Optimization of Well Sidetrack under Uncertainty using Response Surface and Decision Support. I. Primary Recovery Mechanism

Abstract

The Optimal sidetrack time (tR-OPT) has been estimated for uncertainty of the probability of success (POS) of the sidetrack operation, reservoir properties and economics for a reservoir under primary recovery mechanism. The case studies worked on in literature considered in this study are for those for primary recovery in which production profiles were represented by empirical and analytical models. However, not all recovery can be adequately replicated by these analytical models. Hence, the need to apply proxy models not just to predict cumulative production but net-present-value (NPV). In this study the analysis of a decision tree with several branches is carried out to maximize NPV that is evaluated under the influence of production stoppage due to the sidetrack into another non-communicating upper zone with uncertainty of reservoir properties. The optimal sidetrack time adds a severe non-linearity in the response of the resulting proxy model and expected monetary value (EMV), the objective function. Multi -objective functions of proxy models over time-intervals for highly time impacted terminal branches, known as split design was applied to evaluate when to conduct a well sidetrack operation under risk and uncertainty in order to resolve severe non-linearity of the NPV solved by a standard optimization algorithm in a spreadsheet. The Predicted values of optimal sidetrack time by the developed workflow was relatively reasonable and highly satisfactory in comparison with simulation results and that of empirical and analytical models. Though, further performance improvement is possible, the constraint on computational time for multi-objective optimization must be weighed against the desired result. Monte Carlo implementation on EMV based on uncertainty of reservoir properties and varying POS acknowledges the fact that for favourable POS, that is values approaching 1.0, tR-OPT clustered at early production life with a spike and the later for unfavourable values.