Method and system for modeling small-scale cracks in fault control karst area
By extracting the characteristic parameters and geological parameters of small-scale fractures in the fault-controlled karst area, establishing karst phase models and geological mechanics models, and combining these models with random fracture modeling methods, the problem of low modeling accuracy of small-scale fractures in the existing technology is solved, and higher identification and modeling accuracy is achieved, providing a better geological basis for reservoir development.
Patent Information
- Application Number
- CN202311810618.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-26
- Publication Date
- 2025-06-27
AI Technical Summary
The prior art is difficult to finely identify and model small-scale fractures in broken karst areas, and the constraints on the main stress are less, resulting in low modeling accuracy.
By extracting the characteristic parameters and geological parameters of small-scale fractures, a karst phase model is established under the constraints of geological laws, and a geological mechanical model is established under the constraints of large-scale fractures. Combining the karst phase model and geological mechanical model, a small-scale fracture network model is established by the random fracture model, and finally a small-scale fracture model for the fault-controlled karst area is established through the porosity threshold value truncation method.
It effectively improves the identification accuracy and modeling accuracy of small-scale cracks in the broken-controlled karst area, provides more accurate geological basis, and provides support for the recognition of residual oil distribution, connection path analysis and well network improvement.
Smart Images
Figure CN120217620A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of unconventional oil and gas reservoir energy development, and particularly to a small-scale fracture modeling method and system in a fault-controlled karst area. Background Art
[0002] Based on the progress of reservoir basic geological research and fracture characterization technology, the fracture modeling technology for fracture-vuggy reservoirs has successively gone through Discrete fracture network the three stages of DFN + implicit fracture model IFM, artificial interpretation of faults + DFN, and artificial interpretation of faults + DFN embedded with fracture-vug carving results. Mainly from 2006 to 2010, a technical method of large-scale faults + medium and small-scale fractures with seismic sensitive attribute constraints as the core has been initially formed. For large and medium-scale fracture (fracture) models, the current modeling methods are relatively mature and the application effects are good. However, for small-scale fractures, due to their small length and low seismic identification accuracy, they cannot be accurately characterized.
[0003] Regarding the problem of fracture (fracture) classification, according to the development length of the fracture / fracture and combined with the accuracy of seismic identification of the fracture / fracture, the fracture / fracture is divided into large-scale fractures (500 - 1000 m), medium-scale fractures (50 - 500 m), and small-scale fractures (0.5 - 50 m). For large-scale and medium-scale fractures, based on the ant body, through steps such as fracture fragment extraction, fracture network model establishment, and fracture equivalent processing, a deterministic modeling method is used to establish them. For small-scale fracture models, most of the existing methods first extract the fracture characteristic parameters of imaging logging to establish a single-well fracture intensity curve; secondly, on the basis of coarsening the single-well fracture intensity curve, with the pore phase as the boundary constraint condition, a sequential Gaussian simulation method is used to establish a fracture distribution intensity volume; then, with the fracture intensity distribution volume as the constraint, a stochastic fracture modeling method is used to group and establish fracture models; finally, a fracture equivalent processing method is used to establish a small-scale fracture model, forming a sub-scale reservoir geological modeling technology for fault-controlled oil reservoirs.
[0004] For example, in the existing methods: 1) The karst genetic types of fractured-vuggy reservoirs are considered. According to different karst genetic types, the reservoir body types and distribution laws are determined respectively. Different modeling algorithms are used for simulation for different types of reservoir bodies, and classified reservoir body models under different karst genetic backgrounds are constructed. Different fusion methods are used to fuse the classified reservoir bodies under different genetic backgrounds, and the geological model is optimized based on various production dynamic data, which can improve the characterization accuracy of the strong heterogeneity characteristics of fractured-vuggy reservoirs and provide a reliable geological basis for reservoir development. However, this method does not involve the content related to the modeling of small-scale fractures in fault-controlled karst areas. 2) Effective seismic attributes for depicting the boundaries of karst reservoir bodies are involved, and an attribute fusion body is obtained; the depth of the well is determined based on the characteristics of the boundaries of karst reservoir bodies from drilling data; based on the well depth and combined with the attribute fusion body, effective attribute values are determined; by combining drilling data, a geological model of the boundaries of ultra-deep fault-controlled karst reservoir bodies is established; based on the geological model, seismic forward modeling is carried out to establish a boundary quantization identification template based on forward modeling, and a quantization identification threshold value is obtained; the effective attribute values are combined with the quantization identification threshold value to achieve intelligent quantization identification. However, this method still does not involve the content related to the modeling of small-scale fractures in fault-controlled karst areas. 3) Obtaining the seismic data volume and logging data of the study area is involved; after transforming the seismic data volume to the Wheeler domain, feature extraction is carried out to obtain the weak seismic reflection feature data in the Wheeler domain; inverse Wheeler domain transformation is performed on the weak seismic reflection feature data in the Wheeler domain to obtain the weak seismic reflection feature data in the structural domain; based on the weak seismic reflection feature data in the structural domain and the logging data, inversion data characterizing small-scale fault-controlled karst reservoirs are obtained. By transforming the seismic data volume to the Wheeler domain and then carrying out feature extraction, weak amplitude seismic reflection feature reservoirs can be effectively identified, and the internal structural characteristics of small-scale fault-controlled karst reservoirs can be identified. This method also does not involve the content related to the modeling of small-scale fractures in fault-controlled karst areas.
