A review of conventional and alternative cementitious materials for geothermal wells

Geothermal energy is a promising alternative to conventional fossil-based energy sources. Geothermal reservoirs are pools of water heated by magma deep below the Earth's crust, the steam of which can be used to power turbines or pass through heat pumps. Recovering this heat to the surface requires construction and subsequent cementation of subsurface geothermal wells. The conditions to which the cemented annulus is exposed are frequently harsher and more extreme than that of oil and gas wells. Cement slurries used in geothermal wells are vulnerable to acidic and carbon dioxide-rich brine and temperatures above 500 °C. Overall, well failure is a consequence of degradation of cemented annuli and cracking due to exposure to these severe conditions. This literature review addresses the durability problems associated with the use of inadequate cementing materials for such harsh conditions. New alternative cementitious formulations that have been developed in response to the weaknesses of conventional cementing materials are discussed. Relevant studies are compiled and broken into main sections such as current cementing methods and challenges, alternative cementitious materials, monitoring systems, and environmental impact. This work introduces a thorough analysis of materials from the early 1950s until 2021 identifying the significant knowledge gaps. These gaps include designing chemical additives for geothermal well cements and understanding the broad chemical composition of alternative cementitious materials. The review also proposes promising sources for potential geothermal well cements based on technologies in other harsh environments, such as marine and fire-prone applications.