珠江口盆地惠州凹陷文昌组砂岩孔隙定量演化模式——以HZ-A地区辫状河三角洲储层为例

A Quantitative Porosity Evolution Model of Sandstone for Wenchang Formation in Huizhou Depression,Pearl River Mouth Basin: A case study for braided fluvial delta reservoir of HZ-A area

珠江口盆地惠州凹陷HZ-A地区文昌组沉积一套重要的辫状河三角洲相的砂岩储层,现今埋深超过3 500m。基于岩石薄片、阴极发光、X衍射、扫描电镜及储层物性等资料,对HZ-A地区文昌组砂岩储层特征、成岩作用和孔隙度演化进行了详细研究,采用孔隙度参数演化的定量分析方法,建立了储层孔隙度定量演化模式。研究表明,文昌组储层岩石类型以岩屑砂岩为主,成分成熟度和结构成熟低;储集层目前正处于中成岩A2阶段,先后经历了压实、早期胶结、溶蚀作用和晚期胶结作用。强烈的机械压实及晚期胶结作用对物性破坏性最大,酸性溶蚀是改善储层物性的唯一成岩因素。储层初始孔隙度约35.1%,持续性的埋藏压实导致原生孔隙减少15.4%,早期胶结减少孔隙3.4%,之后酸性流体进入发生溶蚀增孔7.2%,晚期胶结作用损失孔隙度11.5%,其中以黏土胶结和碳酸盐胶结为主,结果形成低孔低渗储层。

A significant sandstone reservoir at the present burial depths greater than 3 500 m,located in the Wenchang Formation of HZ-A area in Huizhou depression,Pearl River Mouth Basin,was deposited in the braided fluvial delta environment. Based on comprehensive analysis of thin sections,cathodeluminescence microscope,X-ray diffractometor,scanning electronic microscope,physical property analysis and so on,the characteristic of reservoir,diagenesis and pore evolution in Wenchang Formation of HZ-A area were studied in detail. Authors have established a quantitative model for their pore evolution during the geodynamic history by using quantitative analysis method. The results show that the sandstones are mostly lithic sandstone characterized by low compositional and textural maturity. The reservoir has mainly experienced the compaction,early cementation,dissolution and late cementation in sequence and has been at the middle diagenetic A2 stage. Dissolution was the only diagenetic factor resulting in the improvement of reservoir physical property. Both mechanical compaction and late cementation mainly resulted in pore destruction.The original porosity of the reservoir was 35. 1% and had the loss of 15. 4% by mechanical compaction and the loss of3. 4% due to early cementation. Acid dissolution increased the porosity of 7. 2%. The pores were occluded by late clay minerals and carbonate cements,resulting in the reduction of 11. 5%. Consequently,the low-porosity and lowpermeability reservoir is formed.