[0005] To sum up, due to the limitations of seismic accuracy and identification methods, the existing methods still cannot finely identify small-scale fractures (0.5 - 50 m) in fault-controlled karst areas. It is necessary to study the geological laws of fracture distribution, select appropriate seismic attribute bodies to constrain the distribution of small-scale fractures. Moreover, the existing modeling methods for small-scale fractures in fault-controlled karst areas consider less the constraint of principal stress, and it is necessary to increase the research on principal stress to improve the accuracy of small-scale fracture models. Summary of the Invention
[0006] To solve the problems existing in the process of establishing a small-scale fracture model, such as low seismic accuracy, great difficulty in identification, inability to accurately identify small-scale fractures, less consideration of the constraints of principal stresses, and low modeling accuracy, the present invention provides a method for modeling small-scale fractures in a fault-controlled karst area. Based on small-scale fracture parameters, a karst facies model is established under the constraint of geological laws, and a mechanical model is established under the constraint of large-scale fractures. A small-scale fracture network model is established under the multi-factor constraint of "karst facies model + fracture density intensity body + principal stress attribute body", and a small-scale fracture model in the fault-controlled karst area is constructed, providing a geological basis for the understanding of remaining oil distribution, the analysis of communication paths, and the improvement of well patterns. The present invention also relates to a system for modeling small-scale fractures in a fault-controlled karst area.
[0007] The technical solution of the present invention is as follows:
[0008] A method for modeling small-scale fractures in a fault-controlled karst area, characterized by comprising the following steps:
[0009] Parameter extraction step: Extract the characteristic parameters and geological parameters of small-scale fractures in the fault-controlled karst area;
[0010] Model establishment step under geological law constraints: Obtain the lithology of the rock in the first depth range longitudinally of the small-scale fractures in the fault-controlled karst area, and obtain the open-hole leakage section located in the second depth range longitudinally for characterizing the degree of rock fragmentation. Obtain the development degree of the first small-scale fractures corresponding to the first depth range according to the lithology of the rock in the first depth range, and obtain the development degree of the second small-scale fractures corresponding to the second depth range according to the degree of rock fragmentation corresponding to the open-hole leakage section in the second depth range. Establish a karst facies model under the constraint of geological laws based on the development degree of the first small-scale fractures, the development degree of the second small-scale fractures, and seismic attributes;
[0011] Geological mechanics model establishment step: Classify the fractures into tensile fractures, shear fractures, and sutures according to the fracture dip angle in the characteristic parameters. Process the three-dimensional seismic data volume in the geological parameters by using the ant body tracking algorithm to obtain the ant body attributes, and convert the ant body attributes into a fault model by using the fault slice extraction method. Based on the tensile fractures, shear fractures, sutures, and the dip angle and dip direction of the faults in the fault model, establish a geological mechanics model by using the boundary element simulation algorithm, and obtain the fracture density intensity body, dip angle body, dip direction body, and maximum principal stress direction according to the geological mechanics model;
[0012] Steps for establishing a small-scale fracture model: Based on the dual constraints of the fracture density intensity volume and the karst facies model, combined with the dip volume and the trend volume, under the control of the maximum principal stress direction, a random fracture modeling method is used to establish a small-scale fracture network model. According to the density and geometric parameters of multiple groups of fractures in the small-scale fracture network model, a small-scale fracture porosity model is calculated. Then, based on the small-scale fracture porosity model and using the porosity threshold truncation method, a small-scale fracture model in the fault-controlled karst area is established.
[0013] Preferably, in the parameter extraction step, the extracted characteristic parameters include the fracture length and width extracted through core data analysis, the fracture aperture, fracture dip, fracture trend, and maximum principal stress direction extracted through imaging logging data, and the permeability extracted through field well test interpretation data.
[0014] Preferably, in the parameter extraction step, the geological parameters include 3D seismic data volume, fracture development degree, and fracture depth range.
