Stanford Geothermal WorkshopFebruary 9-11, 2026

As the world population increases by the day, so does the energy demand. Along with this phenomenon, global warming is taking its toll on the climate. Therefore, to address these issues, sustainable and green energy production is required, in which geothermal energy plays a crucial role. It is a clean, renewable, and continuous source of energy that remains in operation mode for more than 90% of the time and is not weather-dependent. To ensure the smooth transition of energy from the subsurface to the well head, the well integrity has to be assured. The main component that controls well integrity is the well cement and casing. In a geothermal environment, these barriers are exposed to severe thermal cycling and high-temperature gradients that can induce mechanical stress, create microannuli, and impact long-term material degradation, posing significant risks to well integrity. Therefore, it is important to properly analyze cement properties before placing it in the geothermal well. In that respect, this paper presents the experimental results of the impact of thermal loading on the interfacial bonding strength of the Class G cement, which is the most commonly used cement in the wells. The method utilizes a novel apparatus that incorporates an ISCO pump to quantify the interfacial debonding strength of the cement. The preparation of the cement was according to the API standard, after which it was poured into 2-inch diameter, 6-inch long steel pipes and was cured for 14 days. To simulate the geothermal well condition, the samples were exposed to 5 and 10 thermal cycles loading at 95 °C. In one cycle, there is 1 hour of heating and 3 hours of cooling. From the testing, it was noted that before the debonding of the sample occurs, a leakage of water, termed the “wetting phase,” is observed at a pressure lower than that of the interfacial debonding pressure. It was also observed that cyclic loading had an impact on the debonding strength, which decreased as the number of cycles increased. Hence, it was concluded that the primary mode of failure was caused by shear debonding, which is facilitated by the creation of microannuli at the interface between the casing and the cement, and is exacerbated by thermal loading. Therefore, before cement placement, it should be ensured that the cement debonding strength is sufficient to resist thermal loading and maintain its integrity throughout the project's life. Otherwise, the subsurface fluid can make its way to shallower formations and ultimately reach the surface, which will jeopardize the success of the geothermal project.

Topic: Drilling