柴西南地区E3^1构造岩性油气藏形成条件及有利勘探区带

Formation Conditions of Structural Lithological Oil and Gas Reservoirs and Exploratory Prospects in the Southwest of the Qaidam Basin,China

柴西南地区具备E13构造岩性油气藏形成的地质条件。生油岩地球化学特征和油源对比研究表明,柴西南地区下第三系发育扎哈泉和英雄岭2个大的生油凹陷,凹陷内发育E13和E232套有效生油岩,为构造岩性油气藏形成提供了油源条件。柴西南地区存在与英雄岭和扎哈泉生油凹陷相接的红柳泉—跃进、铁木里克和昆北断阶带3个古斜坡,为构造岩性油气藏形成创造了大型的古构造斜坡背景。柴西南地区昆北断阶带和尕斯断陷内存在下倾方向与生油凹陷相邻的成排成带发育的断背斜和断鼻等构造,为构造岩性油气藏的形成提供了局部构造斜坡背景。在区域和局部构造斜坡背景上柴西南地区下干柴沟组下段(E13)沉积时期存在辫状河三角洲和湖泊相构成的沉积体系,发育了6个辫状河三角洲。柴西南辫状河三角洲外前缘发育河口坝、远端坝和席状砂,主要分布在尕斯断陷内的构造圈闭的斜坡区,油源和圈闭条件优越,是构造岩性油气藏勘探最有利的地区。柴西南辫状河三角洲前缘发育水下分流河道砂体,分布在昆北断阶带和尕斯断陷部分断鼻或断背斜的斜坡带,油源较充裕,但封堵条件较差,是构造岩性油气藏勘探较有利的区带。

E13 of Southwestern Qaidam Basin possesses the geological conditions to form the structural lithologic reservoirs.Characteristics of source rocks and study of oil source correlation show that two large petroleum generative depressions,i.e.,the Zhahaquan and Yingxiongling depressions,developed in the lower Tertiary,including two sets of effective source rocks of E13 fand E23,providing the oil source conditions for the formation of structural lithologic reservoirs.The existence of three structural slopes of Hongliuquan-Yuejin,Tiemulike and the Kunbei fault step zone in Southwestern Qaidam basin,connecting the depressions of Zhahaquan and Yingxiongling,created large structural slope backgrounds for the formation of structural lithologic reservoirs.The Kunbei fault step zone and the Gasi faulted depression in Southwestern Qaidam basin have structures of fault anticlines,fault noses and so on aligned in belts,with downdip direction adjacent to petroleum generative depressions,providing the local structural slope backgrounds for the formation of structural lithologic reservoirs.In the backgrounds of regional and local structural slopes,Southwestern Qaidam basin existed braid delta and lacustrine facies depositional systems,and developed six braid deltas during the period of the lower Ganchaigouzu（E13） Formation.There developed mouth bars,distal bars and sheet sands in delta front outer zones of Southwestern Qaidam basin mainly in the slope areas of structural traps in the Gasi fault depression where there are superior trap conditions and were the most favorable areas for the exploration of structural lithologic reservoirs.Delta fronts of Southwestern Qaidam basin developed underwater distributary channel sands in the slope belts of the Kunbei fault step zone and certain fault noses or fault anticlines of the Gasi fault depression,where there are rich oil source and poor sealing conditions and were more favorable for the exploration of structural lithologic reservoirs.