Convective Heat Transfer Coefficients of Newtonian and Non-Newtonian Geothermal Drilling Fluids

Abstract

This paper deals with the estimation of convective heat transfer coefficients (CHTCs) of Newtonian and non-Newtonian geothermal drilling fluids for both the drill pipe and annulus of a geothermal well while drilling. Five empirical correlations were used to calculate the CHTC for fully developed laminar and turbulent flow conditions. Transport properties of Newtonian drilling fluids represented by water and non- Newtonian drilling fluids, measured in the rheology laboratory, were compared and later used for calculating CHTCs in the temperature interval of 50 to 180 °C. It was found that the viscosities of Newtonian and non-Newtonian drilling fluids as function of temperature may differ by up to 98%, and thus viscosity is one of the main properties that affect the estimation of the CHTC. Such differences are reflected in the estimated values of the CHTC of Newtonian and non-Newtonian drilling fluids which differ by up to 390% and thus strongly affect the estimation of wellbore temperatures by means of numerical thermal simulators under drilling fluid circulation.