莱州湾凹陷北洼沙河街组三段砂岩储层孔隙定量演化模式

Quantitative pore evolution model of sandstone reservoirs for Member 3of Shahejie Formation in the northern subsag of Laizhouwan sag

莱州湾凹陷位于渤海湾盆地南部,是一个"小而肥"的富烃凹陷,其储层成岩作用的研究程度较低。铸体薄片、扫描电镜、X射线衍射和阴极发光等多种技术手段的分析结果显示,莱州湾凹陷沙河街组三段中—深层储层的岩性主要为中粒—细粒岩屑长石砂岩,其成分成熟度和结构成熟度为中等偏好,属于中孔、中—低渗储层类型,储集性能良好,成岩作用处于中成岩阶段A1期。地层埋藏史、热演化史、烃源岩生烃史和成岩演化史的综合分析指示,储层孔隙空间的演化主要经历了机械压实减孔、早期胶结减孔、酸性溶蚀增孔和晚期胶结减孔4个阶段,其孔隙度的变化量分别为7.73%、4.61%、5.99%和2.54%,由此可建立储层孔隙定量演化的综合模式。受长期浅埋环境和成岩演化阶段影响,莱州湾凹陷沙河街组三段在古成藏期的储层孔隙度约为25%,油气充注情况良好。现今的孔隙类型仍以原生粒间孔为主,油气保存情况较好,勘探潜力较大。这一认识可为研究区的进一步勘探开发提供理论支持。

The Laizhouwan sag, located in the southern part of the Bohai Bay Basin, is small but rich in hydrocarbons, and there is little research on reservoir diagenesis. The analysis results obtained by various technical means such as thin sections, SEM, X-ray diffraction, and cathodoluminescence show that the lithology of the middle-deep reservoirs in Member 3 of Shahejie Formation is mainly medium-fine grained lithic feldspar sandstone in the Laizhouwan sag, with medium-high compositional and textural maturity, good reservoir performance characterized by medium porosity and medium-low permeability, and at the stage A1 of mesodiagenesis. The comprehensive analysis of stratigraphic burial history, thermal evolution history, hydrocarbon generation history of source rocks and diagenetic evolution history indicates that the evolution of the reservoir pore spaces has 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, and the corresponding changes in porosity are 7.73%, 4.61%, 5.99% and 2.54%, respectively. On this basis, a comprehensive model of quantitative evolution of reservoir pores can be established. Affected by the long-term shallow burial environment and the diagenetic evolution stage, the porosity of ancient reservoir of Member 3 of Shahejie Formation in the Laizhouwan sag was ca. 25% in the accumulation period under good hydrocarbon charging conditions. At present, the pore type is still dominated by primary intergranular pores, showing good oil and gas preservation conditions and great exploration potentials. This understanding can provide theoretical support for further exploration and development in the study area.