Undoubtedly, the extraction of oil and gas from the reservoirs requires drilling processes. Drilling fluid is also required to perform drilling processes. The drilling fluid has several applications and one of its functions is to cool the bit. Normally, drilling fluids used in the world have a relatively low ability to transfer the heating from the bit. Therefore, cooling the bit is not done well. Therefore, solutions to increase the efficiency of drilling fluids in the field of heat transfer should be proposed. It is obvious that specific surface area is one of the variables affecting heat transfer. In other words, if the specific surface area of the drilling fluid molecules increases, the rate of heat transfer will increase. Since nanoparticles have a very high specific surface area, their use can be suggested. Because nanoparticles have a very high specific surface area, they can be used in the structure of drilling fluid components. Therefore, in this study titanium dioxide nanoparticle and carbon nanotube have been used to change the thermo-physical properties of drilling fluid. Results show the amount of specific heat increases about 1.26% by decreasing the size of titanium dioxide nanoparticles from 76 nm to 54 nm. In addition, experimental results show that the ratio of convective heat to conductive heat for drilling fluid integrated with carbon nanotubes is about 30% higher than drilling fluid integrated with titanium dioxide nanoparticles. Results show that the rate of heat transfer coefficient increases from about 2900/m(2). degrees C to about 4000 W/m(2). degrees C by decreasing the size of titanium dioxide nanoparticles from 76 nm to 54 nm. Also, it has been observed that the convective heat transfer coefficient increases from 2950 W/m(2). degrees C to 3360 W/m(2). degrees C by decreasing the average size of the carbon nanotubes from 76 nm to 54 nm. (C) 2021 Elsevier B.V. All rights reserved.