The Tectonic Control on Shale Oil Migration and Accumulation of the Lower Jurassic Daanzhai Member of the Ziliujing Formation, Sichuan Basin, China

In order to understand the tectonic control on shale oil migration and accumulation, samples of the Daanzhai Member of the Lower Jurassic Ziliujing Formation from the well core in a tectonically stable area and upright anticline outcrop were selected for total organic carbon (TOC) content analysis, rock pyrolysis, fluorescence scanning, and scanning electron microscopy. The results show the following: (1) In the tectonically stable area, the TOC of shale oil reservoirs is positively correlated with S 1 , and a high OSI interval usually occurs in high-TOC shales. The oil content of the limestone lamina decreases with an increasing distance from black shale. The vertical migration of shale oil into or across the lamina is not obvious and is mainly micro-scale. (2) The migration pathway includes a lamina interface, shell–clay interface, calcite cleavage, feldspar or calcite dissolution pores, and quartz or kaolinite intergranular pores. Large-scale shale oil migration time occurs at the peak of oil generation. (3) In the area of strong tectonic deformation, the formation of fractures in limestone further promotes the migration of oil from shale into the lamina. (4) The re-migration of shale oil during the uplift and deformation period involves three processes: upward migration in a clay matrix, then entry and migration along the limestone–shale interface from the lateral pinch-out points of the lamina, migration into the lamina joints, and then short diffusion into the limestone. (5) The migration of shale oil in the Daanzhai shale was controlled by the history of hydrocarbon generation and tectonic deformation and occurred in several stages.