渤海湾盆地歧口凹陷古近系油气运聚特征分析与数值模拟

Features and numerical simulation of Paleogene hydrocarbon migration and accumulation in Qikou sag,Bohai Bay Basin

应用油藏地球化学方法对歧口凹陷古近系和新近系油气运移方向和路径进行了精细刻画,建立歧口凹陷输导系统的空间组构模型,并采用盆地模拟技术恢复凹陷古流体场演化特征,综合研究流体动力特征、流体输导系统结构、油气分布特点。含氮化合物和原油性质分析表明该区油气总体上具有由凹陷中心向四周构造高部位运移聚集的趋势,其中凹陷中心为自生自储,中环带经历了短距离侧向运移和纵向运移,外环带油气均经历了较长距离的侧向和纵向运移。油气的运移通道是由断层、连通砂体以及不整合组合而成的复杂立体网络体系,进一步可识别出源内砂岩斜坡带近源侧向运聚、近源垂向运聚、远源阶梯状3种油气运聚成藏模式,其中近源垂向运聚成藏模式是歧口凹陷最有利的油气运聚成藏模式。盆地模拟结果表明,主要生烃层系的水势、气势、油势以及流线主要表现为继承性发育的特点,流体势流线的继承性汇聚区控制了现今油气分布格局。

The reservoir geochemical method was used to particularity describe the migration direction and path of the Paleogene and Neogene in Qikou sag.The spatial configuration model of the transportation system in Qikou sag was established,the basin simulation technique was adopted to restore the evolutionary characteristics of the Paleo-fluid field in the sag.The author comprehensively studied the dynamic characteristics of fluid,fluid transporting system,as well as the characteristics of hydrocarbon occurrence.The analysis of the properties of the nitrogenous compounds and crude oil showed that oil and gas in this area had a tendency of migration and accumulation from the center of the sag to the high site around the structure,the center of the sag is self-generating and self-preserving,the oil and gas of central belt has experienced short-distance lateral migration and vertical migration.The oil and gas of outer ring zone experienced longdistance lateral and vertical migration.The migration channel of oil and gas is a complex stereonet system composed of faults,interconnected sand bodies and unconformity.Further,3modes of hydrocarbon migration and accumulation atintra-source sandstone slope can be identified,they are nearsource lateral migration and accumulation,near-source vertical migration and accumulation and distant source stepped migration and accumulation,the near-source vertical migration and accumulation is the most favorable model for hydrocarbon migration and accumulation in Qikou sag.The results of basin simulation showed that the water potential,gas potential,oil potential and flow line of the main hydrocarbon generating strata are mainly characterized by inherited development,and the succession area of the fluid potential streamlines controls the current oil and gas distribution pattern.