鄂尔多斯盆地延长组长_8段相对高孔渗砂岩储集层的控制因素分析

Control factors for forming higher porosity and permeability sandstone reservoirs in Chang 8 member of Yanchang Formation, Ordos Basin

鄂尔多斯盆地三叠系延长组长8 段砂岩发育于盆地东北三角洲沉积体系和盆地西南辫状三角洲沉积体系,以岩屑长石砂岩和长石岩屑砂岩为主,为低孔、低渗储集层,但其中存在达到建产规模要求的相对高孔渗砂岩。通过大量地质分析、室内实验研究,认为有利于相对高孔渗砂岩储集层原生孔隙保存的主要影响因素为:有利的沉积微相(席状砂、分流河道和河口坝),异常压力差,与成岩作用有关的烃类早期充注占位,绿泥石包膜的发育和分散的石英胶结支撑作用;在此基础上有机酸溶蚀作用形成的各类次生孔隙进一步改善了砂岩储集层的物性。在具备上述基本地质条件且几种影响因素同时作用的地区,有望发现相对高孔渗砂岩储集层及商业性油气藏。

The Chang 8 member sandstone reservoir, Triassic Yanchang Formation , Ordos Basin, developed in NE deltaic sedimentary system and SE braided stream delta sedimentary system, which are mainly debris-feldspar and feldspar-debris sandstone with low porosity and penetrability. The geological data suggest that the key factors for the primary pore conservation are sedimentary facies (sand sheets, distributary channel and mouth bar), abnormal pressure difference, early hydrocarbon filling, chlorite lining and cementation of dispersive quartz. Organic acidization developed the secondary pores, which in turn improved the physical property. These areas are potential high porosity and permeability reservoirs.