Syn-Kinematic Effects on Depositional Facies and Stratal Architecture within a Slope Valley Fill: Implications for Reservoir Distribution and Modeling

O'Byrne, Ciaran J.¹ (1) Shell Exploration and Production Company, Houston, TX

Much has been learned in the last decade on the evolution of slope depositional systems developed above mobile sub-strates and the relationships between local gradient controls and accommodation space on deepwater stratal architecture. This talk will present evidence for more subtle stratigraphic expressions of syn-depositional structural activity during the infill history of a deeply incised slope valley complex within the Bonga system in OPL 211, offshore Nigeria.

Whilst evidence of obvious growth fault activity, structural inversions and other syn-kinematic features provide clear linkages with depositional style, less pronounced active structures can have equally significant effects on reservoir distribution and preserved depositional architecture. Recognition of such activity may have significant implications on how we model heterogeneity within slope valley fills and other deepwater depositional environments.

The slope valley fill described here at first pass would appear to be largely consistent with many seemingly analogous systems interpreted to have formed during tectonically quiescent periods. In detail however, through careful integrated ‘loop'-scale seismic facies analysis, a number of discriminating observations can be made such as 1) large scale slumping from outside the scalloped valley wall entering the valley late in it's fill history, 2) a valley thalweg gradient that maintains and advances rather than heals through time and 3) continued deep entrenchment of meander belt scale elements throughout the fill history. This talk will focus on stratigraphic evidence for syn-kinematic structural activity and discuss the implications for preserved depositional architecture and conceptual slope depositional models for reservoir modeling on margins with mobile substrates.