Characteristics of deep water gravity flows sediments in sublacustrine fan of the Chang 6 interval of Yanchang Formation in Huachi area, Ordos Basin

Base on core observations, well logging and logging, and analyses of sedimentary facies such as petrologic characteristics and primary sedimentary structures, the thick-bedded massive sand bodies of the Chang 6 interval of Yanchang Formation in the Huachi area belong to gravity flow sediments in deep lake. Three types of subfacies are recognized, i.e., inner fan, middle fan and outer fan facies, with the middle fan mainly developed in huachi area. Four sedimentary types, i.e., fluidized sedimentary flows, sandy debris flows, proximal and distal turbidity currents are identified, while the mode of deep water gravity flow in sublacustrine is reconstructed. The deposition of sandy debris flow is the most widely distributed in local area. The sand bodies of sandy debris flow always have the best reservoir physical properties and are the most favorable reservoirs in the Chang 6 interval of Yanchang Formation in Huachi area.