Numerical study of the effects of contact angle and viscosity ratio on the dynamics of snap-off through porous media

摘要

Snap-off is a pore-scale mechanism occurring in porous media in which a bubble of non-wetting phase displacing a wetting phase, and vice-versa, can break-up into ganglia when passing through a constriction. This mechanism is very important in foam generation processes, enhanced oil recovery techniques and capillary trapping of CO2 during its geological storage. In the present study, the effects of contact angle and viscosity ratio on the dynamics of snap-off are examined by simulating drainage in a single pore-throat constriction of variable cross-section, and for different pore-throat geometries. To model the flow, we developed a CFD code based on the Finite Volume method. The Volume-of-fluid method is used to track the interfaces. Results show that the threshold contact angle for snap-off, i.e. snap-off occurs only for contact angles smaller than the threshold, increases from a value of 28 degrees for a circular cross-section to 30-34 degrees for a square cross-section and up to 40 degrees for a triangular one. For a throat of square cross-section, increasing the viscosity of the injected phase results in a drop in the threshold contact angle from a value of 30 degrees when the viscosity ratio (mu) over bar is equal to 1 to 26 degrees when (mu) over bar = 20 and down to 24 degrees when (mu) over bar = 20.