Technical recoverable volumes estimation and reserves booking are two of the most significant and complex tasks in the petroleum industry, since figures add value to company assets and/or the economy of a country. Both processes, which not always are quite compatible because of project maturity or non-technical issues, usually embrace uncertainty due to lack of information and different criteria of reserves auditors.

Conventional incremental deterministic approach ruled by guidelines of the Petroleum Resources Management System (PRMS-SPE/WPC/AAPG/SPEE) and the Securities Exchange Commission framework is quite restrictive to book for proved reserves of a field in an early development phase or few years of production history; in addition, 2P and 3P estimations are closely linked to current geological interpretation, and are not flexible to account for the whole uncertainties inherent to project at that level of maturity.

A new probabilistic approach has been proposed to provide consistency and confidence to conventional 1P, 2P and 3P deterministic estimations in recent gas condensate fields. The incorporation of strong descriptive statistics concepts in traditional probabilistic volumetric models, such as central limit theorem, dependency between model inputs (Bayes’ theorem), aggregation of volumes, as well as, the use of the standard error of mean, have given consistency to volumetric model outputs. These probabilistic calculations, adjusted to SEC definitions for proved reserves, and SPE standards, for 2P and 3P reserves categories, as well as, contingent resources, allows dealing with uncertainty inherent to a new field on development phase.

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