Nanotechnology comprises oil treatment processes because they occur on the nano-scale and involve interaction of charged mono- and polyvalent ions found in the interacting oil and reservoir water. A mathematical model for thermochemical dehydration of oil is proposed considering the specific features (nano-scale effects) of oil emulsion formation and breaking. Procedures for estimating the effectiveness of the intermediate emulsion layer and analytical expressions for determining the residence time of oil emulsions in settlers of thermochemical oil treatment facilities are proposed.