Phase change material microcapsules for smart temperature regulation of drilling fluids for gas hydrate reservoirs

In natural gas hydrate drilling operations, hydrate decomposition can lead to serious wellbore instability. In this study, the use of encapsulated phase change materials (PCMs) is proposed to smartly regulate the temperature of drilling fluids to inhibit hydrate decomposition. PCM microcapsules containing tetradecane in the core and a melamine-urea-formaldehyde resin as the shell were prepared by in-situ polymerization. The structure and properties of the PCM microcapsules were characterized, the temperature-regulating performance of the microcapsule and its effect on borehole stability were analyzed, and the compatibility was evaluated. The results showed that the melting point and latent heat of the PCM microcapsules were 6.7 °C and 116 J/g, respectively. The surface of microcapsules was hydrophilic and negatively charged, and the shell had good shear strength and sealability. PCM microcapsules effectively reduced the heating/cooling rate and the highest temperature of aqueous suspensions, thus decreasing the borehole enlargement rate. The temperature-regulating performance was unchanged after 15 heating/cooling cycles. After adding 5–10 wt% microcapsules, the rheological and filtration properties of the water-based drilling fluid remained in a reasonable range, indicating that the PCM microcapsules were compatible with drilling fluids. This study provides a new method for inhibiting hydrate decomposition in gas hydrate drilling.