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Reduction of proven gas and oil reserves and increasing demand for energy forces the petroleum industry to drill deeper and more complicated wells. Drilling in these harsh environments requires drilling fluids with specific characteristics. So, improvement of the drilling fluids that can act as proper fluids at high pressure and high temperature conditions is vital in the drilling industry. The purpose of this study is examining the effects of SnO2 nanoparticles on the properties of drilling fluids and determining of the extent of improvement of water‐based drilling fluids performance. These nanoparticles were added to polymeric water‐based drilling fluids in various concentrations of 1, 2.5, 5, and 7.5 g/L in the presence of KCl at concentrations of 5, 15, 30, 60, and 100 g/L. The experiments were done at temperatures of 30, 50, 70, and 90 °C. Electrical conductivity, thermal conductivity, and thixotropy of the resulting drilling fluids were investigated. Moreover, filtration of the drilling fluids at room temperature, 65, and 95 °C and pressures of 0.6895 MPa (100 psig) and 2.758 MPa (400 psig) and various nanoparticle concentrations were studied. It was found that electrical conductivity and thermal conductivity were increased by 30 % and 15 %, respectively. Finally, in order to have more accurate hydraulic calculations, five rheological models were studied and compared together. It was observed that the Herschel‐Bulkley‐Papanastasiou model showed the highest accuracy with an absolute relative error of 1.1 %.

In petroleum industries, nanofluids have the potential to improve the characteristics of the fluids used in drilling wells or Enhanced Oil Recovery (EOR) processes. In this study, a water based mud containing polymer was considered as the base fluid. Different concentrations of TiO2 nanoparticle (0, 0.5 and 0.75 wt%) and different concentrations of KCl salt (0, 0.5, 1.5, and 3 wt%) were added to the base fluid and exposed to different temperatures (30, 50, 70 and 90 °C) with 19 different shear rates for investigating the effects of nanoparticle concentration, salt concentration, temperature and shear rate on viscosity of the base mud. Presence of TiO2 particles enhanced not only the rheological behavior but also electrical and thermal conductivity of fluid up to 25% and 43%, respectively. Furthermore, the stability of the fluid containing salt and nanoparticle was investigated in these temperatures owing to the fact that the temperature could cause degradation of the fluid. For the purpose of investigating this phenomenon, the after cooling experiment was conducted. In addition, the data gathered in this investigation were examined by using three famous rheological models (Power law, Herschel-Bulkley and Herschel-Bulkley-Papanastasiou models) and the rheological parameters of each model were determined.