Deep-water lobes, from pancakes to spaghetti: a wide spectrum of reservoir geometries and sand partitioning revealed by very-high resolution subsurface data

In recent years, sandy turbidite lobe reservoirs have re-emerged as key targets for the energy industry, driven by their significant potential for deepwater CO2 storage and major hydrocarbon discoveries, notably in West Africa. Two decades of research have provided important resource and storage evaluation rules (e.g., net-to-gross distributions) and geomodelling strategies, largely thanks to detailed outcrop (e.g. Karoo) and Pleistocene analogues (e.g. Golo Fan). However, several aspects remain poorly constrained: (i) the degree of channelization and its impact on sand/mud partitioning; (ii) second-order architectural complexity at the lobe-element scale; and (iii) the geometries and distribution of channel-lobe transition facies belts.

Here, we use high-resolution 3D seismic reflection data from offshore Mauritania and Senegal to reveal the internal architecture of deep-water lobes at horizontal resolutions (12.5 m) previously only attainable with bathymetric datasets. Results reveal two geometric end-member lobe types: Type 1—highly channelized, composed of numerous distributaries formed by successive avulsions; and Type 2—less channelized sheet-like lobes. Sand distribution, and predicted connectivity, differ fundamentally between these types, as do their aspect ratios. In Type-2 complexes pervasive channel-mouth geomorphologies (cyclic steps, scours, “headless” erosive channels) are distributed throughout the lobes as feeder channels propagate and migrate. Most Type-2 lobe complexes also appear built by laterally amalgamated elongated sandy units (“filaments”), less than 1 km wide and extending over tens of km downslope. These internal distributary channels, channel-mouth geometries, and elongated “filaments” are not captured by either existing turbidite lobe conceptual models or current geomodelling strategies, though they can constitute important heterogeneities and baffles to fluid flow.

These examples demonstrate that turbidite lobes exhibit more complex internal architectures than previously appreciated, with direct implications for subsurface storage and resource development.