Differences in and factors controlling organic matter enrichment in the Ziliujing Formation shale in the Sichuan Basin

Lacustrine shale oil and gas are important fields for unconventional exploration and development in China, and organic-rich shale deposition lays down the critical foundation for hydrocarbon generation. There are two sets of shale, the Dongyuemiao and Da’anzhai Members, in the Ziliujing Formation in the Sichuan Basin. To identify the differential enrichment characteristics of organic matter and clarify its controlling factors, geochemical analyses of organic and inorganic geochemical analyses were performed. The results showed that the total organic carbon content of the Dongyuemiao shale (1.36%) is slightly higher than that of the Da’anzhai shale (0.95%). The enrichment of organic matter in the two shales resulted from the comprehensive controls of paleoproductivity, paleoenvironment, and terrigenous input, but different factors have different effects. In addition, driven by climate, the change in the sulfate concentration in the bottom water further led to the different intensities of bacterial sulfate reduction in early diagenesis. This made a great difference regarding organic matter accumulation in the two members. In general, climate may have played a dominant role in organic matter enrichment in the two sets of shale.