Formation characteristics of oil shale in the Lower Cretaceous Dalazi Formation in the Luozigou basin

Abstract：Oil shale of the Luozigou basin is hosted in the 2nd Member of the Lower Cretaceous Dalazi Formation. It is buried at shallow depth with a gentle dip of strata and contains 3.51 to 14.37wt% of oil equivalent. Oil shale formed in a typical inland lake environments and contains many animal and plant fossils. Its genetic types are sapropel type(Ⅰmodel) and saprolite-sapropel type(Ⅱ1 model). The Dalazi Formation is a complete third-order sequence and the main oil shale beds, which have a high oil content and are persistent, formed in a transgressive systems tract (TST) and a highstand systems tract (HST). In a plan view, high-grade oil shale is located near the CK26, CK30, CK35 and CK40 holes and distributed in an E-W-trending strip. Vertically, a total of 29 oil shale beds are found, of which seven beds are extractable. Oil shale beds 2 and 3 occur as continuous and persistent beds with a high oil content. They have great economic value.