Geothermal energy is emerging as a promising sustainable energy resource, particularly with increasing interest in exploiting high-temperature, high-pressure (HTHP) reservoirs. The use of downhole acoustic well logging tools is vital for monitoring casing and cement integrity. However, the development of technology for diagnostics in such extreme conditions remains challenging. Conventional acoustic well logging tools fail to obtain reliable measurements for prolonged periods under the combined effects of high pressure and temperature during exposure to highly corrosive fluids present in geothermal wells. Therefore, there is a need to better ruggedize acoustic logging tools for reliable operation and survival in these harsh conditions. We developed two design approaches to evaluate the passive cooling mechanisms of candidate material composites under HTHP conditions. The first approach focused on thermal energy storage by including layers of Phase Change Materials (PCMs) embedded between silicon aerogel insulation layers. The second method incorporated a vacuum layer enclosed between alternating PCM and silicon aerogel layers. Both designs were evaluated by implementing heat transfer equations in COMSOL Multiphysics under the finite element framework. We employed Fourier’s law and the conservation of energy equation to evaluate thermal resistance and heat flow in both configurations under HTHP condition. Results demonstrated that PCM layers significantly delayed temperature breakthrough by absorbing and storing thermal energy during phase change. Moreover, the hybrid PCM-silicon aerogel configuration significantly outperformed a single aerogel layer supporting enhanced thermal resistance and heat transfer delay at HTHP conditions. The second design with vacuum encapsulated between PCM and aerogel layers displayed the best thermal performance demonstrating the added benefits of controlling latent heat absorption/release. Our designs demonstrate a high potential for passive cooling via thermal energy storage and insulation essential in extended downhole acoustic monitoring of casing and cement integrity.

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