio of the fracture volume to the volume of sandstone or mudstone is given, w represents the fracture width, n represents the indicator function, and t represents the matrix seepage time.

[0060] It should be noted that in the third longitudinal fracture propagation model, n=1 when the direction of the fracturing fluid flow within the fracture is perpendicular to the fracture normal.

[0061] Based on the above-described method for evaluating the longitudinal penetration capability of interbedded sandstone and mudstone fractures, this embodiment of the invention also provides a system for evaluating the longitudinal penetration capability of interbedded sandstone and mudstone fractures (hereinafter referred to as the "penetration capability evaluation system"). Figure 5 This is a block diagram of a system for evaluating the longitudinal cross-layering capability of fractures in interbedded sandstone and mudstone, according to an embodiment of this application.

[0062] like Figure 5 As shown, the layer penetration capability evaluation system in this embodiment of the invention includes: a model establishment module 51, a parameter calculation module 52, and a layer penetration capability evaluation module 53. Specifically, the model building module 51 is implemented according to the method described in step S110 above, and is configured to obtain the thickness of sandstone and mudstone at different layers in the interbedded rock to be analyzed, as well as the minimum horizontal principal stress, based on the profile characteristics of the strata where the interbedded rock to be analyzed is located and combined with well logging data. Based on this, a vertical model of the interbedded sandstone and mudstone is established. The parameter calculation module 52 is implemented according to the method described in step S120 above, and is configured to conduct rock mechanics experiments on sandstone cores and mudstone cores of the strata where the interbedded rock to be analyzed is located, obtain the corresponding rock mechanics parameters, and calculate the interface strength of the current interbedded sandstone and mudstone based on the rock mechanics parameters. The cross-layer capacity evaluation module 53 is implemented according to the method described in step S130 above, and is configured to simulate the vertical cross-layer fractures of the interbedded rock to be analyzed based on the vertical model of the interbedded sandstone and mudstone, as well as the rock mechanics parameters and interface strength, combined with the relevant parameters affecting the vertical cross-layer characteristics of the fractures in the interbedded sandstone and mudstone, thereby evaluating the vertical cross-layer capacity of the fractures in the interbedded sandstone and mudstone.

[0063] Example 2

[0064] In a specific embodiment of this application, the interbedded sandstone and mudstone of the Xujiahe Formation is used as an example for detailed explanation.

[0065] Based on the geological profile and well logging data, the thickness of the sandstone and mudstone and the minimum horizontal principal stress of well Y in the Xujiahe Formation were determined, as shown in Table 1.

[0066] Table 1. Thickness and minimum horizontal principal stress of sandstone and mudstone in Well Y of the Xujiahe Formation.

[0067] Interbedded lithology Thickness m Minimum horizontal principal stress (MPa) sandstone 7.5 55 mudstone 5 60 sandstone 5 55 mudstone 5 60 sandstone 5 55 mudstone 5 60 sandstone 5 55 mudstone 5 60 sandstone 7.5 55

[0068] In this embodiment, based on the thickness of the sandstone and mudstone, the perforation design scheme, and the engineering modification goals, the longitudinal dimension of the sandstone-mudstone interbedded longitudinal model is comprehensively determined to be 50m, and the transverse dimension is 30m. Based on this, a model is established as follows: Figure 2 The vertical model of interbedded sandstone and mudstone is shown.

[0069] Next, sandstone and mudstone cores were collected from Well X of the Xujiahe Formation, and triaxial rock mechanics experiments were conducted to obtain the rock mechanics parameters of the sandstone, mudstone, and sand-mud interface in the cored strata of Well X. Then, using well logging data, the confining pressure of the cored strata in Well X was calculated. Subsequently, the rock mechanics parameters of the sandstone, mudstone, and sand-mud interface were fitted to the confining pressure, respectively, to obtain the following results: Figure 3 The figures shown are fitted curves of Young's modulus versus confining pressure and Poisson's ratio versus confining pressure for sandstone, mudstone, and sand-mud interface.

