Model-based Optimization of Oil Recovery: Robust Operational Strategies

The process of depleting an oil reservoir can be poured into an optimal control problem with the objective to maximize economic performance over the life of the ?eld. Despite its large potential, life-cycle optimization has not yet found its way into operational environments. The objective of this thesis is to improve operational applicability of model-based optimization of oil recovery. The reluctance of oil and gas companies to adopt this technology in their operational environments can mainly be contributed to the large uncertainties that come into play when optimizing production over the entire life of a ?eld and - in effect - the lack of faith that exists in the available methods and models. These uncertainties are of varying nature and originate from different sources. This leads to the main research question of this thesis: Can the performance of model-based life-cycle optimization of oil and gas production in realistic circumstances be improved by addressing un-certainty in the optimization problem? In this thesis, two approaches to address this research question are presented, related to the choice for a ?xed or adaptive operational strategy. For a ?xed strategy, three methods are described: hierarchical optimization, robust optimization, and integrated dynamic optimization and feedback control. For adaptive operational strategies, two aspects are investigated in a more exploratory setting: the combination of different data sources and the frequency of sequential model updating and re-optimization. The methods laid out in this thesis provide improved economic life-cycle performance under uncertainty in a number of examples. While presented as separate methods, they are not mutually exclusive and could be combined into a single work?ow. Although all the examples involve water?ooding as recovery mechanism, the scope for life-cycle optimization may be larger for enhanced (tertiary) oil recovery methods because of the generally higher up- and downside potential of these techniques. Application of the methods on a real petroleum reservoir is still required to evaluate their merit in a truly realistic environment