鄂尔多斯盆地麻黄山西区块延8段成岩相特征及油气地质意义

Diagenesis facies and significance of petroleum geology in the 8th member of the Yanan formation,west of the Mahuangshan,Ordos basin

通过岩心观察、薄片鉴定,采用扫描电镜等技术,结合测井录井资料,分析鄂尔多斯盆地麻黄山西区块中生界延安组延8段储层砂体成岩相特征及油气地质意义.结果表明:延8段砂体储层为致密低渗透砂岩储层,优质储层主要发育在三角洲平原分流河道微相中,识别4种成岩相,即强烈压实致密相、胶结致密相、弱压实弱胶结相及强烈溶蚀相,其中弱压实弱胶结相和强烈溶蚀相中发育优质储层;研究区南部刚性颗粒含量高、黏土环边发育的层段主要呈弱压实弱胶结特征,能够保留较高的孔隙度;受埋藏期成岩酸性水及表生期大气淡水溶蚀强烈层段发育大量的次生孔隙,同时早成岩期压实作用较弱的砂体能够保存更多的剩余原生孔,为后期酸性水及大气淡水溶蚀提供良好的地层水输导通道.

Based on the data of core observation,cast thin section,SEM analyses data and cathodoluminescence,this paper deals with characteristic of diagenesis facies and significance for petroleum geology of the 8th member in Yanan Formation of Mesozoic Erathem in Western Mahuangshan Area of Ordos.The results demonstrated that clastic reservoirs of the Yan-8 Formation were developed in the distributary channel of delta plain.Four types of diagenesis facies were recognized:intense compaction tight diagenetic face,cementation tight diagenetic face,weak compaction and cementation diagenetic face,and intense dissolution diagenetic face,and fine reservoirs were created in weak compaction and cementation diagenetic face and intense dissolution diagenetic face.The results also showed that the stratigraphic position with high content of stiff grains and clay rim in north area have characteristic of weak compaction and cementation,their porosity was high.The stratigraphic position corroded by diagenesis acidulous water and air fresh water had more secondary pore,and the sand body which was compacted poorly in the early period of diagenesis could save more primary origin pore,the pore could offer passageway for later stage acidulous water and air fresh water.