[0015] Preferably, in the model establishment step under geological law constraints, the karst facies model is determined comprehensively according to geological laws and seismic attributes. The geological laws include lithology and rock fragmentation degree, and the seismic attributes include tensor, wave impedance, AFE attribute, and likelihood attribute.
[0016] Preferably, in the small-scale fracture model establishment step, based on the small-scale fracture porosity model, a small-scale fracture model in the fault-controlled karst area is established using the porosity threshold truncation method with a porosity greater than or equal to a preset threshold.
[0017] The geometric parameters include length, thickness, and height.
[0018] A small-scale fracture modeling system in a fault-controlled karst area, characterized by including a parameter extraction module, a model establishment module under geological law constraints, a geomechanical model establishment module, and a small-scale fracture model establishment module connected in sequence.
[0019] The parameter extraction module extracts the characteristic parameters and geological parameters of small-scale fractures in the fault-controlled karst area.
[0020] The model establishment module under geological law constraints obtains the lithology of rocks in the first depth range in the vertical direction of small-scale fractures in the fault-controlled karst area, and obtains the emptying and leakage section located in the second depth range in the vertical direction to characterize the degree of rock fragmentation. The development degree of the first small-scale fractures corresponding to the first depth range is obtained according to the lithology of the rocks in the first depth range, and the development degree of the second small-scale fractures corresponding to the second depth range is obtained according to the degree of rock fragmentation corresponding to the emptying and leakage section in the second depth range. A karst facies model under geological law constraints is established based on the development degree of the first small-scale fractures, the development degree of the second small-scale fractures, and seismic attributes;
[0021] The geomechanical model establishment module classifies fractures into tensile fractures, shear fractures, and sutures according to the fracture dip angle in the characteristic parameters, processes the three-dimensional seismic data volume in the geological parameters using the ant body tracking algorithm to obtain ant body attributes, and converts the ant body attributes into a fault model using the fragment extraction method. Based on the tensile fractures, shear fractures, sutures, and the dip angle and dip direction of the faults in the fault model, a geomechanical model is established using the boundary element simulation algorithm, and the fracture density intensity volume, dip angle volume, dip direction volume, and maximum principal stress direction are obtained according to the geomechanical model;
[0022] The small-scale fracture model establishment module, under the dual constraints of the fracture density intensity volume and the karst facies model, and in combination with the dip angle volume and dip direction volume, uses the stochastic fracture modeling method to establish a small-scale fracture network model under the control of the maximum principal stress direction. The small-scale fracture porosity model is calculated according to the density and geometric parameters of multiple groups of fractures in the small-scale fracture network model, and then a small-scale fracture model in the fault-controlled karst area is established based on the small-scale fracture porosity model using the porosity threshold truncation method.
[0023] Preferably, in the parameter extraction module, the extracted characteristic parameters include the fracture length and fracture width extracted through core data analysis, the fracture aperture, fracture dip angle, fracture dip direction, and maximum principal stress direction extracted through imaging logging data, and the permeability extracted through on-site well test interpretation data.
[0024] Preferably, the geological parameters include a three-dimensional seismic data volume, the fracture development degree, and the depth range of fractures.
[0025] Preferably, in the model establishment module under geological law constraints, the karst facies model is comprehensively determined according to geological laws and seismic attributes. The geological laws include lithology and the degree of rock fragmentation, and the seismic attributes include tensor, wave impedance, AFE attribute, and likelihood attribute.
[0026] Preferably, in the small-scale fracture model building module, based on the small-scale fracture porosity model, a small-scale fracture model in the fault-controlled karst area is established by using the porosity threshold truncation method with the porosity being greater than or equal to the preset threshold value.
[0027] The geometric parameters include length, thickness and height.
