Experimental calibration of a numerical model describing the alteration of cement/caprock interfaces by carbonated brine

In this manuscript we focus on the development of geochemical model that describes the alteration of both the cement and the caprock. In our experiments, chemical alteration of the cement significantly exceeded any dissolution of carbonate minerals within the caprock and fracture geometry played no role on the extent of reaction. The experimental data was used to calibrate a numerical model of wellbore-caprock interfaces coupling reaction-front chemistry, fluid flow and transport of dissolved species. The geochemical model adopts an idealized representation of the cement chemistry in which appropriate equilibrium conditions are enforced at a series of discrete reaction fronts. The equilibrium conditions are coupled by diffusive transport between the fronts, which also determines the rate of front propagation. Despite its simplicity, the calibrated model accurately reproduces the reaction-zone growth and effluent chemistry for the range of experimental conditions considered and allowed key parameters to be confirmed or calibrated. These include the use of portlandite, calcite, and analcime solubility as equilibrium controls at specific reaction fronts within the cement; the use of constant effective diffusivity for each alteration zone; and diffusive growth of the alteration layers.