Modern Deepwater Analogues for Turbidite Reservoir Architecture: The Development and Distribution of Linked Debrites in the Moroccan Turbidite System

Hunt, James E.¹; Wynn, Russell B.¹
(1) Marine Geoscience, National Oceanography Centre, Southampton, United Kingdom.

Targeted piston coring, swath bathymetry and shallow seismic reflection studies provide details on the topography and shallow basin fill of modern systems. The combined sedimentary and geophysical analyses of modern systems can enable detailed analysis of reservoir quality sediments and potential heterogeneities analogous to those found in petroleum systems.

The Moroccan Turbidite System is a deepwater province on the Northwest African passive margin. This system comprises three interconnected basins (Agadir, Seine and Madeira Abyssal Plains) that present complex seafloor bathymetry analogous to the sub-basin topography of the Gulf of Mexico.

The AB5 event originates from a catastrophic Moroccan Shelf failure (~60ka). The AB5 turbidity current in the Agadir Abyssal Plain has been identified as containing a significant linked debrite. A linked debrite contains a well-sorted graded sand base, a poorly sorted mud-rich debrite and finally a well-sorted graded mudcap. The basal turbidite facies represents good reservoir quality, while the debrite facies would present a major baffle to flow.

Although the extent of the linked debrite can be highlighted in the cores the presence of this facies between core sites can be seen in shallow 3.5 kHz seismic reflection profiles. Previous work on linked debrites has associated them with the suppression of turbulence and onset of laminar flow in the distal region of the fans. However, core and seismic profiles of the present study have shown this linked debrite to develop within the core of the flow. This has major implications in regards to evaluating the reservoir characteristics of turbidites from basins with complex topography. Since one model predicts the linked debrite in the distal fringes, while the over predicts its presence in the core of the deposit.

Grain-size and petrophysical analysis has also enabled physical property analysis of the linked debrite facies, and shown the increased mud content in the matrix and poorly sorted nature of the debrite unit, which implies lower porosity and permeability.

The present study provides a better understanding of the depositional processes and distribution of reservoir quality facies within this environment. The petrophysical studies could also potentially enable remote identification of these fine scale heterogeneities from borehole data. These deposits are also ubiquitous in additional deepwater basins, further supporting the need for their study.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.