[0028] The beneficial effects of the present invention are as follows:
[0029] The present invention relates to a method for modeling small-scale fractures in a fault-controlled karst area. Based on the characteristic parameters and geological parameters of small-scale fractures in the fault-controlled karst area, the lithology of the rock in the first depth range of the small-scale fractures in the vertical direction in the fault-controlled karst area is obtained, and the emptying and leakage section used to characterize the degree of rock fragmentation in the second depth range in the vertical direction is obtained. The development degree of the first small-scale fractures corresponding to the first depth range is obtained according to the lithology of the rock in the first depth range, and the development degree of the second small-scale fractures corresponding to the second depth range is obtained according to the degree of rock fragmentation corresponding to the emptying and leakage section in the second depth range. A karst facies model is established based on the development degree of the first small-scale fractures, the development degree of the second small-scale fractures and seismic attributes. By considering the geological law of fracture distribution and under the constraint of the geological law, combined with the AFE seismic attribute volume that can better reflect the vertical development characteristics of small-scale fractures, the distribution of small-scale fractures is constrained, and the recognition accuracy of small-scale fractures in the fault-controlled karst area can be effectively enhanced. Then, according to the fracture dip angle in the characteristic parameters, the fractures are divided into tensile fractures, shear fractures and sutures. The ant body tracking algorithm is used to process the three-dimensional seismic data volume in the geological parameters to obtain the ant body attributes, and the ant body attributes are converted into a fault model by using the fragment extraction method. Based on the dip angle and dip direction of the tensile fractures, shear fractures, sutures and faults in the fault model, and using the boundary element simulation algorithm, a geomechanical model is established. According to the geomechanical model, the fracture density intensity volume, dip angle volume, dip direction volume and maximum principal stress direction are obtained. By considering the constraints of multiple principal stresses, the accuracy of the small-scale fracture model is effectively improved. Finally, based on the fracture density intensity volume and the karst facies model, combined with the dip angle volume and dip direction volume, under the control of the maximum principal stress direction, a random fracture modeling method is used to establish a small-scale fracture network model. The small-scale fracture porosity model is calculated according to the density and geometric parameters of multiple groups of fractures in the small-scale fracture network model. Then, based on the small-scale fracture porosity model and using the porosity threshold truncation method, a small-scale fracture model in the fault-controlled karst area is established, providing a geological basis for the understanding of remaining oil distribution, the analysis of communication paths and the improvement of well patterns. The present invention can provide a set of reasonable, comprehensive and feasible identification methods for the analysis of water drive / gas drive paths in the fault-controlled karst area, and has strong guiding significance for well pattern construction and the understanding of remaining oil in the development field.
[0030] Aiming at the problem that small-scale fractures cannot be finely characterized, the present invention considers extracting small-scale fracture parameters, establishing a karst facies model under the constraint of geological laws, and establishing a mechanical model under the constraint of large-scale fractures. A small-scale fracture network model is established under the multi-factor constraint of "karst facies model + fracture density intensity body + principal stress attribute body", and a three-dimensional geological model of small-scale fractures in a fault-controlled karst area - namely, the small-scale fracture model in a fault-controlled karst area is constructed, avoiding the inapplicability of the current fracture modeling method in the fine description of fracture-vuggy reservoirs. The created analysis idea, characterization method, and analysis steps can more reasonably and comprehensively characterize the small-scale fracture structure in the fault-controlled karst area, with strong pertinence, more convenient operation, good adaptability in field applications, and stronger practicability. On the basis of the existing technology, a small-scale fracture model in the fault-controlled karst area is further constructed, providing a more direct method for analyzing the water drive / gas drive path in the fault-controlled karst area, and being more effective in guiding the construction of injection-production well patterns and the understanding of remaining oil during the injection-production process in the oil reservoir development site, having strong guidance for the development of fracture-vuggy reservoirs. Therefore, the method described in the present invention has broad application prospects.
[0031] The present invention also relates to a small-scale fracture modeling system in a fault-controlled karst area. This system corresponds to the above-mentioned small-scale fracture modeling method in a fault-controlled karst area and can be understood as a system for implementing the above-mentioned small-scale fracture modeling method in a fault-controlled karst area. The system includes a parameter acquisition module, a model establishment module under the constraint of geological laws, a geological mechanics model establishment module, and a small-scale fracture model establishment module connected in sequence. Each module works in coordination with each other. Based on small-scale fracture parameters, a karst facies model is established under the constraint of geological laws, considering the geological laws of fracture distribution and the AFE seismic attribute body that can better reflect the longitudinal development characteristics of small-scale fractures, constraining the distribution of small-scale fractures, and being able to effectively enhance the recognition accuracy of small-scale fractures in the fault-controlled karst area; and a geological mechanics model is established under the constraint of large-scale fractures, effectively improving the accuracy of the small-scale fracture model through the constraint of various characteristic parameters; and a small-scale fracture network model is established under the multi-factor constraint of "karst facies model + fracture density intensity body + principal stress attribute body", and a small-scale fracture model in the fault-controlled karst area is constructed, providing a geological basis for the understanding of remaining oil distribution, the analysis of connectivity paths, and the improvement of well patterns. BRIEF DESCRIPTION OF THE DRAWINGS
[0032] Figure 1 It is a flowchart of the small-scale fracture modeling method in the fault-controlled karst area of the present invention.
[0033] Figure 2 It is a schematic diagram of the geological mechanics model of the present invention.
[0034] Figure 3 It is a schematic diagram of the small-scale fracture network model of the present invention.
[0035] Figure 4Schematic diagram of the small-scale fracture model after roughening of the present invention. Detailed implementation manners
[0036] To better understand the content of the present invention, it will be described in detail in conjunction with the accompanying drawings and embodiments.
