Reservoir-Prone Mass Transport and Slump Deposits

Lawrence D. (Trey) Meckel
Woodside Energy Ltd, Perth, Australia

Mass-transport deposits are common in the deepwater stratigraphic record, but are rarely considered to contain reservoir-quality sands. However, numerous recent publications have documented sand-prone mass flows and slumps, including reservoirs in several prolific oil and gas fields as well as shallow drilling hazards. These observations suggest that such remobilized sands are more common than previously suspected, and may be a more significant component of deepwater hydrocarbon systems than has been generally acknowledged.

Given that such ‘degradational' reservoirs are not uncommon in nature, identifying and characterizing them accurately is critical (but can be controversial). For instance, understanding whether a reservoir is in a debrite complex or a turbidite system can have dramatic implications in terms of understanding reservoir potential and spatial distribution, and in terms of generating models with representative rock properties away from control points. These implications become increasingly important given ever-increasing costs associated with developing deepwater fields.

This paper uses examples from producing fields, the seafloor and shallow subsurface, outcrop, and flume tank experiments to illustrate specific criteria to aid in the recognition of sandy debrite complexes in the subsurface. None of these criteria is probably sufficient by itself to distinguish between a debrite complex and a turbidite system; however, in aggregate, these criteria are sufficiently diagnostic to identify mass-transport deposits that are likely to be reservoir-prone.