Sedimentary facies and model of gentle slope shallow-water braided river delta in the Jurassic Sangonghe Formation, Yanqi Basin, China

Abstract

The Jurassic Sangonghe Formation of Yanqi basin develops a set of shallow braided river delta deposits, and it is of great significance for the exploration and development of Baolang oilfield to study its sedimentary characteristics. Based on the core data and wire-line log data in the study area with a highly dense well pattern, this work aims to provide the sedimentary features and sedimentary petrofacies distribution of this deposit, and present a sedimentary model for this study area. By analyzing characteristics of lithology–electricity responses, the wire-line log responses of different sedimentary petrofacies in the study area are summarized and the electrofacies recognition template is established. Meanwhile, the planar and profile sedimentary petrofacies distribution is further examined in detail. The results demonstrate that the study area develops coarse clastic sediments, and the sediments are dominated by conglomerate, sandstone, and mudstone, with a characteristic of “rich in sandstone and poor in mudstone”. Sedimentary petrofacies are primarily the subaqueous distributary channel facies, with vertically stacked and laterally extensive sandstone bodies. The sedimentary model of shallow-water braided river delta in the study area is characterized by gentle slope, strong current, lacustrine level rising and falling frequently and the thick and wide sandstone bodies.