东营凹陷中央隆起带油-源特征分析

An analysis of oil-source characteristics of central uplift belt in Dongying depression

东营凹陷的沙河街组三段的烃源岩具有姥鲛烷占优势 ,姥植烷比为 0 .5～ 1.0 ,微弱的伽马蜡烷等特征 ;沙河街组四段烃源岩具有较强的植烷优势 ,姥植烷比小于 0 .5 ,丰富的伽马蜡烷等特征。根据这一显著差异 ,将东营凹陷中央隆起带上各油田的油源类型划分为沙三型、沙四型以及混合型 ,其中以沙三型和混合类型为主。不同地区和不同层系原油的来源存在较大差异 ,通过对构造特征与地化特征的平面分布规律研究 ,认为石油遵循就近运移聚集的规律 ,各洼陷中心即为油源中心 ;西部地区的油源主要以利津洼陷沙河街组三段烃源岩为主 ;少量东南部的原油由牛庄洼陷沙河街组四段烃源岩供应 ;而东北部的则由民丰洼陷烃源岩供给。断裂发育处混源石油较为普遍 ,说明了断裂对混源的作用较大。

Source rocks in Es 3 (the third member of Shahejie Formation) in Dongying depression are characterized by the predominance of pristane with a pristane/phytane ratio of 0.5～1.0 and small amount of gammacerane; while source rocks in Es 4 (the fourth member of Shahejie Formation) are characterized by the relative abundance of phytane with a pristane/phytane ratio of below 0.5 and rich in gammacerane.Based on this remarkable difference, the oil sources of oilfields in the central uplift belt of Dongying depression are classified into Es 3, Es 4 and mixing types,of which the Es 3 and mixing types are predominant. Sources of oil in different regions and different horizons vary greatly. Study on structural features and areal distribution of geochemical properties reveal that the hydrocarbons would migrate preferentially into the nearest reservoirs, thus the center of each sag consists of the center of oil source.The oil in the western area come mainly from the Es 3 source rocks in Lijin sag; small amount of oil in the southeastern area come from the Es 4 source rocks in Niuzhuang sag;while oil in the northeastern area have been generated by the source rocks in Minfeng sag. Oil of mixing type commonly occur in areas where faults are well developed, indicating that faults have large impacts on mixing type oil.