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

Abstract

Snap-off is a pore-scale mechanism occurring in porous media in which a bubble of nonwetting 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 CO 2 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 • for a circular cross-section to 30-34 • for a square cross-section and up to 40 • 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 • when the viscosity ratio µ is equal to 1 to 26 • when µ = 20 and down to 24 • when µ = 20.

Preferential Paths of Air-water Two-phase Flow in Porous Structures with Special Consideration of Channel Thickness Effects

“…Since the effect of preferential flow will be remarkable in leading the non-equilibrium fluid flow subsurface, accurate knowledge and description the preferential paths and interfacial dynamic of immiscible two-phase flow in rock mass and its influence factors are of great significance for the evaluation of oil or gas recovery 1,2 and predication of roadway rock disasters 3 due to the gas-liquid flow. Many studies have been conducted to analyze preferential flow in order to explore the influence factors including wettability 4–6 , capillary pressure 7,8 , injection rate 9 , viscosity ratio 6 and capillary number 10 . However, few experimental and numerical studies are available for quantitatively and visually elaborating the fundamental processes of preferential flow in real rock structures through the effect of pore morphology and channel size, due to the complexity and heterogeneity of porous structures of natural rocks.…”

Droplet breakup in the square microchannel with a short square constriction to generate slug flow

“…Roof 12 theoretically analyzed the droplet breakup in a microconstriction under the assumption that the oil droplet moved at a negligible velocity (i.e., quasistatic breakup), and concluded that the droplet breakup occurred in a microconstriction when the capillary pressure of the droplet head was equal to that of the neck. This conclusion was widely verified at extremely low droplet velocity and laid a foundation for the research on droplet breakup in more complicated constrictions 13–19 . However, Roof's 12 breakup criterion was not applicable in a larger range of droplet velocity.…”

“…This conclusion was widely verified at extremely low droplet velocity and laid a foundation for the research on droplet breakup in more complicated constrictions. [13][14][15][16][17][18][19] However, Roof's 12 breakup criterion was not applicable in a larger range of droplet velocity. Wang et al 20 and Liang et al 21 experimentally investigated the breakup of the droplet flowing through a locally constrictive microchannel at a nonignorable velocity (i.e., dynamic breakup), concluding that the daughter droplet size was underestimated based on Roof's 12 theory.…”

On the concept of macroscopic capillary pressure in two-phase porous media flow

“…For the sake of simplicity, the viscosity ratio is taken equal to 1. A numerical study on the effects of viscosity ratio on the two-phase flow dynamics in constricted pore-throat geometries can be found in Starnoni and Pokrajac (2018). Boundary conditions consist of prescribed pressure at the outlet and velocity equal to 5 mm/s at the inlet.…”