Mechanical and hydraulic coupling in cement–caprock interfaces exposed to carbonated brine

This paper investigates the effects of carbonated brine induced reaction zones on the mechanical and hydraulic properties of fractures and interfaces in wellbore cement. We present results from a suite of core flood experiments in which carbonated brine was introduced into artificial fractures separating wellbore-cement and tight-sandstone half-cores. We describe how the propagation of the resulting reaction zones affected the hydraulic aperture of the core flood samples, and how these changes are related to the fracture geometry. We also examine the influence of the altered mechanical properties on the hydraulic aperture: by testing the mechanical properties of the individual reaction layers using nano-indentation; and by analyzing the deformation of the cores as a whole with a combination of X-ray tomography and digital image correlation. Based on the experimental data, we propose a model describing the relationship between the reaction layers and the mechanical response of the cement interfaces, and discuss the implications for the long time behavior of wellbore cement interfaces – illustrated by means of a numerical simulation.