Monitoring CO2 injection in the Kızıldere geothermal field

Abstract

High-enthalpy geothermal systems in Turkey emit significant amounts of non-condensable gases (NCGs), primarily CO₂, during energy production. Recent advances in carbon capture and storage technologies have enabled low emissions by re-injecting produced CO₂. However, CO₂ injection carries risks, necessitating proper evaluation due to potential buoyant migration and leakage. Monitoring is essential before, during, and after CO₂ re-injection to ensure the gas is not transported to the surface through fault zones or well cement failure. As part of the GECO H2020 project, 980 tons of CO₂ were captured from the Kızıldere III geothermal power plant and injected as dissolved in effluent water over six months into the Kızıldere reservoir. This study aims to demonstrate the behavior of injected CO₂ by tracking the CO₂-effluent fluid mixture, evaluating the chemistry of geofluids from neighboring production wells, analyzing shallow groundwater quality, and monitoring soil CO₂ fluxes. The four-year survey established a baseline before CO₂ re-injection and observed changes afterward. To determine the movement of injected CO₂ within the reservoir, a 2.6 Naphthalene DiSulfonate tracer was injected. The tracer reached all nearby observation wells and confirmed the hydraulic connection between the wells. Monitoring revealed that injected CO₂ is predominantly stored as dissolved CO₂ in the reservoir water rather than through mineral sequestration. There were no significant changes in shallow groundwater composition and soil CO₂ fluxes before, during, and after the CO₂ injection. This successful pilot demonstration showed that CO₂ injection reduces emissions from the power plant and enhances re-injection efficiency by facilitating carbonate dissolution in the reservoir. These findings suggest that similar CO₂ injection strategies could improve re-injection performance in other geothermal fields with carbonate-bearing reservoir lithologies and enhance natural pumping effects at production wells. Such advancements could lead to reduced operational costs and promote sustainable geothermal energy production with net-zero emissions.