乌石凹陷南部陡坡带流二段大型储集体发育条件及特征

综合钻井、古生物、地震、薄片等资料，分析了乌石凹陷南部陡坡带大型储集体的发育条件、类型、特征及有利勘探方向。研究结果认为:提出湖平面、物源、断裂及古地貌等耦合控制了断陷湖盆陡坡带大型储集体的发育，其中强烈的湖退事件是发育大型储集体的古湖盆演化基础；充足的物源供给是形成大型储集体的物质保证；显著的断裂聚砂效应和适宜的地貌条件是构建大型储集体的重要汇水机制。大型储集体的主要类型为扇三角洲和辫状河三角洲，其中扇三角洲主要受断面缓坡带及沟谷地貌的控制，沉积上岩性较粗，微相以水下分流河道和水下分流间湾为主；辫状河三角洲主要受转换断阶带、帚状断阶带及相对宽缓地貌的控制，沉积上岩性较细，微相除水下分流河道、水下分流间湾以外，河口坝及远砂坝也较为发育。在此基础上，结合大型储集体的发育特征，明确了乌石凹陷南部陡坡带东段的有利勘探层系为流二段下层序高位域，西段的有利勘探层系为流二段上层序低位及湖侵域；而各大型储集体的前端，由于岩性圈闭、岩性-构造圈闭及构造圈闭等发育，且埋藏浅、靠近生烃中心，还位于油气运聚的优势方向，为有利的勘探区域。

Large Reservoirs Development Condition and Characteristics of the Second Member of Liushagang Formation in the Southern Steep Slope Zone,Wushi Depression

Comprehensive analysis of drilling, palaeontology, seismic, sections and other data, the large reservoirs development conditions,types,characteristics and the favorable exploration directions of the southern steep slope zone in Wushi depression was analyze. It proposed that the lake level, provenance, fracture and paleogeomorphology cou-pling controlled the development of large reservoirs in the steep slope of fault-depressed lacustrine basin.Among them, the strong lake retreat was the basic condition of the Palaeo-lake evolution for developing large reservoirs,the enough supply of provenance was the material guarantee for forming large reservoirs,the significant fracture accumulated sand effect and suitable topography were the important catchment mechanism for constructing large reservoirs.The main types of large reservoirs were fan delta and braided river delta.The fan delta was mainly controlled by the fracture sur-face gentle slope zone and valley topography, the lithology was relatively coarse, the sedimentary microfacies were mainly underwater distributary channel and subaqueous inter-distributary bay.The braided river delta was mainly con-trolled by transition fault zone, broom fault zone as well as relatively wide and gentle topography, the lithology was relative fine,the sedimentary microfacies were mainly distributary mouth bar and distal bar, besides underwater dis-tributary channel and subaqueous inter-distributary bay.On this basis and combined with the characteristics of large reservoirs,it suggested that the favorable exploration layer for the eastern part of the southern steep slope zone was the highstand system tracts of lower sequence and for the western part of the southern steep slope zone was the lowstand and transgression systems tracts of upper sequence in the second member of Liushagang,Wushi depression.Due to the front of the large reservoirs lithologic traps,lithological-structural traps and structural traps were developed,and were shallow buried,closed to the hydrocarbon supply center,at the same time located in the dominant direction of oil and gas accumulation,therefore,was the favorable exploration area.