Gas reservoir characteristics of tidal flat carbonate: A case study from the Middle Triassic Leikoupo Formation in the western depression of Sichuan Basin

Over the long term, the exploration direction of marine carbonate rocks in Sichuan Basin is mainly to find "reef-shoal type" gas reservoirs and "karst type" gas reserviors. The discovery of large-scale tidal flat carbonate reservoirs and new gas field in the Middle Triassic Leikoupo Formation in western Sichuan Depression proves that tidal flat carbonate gas reservoirs also have important exploration value. Therefore, it is especially necessary to summarize its accumulation characteristics and distribution pattern. In this paper, characteristics of gas reservoir formation of tidal flat carbonate in Leikoupo Formation, western Sichuan Depression are thoroughly studied and summarized. 1) In terms of reservoir, tidal flat facies of carbonate rocks develop not only conventional granular dolomite, but also large-scale microbial dolomite which makes a great contribution to the reservoir. The reservoir is characterized by thin, multi-layered superposition and stable lateral distribution. 2) In terms of hydrocarbon source, multi-source hydrocarbon supply is the basis for regional accumulation. The Leikoupo Formation in western Sichuan Depression not only developed its own source rocks, but also developed the distal main source rocks of the underlying Permian and the secondary argillous source rocks of the Maantang Formation and Xiaotangzi Formation overlying. 3) In terms of hydrocarbon migration, faults and fractures form a network transport system in various combinations, providing migration channels for regional oil and gas accumulation. Oil and gas accumulation is controlled by both structure and stratum, and various types of gas reservoirs are formed in the positive tectonic zone and slope zone. The process of oil and gas accumulation is manifested as early oil and gas accumulation and late adjustment. There is breakthrough of tidal flat facies carbonate gas reservoirs in the theoretical understanding and exploration concept of reservoir formation, hydrocarbon generation and accumulation, which has reference significance for natural gas exploration in the marine field of Sichuan Basin and exploration with similar geological background at home and abroad.