油气运移聚集过程中的地球化学作用

原油组成虽然受源岩有机质类型和成熟度的控制,但运移过程中和成藏后的次生变化可以彻底改变其原来的面貌。原油排出后遭受的溶解和吸附作用对集聚原油的组成有一定的影响,由于油藏温压条件的变化、断层活动、剥蚀、地震或盖层微渗漏等导致的运移分馏作用对原油组成的影响更为重要。运移分馏作用可以产生衍生凝析油和残余油。衍生凝析油中轻组分非常富集,且通常聚集在较浅的储层中;而残余油中富含高分子量化合物,尤以含蜡量增加较为明显。可见凝析油和高蜡油的形成并非单纯由母源和成熟度控制,认识到运移分馏作用的影响有助于人们避免对地化资料的错误解释。

GEOCHEMICAL PROCESSES IN PETROLEUM MIGRATION AND ACCUMULATION

The composition of crude oil, although initially controled by the types and maturity of organic matter in source rocks, will be changed thoroughly by the secondary modification during migration and after pool formation. The dissolution and adsorption subjected by crude oil after expulsion have certain effects on the cpmposition of accumulated crude oil, but the influences of migration fractionation caused by the changing of temperature and pressure conditions in reservoirs, fault activties, denudation, earthquakes or the micropercolation of covers on the composition of crude oil are particularly important. Migration fractionation can form derived condensate and residual oil. Light components are very enriched in derived condensate and usually accumulate in shallower reservoirs, while high molecular weight compounds are enriched in residual oil which is characterized by the more obvious increase of wax content.It is thus clear that the formation of condensate and a high wax oil is not simply controled by parent sources and maturity. Understanding the effects of migration fractionation will be helpful to avoid the mistaken interpretation of geochemical data.