| Taking the shale reservoir of well Ning 201 area of Changning Block of Sichuan Basin as an example, seismic structural interpretation was carried out based on original seismic amplitude cube and derived ant-tracking cube, and then the technologies of finite-element horizon flattening, orthogonal decomposition principal component analysis(PCA), fracture/fault patch auto-extraction, paleo-stress field inversion were applied, combined with the existing regional structural geological knowledge and single well fracture information, to figure out the staging and grouping of seismic-scale fracture system, at the same time to clarify the regional tectonic evolution and its genetic relationship with fractures at different scales. The following results were obtained：(1) the main tectonic movements that affect the development of the seismic-scale fracture system of the target interval occurred in the Yanshanian-Himalayan periods, including the near S-N compression of the late Yanshanian tectonic episode, the NNE-SSW compression of the early Himalayan tectonic episode, and the NWW-SEE compression of the middle Himalayan tectonic episode; (2) the Late Yanshanian tectonic event mainly formed the near E-W long-axis anticlines and synclines, near E-W thrust faults and fault-related fractures, and fold-related fractures in different directions; (3) the Early Himalayan tectonic event mainly formed genetically related conjugate fracture sets including strike-slip faults and shear fractures both in NNW and NE directions, and transverse extensional fractures;(4) the Middle Himalayan event chiefly formed thrust faults, and related fractures and folds in NNE-NE direction, and transverse extensional fractures. It is concluded that such analysis of seismic-scale fracture system for specific shale gas reservoirs is of great significance in building discrete fracture model, providing precautionary advice for drilling engineering, and optimizing well completion program and field development plan, etc. |
