Preparation of medium temperature phase-change nanocapsules for thermal regulation of deep well drilling

Nanoencapsulated phase-change material containing urea was synthesized by an interfacial polymerization method using SiO 2 as shell material. The physicochemical properties of the nanocapsules were characterized through various techniques. The nanocapsules were evaluated for acid and alkali resisting performance, wear resistance, cyclohexane recycling and drilling fluid circulation. The melting temperature, latent heat, encapsulation ratio and yield of nanocapsule were determined to be 133.4 °C, 183.5 J/g, 84.7% and 93.7%, respectively. After 100 melting-freezing cycles, the melting latent heat and freezing latent heat still maintained at 175 J/g and 164.3 J/g. The inclusion of these nanocapsules did not alter the fundamental properties of the drilling fluid, yet it reduced the peak temperature. Besides, the as-prepared nanocapsule showed a good reusability, and the difference in cooling effect between the two cooling experiments did not exceed 1.5 °C. Therefore, the urea@SiO 2 nanocapsule is found to be a promising candidate for thermal regulation of deep well drilling.