[0070] The development layer (currently analyzed interbedded rocks) of Well Y in the Xujiahe Formation has a different vertical depth than the core layer of Well X, and the difference in vertical depth is significant. The confining pressure of the development layer (currently analyzed interbedded rocks) in Well Y was calculated to be 30 MPa. Substituting this confining pressure into the fitted curve, the Young's modulus of the sandstone in the development layer of Well Y was found to be 37.2 GPa and Poisson's ratio to be 0.25; the Young's modulus of the mudstone was 32.9 GPa and Poisson's ratio to be 0.23; and the Young's modulus of the sandstone-mudstone interface was 33.6 GPa and Poisson's ratio to be 0.21. Next, tensile strength tests were conducted, yielding a tensile strength of 9 MPa for the sandstone, 7 MPa for the mudstone, and 7 MPa for the sandstone-mudstone interface in the core layer of Well X. Since the cored layer of Well X and the development layer of Well Y (the currently analyzed interbedded rocks) are located in the same stratum, the tensile strength of the sandstone, mudstone and sand-mud interface in the development layer of Well Y is consistent with that in the cored layer of Well X.

[0071] After calculating the ratios of mudstone tensile strength to sandstone tensile strength, the ratio of sand-mud interface tensile strength to sandstone tensile strength, the ratio of mudstone Young's modulus to sandstone Young's modulus, and the ratio of sand-mud interface Young's modulus to sandstone Young's modulus, the interfacial strength of the sand-mudstone interlayer in Well Y was found to be 0.78.

[0072] In this embodiment, the formation porosity is 5%, the formation permeability is 0.2 mD, the fracturing fluid viscosity is 3 mPa·s, and the fracturing flow rate is 10 m³ / s. 3 / min, construction fluid volume is 1000m 3 Based on the above data, the following results were obtained: Figure 4 The fractures shown are longitudinally penetrating layers. At this point, the fractures in the sandstone-mudstone interbedded layer of well Y longitudinally penetrate at least two interfaces and at most three interfaces.

[0073] This invention discloses a method and system for evaluating the longitudinal penetration capability of fractures in interbedded sandstone and mudstone. The method first establishes a physical model of the interbedded rock formation based on the thickness of the sandstone and mudstone and the minimum horizontal principal stress. Next, multiple longitudinal fracture propagation models of the interbedded rock formation are established using geostress parameters, formation property parameters, and construction parameters. Then, using each longitudinal fracture propagation model, characteristic information that influences the formation effect of longitudinal penetration fractures (stress field characteristics, matrix seepage characteristics, and fracturing fluid flow characteristics within the longitudinal fractures) is obtained, thus yielding a physical model of the interbedded rock formation considering the aforementioned characteristic information. Finally, the current physical model is combined with the rock mechanics parameters of the sandstone, mudstone, and sand-mudstone interfaces of the interbedded rock formation, as well as the interface strength of the sandstone-mudstone interbedded rock formation obtained from the rock mechanics parameters, to simulate the morphology, trajectory, and other characteristics of the longitudinal penetration fractures. Therefore, this invention evaluates the longitudinal penetration capability of fractures in interbedded sandstone and mudstone based on the intuitive longitudinal penetration effect of the fractures, thereby obtaining accurate and reliable evaluation results. Meanwhile, this method also provides theoretical guidance for optimizing the layered development of vertical wells with interbedded sandstone and mudstone formations in the Xujiahe Formation.

[0074] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

[0075] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

[0076] Those skilled in the art will understand that the modules or steps of the present invention described above can be implemented using general-purpose computing devices. They can be centralized on a single computing device or distributed across a network of multiple computing devices. Optionally, they can be implemented using computer-executable program code, thereby storing them in a storage device for execution by a computing device, or fabricating them separately as individual integrated circuit modules, or fabricating multiple modules or steps as a single integrated circuit module. Thus, the present invention is not limited to any particular hardware and software combination.

