潜江凹陷东部地区新沟咀组下段为江汉盆地重要的产层之一,也是油田今后寻找岩性油气藏的目标区.本文通过岩心观察、镜下薄片鉴定分析、测井资料的综合分析,并结合岩石学、古气候、沉积构造等沉积相标志研究,以及构造活动弱、地形平缓等区域沉积背景,确定该区新沟咀组下段发育浅水三角洲沉积,并具有发育的水下分流河道、不甚发育的河口坝、广泛分布的席状砂和前三角洲泥与前缘沉积频繁交替等特征,以及各相带平缓相接,无明显的转折,不存在Gilbert型三角洲三层式结构的沉积模式.沉积演化过程中,受古气候、河流作用和湖平面波动等众多因素的影响强烈,特别是对水下分流河道的形态和发育程度的控制更明显,形成或强或弱席状化改造的前缘砂体,而良好的生储盖配置关系对该新沟咀组有利于岩性油气藏的形成.%The lower segment of the Xingouzui Formation in eastern Qianjiang depression is an important horizon for finding lithologic hydrocarbon reservoir in the future. Based on a synthetic analysis of core description as well as thin section and logging data in combination with sedimentary marks of lithology.paleoclimate, sedimentary structure,and the depositional background of weak tectonic movement and flattened palaeotopography.the authors hold that the lower segment of the Xingouzui Formation is of a shallow water delta depositional system. The shallow water delta has the following characteristics: ①there exist well-developed underwater distributary channel microfacies, underdeveloped mouth bar,extensive sand sheet,and frequently alternate pre-delta and front deposition; ②various fades belts are smoothly connected with each other without apparent slope gradient; ③depositional model has no three-layer structures like "Gilber delta". During the depositional evolution,the shallow water delta deposition was affected by such factors as palaeoclimate,density contrast of stream and salt lake, fluviatile action and lake surface fluctuation., and the shape and the development extent of the underwater distributary channel were especially apparently controlled by these factors, forming strong or weak reformed front sand. Favorable allocation for generating reservoirs and cap rocks in the lower segment of the Xingouzui Formation was favorable for forming lithologic hydrocarbon reservoirs.
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