Rock-CO2-water reactions

Monitoring physical and elastic rock changes in rock-CO2-water reactions

Fluid-rock reactions (FRR) produce mineral dissolution and precipitation in subsurface settings, such as fluid conducting faults and volcanoes. Seismic waves can be used to monitor FRR, because FRR alters the elastic parameters of the rocks. However, rock core measurements are needed to quantify the correlation between field seismic data and the process of FFR. We are currently analyzing changes to the rock microstructure in sandstones and basaltic rocks and study ways to monitor such changes with elastic waves in laboratory measurements, borehole logs and seismic.

SEM images of basalt samples and carbonate precipitations.
SEM images of basalt samples and carbonate (crb) precipitations.

 

In Adam et al. (2013) we found that carbonates precipitated in microfractures of Snake River Plain Basalt samples, stiffening the rock and reducing the rock permeability.

Time lapse laser-ultrasonic scans on a basalt sample. Note the direct P-wave arrival time is shorter (faster velocities) after 15 and 30 weeks of CO2-water-basalt reactions
Time lapse laser-ultrasonic scans on a basalt sample. Note the direct P-wave arrival time is shorter (faster velocities) after 15 and 30 weeks of CO2-water-basalt reactions

In Kanakiya et al. (accepted to JGR 2017) we observed that carbonates (mostly ankerite) precipitate due to CO2-basalt reactions. However, rock  dissolution affects the physical properties of the rock more significantly than carbonate precipitation. We obseved that there is a correlation between volcanic glass content and dissolution for Auckland Volcanic Field basalt samples.

Electron microprobe photographs of carbonates                                                  Correlation between rock dissolution (loss of mass) and glass

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