涠西南凹陷流一段高位体系域湖底扇沉积特征及勘探意义

Sedimentary characteristics and exploration significance of sub-lacustrine fan of highstand system tract in the first member of Liushagang Formation in the Weixinan sag

涠西南凹陷B洼流一段高位体系域湖底扇是岩性油气藏勘探的重要领域,但是在湖底扇的特征、分类、展布、成因机制和发育模式等方面认识不清,制约了勘探进程和成效。基于钻井、岩心、测井、分析化验及三维地震等资料,对B洼流一段高位体系域湖底扇进行了系统刻画,研究结果表明:①B洼流一段高位体系域湖底扇可分为两大类4个小类,分别为高位早期的块体流型湖底扇(又可分为下切水道中心型、下切水道侧翼型)和高位晚期碎屑流型湖底扇(又可分为无水道化富砂型和无水道化富泥型)。②各类湖底扇在岩性、测井和地震上都表现为不同的特征。③湖平面变化、物源体系、搬运路径等耦合控制了两种发育模式,分别为轴向西物源曲流河三角洲—沉积挠曲坡折—富泥型湖底扇沉积模式和西北物源扇三角洲—断裂转换坡折—富砂型湖底扇沉积模式。④由西北向扇三角洲供源的下切水道中心型块体流和无水道化富砂型碎屑流湖底扇砂体埋深浅、物性好,与流一段湖相泥岩形成自生、自储、自盖的成藏组合,具有较大勘探价值。

The sub-lacustrine fan of highstand system tract in the first member of the Liushagang Formation(hereinafter referred to as Liu-1 member) in B sub sag of the Weixinan sag is an important field for lithologic reservoir exploration. However, the characteristics, classification, distribution, genetic mechanism, and development pattern of sub-lacustrine fan are not well understood, which restricts the exploration process and effectiveness. Based on data from drilling, core, well logging, laboratory analysis and 3D seismic data, the sub-lacustrine fans of highstand system tract in the Liu-1 member in B subsag have been systematically described. The results show that:(1) The sub-lacustrine fans of highstand system tracts in the Liu-1 member in B sub-sag can be divided into two major types and four sub-types, which are mass flow sub-lacustrine fans in early highstand stage(which can be further divided into incised channel center type and incised channel flank type) and debris flow sub-lacustrine fans in late highstand stage(which can also be further divided into non-channelized sand-rich type and non-channelized mud-rich type).(2) All kinds of sub-lacustrine fans have different characteristics in lithology and on well logging and seismic data.(3) There are two development models jointly controlled by lake level change, sediment source system and transport routes. The first depositional model is meandering river delta-sedimentary flexure slope break-mud-rich sub-lacustrine fan with west axial sediment source. The second depositional model is fan delta-fault transition slope break-sand-rich sub-lacustrine fan with northwest sediment source.(4) The sub-lacustrine fan sand bodies of the incised channel center mass flow type and the non-channelized sand-rich debris flow type, supplied by the northwest fan delta sediments, have shallow-buried depth and good reservoir properties, and form a hydrocarbon accumulation assemblage of self-generating, self-storage and self-sealing with the lacustrine mudstones in the Liu-1 member, which has great exploration potential.