Multi-lithofacies Pore Structure-oil-bearing Difference and Shale Oil Enrichment Model of the Es4 Shale in the Western Sag of Liaohe, Bohai Bay Basin

Xin He^1*Ruifei Wang¹Xuejuan Zhang²Lei Zhang²Rongjin Gao³Ruhao Liu²Wenwen Lei³

• ¹Xi'an Shiyou University, Xi'an, China
• ²Chongqing University of Science and Technology, Chongqing, China
• ³China National Petroleum Corp Liaohe Oilfield Exploration and Development Research Institute, Panjin, China

ABSTRACT: The complex pore structures and unclear oil-bearing controls in lacustrine shale (such as the Es4 member of the Liaohe Depression) constrain sweet spot prediction. The lithofacies types of reservoirs were divided by mineral composition and organic matter content. Combined with field scanning electron microscopy, high-pressure mercury injection, nuclear magnetic resonance, low-temperature N2 adsorption (pre-and post-oil washing), rock pyrolysis experiments, the pore structure, oil-bearing characteristics and influencing factors of shale oil reservoirs with different lithofacies were studied. The results show that study identifies five lithofacies in the Es4 interlayer shale, with organic-rich calcareous, felsic, and mixed shales being dominant. Among these, the superior oil content in organic-rich calcareous shale is fundamentally linked to its well-developed pore-network, characterized by a higher proportion of macropores and well-connected mesopores as quantified by MIP and NMR. Inorganic mineral content primarily controls the inherent pore structure framework, while it is the integration of lithofacies and resultant pore geometry that ultimately governs the oil-bearing of shale oil. The organic-rich calcareous, felsic, and mixed shale facies in the Es4 exhibit distinct enrichment modes: dissolution-large pore free oil; microfracture-ink bottle pore dual-mode; and multi-stage-composite pore, respectively. These findings not only provide critical insights into shale oil enrichment mechanisms and sweet spot prediction in the Es4 shale, but also provides a reference method for shale oil enrichment prediction in other complex lacustrine basins around the world.