Formation of an amorphous silica gel barrier under CO2 storage conditions

Risk assessments of Carbon Capture and Storage (CCS) have identified that in some instances carbon dioxide (CO2) leakage through the caprock cannot be entirely precluded, e.g. through high permeability undetected zones. This study recommends the use of a geochemical barrier that forms upon reaction with CO2, as a means to mitigate and remediate CO2 leakage. The proposed technology is based on the injection of an alkaline sodium silicate solution that reacts with the leaking CO2, leading to silica gel formation. Laboratory studies undertaken to evaluate this technology, included flow-through and core-flood experiments at ambient and reservoir conditions, respectively. The tests aim was to assess the barrier formation performance by changes in pressure as an indicator of permeability reduction. Results show that the formation of the silica barrier was controlled by the mixing gradient of the two reactants, where the reaction resulted in a permeability reduction between one and three orders of magnitude under reservoir conditions. Thus, using sodium silicate as a reagent for forming a barrier is a promising technology to abate CO2 leakage for CCS purposes. Further research using reactive transport modelling to investigate barrier formation in a reservoir model is needed before applying this technology at the field scale.