Deep eutectic solvent modified graphene as a lubricant for water-based drilling fluid

Deep and ultra-deep drilling technology development is critical to the exploitation of ultra-deep oil and gas deposits. As the number of ultra-deep wells increases, the bottom hole temperature of certain ultra-deep wells approaches 250°C. The high-temperature and high-pressure environment can influence the stability and longevity of drilling instruments, as well as the density, rheology, and stability of drilling fluid, making wellbore stability difficult to maintain. Problems such as high torque and high friction affect the safety of downhole drilling and drilling efficiency. Adding lubricant to drilling fluid is an effective way. In this study, choline chloride (ChCl) and polyethylene glycol (PEG) were used to synthesize a deep eutectic solvent (DES), and an environmentally friendly water-based drilling fluid lubricant DES/G was prepared by compounding the DES with graphene (G). Infrared spectrum, particle size analysis, and electron microscope tests were used to characterize the structure of the lubricant. At the same time, the effect of lubricant was evaluated by extreme pressure lubricity tester and friction and wear tester, and the adhesion coefficient of filter cake was tested. At temperatures below 200°C, DES/G demonstrated a significant enhancement in the lubricating properties of drilling fluids and filter cakes. The adhesion coefficient was controlled within 0.1, and the reduction rate was exceeding 30%. With increasing dosage of the lubricant, DES/G consistently maintained a low adhesion coefficient value of 0.03803 to 0.06253 (at 180°C) and 0.0414 to 0.07337 (at 200°C). Furthermore, it exhibited higher values of reduction rate, reaching a maximum of 64%. The lubricant can increase lubricating performance by adsorbing on the metal surface to generate a strong lubricating coating and converting the sliding friction between drilling tools to rolling friction.