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    饶阳凹陷沙河街组辫状河三角洲沉积特征及储集性

    Sedimentary characteristics and reservoir properties of the Shahejie Formation braided river delta in Raoyang Sag

    • 摘要: 提要:饶阳凹陷沙河街组主要为砾岩、含砾砂岩、砂岩、粉砂岩和泥岩构成的一套碎屑岩组合,根据沉积特征将其确定为辫状河三角洲沉积。该沉积三层结构清楚,由下而上出现前辫状河三角洲亚相、辫状河三角洲前缘亚相及辫状河三角洲平原亚相,呈明显的进积层序,主要发育辫状河道、洪泛平原、水下分流河道、水下分流河道间、河口坝和席状砂等沉积微相。据其岩性、沉积构造、粒度及沉积序列等特征,建立了沉积模式。从岩性特征看,沙河街组辫状河三角洲沉积物具有分布较广、储集物性较好的特点,辫状河三角洲前缘水下分流河道砂体和河口坝砂体储集物性最好,是下一步勘探的有利目标。

       

      Abstract: Abstract:The Shahejie Formation in Raoyang Sag mainly comprises a set of terrigenous clastics such as conglomerate, conglomeratic sandstone, sandstone, siltstone and mudstone. A study of sedimentary characteristics led to the recognition of typical braided river delta deposition, whose characteristics are distinct and significantly different from other types of deltas resulting from river tractive current sedimentation which are generally controlled by torrential flood and seem to be seasonal sediments. The most notable feature of the braided river delta deposition in this area is the existence of a three-layer structure, which is composed from bottom to top of pre-braided river delta subfacies, braided river delta front subfacies and braided river delta plain subfacies, showing an obvious progradational sequence. There are several main microfacies, such as braided distributary channel, flood plain, subaqueous distributary channel, subaqueous inter-distributary channel, mouth bar and sheet bar. According to lithologic characteristics, sedimentary structure, grain size and sedimentary sequence of the braided river delta, a sedimentary model for the braided river delta was established. From lithologic characteristics of deposition, it is thought that the thickly-bedded conglomerate and conglomeratic sandstone developed in the braided river delta are widely distributed and constitute favorable oil and gas reservoirs. The sand bodies of the subaqueous distributary channel and mouth bar make up the most beneficial reservoirs and can form useful lithologic reservoirs. These places deserve much attention in future exploration.

       

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