Evaluation of potential nonisothermal processes and heat transport during CO_2 sequestration

摘要

Injection of CO_2 may perturb subsurface temperatures, leading to a dynamic temperature system in the storage formation and adjacent seal strata. In most cases, the individual effects from wellbore dynamics, solvation reactions, and phase changes are incremental, but collectively these relevant processes may cause significant temperature changes compared to ambient conditions. In this work, we evaluated several potential nonisothermal effects resulting from CO_2 injection activity. These include the Joule-Thomson (heating and cooling) effect, exothermic CO_2 dissolution, and heat changes associated with concomitant water vaporization. Results suggest that three effects: a) the adiabatic (de-) compression of CO_2, b) the frictional energy losses, and c) conductive heat exchange between the injected CO_2 and surrounding fluid/rock, govern the resulting CO_2 thermal profiles within an injection well. In addition, as supercritical-phase CO_2 comes into contact with formation brine, the CO_2will dissolve into the aqueous phase, and such dissolution is exothermic at typical conditions for CO_2 sequestration. However, we still seek a better understanding of heat effects associated with water vaporization into the supercritical-phase CO_2. Finally, sensitivity studies, simulating supercritical-phase CO_2 injection into a 1-D radially symmetric domain, are conducted to evaluate the magnitude of different heat disequilibrium potentials and spatial location in the CO_2 plume affected by thermal processes. In addition, time-scales associated with migration rates of temperature fronts, pressure pulses, and dissolved- and supercritical-phase CO_2 profiles are investigated with a function of heat capacities of rock, different effective thermal conductivities, penneabilities, and porosities. Our results demonstrate that adiabatic CO_2 compression occurring in injection wells could have the most significant impact on the temperature change whilst the exothermic CO_2 dissolution occurred at the largest spatial domain.