A fully coupled reservoir-geomechanics model is developed to simulate the enhanced production phenomena both in heavy-oil reservoirs (i.e. Northwestern Canada) and conventional oil reservoirs (i.e. North Sea). The model is implemented numerically by fully coupling an extended geomechanics model to a two-phase reservoir flow model. A sand erosion model is postulated after the onset of sand production, which is determined based on the degree of plastic deformation inside the reservoir formation calculated by the coupled reservoir-geomechanics model. Both the enhanced production and the ranges of the enhanced or sanding zone are calculated, the effect of solid production on oil recovery and enhancement are analyzed. Our studies indicate that the enhanced oil production can be contributed by a combined effect of higher fluid velocity due to the movement of the sand particles according to the modified Darcy's flow and an effective well radius increase or negative skin development due to sand erosion. Despite of such an improvement on mobility may reduce the near well pressure gradient so that the sanding potential is weakened, it permits an easier path for oil to flow into the well due to an enhanced permeability. Two-phase flow can affect pressure gradient and formation residual cohesion due to capillary pressure buildup. Indirectly, production enhancement strategy can be controlled by the water saturation distribution and development, as the success and economic value of a field operation can depend on whether sand production can be induced or not. Such an analogy can also be used for a completion strategy by allowing a certain amount of sand production before sand control strategy implemented in high flow-rate reservoir, when the optimum production is desirable and
when the reservoir productivity does not vitally rely on sand production.
Sand production is a phenomenon that occurs during aggressive production induced by a combined impact of viscous fluid flow and the in-situ stress concentration near a wellbore and perforation tips in poorly cemented formations. Such a solid production compromises oil production, increases completion costs, and reduces the life cycles of equipment down hole and on the surface. Sand production has been a major concern to production engineers for decades, either in poorly consolidated reservoirs or from those formations with cement. These sanding effects often are associated with high fluid viscosities and production rates, and the issue is becoming more critical these days as operators are following more aggressive production schedules. Sand production, on the other hand, has been proven a most effective way to increase well productivity both in heavy oil and light oil reservoirs1,7. A typical 4–10 fold increase in oil production is normal in heavy oil reservoirs (Cold Production)1–3, and up to a 44% increase in sand-free rate after a certain amount of sand production in conventional oil reservoirs has been reported8,9. For conventional oil producers, both enhanced production and improved sand-free rate are highly desirable. Whereas for the heavy crude operators, other than the improved productivity, operating cost reduction is vital for a profitable operation, because the price margin between heavy oil and light oil is high (this is particularly important for cold production operators in northwestern Canada).