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Drainage Systems in Rift Basins: Implications for Reservoir Quality


Ancient and modern rift basins can be found on every continent of the world and account for 31% of giant fields discovered (Mann et al., 2003) with over 620,000 (MMBOE) of estimated recoverable hydrocarbons worldwide. New rift plays are just being discovered as we explore beneath salt deposits and penetrate deeper continental margin strata. The biggest challenge in these basins is understanding reservoir location, quality, and extent. Axial- and marginal-sourced rivers provide very different sediments to the system and have significant geomorphologic differences. The architecture of rift systems varies dramatically from those located within continental versus coastal/marine environments (Gawthorpe and Leeder, 2000). A three phase study of rift drainages was undertaken to document these differences and quantify the various morphologies of drainage that characterize rifts. A literature and imagery review of ancient and modern rift drainage systems was undertaken with the focus on ancient systems being issues and challenges to producing discovered, developed, and undeveloped hydrocarbon in rift system reservoirs. In the second phase of this work, a study of the morphology of a modern rift setting in East Africa using ArcGIS and satellite imagery allowed mapping and quantification of rift drainage morphologic characteristics, such as: drainage architecture, rift size, channel size and flow characteristics and the overall drainage nature versus catchment area. Phase 3 of this study focuses on applying the criteria and knowledge built in Phases 1 and 2 to improve prediction of drainage nature and subsequent reservoir distribution and development in a high resolution 3D seismic survey in the Dampier Sub-basin off the NW coast of Australia. Quantitative seismic geomorphological techniques have been employed to assess the morphology, flow character and drainage size of this paleo-rift system toward a better understanding of reservoir distribution and risk.