Quantifying Production Strategy Impact in Risk Analysis of an E&P Project Using Reservoir Simulation

Abstract

Abstract Recent computer developments allow the quantification of geological and physical uncertainties in the appraisal phase of a reservoir using numerical flow simulation. However, such a process is normally performed with a fixed production strategy because a variable strategy is very time consuming. The objective of this work is to study the impact of the production strategy in the risk analysis process. That risk analysis methodology comprises: definition of the uncertain attributes, construction of a base simulation model, selection of the most critical attributes using sensitivity analysis, simulation of all possible models, risk calculation using the Net Present Value (NPV) as the objective function, and choice of a few simulation models that represent the geological uncertainty. An optimization procedure is applied to both base and representative models. Finally, the changes in the objective function are measured and some conclusions and recommendations are made. In this work, two examples are analyzed. In the first case, the study is applied to a real offshore field in Brazil. In the second one, it is considered a very heterogeneous reservoir with greater uncertainty in the structural model and in the hydraulic connectivity between reservoir blocks. Both cases are solution gas drive reservoirs with water injection. In the cases studied, the variation in the NPV due to optimization procedure was small when compared with the uncertainty in the geological model, and changes in the optimized production strategy and investments are not significant, leading to the conclusion that, in such cases, the optimization procedure can be applied only to the base model. The use of a unique production strategy in the whole process can reduce significantly the computational effort. It is also shown that a more accurate result can be obtained by optimizing only selected models called here representative models.