塔里木盆地气－液溶解平衡机制下的原油轻烃行为及其地质意义

塔北地区普遍存在气顶型凝析气藏和带油环的凝析气藏。与传统烃类热演化理论相矛盾的是:１）天然气的成熟度远高于油环原油或凝析油；２）高－过成熟天然气与同藏的原油间存在明显的物性不匹配。结合地质背景，认为这种矛盾是由后期形成的干气进入已形成的油藏并溶解原油轻烃这一过程所致，凝析气中的轻烃是气－液溶解平衡的产物。地质历史时期凝析气与油环分离或产生凝析油气藏或混入其它油藏的蒸发分馏作用过程导致了轻烃的油藏再分配，形成了塔北地区纵向上原油轻烃的“反序”分布趋势及某些参数的异常分布。认为烃类的气－液相溶解平衡作用是原始原油轻烃分布特征后期演变的主要控制机制之一。其实质是不同性质轻烃气液两相差异性分配基础上的物理化学分异过程。

Geological Significance and Behavior of Petroleum Light Hydrocarbons under Vapour-Liquid Equilibrium Mechanism in Tarim Basin

There are a lot of gas-condensate reserviors bearing gas-caps or oil-rings found in the north of Tarim Basin. The calculated Ro data demonstrate that the natural gases possess much higher maturity (Ro2. 3%) than that of the associated oils and condensates (Ro1. 1 %),taking unfitable physical properties of the ring-oil into consideration, we concluded that the natural gas is a allochthonous one and the condensate is the product of vapor-liquid equilibrium between the all chthonous natural gas and the oils in reservior, in this physical-chemistry proccess, all light hydrocarbons, having distributed themselves according to their vepor-liquid equilibrium constants, would occur in different proportions in the vapor and liquid phases. On the basis of the above conclusion, we suggest that the separation of gas-cap from oil-ring once occured in the past geological time, there would be independent gas Condensate accumulation fromed in Tarim Basin, and meanwhile the light hydrocarbons of the primary reservior fractionated, which caused the unusual distribution of light hydrocarbons in Ordovician to Cretaceous reserviors.