南海西北部晚中新世红河海底扇储集层特征

Reservoir characteristics of Late Miocene Red River submarine fan,northwestern South China Sea

通过粒度分析、岩石铸体薄片、物性分析和扫描电镜等手段,分析远源红河海底扇储层的岩石学特征、成岩作用、孔隙结构及物性演化,研究海底扇储层的储集性能及成因机制。研究结果表明:红河海底扇主要储层可以分为碎屑流成因的中扇水道砂体、浊流成因的下扇水道砂体和末端朵叶砂体3类。储层具有较好的孔隙度,但渗透率较低,以中孔特低渗为典型特征,孔隙类型以粒间溶蚀扩大孔为主,喉道一般为分选中等的细喉型、砂岩内部发育致密的薄层钙质砂岩。优质储层发育在海底扇前端的下扇末端朵叶体,岩性为厚层的岩屑质石英细砂岩和中砂岩。储层孔隙度较高得益于远源重力流砂岩具有良好的颗粒骨架且泥质含量较低,早期碳酸盐胶结物得以大量发育并在晚期发生强烈溶蚀;渗透率较低的主要原因是后期绿泥石胶结物的广泛发育从而堵塞了喉道。

The grain size analysis, casting thin section, reservoir properties analysis, scanning electron microscope and other technologies were applied to analyze the petrology characteristics, diagenesis, pore structure and reservoir properties evolution of distant source Red River submarine fan reservoir, and the reservoir properties of submarine fan and generation mechanism were researched. The results show that the main lithofacies of Red River submarine fan are composed of mid-fan channel sandstone brought by debris flow, the lower fan channel sandstone brought by turbidity current and terminal lobe sandstone. The reservoir is characterized by relatively high porosity and low permeability. The typical characteristic has medium porosity and extra-low permeability. The pore type is mainly intergranular dissolution with enlargement. The pore throat is generally thin with medium sorted. Thin tight calcareous sandstone is developed within the main sandstone. The good quality reservoir is developed at the terminal lobe of lower fan in submarine fan front, and the lithofacies has thick lithic quartz fine sandstone and middle-grained sandstone. The relatively high porosity is due to the gravity flow sandstone from distant source which contains good particle skeleton with low clay content. The early carbonate cements can extensively develop and form strong dissolution. The low permeability is due to wide development of chlorite cements at late stage, which blocks the pore throat.