塔里木盆地顺南地区奥陶系鹰山组白云岩形成机制及其发育模式

Formation mechanisms and development models of dolomite reservoirs in Ordovician Yingshan Formation in Shunnan area,Tarim Basin

为深化对塔里木盆地顺南地区白云岩储层的认识,明确奥陶系鹰山组白云岩的成因和发育模式,指导油气勘探,在岩心观察和薄片鉴定的基础上,运用扫描电镜观察、阴极发光分析、碳氧同位素测试和稀土元素分析等手段,研究了顺南地区奥陶系鹰山组白云岩储层的岩相学特征和地球化学特征,分析了白云岩的形成机制,构建了不同成因类型的白云岩发育模式。岩相学分析表明,鹰山组主要发育粉—细晶白云岩(石)、细—中晶白云岩(石)和缝洞充填中—粗晶白云石等3种白云岩(石);地球化学特征揭示,粉—细晶白云石形成于盐度较高的水体中,是近地表环境蒸发泵白云石化的产物;细—中晶白云石形成于埋藏环境;中—粗晶白云石形成于相对封闭的成岩环境,是构造—热液白云石化的产物。中—深埋藏白云石化可形成孔隙较发育的规模化细—中晶白云岩,是最有利于储层发育的白云石化作用。

The dolomite reservoirs of the Ordovician Yingshan Formation in Shunnan area of the Tarim Basin have a great oil and gas potential.However,the genesis of different types of dolomite reservoirs is still subject to debate.In order to further deepen the understanding of the dolomite reservoirs in Shunnan area and clarify the genesis and development models of the dolomites in the Ordovician Yingshan Formation,the petrography and geochemistry of the dolomites were studied in detail,and some dolomitization models were established based on observation of core samples and thin section identification,using SEM,cathodoluminescence,carbon and oxygen isotope data and rare earth element pattern analysis.The petrographic analysis shows that the Yingshan Formation mainly develops three types of dolomite:powder-fine crystalline dolomite,fine-medium crystalline dolomite and fractured vug filling medium-coarse crystalline dolomite.Geochemical characteristics reveal that powder-fine crystalline dolomite is formed in water with higher salinity,which is the product of near⁃surface environment evaporation pump dolomitization.Fine-medium crystalline dolomite is formed in a buried environment.Mediumcoarse crystalline dolomite is formed in relatively closed diagenetic environment,which is the product of tectonichydrothermal dolomitization.Medium-deep buried dolomitization can form large⁃scale fine-medium crystal dolomite with well⁃developed pores,which is the most favorable dolomitization for reservoir development.