Paper No. 300-5
Presentation Time: 2:30 PM
MODELING CO2-WATER-BASALT REACTIONS EFFECT TO FRACTURE ALTERATION IN A BASALT FRACTURE NETWORK
Anthropogenic CO2emissions are strongly implicated in increasing global temperatures and other serious environmental issues. Carbon capture and sequestration (CCS) is an engineering-based approach designed to reduce the total mass of atmospheric CO2 releases. Recently, basalt formations have been shown to accommodate rapid mineral trapping of injected CO2. In basalt reservoirs, CO2 dissolution in formation water releases H+ to drive mineral dissolution of olivine and pyroxene, which releases divalent cations (Ca2+, Mg2+, Fe2+) that react with bicarbonate to form secondary mineral phase, e.g., calcite, magnesite, siderite. Research investigating multiphase CO2-brine flows in the fracture basalt formations shows that CO2 tends to accumulate at fracture intersections before diverging into branching fractures, where CO2 relative permeability and mobility are low. This later study implies the following hypotheses: (1) secondary mineral precipitation focuses at the branching fracture as a result of CO2accumulation in fracture intersections and (2) secondary alteration at fracture intersections inhibits the vertical migration of gas phase CO2 resulting from fracture permeability decrease. In order to test these hypotheses, five numerical simulations with different permeability alteration effects are implemented in a 2.5 m × 2.5 m basalt fracture system with one single fracture in the middle. The aperture of this fracture is 5 cm, and it diverges into two branching fractures with 90o at the height 2/5 of the model. Results from this study show that (1) carbonate and clay minerals focus at the branching fractures, where the system is dominated by diffusion and (2) gas phase CO2 vertical migration is inhibited by mineral precipitation, which causes fracture permeability decrease. In addition, a mass balance is used to test the carbonation efficiency in the fracture system with different permeability alteration exponents. It shows a large carbon mineralization ratio with permeability alteration, and this provides support that the fracture system could turn into a self-sealing system resulting from secondary mineral precipitation. In conclusion, permeability alteration resulting from carbon mineralization should be considered when modeling the CO2 sequestration in basalt reservoirs.