鄂尔多斯盆地延长组长8储层定量化成岩作用及成岩相分析

Quantitative Diagenesis and Diagenetic Facies Analysis on Chang 8 Reservoir of Yanchang Formation in Ordos Basin

通过对鄂尔多斯盆地延长组长8油层组大量的薄片观察和实验分析,认为长8油层组主要发育机械压实、碳酸盐胶结、绿泥石膜胶结和溶蚀4种成岩作用类型。通过开展视压实率、视胶结率和视溶蚀率的计算,结合研究区沉积背景,进行了分区对比,定量评价了各成岩作用对各沉积区孔隙度的影响。东北沉积区受强压实作用和强胶结作用的控制,原始孔隙损失最大;西部沉积区受弱压实和中等胶结作用的控制,原始孔隙损失最小;西南沉积区受中等压实和中等胶结作用的控制,原始孔隙度损失较小;西北沉积区受强压实作用和强溶蚀作用的控制,原始孔隙度损失较大。并划分了四大成岩相类型:绿泥石膜—粒间孔成岩相、长石溶蚀成岩相、碳酸盐胶结成岩相和弱压实成岩相。西部沉积体系主要为弱压实成岩相,压实程度较低,颗粒多呈点接触,物性最好;西南沉积体系主要为绿泥石膜—粒间孔成岩相发育区,物性很好;西北沉积体系主要为长石溶蚀成岩相发育区,绿泥石膜相对不发育,物性较好;东北沉积体系主要为碳酸盐胶结成岩相,溶蚀作用相对较弱,绿泥石膜不发育,物性较差。

Through a large number of thin section observations and experimental analyses about Chang 8 interval of Yanchang Formation in Ordos Basin, four main diagenesis types were proposed：mechanical compaction, carbonate cementation, chlorite film cementation and dissolution in Chang 8 interval. Based on the calculation of optic compac- tion rate, apparent cement ratio and optic dissolution rate,combined with the depositional background of study area, we performed division comparison,quantitatively evaluated the diagenetic effects on porosity of different sedimenta- ry areas. The northeastern sedimentary area was controlled by strong compaction and strong cementation, which re- sulted in the maximum primary pore loss. The western sedimentary area was controlled by weak compaction and moderate cementation, which resulted in the minimum primary pore loss. The southwestern sedimentary area was affected by moderate compaction and moderate cementation, which resulted in relatively less primary pore loss. The northwestern sedimentary area was controlled by strong compaction and strong dissolution,which resulted in rela tively greater primary pore loss. Four types of diagenetic facies have been proposed： chlorite membrane and interg- ranular pore diagenetic facies, feldspar dissolution diagenetic facies, carbonate cementation diagenetic facies, and weak compaction diagenetic facies. The western sedimentary system belongs to weak compaction diagenetic facies, where compaction degree is lower, particles are in point contact, and physical property is best. The southwestern sedimentary system mainly developed chlorite membrane and intergranular pore diagenetic facies with good physical property. The northwestern sedimentary system mainly developed feldspar dissolution diagenetic facies,where chlo rite membrane is relatively not well developed and the physical property is relatively good. The northeastern sedi- mentary system mainly developed carbonate cement dissolution diagenetic facies, where chlorite membrane is rela- tively weak,intergranular pore is not developed,and physical property is poor.