西湖凹陷花港组低孔低渗砂岩储层中绿泥石环边的成因及其意义

西湖凹陷中北部渐新统花港组深层砂岩储层物性整体为低孔低渗,物性较好、测试产能高的优质储层以发育绿泥石环边为特征。根据铸体薄片、扫描电镜、X射线衍射、能谱等分析绿泥石环边成因及形成时间并探讨其意义。结果表明:环边里层是沉积时包裹碎屑颗粒的黏土微粒在成岩过程中铁离子的影响下绿泥石化而成;外层是由于铁离子的持续供给,围绕里层环边生长而成。绿泥石环边形成于溶蚀作用发生以前,并且早于石英加大边形成,既能缓解压实作用,又能抑制其他胶结物的形成,利于在深埋条件下保存原生孔隙;同时还能在保存原生孔隙的基础上促进后期溶蚀作用;另外,绿泥石环边利于形成较好的孔喉结构,并能提高成藏时油气充注程度。绿泥石环边是花港组深层形成优质储层的重要因素,对寻找优质储层和指导油气勘探具有重要意义。

Genesis of chlorite rims and its significance to low porosity and low permeability sandstone reservoir of Huagang Formation in north central Xihu sag,East Sea of China

Sandstone reservoir of Oligocene Huagang Formation in north central Xihu sag is characterized by low porosity and low permeability with good physical property and its high-quality reservoir with high tested productivities attributes to the development of chlorite rims in the sandstones.Based on the study of casting thin sections,SEM,X-ray diffraction and quartz fluid inclusion,the genesis of chlorite rims is determined and its significance to the reservoir is discussed.It reveals that the innermost layer of chlorite rims is formed by clay particles unable to precipitate surrounding clastic grains,influenced by ferric ions in later digenesis,and the outer layer of the rims surrounded the inner layer and resulted from continuous supply of ferric ion from volcanic debris and volcanic tuff.Chlorite rims are formed before dissolution and quartz overgrowth,so the rims can not only relieve subsequent compaction and restrain cementation,but also protect primary pores and promote later dissolution.In addition,chlorite rims plays a role in the formation of favorable pore throat structure and in the improvement of oil and gas saturation.Therefore,the occurrence of chlorite rims is an important factor for the development of high quality reservoirs.The study of chlorite rims in sandstones can promote the exploration of oil and gas.