Geochemical features and classification of crude oils in the Hailaer Basin, Northeast China

Majority of crude oils in the Hailaer Basin is the oil with normal density, middle to high wax and low sulfur content. Partial oils are light and mature with middle wax, and minority is heavy oils with low to middle wax. The carbon isotopic ratio of the crude oils ranges from - 34‰ to - 25‰ , and biomarker features are quite different among the crude oils, indicating a great difference in components of organic matter and depositional environments. According to carbon isotopic composition and biomarker features the crude oils can be divided into five groups (1) with the low carbon isotope ratio, high concentration of gammacerane, no diasteranes, and occurs in the Bayanhusu Sag; (2) the oil occurs in the southern part of the Wuerxun Sag, characterized by low carbon isotopic ratio, low to middle content of diasteranes and gammacerane; (3) the oil in the northern part of the Wuerxun Sag and Beier Sag, with lower carbon isotopic ratio, low content of gammacerane, high concentration of diasteranes, Ts , C29 Ts , and C30 diahopane; (4) the oil in the Hulunhu Sag, with high carbon isotopic ratio, rich in diasteranes, Ts , C29 Ts, and low to middle content of gammacerane; (5) the oil occurs in the Huhehu Sag, is derived from coal-bearing strata, and is characterized with heavy carbon isotopic composition, high Pr/Ph ratio, high content of C29 steranes and diasteranes, low content of C27 steranes, and no gammacerane.