Geologic Field Number and Size Assessments of Oil and Gas Plays
Assessments of undiscovered oil and gas potentials for a group of geologically related, untested prospects can be effectively made from an estimate of the possible ranges in number and size of potential fields, assuming that the play exists, coupled with an evaluation of geologic risks that it might not exist Field size distributions are constructed from known field reserves in geologically similar plays, from assessments of representative prospects in the play, or from simulations of distributions of the play’s prospect areas, reservoir parameters, and potential hydrocarbon relationships. The field size distributions are truncated at both ends: at a practical minimum and at the largest size reasonably expected in the play. The possible range of the number of potential fields is estimated from the counted and postulated number of untested prospects in conjunction with a success ratio, or it is estimated from look-alike field densities. The chance that the play exists is the chance that there is at least one field of at least the minimum size assessed. The final assessment curves, developed in a Monte Carlo simulation, give the exceedance probability versus the range of possibly recoverable hydrocarbon potentials.
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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.