CO_(2)充注对油气藏相态的影响及凝析气藏成因分析——以渤中19-6凝析气藏为例

Influence of CO_(2)injection on phase behavior of oil and gas reservoirs and analysis of gas condensate reservoir genesis:A case study of BZ19-6gas condensate reservoir

油气藏中的CO_(2)对油气相态具有重要的影响控制作用。为了探究CO_(2)对渤海湾盆地渤中19-6凝析气藏成因的影响意义,基于渤中19-6凝析气藏5口井8组凝析气样品的组分及物性数据,利用PVTsim相态分析技术模拟CO_(2)充注,对CO_(2)充注前后渤中19-6凝析气藏流体相态变化进行了定量分析。研究表明:①渤中19-6气藏CO_(2)为无机幔源成因,含量在9.15%~15.76%,δ13 CCO_(2)在-7‰~14.4‰。②CO_(2)能明显降低流体的临界温度(T_(c))、临界压力(P_(c))、临界凝析温度(T_(m))和临界凝析压力(P_(m)),使流体相态从挥发油逐渐过渡到近临界态,最终转变成凝析气。结合研究区油气充注史发现,虽然研究区经历了“早油晚气”的两期成藏过程,但天然气充注后流体相态仍为挥发油,CO_(2)的充注才使古油藏最终转变成现今的凝析气藏。

The CO_(2)in oil and gas reservoirs plays an important role in controlling the phase behavior of oil and gas.In order to explore the significance of CO_(2)’s impact on the genesis of BZ19-6 gas condensate reservoir in Bohai Bay basin,PVTsim phase analysis technology was applied to simulate CO_(2)charging and quantitatively analyze the phase behavior of fluids in BZ19-6 gas condensate reservoir before and after CO_(2)charging in this paper based on the composition and physical property data of 8 groups of gas condensate samples from5 wells in BZ19-6 gas condensate reservoir.Research results showthat:①The CO_(2)in BZ19-6 gas reservoir is of inorganic mantle origin,with the content ranging from9.15%to 15.76%and theδ13CCO_(2)ranging from-7‰to 14.4‰.②CO_(2)can significantly reduce the critical temperature(T_(c)),critical pressure(P_(c)),cricondentherm(T_(m)),and cricondenbar(P_(m))of the fluid,gradually transitioning the phase state of the fluid from volatile oil to near critical state and ultimately transforming it into condensate gas.Based on the history of oil and gas charging in the study area,it was found that although the study area experienced two stages of reservoir formation:“early oil and late gas”,the fluid phase after natural gas charging remained volatile oil,and CO_(2)charging ultimately transformed the ancient oil reservoir into the current gas condensate reservoir.