西湖凹陷中央反转构造带花港组储层物性演化

Physical property evolution of Huagang formation in central inversion tectonic belt in Xihu depression

为了阐明西湖凹陷中央反转构造带花港组储层物性演化规律,以南部和中部地区花港组为研究对象,依据铸体薄片、扫描电镜、X-衍射、高压压汞、镜质体反射率等手段,以储层物性和储盖组合研究为基础,结合埋藏史恢复,分析储层孔隙演化规律及其主控因素,认为不同储盖组合在埋藏史控制下经历不同的成岩演化过程,形成现今的储层特征.研究结果表明:南部地区远离早期沉降中心,缓慢沉降期原生孔隙保存,快速沉降期和构造抬升期溶蚀发育,稳定沉降期发育少量晚期胶结,压实损失孔隙度(Ф_(COM))、胶结损失孔隙度(Ф_(CEM))和溶蚀增加孔隙度(Ф_(DIS))分别为20.86%,7.65%和7.78%,相对浅埋及半开放成岩环境形成相对弱压实、弱胶结和强溶蚀常规-低渗储层;中部地区靠近早期沉降中心,缓慢沉降期压实较强,快速沉降期有利的储盖组合形成的欠压实超压抑制压实,构造抬升期发育不同程度溶蚀,稳定沉降期发育晚期胶结,花港组上段Ф_(COM),Ф_(CEM)和Ф_(DIS)分别为21.82%,9.01%和5.64%,花港组下段Ф_(COM),Ф_(CEM)和Ф_(DIS)分别为23.84%,9.05%和4.50%,相对深埋及封闭成岩环境形成相对强压实、强胶结和弱溶蚀的花港组上段低渗-致密储层和花港组下段致密储层.

Based on the studies of reservoir physical property, reservoir-seal association and burial history, the physical property evolution and controlling factors of south and middle Huagang formation in central inversion tectonic belt of Xihu depression were investigated by using analysis of casting thin section, scanning electron microscopy, X-ray, mercury intrusion and vitrinite reflectance. The results show that different reservoir-seal associations undergo different diagenetic evolutions by the control of burial history. The southern region is far away from early subsidence center. Primary pores are preserved during the slow subsidence period, which benefits the dissolution in the rapid subsidence and tectonic uplift stage. Late cementation is not abundant in the period of steady subsidence. Values of OCOM （compaction porosity loss）, ФCEM （cementation porosity loss） and ФDIS （dissolution porosity increase） are 20.86%, 7.65% and 7. 78% respectively. Shallow buried and half-open diagenetic environment leads to conven-tional and low permeability reservoir with relatively weak compaction, weak cementation and intensified dissolution. By comparison, the central region is close to the early subsidence center. Primary pores are completely destroyed during slow subsidence. The compaction is inhibited by the undercompaction overpressure resulting from beneficial reservoir-seal association during rapid subsidence. The dissolution is apparently different during tectonic uplift. I.ate ce- mentation is comparatively rich in steady subsidence. For upper members of Huagang forma- tion, the values of ФCOM,ФCEM and ФDIS Of are 21. 82%, 9. 01% and 5. 64%; for lower mem- bers, the values are 23.84%, 9.05% and 4.50% respectively. Deep buried and closed diagenetic environment leads to low permeability and tight reservoir in upper member and tight reservoir in lower member, both with relatively intensified compaction, strong cementation and weak dissolution.