Slope and grain-size controls on sediment bypass by turbidity currents with application to upslope stratigraphic-pinchout prediction

The abrupt-margin play type has become a prime exploration target for many petroleum companies over the last decade. This play type is high risk owing to its reliance on updip stratigraphic trapping of ‘detached’ turbidite... [ view full abstract ]

The abrupt-margin play type has become a prime exploration target for many petroleum companies over the last decade. This play type is high risk owing to its reliance on updip stratigraphic trapping of ‘detached’ turbidite reservoirs. Seismic is critical for defining such prospects but limited in terms of detecting thin sands and gravels that may extend updip causing hydrocarbon leakage. Here we use a sediment transport model to aid pinchout prediction. Turbidity currents on inbound slopes may erode and bypass sediment downslope forming sand-starved slope conduits and detached reservoir bodies. In contrast, flows that cannot suspend their sediment will deposit on slopes, forming coarse-grained slope conduits and upslope-attached reservoir bodies. Using an analytical diffusion-based model of sediment suspension, erosion and deposition for turbulent flow, we explore threshold shear velocities required for total sediment suspension and bypass. The results are used to estimate the minimum slope gradients required for total sediment bypass in flows of varying grain-size distributions and concentrations. The analysis helps constrain critical slope gradients for sediment bypass required to form upslope pinchouts and may be used to augment the risking of upslope turbidite stratigraphic traps.