251 / 2019-06-30 16:52:39

Petrological Characteristics and Alkaline Diagenesis of Zhuhai Formation Reservoir in Eastern Huizhou Sag

Pearl River Mouth Basin,Huizhou Sag,Zhuhai Formation,Alkaline Diagenetic Environment,Petrological Characteristics,Diagenesis

Huizhou Sag which has an abundance of hydrocarbon is located in the middle of Zhu I Depression, Pearl River Mouth Basin. The Paleogene Zhuhai Formation in this sag is rich in sand-body. The recent explorations have indicated that Zhuhai Formation is the key horizon with great exploration potential. Based on the data of cores, cast thin sections, scanning electron microscopy and X-ray diffraction, the petrological characteristics, diagenesis and diagenetic evolution of Zhuhai Formation reservoir in eastern Huizhou Sag have been studied. The types of reservoir rocks of Zhuhai Formation in eastern Huizhou Sag are mainly lithic sandstone, feldspathic lithic sandstone, lithic quartz sandstone and lithic feldspathic sandstone with low compositional maturity. Debris particles have the characteristics of medium to poor sorting, poor roundness and low structure maturity. There are obvious alkaline diagenesis during the sandstones burial process, such as quartz dissolution and metasomatism, carbonate cementation, precipitation and transformation of illite and chlorite, and albitization. The alkaline diagenesis has many effects on pores, including quartz dissolution to form secondary solution pores, carbonate cements precipitation to lose intergranular pores and clay mineral precipitation to form intergranular micropores. The Zhuhai Formation in the study area mainly develops intragranular and intergranular dissolved pores, with less primary pores. The reservoir is in the middle diagenetic stage A, which experienced strong compaction. The early diagenetic stage is alkaline diagenetic environment. In this stage, quartz dissolves and the cement of carbonate, sulfate and illite precipitates. The stage A of middle diagenesis is acidic diagenetic environment. During this time, feldspar and debris dissolve; quartz forms secondary overgrowth edges, and kaolinite precipitates.
惠州凹陷位于珠江口盆地珠一坳陷中部，是非常重要的富烃凹陷。该凹陷古近系珠海组富含砂体，近年来的油气勘探实践证明珠海组具有良好的油气勘探潜力，是现阶段的重点研究层位。根据岩心、铸体薄片、扫描电镜、X衍射等资料，对惠州凹陷东部珠海组储层的岩石学特征、成岩作用和成岩演化过程进行分析研究。研究认为，惠州凹陷东部珠海组储层的岩石类型以岩屑砂岩、长石质岩屑砂岩、岩屑质石英砂岩和岩屑质长石砂岩为主，成分成熟度低。碎屑颗粒分选中等到差，磨圆较差，结构成熟度较低。砂岩埋藏过程中经历了明显的碱性成岩作用：石英的溶蚀与交代、碳酸盐矿物胶结、伊利石和绿泥石的沉淀与转化以及钠长石化等。碱性成岩作用对孔隙的影响包括：石英溶蚀形成次生溶孔、碳酸盐胶结物沉淀损失粒间孔隙、粘土矿物沉淀形成晶间微孔。研究区珠海组主要发育粒内溶孔和粒间溶孔，原生孔隙较少。储层现今处于中成岩阶段A期，早期经历了强烈的压实作用，早成岩阶段为碱性成岩环境，发育石英溶蚀作用以及碳酸盐、硫酸盐、伊利石等矿物的胶结作用；中成岩A期为酸性成岩环境，长石、岩屑等发生溶蚀，石英形成次生加大边、高岭石发生沉淀。