Effect of an Anionic Surfactant on the Self-Healing Capacity of a Well-Bore Cement Fracture Created in a Microfluidic Flow Cell

Geological carbon sequestration (GCS) is a promising strategy to achieve net-zero emissions and mitigate climate change. However, poor wellbore integrity, including fractures in cement, can serve as conduits for CO2 escape. This study investigates the effect of an anionic surfactant, internal olefin sulfonate (IOS), on self-healing of a cement fracture flushed with CaCl2 amended CO2-saturated water and created in a novel polydimethylsiloxane (PDMS)-encapsulated microfluidic system. Geochemical modeling results indicate mineral precipitation is favored downstream from the fracture inlet after sufficient portlandite cement dissolution, regardless of IOS presence. However, cement fractures only self-heal in the presence of IOS over 12 h, not in its absence. Scanning electron microscopy, X-ray diffraction, and Raman spectroscopy results indicate IOS alters calcium carbonate precipitation dynamics in the fracture, promoting vaterite formation near the inlet, and smaller, more uniform precipitates downstream. Zeta potential measurements indicate IOS adsorption to mineral surfaces creates more negatively charged carbonate mineral surfaces, and self-healing with IOS is attributed to stronger binding of these particles to positively charged cement surfaces. These results highlight the potential for anionic surfactants to enhance GCS security, but work is needed under more representative geochemical conditions to fully assess this fracture healing approach.