Tahiti: Assessment of Uncertainty in a Deepwater Reservoir Using Designof Experiments

摘要

Tahiti prospect in deepwater Gulf of Mexico is a three-wayrnanticlinal structure trapped against salt, with primary payrnsands ranging from 24,000 to 27,000 ft TVD. The fieldrncontains several hydrocarbon-bearing turbidite sands. Therndiscovery well was drilled in 2002, and two appraisal wellsrnwere drilled soon afterwards. Due to significant uncertaintiesrnremaining after appraisal, probabilistic methods were used tornassess development plan alternatives and reserves. Thernprimary purpose of this paper is to show the integrated earthrnmodeling and reservoir simulation workflow, whichrnincorporates uncertainty analysis and experimental design.rnThe first step of the reservoir simulation workflow was thernidentification of the uncontrollable parameters that mightrninfluence performance predictions. These uncontrollablernparameters included the earth model, water-oil contactrnlocation, faulting and compartmentalization, reservoirrnanisotropy, aquifer support, relative permeability curves, porernvolume compressibility, rock compaction and dilation, fluidrncharacterization, skin factor and well pressure drawdown. Thernanalysis of available information from Tahiti field and analogrnfields with simple statistical techniques allowed the unbiasedrnestimation of low, medium and high values of eachrnuncontrollable parameter. The second step was the applicationrnof design of experiments to evaluate the impact of eachrnuncertainty on reservoir performance. Monte Carlo simulationrnwas used to estimate P10, P50 and P90 oil recovery andrndiscounted oil recovery for each reservoir. Finally, werndeveloped reasonable P10, P50 and P90 reservoir simulationrnmodels that incorporate the full range of each significantrnreservoir uncertainty.Probabilistic production forecasts for primary depletion andrnwaterflood strategies supported project decisions like numberrnof pre-drills, total well count, bottom-hole locations,rnwaterflood strategies and facility capacity. Reservoirrnsimulation results also supported proved reserves estimationrnand economic evaluation of the project.