从岩石结构和地化特征看巴楚隆起上寒武统白云岩的成因及演化

Lithological and Geochemical Characteristics Indicating Genetic Mechanism and Evolution of Upper Cambrian Dolostone in Bachu Uplift, Tarim Basin

塔里木盆地巴楚隆起上寒武统发育一套极具勘探价值的厚层白云岩。基于该白云岩的钻井取心与薄片鉴定,将其分类为结晶白云岩、泥微晶白云岩、具残余(颗粒)结构白云岩及过渡型白云岩。运用多种地化分析和测试手段,认为上寒武统白云岩主要经历了(准)同生(蒸发泵、渗透回流)白云石化—埋藏白云石化—后期局部热液改造三个阶段,导致研究区白云石化的流体主要为高盐度卤水、埋藏残余海水以及深部热液流体,整个白云石化过程中岩石结构也发生相应演化。泥微晶白云岩主要形成于(准)同生期萨布哈环境,过渡型白云岩及残余结构白云岩由白云石化不彻底或选择性白云石化作用形成,结晶白云岩由埋藏白云石化作用形成。存在自生矿物、高Ba/Sr值、稀土Eu富集以及包裹体测温均显示深部热液对白云岩具有局部改造作用,该类白云石通常具有波状消光的特征。经过热液溶蚀改造的白云岩储集空间变好,这对白云岩储层的勘探具有指示意义。

A set of prospective thick Upper Cambrian dolostone develops in Bachu Uplift, Tarim Basin. Based on analysis of drilled cores and thin sections, the dolostone may be divided into crystalline dolostone, micritic dolostone, residual（granular） dolostone and transitional dolostone. Lithological and geochemical analyses have revealed that the dolostone experienced three stages of diagenesis： peneconcontemporaneous-contemporaneous（evaprite pumping and penetrative reflux） dolomitization, burial dolomitization and locally hydrothermal dolomitization, during which rock structures changed correspondingly in the dolostones. The fluids associated with dolomitization chiefly are high-salinity reflux brine, burial residual seawater and hydrothermal fluid from crust deep. All of indexes, including Existence of ausiginetic minerals, high Ba/Sr ratios, REE Eu enrichment and homogenization temperature of fluid inclusions, indicate that the dolostone was affected with locally dissolution and reformation by hych-othermal fluid from deep. Reservoir space will be advanced in the resolved dolostone, which means a prospective significance to the dolostone reservoirs in this area.