Residual and Solubility trapping during Geological CO2 storage : Numerical and Experimental studies

Abstract: Geological storage of carbon dioxide (CO2) in deep saline aquifers mitigates atmospheric release of greenhouse gases. To estimate storage capacity and evaluate storage safety, knowledge of the trapping mechanisms that retain CO2 within geological formations, and the factors affecting these is fundamental. The objective of this thesis is to study residual and solubility trapping mechanisms (the latter enhanced by density-driven convective mixing), specifically in regard to their dependency on aquifer characteristics, and to investigate and develop methods for quantification of CO2 trapping in the field. The work includes implementation of existing numerical simulators and inverse modeling, as well as the development of new models and experimental methods for the study and quantification of CO2 trapping.A comparison of well-test designs in regard to their abilities to estimate the in-situ residual gas saturation (that determines the residual trapping of CO2) is presented, as well as a novel indicator-tracer approach to obtain residual gas saturation conditions in a formation. The results can aid in the planning of well-tests for estimation of trapping potential during site characterization.Pore-network modeling simulations were conducted to study the effects of co-contaminant sulphur dioxide and formation thermodynamic and salinity conditions on residual CO2 trapping.Furthermore, an analysis tool was developed and used to study the prerequisites for density-driven instability and convective mixing over broad geological storage conditions, including the relative influences of formation characteristics on factors controlling the convective process. The results show which conditions favour or disfavour residual and solubility trapping, knowledge useful for long-term predictions of the fate of injected CO2, and safety assessments during site selection.An optical experimental method, the refractive-light-transmission (RLT) technique, and an analogue system design were developed for studying density-driven flow in porous media. The method exploits changes in light refraction to visualize convective flow, and incorporates a calibration procedure and an image post-processing scheme that enable quantification of solute concentration, density and viscosity within porous media. The experimental setup was used to study the dynamics of convective mixing, and to derive scaling laws for the onset time and mass flux of convection.