Genetic connection between mud shale lithofacies and shale oil enrichment in Jiyang Depression, Bohai Bay Basin

By using microscope, argon ion polishing technology, nuclear magnetic resonance (NMR), scanning electron microscopy, and hydrocarbon generation and expulsion simulation, reservoir properties, oiliness and shale oil mobility of different mud shale lithofacies were examined with the mud shale in Jiyang Depression, Bohai Bay Basin as the example. The relationship between lithofacies type and shale oil enrichment was analyzed. Based on the rock composition, sedimentary structures and abundance of organic matter, a mud shale lithofacies classification standard for the upper submember of the 4th Member to the lower submember of the 3rd Member of Paleogene Shahejie Formation (Es4s-Es3x) was established. Six lithofacies are developed in the target formation, in which the laminar organic-rich lithofacies formed in the alternating mechanical transportation deposition and chemical deposition, not only has the highest TOC, S1, oil saturation, movable oil saturation, content of low-carbon light components and oil generation and expulsion rate, but also has various types of reservoir space, abundant pores, and organic network system and interlayer micro-fracture system which can serve as high-speed channels for shale oil and gas migration, so this lithofacies is favorable for shale oil enrichment.