Quantification of CO2 trapping through free convection process in isothermal brine saturated reservoir

Abstract:

Dissolution trapping of supercritical CO₂ into formation brine has been touted as a mechanism for reducing buoyancy force in carbon storage formations. This study attempts to quantify exactly how much CO₂ can be stored through dissolution trapping assuming the free CO₂ will be dissolved continuously on the top of perturbed brine phase. To our knowledge, most former investigations focused on physical explanations of density-driven free convection instability. Our aim is to compute the amount of CO₂ (by mass) captured by dissolution trapping until the model reservoir reaches steady state. The numerical experimentation is done using dimensionless mass and momentum conservation laws. Reservoir is impervious from both sides and bottom, only open to CO₂ at the top. The major problem parameter here is the solutal Rayleigh number of which we carry out an extensive survey to find out low and high ends based on real field data. Because density difference is the main driving force, we also investigate the effects of possible impurities retained in CO₂ stream and the resulting effect on density contrast. We study results of both homogeneous and heterogeneous permeable reservoirs. Also, computations of zero gradient and zero flow boundary conditions are compared to understand the boundary effects. In all cases we set to run simulations for extended period of times (> 20,000 years) to achieve conclusive results.