Geochemical Characteristics of Permian Heavy Oil and Its Origin in Jimsar Sag,Xinjiang Province

In the thick oil girdle of the slope area of Jimsar sag,the oil as ordinary heavy oil is characterized as high density,high viscosity,high initial boiling point,low freezing points and low wax content.This heavy oil at low maturity has well preserved β-carotane and-carotane,regular sterane as the main ingredient,low level of triterpene terpane,and the increased content range of hopane.The low-matured heavy oil is liable to become heavy oil.The integrated geologic factors control the distribution of heavy oil.Biodegradation may be the biggest factor of oil densification.The heavy oil in this sag was accumulated by a short-distance migration,and the oil source is located at the deep part of this sag.Two times of oil filling happened in the Jimsar sag.The heavy oil was derived from the low-matured crude oil at the first phase and became the heavy oil by biodegradation.