Microscopic Occurrence Characteristics and Sweet Spot Prediction of Shale Oil in the Fengcheng Formation, Northwestern Junggar Basin

HIGHLIGHTS (1) A method for analyzing controls on shale oil occurrence in complex lithofacies was established via FE-SEM, NMR and stepwise hydrocarbon extraction. (2) Shale oil in the Fengcheng Formation of the study area mainly exists in two states: free and adsorbed. (3) Free oil mainly exists in pores and micro-fractures larger than 50 nm, while adsorbed oil is mainly present in the form of oil films on the surface of clay minerals and within pyrite aggregates. (4) Calcareous mudstone/shale is the most favorable lithofacies, followed by dolomitic mudstone/shale and dolomitic tuff.