Geochemical characteristics of crude oils from Zao-V oil measures in Shenjiapu oilfield

Abstract

The geochemical characteristics of crude oils from Zao-V oil measures in the Shenjiapu oilfield are systematically described in terms of the fractional composition of crude oils, GC characteristics of saturated hydrocarbon fraction of crude oils and the characteristics of their bio-markers. The depositional environment, type and evolution of the biological source are also discussed. All pieces of evidence such as low saturated hydrocarbon fraction, high resin and asphalt, high isoprenoid alkane, weak odd-carbon number predominance ( CPI ranging from 1.23 to 1.29, OEP ranging from 1.14 to 1.16) and low sterane and terpane maturity parameters show these crude oils are immature oils. Low Pr/Ph ratios (0.66–0.88) and high gammacerance/C31 hopane ratios (0.59–0. 86) indicate the source rocks were formed in a slightly saline to brackish reducing lake depositional environment. Gas Chromatographic characteristics of the saturated hydrocarbon fraction and the predominance of C30 hopane in terpane series and C29 sterane in sterane series indicate the biological source of the crude oils is composed mainly of bacterial and algal organic matter, and some algae are perhaps the main contributor of organic matter to the source rocks.