塔里木盆地奥陶系孔隙型白云岩储层成因

GENESIS OF ORDOVICIAN MATRIX-POROSITY DOLOMITE RESERVOIR IN THE TARIM BASIN

塔里木盆地下奥陶统存在大量基质孔隙发育的深埋白云岩,是一类优质储层。岩心、薄片观察和阴极发光分析表明该类白云岩的发育具有明显的相控特征,以滩相颗粒灰岩为原岩。岩石学特征和微量元素、有序度及包裹体均一温度特征研究表明,该类白云岩形成于埋藏环境中,属埋藏白云石化作用的产物。由微量元素、稀土元素及锶同位素特征判断白云石化流体为受改造的海水,很可能与深部封存的蒸发台地相海水有关。推断塔里木盆地二叠纪大规模火山活动是台地相区白云石化作用的主要驱动机制,寒武系蒸发台地中富含镁离子的海水在广泛的热作用驱动下交代其上覆灰岩而形成白云岩。

There is a large quantity of deeply buried dolomite with well-developed matrix porosity in the Lower Ordovician of the Tarim Basin which can be quality reservoir. The development of this kind of dolomite is facies-controlled and the initial rock is grainstone of grain bank faeies, according to the analyses of cores, thin sections and eathodelumineseence. The dolomite formed under burial condition which is the product of burial dolomitization, based on the study of petrology, trace element, degree of order and homogenization temperature of the dolomite. It is predicted from the trace element, rare earth element and Sr isotope that the dolomitizing fluid is modified seawater which may be related to Mg2＋ bearing seawater in Cambrian evaporative platform. Permian volcanic activity is supposed to be the driving force of dolomitization over the entire platform and the burial dolomite in the Lower Ordovician formed by means of the replacement of overlying limestone by underlying Mg2＋-bearing seawater in Cambrian evaporative platform through thermal convection.