  Creep deformation in shale rocks is an important factor in many applications,
such as the sustainability of geostructures, wellbore stability, evaluation of
land subsidence, CO2 storage, toxic waste containment, and hydraulic
fracturing. One mechanism leading to this time-dependent deformation under a
constant load is the dissolution/formation processes accompanied by
chemo-mechanical interactions with a reactive environment. When
dissolution/formation processes occur within the material phases, the
distribution of stress and strain within the material microstructure changes.
In the case of the dissolution process, the stress carried by the dissolving
phase is distributed into neighboring voxels, which leads to further
deformation of the material. The aim of this study was to explore the
relationship between the microstructural evolution and time-dependent creep
behavior of rocks subjected to chemo-mechanical loading. This work uses the
experimentally characterized microstructural and mechanical evolution of a
shale rock induced by interactions with a reactive brine (CO2-rich brine) and a
non-reactive brine (N2-rich brine) under high-pressure and high-temperature
conditions to compute the resulting time-dependent deformation using a
time-stepping finite-element-based modeling approach. Sample microstructure
snapshots were obtained using segmented micro-CT images of the rock samples
before and after the reactions. Coupled nanoindentation/EDS provided spatial
alteration of the mechanical properties of individual material phases due to
the dissolution and precipitation processes as a result of the chemo-mechanical
loading of the samples. The time-dependent mechanically informed
microstructures were then incorporated into a mechanical model to calculate the
creep behavior caused by the dissolution/precipitation processes independent of
the inherent viscous properties of the mineral phases.
