塔里木盆地原油酸值特征及成因

塔里木盆地原油酸值总体不高,一般低于3 mg/g,三叠系、侏罗系原油酸值相对较高,一般在0.96～1.12 mg/g,但也只有部分地区原油刚达到高酸原油级别(酸值为1.0～5.0 mg/g),石炭系、奥陶系原油酸值较低,大部分在0.5 mg/g以下.塔里木盆地原油属于混合型中、低酸原油,有机酸主要来自于原油的生物降解,少量为原生的有机酸.奥陶系碳酸盐岩油藏原油曾经历严重降解,但产生的大量有机酸在随后的酸-岩反应中被消耗,呈高降解低酸值特征,侏罗系、三叠系、石炭系原油酸值的形成主要与地层水活动造成的晚期降解有关.图9表1参33

Acidity features and origin of crude oil in Tarim Basin

Crude oil in Tarim Basin belongs to mixed-type low and medium-acidity oil. Organic acids in the oil come mainly from biodegradation of the oil, and secondly from original organic acids. The oil has a lower acid number, below 3 mg/g in general, and the oil of Triassic and Jurassic reservoirs in the Lunnan area has a relatively high acid number, about 0.96-1.12 mg/g, only some local oil reaches the level of the high-acidity oil (1.0-5.0 mg/g); the oil in Ordovician and Carboniferous reservoirs has a lower acid number, mostly below 0.5 mg/g. The oil in Ordovician carbonate reservoirs experienced intense degradation, but the followed acid-rock reaction consumed almost all the early organic acids and depressed the oil acidity. The Jurassic, Trassic and Carboniferous oil acidity is related to the late-biodegradation due to active formation water.