Lithofacies Characteristics and Controlling Factors of Fine-Grained Sedimentary Rocks in the Lower First Member of the Shahejie Formation in the Northern Lixian Slope of Raoyang Sag, China

In order to further explore the potential of unconventional oil and gas in the northern Lixian Slope of Raoyang Sag, the lithofacies types and their controlling factors of the lower first member of the Shahejie Formation (Es1L) in the Xiliu area were analyzed through the comprehensive application of core log studies, micro-sections and their magnified analyses, mineral suits recognitions with XRD, and major and organic geochemistry. The results show that the lacustrine sedimentary rocks of Es1L in the Xiliu area comprise five lithofacies types: medium organic silty mixed fine-grained rock, medium organic massive clay rock, high organic shale calcareous mixed fine-grained rock, high organic matter shale calcareous clay rock, and high organic matter shale limestone. The vertical variation of the characteristic element reflects that the deposition in Es1L has different stages; that is, the bottom of Es1L is formed with low source influence, high water salinity, and strong reduction conditions, while the upper fine-grained rocks are formed in a sedimentary environment with high source influence, low water salinity, and weak reduction conditions. The change of the sedimentary environment controls the development of lithofacies and the occurrence of organic matter. These results advocate for the basic research of fine-grained sedimentary rocks in the faulted lacustrine basin aid for further unconventional oil and gas exploration.