摘要
塔里木盆地西北部志留系具有良好的油气勘探前景，但是沉积体系和沉积规律认识不清，制约了对该地区志留系沉积体系的整体认识。文中利用岩心、露头、薄片鉴定以及测井、地震、单井等资料，明确了塔里木盆地西北部志留系沉积相类型、沉积体系演化及储盖组合发育特征。研究表明：1）塔里木盆地西北部志留系发育潮控型海湾复合沉积体系，柯坪塔格组发育潮控三角洲沉积，分布在柯坪断隆和阿瓦提凹陷；2）塔里木盆地西北部志留系发育在向西开口的海湾古地理背景之上，柯下段沉积期发育大型潮控三角洲沉积，柯中段沉积期发育广泛的内浅海泥岩沉积，柯上段沉积期发育大面积的潮下砂体，整个志留纪经历了由开阔到闭塞、由较深水到浅水的演化过程；3）受沉积演化的影响，沙井子构造带志留系发育由柯下段砂岩储层与柯中段泥岩盖层、柯上段砂岩储层与塔下段泥岩盖层、塔上段砂岩储层与依木干他乌组泥岩盖层构成的3套储盖组合。研究成果对深化塔里木盆地西北部志留系沉积体系认识、确定下步勘探方向提供了有效指导。
Abstract
The Silurian in northwest Tarim Basin has good prospects for oil and gas exploration, but the unclear understanding of depositional system and depositional law restricts the overall understanding of Silurian sedimentary system in this area. Based on core, outcrop, thin section identification, logging, seismic and single well data, the evolution of sedimentary facies and reservoir-cap assemblage of Silurian in northwest Tarim Basin are clarified. The results show that: (1) the Tarim Basin Silurian developed tide-controlled bay composite depositional system, and the Kepingtage Formation developed tide-controlled delta facies, which distributed in the Keping fault uplift and Awati depression;(2) the Silurian in northwest Tarim Basin developed on the background of the bay palaeogeography which opens westward. Large tidal-controlled braided river delta deposits were developed during the sedimentation period of the lower Ke member, inner shallow-sea mudstone deposits were developed extensively in middle Ke member, and large area of subtidal sand bodies were developed in upper Ke member. The whole Silurian underwent the evolution process from opening to blocking and from deeper water to shallow water; (3) influenced by sedimentary evolution, three sets of reservoir-seal assemblages were developed in Silurian of Shajingzi structural belt, namely the sandstone reservoir of lower Ke member and the mudstone cap of middle Ke member, the sandstone reservoir of upper Ke member and mudstone cap of lower Ta member, and the sandstone reservoir of upper Ta member and mudstone cap of Yimugantawu Formation. The results provide an effective guide for deepening the understanding of Silurian depositional system and determining further exploration direction in northwest Tarim Basin.
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