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The Quaternary continental slope of the Baiyun Sag in northern South China Sea is characterized by a complex topography and abundant gravity flow sedimentation. High-resolution 3-D seismic data in this area allow for a detailed study of the seismic geomorphology and deep-water gravity flow depositional process. The Quaternary continental slope in the northern South China Sea is an above-graded slope. An intraslope basin lies within the above-grade continental slope. Slump, erosion, and deposition processes tend to develop a gentle topography and consequently a graded slope. The upper continental slope, which is above the slope equilibrium profile, is dominated by erosion and slumping. Slides, slumps and erosional channels are developed within this continental slope. The intraslope basin is located below the slope equilibrium profile and is potential accommodation space where sediments transported by gravity flows could be deposited, forming lobe aprons. Under the influence of gravity flow supply, gravity flow duration, continental slope topography, equilibrium profile, and accommodation, a slump-erosional channel-lobe depositional system is developed in the Quaternary continental slope in the Baiyun Sag. The deep-water gravity flow depositional process and the distribution of gravity flow sediments are greatly influenced by the continental slope topography, while the continental slope topography at the same time is reshaped by deep-water gravity flow depositional process and its products. The study of the interplay between the continental slope and gravity flow is helpful in predicting the distribution of the deep-water gravity flow sediments and the variation of sediment quality. [ABSTRACT FROM AUTHOR]

Abstract: The Shenhu area on the northern continental slope of the South China Sea is one of the most promising fields for gas hydrate exploitation. Drilling and sampling has indicated high saturations of methane hydrate in clay silty sediments at drilling site SH2. The hydrate-bearing layer is overlain and underlain by permeable zones of mobile water, and the system does not appear to be bounded by low-permeability strata. In this study a huff-and-puff method is used to producing gas from the hydrate accumulation. We simulate numerically the hydrate dissociation and gas production by alternately injecting hot water and producing fluids at a vertical well. The simulations show the gas production rate in huff-and-puff operations is very small (50–140m3/d), and unacceptable for commercial production. The calculation also indicated secondary hydrates forms at the very early period of injecting operations, and then gas is released due to the thermal stimulation of hot water, but the amount of released gas in the injection periods of hot water is much smaller than that converts into secondary hydrates. In the production operations, much of gas is released from the hydrates due to a small depressurization at the well, but the released gas can not produce effectively due to the small pressure gradient, and thus remains in the reservoir and converts into secondary hydrates in the next operation of injecting hot water. The study provides an insight into the production potential of the Shenhu hydrate accumulations through the huff-and-puff method, and a basis for the analysis of the economic feasibility of gas production from that area. [Copyright &y& Elsevier]