To permanently remove CO2 from the atmosphere large scale injection of CO2 from stationary sources such as coal fired power plant and heavy oil production into brine filled formation is seen as one of the most viable options. One of the main risks identified with storing CO2 into the subsurface is the potential for leakage through existing wells penetrating the cap rock. The wellbore system has several components which can fail and create leakage paths such as type and placement of wellbore casing and cements, completion method, abandonment and wellbore expansion or contraction by changes in temperature and pressure. Of the 1000 wells in the study area near Lake Wabamun, Alberta 95 wells penetrated the immediate cap rock above the proposed Nisku injection formation and was identified as potential leakage pathways. The leakage risk of these wells was evaluated based on the knowledge of well design, current well status and historical regulation’s in the area. For the subset of 27 well studied on only 4 wells were identified as wells requiring work over which was less of a problem than anticipated. To evaluate the risk of creating leakage paths by thermal and pressure changes caused by CO2 injection, a three dimensional finite-element model was built which used elasto-plastic material models for cement and formation. Multi-stage simulations for casing-cement and cement-formation interactions with temperature enabled elements were conducted. Because of the uncertainty on cement properties in old wells, a parametric study of cement properties was conducted. The simulation results indicated that thermal cooling might reduce near-wellbore stresses which will increase risk of integrity loss in casing-cement and cement-formation. The parametric study reviled that the risk of debonding and tensile failure will increase with increasing Young’s modulus and Poisson’s ratio of the cement under dynamic loading conditions. In addition, low mechanical cement strength will increase risk of shear failure in the cement.