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Assessment of Global Uncertainty for Early Appraisal of Hydrocarbon Fields

This paper was selected for presentation by an SPE Program Committee following review of information contained in a proposal submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Papers presented at SPE meetings are subject to publication review by Editorial Committees of the Society of Petroleum Engineers. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to a proposal of not more than 300 words; illustrations may not be copied. The proposal must contain conspicuous acknowledgment of where and by whom the paper was presented. Abstract We propose a workflow to assess the uncertainty about a global reservoir parameter such as net-to-gross during early exploration. As opposed to traditional statistical approaches that assume data independence and cannot easily account for either seismic data or geological interpretation, this model, based on multiple point statistics, integrates the main components of uncertainty, namely: • the choice of a geological scenario, probably the most important factor at the appraisal stage. • The location of wells, which could have been drilled elsewhere, giving a different picture of the reservoir. • The calibration of the seismic to the well data. This global uncertainty model is demonstrated on a large 3D fluvial reservoir. Introduction Advances in deep water drilling technologies have cleared the path for new domains of hydrocarbon exploration. The appraisal of such deep offshore reservoirs is a high risk exercise: in addition to political and economical unknows, the sparsity of early exploration data compounds with the geological complexity of turbiditic formations, making any global reserve estimate highly uncertain. However, early in the appraisal stage, corporate decisions must be made about developing the field by drilling one or several new wells, or just abandoning the field and moving on to a safer prospect. Decision science provides tools to address this type of issue 1 , but calls for a sound assessment of uncertainty about the reservoir potential. In deep offshore reservoirs, the uncertainty on the oil in place is controlled in great part by the reservoir geometry and the pore volume, the latter …