关键词: 原油, 酸值, 生物降解, 前陆盆地, 裂谷盆地

Abstract: The acidity of crude oil is expressed by its total acid number (TAN),which is the number of KOH determined by non-aqueous titration needed to neutralize the acidity in one gram of oil. According to the distribution of TAN of oil in the world, crude oils can be classified into four types including conventional oil, low-acidity oil, high-acidity oil and extremely high-acidity oil. Oil with more than 1 mg/g of TAN is defined as high-acidity oil. On the basis of the origins of oil accumulations, the high-acidity oil can be divided into three types of primary-type, secondary biodegradation-type and mixed-type oils. The TAN of crude oil at any given biodegradation ranking tends to increase in the order of marine oils less than lacustrine oils. In the world, most of high-acidity oils were caused by biodegradation and accumulated mainly in stratigraphic traps of foreland basins, and secondly distributed in anticline, fault-block and stratigraphic traps of rift basins, passive continental marginal basins and cratonic basins.

Key words: crude oil, total acid number, biodegradation, foreland basin, rift basin