Experimental Simulation Study of the Sedimentary Characteristics of Braided Deltas in a Paleogene Salty Lake, Qaidam Basin, China

摘要

In recent years, oil reservoirs in the large-scale delta sedimentary system of a salty lake have been discovered in the Lower Ganchaigou Formation(E_3~1) and the Lower Youshashan Formation (N_2~1) in the western part of Qaidam Basin (referred to as WQ), constituting an oil and gas exploration breakthrough in Qaidam Basin. To expand the scale of exploration, a braided delta deposition model of the salty lake was developed, and the regular patterns of sand gathering from three source areas, Alar, Niubiziliang, and Tiemulike, were clarified. Based on the experimental simulation technique of large flume deposition under a background of salty lake, these areas were then chosen as sedimentary prototypes to carry out a physical simulation experiments to examine large flume deposition, the dynamic process of braided delta deposition, and the model of sand gathering. The results show that a braided delta has the sedimentary characteristics of a small delta front with a large delta plain and development of underwater distribution channels and a mouth bar in a saltwater environment. Lake salinity controlled not only grain size, thickness, spatial distribution regularity, and particle transport distance, but also the scale of development of the underwater distribution channels and the mouth bar. Because of the dynamic complexity of lake inputs due to the vertical stratification of salinity, the authors believe that the braided branch channels of the braided delta plain and the mouth bar of the braided delta front may hold good reservoirs.