Basin Analysis of South Mozambique Graben

J. Iliffe, I. Lerche, M. De Buyl

Basin analysis of the South Mozambique graben between latitudes 25° and 26° and longitudes 34° and 35° demonstrates how modeling techniques may help to assess the oil potential of a speculative basin with only minimal seismic data.

Two-dimensional restoration of the seismic profiles, using a backstripping and decompaction program on pseudowells linked with structural reconstruction, assesses the rift's two-phase extensional history.

Since no well or thermal indicator data exist within the basin, the thermal history had to be derived from extensional models. The best fit of observed subsidence curves and those predicted by the models results in values of lithospheric extension (gamma).

The disagreement in observed and theoretical basement subsidence curves was minimized by taking a range of gamma for each model for each well. These extension factors were then used in each model's equations for paleoheat flux to derive the heat-flow histories. (It is noted that a systematic basinwide variance of gamma occurs.) The heat-flux histories were then used with a one-dimensional fluid flow/compaction model to calculate TTI values and oil windows. A Tissot generation model was applied to each formation in every well for kerogen Types I, II, and III. The results were contoured across the basin to assess possible oil-and gas-prone formations.

The extensional, burial, and thermal histories are integrated into an overall basin development picture and provide an oil and gas provenance model. Thus we estimate the basinwide hydrocarbon potential and also gain insight into the additional data necessary to significantly decrease the uncertainty.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.