Sidetrack and Recompletion Risks in Oil Fields IV. Recompletion Decisions and Effects of Uncertain Parameter Values and Distribution Choices

Abstract

This paper describes a procedure for the assessment of risks and uncertainties for the problem of deciding whether to do a recompletion job in an undeveloped oil-bearing horizon in a producing oil field. The model used for calculating estimated recompletion worth incorporates a set of parameters, such as the estimated gains and costs of both the producing and the recompletion horizons as well as the chances of killing the producing well or of doing a successful recompletion. However, these parameters are themselves uncertain and therefore contribute to the uncertainty in the estimates of recompletion worth. A probabilistic approach to this problem, using Monte Carlo simulation techniques, is used here. The method quantifies three different types of uncertainties that contribute in different proportions to a total uncertainty related to the recompletion worth. These types are: the uncertainty related to probability that the path outcome is successful (path uncertainty); the uncertainty arising from value ranges for each parameter (parameter uncertainty); and uncertainty that influences recompletion worth by allowing different distribution types to be used from which are drawn the various ranges of the input parameters (distribution uncertainty). The evaluation of the different relative contributions (%RC) of these three components to recompletion worth enables one to determine precisely where to focus efforts to improve accuracy of recompletion worth and so to decrease risk. This enablement is done by focusing on the relative sensitivity of the parameters contributing to the different types of uncertainties and optimizing these coherently. Several numerical illustrations are given to illustrate how one can rapidly evaluate the different uncertainties in a system in terms of present-day worth.