宜川—旬邑地区长6～长8油层组成岩作用特征

DIAGENESIS CHARACTERISTICS OF THE CHANG8-CHANG 6 MEMBER OF YANCHANG FORMATION IN YICHUAN—XUNYI AREA,ORDOS BASIN

通过岩芯观察,铸体薄片、扫描电镜、阴极发光、碳氧同位素、粘土矿物X衍射及流体包裹体等测试分析指出,宜川—旬邑地区延长组长6～长8油层组主要为灰色、灰褐色、灰白色长石砂岩和岩屑长石砂岩,储集层砂岩经历了机械压实、胶结、溶蚀和交代等一系列成岩作用。X衍射分析显示该区常见的粘土矿物主要是伊利石、伊利石/蒙皂石混层、绿泥石等,镜质体反射率测试Ro为1.03～1.31,结合包裹体测温及成岩现象等综合研究表明:该区油层组砂岩主要进入了晚成岩A2亚期,部分已经达到了晚成岩B早期,且厘定了该区的成岩作用序列,指出压实作用和胶结作用是导致该区储层物性变差的主要因素,长6长8油层组因压实作用与胶结作用损失的孔隙分别达23.82%,25.65%,3.99%和3.31%,溶蚀作用新增孔隙度分别仅为0.84%和0.83%,储集层砂岩绿泥石环边的生长与早期石英弱次生加大对原生孔隙的保存起到了极大的积极作用,旺9井—旺16井区、旺6井区及庙38井区为该区有利成岩相展布区域,在平面上开展有利成岩相研究可以有效地指导该区优质储层的识别与预测,为该区油气勘探服务。

Through the core observation,thin section analysis,scanning electron microscopy,cathode luminescence, carbon and oxygen isotopes,clay minerals X-ray diffraction and temperature of fluid inclusions,etc,the chang6-chang8 member of Yangchang formation is studied and the results show that it consists mainly of gray feldspathic sandstone and lithic feldspathic sandstone,which experienced a series of diagenesis like mechanical compaction, cementation,dissolution. X diffraction analysis shows that clay minerals are mainly illite,illite/smectite mixed layer,chlorite,and vitrinite reflectance Ro test between 1.031.31,combined with inclusion temperature and diagenetic phenomena comprehensive study indicates that the main sandstone reservoir area come into the late diagenetic A2 sub-period,some of which have reached the early period of late diagenesis B. Besides,the diagenetic sequence is determined.Based on the diagenesis analysis,the research shows that the porosity of Chang8-Chang6 member respectively loss 23.82% and 25.65% because of compaction,and 3.99% and 3.31% because of cementation, and that porosity are added by 0.84%and 0.83%respectively due to dissolution.The compaction and cementation are major factors in deterioration of physical properties,but the reservoir sandstones,which have chlorite central side of the weak growth and early secondary quartz,play a significant role in the preservation of primary porosity. It is pointed out that the favorable diagenetic facies study can effectively guide the identification and prediction of reservoir,which is useful for the oil and gas exploration.