Basalt Reactivity Variability with Reservoir Depth in Supercritical CO2 and Aqueous Phases

Journal Article · Fri Apr 01 00:00:00 EDT 2011 · Energy Procedia

DOI:https://doi.org/10.1016/j.egypro.2011.02.468· OSTI ID:1036424

Schaef, Herbert T; McGrail, B Peter; Owen, Antionette T

Long term storage of CO{sub 2} in geologic formations is currently considered the most attractive option to reduce greenhouse gas emissions while continuing to utilize fossil fuels for energy production. Injected CO{sub 2} is expected to reside as a buoyant water-saturated supercritical fluid in contact with reservoir rock, the caprock system, and related formation waters. As was reported for the first time at the GHGT-9 conference, experiments with basalts demonstrated surprisingly rapid carbonate mineral formation occurring with samples suspended in the scCO{sub 2} phase. Those experiments were limited to a few temperatures and CO{sub 2} pressures representing relatively shallow (1 km) reservoir depths. Because continental flood basalts can extend to depths of 5 km or more, in this paper we extend the earlier results across a pressure-temperature range representative of these greater depths. Different basalt samples, including well cuttings from the borehole used in a pilot-scale basalt sequestration project (Eastern Washington, U.S.) and core samples from the Central Atlantic Magmatic Province (CAMP), were exposed to aqueous solutions in equilibrium with scCO{sub 2} and water-rich scCO{sub 2} at six different pressures and temperatures for select periods of time (30 to 180 days). Conditions corresponding to a shallow injection of CO{sub 2} (7.4 MPa, 34 C) indicate limited reactivity with basalt; surface carbonate precipitates were not easily identified on post-reacted basalt grains. Basalts exposed under identical times appeared increasingly more reacted with simulated depths. Tests, conducted at higher pressures (12.0 MPa) and temperatures (55 C), reveal a wide variety of surface precipitates forming in both fluid phases. Under shallow conditions tiny clusters of aragonite needles began forming in the wet scCO{sub 2} fluid, whereas in the CO{sub 2} saturated water, cation substituted calcite developed thin radiating coatings. Although these types of coatings were sparse, conditions corresponding to deeper depths showed increasing carbonate precipitation. Basalts exposed to aqueous dissolved CO{sub 2} (25.5 MPa, 116 C) for 30 days were coated in tiny nodules of precipitate ({approx}100 {micro}m in diameter) that were identified by micro x-ray diffraction as ankerite, [Ca(Fe,Mg)(CO{sub 3}){sub 2}], a variety of dolomite commonly associated with hydrothermal and metamorphic environments. Surface characterization by SEM revealed well-developed round nodules composed of discrete individual platelets. In contrast, reaction products forming on the basalt in the corresponding wet scCO{sub 2} phase had completely different morphology, appearing in an optical microscope as a surface coating instead of discrete nodules. Examination by SEM revealed layers of discrete platelets forming a cover over a few discrete nodules. Longer test durations (180 days) produced severe iron staining along with minerals structures similar to rhodochrosite and kutnohorite. These preliminary experiments show strong evidence of the faster rate of increase in mineralization reactions taking place in the scCO{sub 2} phase, transformation reactions that are just beginning to be explored in detail.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1036424
• Report Number(s): PNNL-SA-74778; AA3010000; TRN: US201206%%297
• Journal Information: Energy Procedia, Vol. 4
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
54 ENVIRONMENTAL SCIENCES
ANKERITE
AQUEOUS SOLUTIONS
ARAGONITE
BASALT
BOREHOLES
CALCITE
CARBON DIOXIDE
CARBONATE MINERALS
CARBONATES
CATIONS
COATINGS
DOLOMITE
GEOLOGIC FORMATIONS
GREENHOUSE GASES
INTERSTITIAL WATER
IRON
MINERALIZATION
MORPHOLOGY
OPTICAL MICROSCOPES
PRECIPITATION
RESERVOIR ROCK
SURFACE COATING
X-RAY DIFFRACTION
carbon sequestration
mineralization