致密砂岩盖层特征及分类评价标准——以满加尔-英吉苏凹陷为例

满加尔-英吉苏凹陷位于塔里木盆地东部,勘探目的层为志留系柯坪塔格组和塔塔埃尔塔格组,研究区发育致密砂岩盖层。文中采用最小孔喉半径法、束缚水饱和度法和经验统计法综合确定致密砂岩盖层物性上限,优选排驱压力、孔隙度和渗透率、平均孔喉半径以及方解石体积分数,建立了研究区志留系致密砂岩盖层分类的评价标准。致密砂岩盖层的形成机理为高泥质含量的岩屑砂岩经过强烈的压实作用和碳酸盐岩胶结作用、自生黏土矿物胶结作用使岩石物性变差,孔隙中网状黏土发育并产生水锁效应,导致渗透率大幅下降。研究表明,满东地区志留系塔塔埃尔塔格组底部致密砂岩平面分布连续,柯坪塔格组砂岩埋深较浅,储层物性较好,同时发育构造圈闭,可作为有利勘探区。

Characteristics and classification evaluation criteria of tight sandstone caprock:taking Manjiaer-Yingjisu Sag as an example

The Manjiaer-Yingjisu sag is located in the eastern Tarim Basin,the exploration target layers are the Silurian Kalpintag and Tataertage formation,and the tight sandstone caprock is developed.The upper limit of the physical property of the caprock of tight sandstone is determined by the combination of minimum pore throat radius method,bound water saturation method and empirical statistics.On this basis,the evaluation criteria of the Silurian tight sandstone caprock in the Manjiaer-Yingjisu sag are established with the parameters of displacement pressure,average pore throat radius,porosity permeability and calcite content.The formation mechanism is that the lithic sandstone with high shale content has a strong compaction and carbonate cementation,and the cementation of the authigenic clay minerals,which make the physical property worse.The reticular clay in the pores develops and produces water locks,which greatly reduces the permeability.The results show that the plane distribution of tight sandstone at the bottom of the Silurian Tataertage formation is continuous,and the Kalpintag formation sandstone is shallow,with better reservoir properties.At the same time,structural traps are developed,so the area can be used as favorable exploration area.