Incorporating Uncertainty into Geological and Flow Simulation: Application to a Pre-Development Field, Offshore West Africa

Andrew W. Harding¹, Avi Chakravarty¹, and Robert Scamman^2
1 ChevronTexaco Energy Technology Company, San Ramon, CA
² ChevronTexaco Overseas Petroleum, Bellaire, TX

This is a reservoir-modelling case history of a ChevronTexaco-operated field, Offshore West Africa, designed to evaluate development options. We have used multiple point geostatistical modelling, reservoir-property uncertainty analysis and design-of-experiments-based flow simulation to select a preferred development option.

The multiple-point geostatistical simulation uses a training image, which is a three-dimensional conceptual model of depositional facies and their associations. The simulation was also conditioned by multiple cases of a facies probability cube with different combinations and proportions of seven facies.

In modelling the reservoir properties, uncertainties in porosity, permeability and water saturation (“PKS”) were taken into account. Five models were produced, reflecting the combinations of high- and low-case reservoir facies, high- and low-case PKS properties and a mid-case; each was scaled-up and re-calibrated by adjusting Dykstra-Parsons coefficients.

Twelve development alternatives for the field were defined and deterministic economics were run to reduce the number of alternatives to be carried forward into probabilistic analysis to five. The Design of Experiments (DoE) approach was used to evaluate the key subsurface uncertainties and design an overall development plan. The probabilistic simulation results and Decision Analysis (DA) allowed us to identify a phased development, which would mitigate potential downside risks while preserving the ability to capture upside potential.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005