元坝-通南巴地区须家河组绿泥石膜胶结相砂岩发育控制因素与分布规律

Control Factors and Distribution of Chlorite-Cemented Facies in the Xujiahe Sandstone, Yuanba and Tongnanba Area

川东北元坝-通南巴地区须家河组砂岩普遍超致密,仅绿泥石环边胶结物含量大于1.5%的砂岩(即绿泥石膜胶结相砂岩)物性较好.综合运用岩石学和测井地质学的方法,基于薄片、扫描电镜及粒度分析等资料分析绿泥石膜胶结相砂岩的岩石组构特征和形成控制因素,运用薄片鉴定、测录井等资料,明确绿泥石膜胶结相砂岩的测井响应特征并明确其发育分布规律.结果表明,绿泥石膜的发育具有较强的相控性和岩石组构的选择性,即发育于水下分流河道原始结构较好的砂岩.该类砂岩结构成熟度和成分成熟度较高,通常具有较低的杂基和塑性岩屑含量,且含有适量的火山岩岩屑(2%~6%).较低的杂基和塑性岩屑含量为绿泥石沉淀提供所需的孔隙空间,火山岩岩屑为绿泥石膜沉淀提供物质来源.

The sandstones reservoirs of the Xujiahe Formation in the Yuanba and Tongnanba area,Sichuan Basin have poor qualities,and only those with chlorite rim,which has a content of more than 1.5%(i.e.chlorite-cemented facies)show a higher porosity.Based on lithology and well-logging geology,composition and control factors of formation of sandstones with chloritecemented facies are analysed with thin section analysis,scanning electron microscopic analysis and grain size analysis,well log responses and distribution of sandstones with chlorite-cemented facies are identified with thin section and well logging data.The formation of chlorite rim has strong environmental specificity and sandstone composition selectivity,that is,it develops in the sandstones with good original porosity in the subaqueous distributary channel.Sandstone with chlorite-cemented facies has higher texture maturity and composition maturity,with lower contents of matrix and plastic rock fragment,and it also has a certain amount of volcanic rock fragments(2%~6%).Lower contents of matrix and plastic rock fragment provided space for precipitation of chlorite,and volcanic rock fragments provided source of chlorite precipitation.