Comparison of Predrilling Predictions with Postdrilling Outcomes, Using Shell’s Prospect Appraisal System
D. Sluijk, J. R. Parker, 1986. "Comparison of Predrilling Predictions with Postdrilling Outcomes, Using Shell’s Prospect Appraisal System", Oil and Gas Assessment: Methods and Applications, Dudley D. Rice
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Since 1975 Shell Internationale Petroleum Maatschappij has used a Monte Carlo simulation model for worldwide prospect appraisal. The input parameters to this model describing charge (oil and gas available for trapping and retention), structure, reservoir, and retention (seal characteristics) are given in the form of probability distributions. For the estimation of charge and retention, the model follows a scheme of Bayesian update and uses equations derived from calibration studies, that is, statistical analysis of extensive data sets with a worldwide distribution. Comparison of predrilling predictions with postdrilling results suggests that the underlying calibration procedure is sound. It also demonstrates the importance of assessing geologic uncertainty in a quantitative manner. Geologists appear to have been successful in describing the geologic setting of prospects with respect to hydrocarbon charge and retention (the calibrated parts of the system); however, serious overestimation has occurred with respect to reservoir parameters, trap existence, and related factors (the uncalibrated parts of the system).