Abstract: We studied the geological characteristics and accumulation mechanism of continental shale oil in Jimusaer sag,based on the data collected from core and casting thin section observation,well log,Rock-Eval pyrolysis,field emission scanning electron microscopy (FE-SEM),laser-scanning confocal microscopy and high pressure mercury injection.The results show that the Lucaogou Formation in Jimusaer sag is originated from the organic-rich sediments in saline lacustrine basins,which serve as both source rocks and reservoirs,and the shale oil reservoirs herein are geologically characterized by "indigenous accumulation".There are two types of lithologic associations:one is siltstone-mudstone,and the other is dolomite-mudstone.Oil is pervasive in the Lucaogou Formation,enriches in "sweet spots",and has lower maturity.The shale oil reservoir is oil-wet,and pressurization caused by hydrocarbon generation is the main driving force for its shale oil migration and accumulation.The micro-and nano-pore throats,bedding-parallel fractures and tectonic fractures are favorable reservoir space and vadose channels for the Lucaogou shale oil in Jimusaer sag.The shale oil accumulates within or close to the source rocks as a whole,and occurs in the "sweet spots" and shale intervals in free or absorbed phases.

Key words: pressurization caused by hydrocarbon generation, shale oil, hydrocarbon source rock, indigenous accumulation, enrichment mechanism, saline lacustrine basin, Lucaogou Formation, Jimusaer sag, Junggar Basin