Effect of Growing Structures on Stratigraphic Evolution, Channel Architecture and Submarine Fan Distribution, Niger Delta, West Africa

Bakare, Olusola¹, Neil Hurley², Timothy McHargue³ (1) Chevron International Exploration and Production, Lagos, Nigeria (2) Colorado School of Mines, Golden, CO (3) ChevronTexaco, San Ramon, CA

The goal of this study is to determine the influence of mud diapirs and syndepositional extensional growth faults on depositional processes, sedimentation, stratigraphy, and facies evolution in part of the Niger delta, offshore West Africa. The data set consists of a conventional 3D seismic survey and a coherency-processed seismic volume. There are wells in the area, but there are no logs or cores in the study interval.

The study area is characterized by numerous mud diapirs that grew and caused changes in depositional axes with time. This determined the development, distribution and architecture of reservoir facies in intra-slope basins.

Depositional cycles in the study area have mass transport complexes (MTCs) at the base, overlain by amalgamated or accretionary channel complexes (ACCs), or distributary channel and lobe complexes (DLCs), depending on the location within a mini-basin. Each depositional cycle is capped by a drape complex (DC).

Mud diapirs controlled stratigraphic evolution and fan distribution. Channel morphology changed from highly sinuous at depth to relatively straight in shallower intervals. Sinuous older channels are considerably wider, and had reservoir facies deposited both within channel axes and as lobes. The less sinuous, younger channels are narrower, and have reservoir facies deposited as lobes across slope-gradient reversals. The architecture and stacking patterns of the associated reservoir deposits vary from one channel to the other. Due to movement of mud diapirs through time, depositional axes changed both spatially and temporally, which resulted in different depositional sites for associated submarine fans.