Characteristics of drilling fluids at low temperature range and heat transfer model between casing pipe and strata

This paper presents the thermophysical and rheological properties of water-base drilling fluids at low temperature range (-5 to 20°C) expected for the fluid temperature of the offshore drilling at the Nankai Trough. These physical properties are fundamental data for the drilling simulator and also design factors for a heat exchanger to cool down the drilling fluids. The measurement systems for the rheological and thermal characteristics, such as thermal conductivity and heat capacity, have been set up. The drilling fluid density were varied from 1100 to 2000 kg/m³ (9.16 to 16.7 ppg) using barite. Especially, the drilling fluids with high salt concentration were mainly focused in present measurements. Then, the experimental equations against the fluids density for the thermal and rheological properties have been presented in order to estimate the parameters used in the simulations. Furthermore, a simplified estimation for heat transfer rate at casing pipe has been carried out using the measurement data to investigate the effect of the property changes in the casing pipe.