Abstract:

Lunnan area was an important petroliferous province in the northern Tarim Basin. The acid value of the crude oil in the Ordovician carbonate reservoirs was generally low, 001141 mg KOH/g on the whole, and most of them were low, some were acidic oil or high acidvalue oil. In horizontal, acid value was high in the west and low in the east. According to the study of oil physical properties, geochemical characteristics and accumulation processes, acid value of crude oil was related to kerogen type, maturity and hydrocarbon charging processes, especially biodegradation. Based on biomarkers analysis, the acidiferous oil was of mixing origin in this area, which was consistent with analytical results of hydrocarbon accumulation. The acidic substances content of crude oil would affect oil nature, so the acid value of crude oil was obviously accorded with physical properties. In the Lunnan area, the properties of oil and gas are significantly different, with distribution pattern of “oil in the west and gas in the east”. The density, gumasphaltene content and sulfur content of crude oil also had the distribution of “high in the west and low in the east”, while the gasoil ratio and wax content had the opposite characteristics.

Key words:  acidic oil, acidic value, carbonate rock, Ordovician, Lunnan area, Tarim Basin