Accumulation characteristics and orderly distribution of whole petroleum system in Middle Jurassic Lianggaoshan Formation, Sichuan Basin

The Middle Jurassic Lianggaoshan Formation in the Sichuan Basin has abundant oil and gas resources and exhibits favorable accumulation conditions, showing great exploration and development potential. It represents an important area for recent reserve growth and production enhancement in the Sichuan Basin. Through analytical methods such as core observation, thin section identification, cathodoluminescence, laser confocal microscopy, scanning electron microscopy (SEM), and geochemical analysis, the lake basin sedimentary evolution and accumulation conditions of the Lianggaoshan Formation were systematically studied. The study clarified the distribution characteristics of source rocks and sand bodies, the source-reservoir configuration relationships, and the oil and gas distribution patterns. The Lianggaoshan Formation in the Sichuan Basin mainly developed a lacustrine-deltaic sedimentary system, with the delta front comprising various sand body types, including subaqueous distributary channels, mouth bars, subaqueous natural levees, sheet sands, and beach-bar sands. Vertically, two sets of source rocks developed: the lower and middle-upper sub-members of the second member of the Lianggaoshan Formation. Horizontally, three hydrocarbon generation centers were identified in northern, central, and eastern Sichuan Basin. Overall, the Lianggaoshan Formation in the Sichuan Basin showed accumulation characteristics of the whole petroleum system, with multi-layer and multi-type reservoirs overlapping and coexisting orderly. Vertically, from bottom to top, the reservoirs included intra-source shale oil and gas, intra-source tight oil and gas in beach-bar sandstones, near-source tight oil and gas in channel sandstones, and extra-source tight gas in channel sandstones. Horizontally, these four types of favorable zones extended from the lake basin center towards its margins. The whole petroleum system accumulation-enrichment model of the Middle Jurassic Lianggaoshan Formation in the Sichuan Basin established based on this understanding has effectively guided exploration breakthroughs of different reservoir types in this area, holding important reference significance for hydrocarbon exploration in similar areas.