TAHITI: DEVELOPMENT STRATEGY ASSESSMENT USING DESIGN OF EXPERIMENTS AND RESPONSE SURFACE METHODS

Tahiti prospect in Deepwater GOM is a three way anticlinal structure trapped against salt, with hydrocarbon bearing turbidite sands ranging from 24,000 to 27,000 ft TVD. The discovery well was drilled in 2002, and two appraisals were drilled soon afterwards. In May 2004, Tahiti progressed to Chevron's project management process Phase 3 (developed preferred alternatives). In this phase we proposed an innovative application of design of experiments (DOE) and response surface methods to accomplish a more mature assessment of the development strategy.

Initially, the classical DOE approach was applied and reasonable P10/P50/P90 reservoir simulation models were designed. Next, a second round of D Optimal design runs was performed. The uncontrollable uncertainties were consolidated to critical few parameters (OOIP, reservoir energy and faulting) and controllable uncertainties were added (well count and injection timing). The goal was to validate that the previously designed models reasonably represented P10/P50/P90 reservoir behaviors for various development alternatives. Finally, the response surfaces for oil recovery and NPV were used to explore multiple scenarios by varying controllable uncertainties across the range of uncontrollable uncertainties.

Low, mid and high well counts were identified. Both DOE analysis consistently sustained 9 producers and 3 injectors as the preferred development, providing robustness to the decision. Although response surface methods allowed a quick evaluation of the impact of different uncertainties and development scenarios on oil recovery and NPV, the match between the response surface and the simulations must be of supreme quality to continue further analysis of a project relying only on proxy results.

This study enhances the use of DOE by linking the technique with response surface methods. This approach could help in evaluating development alternatives and well count for greenfields, supplying a new perspective to the economic analysis of project decisions.