The occurrence of fatty acids in immature source rocks and their distribution characteristics

Abstract

The fatty acids in extractable bitumen and kerogen of immature source rocks of the Liaohe Basin and Jiyang sag were investigated in this study. The result showed that the bitumen fatty acids were mainly associated with non-hydrocarbon fraction and that the kerogen fatty acids with some tightly bound fatty acids were mainly bounded in a net structure of kerogen by ester bonds. For the investigated source rocks, the fatty acids in bitumen, bound fatty acids and tightly bound acids in kerogen ranged in 0.01%–0.073 9%, 0.005%–0.045 5% and 0.005%–0.010% respectively. Among the fatty acids analyzed in this study, mono-carboxylic acids, α, ω)-di-carboxylic acids and hydroxy acids accounted for 70%–100%, 0%–30% and <10% respectively. It was also found that the monocarboxylic acids with longer chains mainly existed in bitumen, and that the α, ω)-di-carboxylic acids and hydroxy acids mainly existed in kerogen. From above, it was assumed that the monocar-boxylic acids in bitumen might have played an important role in the hydrocarbon generation from fatty acids in immature source rocks.