AAPG Annual Convention and Exhibition

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Upslope Turbidite Stratigraphic Traps: Understanding Pinchout Development


Deepwater turbidite systems with stratigraphic pinchout moving updip towards the proximal basin margin have become prime targets for exploration companies attempting to copy past commercial successes: including those from offshore Ghana (Jubilee Field and TEN Development Complex), the UK Central North Sea (Buzzard Field), UK West of Shetland (Foinaven Field) and Brazil Campos Basin (Marlim Field). This play type offers potentially large trapped hydrocarbon volumes. However, such targets remain high risk, notably due to trap failure related to hydrocarbons leakage updip via coarse-grained thief zones that may be thin and seismically difficult to image. Given the complexity of slope system evolution and basin margin architecture and the limitation of any single data type, a multifaceted approach is best employed to advance models for pinchout development and understand stratigraphic trap risk. This contribution will outline a number of approaches being used to better understand upslope pinchout development in turbidite systems including the assessment of global reservoir examples, studying modern seafloor, shallow buried and ancient outcrop systems and utilising sediment transport models for turbidity current erosion-bypass. Analysis of reservoir examples indicates that effective pinchouts may form in association with a number of processes including sediment bypass and truncation by mud-filled channels and mass transport complexes. Reservoirs come from different margin types including a range of tectonic setting and graded as well as ungraded slope profiles. Sediment transport models indicate slope gradient but also grain size and grain-size distribution are key variables dictating bypass-related pinchout development. Systems with steep slopes and relatively fine maximum grain sizes likely offer lowest risk for updip leakage.