(389h) Effect of Calcite Dissolution On the Leakage Through Abandoned Wells in Geological CO2 Storage

Deep saline aquifer is used for the CO₂ and radioactive waste disposal geological storage. Several works have been published in the last few decades that describe the CO₂ storage in deep saline aquifer (Holger C. et al., 2009; Andreas K. et al., 2010; George S.H. Pau, 2010;…). During the last years the behavior of CO₂ and other substances in the groundwater has become of great interest, since techniques are developed and investigated to inject CO₂ in the subsurface in order to counteract the greenhouse effect. A very undesirable effect would be the leakage from the storage. When the CO₂ injection is made into the brine layer in oil or gas field production, The greatest risk for escape of CO₂ may come from other wells, typically those for oil and gas production, which penetrate the storage formation. Injection of CO₂ in the subsurface leads to a relatively rapid response (decrease) on the pH. This decrease will then be buffered by mineral reactions, such as calcite dissolution. Calcite dissolution can induce an increase in the porosity and can enhance further leakage and provide more pathways for the CO₂ (K. Caldeira, G.H. Rau, 2000). The majority of the studies quantify these hydrogeological systems using traditional multi-phase flow model and do not consider the effects of the density dependent flow and the chemical reactions. Interdependence of density dependent flow and chemical reactions and their effects on the porosity and permeability are the most important keys towards a better knowledge of these coupled processes for the design of safer installations. The density dependent multi-phase flow and reactive multispecies model GEODENS (Bouhlila and Laabidi, 2008) is presented here and used to simulate the effects of the calcite dissolution on the flow patterns around a CO2 injection well and on the leakage through abandoned wells in a deep carbonate layer. The simulated domain is 1000 × 160 × 1 m and concerns a vertical slice confined aquifer separated by a thin aquitard, a leaky well is located at the centre of the domain and an injection well is 100 m away. A constant head boundary is applied in the two lateral boundaries (Nordbotten, J.M., Celia, M.A., 2006). The target of the first simulation is to quantify the leakage of CO2 from the aquifer through the leaky well, and the second simulation consists on the evaluation of the effect of the geochemical reactions (calcite dissolution and precipitation) on this leakage ratio.