A review of producing fields inferred to have upslope stratigraphically trapped turbidite reservoirs: Trapping styles (pure and combined), pinch-out formation, and depositional setting

Abstract

Siliciclastic turbidite systems that pinch out updip toward their proximal margin are prime targets for hydrocarbon exploration, especially in deep-water basins. Such “upslope stratigraphic traps” potentially offer large-volume discoveries but have significant geological risks, notably because of ineffective closure or containment. In the published literature, at least 20 fields from 11 basins globally with 6–7 billion BOE of cumulative discovered reserves have been inferred to be reliant on upslope pinchout traps. These fields are reviewed in terms of their interpreted trapping styles, pinch-out formation process, and depositional-tectonic setting. Reservoirs display a range of upslope trapping styles, including pure (depositional and erosional) stratigraphic pinch-outs and combined stratigraphic-structural traps. In one-third of cases, faulting appears intimately linked to updip trapping, either through offsetting slope feeder conduits or assisting pinch-out development, and in some cases, faulting may be the most important updip trapping element. Sediment bypass and erosion in proximal areas is the most common inferred pinch-out formation mechanism. Some reservoirs also demonstrate the ability of erosional truncation by mud-prone channels and mass transport deposits to form viable stratigraphic traps and seals. Encouragingly for exploration, robust pinchout traps occur in various tectonic settings on a variety of different slope types and positions along the slope profile. Most large-volume discoveries to date, however, are restricted to the toe-of-slope environment in graded passive margins or out-of-grade rift and transform margin settings. Insights into the nature and occurrence of upslope stratigraphic traps are important for future exploration, especially for evaluating new license areas and risking prospects.