Congo Canyon Evolution: Subsurface and Geohazard Analysis

Combellas Bigott, Ricardo I.¹, Michael Angel², Neil Delfino³, Dan Orange⁴, Kent Rinehart³, Nigel Tootill⁵ (1) Chevron, Houston, TX (2) William Lettis & Associates, N/A, (3) Chevron, N/A, (4) AOA Geophysics, Inc, N/A, (5) Intec Engineering, N/A,

A unique integrated study with new surface and subsurface data was performed to understand the slope processes and evolution of the first 80 Kms of the Congo Canyon from the coast line. The study evaluates potential shallow and subsurface hazards for the construction of pipelines and directional wellbores through the canyon. Assessment of potential risks and uncertainties related with slope stability of canyon walls, activity of turbidity flows, and stratigraphy of the canyon defined the doability and location of future facilities in the area.

A comprehensive integration of high resolution surface and subsurface data allowed characterized the stratigraphy and geohazards currently active in the Canyon. A striking asymmetric filling of the north and south canyon rim illustrates a complex-multistory Canyon fill. A basal Upper Miocene-Pliocene unconformity represents the origin of the Canyon on top of NW-SE truncated-deep-seated normal faults. Even though part of the canyon fill was formed by catastrophic failure and turbidity events, there are many regions of the canyon fill that display a long-period of quite deposition derived from raining terrigeneous sediments and lateral debris flows.

The current geomorphology of the canyon changes dramatically from an updip dendritic tributary canyon walls to a cauliflower shape canyon walls downdip. Most tributary canyons are relict features dominated by lowstand longshore-drift current deposits and do not represent geohazards for facilities. Downdip, canyon walls are subject to two different types of sea-floor erosion: Head-ward migrating erosion, and top-down erosion from sidewall deposits. Many of the terraces are relict, paleo-sidewall deposits with absent of basal turbidity overflows, which represent potential safe locations for facilities.