Simulation of Physical-Chemical Processes During Carbon Dioxide Sequestration in Geological Structures

Abstract

AbstractUnderground storage of carbon dioxide, CO2, is one way to reduce atmospheric releases of greenhouse gases. The sequestration of CO2 in a depleted gas reservoir is simulated, incorporating molecular diffusion between CO2 and the natural gas, dispersion, dissolution of CO2 in water, and chemical reactions of the CO2 with the aqueous phase and host rock.This study is applied to a depleted gas reservoir located in the North of Italy. Since the end of production the field has been used for gas storage, and in this work it has been considered for a pilot project of CO2 injection. The different physical and chemical phenomena acting in the reservoir are simulated to investigate their influence on the total storage capacity. The effect of injection rate, the point of injection and the purity of the injection fluid are analyzed.While molecular diffusion of CO2 in methane can be neglected, the dissolution of CO2 in water increases the maximum storage capacity. Both the pattern of reservoir heterogeneity and the degree of mechanical dispersion has a notable impact on the results. Particular attention should be given to the composition of the injection fluid, because the presence of impurities strongly affects the total stored mass.Low injection rates give a larger total stored mass, since gravitational forces act to transport the CO2 to the top of the aquifer, but only after long periods of injection. Near the gas/water contact, the residual gas saturation has a significant impact on storage.Precipitation reactions render the CO2 immobile in a solid phase, but over a very long timescale.