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

Shale gas exploration and developmentis regarded asone of thevital areas in which breakthroughs are urgently needed. The LongmaxiFormation shale in the Weiyuan Block was considered a case study.Based on the analysis of the physical evolution, burial history, thermalhistory, as well as hydrocarbon generation history of the LongmaxiFormation shales, the impact of uplift amplitude on the shale gasreservoirs, the shale gas transport pattern and direction in the adjustmentstage, and the shale gas enrichment pattern are discussed in thisstudy. The results from this study showed that (1) the Weiyuan Blockcould reach the maximum burial depth in the Late Middle Cretaceous,and then there was uplifting and erosion of the strata, with an erosionamount of 2000-4200 m. (2) The migration of shale gas is mostlycontributed by Darcy flow and slippage flow. In addition, Darcy flowcontributed to larger migration, which is about 100 times that ofslippage flow. Darcy flow occurs in about 13.7% of the pores in theLongmaxi Formation shale. (3) The enrichment of shale gas can be significantlyimpacted by the uplift amplitude. The gas reservoirs with uplift amplitudeshigher than 3000 m and lower than 3000 m differ significantly in termsof their physical characteristics, pressure coefficients, and gasconcentrations. (4) The Longmaxi Formation shale gas reservoirs canbe 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 thenloss, a gas reservoir first loss and then enrichment, and a supplygas reservoir. Although the supply gas reservoir occupies the largestarea, the enriched gas reservoir is the key zone for analysis, aswell as the development of the Longmaxi Formation shale gas in theWeiyuan Block.