Abstract
The peridotite section of the Samail Ophiolite in the Sultanate of Oman offers insight into the feasibility of mineral carbonation for engineered, in situ geological CO.sub.2 storage in mantle peridotites. Naturally occurring CO.sub.2 sequestration via mineral carbonation is well-developed in the peridotite; however, the natural process captures and sequesters CO.sub.2 too slowly to significantly impact the concentration of CO.sub.2 in the atmosphere. A reaction path model was developed to simulate in situ CO.sub.2 mineralization through carbonation of fresh peridotite, with its composition based on that of mantle peridotite in the Samail Ophiolite and including dissolution kinetics for primary minerals. The model employs a two-stage technique, beginning with an open system and progressing to three different closed system scenarios- a natural system at 30[degrees]C, an engineered CO.sub.2 injection scenario at 30[degrees]C, and an engineered CO.sub.2 injection scenario at 90[degrees]C. The natural system model reproduces measured aqueous solute concentrations in the target water, signifying the model is a close approximation of the natural process. Natural system model results suggest that the open system achieves steady state within a few decades, while the closed system may take up to 6,500years to reach observed fluid compositions. The model also identifies the supply of dissolved inorganic carbon as the limiting factor for natural CO.sub.2 mineralization in the deep subsurface. Engineered system models indicate that injecting CO.sub.2 at depth could enhance the rate of CO.sub.2 mineralization by a factor of over 16,000. CO.sub.2 injection could also increase mineralization efficiency - kilograms of CO.sub.2 sequestered per kilogram of peridotite - by a factor of over 350. These model estimates do not include the effects of precipitation kinetics or changes in permeability and reactive surface area due to secondary mineral precipitation. Nonetheless, the faster rate of mineralization in the CO.sub.2 injection models implies that enhanced in situ peridotite carbonation could be a significant sink for atmospheric CO.sub.2.