Hydrogen and CO₂ Co-Storage in Mature Reservoirs: A New Frontier for the Energy Transition

Shokhan Ibrahim, Kaiwan HamaSalih, Sizar Ibrahim, Haval Kukha Hawez

The shift towards low-carbon energy systems necessitates large-scale strategies for managing carbon dioxide (CO₂) and storing renewable energy. Geological formations beneath the Earth's surface, which have been traditionally utilized in the petroleum sector for extracting hydrocarbons, present considerable potential for energy transition technologies like geological carbon storage (CCS) and underground hydrogen storage (UHS). This research assesses the technical viability, geological appropriateness, risks, and future prospects of subsurface energy storage systems. It examines key geological formations such as depleted oil and gas reservoirs, deep saline aquifers, and salt caverns for their storage capacity, containment integrity, and long-term stability. The study delves into significant technological challenges related to subsurface storage, including geomechanical stability, fluid migration, wellbore integrity, and monitoring needs. Additionally, it discusses risk assessment methods and uncertainty quantification techniques to evaluate potential environmental and operational risks. Emerging engineering solutions, such as advanced monitoring technologies, improved reservoir modeling, and enhanced sealing materials, are emphasized as crucial developments for ensuring safe and reliable storage operations. Moreover, the study investigates the integration of geological storage systems with renewable energy infrastructure, particularly focusing on hydrogen as a long-term energy carrier and CCS as a vital strategy for mitigating industrial emissions. Policy frameworks, regulatory governance, and public acceptance are also identified as critical factors influencing the large-scale implementation of these technologies. Overall, the findings indicate that subsurface energy storage offers a promising route for supporting global decarbonization efforts, while highlighting the need for ongoing research, technological innovation, and interdisciplinary collaboration to tackle remaining technical and societal challenges.