In this study, thermophysical properties of graphene nanosheets � hydrogenated oil based nanofluid was investigated for the improvement of drilling fluids. Graphene nanosheets powder were dispersed through two-steps method which utilizes hydrodynamic and acoustic cavitation (HAC) combination process. The weight concentrations of dispersed graphene nanosheets powder in this study are 25 ppm, 50 ppm and 100 ppm respectively. The thermophysical properties investigated include thermal conductivity and rheological properties of graphene nanosheet � hydrogenated oil based nanofluid. At the highest nanoparticle concentration, thermal conductivity (TC) enhancement is able to reach up to 14.4 at 50 °C while viscosity and shear stress values increased up to 33 at 30 °C. Both properties are observed to increase with respect to nanoparticle concentrations. The TC models were able to predict consistently with experimental data at lower nanoparticle concentration but underpredicted at higher nanoparticle concentration. The Bingham model has proven to fit well with the rheological data obtained in this study. Cavitation number, K and coefficient of discharge, CD parameters used to evaluate hydrodynamic cavitation dispersion were found to be 1.025 and 0.3313 respectively. Both parameters had denoted that hydrodynamic cavitation had taken place in the system successfully. © 2017 Elsevier Ltd