Integration of Borehole Data with the Regional Seismic/Sequence Stratigraphic Framework of the Western Offshore, South Africa

MUNTINGH, ANDRE, S. ROBSON, E. JUNGSLAGER, P. BURDEN, and P. STRAUSS, SOEKOR (Pty) Ltd., Parow, South Africa

A sequence/stratigraphic framework for the west coast of South Africa was constructed applying sequence-stratigraphic concepts developed by Exxon to interpret 10,000 km of seismic data within an area of 90,000 sq km.

A sequence-stratigraphical analysis of the west coast exhibits 34 cyclical depositional sequences interpreted to document the response of the passive margin to cyclical changes in relative sea-level from Mid-Aptian to Late Maastrichtian times.

Exploration on the west coast was historically targeted toward synrift lacustrine systems or post-rift highstand paralic systems limiting the exploration for lowstand systems tract reservoirs to the two most recent boreholes.

The sequence-stratigraphic framework and depositional model generated are tested against geophysical log, core, and paleontological data of 31 wells.

Depositional systems tracts identified in well logs using parasequence-stacking patterns and facies interpretation from cores and cuttings are calibrated with interpreted seismic data and substantiate the validity of most of the depositional systems tracts and inferred cyclicity.

Source bed and paleontological data indicate a reliable correlation with interpreted marine condensed sections of the constructed sequence-stratigraphic framework.

One discovery well intersected stratigraphically trapped incised valley-fill reservoirs supporting this lately developed approach to hydrocarbon exploration.

The interaction of the sequence-stratigraphic model and substantive, paleontological, source bed, and lithological information leads to a more reliable and refined geological model of the evolution of the Orange basin.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)