Abstract: Modeling of Regional 3D Cube, Offshore Cabinda, Angola

Gaulier, J. M. - lnstitut Français du Pétrole;Schoellkopf, N. B. - Chevron Overseas Petroleum Inc.

To accurately reconstruct the migration history of the multiple petroleum systems offshore Cabinda, we built a regional 3D cube comprising 25 structural depth maps and associated lithologic data. These included source richness, regional migration conduits, reservoirs and seals. We applied several modeling methods: 2D migration (TEMISPACK), multi-1D geochemical simulations and 3D migration analysis (IFP's PEGASE prototype).

We calibrated the thermal and maturity history at 55 wells, from which we created a regional heat flow map. Using a thermal rift and subsidence model, we derived the temporal evolution of heat flow from the crustal structure. Then, we computed the maps of transformation ratio and expelled HC amounts through time.

For the migration simulations, we extracted 2D regional sections from the 3D cube. Three features largely control the hydrocarbon movement: the Loeme salt overlying the Chela migration conduit, the organic-rich Middle Bucomazi shales and the marine labe shales. These regional seals create complex migration pathways. For example, different generative depressions are responsible for pre- and post-salt accumulations in the same fields.

The Middle Bucomazi seal largely controls migration into pre-salt prospects, often preventing direct vertical migration. Salt windows are a key feature for charging post-salt reservoirs. Widespread lateral migration is likely in the Upper Cretaceous.

Combining 3D fetch analysis for the reservoir units and the main regional migration pathways with information on source prolificity allows evaluation of the charge risk.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil