陕北志丹地区长_6—长_2油层组水退型三角洲沉积演化特征

Sedimentary and evolutionary characteristics of dereliction deltas in Chang 6-Chang 2 oily members,Zhidan region,northern Shaanxi

根据测井、录井资料,运用沉积学方法综合研究了陕北志丹地区中生界延长组长6—长2油层组沉积及演化特征。结论认为:长6—长2沉积期志丹地区为大型三角洲与大型湖泊沉积体系进退发育之地,形成了区内良好的生储盖组合与广泛分布的众多含油层系。在近南北向剖面上,长6—长2沉积组合自下而上、由北向南显示出三角洲不断向湖超覆,形成向上变粗的水退型沉积序列;沉积相带自北向南不断向湖中心推移,三角洲前缘大面积展布并多期次叠合,形成区内的沉积主体。三角洲前缘亚相可以进一步分为水下分流平原亚相与前缘河口亚相两大部分,骨干砂体分别为分流河道砂与河口坝砂;长6沉积期区内前缘河口亚相极为发育,到长2沉积时水下分流平原亚相扩大发展,三角洲平原亚相开始进入区内。

The study using well logging data and the sedimentological method reveals that large deltas and lake systems developed time and again in the Chang 6 - Chang 2 depositional stage in the Zhidan region, and a good intraplot source-reservoir-cap assemblage and widely spread oil-beating series are formed. In sub-south-north cross-section, the Chang 6 - Chang 2 sedimentary association shows that deltaic deposits progressively overlapped lake deposits from bottom to top and from north to south, forming upward coarsening dereliction depositional sequences; sedimentary facies belts moved continually towards the lake center from north to south, deltafront subfacies spreaded extensively.and overlapped in multiphases, forming the main intraplot depositional body. Deltafront subfacies may be subdivided into underwater distributaries plain and anterior margin river mouth subfacies, and the main sand bodies are river mouth sand bank and distributaries channel sand body; the Chang 6 stage＇s anterior margin river mouth subfacies in the region were well-developed; to Chang 2 stage, underwater distributaries plain subfacies extended and developed rapidly, and deltaic plain subfacies began to come into the region.