Uncertainty in N/G ratio in early reservoir development

Early uncertainties about global reservoir parameters are, possibly, the most consequential from an investment point of view and for the reservoir feasibility. One such important parameter is the global net-to-gross (N/G) or pay-to-nonpay ratio, which conditions estimate of the original oil in place (OOIP). How the N/G estimate is obtained is very much case-specific, but it remains an estimate and its uncertainty should be assessed. This paper proposes a general methodology for such early uncertainty assessment; the methodology is based on the concept of bootstrap or spatial resampling from stochastic simulation of, e.g., the facies spatial distribution. The resampling results provide a measure of uncertainty. The resampling paradigm allows also evaluating the reduction of uncertainty that would be brought by additional wells: it suffices to sample the “simulated” data corresponding to these additional wells. An example case study is presented.