Despite the many publications about the production mechanisms of heavy oil reservoirs, there is still no consensus as to what is behind the anomalous production rates observed in some reservoirs in Venezuela and Canada. Many authors attribute the recovery of a much higher fraction of the original oil in place to a special phenomenon associated to the solution-gas drive mechanism, known as "foamy" or "bubbly oil", present in heavy oil reservoirs. However, the "foamy oil" behavior cannot clearly explain the mechanism of the observed oil production rate enhancement.

Considering the physical principles of two-phase flow through porous media, the viscous coupling or momentum transfer between the flowing phases would appear as a hidden driving mechanism to explain the improved oil mobility. The use of capillary models has provided a new insight into the effect of the viscosity ratio on relative permeabilities and the importance of water lubrication in heavy oil-water two-phase flow. However, despite the models predictions show that the viscosity ratio affects the relative permeabilities, especially in systems involving very viscous oil, the lack of experimental results makes it difficult to support the theoretical observations.

As a result of the considerable ambiguity in the literature regarding the viscous coupling effects, the focus of this work is to provide new experimental results on the effect of the viscosity ratio on the oil mobility at the pore scale. Flow visualization experiments are conducted in a 2D etched network micromodel. Observations and measurements are presented.

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