In the quest to decarbonize the energy sector, researchers are delving into innovative geothermal power generation methods that could revolutionize how we harness Earth’s heat. A recent study published in Energies, the International Journal of Energy, has shed new light on the interactions between carbonated water and basaltic rocks, a critical component in the development of CO2 geothermal power systems. This research, led by Sakurako Satake from the University of Toyama’s Graduate School of Sustainability Studies for Research, offers promising insights into the future of geothermal energy.
Japan, with its ambitious goal of achieving carbon neutrality by 2050, is at the forefront of exploring new renewable energy sources. Geothermal power, which taps into the Earth’s heat, holds immense potential. The country’s geothermal resources could theoretically provide up to 20% of its electricity needs, but current utilization is a mere fraction of that capacity. One of the main challenges is the limited availability of geothermal fluids in high-temperature areas, making traditional geothermal power generation difficult.
Enter CO2 geothermal power generation, a novel approach that uses supercritical CO2 as the heat transfer medium. This method involves injecting supercritical CO2 into geothermal reservoirs, where it heats up and is then extracted to drive turbines. The advantage? CO2 has a lower boiling point than water, making it more efficient in low-temperature and low-pressure conditions. This could significantly expand the areas suitable for geothermal power generation and improve overall efficiency.
However, the interaction between injected CO2 and the surrounding rocks and water is complex and not fully understood. This is where Satake’s research comes in. Her team conducted laboratory experiments to investigate how carbonated water reacts with basaltic rocks, a common type of rock found in geothermal reservoirs. The experiments involved reacting basalt from Rishiri Island with distilled water at high temperatures (250°C) and varying CO2 concentrations over 15 days.
The results were enlightening. “We found that the pH of the fluid remained acidic throughout the experiment, which prevented the formation of carbonate minerals,” Satake explained. Instead, the primary reaction was the dissolution of chemical components from the rock, particularly the glassy parts of the basalt. This means that in the vicinity of the injection well, the supercritical CO2 fluid and carbonate water would likely flow through the spaces between the rocks without significantly altering the permeability.
This finding has significant implications for the energy sector. It suggests that CO2 geothermal power systems could be more feasible than previously thought, as the injection of CO2 would not necessarily lead to rapid clogging of the reservoir. Instead, the CO2 could flow through the rock, heating up and being extracted to generate power. Over time, as the CO2 concentration decreases or the fluid mixes with existing geothermal fluids, the pH could increase, leading to the precipitation of carbonate minerals and other secondary minerals.
The study, published in Energies, is just the first step in understanding these complex interactions. Future research will involve long-term experiments and testing with different types of geothermal reservoir rocks, from basalt to granite. This work could pave the way for more efficient and widespread use of CO2 geothermal power generation, contributing to Japan’s carbon neutrality goals and potentially revolutionizing the global energy landscape.
As the world seeks to transition to cleaner energy sources, innovations like CO2 geothermal power generation offer a glimpse into a future where we can harness the Earth’s heat more effectively and sustainably. With continued research and development, this technology could play a crucial role in reducing carbon emissions and mitigating climate change. The energy sector is watching closely, and the potential impacts are substantial.
