Sedimentary Genesis and Model Analysis of Shale Lithofacies in Jiyang Depression

Based on core observation, rock thin sections, logging data, and testing data, taking the shale of the upper submember of the 4th Member to the lower submember of the 3rd Member of Paleogene Shahejie Formation in Jiyang Depression of Bohai Bay Basin as an example, we determine the lithofacies division scheme, divide the main lithofacies types, analyze the sedimentary origin and development location of different shale lithofacies, establish the continental lake basin sedimentary model, determine the types and enrichment areas of favorable lithofacies, and provide guidance for the exploration and development of Shale oil. The results show that: (1) According to the mineral composition, sedimentary structure, and organic matter abundance, the division scheme of shale lithofacies in the study area is proposed, and the shale lithofacies of the study area was mainly divided into 17 types. (2) Based on the lithologic changes, the lacustrine sedimentary shale area was divided into muddy water area, transition area, and clear water area. (3) Under the background of locally uplifted slope paleogeomorphology, considering the combined effects of climate, topography, hydrodynamic, mechanical, and chemical differentiation of sediments and biological habits, the sedimentary model of shale was established. (4) Organic-rich shale was mainly deposited between the clear water area and the end of the muddy water area, with the characteristics of water, brackish water, strong reduction, and water stratification, and was mainly enriched in the low-lying parts of paleotopography.