The Main Controlling Factors And Critical Conditions Of Shale Oil Enrichment In The Lower Es₃, Zhanhua Sag

As an important unconventional oil resource,shale oil is different from conventional oil resources in accumulation mechanism and distribution regularity.The research on the main controlling factors and critical conditions of shale oil enrichment is of great significance for revealing shale oil enrichment mechanism and guiding continental shale oil exploration.The lower Es₃ in Zhanhua Sag is important for China shale oil exploration,which provides a good condition for researches on the main controlling factors and critical conditions of shale oil enrichment.Therefore,this paper took the lower Es₃ shale in Zhanhua Sag as the object of study.Several methods,including literature report research,drilling and logging data analysis,field emission-scanning electron microscopy,CO₂ adsorption,N₂ adsorption,high-pressure mercury injection,Rock-Eval pyrolysis and nuclear magnetic resonance analysis,were used to analyze the main controlling factors and boundaries of shale oil enrichment.The geological factors of shale oil enrichment are thick shale thickness and favorable lithofacies.The geological critical conditions of shale oil enrichment are that the shale thickness is more than 10m,and the main lithofacies is inter-bedded argillaceous limestone.The geochemical factors of shale oil enrichment are high organic matter abundance,organic matter type mainly generating oil and moderate maturity.The geochemical critical conditions of shale oil enrichment are TOC>2%,S₁/TOC>100 and0.8%<Ro<1.2%.Besides,the kerogen type is dominated by type I.The reservoir factors of shale oil enrichment are high porosity,high permeability and high oil saturation.The reservoir critical conditions of shale oil enrichment are that the porosity is higher than 4.0%,the permeability is higher than 2×10^-5mD and the oil saturation is higher than 60%.The adsorption shale oil is mainly adsorbed on the surface of clay minerals.The enriched pore size of adsorption shale oil ranges from 0.5 to 0.6 nm.The free shale oil is mainly concentrated in carbonate denudation pores,intercrystal pores and fractures.The enriched pore size of free shale oil is more than 50nm.