Experimental
Observation of Permeability Changes In
Dolomite at CO<sub>2</sub> Sequestration Conditions
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Abstract
Injection
of cool CO<sub>2</sub> into geothermally warm carbonate
reservoirs for storage or geothermal energy production may lower near-well
temperature and lead to mass transfer along flow paths leading away
from the well. To investigate this process, a dolomite core was subjected
to a 650 h, high pressure, CO<sub>2</sub> saturated, flow-through
experiment. Permeability increased from 10<sup>–15.9</sup> to
10<sup>–15.2</sup> m<sup>2</sup> over the initial 216 h at
21 °C, decreased to 10<sup>–16.2</sup> m<sup>2</sup> over
289 h at 50 °C, largely due to thermally driven CO<sub>2</sub> exsolution, and reached a final value of 10<sup>–16.4</sup> m<sup>2</sup> after 145 h at 100 °C due to continued exsolution
and the onset of dolomite precipitation. Theoretical calculations
show that CO<sub>2</sub> exsolution results in a maximum pore space
CO<sub>2</sub> saturation of 0.5, and steady state relative permeabilities
of CO<sub>2</sub> and water on the order of 0.0065 and 0.1, respectively.
Post-experiment imagery reveals matrix dissolution at low temperatures,
and subsequent filling-in of flow passages at elevated temperature.
Geochemical calculations indicate that reservoir fluids subjected
to a thermal gradient may exsolve and precipitate up to 200 cm<sup>3</sup> CO<sub>2</sub> and 1.5 cm<sup>3</sup> dolomite per kg of
water, respectively, resulting in substantial porosity and permeability
redistribution