Geochemical features of oil-bearing samples from the well in Buqu Formation in the Qiangtang Basin, northern Tibet, and their implications

The Qiangzi-11 and 12 wells are the data well to reveal the distribution regularities of Longeni-Angdaerco palaeo-oil reservoirs. Together with the hydrocarbon source rock data of Buqu Formation, Xiali Formation, and Quse Formation from Qiangzi-2 well, the authors analyzed the oil-rock correlations based on the biomarker parameters composed of isoprenoid, steranes, and ter-panes. The property of crude oil from Qiangzi-11 and 12 wells is of the same type. However, the biodegradation degree from Qiang-zi-11 well is higher than that from Qiangzi-12. The biomarker parameters reveal that the organic matter mainly originated from al-gae. The crude oil was formed under weak reduction-reduction conditions and in a slightly salty water environment. The biomarkers of crude oil, composed of isoprenoid, terpane, and sterane, are closely related to those of the Buqu Formation in Qiangzi-2 well, and also show good correlation with those of the Xiali Formation and Quse Formation in Qiangzi-2 well. Combined with the TOC data of the hydrocarbon source rock in south Qiangtang Basin, the authors hold that the crude oil of the Longeni-Angdaerco palaeo-oil reservoir was mainly from the source rocks of Quse Formation, and partly from the Xiali and Buqu Formations, suggesting a mixture of sources. The result of this study may have some guidance significance for further oil-gas exploration.