Simulation of the sedimentary characteristics of braided deltas in a Paleogene salty lake, Qaidam Basin, China

Abstract

Abstract In recent years, oil reservoirs have been discovered in the large-scale delta sedimentary system of a salty lake in the Lower Ganchaigou Formation (E31) and the Lower Youshashan Formation (N21) in the western part of the Qaidam Basin. This discovery represented the start of an oil and gas exploration breakthrough in the Qaidam Basin. In this study, a braided delta deposition model of the salty lake was developed, and the regular patterns of sand accumulation from three source areas of Alar, Niubiziliang, and Tiemulike were investigated. These areas were then selected as sedimentary prototypes to conduct physical simulation experiments to examine large flume deposition, dynamic braided delta deposition processes, and models of sand accumulation. The results showed that the braided delta had sedimentary characteristics of a small delta front, with a large delta plain, underwater distribution channels, and a mouth bar in a saltwater environment. The lake salinity controlled the grain size, thickness, regularity of the spatial distribution, and particle transport distance, as well as the scale of development for the underwater distribution channels and the mouth bar. Due to the dynamic complexity of the lake inputs caused by the vertical stratification of salinity, the braided branch channels of the braided delta plain and the mouth bar of the braided delta front may hold good reservoirs.