Formation mechanism and Hydrocarbon charging of Jurassic reservoirs in Hashan area northern sloping zone of Junggar Basin

In recent years, Chunhui and Alade Oilfields are the significant breakthroughs of hydrocarbon exploration in the northern margin of the Hashan area, Junggar Basin. At present, it has proved geological reserves more than 5 850×104t in the Badaowan Formation and Xishanyao Formation. Through analysis of the geochemical crude oils, the occurrence, the icrofluorometry characteristics and homogenization temperature of fluid inclusions, as well as the analysis of burial and hydrocarbon generation history of the source rocks, the origin and formation mechanism of heavy oil and the process of hydrocarbon accumulation are defined. The Jurassic crude oil is mainly originated from the Fengcheng Formation source rocks of Mahu Depression. As the migrating distance increases, and the light hydrocarbon escapes, the oil charges gradually change by migration from normal oil into complete heavy oil with the burial depth becoming shallower. It is considered that the heavy oil is mainly of secondary origin. The alteration of heavy oil would be divided into biodegradation, oxidation and water washing, of which the biodegradation is the most important. Based on the systematic analyses of the different maturity and geochemical characteristics of crude oil, it's considered that there were two stages of hydrocarbon charges, i. e., the first charging period occurred in Late Jurassic, which is the dominant hydrocarbon charging period, and the later hydrocarbon charging occurred in Late Cretaceous. The hydrocarbon accumulation models are established, including one-stage charge and two-stage charge, which provides theoretical basis for the prediction the distribution of heavy oil in Hashan area. ©, 2015, Science Press. All right reserved.