牵引流化重力流沉积过程与堆积机制:以渤海湾盆地歧口凹陷为例

Sedimentary process and accumulation mechanism of traction fluidization gravity flow:An example from Qikou Sag,Bohai Bay Basin

以具备牵引流特色的重力流沉积体为载体的高效储集体,是陆相湖盆沉积学研究与勘探突破的重要领域.渤海湾盆地歧口凹陷沙一段发育的大规模多期次陆相重力流具有其沉积特征的独特性(面积约940km2,纵向分布厚度约1.1km).依据水动力条件及沉积过程机制,存在层级递进继承型、渐进过渡型、兼并融合型3种牵引流与重力流动力学过程,细分为泥质碎屑流、砂质碎屑流、过渡型同生流、(高密度-低密度悬浮)似涌浪浊流、(高密度-低密度)准稳态浊流5种机制类型,并依据其发育背景识别出了滨海地区中央隆起带上以重力流水道为主导特征的水道型重力流沉积体系和受次洼地貌控制的面流型重力流.本研究细化了沉积动力学过程-堆积机制-沉积相-岩相一体化的关联性,确定了牵引流化重力流发育的关键控制因素.作为极具潜力的优质储层目标,陆相牵引流化重力流沉积体的研究成果在丰富理论体系的同时,对油气勘探新领域的拓展与突破具重要意义,具备生产实践价值,对于其他陆相湖盆油气勘探具有重要的借鉴作用.

The high efficiency reservoir in gravity flow deposits with traction flow features is one of the most important aspects in sedimentary research and exploration.The large-scale and multi-stage lacustrine gravity flow deposits developed in the first member of Shahejie Formation in Qikou Sag of Bohai Bay Basin exhibit their unique sedimentary features(The dimensions of gravity flow deposits are about 940 km2 in transverse area and 1.1 km in vertical scale).According to the hydrodynamic conditions and sedimentary process mechanism,the large-scale lacustrine gravity flow depositional system shows three types of rela-tionships between tractive currents and gravity currents,which are identified as①hierarchical progressive inheritance type,②progressive transition type,③merger fusion type.The sedimentary mechanism of gravity flow is divided into five types:muddy debris flow,sandy debris flow,transitional contemporane-ous flow,high/low-density turbidity flow and high/low-density quasi-steady turbidity flow.The channel-ized gravity flow depositional system with gravity flow channel is the dominant feature in the central uplift zone of coastal area in the west,as the sheet flow pattern is controlled by the sub-sag morphology in the east.This study aims to realize and refine the integration and relevance among sedimentary dy namic process,accumulation mechanism,sedimentary facies,and lithofacies,as well as determine the dominant control factors for the traction fluidized gravity flow.As a potential efficient reservoir target,the research results of traction fluidized gravity flow deposits can improve the theoretical system of lacustrine gravity flow,and at the same time,are significant for frontier breakthrough in petroleum exploration.It has prac-tical production value and important reference for other continental lake basin oil and gas exploration.