Organic geochemical characteristics and genesis of crude oils of triassic Tahe oilfield

Biomarkers and their genesis were studied.The data of(w(Pr))/(w(Ph)),(w(Pr))/(w(nC_(17))) and(w(Ph))/(w(nC_(18))) indicated that oils formed from sapropel organic matters of reducing environment.Abundance of gammaceraneC_(30) hopane indicated that the oils formed from saltwater environment.The abundance of C_(27) sterane,tricyclic terpane,tetracyclic terpane and higher tricyclic terpane/hopane parameters showed that original source materials were homonemeaes.The abundance of rearranged sterane was higher and higher(w(Ts))/(w(Ts+Tm)) and (w(C_(29)ββ))/(w(ββ+αα)) sterane showed that the maturity of the oils was higher.The detection of 25-norhopane indicated that the oils met with biodegradation and,together with integral distribution of n-alkane,it showed that oil pool underwent no less than two oil accumulating processes.