塔里木盆地南华纪—中寒武世构造沉积演化及其盐下勘探选区意义

Study on tectonic and sedimentary evolution during the Nanhua-Middle Cambrian and its significance for subsalt exploration,Tarim Basin

中深1井、柯探1井(京能)、轮探1井相继发现,塔里木盆地寒武系盐下白云岩展现出巨大的勘探潜力。沉积演化认识不清楚、沉积相图不准确,导致源储分布认识程度低是近年来一些探井失利的主要原因。基于新增的高精度地震资料探讨南华纪—中寒武世的构造—沉积演化并开展新一轮沉积相编图,旨在厘定寒武系盐下重要层系源储盖层分布,指导寒武系盐下白云岩勘探区带优选。研究发现,南华纪—寒武纪经历3期大型构造运动,即塔里木运动、库鲁克塔格运动与柯坪运动,形成南华系底、震旦系底与寒武系底3个大型不整合面,控制南华系裂陷—坳陷、震旦系坳陷—碳酸盐台地与寒武系缓坡—碳酸盐台地3层沉积结构;隆起演化经历南华纪“三坳两隆”、震旦纪“连片隆起”到寒武纪“马蹄形隆起”的演化过程。基于地质结构研究、地震资料精细解释,编制了重点层系的沉积相图。在新的沉积相认识指导下,提出3个继承性坳陷控制烃源岩广覆式发育,两个继承性隆起控制两套白云岩储层大面积发育,中寒武统蒸发盐岩区域盖层广泛分布的认识;指出轮南周缘与塔中—古城地区是盐下勘探优选区带,阿瓦提周缘与和田河气田周缘是潜在勘探领域。

The successive discoveries in Wells Zhongshen 1,Ketan 1(by Jingneng)and Luntan 1 demonstrate the great exploration potential of Cambrian subsalt dolomite reservoir.However,the low level of understandings on the distribution of source rocks and reservoirs lead to the failure of some exploratory wells due to the unclear understandings of sedimentary evolution and sedimentary facies.In this study,tectonic and sedimentary evolutions from the Nanhua to Cambrian are discussed and new sedimentary facies maps of key formations compiled based on geological structures and new high-precision seismic data,so as to determine the distribution of source rock,reservoir and caprock of Cambrian subsalt play,and guide the selection of exploration target.Tarim Basin has experienced three stages of large-scale tectonic movements,namely the Tarim movement,the Kuruktag movement and the Keping movement,resulting three major unconformities at base Nanhua,Sinian and Cambrian,which control the three deposition structures of Nanhua rift-depression,Sinian depression-carbonate platform and Cambrian rampcarbonate platform.The evolution of uplifting has experienced the process of“two uplifts and three depressions”in the Nanhua,“continuous uplift”in the Sinian and“horseshoe-shaped uplift”in the Cambrian.Guided by the sedimentary facies maps,it is proposed that three inherited depressions control the extensive deposition of source rocks,two inherited uplifts control the wide distribution of two sets of dolomite reservoirs,and caprocks are widespread in the evaporating salt rock development area of the Middle Cambrian.The peripheral area of Lunnan Uplift and Tazhong-Gucheng area are the favorable exploration plays for subsalt exploration,and the peripheral areas of Awati Slope and Hetianhe Gasfield are potential exploration targets.