In reservoirs with limited or poor seismic resolution, faults with throws below the seismic resolution can often act as flow-restricting barriers. Hence, the uncertainty related to the small-scale fault pattern may have significant impact on the precision of the production profile predictions and recovery estimates. This paper discusses the impact of undetectable, small faults on the field production performance. A consistent methodology for incorporating the combined effect of uncertainty in the geometric fault pattern and uncertainty in the fault transmissibilities is presented. The subseismic faults are assigned to the numerical grid through a stochastic approach where fault densities, fault dimensions, and fault throw distributions are specified. In addition to the juxtaposition of the model layers at the various fault locations, alteration of flow potential across the faults (caused by for example mechanical or chemical sealing), is introduced as stochastic fault transmissibility multipliers. An example, based on data from a highly overpressured North Sea reservoir which has been evaluated for a possible field development, is presented to illustrate the usefulness and flexibility of the proposed stochastic fault modeling procedure.

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