Strata Uplift Controlled Deep Shale Gas Accumulation Modes: A Case Study from the Weiyuan Block, Sichuan Basin

Shale gas exploration and development is regarded as one of the vital areas in which breakthroughs are urgently needed. The Longmaxi Formation shale in the Weiyuan Block was considered a case study. Based on the analysis of the physical evolution, burial history, thermal history, as well as hydrocarbon generation history of the Longmaxi Formation shales, the impact of uplift amplitude on the shale gas reservoirs, the shale gas transport pattern and direction in the adjustment stage, and the shale gas enrichment pattern are discussed in this study. The results from this study showed that (1) the Weiyuan Block could reach the maximum burial depth in the Late Middle Cretaceous, and then there was uplifting and erosion of the strata, with an erosion amount of 2000–4200 m. (2) The migration of shale gas is mostly contributed by Darcy flow and slippage flow. In addition, Darcy flow contributed to larger migration, which is about 100 times that of slippage flow. Darcy flow occurs in about 13.7% of the pores in the Longmaxi Formation shale. (3) The enrichment of shale gas can be significantly impacted by the uplift amplitude. The gas reservoirs with uplift amplitudes higher than 3000 m and lower than 3000 m differ significantly in terms of their physical characteristics, pressure coefficients, and gas concentrations. (4) The Longmaxi Formation shale gas reservoirs can be separated into five categories based on the uplift amplitudes, migration characteristics, and pressure coefficients: a lost gas reservoir, an enriched gas reservoir, a gas reservoir first enrichment and then loss, a gas reservoir first loss and then enrichment, and a supply gas reservoir. Although the supply gas reservoir occupies the largest area, the enriched gas reservoir is the key zone for analysis, as well as the development of the Longmaxi Formation shale gas in the Weiyuan Block.