Laboratory and Theoretical Results from Investigations of CO2 Solubility in Geothermal Reservoirs

Abstract

This paper considers the idea of CO2 injection into deep thermal reservoirs. The application of this research is either to the goal of carbon sequestration or the use of CO2 as the working fluid in an Engineered Geothermal Systems (EGS). Sequestration may occur in a number of ways such as via: solubility trapping, mineralization, impermeable caprocks, or capillary forces. This research presents evidence for a new phenomenon named “active phase change” (APC), which refers to the combined effect of CO2 solubility with standard hydrodynamics on the multiphase flow of CO2 and water through porous media. Laboratory experiments and theoretical work were designed to investigate thermodynamic effects that may occur when solubility is taken into account. A core-scale experiment measured relative permeabilities in the two-phase system, a micromodel experiment qualitatively observed the dynamic dissolution phenomenon, and theoretical analyses put the findings in context and provided a framework to predict results under varied conditions. The purpose of this research was to analyze and quantify the magnitude of dissolution effects through laboratory and theoretical work. An additional goal was to evaluate the time and length-scales of dissolution and diffusion effects relative to standard hydrodynamic behavior. This paper concludes with recommendations for improvements to the experimental set-up and for future work.