Deep saline aquifers are considered as a promising option for long-term storage of carbon dioxide. However , risk of CO2 leakage from the aquifers through faults , natural or induced fractures or abandoned wells cannot be disregarded. Therefore , modeling of various leakage scenarios is crucial when selecting a site for CO2 sequestration and choosing proper operational conditions. Carbon dioxide is injected into wells at supercritical conditions (t˚ > 31.04 ˚C , P > 73.82 bar) , and these conditions are maintained in the deep aquifers (at 1-2 km depth) due to hydrostatic pressure and geothermal gradient. However , if CO2 and brine start to migrate from the aquifer upward , both pressure and temperature will decrease , and at the depth of 500-750 m , the conditions for CO2 will become subcritical. At subcritical conditions , CO2 starts boiling and the character of the flow changes dramatically due to appearance of the third (vapor) phase and latent heat effects. When modeling CO2 leaks , one needs to couple the multiphase flow in porous media with geomechanics. These capabilities are provided by Dynaflow , a finite element analysis program ; Dynaflow has already showed to be efficient for modeling caprock failure causing CO2 leaks [2 , 3]. Currently we have extended the capabilities of Dynaflow with the phase transition module , based on two-phase and three-phase isenthalpic flash calculations . We have also developed and implemented an efficient method for solving heat and mass transport with the phase transition using our flash module. Therefore , we have developed a robust tool for modeling CO2 leaks. In the talk we will give a brief overview of our method and illustrate it with the results of simulations for characteristic test cases. References:  J.H. Prevost , DYNAFLOW: A Nonlinear Transient Finite Element Analysis Program. Department of Civil and Environmental Engineering , Princeton University , Princeton , NJ. http://www.princeton.edu/~dynaflow/
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