Apportioning Estimates of Basin Potential to Fields

Abstract Economic evaluation of oil and gas resources requires that the estimates of potential be divided into fields. At present, the most adequate model for field size distribution is the lognormal distribution. This distribution has been converted such that the percentage of the total basin resource that is contained in a field is a function of the total number of fields in the basin and the logstandard deviation of the distribution. It appears that basins can be categorized on the basis of the logstandard deviation of the oil and gas field size distributions. Because the percent-rank equation does not require the mean size for solution, analogue basins and standard deviation can be selected on the basis of nature of the geology regardless of the absolute size of fields. This significantly reduces the problem of selection of analogues. Use of the percent-rank equation does three things: 1. it honors the concept of lognormal field size distributions; 2. it provides for consideration of a large number of fields which, even though they are small, contribute significantly to the total; 3.because of the use of logstandard deviation, it allows selection of analogue basins on the basis of geologic configuration regardless of sizes of the basins.