Geochemical characteristics of coal-derived oil in Santanghu basin

According to the distribution and assemblage of biomarkers, the crude oil and oil shows from Santanghu basin can be classified into two groups, such as Mesozoic coal-derived oil and oil of upper paleozoic lake facies genesis. The crude oil from Xishanyao formation of Jurassic system in well Tangcan 1 is a representative of Mesozoic coal-derived oil. It has the characteristics of odd-carbon predominance in normal alkane series, Pr/Ph value is high(>4.0). In addition, the relative abundance of C24-C26 tetracyclic terpanes is higher than C19-C25 tricyclic terpanes (>1.0), C19 and C20 components are higher than C21 and C23 in tricyclic terpanes, C31 hexcyclic hopane is identified but gammacerane is not, C29 components are unusually abundant in C27-C29 steranes. The crude oil is originated from a coal-measure source rock. Oil from upper Paleozoic lake facies genesis includes the oil shows from wells of Tangcan 3, Tiao 2 and Tiao 3. They don't have the characteristics of odd carbon predominance in normal alkanes and have lower Pr/Ph value. Besides, the tricyclic terpanes are more abundant than tetracyclic terpanes (only C24 is detected) and the relative abundance of C23 and C21 components is higher than tricyclic terpanes, C31 hexcyclic hopane is substituted with abundant gammacerane and β-carotane. The abundance of C27 steranes are comparatively higher, which are originated from the upper Paleozoic lake facies source rocks.