Shale gas geological partition evaluation method under complex background

Abstract

The invention discloses a shale gas geological partition evaluation method under a complex background, which comprises the following steps: acquiring shale quality characteristics of a shale gas exploratory well or an evaluation well of a development block, and carrying out longitudinal and plane characteristic comparative analysis; determining fine features of development area construction; through carrying out earthquake processing and interpretation, the structure unit characteristics are determined; determining the influence of the development zone fault on shale gas preservation; compiling a target stratum structure map, and compiling a development block target stratum burial depth map in combination with the surface elevation information; compiling a target stratum dip angle map on the basis of the target stratum structure map; determining natural fracture characteristics of a target layer of a development area; determining the longitudinal stress interlayer distribution condition of the target layer of the development area; solving the minimum horizontal stress gradient of the development area; determining the maximum principal stress direction of the development block; and according to the data, in combination with the geological characteristics of the development area, preferably selecting parameters which fully reflect the gas content and compressibility of the development area, and carrying out geological zoning standard evaluation research, so that a geological zoning result of the development area is obtained on the basis.

Description

Technical Field

[0001] This invention belongs to the field of shale gas development technology, specifically relating to a method for evaluating geological zoning of shale gas. Background Technology

[0002] Developing shale gas is one of the important measures to ensure my country's energy security and comprehensively improve resource utilization efficiency. my country is rich in shale gas resources, with the world's largest recoverable resources. However, compared with North America, shale gas is characterized by older strata, higher thermal evolution, stronger tectonic deformation, greater burial depth, more complex surface conditions, and more diverse fluid properties. Shale gas is mainly distributed in complex tectonic areas, making effective utilization more difficult.

[0003] With the advancement of shale gas exploration and development, domestic marine shale gas is gradually moving towards complex tectonic areas such as deep layers, normal pressure zones, and fault-developed areas. The exploration and development targets are becoming increasingly complex, and the difficulty of profitable development is constantly increasing. Against this background, the applicability of the previous shale gas exploration and development experience based on tectonically stable zones still needs to be further verified, and there is an urgent need to establish an evaluation method for shale gas exploration and development suitable for complex tectonic backgrounds.

[0004] Current research primarily focuses on the selection of favorable areas for shale gas exploration and development. Both domestically and internationally, static geological parameters are typically used for qualitative evaluation of shale gas exploration areas, such as regional geological background, source rock characteristics, and preservation conditions. However, relatively little research is available on how to further evaluate these selected favorable areas to achieve efficient development. The exploration and development practice of the Fuling shale gas field shows that as exploration and development gradually advances into deeper, more atmospheric, fault-prone, and stress-field-complex areas, the development results can vary significantly even for the same favorable development area. Before a block officially enters development, it is necessary to conduct targeted studies on shale quality, structural details, and geostress fields to clarify the differences in geological conditions, determine reasonable geological zoning, and formulate different development technology policies for different geological zones, thereby ensuring maximum development benefits. Summary of the Invention

[0005] The purpose of this invention is to solve the problem of how to achieve geological zoning in shale gas development blocks under complex backgrounds. It provides a reasonable geological zoning evaluation method to address the shortcomings of existing technologies and improve the utilization of block reserves and the efficiency of gas field development.

[0006] To achieve the above objectives, the following technical solution is adopted: A method for evaluating shale gas geological zoning under complex backgrounds includes the following steps: S1, obtain the shale quality characteristics of shale gas exploration wells or appraisal wells in the development block, and conduct vertical and planar characteristic comparison analysis; S2, clarifying the detailed structural features of the development zone; through seismic processing and interpretation, clarifying the characteristics of structural units; S3, clarify the impact of faults in the development zone on shale gas preservation; S4. Compile a structural map of the target layer and, in conjunction with surface elevation information, compile a burial depth map of the target layer for the development block. S5. Based on the structural map of the target layer, compile the dip angle map of the target layer. S6, clearly define the natural crack characteristics of the target layer in the development zone; S7, clarify the distribution of longitudinal stress barriers in the target layer of the development zone; S8, calculate the minimum horizontal stress gradient in the development zone; S9, clearly defines the direction of the maximum principal stress in the development block; S10. Based on the above data and combined with the geological characteristics of the development zone, select parameters that fully reflect the gas content and compressibility of the development zone, conduct a geological zoning standard evaluation study, and obtain the geological zoning results of the development block on this basis.

