Quantifying Production Strategy Impact in Risk Analysis of an EP Project Using Reservoir imulation

摘要

Recent computer developments allow the quantification ofgeological and physical uncertainties in the appraisal phase ofa reservoir using numerical flow simulation. However, such aprocess is normally performed with a fixed productionstrategy because a variable strategy is very time consuming.The objective of this work is to study the impact of theproduction strategy in the risk analysis process. That riskanalysis methodology comprises: definition of the uncertainattributes, construction of a base simulation model, selectionof the most critical attributes using sensitivity analysis,simulation of all possible models, risk calculation using theNet Present Value (NPV) as the objective function, and choiceof a few simulation models that represent the geologicaluncertainty. An optimization procedure is applied to both baseand representative models. Finally, the changes in theobjective function are measured and some conclusions andrecommendations are made. In this work, two examples areanalyzed. In the first case, the study is applied to a realoffshore field in Brazil. In the second one, it is considered avery heterogeneous reservoir with greater uncertainty in thestructural model and in the hydraulic connectivity betweenreservoir blocks. Both cases are solution gas drive reservoirswith water injection. In the cases studied, the variation in theNPV due to optimization procedure was small when comparedwith the uncertainty in the geological model, and changes inthe optimized production strategy and investments are notsignificant, leading to the conclusion that, in such cases, theoptimization procedure can be applied only to the base model.The use of a unique production strategy in the whole processcan reduce significantly the computational effort. It is alsoshown that a more accurate result can be obtained byoptimizing only selected models called here representativemodels.