Stability of a leakage pathway in a cemented annulus

The risk minimization of carbon dioxide (CO2) storage relies to some extent on well integrity assurance. While chemical reactions between the constitutive materials of the wellbore - such as cement - and stored CO2 do not jeopardize the efficiency of a defect-free cement sheath, the reactive flow through an existing pathway in a cemented annulus may alter its initial properties, and thus change the associated risk. On one hand, the cement will react with the CO2 rich fluid, and be leached away by the leaking flow. On another hand, under specific conditions, the released minerals can re-precipitate downstream and clog the pathway. The evolution of a CO2 leak through a pre-existing leak path in the cement sheath is examined theoretically and numerically. A numerical model of the flow has been built, that takes into account the particular physics and geometry of the problem. The governing equations are investigated in order to identify the driving mechanisms and define the dimensionless groups that rule the process, leading to a reduction in the dimension of the parameters space. We use this analysis to predict the domain of stability of the defect by extracting a general criterion corresponding to the clogging conditions. (C) 2011 Published by Elsevier Ltd.