莺歌海盆地乐东区上新统坡折带演化特征及有利区预测OA

During the deposition of the first member of the Yinggehai Formation(Ying-1 Member)in the Ledong Area of the Yinggehai Basin,the shelf margin prograded continuously seaward,resulting in dep-ositional systems controlled by slope breaks with diverse types and complex spatial configurations.Based on high-resolution 3D seismic and drilling data,we delineated the migration trajectories of the shelf-edge slope-break belts,analyzed the evolutionary characteristics of the slope-break belts and their sand-control depositional models in the Ledong Area,identified the distribution of favorable facies belts,and predicted favorable zones.The results show that the migration angle of the slope-break belts in the study area initially increases and then decreases,and the slope breaks can be classified into three types of shelf-margin migration trajectories:flat,low-angle rising,and high-angle rising.These trajectory types reflect the ratio of the rate of change in accommodation space to sediment supply.Eight types of micro-facies are recognized:basin-floor fans,mass-flow deposits,slope fans,slump fans,slumps,beach bars,turbidite channels,and turbidite lobes.Three corresponding sand-control depositional models were established:the flat,low-angle rising,and high-angle rising shelf-margin migration trajectory models.Under the flat trajectory model,large-scale instability and slumping tend to occur at the shelf edge,generating widely distributed slump and debris-flow deposits on the continental slope.The low-angle rising trajectory promotes sediment differentiation along a long,gentle slope,forming slope-fan depositional systems.The high-angle rising trajectory favors vertical aggradation and preservation of strata but delivers relatively limited sediment downslope.The late stage of the Ying-1 Member deposi-tion is a critical period for the development of favorable sand bodies.The low-angle rising shelf-margin migration trajectory represents the favorable slope-break belt type,with beach bars and slope fans ser-ving as good reservoir bodies.Potential favorable targets include lithologic traps within beach-bar en-richment zones above the slope-break belts on diapir flanks,and lithologic traps between the slope-fan development areas on the slope-break belts and the gas fields.These results provide a basis for integrat-ed exploration and development target evaluation in the study area.