10:15 AM - 10:30 AM
[HSC06-06] Permeability changes during CO2-induced geochemical reactions: a comparison of basalt and andesite
Keywords:Permeability, CO2 geothermal power generation system, CO2-water-rock interaction, Basalt, Andesite
As a means of reducing CO2 emissions into the atmosphere, it has been proposed to use CO2 instead of water to extract heat from a geothermal reservoir. In Japan, the Japan Organization for Metals and Energy Security (JOGMEC) has developed this technique, in which CO2 is injected into hot volcanic rocks, such as basalt and andesite, at temperatures of 200–300°C. Injection of CO2 into hot volcanic rocks enhances geochemical reactions such as mineral dissolution and precipitation, potentially altering permeability. Here, we investigated the influence of CO2-induced reactions on permeability of basalt and andesite and how the permeability change differs depending on the rock type.
Cylindrical cores (30 mm in diameter and 200 mm in length) of basalt from Daikon-jima, Shimane Prefecture, and andesite from Asama-yama, Gunma Prefecture, were used for flow-through experiments. The porosity of the basalt and andesite is 30 % and 22 %, respectively. In the experiments, CO2-dissolved water with pCO2 = 10−14 MPa was injected into the rock core at 200 °C and pore pressure of 10 MPa for 19−42 days.
Injection of CO2-rich water into the basalt induced a continuous decrease in permeability from 2.6 × 10-16 m2 to 3.2 × 10-18 m2, while porosity change was minor (<1 %). The style of CO2-induced reactions varied along the flow direction. Near the inlet, the dissolution of primary minerals was strongly promoted, creating a highly porous reaction zone. The reaction further downstream is represented by less intense dissolution and concurrent phyllosilicate precipitation, forming 1–10 μm-thick phyllosilicate coatings on pore surfaces. Carbonate precipitation was lacking. Clogging of the main flow path due to phyllosilicate precipitation most likely caused the permeability decrease. For andesite, the permeability decreased during the first 7 days, after which the permeability began to increase, reaching approximately three times the initial value at the end of the experiment. Our results suggest that the permeability change due to CO2-induced reactions varies depending on the rock type.
Cylindrical cores (30 mm in diameter and 200 mm in length) of basalt from Daikon-jima, Shimane Prefecture, and andesite from Asama-yama, Gunma Prefecture, were used for flow-through experiments. The porosity of the basalt and andesite is 30 % and 22 %, respectively. In the experiments, CO2-dissolved water with pCO2 = 10−14 MPa was injected into the rock core at 200 °C and pore pressure of 10 MPa for 19−42 days.
Injection of CO2-rich water into the basalt induced a continuous decrease in permeability from 2.6 × 10-16 m2 to 3.2 × 10-18 m2, while porosity change was minor (<1 %). The style of CO2-induced reactions varied along the flow direction. Near the inlet, the dissolution of primary minerals was strongly promoted, creating a highly porous reaction zone. The reaction further downstream is represented by less intense dissolution and concurrent phyllosilicate precipitation, forming 1–10 μm-thick phyllosilicate coatings on pore surfaces. Carbonate precipitation was lacking. Clogging of the main flow path due to phyllosilicate precipitation most likely caused the permeability decrease. For andesite, the permeability decreased during the first 7 days, after which the permeability began to increase, reaching approximately three times the initial value at the end of the experiment. Our results suggest that the permeability change due to CO2-induced reactions varies depending on the rock type.