Precious Ogbeiwi, Karl D Stephen

The numerical simulations required for the robust optimisation of the alternating injection of water and CO2 in hydrocarbon reservoirs are computationally expensive due to engineering, geological, and economic uncertainties. Using approximation models of the desired objective function(s) can significantly decrease the cost associated with the optimisation routines while providing an adequate parameter space sampling for the input variables/ uncertainties. In this study, we optimised the value of a water-alternating-gas injection project in a Niger-Delta oil reservoir by applying the Markowitz classical theory to a suitable approximation model of the objective function. Our robust optimisation methodology incorporated significant geological and economic uncertainties, such as uncertainties due to upscaling the reservoir model, and those due to the lack of other relevant geological and economic data, to the optimisation routine to create better operating strategies for the project that are risk quantified. To compute the objective function, we applied a new economic model for the CO2 sequestration processes in the Niger Delta hydrocarbon basin. The result showed that an NPV of at least 65.98 million USD was derived from the project depending on the engineer's or user's confidence level. Although this result was 63.84% lesser than the solution of the nominal optimisation (182.46 million USD), it was more realistic. Overall, the applicability of proxy models to robust optimisation routines was demonstrated, and investment decisions that included uncertainties were made.