Naphthenic acids that are naturally carboxylic compounds contained in heavy crude oil are the main source of corrosion and blockage in a crude oil pipeline. The blockage is due to the formation of naphthenate deposits through a reaction of naphthenic acid with metal ions present in the crude oil. In the present study, model oil is used to evaluate the effect of water cut in the range of 10�90, brine pH in the range of 6�10, Ca2+ concentration in the range of 0.5�2.5 and temperature in the range of 30 °C�60 °C towards naphthenate deposition with the aid of response surface methodology. Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared (FTIR) were used to evaluate the structure of the naphthenic acids used. Results show that Ca2+ concentration contributes mostly to the naphthenate deposition, followed by brine pH, water cut and temperature. Two mathematical models were developed to predict the final pH of the oil-brine system and the mass of precipitates with average relative errors (AREs) of 0.0328 and 0.0325 respectively. The effects of two ionic liquids (ILs), 1-ethyl-3-methylimidazolium chloride (EMIM-Cl) and 1-butyl-3-methylimidazolium chloride (BMIM-Cl), on naphthenates precipitation, were also evaluated. Analysis showed that both ILs can reduce the amount of naphthenate deposited, with the BMIM-Cl showing better performance than the EMIM-Cl. © 2021