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).
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There is a continual need to update estimates of oil and gas resources remaining to be discovered, and also to refine the methodologies for making these assessments. In 1974, AAPG sponsored a research conference dealing with the above topics, and many of the papers presented there were published in AAPG Studies in Geology 1. As a follow-up to that volume, a U.S. Geological Survey workshop was held in 1983, and many papers from talks presented there, in addition to several other papers, are contained within this volume. The 22 papers have been grouped into two types: those describing methodologies for evaluating resources and those presenting assessments of both conventional and unconventional resources.