1:45 PM - 3:15 PM
[HSC04-P06] Influence of hydrothermal reactions on permeability of basalt
Keywords:CO2 ehnaced geothermal system, Basalt, Permeability, Mineral-water reactions
The injection of CO2 into an Enhanced Geothermal System (CO2-EGS) for geothermal energy production is proposed as a means of reducing CO2 emissions into the atmosphere. In the CO2-EGS, water in the reservoir is acidified by the dissolution of injected CO2, which promotes the mineral dissolution. Mineral dissolution releases divalent ions such as Ca2+, Mg2+, and Fe2+, resulting in precipitation of carbonate minerals. Such geochemical reactions caused by CO2 injection are likely to change porosity and pore size of the reservoir, which in turn may change the permeability. Here, as a preliminary study of reservoir permeability before CO2 injection, we investigated how the permeability changes by the geochemical reactions under the flow of hot water.
We conducted a flow-through experiment using a basalt core from Rishiri Island, Japan, because basalt formation is considered one of potential reservoirs in an ongoing CO2-EGS project in Japan. The basalt is mainly composed of plagioclase, glass, and pyroxene. Connected porosity and mean pore radius are 7.5 % and 0.6 μm, respectively. For the flow-through experiment, we developed a hot supercritical CO2 flow-through apparatus designed to flow water, supercritical CO2, and their mixture through a long core 200 mm in length at a maximum. The maximum temperature that can be used is 300 °C. By applying a constant differential pressure to the basalt core, hot water was flowed at 250 °C and the flow rate was monitored for 23 days. Pore pressure and confining pressure are 10 MPa and 14-15 MPa, respectively.
The result shows that the basalt has a low permeability of ~4 x 10−20 m2. The flow rate is approximately constant for 23 days of the hot water flow, suggesting that mineral dissolution and precipitation under the hot water flow did not significantly affect the permeability. Our result may reflect that when the hot water infiltrates into the low-permeable basalt, the solute concentration increases to the equilibrium concentration of minerals, which retards mineral dissolution. We will conduct the flow-through experiment using a hot CO2-dissolved water to investigate the effect of dissolution and precipitation on the permeability in the presence of CO2.
We conducted a flow-through experiment using a basalt core from Rishiri Island, Japan, because basalt formation is considered one of potential reservoirs in an ongoing CO2-EGS project in Japan. The basalt is mainly composed of plagioclase, glass, and pyroxene. Connected porosity and mean pore radius are 7.5 % and 0.6 μm, respectively. For the flow-through experiment, we developed a hot supercritical CO2 flow-through apparatus designed to flow water, supercritical CO2, and their mixture through a long core 200 mm in length at a maximum. The maximum temperature that can be used is 300 °C. By applying a constant differential pressure to the basalt core, hot water was flowed at 250 °C and the flow rate was monitored for 23 days. Pore pressure and confining pressure are 10 MPa and 14-15 MPa, respectively.
The result shows that the basalt has a low permeability of ~4 x 10−20 m2. The flow rate is approximately constant for 23 days of the hot water flow, suggesting that mineral dissolution and precipitation under the hot water flow did not significantly affect the permeability. Our result may reflect that when the hot water infiltrates into the low-permeable basalt, the solute concentration increases to the equilibrium concentration of minerals, which retards mineral dissolution. We will conduct the flow-through experiment using a hot CO2-dissolved water to investigate the effect of dissolution and precipitation on the permeability in the presence of CO2.