High temperature thermal regulation supramolecular phase change microcapsule: Cucurbit [7]uril encapsulated erythritol based on a biochar framework

In ultra-deep well drilling, downhole thermal damage (DTD) poses significant challenges for oil, gas, and geothermal resource development. This study introduces a supramolecular phase change microcapsule (CLE) made from erythritol (Ery), loofah biochar (LB), and cucurbit[7]uril (CB[7]) aimed at mitigating DTD through solid-liquid phase change thermal regulation. Ery fills LB's pores, forming a multi-walled core-shell structure, while CB[7] enhances binding strength through esterification and hydrogen bonding. CLE exhibits excellent leakage resistance, thermal conductivity (0.9167 W/m·K), melting enthalpy (242.5 J/g), and stability over 1000 cycles. When added to oil-based drilling fluid (OBDF) at 3 wt%, it increases stability by 23%, reduces fluid loss by 44%, and improves lubricity by 41%, while showing some corrosion inhibition on M42 steel. Under heating, the OBDF with CLE reaches 149.8 °C compared to 153.5 °C for the base fluid, resulting in a ΔT of 3.7 °C, signifying a 15% slower thermal increase rate. In conclusion, this study not only designs stable, recyclable, high thermal conductivity, and high latent heat phase change materials (PCMs), but also provides a novel thermal regulation strategy for ultra-deep well drilling operations.