[0007] According to the above scheme, in step S1, the shale quality characteristics of the shale gas exploration wells or appraisal wells in the development block include the organic carbon content and porosity of the target layer.

[0008] According to the above scheme, in step S2, the detailed structural features include the division of the target layer structural units in the development area, fracture features, burial depth, and stratum dip angle.

[0009] According to the above plan, in step S3, the impact of faults in the development area on shale gas preservation is clarified by conducting research on fault phases, causes, and fault displacements.

[0010] According to the above scheme, in step S6, based on the high-precision seismic curvature attributes of the optimized scan, the natural fracture characteristics of the target layer in the development area are clarified, which are usually characterized by curvature characteristics in the study.

[0011] According to the above plan, in step S7, the characteristics of the geostress field of the target shale layer in the development area are analyzed, and the distribution of the longitudinal stress strata of the target shale layer in the development area is clarified through rock mechanics tests in exploration wells or appraisal wells.

[0012] According to the above scheme, in step S7, the stress field characteristics of the target shale in the development area include stress stratification distribution, direction of maximum horizontal principal stress, maximum horizontal principal stress, minimum horizontal principal stress, vertical stress, and gradient of minimum horizontal principal stress.

[0013] According to the above scheme, in step S8, the plane distribution of the minimum principal stress in the development area is obtained based on the finite element stress field simulation results. Based on this, the plane distribution of the minimum principal stress is corrected using the segmented closure pressure data of the horizontal well. The minimum horizontal stress gradient in the development area is obtained by combining the characteristics of the burial depth plane distribution.

[0014] According to the above plan, in step S9, the direction of the maximum principal stress in the development block is determined by using the wellbore of the exploration well or appraisal well, wellbore collapse, and special logging materials.

[0015] According to the above scheme, in step S10, the geological zoning standard evaluation study includes determining various parameters such as comprehensive shale quality, shale structural characteristics, and shale stress field characteristics.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This application provides a method for evaluating shale gas geological zoning under complex backgrounds, which identifies the fine structural characteristics of shale gas development areas, formulates evaluation standards for geological zoning of development areas, clarifies the geological zoning results, and guides the preparation of shale gas development plans and the deployment of development well locations.

[0017] This invention can make full use of the differences in geological conditions, formulate reasonable development technology policies for different zones, significantly improve the utilization of block reserves and the development efficiency of gas fields, and provide a reference for the determination of shale block development zones. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0019] Appendix Figure 1 Flowchart of the shale gas geological zoning evaluation method under complex background described in this invention.

[0020] Appendix Figure 2 : Composite columnar section of single wells in the Pingqiao block of the Fuling shale gas field.

[0021] Appendix Figure 3 : Diagram of the Wufeng Formation bottom fault system in the Pingqiao Block of the Fuling Shale Gas Field.

[0022] Appendix Figure 4 Contour map of the burial depth of the Wufeng Formation in the Pingqiao Block of the Fuling Shale Gas Field.

[0023] Appendix Figure 5 Dip diagram of the Wufeng Formation bottom strata in the Pingqiao Block of the Fuling Shale Gas Field.

[0024] Appendix Figure 6 : Map showing the division of the Wufeng Formation bottom structural unit in the Pingqiao Block of the Fuling Shale Gas Field.

[0025] Appendix Figure 7 Curvature diagram of the Wufeng Formation bottom in the Pingqiao Block of the Fuling Shale Gas Field.

[0026] Appendix Figure 8 Plan view of minimum horizontal principal stress in the target layer of the Pingqiao block of the Fuling shale gas field.

[0027] Appendix Figure 9 : Distribution map of minimum horizontal principal stress gradient of the target layer in the Pingqiao block of the Fuling shale gas field.

[0028] Appendix Figure 10 Longitudinal stress characteristics of the target layer in the Pingqiao block of the Fuling shale gas field.

[0029] Appendix Figure 11 Comprehensive evaluation zoning map of the Pingqiao block of the Fuling shale gas field. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0031] The specific implementation provides a method for evaluating shale gas geological zoning under complex backgrounds, as detailed in the appendix. Figure 1 As shown in the flowchart, the geological zoning of the Pingqiao block of the Fuling shale gas field is taken as an example: S1: Obtain the shale quality characteristics of shale gas exploration or appraisal wells in the Pingqiao block of the Fuling shale gas field, and conduct vertical and planar characteristic comparative analysis.

