Study on the tribological behaviors of high-temperature-resistant targeted-release microcapsule lubricant

Synthetic ester, alcohol ether and vegetable oil-based lubricants are extensively applied in water-based drilling fluids due to their favorable environmental compatibility and excellent lubricating performance. However, these lubricants are vulnerable to oxidation and hydrolysis at high temperatures, which diminishes their lubricating efficacy and restricts their application in high-temperature deep and ultra-deep wells. To improve the high-temperature stability and persistent lubricity of such lubricants, pentaerythritol oleate (PETO) was encapsulated in silica (SiO 2 ) by the sol-gel method to prepare a high-temperature-stable microcapsule lubricant (PETO@SiO 2 ). At temperatures between 180°C and 240°C, the lubricating qualities of PETO@SiO 2 and neat PETO were evaluated. The results reveal that the microcapsule structure markedly enhances the high-temperature stability and durable lubricity of PETO. A rock-metal friction pair was implemented to evaluate the antiwear performance of PETO@SiO 2 , and it was found that PETO@SiO 2 can significantly increase the surface flatness of lower samples. After hot rolling at 180°C, the wear loss of the sample is reduced by 39.6%. The SiO 2 wall material can isolate the high temperature, sustain the stability of the microcapsule structure, and have a rolling lubrication effect. High shear causes the microcapsules to burst, releasing the PETO core material and creating a lubricating film at the friction interface that lowers torque and friction resistance. This study provides experimental evidence and theoretical support for the design of drilling fluid lubricants for high-temperature deep and ultra-deep wells.