Offshore Namibia: an Ideal Setting for Applying Seismic and Sequence Stratigraphy?

Joanne G. Bagguley

The passive continental margin offshore Namibia remains one of the few relatively unexplored, frontier areas for hydrocarbon exploration. The availability of 14,300 km of speculative, non-exclusive seismic reflection data has provided the opportunity to build up a sequence stratigraphic framework for this margin, with a view to hydrocarbon play analysis and prediction.

Seismic Observations

The high seismic resolution of the data allows the definition of a number of megasequences, each representing a major phase of basin evolution. The post-rift prograding wedge (MS SO) can be divided into a lower MS50a (Aptian-Maastrichtian) and an upper MS50b (Tertiary) unit. Internally, these units are composed of a number of T/R cycles.

Isopach maps for MS50a and MS50b have been constructed. The information from these can be supplemented by river system and drainage basin analysis to gain some insight into the types of sediment expected to be deposited offshore at different times during the evolution of the margin.

A number of different features can be identified from the data which can help place the post-rift units into a sequence stratigraphic framework. Channel forms and slump-related features are observed which may form in response to relative sea level changes or tectonic triggering. The seismic expressions of these features enables the causative process to be determined.

Basin Modelling

By constructing geohistory curves using a basin modelling program, the structural and stratigraphic evolution of the Namibian margin may be further elucidated. Such geohistories pinpoint the location of possible source rock horizons which, when fed back into the sequence stratigraphic framework, may aid the prediction of potential hydrocarbon plays.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995