Characteristics and identification of high quality deep-water gravity flow sandstone reservoirs in Baiyun sag, Pearl River Mouth Basin, South China Sea

The characteristics and identification methods of high quality deep-water gravity flow sandstone reservoirs in Baiyun sag of the Pearl River Mouth Basin are examined based on three-dimensional seismic and drilling data, and deep water sedimentary theory. The oil and gas discovered in the deep water of the Baiyun sag are dominantly from high quality gravity flow sandstones, including channel complexes, sheets, and channel-levee complexes. The analyses of the sediment supply, feeding channel, internal architecture of sedimentary bodies, depositional process and flow regime show that the development of three types of high quality reservoirs are controlled by sediment composition of the provenance (continental margin): Under the background of rich sand provenance, sandy debris flow is likely to form, giving rise to high quality reservoirs like channel complexes and sheets down dip the shelf-slope break. These reservoirs can be identified by seismic reflections such as incised valley, mound shape, and amplitude anomaly, and described by combining single sand body tracking with waveform recognition of sands and seismic attribute analysis. Under the background of sand-mud mixed provenance, gravity flow deposits are to occur below the shelf-slope break, where sedimentation differentiation is the key to the formation of high quality reservoirs. In the case that channel-levee complex is formed, high quality sandstone reservoirs, usually in the channel or the fan lobe below, can be identified and described by seismic features like U-shaped erosion on seismic profile, amplitude anomaly, bird-wing shaped seismic reflection, and waveform recognition.