[0037] The present invention relates to a method for modeling small-scale fractures in a fault-controlled karst area. The flow chart of the method is as Figure 1 shown and successively includes the following steps:
[0038] I. Parameter extraction step: Extract the characteristic parameters and geological parameters of small-scale fractures in the fault-controlled karst area. Specifically, parameters such as fracture length and fracture width can be analyzed and obtained through core data. Through imaging logging data, parameters such as fracture dip angle, fracture strike, fracture aperture, and maximum principal stress azimuth can be extracted. At the same time, the permeability is determined through on-site well test interpretation data. Among them, the fracture dip angle can reflect the fracture properties (such as high-angle fractures, horizontal dissolution fractures), and the fracture aperture is generally relatively low (such as 0.00023 - 0.00069 cm in the TP37 well area). In addition, the maximum principal stress azimuth is determined through the caving wellbore azimuth, drilling-induced fractures, and fast shear wave azimuth.
[0039] II. Model establishment step under geological law constraints: Obtain the lithology of the rock in the first depth range of the small-scale fractures in the fault-controlled karst area longitudinally, and obtain the open-hole leakage section used to characterize the degree of rock fragmentation in the second depth range longitudinally. According to the lithology of the rock in the first depth range, obtain the corresponding development degree of the first small-scale fractures in the first depth range. According to the degree of rock fragmentation corresponding to the open-hole leakage section in the second depth range, obtain the corresponding development degree of the second small-scale fractures in the second depth range. Based on the development degree of the first small-scale fractures, the development degree of the second small-scale fractures, and seismic attributes, establish a karst facies model under geological law constraints.
[0040] Specifically, small-scale fractures in the fault-controlled karst area are mainly affected by rock lithology and rock fragmentation degree in the vertical direction. That is, geological laws include rock lithology and rock fragmentation degree. Therefore, according to the core, the rock lithology in the first depth range (i.e., the surface of the development zone, located at 0-30m) in the vertical direction of small-scale fractures in the fault-controlled karst area is obtained. First, the core at 0-30m near the top of the Yijianfang Formation is obtained. The core shows that the lithology at 0-30m is yellowish-gray sandy micrite limestone intercalated with gray muddy bands. This lithology results in a low degree of development of small-scale fractures within the range of 0-30m. Then, the information of the blowout and leakage section used to characterize the rock fragmentation degree in the second depth range (i.e., the deep part of the development zone, located below 30m) in the vertical direction is obtained. According to the rock lithology of the surface of the development zone, the development degree of the first small-scale fractures (which can also be called the development degree of small-scale fractures on the surface of the development zone) is obtained. Among them, the rock fragmentation degree can be characterized by the blowout and leakage section of the actual drilled well, and the blowout and leakage section generally corresponds to the area with strong rock fragmentation degree. Therefore, according to the analysis of the rock fragmentation degree corresponding to the blowout and leakage section in the deep part of the development zone, the development degree of the second small-scale fractures (which can also be called the development degree of small-scale fractures in the deep part of the development zone) within the range of 30-50m is relatively high. In addition, by comparing seismic attributes such as tensor, wave impedance, AFE, and likelihood, it is found that the AFE seismic attribute can better reflect the longitudinal development characteristics of small-scale fractures. Therefore, a karst facies model under the constraint of geological laws is established based on the development degree of the first small-scale fractures, the development degree of the second small-scale fractures, and the AFE seismic attribute (preferably the threshold value ≥80). Therefore, the karst facies model is comprehensively determined according to geological laws and seismic attributes. This step fully considers the geological laws of fracture distribution and the AFE seismic attribute volume that can better reflect the longitudinal development characteristics of small-scale fractures, restricts the distribution of small-scale fractures, and can effectively enhance the recognition accuracy of small-scale fractures in the fault-controlled karst area.
[0041] III. Steps for establishing a geomechanical model: According to the fracture dip angle in the characteristic parameters, fractures are divided into tensile fractures, shear fractures, and sutures. The ant body tracking algorithm is used to process the three-dimensional seismic data volume in the geological parameters to obtain the ant body attribute, and the fragment extraction method is used to convert the ant body attribute into a fault model. Based on the tensile fractures, shear fractures, sutures, and the dip angle and dip direction of the faults in the fault model, the boundary element simulation algorithm is used to establish a geomechanical model. According to the geomechanical model, the fracture density intensity volume, dip angle volume, dip direction volume, and maximum principal stress direction are obtained. This step can also be understood as the steps for establishing a geomechanical model under the constraint of large-scale fractures.
