Key Controlling Factors And Enrichment Model Of Shale Oil Enrichment In The Fengcheng Formation,Mahu Sag

The shale of the Lower Permian Fengcheng Formation in Mahu Depression of Junggar Basin is the oldest alkali-lake sedimentary hydrocarbon source rock discovered so far,which has great shale oil resource potential and is an important target for shale oil exploration in China.It is of great significance for the exploration of shale oil in the alkali lake sediments to investigate the main controlling factors and patterns of shale oil enrichment in Fengcheng Formation of Mahu Sag and to reveal the mechanism of shale oil enrichment.In this paper,by sampling cores from the whole well section of well MY1 and some cores from the well FN7 and FN14 etc.,we conducted analytical test experiments such as rock pyrolysis,XRD diffraction,high-pressure mercury compression,N2 adsorption,CO2 adsorption and scanning electron microscopy,and combined with multiple methods such as core observation,geological profiling and numerical simulation to analyze the main controlling geological factors affecting shale oil enrichment in Fengcheng Formation and the shale oil enrichment conditions were analyzed,and the shale oil enrichment model of Fengcheng Formation was established,based on which the sweet spot section for shale oil enrichment was selected.The results show that the enrichment of shale oil in Fengcheng Formation is mainly controlled by hydrocarbon generation potential,storage capacity,micro-transport hydrocarbon volume and lithofacies type,and lamellar feldspar-quartz shale and thick feldspar-quartz shale are favorable lithofacies for oil enrichment in Fengcheng Formation of Mahu Sag.Under the influence of the main controlling factors,Fengcheng Formation of Mahu Sag has formed a "source-reservoir integrated" shale oil enrichment model with high generation and excellent reservoir and a "micro-migration" shale oil enrichment model with low generation and excellent reservoir.Based on the "three-point method" combined with oil saturation index(OSI),the evaluation indexes of shale oil enrichment resources in Fengcheng Formation are determined as S1 > 2mg/g,OSI > 100 mg HC/g TOC.Furthermore,the favorable conditions for shale oil enrichment in Fengcheng Formation are defined as follows:(1)Organic matter abundance met TOC > 0.8%,organic matter type is type Ⅰ or Ⅱ,thermal evolution degree met 0.70%<Ro<1.35%;(2)The shale has a high proportion of large pores,high porosity and permeability,micro-fractures are developed and the fracture width is less than 5μm.(3)ΔS1<0mg/g indicates that there are foreign hydrocarbon charging in shale units.(4)The development of lamellar felsic shale phase and thick lamellar felsic shale phase.Accordingly,in combination with the favorable conditions for shale oil development,six transversely continuous dessert layers are selected on the continuous well section of FN7-FN14-FN4-MY1 and concentrated at the top of the P1f1,the whole of P1f2 and the bottom of the P1f3.