深层砂岩储层特征及成岩差异演化过程——以辽河坳陷东部凹陷牛居—长滩洼陷沙三上亚段为例

Reservoir characteristics and differential diagenetic evolution process of deep buried sandstone reservoirs:Case study of the upper Es_(3) in Niuju-Changtan subsag of Eastern Sag,Liaohe Depression

辽河坳陷东部凹陷牛居—长滩洼陷深层沙三上亚段沉积体系复杂、储层横向变化大,深层探井少,储层成岩作用研究程度较低。利用铸体薄片、扫描电镜、X-射线衍射、流体包裹体等多种技术手段,对沙三上亚段储层性质、成岩演化特征进行了分析,划分了成岩相类型,并对比了不同类型储层成岩差异演化过程。结果表明,沙三上亚段储层岩性为中—细粒岩屑砂岩,以低孔、特低渗为主,储集空间主要为次生溶蚀孔隙,储层经历了压实减孔、早期胶结减孔、有机酸溶蚀增孔、晚期胶结减孔4个阶段。不同类型储层成岩演化过程具有明显差异,强压实相和强钙质胶结相砂岩致密化时间最早,中等成岩相砂岩次之,强溶蚀相砂岩最晚。强压实相和强钙质胶结相砂岩受高杂基含量和高碳酸盐胶结含量的影响,成岩早期孔隙度快速减少,导致晚期有机酸溶蚀的范围和强度有限;而强溶蚀相砂岩由于早期压实程度相对较弱,保留一定粒间孔隙,受有机酸溶蚀作用的影响较大,储层物性得到良好改善。

The deep buried sandstone reservoirs in the upper member of Es_(3) in Niuju-Changtan subsag of Eastern Sag, Liaohe Depression are characterized by complex sedimentary system, large lateral variation of reservoir and few deep exploration wells, but there is little research on reservoir diagenesis. Based on casting thinsections, SEM, X-ray diffraction, fluid inclusions and other technical means, this paper analyzed the properties, diagenesis characteristics and evolution of deep sandstone reservoirs in the upper third member of Shahejie Formation in Niuju-Changtan subsag, divided the reservoir diagenetic facies types, and compared the differential diagenetic evolution process of different types of reservoirs. The results show that the lithology of the upper third member of Shahejie Formation is mainly medium-fine grained lithic sandstones in the study area with low porosity and ultra-low permeability, and the reservoir pore type is mainly secondary dissolution pores. The diagenetic evolution of reservoir mainly experienced four stages including mechanical compaction for porosity reduction, early cementation for porosity reduction, acidic dissolution for porosity increase and late cementation for porosity reduction. The diagenesis and pore evolution of different types of sandstone reservoirs are significantly different.The densification time of sandstones from tight compaction facies and tight calcite cementation facies is the earliest, followed by sandstones from moderately diagenetic facies, and sandstones from strong dissolution facies are the latest. The sandstones of tight compaction facies and tight calcite cementation facies are affected by high matrix content and high carbonate cementation content respectively, and the porosity decreases rapidly in the early stage of diagenesis, resulting in the limited range and intensity of organic acid dissolution in the late stage. Due to the relatively weak compaction degree in the early stage, the sandstones of strong dissolution facies retain some intergranular pores, which are greatly affected by the dissolution of organic acids, and the reservoir physical properties are improved.