[0042] Specifically, small-scale fractures in the fault-controlled karst area are mainly constrained by the principal stress in the plane. Currently, only the principal stress data of the well points are available, while the principal stress data between wells are missing. Therefore, according to the relationship between the principal stress and the fractures, the fractures can be classified into tensile fractures, shear fractures, and sutures according to the fracture dip angle in the characteristic parameters first. Then, the ant body tracking algorithm is used to process the 3D seismic data volume in the geological parameters to obtain the ant body attributes. Next, the fragment extraction method is used to convert the ant body attributes into a fault model. Based on the tensile fractures, shear fractures, sutures, and the dip angle and dip direction of the faults in the fault model, the boundary element simulation algorithm is used to establish a geomechanical model. According to the geomechanical model, the fracture density intensity volume, dip angle volume, dip direction volume, and maximum principal stress direction are obtained. By establishing a geomechanical model under the constraint of large-scale fractures (the large-scale fractures provide the dip direction and dip angle), the geomechanical model is as Figure 2 shown. Through the series of logics of fracture slices (tensile fractures, shear fractures, and sutures) - fault model - stress attribute map - fracture intensity volume (fracture density intensity volume), the stress attribute map, that is, the geomechanical model, is obtained. This step takes into account the constraint of large-scale fractures and effectively improves the accuracy of the small-scale fracture model.
[0043] IV. Steps for establishing a small-scale fracture model: Based on the double constraints of the fracture density intensity volume and the karst facies model, combined with the dip angle volume and dip direction volume, under the control of the maximum principal stress direction, a random fracture modeling method is used to establish a small-scale fracture network model; according to the density and geometric parameters of multiple groups of fractures in the small-scale fracture network model, the small-scale fracture porosity model is calculated. Then, based on the small-scale fracture porosity model and using the porosity threshold truncation method, a small-scale fracture model in the fault-controlled karst area is established. This step can also be understood as the step for establishing a small-scale fracture model with multi-factor constraints of "karst facies + fracture intensity volume + principal stress attribute volume".
[0044] Specifically, under the double constraints of the fracture density intensity volume and the karst facies model, combined with the principal stress attribute volumes such as the dip angle volume and dip direction volume, under the control of the maximum principal stress direction, a random fracture modeling method is used to establish a small-scale fracture network model. Then, according to the density and geometric parameters (i.e., length, thickness, and height) of multiple groups of fractures in the small-scale fracture network model, the small-scale fracture porosity model is calculated. Finally, based on the small-scale fracture porosity model and using the porosity threshold truncation method with the porosity greater than or equal to the preset threshold (porosity ≥ 0.002), a small-scale fracture model in the fault-controlled karst area is established, providing a geological basis for the understanding of remaining oil distribution, the analysis of communication paths, and the improvement of well patterns. Among them, the small-scale fracture network model is as Figure 3 shown. Through the stress attribute map - fracture intensity volume - dip angle volume - dip direction volume - dissolved pore facies (karst facies model), the small-scale fracture network model is obtained; then, the small-scale fracture porosity model is calculated, and a small-scale fracture model in the fault-controlled karst area is established. The coarsened small-scale fracture model is as Figure 4as shown
[0045] The present invention also relates to a small-scale fracture modeling system for fault-controlled karst areas. This system corresponds to the above-mentioned small-scale fracture modeling method for fault-controlled karst areas and can be understood as a system for implementing the above-mentioned small-scale fracture modeling method for fault-controlled karst areas. The system includes a parameter extraction module, a model establishment module under geological law constraints, a geomechanical model establishment module, and a small-scale fracture model establishment module that are connected in sequence. Specifically,
[0046] The parameter extraction module extracts the characteristic parameters and geological parameters of the small-scale fractures in the fault-controlled karst area;
[0047] The model establishment module under geological law constraints obtains the lithology of the rock in the first depth range longitudinally located in the small-scale fractures in the fault-controlled karst area, and obtains the emptying and leakage section used to characterize the degree of rock fragmentation in the second depth range longitudinally. According to the lithology of the rock in the first depth range, the corresponding development degree of the first small-scale fractures in this first depth range is obtained. According to the degree of rock fragmentation corresponding to the emptying and leakage section in the second depth range, the corresponding development degree of the second small-scale fractures in this second depth range is obtained. Based on the development degree of the first small-scale fractures, the development degree of the second small-scale fractures, and seismic attributes, a karst facies model under geological law constraints is established;
[0048] The geomechanical model establishment module classifies the fractures into tensile fractures, shear fractures, and sutures according to the fracture dip angle in the characteristic parameters, processes the three-dimensional seismic data volume in the geological parameters using the ant body tracking algorithm to obtain ant body attributes, and converts the ant body attributes into a fault model using the fault extraction method. Based on the dip angle and dip direction of the tensile fractures, shear fractures, sutures, and faults in the fault model, a geomechanical model is established using the boundary element simulation algorithm. According to the geomechanical model, a fracture density intensity body, a dip angle body, a dip direction body, and a maximum principal stress direction are obtained;
[0049] The small-scale fracture model establishment module, based on the dual constraints of the fracture density intensity body and the karst facies model, and combined with the dip angle body and the dip direction body, under the control of the maximum principal stress direction, uses the stochastic fracture modeling method to establish a small-scale fracture network model. According to the density and geometric parameters of multiple groups of fractures in the small-scale fracture network model, a small-scale fracture porosity model is calculated, and then based on the small-scale fracture porosity model and using the porosity threshold truncation method, a small-scale fracture model for the fault-controlled karst area is established.
