Mechanisms of the differential enrichment and high productivity of deep to ultradeep marine shale gas reservoirs

Deep to ultra-deep marine shale gas has emerged as an important target for shale gas exploration and exploitation in China. In this study, we reveal the mechanisms governing the differential enrichment and high productivity patterns of deep to ultra-deep shale gas in the Sichuan Basin by analyzing representative shale gas reservoirs. The results indicate that the deep to ultra-deep shale gas reservoirs in the Longmaxi and Qiongzhusi formations can be categorized into three distinct types: high enrichment-high productivity, high enrichment-low productivity, and medium enrichment-high productivity. The achievement of the high enrichment and high productivity of deep to ultra-deep shale gas is predominantly governed by the synergistic coupling of positive structural setting, favorable preservation conditions, and moderately developed fractures. This finding contributes to the establishment of a high enrichment-high productivity model, characterized by structure-controlled shale gas accumulation, preservation condition-controlled shale gas enrichment, and fracture-controlled shale gas productivity (collectively referred to as the triple-control model). It is recommended to strengthen the engineering sweet spot evaluation for deep to ultra-deep shale gas play fairways under the guidance of the triple-control model, with particular emphasis placed on areas featuring inherited positive structures and microfractures. Furthermore, differential fracturing techniques should be developed for various types of shale gas reservoirs. These efforts are expected to facilitate the discovery of new types of large-scale shale gas resources in new sequences and regions.