T22 Science of Geologic Carbon Sequestration

Sunday, 18 October 2009
8:00 AM - 12:00 PM
D135/136

CARBON SEQUESTRATION IN BASALTIC ROCKS: EXPERIMENTAL RESULTS AND GEOCHEMICAL MODELING

Paper number: T22-4
Program: Technical Sessions
Time: 8:50 AM – 9:05 AM

Authors

Abstract

Basaltic rocks have potential as reservoirs for carbon dioxide (CO2) sequestration because of their high capacity for mineral trapping of CO2 in the form of divalent metal carbonate minerals such as calcite, magnesite, siderite, and dolomite. We carried out a suite of geochemical models and experiments, reacting basalt with CO2-charged fluids over a range of conditions from 50°C to 150°C and from 100 bars to 300 bars. Experiments were conducted in flexible gold-cells with a serial online fluid sampling capability that allows for monitoring reaction progress. Experiments were also carried out in fixed-volume titanium reaction cells to investigate batch reactions. We conclude that basalt has a high reactivity to supercritical CO2 and carbonic acid. Moreover, batch experiments reacting olivine basalt with supercritical CO2 at 100°C, 300 bars PCO2 for two months produced almost complete alteration of the rock with 90% of the divalent cations (primarily Mg, Fe, and Ca) having been incorporated into carbonates.

In experiments with basalt and CO2-charged fluids that were under-saturated with respect to CO2, initial reaction caused a rapid drop in fluid pH and an increase in dissolved cations including Ca, Mg, Fe, and Mn then a decline toward steady-state values. An asymptotic CO2 decrease to steady-state concentrations was found to follow a repeatable pattern after re-injection of CO2 into the experiment. These results showed that the basalt continued to have a capacity to react with CO2.

Predictions based on reaction path simulations suggested that calcite would initially precipitate then dissolve following the sequential addition of PCO2 and would be later replaced by dolomite and siderite at final equilibrium. In contrast to model prediction, SEM analyses of the solid reaction products found only Fe- and Mg-bearing phases. These results are consistent with important kinetic barriers to forming dolomite. Continued experiments are underway to optimize conditions for basalt reaction with CO2.