Value of information : reliability of 3D reflection seismology in exploration

Abstract

Decision makers who face uncertain prospects often gather information with the intention of reducing uncertainty. If we can reduce uncertainty about future outcomes, then we can make choices that give us a better chance at a good outcome. At least it is so in a perfect world where information is free and indicates the outcome of the uncertain event with certainty. In the real world business nothing comes for free and information has a cost. Therefore we should investigate the benefits of the new information before spending time and money to collect it. Value of information, VoI, is a decision-analytic tool used for this purpose. Schlafer (1959) was the first to discuss it in a general context and Grayson (1960) applied it to the oil-and gas industry. It has grown in use during the last years. In this work the VoI-concept is described with emphasis on the question of shooting a 3D seismic-survey before drilling a wildcat or not. This is a question often encountered in the petroleum-industry. The different steps in the working-process are described and Bayes’ Theorem is introduced for probability updating. The reliabilities needed in this calculation and how to assess them is the main part of this work. An overview of how this is done in previous publications is made, and the different approaches are discussed. Then a model is developed to aid in the assessment of reliabilities for seismic data gathering. The model is closely linked to the data acquired in the 3D seismic survey and to the properties of the actual prospect. The reliability assessment-model is subjective, but let the experts express their knowledge through weights and the degree of presence of prospect-properties instead of probabilities. This is directly related to their professional and technical skills. Probability is not.