Solubility Trapping Of CO2: Analog Experiment and Three-Dimensional Numerical Modeling

Jayabrata Dhar (1) , François Nadal (2) , Tanguy Le Borgne (1) , Patrice Meunier (3) , Yves Méheust (1)

1 GR - Géosciences Rennes
2 Loughborough University
3 IRPHE - Institut de Recherche sur les Phénomènes Hors Equilibre

Solubility trapping is one of the trapping mechanisms by which CO2 can be stored in deep aquifers. The CO2 being less dense than the resident brine, it rises to the top of the aquifer, above the brine, after injection. It is also partially miscible into the brine, so a layer of CO2-brine mixture appears at the interface between the brine and CO2. This mixture happens to be denser than the brine, which triggers a gravitational instability. The subsequent convection, fuelled by the continuous partial dissolution of CO2 at the top, allows irreversible storage to occur at the bottom of the aquifer. Most studies of this complex process have so far been performed using Darcy scale (mostly 2D) simulations and Hele-Shaw-based experiments. In order to unravel the timescales and efficiency of this solubility trapping, we have simultaneously developed a lab experiment based on a granular porous medium and a 3D numerical model. We first study the gravitational instability, convection and mixing without coupling to the continuous partial dissolution at the upper boundary of the system, using analogue fluids. The largest dimension of the medium is 45 cm, while the grain size ranges between 1mm to 3mm. The optical index of the lower, less dense, fluid is matched to that of the transparent solid grains, which renders the medium transparent and allows for optical visualization of the convection’s 3D structure. This visualization is based on a laser dye that is added to the denser liquid, and on swiping the medium with a laser sheet. Simultaneously, a numerical 3D in-house code is developed using the multigrid method solution and finite difference approximation, to better understand the instability phenomenon and convection development. The flow is modelled using the Brinkman equation, with the permeability and porosity corresponding to those measured in the experimental setup. The present Multigrid solver developed has the advantage of being fast and can run in parallel for large systems. We attempt to achieve consistency between the pore-scale results of the experiments and the Darcy-scale results of the simulation. We characterize the trapping efficiency as a function of the medium’s permeability, and the miscibility and density difference of the two fluids.

Domains: Fluid Dynamics [physics.flu-dyn]

Jayabrata Dhar, François Nadal, Tanguy Le Borgne, Patrice Meunier, Yves Méheust. Solubility Trapping Of CO2: Analog Experiment and Three-Dimensional Numerical Modeling. European Geosciences Union General Assembly 2019, Apr 2019, Vienne, Austria. , 21, pp.EGU2019-17594, 2019, Geophysical Research Abstracts. ⟨insu-02090913⟩