The genesis of viscous crude and asphalt of Qingxi Oilfield in Jiuquan Basin, Northwest China

Much crude oil of the Qingxi Oilfield in Jiuquan Basin, northwest China has a normal density. However, the viscous crude and asphalt are found in some exploration wells. The study of the genesis mechanism of viscous crude and asphalt is helpful for resolving the long argued problems of the evolution and periods of the source rocks. The physical property and geochemistry parameters analysis of the viscous crude and asphalt reveals that both of them come from the same source rock and they are in the maturation state. The correlation of 17 indexes,including native rock property, sedimentary envi-ronment, maturity and microbial action,suggests both of them come from the same source rock and they are in the maturation state. The genesis of viscous crude is attributed to the crude oil mixing of internal reservoirs and the reservoir differentiation, while the viscous crude is generated from the mixture of crude oil in reservoirs and the reservoir rock differentiation and asphalt is generated by the gas de-asphalt of the associated gas of the oils.