[0032] The development strata of the Pingqiao block in the Fuling shale gas field are the gas-bearing shale section of the Wufeng-Longmaxi Formation, which can be vertically divided into nine sub-layers, ①-⑨ (see appendix). Figure 2 Among them, the shale quality of layers ①-⑤ is stable in planar distribution, with organic carbon content ranging from 2.5% to 3.7%, silica content ranging from 55% to 75%, porosity ranging from 4.0% to 4.5%, and gas saturation ranging from 55% to 67%, and the geological characteristics are relatively stable.

[0033] S2, clearly defines the detailed structural features of the Pingqiao block in the Fuling shale gas field.

[0034] ① The Pingqiao Block of the Fuling Shale Gas Field has approximately 45 faults of varying sizes, generally trending northeast. About 25 of these faults have a displacement greater than 50 meters, including three third-order faults: the Pingqiao West Fault, the Pingqiao East No. 1 Fault, and the Pingqiao East No. 2 Fault. The Pingqiao West Fault is the dominant fault in the Pingqiao Block, forming a fault-spreading fold. The Pingqiao East No. 1 and No. 2 Faults developed through thrust faulting, jointly controlling the anticline structure. Secondary faults mainly develop along the leading edge of the Pingqiao West Fault, with sporadic small faults also associated along the leading edge of the Pingqiao East No. 1 Fault (see Appendix). Figure 3 ).

[0035] ② The burial depth of the Pingqiao block in the Fuling shale gas field varies greatly in planar direction, ranging from 2500 to 4400 m. The depth increases from south to north and from the center outwards. The core of the Pingqiao anticline has the shallowest burial depth, while the depth gradually increases in the western and eastern flanks (see appendix). Figure 4 ).

[0036] ③ The dip angle of the formations in the Pingqiao block of the Fuling shale gas field varies rapidly. The core of the Pingqiao anticline has a generally gentle dip, becoming steeper near the limbs, with a dip angle of 5-30°; the limbs of the anticline have a larger dip angle (15-50°); the eastern slope of Pingqiao is generally steep, with a dip angle of 20-50° (see appendix). Figure 5 ).

[0037] ④ The Pingqiao Block of the Fuling Shale Gas Field is a fault-antic structure sandwiched between the Pingqiao West and Pingqiao East No. 2 faults. It can be broadly divided into two fourth-order structures: the Pingqiao East Slope and the Pingqiao Main Area. The Pingqiao East Slope has a simple structure with a large dip angle and considerable depth. The Pingqiao Main Area is further subdivided into three fifth-order structures. The western wing of the Pingqiao anticline has well-developed faults, adjacent to the Pingqiao West main control fault, with steep strata and strong deformation. The core of the anticline has a gentler dip, less developed faults, and moderate depth. The eastern wing of the anticline is adjacent to the Pingqiao East No. 1 fault (which disappears in the central and northern parts of the block), with scattered small faults (see Appendix). Figure 6 ).

[0038] ⑤ The Pingqiao Block of the Fuling Shale Gas Field has well-developed natural fractures, mainly high-angle fractures. Vertically, layer ① has the highest degree of development, followed by layers ④-⑦; layers ⑧ and ⑨ have smaller fracture widths. Curvature prediction of the Pingqiao Block shows that the natural fractures in the Pingqiao Block exhibit an east-west zonation, with stronger fractures in the east and west and relatively weaker fractures in the core. A distinct fold belt develops at the structural ridge. The curvature plane can be divided into three types: a fracture-developed area in the western wing of the main body, an undeveloped area in the core and eastern wing of the main body, and a fracture-developed area on the eastern slope. In the western wing of the main Pingqiao area, the fractures are basically located on the fault zone, with higher curvature near the fault and a dense distribution of high-curvature fractures. In the core and eastern wing of the main Pingqiao area, fractures are generally undeveloped, with a fold belt developing in the middle. On the eastern slope of Pingqiao, the fractures are basically located on the fault zone, with higher curvature near the fault and a dense distribution of high-curvature fractures (see Appendix). Figure 7 ).

[0039] S3, analyze the geostress field characteristics of the target shale layer in the Pingqiao block of the Fuling shale gas field.

