Abstract:

In order to clarify the strata and sedimentary filling characteristics of the Lower Jurassic Lianggaoshan Formation in eastern Sichuan basin, for effectively guiding the hydrocarbon exploration, this study comprehensively utilizes the research tools of outcrop survey, core observation and analysis of sedimentary petrology and petroleum geology. On the basis of systematically sorting out the stratigraphic structure and sedimentary facies in the study area, we further discuss the synergistic reservoir-forming rule between shale oil and gas and tight oil and gas under the constraints of sedimentary sequence. The results show that typical dichotomy sequence stratigraphic structure is developed in the study area. In the early lake transgression stage, the Lower Lianggaoshan Formation formed a landward stepping parasequence set, which was composed of delta front, prodelta, semi-deep lake and deep lake. In the late lake regression stage, a seaward stepping parasequence set is developed in the Upper Lianggaoshan Formation, which can be subdivided into three parasequences or subsections, showing the evolution from semi-deep lake to delta front, shore and shallow lake. The mudstones and shales of semi-deep lake, deep lake and prodelta facies are vertically superimposed with the sandstone bodies of underwater distributary channel in the delta front subfacies, forming various source-reservoir contact relationships, such as “self-generation and self-storage, lower generation and upper storage, side generation and side storage”. This provides a geological basis for the coordinated accumulation of shale oil and gas in the Lower Lianggaoshan Formation and tight oil and gas in the Upper Lianggaoshan Formation.

Key words: stratigraphic framework, delta, Lianggaoshan Formation, shale oil and gas, tight oil and gas, eastern Sichuan basin