Gas source and exploration direction of the Middle Triassic Leikoupo Formation in the Sichuan Basin, China

摘要

Natural gas exploration in the Middle Triassic Leikoupo Formation (T2l) in the Sichuan Basin of China has achieved a remarkable breakthrough in recent years and thus attracts wide attention. However, there is no consensus on the gas source. The genetic identification and gas–source correlation based on the geochemical characteristics of natural gas indicate that the natural gas in the Leikoupo Formation is mainly from the underlying Upper Permian Longtan/Wujiaping Formation (P3l/P3w) source rocks (Moxi). Nevertheless, it has assistance (Zhongba) or hydrocarbon supply condition (Chuanxi) brought by the source rocks in the 1st Member of the Upper Triassic Xujiahe Formation (T3x), or mainly from the T3xsource rocks with a specific contribution by the T2lsource rocks (Yuanba and Longgang). The T2lgas pools display three types of source-reservoir assemblages, and they suggest different exploration directions. The P3lsource rocks serve as main source rocks that can constitute the lower-generation and upper-accumulation pattern. The positive structures around the deep faults connecting the P3land T2lare the most favorable areas to explore large-scale T2lgas pools. The source rocks at the bottom of T3xand the reservoirs at the top of the T2lcan constitute the side-generation and side-accumulation pattern, which is favorably developed in the residual karst hills or the local tectonic high position of the karst slope. The T2lcan constitute self-generation and self-accumulation pattern, which assists in the formation of gas pools.