Specification of deep-water gravity flow sedimentation model and sandbody facies in the eastern South China Sea

Deep-water gravity flow deposits in the eastern South China Sea host abundant oil and gas resources. Understanding the sedimentation model and sandbody facies can guide the efficient oil and gas development. Taking A gas field in the northeast of Baiyun Depression as an example, based on drilling, logging, and high-resolution seismic data, the sedimentary types and evolution models of gravity flow were specified, the sandbody facies and their superposition patterns were analyzed. Results show there are four types of gravity flow sedimentary microfacies in A gas field: sliding-slumping, unconfined channels, overbank, and channelized lobes. The 7^th Member of the early Miocene Zhujiang Formation (ZJ7) is dominated by channelized lobe deposits, and the 6^th Member (ZJ6) is dominated by sliding-slumping deposits and multi-phase water channel-overbank deposits. The thickness of the single channel is 16-31 m, the width is 280-330 m, while the thickness of the single lobe is 16-22 m, the width is 400-650 m. The sandbody superposition patterns could be classified as discrete, superimposed and cut-superimposed types, and the superposition direction is mainly in horizontal, by which superimposed channels and lobes constitute the major reservoirs. A three-dimensional fine geological model depicting sedimentary facies and channel-lobe nesting was established, providing a support for the fine development of oil and gas resources in the study area.