[0040] ① The main anticline region of the Pingqiao block in the Fuling shale gas field exhibits tensile stress characteristics, with minimum principal stresses ranging from 50 to 80 MPa; the eastern slope exhibits compressive stress characteristics, with minimum principal stresses ranging from 80 to 110 MPa (see appendix). Figure 8 The direction of the maximum principal stress in the Pingqiao block is northwest-southeast (105-135°).

[0041] ② The Pingqiao block of the Fuling shale gas field is affected by tectonic compression, resulting in strong heterogeneity of the stress plane and obvious stress concentration zones. The minimum stress gradient in the Pingqiao block is generally less than 2.5, while in the core of the main area and the local stress concentration zones of the eastern wing, the minimum stress gradient is between 2.5 and 2.8 (see Appendix). Figure 9 ).

[0042] ③ In the Pingqiao block of the Fuling shale gas field, the longitudinal stress curve of the target layer generally exhibits a tooth-like shape, with occasional finger-shaped, funnel-shaped, and box-shaped high-stress strata. The strata thickness ranges from 2.5 to 5.4 m. The maximum stress value of the strata and the stress difference between the upper and lower overlying strata range from 4 to 11 MPa. It can be divided into six stress segments: three high and three low. Among them, layer ⑨ is the low-stress segment, layer ⑧ is the stable medium-high stress segment, and from north to south, the high-stress segment gradually thickens from layers ⑥-⑦ to layers ④-⑦, while the lower low-stress segment gradually thins. Finger-shaped high-sharp stress strata develop under the low-stress background of layer ① (see Appendix). Figure 10 ).

[0043] S4. Based on the data and analysis results obtained in steps S1, S2 and S3, seven parameters, namely organic carbon, porosity, geological deformation intensity, stratum dip angle, curvature characteristics, stratum burial depth and stress gradient, are selected to carry out geological zoning standard evaluation research and obtain zoning results, as shown in Table 1.

[0044] Table 1 Evaluation Criteria for Typical Shale Gas Geological Zoning under Complex Backgrounds

[0045] This invention patent primarily addresses the complex geological zoning of shale gas, adding stress gradient as an evaluation parameter for zoning standards. The stress gradient is calculated based on the minimum principal stress magnitude planar distribution obtained from finite element stress field simulation results. Using this as a foundation, the stress magnitude planar diagram is further corrected using horizontal well segmented closure pressure data, and the minimum horizontal stress gradient is obtained by combining the burial depth planar distribution characteristics. Previous studies often focused only on static parameters such as organic carbon and porosity, neglecting the impact of engineering modification parameters on geological zoning. Therefore, this invention emphasizes the innovation of evaluation parameters.

[0046] Based on the structural unit division, and taking into account factors such as shale quality, structural deformation intensity, formation dip angle, curvature characteristics, and burial depth (3800m), the Pingqiao block of the Fuling shale gas field is divided into three major regions: central, eastern, and western. These are further subdivided into seven smaller regions: Central Region 1, with organic carbon 3.0-3.5%, porosity 3.7-4.1%, strong structural deformation, formation dip angle 5-30°, developing patchy weak curvature, and a burial depth of 2450-3000m, is technically recoverable with single wells. The average reserves are 109 million cubic meters; in Zone 2, organic carbon is 3.0-3.5%, porosity is 3.7-4.1%, structural deformation is relatively weak, the formation dip angle is 5-30°, and it develops banded weak curvature and strong curvature at the ridge, with a burial depth of 2700-3100m. The average technically recoverable reserves per well are 64 million cubic meters; in Zone 3, organic carbon is 3.0-3.5%, porosity is 3.7-4.1%, structural deformation is strong, the formation dip angle is 5-30°, and it develops banded weak curvature, with a burial depth of 2800-3800m. The average technically recoverable reserves per well are 64 million cubic meters. The average technically recoverable reserves are 0.89 billion cubic meters; in Zone 4, organic carbon is 2.5-3.2%, porosity is 3.5-3.8%, structural deformation is weak, the formation dip angle is 10-20°, with banded strong curvature, burial depth is 3800-4400m, and the average technically recoverable reserves per well are 0.38 billion cubic meters; in Zone 1, organic carbon is 3.0-3.5%, porosity is 3.4-3.8%, structural deformation is weak, the formation dip angle is 20-55°, with banded strong curvature, burial depth is 3500-3800m, and the average technically recoverable reserves per well are 0.38 billion cubic meters. The average technically recoverable reserves per well are 103 million cubic meters. In the East 2 area, organic carbon is 3.0-3.5%, porosity is 3.4-3.8%, tectonic deformation is relatively weak, formation dip angle is 10-25°, with spotted strong curvature, burial depth 3800-4400m, and average technically recoverable reserves per well are 64 million cubic meters. In the West area, organic carbon is 2.4-3.0%, porosity is 3.5-4.0%, tectonic deformation is relatively weak, formation dip angle is 15-45°, with striped strong curvature, burial depth 3000-4200m (see appendix). Figure 11 ).

