Probabilistic methods in petroleum resource assessment, with some examples using data from the Arabian region

High risks are inherently entrenched in any petroleum assessment and exploration because of the uncertainties in geological and economic factors related to the hidden resources. These risks can never be eliminated, but can be reduced by using probability methods at different stages of assessment and exploration activities. Probabilistic modeling of the historical discovery trends (discovery process) and of the spatial–temporal relationships between deposit characteristics (size, number) and geology (play analysis) has been accepted as effective methods for evaluating future discoveries, because of their capability of incorporating specific quantitative geological, technological and economic attributes related to exploration. The two major geological uncertainties that play a key role are related to the nature of parent statistical distributions of number and sizes of the fields in a given region of assessment. Statistical distributions of geological parameters can be estimated using Monte Carlo methods, taking care of the correlations, to produce field size distribution in the play or basin. Similarly, distribution of possible number of fields can be estimated incorporating also the drilling parameters. The methodologies are illustrated with examples from different parts of the world, including the Arabian Region.