Geochemical characteristics of crude oil and oil-source correlation in the western Qaidam Basin, China

Abstract

The Cenozoic in the western Qaidam Basin is rich in oil and gas resources and has good prospects for exploration. The maturity, sedimentary environment, and biological source of the crude oil in the western Qaidam Basin are discussed based on the composition characteristics of biomarkers in crude oil and source rocks. The above is performed to classify the genetic types of crude oil and determine the oil source relationship. It is found that the crude oil shows the characteristics of low mature–mature and is formed in the reducing environment with high salinity. The organic matter is from the mixed source with dominant aquatic plants input. According to the sedimentary environment, parent material types, and maturity characteristics, the crude oil in the western Qaidam Basin can be classified into four types. (1) Type I is from the Shizigou-Yuejin areas, which have a high content of gammacerane, a low value of Pr/Ph, C27 sterane predominance, and “tail-upwarping” phenomenon. (2) Type II is from the Qiekelike-Zhahaquan and Nanyishan-Youquanzi areas, which have C27 sterane predominance and no “tail-upwarping” phenomenon. Its content of gammacerane is lower than type I. (3) Type III is from the Dafengshan and Huangguamao areas, which have C29 sterane predominance and no “tail-upwarping” phenomenon. (4) Type IV is from the Kaitemilike area, which has a C27 sterane predominance, no “tail-upwarping” phenomenon, and lower content of gammacerane than that of others. The result of the oil-source correlation shows that the crude oil is dominantly derived from source rocks of the lower Ganchaigou Formation (E3) and the upper Ganchaigou Formation (N1).