苏里格气田苏77区块特低渗储层成岩相识别及分布规律研究

苏里格气田苏77区块中二叠统石盒子组盒8下亚段沉积时期辫状河道发育,储层岩性以岩屑石英砂岩、岩屑砂岩为主。储层经历了压实、压溶、自生矿物胶结以及后期溶蚀作用,大部分已进入中成岩B期,达到低孔—特低渗储层级别。根据主要的成岩矿物、填隙物、成岩作用及孔隙组合,将盒8下亚段储层按照储集性能的优劣划分为石英加大溶孔相(Ⅰ)、黏土矿物充填晶间孔相(Ⅱ)、碳酸盐矿物胶结相(Ⅲ)和压实压溶致密相(Ⅳ)4类成岩相带。其中Ⅰ类成岩相为有利储集相,Ⅱ类成岩相储集性能次之,Ⅲ、Ⅳ类成岩相属于较差储集岩相。根据不同成岩相的测井响应特征可以识别出成岩相的同心、侧变和互层三类组合模式。

Diagenetic facies identification and distribution study of ultra-low permeability reservoir in Su77 block of Sulige Gas Field

Braided channels developed well in the lower part of the 8th member of middle Permian Shihezi Formation in Su77 block of Sulige Gas Field. Lithic quartz sandstone and lithic sandstone are the main lithology of reservoir. After compaction, pressure solution, authigenic mineral cementation and later dissolution, most of re-servoirs that are low porosity and ultra-low permeability ones have entered middle diagenetic stage B. According to the main diagenetic minerals, fillings, diagenesis and pore combination, reservoirs of the lower part of the 8th member of middle Permian Shihezi Formation are divided into 4 diagenetic facies as followed: Ⅰ. quartz overgrowth and dissolved pore facies; Ⅱ. clay minerals filling and intergranular pore facies; Ⅲ. carbonate minerals cementation facies; Ⅳ. compaction and pressure dissolution dense facies. Facies Ⅰ are the best reservoirs and facies Ⅱ are second-best ones. Facies Ⅲ and Ⅳ are poor reservoirs. According to logging facies, diagenetic facies are combined as concentric pattern, lateral variation pattern and cross-layer pattern.