Many reservoirs contain a thin oil column with underlying water or with a gas cap present. To decide on the viability of such fields, detailed single-well simulation studies are often made to forecast oil, gas and water rates through time. This paper investigates the effects of discontinuous shales on the performance of vertical and horizontal wells in these reservoirs. Stochastic techniques are presented for representing shales on a simulation grid.

Conclusions are that it is necessary to include shales explicitly if the variability of behaviour in vertical wells is to be captured; that shales cutting the wellbore have the most significant effect on performance; and that small shales can be represented via an effective vertical permeability for horizontal well simulation.

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