This paper describes some of the results obtained in a large operating company after the implementation of new procedures for reserves calculations in development projects. A number of inconsistencies in historical trends of hydrocarbon-inplace volumes, together with an evolving business environment, justified the introduction of a new methodology where a more realistic assessment of geological uncertainties is emphasised. The experience gained so far indicates that, although the new approach is more manpower intensive, the benefits justify the extra effort. In particular, expectation reserves figures are positively affected, and the general quality of geological interpretations is enhanced. The economics of a few projects appear not to have taken sufficient account of geological risk. Finally, a worthwhile compromise between theory and practical use can be achieved without resorting to excessively sophisticated techniques.

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