Influence of Carbon Dioxide on Micro-cracking in Calcite: An Atomistic
Scale Investigation
Abstract
In candidate formations for geological Carbon Capture and Storage (CCS),
carbonate minerals (e.g., calcite) are ubiquitously presented. The
dynamic process of chemically induced alteration on carbonate-rich
reservoirs due to the injection of supercritical CO2 holds paramount
importance for achieving an economic injectivity and structural
integrity of the system. How carbonate rocks undergo deterioration and
particularly how microcracks develop in the presence of carbon dioxide
remain largely unknown. Here we employ a powerful tool of reactive force
field (ReaxFF) molecular dynamics (MD) simulation, investigating into
the impact of representative CO2 environments on Mode I tensile crack
propagation in calcite at micro-scale. Our simulation results
demonstrate that (1) both dry and wet CO2 environments favor the tensile
crack propagation by lowering the fracture toughness of the pre-existing
crack; (2) the wet CO2 environment promotes the growth velocity of the
subcritical crack compared to the dry CO2 environment, under the same
mechanical loading condition; (3) the interaction between the stressed
crack and the CO2-water mixture diffusing into the crack opening leads
to a small reduction of the system potential energy at an initial stage
of subcritical growth; (4) The crack tip appears to be sharper in both
dry CO2 and wet CO2 environments, albeit at a lower stress intensity
factor than the vacuum case. The atomistic scale findings provide new
insights on the process of subcritical calcite cracking induced by a
reactive environment via CO2 injection, prior to the damage-enhanced
dissolution phase.