Genetic types and sources of Cretaceous crude oil in Shunbei area, Tarim Basin

Abstract

The Cretaceous oil-bearing strata in the Tarim Basin have a good exploration potential. The Shunbei area has good oil and gas shows in the Cretaceous, and a small amount of crude oil has been obtained by testing. The geochemical characteristics of the Cretaceous crude oil as well as the oil-oil and oil-source correlations were studied systematically in order to determine the genesis types and sources of crude oil in the Shunbei area. The saturated hydrocarbon chromatogram of the Cretaceous crude oil in the Shunbei area shows a unimodal distribution. The n-alkanes are intact and the distribution is unchanged without any obvious "UCM". The Pr/Ph values of crude oil range 1.65-1.71. The C21TT/C23TT ratio is >1. In biomarkers, the hopane series are dominant and the ∑tricyclic terpanes/∑hopanes ratio is < 1. The gammacerane and triaryl stanine compounds are abundant, indicating that the crude oil of continental origin is well preserved. The Cretaceous crude oil in the Shunbei area and the Yingmai, Dawanqi and Dalaoba areas around the Kuqa Sag in the north, and the Triassic Huangshanjie mudstones in the Kuqa River area show similar m/z 191 biomarker patterns, which indicates that the crude oil was sourced from the Huangshanjie mudstones in the Kuqa Sag. The thermal evolution degrees of crude oil decrease from Dawanqi, Yingmai to Shunbei. We inferred that the early terrestrial hydrocarbon was sourced in the Triassic source rocks in the Kuqa Sag, and then migrated laterally from north to south through the Cretaceous sand bodies, the T40 unconformity surface and the faults.

Keywords

• terrestrial crude oil
• oil source
• accumulation model
• cretaceous
• shunbei area
• tarim basin