西湖凹陷砂岩储层异常高孔带分布及成因

Distribution and Genesis of the Secondary Pore of Paleogene Reservoir in Xihu Depression,Eastern Sea Basin

依据大量岩石薄片、铸体薄片、碳酸盐碳氧同位素测试、流体包裹体分析、黏土矿物X衍射、激光共聚焦显微镜技术以及物性资料,结合区域构造沉积背景,研究了东海盆地西湖凹陷砂岩储层异常高孔带分布规律及成因。结果表明:储层2 500~3 100 m和3 400~4 400 m的深度段发育大量的次生孔隙,两段次生孔隙带成因不同。第一段次生孔隙是在酸性环境下主要由有机酸等酸性流体溶蚀长石类矿物导致,还有少部分是由TSR反应生成的H2S溶蚀造成。第二段次生孔隙带主要由残余的早期酸性溶蚀孔和碱性环境下高岭石的伊利石化导致,少部分则由碱性流体溶蚀石英颗粒形成,同时异常高压保护深层次生孔隙,而且形成了一定量的裂缝。异常高孔带成因机理有助于优质储层的预测。

This paper mainly discusses the distribution and genesis of secondary pores in Paleogene sandstones in Xihu depression by using a number of the thin section,casting thin section,carbon and oxygen isotopes of carbonate cements,fluid inclusions,clay mineral X-ray diffraction,Laser Scanning Confocal Microscope and porosity and permeability data,combined with regional tectonic sedimentary background. The study results indicate that a large number of secondary pores occurred at two depth ranges of 2 500 ~ 3 100 m and 3 500 ~ 4 400 m; Organic acids dissolving feldspars minerals mainly leads to the first section of the secondary porosity zone,H2 S produced by sulphate thermal oxidation reduction reaction leads to part of the secondary porosity; quartz dissolution and abnormal high pressure leads to the second section of the secondary porosity zone in the alkaline fluid environment. The study concluded that the genesis of secondary pore zone contributes to predict reservoir stratum of high quality.