高演化碳酸盐岩烃源岩生烃演化特征与评价方法

Hydrocarbon generation characteristics and evaluation methods of highly maturity carbonate source rocks

中国在下古生界海相碳酸盐岩层系的油气勘探取得了重大突破,在此背景下,下古生界广泛发育的高演化、低TOC丰度的碳酸盐岩能否成为有效烃源备受关注。碳酸盐岩烃源岩中的成烃生物主要以浮游藻类为主,有机质除了干酪根之外,还存在丰富的可溶有机质和酸溶有机质,这些特殊性质决定了碳酸盐岩中有机质具有较高的生烃转化率。另一方面,在高过成熟阶段,碳酸盐岩烃源岩中存在显著的有机碳向无机碳转化过程,其机理主要与TSR作用和有机酸盐生烃有关,并表现出碳酸盐岩碳同位素组成的负漂。这些因素是导致高演化碳酸盐岩烃源岩表观TOC低的重要因素。因此,不能以TOC低否定高演化碳酸盐岩烃源岩经历的生烃过程和生成烃量。高过成熟碳酸盐岩烃源岩评价应综合考虑成烃生物类型与数量、有机碳同位素组成和无机碳同位素负漂等因素。

Major breakthroughs have been made in the exploration of marine carbonate strata in Lower Paleozoic in China.Under this background,whether the carbonate rocks with highly maturity and low TOC abundance,which are widely developed in Lower Paleozoic,can become effective hydrocarbon sources has attracted much attention.The hydrocarbon-producing organisms in carbonate source rocks are mainly planktonic algae,and there are abundant soluble organic matter and acid-soluble organic matter in addition to kerogen.These special properties determine that organic matter in carbonate rocks has high hydrocarbon generation conversion rate.On the other hand,there is a significant transformation process of organic carbon to inorganic carbon in carbonate source rocks in the highly maturity,and the mechanism is mainly related to TSR and hydrocarbon generation by organic acid salts,and it shows genesis of negative carbon isotope excursion composition of carbonate rocks.These factors are important reasons for low apparent TOC of highly maturity carbonate source rocks.Therefore,the hydrocarbon generation process and amount of high evolution carbonate source rocks cannot be negated by low TOC.In the evaluation of highly maturity carbonate source rocks,the types and quantities of hydrocarbon producing organisms,the carbon isotopic composition of organic and inorganic carbon isotopes excursion should be considered comprehensively.