Genetic analysis of high-yield wells of ultra-deep reef-shoal lithologic gas reservoirs：A case study of reef-shoal facies reservoirs in Changxing Formation, Yuanba area, northeastern Sichuan Basin

Since the exploration breakthrough of year 2007, over 1 million m³ of industrial gas flows have been obtained from the Changxing Formation in the Yuanba area, and it is the deepest reef-shoal lithologic gas field in China which mainly develops reef-shoal facies reservoir in platform margin. To further clarify the controlling factors of natural gas enrichment, through the comprehensive research on geology, well logging and geophysics, it is pointed out that the high-quality reservoir development is the major controlling factor and material basis for the high yields of the Changxing Formation in the Yuanba area. Meanwhile, passage system features and the perfect match between structure and favorable reservoir control hydrocarbon accumulation and redistribution. Reef zones in the northwestern Yuanba area are most favorable for hydrocarbon accumulation. The research results have important practical significances for finding potential areas or strata and expanding exploration.