Differences in preservation conditions of deep shale gas in high-steep complex tectonic belt: taking Qijiang high-steep complex tectonic belt in southeast Sichuan as an example

The southeastern Sichuan Basin is one of the key targets for shale gas exploration in China. Currently, the exploration has gradually been delved into deep and ultra-deep formation fields. However, due to various constraint factors such as drilling and earthquakes, research on the tectonic characteristics and shale gas preservation conditions in this area is inadequate. In order to find out the tectonic deformation characteristics of Qijiang high-steep complex tectonic belt in southeast Sichuan and its impact on the enrichment law of deep shale gas, and to provide a basis for subsequent exploration deployment, a high-steep structural model is established based on the analysis of tectonic deformation characteristics and practice drilling data, and the quantitative evaluation of the main controlling factors of differences in preservation conditions is carried out on the basis of the model. The research results show that: (1) Qijiang high-steep structure has the layered deformation feature of "steep upper part and flat lower part + dominated by gypsolyte + steep front"; (2)There is a widely developed Cambrian gypsum salt layer in the Qijiang area, whose plastic deformation controls the uplift of the overlying structure; (3) The factors affecting the preservation conditions of shale gas in the study area include active deformation strength, fracture system, normal stress of fault plane, angle between structure and geostress, roof detachment layer and other factors. The interaction of multiple factors leads to obvious differences in the preservation conditions in the study area. According to the analysis results, the evaluation criteria for the preservation conditions of Qijiang high-steep structures are established, and it is defined that the Longsheng-Taozidang tectonic belt has single tectonic stress, low active deformation intensity and well-closed structure, which is the main favorable target for the next exploration.