Temperature Influenced Mechanical Stability of Oilwell Cements in Geothermal Operations

Summary Well integrity during geothermal operations are critical, with cementing playing a major role in providing zonal and thermal isolation, casing support and preventing unwanted fluid migration. Traditional oilwell cements (Class C, G, and H) and fly ash-based geopolymers were tested under simulated geothermal conditions to assess their long-term mechanical performance. Over 1,500 samples were cured at temperatures ranging from 25°C to 85°C and tested for uniaxial compressive strength (UCS) after up to 30 days. While higher temperatures accelerated early strength development, samples cured at room temperature ultimately exhibited superior long-term UCS. Class G cement displayed the highest peak UCS (50–60 MPa), making it suitable for high-pressure, high-temperature (HPHT) environments. However, all cement types showed strength degradation at elevated temperatures, with up to 20% reduction in UCS. In contrast, geopolymers demonstrated more consistent and stable mechanical performance across a range of temperatures (averaging 35–45 MPa), indicating their potential as viable alternatives for geothermal wells. The study highlights the need for extended evaluation of cement behavior under real-world geothermal conditions, as thermal cycling and long-term exposure can lead to strength regression and potential well integrity issues. These insights are critical for designing safer, more efficient cement jobs for geothermal projects.