[0047] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for evaluating shale gas geological zoning under complex backgrounds, characterized in that... Includes the following steps: S1, obtain the shale quality characteristics of shale gas exploration wells or appraisal wells in the development block, and conduct vertical and planar characteristic comparison analysis; S2, clarifying the detailed structural features of the development zone; through seismic processing and interpretation, clarifying the characteristics of structural units; S3, clarify the impact of faults in the development zone on shale gas preservation; S4. Compile a structural map of the target layer and, in conjunction with surface elevation information, compile a burial depth map of the target layer for the development block. S5. Based on the structural map of the target layer, compile the dip angle map of the target layer. S6, clearly define the natural crack characteristics of the target layer in the development zone; S7, clarify the distribution of longitudinal stress barriers in the target layer of the development zone; S8, calculate the minimum horizontal stress gradient in the development zone; S9, clearly defines the direction of the maximum principal stress in the development block; S10. Based on the above data and combined with the geological characteristics of the development zone, select parameters that fully reflect the gas content and compressibility of the development zone, conduct a geological zoning standard evaluation study, and obtain the geological zoning results of the development block on this basis.

2. The shale gas geological zoning evaluation method under complex backgrounds as described in claim 1, characterized in that... In step S1, the shale quality characteristics of the shale gas exploration wells or appraisal wells in the development block include the organic carbon content and porosity of the target layer.

3. The shale gas geological zoning evaluation method under complex backgrounds as described in claim 1, characterized in that... In step S2, the detailed structural features include the division of the target layer structural units in the development area, fracture features, burial depth, and stratigraphic dip angle.

4. The shale gas geological zoning evaluation method under complex backgrounds as described in claim 1, characterized in that... In step S3, by conducting research on fault phases, causes, and fault displacement, the impact of faults in the development area on shale gas preservation is clarified.

5. The shale gas geological zoning evaluation method under complex backgrounds as described in claim 1, characterized in that... In step S6, based on the high-precision seismic curvature attributes of the optimized scan, the natural fracture characteristics of the target layer in the development area are identified, which are usually characterized by curvature features in the study.

6. The shale gas geological zoning evaluation method under complex backgrounds as described in claim 1, characterized in that... In step S7, the characteristics of the geostress field of the target shale layer in the development area are analyzed, and the distribution of the longitudinal stress strata of the target shale layer in the development area is clarified through rock mechanics tests in exploration wells or appraisal wells.

7. The shale gas geological zoning evaluation method under complex backgrounds as described in claim 1, characterized in that... In step S7, the stress field characteristics of the target shale in the development area include stress strata distribution, direction of maximum horizontal principal stress, maximum horizontal principal stress, minimum horizontal principal stress, vertical stress, and gradient of minimum horizontal principal stress.

8. The shale gas geological zoning evaluation method under complex backgrounds as described in claim 1, characterized in that... In step S8, the plane distribution of the minimum principal stress in the development area is obtained based on the finite element stress field simulation results. Based on this, the plane distribution of the minimum principal stress is corrected using the segmented closure pressure data of the horizontal well. The minimum horizontal stress gradient in the development area is obtained by combining the characteristics of the burial depth plane distribution.

9. The shale gas geological zoning evaluation method under complex backgrounds as described in claim 1, characterized in that... In step S9, the direction of the maximum principal stress in the development block is determined by utilizing the wellbore of the exploration or appraisal well, wellbore collapse, and special logging materials.

10. The shale gas geological zoning evaluation method under complex backgrounds as described in claim 1, characterized in that... In step S10, the geological zoning standard evaluation study includes determining various parameters such as comprehensive shale quality, shale structural characteristics, and shale stress field characteristics.

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