[0050] Preferably, in the parameter extraction module, the extracted characteristic parameters include the fracture length and fracture width extracted through core data analysis, the fracture aperture, fracture dip angle, fracture dip direction, and maximum principal stress direction extracted through imaging logging data, and the permeability extracted through on-site well test interpretation data.
[0051] Preferably, the geological parameters include 3D seismic data volume, fracture development degree, and depth range of fractures.
[0052] Preferably, in the model establishment module under geological law constraints, the karst facies model is determined comprehensively according to geological laws and seismic attributes. The geological laws include lithology and degree of rock fragmentation, and the seismic attributes include tensor, wave impedance, AFE attribute, and likelihood attribute.
[0053] Preferably, in the small-scale fracture model establishment module, based on the small-scale fracture porosity model, a small-scale fracture model in the fault-controlled karst area is established by using the porosity threshold truncation method with porosity greater than or equal to a preset threshold.
[0054] The geometric parameters include length, thickness, and height.
[0055] The present invention provides an objective and scientific method and system for modeling small-scale fractures in fault-controlled karst areas. Based on small-scale fracture parameters, a karst facies model is established under geological law constraints, and a geomechanical model is established under large-scale fracture constraints. A small-scale fracture network model is established under the multi-factor constraints of "karst facies model + fracture density intensity volume + principal stress attribute volume", and a small-scale fracture model in the fault-controlled karst area is constructed, providing a geological basis for the understanding of remaining oil distribution, connectivity path analysis, and well pattern improvement.
[0056] It should be noted that the above specific embodiments can enable those skilled in the art to understand the present invention more comprehensively, but do not limit the present invention in any way. Therefore, although this specification has described the present invention in detail with reference to the drawings and embodiments, those skilled in the art should understand that the present invention can still be modified or equivalently replaced. In short, all technical solutions and their improvements that do not depart from the spirit and scope of the present invention should be covered by the protection scope of the patent of the present invention.
Claims
1. A small-scale fracture modeling method in a fault-controlled karst area, characterized in that, Including the following steps: Parameter extraction step: Extract the characteristic parameters and geological parameters of small-scale fractures in the fault-controlled karst area; Model establishment step under geological law constraints: Obtain the lithology of the rock in the first depth range in the vertical direction of the small-scale fractures in the fault-controlled karst area, and obtain the emptying and leakage section used to characterize the degree of rock fragmentation in the second depth range in the vertical direction. Obtain the development degree of the first small-scale fractures corresponding to the first depth range according to the lithology of the rock in the first depth range, and obtain the development degree of the second small-scale fractures corresponding to the second depth range according to the degree of rock fragmentation corresponding to the emptying and leakage section in the second depth range. Establish a karst facies model under geological law constraints based on the development degree of the first small-scale fractures, the development degree of the second small-scale fractures, and seismic attributes; Geomechanical model establishment step: Classify the fractures into tensile fractures, shear fractures, and sutures according to the fracture dip angle in the characteristic parameters. Use the ant body tracking algorithm to process the three-dimensional seismic data volume in the geological parameters to obtain the ant body attributes, and use the fragment extraction method to convert the ant body attributes into a fault model. Based on the tensile fractures, shear fractures, sutures, and the dip angle and dip direction of the faults in the fault model, establish a geomechanical model using the boundary element simulation algorithm. Obtain the fracture density intensity volume, dip angle volume, dip direction volume, and maximum principal stress direction according to the geomechanical model; Small-scale fracture model establishment step: Based on the double constraints of the fracture density intensity volume and the karst facies model, and combined with the dip angle volume and dip direction volume, under the control of the maximum principal stress direction, establish a small-scale fracture network model using the stochastic fracture modeling method. Calculate the small-scale fracture porosity model according to the density and geometric parameters of multiple groups of fractures in the small-scale fracture network model, and then establish a small-scale fracture model in the fault-controlled karst area based on the small-scale fracture porosity model and using the porosity threshold truncation method; 2. The small-scale fracture modeling method in the karst area with discontinuous control according to claim 1, wherein In the parameter extraction step, the extracted characteristic parameters include the fracture length and fracture width extracted through core data analysis, the fracture aperture, fracture dip angle, fracture dip direction, and maximum principal stress direction extracted through imaging logging data, and the permeability extracted through on-site well test interpretation data.
