Modeling of Wellbore Cement Core-Flood Experiments

We present a theoretical model of our core-flood experiments in which brine saturated with carbon dioxide (CO₂) is injected through fractured core samples composed of wellbore cement mated with caprock. When exposed to the CO₂-saturated brine, the cement undergoes a series of reactions that leads to the dissolution of minerals like calcium into the brine. These reactions have implications for the long-term efficacy of subsurface CO₂ sequestration, because they may affect the fracture permeability and the mechanical properties of the wellbore cement. The effluent chemistry data from the experiments show that the excess calcium concentration obey a 'super-diffusive' growth. We find that a good match with experimental data can be achieved by introducing a term that represents a constant background source of calcium. Our model provides explanations for the physical origin of this source term.