The evaluation of unconventional resources presents many challenges, one of which is a need to evaluate all resource classes, not only Proved reserves. The evaluation of hydrocarbons is described as consisting of three steps: Estimation, Classification, and Reporting, with a concomitant requirement for auditing. The nature of estimates is discussed, in particular, that there is always an associated uncertainty and some fundamental principles of classification are reviewed. The classification of unconventional hydrocarbons is discussed, with an emphasis on Discovered Petroleum Initially-In-Place and Contingent Resources, which are formulated as a series of Decision rules. Information on production potential, either from tests or analogs, is of particular importance when classifying unconventional hydrocarbons, and the typical lack of defined pool boundaries requires that careful consideration be given to the area assigned to various resource categories, both of which points emphasise the need for an understanding of the detailed reservoir geology.
The Petroleum Resource Management System (PRMS), supplemented by the Canadian Oil and Gas Handbook (COGEH), has provided the basis for the discussion in this paper, but it is impossible in a short paper to capture these systems in full, and reference should be made to the original source documents for details. The emphasis in this paper is on recovery through wells, but some brief mention of mined hydrocarbon recovery is made. The exploitation of unconventional hydrocarbons is in its early stages, and evaluation procedures, including classification, are still under development. Many aspects of the evaluation process are not addressed in this paper, and those that are, are likely to require further development and modification.