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Bryan R. Bracken1
(1) Chevron Overseas Petroleum, San Ramon, CA

Abstract: Predicting Properties and Performance in Shoreface Reservoirs, Cenomanian Vermelha Sandstone, Offshore Cabinda, Angola

Cenomanian shallow-marine shoreface reservoirs in offshore Cabinda, Angola, have complex architectures, the result of sedimentation within active growth-fault systems. So as to better understand controls on reservoir properties, several well-constrained Vermelha reservoirs characterizations were constructed and were used to build an empirical, predictive reservoir model. The intent of the model is to be able to predict flow-unit and flow-barrier architecture and reservoir quality and, therefore, to be able to predict reservoir performance, generate more realistic early generation simulation models (in new fields) and assess remaining reserves (in older fields).

The basic component of this model is a detailed distribution and relationship between sediment texture, petrophysical properties, and depositional facies. This sediment framework is then placed within tectonic, depositional, and eustatic contexts at both field and regional-scale. Finally, from this genetic-stratigraphic characterization a stratigraphic baselevel model was generated.

Although the inter-relationship between controlling variables is complex, preliminary assessment has indicated several fundamental relationships between the rate of creation of accommodation space (relative rate of baselevel rise), reservoir architecture, and distribution of reservoir quality. Three critical relationships are:

1. Sealing capacity of shale beds (flow-barriers) can be estimated. 2. Critical reservoir petrophysical properties (i. e., permeability) and flow unit thickness can be predicted. 3. Flow-unit and flow-barrier geometries are controlled by scale of fault system and position on baselevel cycle.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana