Thermal and rheological properties improvement of drilling fluids using functionalized carbon nanotubes

The application of functionalized/unfunctionalized (multi-walled) carbon nanotubes (CNT) was investigated in the context of formulating nano-based drilling fluids from water/oil-based fluid templates. CNT functionalization was attempted by applying hydrophilic functional groups onto the surface of the nanotubes via acid treatment. Experimental data were collected for thermal conductivity, viscosity/yield point, and filtrate amount in all samples. The time evolution of thermal conductivity was studied, as well as the effects of temperature and CNTs volume fraction on the parameter. Scanning electron microscopy (SEM) was used to monitor CNTs dispersion quality. The thermal conductivity results unveil considerable enhancements, by as much as 23.2 % (1 % vol. functionalized CNT) in CNT-water-based case at ambient temperature, with extended improvement of 31.8 % at an elevated temperature of 50 °C. Corresponding results for the CNT-oil-based case exhibit an improvement in thermal conductivity by 40.3 % (unfunctionalized) and 43.1 % (functionalized) and 1 % volume fraction of CNT. The rheological results follow an analogous improvement trend. For the CNT-oil-based case, the filtration tests conducted at 138 °C and 500 (psi) show a 16.67 % reduction in filtrate amount (1 % vol. CNT). The time evolution of thermal conductivity was found to nearly equalize (at an amount of 9.7 %) after 100 h of sample preparation in both functionalized and unfunctionalized CNT-oil-based cases.