[0077] While the embodiments disclosed in this invention are as described above, the content is merely for the purpose of facilitating understanding of the invention and is not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and variations in form and detail of the implementation without departing from the spirit and scope disclosed herein; however, the scope of patent protection for this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A method for evaluating the longitudinal cross-layer capability of fractures in interbedded sandstone and mudstone, characterized in that, include: Based on the profile characteristics of the strata where the interbedded rocks to be analyzed are located, and combined with well logging data, the thicknesses of sandstone and mudstone at different layers in the interbedded rocks to be analyzed, as well as the minimum horizontal principal stress, are obtained. Based on this, a longitudinal model of the sandstone-mudstone interbedded rocks is established. The direction of the minimum horizontal principal stress is set as the transverse direction of the longitudinal model, and the transverse dimensions of the longitudinal model are determined by extending equidistantly along the transverse direction with the perforation point as the center. The direction of the vertical stress of the interbedded rocks to be analyzed is set as the longitudinal direction of the longitudinal model, and the longitudinal dimensions of the longitudinal model are determined according to the thickness of the sandstone and mudstone in the interbedded rocks to be analyzed. Rock mechanics experiments were conducted on sandstone and mudstone cores of the strata where the interbedded rocks to be analyzed are located to obtain the corresponding rock mechanics parameters, and the interfacial strength of the current sandstone-mudstone interbedded rocks was calculated based on the rock mechanics parameters. Based on the longitudinal model of the sandstone-mudstone interbedded layer, the rock mechanical parameters, and the interface strength, and combined with relevant parameters affecting the longitudinal penetration characteristics of the sandstone-mudstone interbedded layer fractures, the longitudinal penetration fractures of the interbedded rock layer to be analyzed are simulated to evaluate the longitudinal penetration capacity of the sandstone-mudstone interbedded layer fractures. The relevant parameters include in-situ stress parameters, formation physical property parameters, and construction parameters. The step of simulating the longitudinal penetration fractures of the interbedded rock layer to be analyzed by combining relevant parameters affecting the longitudinal penetration characteristics of the sandstone-mudstone interbedded layer fractures includes: Using the aforementioned geostress parameters, a first longitudinal crack propagation model is established to represent the stress field of sandstone or mudstone in the interbedded rock layers to be analyzed. Using the aforementioned formation physical parameters, a second longitudinal fracture propagation model is established to represent the seepage flow in the sandstone or mudstone matrix of the interbedded rocks to be analyzed. Using the construction parameters, a third longitudinal crack propagation model is established to represent the flow characteristics within longitudinal cracks in the interlayered rock to be analyzed.

2. The method according to claim 1, characterized in that, The steps of conducting rock mechanics experiments on sandstone and mudstone cores of the strata containing the interbedded rocks to be analyzed, and obtaining the corresponding rock mechanics parameters, include: The first type of parameters in the rock mechanics parameters were obtained by using the triaxial rock mechanics test method. The first type of parameters includes Young's modulus and Poisson's ratio of mudstone, Young's modulus and Poisson's ratio of sandstone, and Young's modulus and Poisson's ratio of sand-mud interface. The second type of parameters in the rock mechanics parameters are obtained by using tensile strength test methods. The second type of parameters includes the tensile strength of mudstone, the tensile strength of sandstone, and the tensile strength of the sand-mud interface.

3. The method according to claim 2, characterized in that, The steps for obtaining the first type of parameters in the rock mechanics parameters using triaxial rock mechanics experimental methods include: If both the sandstone core and the mudstone core belong to the first core layer with the same vertical depth as the interbedded rock to be analyzed, then the first type of parameters of the first core layer shall be used as the first type of parameters of the interbedded rock to be analyzed. If both the sandstone core and the mudstone core belong to a second core layer with a different vertical depth than the interbedded rock to be analyzed, the confining pressure of the interbedded rock to be analyzed and the second core layer are obtained respectively. The first type of parameters are then fitted with the confining pressure to obtain the fitting coefficients between each sub-parameter of the first type of parameters for the second core layer and the confining pressure. Based on this, and in conjunction with the confining pressure of the interbedded rock to be analyzed, the first type of parameters of the interbedded rock to be analyzed are calculated.

4. The method according to claim 2 or 3, characterized in that, The step of calculating the interfacial strength of the current sandstone-mudstone interlayer based on the aforementioned rock mechanical parameters includes: Calculate the ratios of the tensile strength of mudstone to that of sandstone, the ratio of the tensile strength of the sand-mud interface to that of sandstone, the ratio of the Young's modulus of mudstone to that of sandstone, and the ratio of the Young's modulus of the sand-mud interface to that of sandstone. The minimum ratio is taken as the interfacial strength of the current sand-mudstone interlayer.

