Time-Lapse Seismic Monitoring of Co2 Injection and Storage at the Hellisheiði Geothermal Field, Iceland

Geothermal energy originates from the Earth's core and is stored in rocks and fluids underground. Although geothermal energy is generally considered a clean energy source in terms of environmental impact, large-capacity geothermal power plants can emit significant amounts of CO2 as part of the generated steam. Carbon capture, utilisation and underground storage (CCUS) and developments for the use of geothermal resources are priorities for future clean and renewable energy strategies. One of the main objectives of the SUCCEED (Synergetic Utilisation of CO2 storage Coupled with geothermal EnErgy Deployment) project is to provide a state-of-the-art, cost-effective, and low-environmental impact geothermal CO2 storage monitoring technique. The feasibility of this system has been demonstrated at the Reykjavik Energy (OR) Hellisheiði geothermal field in Iceland, where re-injection of produced CO2 is taking place to permanently store the CO2 in the basaltic reservoir formation through mineralisation. In this work, we focus on the time-lapse active seismic-reflection survey carried out at the Hellisheiði field. The baseline and the time-lapse surveys were conducted during the summers of 2021 and 2022, respectively. The aim of the time-lapse (4D) survey was to detect possible seismic differences that can be related to the migration of the CO2 in the reservoir, demonstrating the effectiveness of a new, low-environmental-impact, electric seismic vibrator (E-Vibe) specially designed for the survey, and Helically Wound Cable (HWC) Distributed Acoustic Sensing (DAS) as a tool for CO2 monitoring in a time-lapse perspective. This is a challenging task as conventional seismic-reflection techniques commonly deliver poor quality data in volcanic environments because of scattering, attenuation and static problems.