3-D Seismic Analysis of Cenozoic Slope Deposits and Fluid Flow Phenomena on the Nigeria Transform Margin

Abstract

The evolution and petroleum systems of Central Atlantic transform margins have attracted increased industry interest over the past decade. This study analysed the Cenozoic succession in a 2,845 km² high-resolution 3D seismic survey from the end of the Romanche transfer zone and the northwestern most fringe of the Niger delta cone. The study found large-scale buried and active mass-transport complexes (MTCs), deposited with deep-water channel complexes and wide range of fluid-flow phenomena formed from fluid migration within the basin. MTCs were mapped at multiple levels and constitute up to 25% of the entire stratigraphy. A very unique characteristic of the MTCs is that the volume of failed sediments increased through time with formation mechanism mainly attributed to margin evolution and increased rate of sedimentation through time.

The fluid-flow phenomena mapped on the present-day seabed and overburden (Pliocene-age) in the area include pockmarks, vertical pipes, gas-hydrate BSRs and a seabed mound. These are spatially distributed above structural highs, faults, active and paleo deep-water channels in the eastern part. A thermogenic origin for fluid was proposed, which could be a direct indication of presence of an active petroleum system in the deeper interval, such that the fluids migrated along planes of deep-seated, faults. Hydrocarbon generation in the basin started in Late Miocene and continued till the present-day, coincides with the appearance of fluid-flow phenomena suggesting they could have formed during hydrocarbon generation.

MTCs could constitute present day hazard if the seabed is unstable, therefore must be properly evaluated prior to installations of offshore facilities. The prolific fluid-flow indicators and direct hydrocarbon indicators (DHIs) bode well for hydrocarbon prospectivity. Collection of samples from pockmarks and mound imaged on the seabed could be used for exploratory and confirmatory data analysis. Integrating all these data with the knowledge gained about their spatial distribution can help build predictive models to identify future reservoirs and reduce exploration risks.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018