江汉盆地潜江凹陷盐湖浅水三角洲沉积特征与发育模式

Sedimentary Characteristics and Development Model of Shallow-water Delta of Salt Lake in Qianjiang Depression

江汉盆地潜江凹陷发育浅水三角洲沉积体系,由于湖盆水体盐度较大,其形成演化和发育模式与淡水环境存在异同点。笔者基于三维地震、钻测井、岩心和地球化学资料明确了该地区浅水三角洲沉积特征与发育模式。潜江凹陷潜江组湖相泥岩颜色较浅,局部井见浅红色泥岩,且泥岩中常见干裂,Mn/Fe值和Sr/Ba值较高,为盐湖浅水沉积环境。碎屑物质借助盐湖水体强携砂能力长距离搬运,相对高密度的携砂水团下沉形成水下分流河道砂体或浊积砂体,相对低密度的携砂水团在湖盆盐水的顶托作用下呈悬浮状或漂浮状进一步向湖盆方向搬运,在远岸处形成滩坝砂或席状砂体。研究区主要为浅水三角洲前缘亚相,包括水下分流河道末端、河口坝、席状砂、远砂坝等多种微相类型,据此建立了潜江组沉积时期盐湖远岸浅水三角洲沉积模式,明确了砂体展布特征及其发育机理,为研究区滚动勘探和后期开发提供了理论依据。

The Qianjiang depression of Jianghan basin develops a sedimentary system in shallow-water delta.Its formation,evolution and development model have some similarities and also differences with the freshwater environment because of high salinity of the lake basin.Based on 3D seismic,well logging,core and geochemical data,this paper clarified the depositional characteristics and development model of shallow water deltas in this area.The lacustrine mudstone of Qianjiang Formation in Qianjiang depression is lighter in color;light red mudstone can be seen in some wells,and mud cracks are common in mudstone with high Mn/Fe ratio and Sr/Ba ratio,being shallow sedimentary environment of salt lake.Detrital materials are transported over long distances by means of the strong sand-carrying capacity of the salt lake water body.The relatively high-density sand-carrying water masses sink to form underwater distributary channel sand bodies or turbidite sand bodies.The relatively low-density sand-carrying water masses are suspended or floating under the support of the salt water in the lake basin and are further transported towards the lake basin,forming beach bar sand or sheet sand bodies on the far shore.The study area is mainly shallow-water delta front subfacies,including various types of microfacies such as the end of underwater distributary channel,mouth bars,sheet sandsand distal bars.Thus,a shallow delta sedimentary model on the far shore of the salt lake was established during the deposition of the Qianjiang Formation.This model clarifies the distribution characteristics and development mechanism of the sand bodies,and provides a theoretical basis for rolling exploration and later development in the study area.