Permeability of serpentinized harzburgite and its implications on mineral carbon storage

Storage of anthropogenic CO₂ as permanent carbonate minerals has emerged as a promising method for control of carbon dioxide. One approach consists of injecting low-pH, CO₂-rich water in ultramafic rock that serves as a buffering medium. Accordingly, the rock dissolution will increase the solution pH such that carbonate minerals can precipitate. The permeability of the rock matrix, however, plays an important role in the buffering (dissolution) process and controls chemical reaction rates. Using X-ray diffraction spectroscopy (XRD), we analyzed the composition of the (i) vein filling material in a serpentinized harzburgite, and (ii) matrix adjacent to the vein. The XRD analysis showed that hydrated carbonates mineralized in the vein as well as the intact matrix adjacent to the surface. Permeability of the serpentinized rock matrix adjacent to the vein surface was then measured using the pulse decay approach. It is shown that a permeability on the order of 10^-21 m² and rock matrix with less than 25% serpentine minerals allowed for fixing CO₂ as thermodynamically stable, hydrated carbonate minerals in the matrix.