Study on Sedimentary Environment Elements and Sedimentary Model of Lacustrine Shale in E1f2 Member, Gaoyou Depression, Subei Basin

Abstract

Although the potential of lake facies shale oil and gas resources is enormous, the lithology is complex, heterogeneous, and obviously controlled by a sedimentary environment. By integrating cores, thin sections, X-ray diffraction analysis, trace elements, organic geochemical indexes, and paleontological data, this work studies sedimentary environment elements and sedimentary model of shale in the E1f2 member, Gaoyou Depression, Subei Basin. The shale in the E1f2 member is completely shore lacustrine deposits forming into the hot dry climate of tropical central and south Asia. The lake basin extended continuously, with brackish water, strong reduction, and medium water stratification. The transgression resulted in the rapid rise of water, salinity, reducibility, and water stratification. As the climate becomes wetter, the E1f2 water level, salinity, reduction, and stratification decrease. The shale in E1f2 members is characterized by sedimentary zones, which are divided into muddy water desalination deposit in the flooded zone, clear water salinization deposit in the transition zone, and still water salinization deposited in the clear water zone. Under palaeotopography settings of E1f2 members, combining characteristics of vertical stratification and the plane zone of the lake, an integrated sedimentary model of lacustrine shale in a flat platform has been established under climate and transgression control. The plane area of the lake could be divided into the slow slope zone, sub-depression zone, processes zone, deep slope zone, and deep depression zone, corresponding roughly to the sedimentary zones of the flooded zone, transition zone, and clear water zone. Moreover, the oil shale enriched in low-lying parts of the paleotopography is mainly deposited at the end of muddy water areas and clear water areas.