The codes and data generated in this study.

The codes and data generated in this study.</p

Experimental Observation of Permeability Changes In Dolomite at CO₂ Sequestration Conditions

Injection of cool CO₂ 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, CO₂ saturated, flow-through experiment. Permeability increased from 10^–15.9 to 10^–15.2 m² over the initial 216 h at 21 °C, decreased to 10^–16.2 m² over 289 h at 50 °C, largely due to thermally driven CO₂ exsolution, and reached a final value of 10^–16.4 m² after 145 h at 100 °C due to continued exsolution and the onset of dolomite precipitation. Theoretical calculations show that CO₂ exsolution results in a maximum pore space CO₂ saturation of 0.5, and steady state relative permeabilities of CO₂ 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 cm³ CO₂ and 1.5 cm³ dolomite per kg of water, respectively, resulting in substantial porosity and permeability redistribution

Experimental Observation of Permeability Changes In Dolomite at CO₂ Sequestration Conditions

Injection of cool CO₂ 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, CO₂ saturated, flow-through experiment. Permeability increased from 10^–15.9 to 10^–15.2 m² over the initial 216 h at 21 °C, decreased to 10^–16.2 m² over 289 h at 50 °C, largely due to thermally driven CO₂ exsolution, and reached a final value of 10^–16.4 m² after 145 h at 100 °C due to continued exsolution and the onset of dolomite precipitation. Theoretical calculations show that CO₂ exsolution results in a maximum pore space CO₂ saturation of 0.5, and steady state relative permeabilities of CO₂ 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 cm³ CO₂ and 1.5 cm³ dolomite per kg of water, respectively, resulting in substantial porosity and permeability redistribution

Permeability Reduction Produced by Grain Reorganization and Accumulation of Exsolved CO₂ during Geologic Carbon Sequestration: A New CO₂ Trapping Mechanism

Carbon sequestration experiments were conducted on uncemented sediment and lithified rock from the Eau Claire Formation, which consisted primarily of K-feldspar and quartz. Cores were heated to accentuate reactivity between fluid and mineral grains and to force CO₂ exsolution. Measured permeability of one sediment core ultimately reduced by 4 orders of magnitude as it was incrementally heated from 21 to 150 °C. Water-rock interaction produced some alteration, yielding sub-μm clay precipitation on K-feldspar grains in the core’s upstream end. Experimental results also revealed abundant newly formed pore space in regions of the core, and in some cases pores that were several times larger than the average grain size of the sediment. These large pores likely formed from elevated localized pressure caused by rapid CO₂ exsolution within the core and/or an accumulating CO₂ phase capable of pushing out surrounding sediment. CO₂ filled the pores and blocked flow pathways. Comparison with a similar experiment using a solid arkose core indicates that CO₂ accumulation and grain reorganization mainly contributed to permeability reduction during the heated sediment core experiment. This suggests that CO₂ injection into sediments may store more CO₂ and cause additional permeability reduction than is possible in lithified rock due to grain reorganization