3. The small-scale fracture modeling method in the karst area with discontinuous control according to claim 1, characterized in that, In the parameter extraction step, the geological parameters include the three-dimensional seismic data volume, the fracture development degree, and the depth range of the fractures.
4. The small-scale fracture modeling method in the karst area with broken control according to claim 1, characterized in that, In the model establishment step under geological law constraints, the karst facies model is comprehensively determined according to geological laws and seismic attributes. The geological laws include the lithology of the rock and the degree of rock fragmentation, and the seismic attributes include tensor, wave impedance, AFE attribute, and likelihood attribute.
5. The small-scale fracture modeling method in the karst area with discontinuous control according to claim 1, characterized in that, In the small-scale fracture model establishment step, based on the small-scale fracture porosity model, establish a small-scale fracture model in the fault-controlled karst area using the porosity threshold truncation method with the porosity greater than or equal to the preset threshold; The geometric parameters include length, thickness, and height.
6. A small-scale fracture modeling system for fractured-controlled karst areas, characterized in that, Including a parameter extraction module, a model establishment module under geological law constraints, a geomechanical model establishment module, and a small-scale fracture model establishment module connected in sequence, The parameter extraction module extracts the characteristic parameters and geological parameters of small-scale fractures in the fault-controlled karst area; The model establishment module under geological law constraints obtains the lithology of rocks in the first depth range in the vertical direction of small-scale fractures in the fault-controlled karst area, and obtains the emptying and leakage section located in the second depth range in the vertical direction for characterizing the degree of rock fragmentation. The development degree of the first small-scale fractures corresponding to the first depth range is obtained according to the lithology of the rocks in the first depth range, and the development degree of the second small-scale fractures corresponding to the second depth range is obtained according to the degree of rock fragmentation corresponding to the emptying and leakage section in the second depth range. Based on the development degree of the first small-scale fractures, the development degree of the second small-scale fractures and seismic attributes, a karst facies model under geological law constraints is established; The geomechanical model establishment module classifies fractures into tensile fractures, shear fractures and sutures according to the fracture dip angle in the characteristic parameters, processes the three-dimensional seismic data volume in the geological parameters by using the ant body tracking algorithm to obtain the ant body attributes, and converts the ant body attributes into a fault model by using the fragment extraction method. Based on the tensile fractures, shear fractures, sutures and the dip angle and dip direction of the faults in the fault model, a geomechanical model is established by using the boundary element simulation algorithm, and the fracture density intensity volume, dip angle volume, dip direction volume and maximum principal stress direction are obtained according to the geomechanical model; The small-scale fracture model establishment module, under the dual constraints of the fracture density intensity volume and the karst facies model, and combined with the dip angle volume and the dip direction volume, controls in the direction of the maximum principal stress, and uses the stochastic fracture modeling method to establish a small-scale fracture network model. The small-scale fracture porosity model is calculated according to the density and geometric parameters of multiple groups of fractures in the small-scale fracture network model, and then a small-scale fracture model in the fault-controlled karst area is established based on the small-scale fracture porosity model and by using the porosity threshold truncation method; 7. The small-scale fracture modeling system for karst areas with discontinuous control according to claim 6, characterized in that, In the parameter extraction module, the extracted characteristic parameters include the fracture length and fracture width extracted through core data analysis, the fracture aperture, fracture dip angle, fracture dip direction and maximum principal stress direction extracted through imaging logging data, and the permeability extracted through on-site well test interpretation data; 8. The small-scale fracture modeling system for karst areas with discontinuous control according to claim 6, characterized in that, The geological parameters include a three-dimensional seismic data volume, the fracture development degree and the depth range of fractures; 9. The small-scale fracture modeling system for karst areas with discontinuous control according to claim 6, characterized in that, In the model establishment module under geological law constraints, the karst facies model is comprehensively determined according to geological laws and seismic attributes. The geological laws include lithology of rocks and the degree of rock fragmentation, and the seismic attributes include tensor, wave impedance, AFE attribute and likelihood attribute; 10. The small-scale fracture modeling system for karst areas with broken control according to claim 6, characterized in that, In the small-scale fracture model establishment module, based on the small-scale fracture porosity model, a small-scale fracture model in the fault-controlled karst area is established by using the porosity threshold truncation method with the porosity greater than or equal to a preset threshold; The geometric parameters include length, thickness and height;