Depositional filling and reservoir distribution patterns of the central canyon in Qiongdongnan Basin

The central canyon is a deep-water channel-levee system developed in parallel to the slope across Qiongdongnan Basin.This study investigated depositional filling characteristics of central canyon in terms of the lithological compositions,the types of sand bodies,the patterns of reservoir distribution,and the controlling factors using2D/3D seismic data combined with core,drilling and well-logging data.The results show that during the period of 10.5-4.2 Ma,the canyon was filled with five-stage secondary channels and deposited with light-gray gravelly fine sandstone,massive and graded fine sandstone,siltstone,dark-black silty mudstone,and mudstone.Four types of depositional filling were developed with hemiplegic deposits and gravity flow of turbidity currents,debris,and slumps.Based on well-seismic calibration and root-mean-square seismic attribution analysis,four types of sand body were identified in the canyon,including canyon-axis sand bodies,natural levee sand bodies,lateral accretion sand bodies,and erosion residual sand bodies.These sand bodies show distinct variations in the vertical distribution.The canyon is mainly filled with sandstone in the bottom to middle part and siltstone in the upper part,with similar characteristics of positive cycles in the secondary fillings.Additionally,the sand bodies show segmented distribution horizontally.Stage 1-3 fillings of sandstone are distributed mainly in the middle reaches of the canyon,while stage 4 and 5 fillings of sandstones are mainly in the middle-upstream.Major factors controlling the distribution of sand bodies in the canyon include lithological composition of the provenance,distant and multiple transports,scale and flow pattern of initial gravity flows,destruction and reconstruction of secondary channels,development mode of the canyon,and tectonic framework of the basin.