Dynamic transformation mechanism for hydrocarbon generation from multiple sources in deep-buried marine carbonates in the northeastern Sichuan Basin: A case study from the Puguang gas field.
川东北地区海相深层多源生烃动态转化机制——以普光气田为例

Petroleum formation mechanism in deep-buried and extremely deep-buried marine carbonates is one of hot and difficult topics in petroleum geology. In this paper, we have made a discussion based on a case study from the Puguang gas field of the northeastern Sichuan Basin, by comprehensively analyzing the oil and gas source and the processes of hydrocarbon generation and accumulation. The methods include assessment of hydrocarbon sources and their geochemical correlation with oil, reservoir bitumen and gas, study on formation, evolution and preservation of hydrocarbon pools, analysis of gas composition, fluid inclusion and simulation of hydrocarbon generation from multiple sources. The results showed that the deep-buried marine source sequences and main hydrocarbon-producing intervals may have experienced high temperatures, high pressures and multi-stage sedimentological and tectonic movements. As a result, various kinds of hydrocarbon sources were formed, including different types of kerogens, accumulated and dispersed soluble organic matters, and insoluble organic matters of organic acid salts. It is common for the continuous and/or overlapping dynamic transformation of various kinds of hydrocarbon sources and multiple origins of hydrocarbons to have contributed to petroleum pools. Based on these results, we propose that the main mechanism for hydrocarbon formation and evolution in deep-buried strata is the dynamic transformation for hydrocarbon generation from multiple sources. The gas generation can be extended to high to extremely high evolution stages. This is favorable for the gas re-filling and accumulation in deep and extremely deep-buried reservoirs.