Pore-Scale Modeling of Drainage Displacement Patterns in Association With Geological Sequestration of CO2

Abstract

We investigate the immiscible displacement (drainage) of a wetting fluid in a porous medium by a nonwetting fluid using multi–graphics processing unit (GPU) lattice Boltzmann simulations with the aim of better understanding the pore-scale processes involved in the geological sequestration of CO2. Correctly resolving the dynamics involved in multiphase flow in permeable media is of paramount importance for any numerical scheme. Generally, the average fluid flow is assumed to be at low Reynolds numbers Reav. Hence, by neglecting inertial effects, this immiscible displacement should be characterized by just two dimensionless numbers, namely, the capillary number Caav and the viscosity ratio, which quantify the ratio of the relevant forces, that is, the viscous and capillary forces. Our investigation reveals that inertial effects cannot be neglected in the range of typical capillary numbers associated with multiphase flow in permeable media. Even as the average Caav and Reav decrease away from the injection point, inertial effects remain important over a transient amount of time during abrupt Haines jumps, when the nonwetting phase passes from a narrow restriction to a wider pore space. The local Rel at the jump sites is orders of magnitude higher than the average Reav, with the local dynamics being decoupled from the externally imposed flow rate. Therefore, a full Navier-Stokes solver should be used for investigating pore-scale displacement processes. Using the Ohnesorge number to restrict the parameter selection process is essential, as this dimensionless number links Caav and Reav and reflects the thermophysical properties of a given system under investigation.