Submarine Canyons: Key Features to Derisk Deep Sea Exploration.

Abstract

Deep sea systems are a classic target for hydrocarbon exploration as reservoirs with good petrophysical properties are encountered in turbiditic and/or contourite impacted deposits. In frontier as well as mature exploration, the spatial distribution of reservoirs is a key element of success. Submarine canyons are large scale incisions which occur mostly in slope environments along continental margins. Canyons are very often neglected because there is a general belief that these geological objects are mud filled, clay rich deposits being recorded as canyon backfilling. However, it is possible to differentiate mud filled passive canyons only related to retrogressive erosion limited to the slope setting (slope confined canyons) and active canyons connected to the shelf through a canyon head (shelf indenting canyons). Active canyons display complex infills, the record of long-term transit of sediments from the shelf to the deep basin. These features are preferential pathways to the deepest part of sedimentary basins and correspond then to the feeders of major deep sea fans. In some very specific cases, they can even display significant sand volumes and thus be considered locally as exploration targets. Shelf indenting canyons are not only key to predict reservoir development in the deep basin even if seismic is not yet accessible, but they also constitute important landmarks, very useful to constrain paleogeographic maps. Their characteristic heads indenting the shelf margin is indeed easily observable on 3D seismic volumes (and sometimes on 2D seismic lines) and allow to precisely constrain the shelf margin location for a given time interval. This study illustrates, through examples from all around Africa, that chasing deep sea reservoir distribution can be largely derisked by the understanding of canyon types and distribution. This can be done providing that the architecture of the canyon is carefully studied in order to differentiate feeder canyons from passive canyons.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018