Controls on shale oil accumulation in alkaline lacustrine settings: Late Paleozoic Fengcheng Formation, northwestern Junggar Basin

Abstract Understanding the potential and controls on shale oil accumulation in alkaline lacustrine settings is essential to evaluate its contribution to global shale oil budget. Here we present a case study in the Late Paleozoic Fengcheng Formation of the Mahu Sag, northwestern Junggar Basin, China. Results show that the fine-grained sedimentary rocks in alkaline lacustrine settings are complex in lithology with mixed contribution from argillaceous rocks, dolomitic rocks, and pyroclastic rocks. The massive argillaceous dolomite (with alkali minerals) and pyroclastic rocks have the highest shale oil potential with average OSI values at 344.67 mg HC/g TOC and 124.65 mg HC/g TOC in the study area, respectively. In terms of controls on shale oil accumulation in these two rocks, both rock types have good hydrocarbon generation potential. Coupled with abundant fractures and various types of pores, large amounts of free hydrocarbons are retained. Therefore, the fine-grained sedimentary rocks in alkaline lacustrine settings host prospective shale oil potential and can serve as an important exploration field. This is generalized that shale oil potential in saline lacustrine settings is promising. The complex relationship between TOC and shale oil potential suggest that more studies are needed to precisely evaluate the shale oil potential with possibly new proxies and standards.