Geothermal energy is attractive because it helps secure energy supply, mitigate climate change, and comply with future green energy policies. The GeoVision study estimates a potential 26-fold increase from 2019 geothermal energy production levels to 60 GW by 2050 in the United States (Bromley et al., 2010;Dobson et al., 2017;Fan, 2020;Hamm, 2019). To expand geothermal energy production, enhanced geothermal system (EGS) is a key candidate technology (Tester et al., 2006). Hydraulic fracturing is a stimulation method for EGS, where high injection pressures are used to create tensile fractures. Hydroshearing is another closely related stimulation method where fluid injection increases pore pressures and then triggers slip along pre-existing fractures. Both
Wellbore integrity analysis should consider the cement setting process in a confined downhole environment, noting that cement is initially a liquid that becomes a solid. In our study, the state of stress of cement specimens is measured during cure from a liquid to a solid at laboratory simulated downhole conditions. We apply accurate control of axial stress, confining pressure, and pore pressure inside cement specimens during the entire setting process combined with strain gauges mounted on the outer surface of the steel pipe to measure the cement's state of stress during the setting process. The setup allows multiple experimental conditions to be investigated, including constant axial stress, constant axial displacement, drained and undrained conditions. Different controlling conditions represent different field scenarios since the process of cement setting in the downhole situations is a highly complex process that depends on the in-situ condition, formation lithology, cement slurry composition, mud cake composition, drill bit type, etc. In this work, the Class-G cement slurry is cured under constant axial stress, confining pressure, and undrained conditions. This represents a field condition where the top of the cement can drop during setting, the vertical component of cement weight is not significantly affected by bonding, and the formation is quite impermeable with a very difficult fluid exchange between formation and cement. Our results show that under such a scenario, no significant pressure drop occurs after seven days of the setting process, and the cement initial total stress is close to its hydrostatic pressure.
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