Abstract
Evaluation of the likely resources to be found in a four-way structural closure is undertaken when there is a chance of an open fault intersecting the structure that can leak hydrocarbons. Because one does not know whether the putative hydrocarbons exist in the structure and, even if they exist, whether they fill the structure to the point that leakage can occur, such assessments have, of necessity, to be probabilistic. We show here that there are two main contributions to the uncertainty on the expected resources: the first arises due to the uncertainty of which outcome will be present, and the second arises because the parameters entering the resource assessment each have uncertainties. Both types of uncertainty components have to be considered when evaluating the expected value of the resources and its total uncertainty. The probability one will find resources in excess of a particular value is also evaluated including both components of uncertainty. The dominance of particular parameters to the uncertainty is also evaluated. Simple numerical illustrations show how one uses the procedure in practical situations to evaluate the individual components and also to address properly the worth of obtaining further information, and the type of information, to narrow the range of uncertainty caused by the probable presence of the leaking fault and the amount of hydrocarbons it might be able to leak from the structure.