Pore-throat structure and its controls on reservoir properties and oil charging threshold of shale reservoirs in the Lucaogou Formation of Jimsar Sag, Junggar Basin, China

To clarify the pore-throat structure characteristics, their correlation with reservoir physical properties, and the oil charging thresholds of continental shale oil reservoirs, this study focuses on the Permian Lucaogou Formation in the Jimsar Sag of Junggar Basin, a typical continental saline lacustrine shale oil play in China. Integrated experimental techniques, including microscopic observation of cast thin sections, high-pressure mercury intrusion, nuclear magnetic resonance, and N 2 adsorption experiments before and after oil washing, were employed to systematically analyze the reservoir pore system, classify pore-throats, analyze property correlation, and clarify oil charging mechanisms. The results indicate that the pore-throat structure can be categorized into 5 major types and 9 sub-types, showing progressive degradation from Type I (high quality reservoirs) to Type V (non-effective reservoirs), which is closely controlled by lithological assemblages and diagenetic alterations. Reservoir permeability is mainly governed by the macropore (>200 nm) content and median pore-throat radius ( R 50 ), while porosity is jointly influenced by pore-throat radius, pore type, and diagenesis, with a segmented correlation between porosity and R 50 . The oil charging pore-throat diameter threshold is determined to be 30 nm via theoretical calculations of hydrocarbon generation pressurization and capillary pressure, as well as experimental verification by oil-washing contrast tests. This study refines the understanding of pore-throat evolution and oil accumulation mechanisms in continental shale oil reservoirs, providing critical theoretical and technical support for reservoir classification and evaluation, sweet spot delineation, and efficient development of the Lucaogou Formation shale oil and similar continental shale oil resources.