Mechano-Chemical Interactions within Engineered Barrier-Geomaterial Interfaces

Coupled chemical and mechanical interactions can lead to leakage pathway development at cement-geomaterial interfaces, reducing the effectiveness of engineered cement barriers against acidified leakage contaminants. We examine chemical/mechanical interactions, acoustic coupling, and pathways to failure in controlled triaxial benchtop experiments, which monitor real time cement-granite interface degradation in situ by ultrasonic and chemical methods, and pre- and post-experiment using microindentation and microCT imaging. Full waveform analysis shows a decrease in a fracture interface wave speed indicating a reduction in fracture specific stiffness likely following portandite dissolution from the surrounding cement matrix, followed by an increase stiffness as the experiment progresses. The sensitivity of the interface wave to fracture conditions make these modes a potential tool for the detection of interface alteration in wellbores. Tomographic images show detailed development of three-dimensional leaching patterns involving reaction fronts migrating from the interface as well as wormhole development within the interface. Results are being used to validate a coupled computational fluid dynamics/mechanics code using COMSOL Multiphysics^TM. Future plans call for using the validated coupled chemo-mechanical model specifically in analyzing the spatio-temporal evolution of other types of interface alteration including carbonation and sulfonation, and in general as a predictive tool for assessment of cement barrier integrity.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525. The interface wave analysis by CW & LJPN was based upon work supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy (EERE), Office of Technology Development, Geothermal Technologies Office. SAND2019-9021 A