Abstract.

Reserve calculation must be performed according to the intended use of this information. It can be considered for the purpose of (1) defining a production strategy or (2) for computing the assets of a company.

When production strategy is the major concern, the amounts and classification of hydrocarbon reserves are to be related to the development policy of a company, and a detailed reporting of these reserves must be required.

Otherwise, if the goal is to compute the assets for the purpose of comparison or loan seciirity, it becomes necessary to follow a common procedure that will lead to universal comprehension and confidence. This standardized process may be insufficient to meet the needs of a development program from a technical standpoint.

Concluding, in spite of a company feeling the necessity of subdividing its reserves into a detailed form to achieve the best planning of production, that same company cannot deny the importance of reporting these into a single and comprehensive classification to meet the requirements of the world.

This paper describes the detailed classification used at Petrobrás to estimate the risk involved in the development program of the Brazilian fields, and how this classification can be adjusted to provide a universal appraisal of the reserves.

1. INTRODUCTION

Why are reserves estimated? When a certain company estimates its reserves it seeks a way to quantify its uncertainties in relation to the volume of petroleum it administrates, as a way to better plan its exploitation activities. When the reserves of a company are low, it should seek to invest in an attempt to discover or acquire new reserves. When these, on the other hand, are high, it should invest in the recovery of these reserves. But this ‘true or false’ simplistic view, is confronted by uncertainties inherent to the process that impede that value from being taken so directly in the development planning, under threat of acting in a less professional way. However, all professionals related to the area seek the quantification of these uncertainties, without really achieving an efficient form of doing so.

But the same company needs to quantify its reserves as a form of evaluating its assets, positioning itself in relation to the market and seeking financing for its development projects. For such venture, it becomes essential that the company adopt a classification for its reserves that could make them comparable and, mainly, acknowledged by external entities. 2. INTERNAL PLANNING AND EXTERNAL R ECOG N IT10 N Internally, one could say that the reserve is a portrait of a company's position forecast. This forecast, since it is not exact, should not be unique but rather, should take in consideration optimistic and pessimistic hypotheses, that is, it should deal with a range to which the efforts of a company should be pro-

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