5. The method according to claim 1, characterized in that, The first longitudinal crack propagation model is established using the following expression: in, x Indicates the depth of crack propagation. z Indicates the crack extension height. express x The normal stress in sandstone or mudstone in the direction of motion. express z The normal stress in sandstone or mudstone in the direction of motion. express xz The shear stress in sandstone or mudstone in the direction of motion. express zx The shear stress in sandstone or mudstone in the direction of motion. express x The rock mass forces of sandstone or mudstone in the direction of the rock mass. express z The rock mass forces of sandstone or mudstone in the direction of the rock mass. express x The acceleration of sandstone or mudstone in the direction of motion. express z The acceleration of sandstone or mudstone in the direction of motion. This indicates the density of sandstone or mudstone.

6. The method according to claim 5, characterized in that, The second longitudinal crack propagation model is established using the following expression: in, x Indicates the depth of crack propagation. z Indicates the crack extension height. express x The direction of matrix seepage velocity in sandstone or mudstone. express z The direction of matrix seepage velocity in sandstone or mudstone. Indicates the injection flow rate at the perforation point. This represents the ratio of the pore volume of sandstone or mudstone to the corresponding volume of sandstone or mudstone. Indicates the matrix permeability of sandstone or mudstone. Indicates the viscosity of the fracturing fluid. Indicates the vertical depth of sandstone or mudstone. g Represents gravitational acceleration. t Indicates the matrix seepage time. This indicates the density of sandstone or mudstone. p This indicates the fluid pressure within the crack.

7. The method according to claim 5 or 6, characterized in that, The third longitudinal crack propagation model is established using the following expression: in, x Indicates the depth of crack propagation. z Indicates the crack extension height. express x The flow velocity within the longitudinal crack in the direction of direction. Indicates the injection flow rate at the perforation point. express z The flow velocity within the longitudinal crack in the direction of direction. This represents the ratio of the fracture volume to the volume of sandstone or mudstone. Indicates the crack width. Indicates an indicator function, This refers to the viscosity of the fracturing fluid. Indicates the vertical depth of sandstone or mudstone. g Represents gravitational acceleration. t Indicates matrix seepage time. This indicates the density of sandstone or mudstone. p This indicates the fluid pressure within the crack.

8. A system for evaluating the longitudinal cross-layer capability of fractures in interbedded sandstone and mudstone, the system comprising the following modules: The model building module is used to obtain the thicknesses and minimum horizontal principal stresses of sandstone and mudstone at different layers within the interbedded rock formations under analysis, based on the profile characteristics of the strata and well logging data. Based on this, a vertical model of the sandstone-mudstone interbedded rock formations is established. The direction of the minimum horizontal principal stress is set as the transverse direction of the longitudinal model, and the transverse dimension of the longitudinal model is determined by extending equidistantly along the transverse direction with the perforation point as the center. The direction of the vertical stress of the interbedded rock to be analyzed is set as the longitudinal direction of the longitudinal model, and the longitudinal dimension of the longitudinal model is determined according to the thickness of the sandstone and mudstone of the interbedded rock to be analyzed. The parameter calculation module is used to conduct rock mechanics experiments on sandstone and mudstone cores of the strata where the interbedded rocks to be analyzed are located, obtain the corresponding rock mechanics parameters, and calculate the interfacial strength of the current sandstone-mudstone interbedded rocks based on the rock mechanics parameters. The cross-layer capability evaluation module is used to simulate the longitudinal cross-layer fractures of the interbedded sandstone and mudstone based on the longitudinal model of the sandstone-mudstone interbedded layer, the rock mechanical parameters, and the interface strength, combined with relevant parameters affecting the longitudinal cross-layer characteristics of the fractures in the sandstone-mudstone interbedded layer, thereby evaluating the longitudinal cross-layer capability of the fractures in the sandstone-mudstone interbedded layer. The relevant parameters include in-situ stress parameters, formation physical property parameters, and construction parameters. The step of simulating the longitudinal cross-layer fractures of the interbedded rock based on relevant parameters affecting the longitudinal cross-layer characteristics of the fractures in the sandstone-mudstone interbedded layer includes: Using the aforementioned geostress parameters, a first longitudinal crack propagation model is established to represent the stress field of sandstone or mudstone in the interbedded rock layers to be analyzed. Using the aforementioned formation physical parameters, a second longitudinal fracture propagation model is established to represent the seepage flow in the sandstone or mudstone matrix of the interbedded rocks to be analyzed. Using the construction parameters, a third longitudinal crack propagation model is established to represent the flow characteristics within longitudinal cracks in the interlayered rock to be analyzed.

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