The identification of micro-faults at the bottom of Wufeng Formation in Changning Area and its influence on shale gas development

Changning Shale Gas Field in Sichuan Basin is one of the pilot targets for shale gas exploration in China.Due to the limitation of seismic resolution, previous studies mainly identified faults with a fault distance greater than 20 m, and ignored minor faults with a fault distance less than 20 m.However, Changning Area generally developed micro-faults with a fault distance less than 20 m, which easily caused complex engineering conditions such as drilling out of the box, sticking, fracturing pressure channeling and casing variation in the development of long horizontal wells.Therefore, how to identify micro-faults in Changning Shale Gas reservoirs and further refine the faults classification has become the top priority of the current work.Based on the understanding of the previous fault interpretation, this paper has improved the identification and description accuracy of micro-faults through the combination of well-seismic, coherence, ant-body and other methods, and summarizes the inherited, accompanying, and strike-slip types.The cause classification of micro-faults, and the classification principle and identification method of fifth-level fractures (micro-faults) have been added to the original four-level classification.The results show that a large number of NE-trending and NW-trending micro-faults are developed in this area.This configuration is basically consistent with the orientation of I-IV grade faults.It conforms to certain genetic laws, and can match and explain the engineering problems in the early drilling and fracturing process.The reliability of micro-faults identification method and the adverse effect of micro-faults on shale gas development engineering are verified.The effective identification of micro-faults can provide early warning treatment basis for trajectory optimization, drilling and fracturing construction, and provide technical support and guarantee for geological sweet spot analysis and shale gas production enhancement.