A transient wellbore temperature model for deepwater drilling considering the thermal resistance of mud cake formed by drilling fluid invasion

Deepwater drilling is characterized by strong thermal contrasts among low-temperature seawater, the circulating wellbore fluid, and high-temperature formations. In the open-hole section, drilling-fluid invasion forms a mud cake that modifies the wellbore–formation heat-transfer boundary. To represent this effect, a transient wellbore-temperature model treated invasion-induced mud cake as an additional thermal-resistance layer. The model also incorporated temperature- and pressure-dependent drilling-fluid rheology and circulation conditions. Comparisons with temperature data from two deepwater field wells yielded maximum relative errors of 2.06% and 2.13%. The model evaluated the effects of drilling conditions, drilling-fluid properties, and mud-cake heat-transfer characteristics. These factors affected different wellbore regions, whereas the mud-cake effect was concentrated mainly in the deep open-hole section and intensified with depth. At 5500 m, increasing mud-cake thermal conductivity from 0.001 to 1.0 W/(m·°C) raised the annular temperature from 56.49 to 107.81 °C. Experiments further showed that increasing the thermal-insulation material dosage from 0 to 5 wt% reduced mud-cake thermal conductivity from 0.7018 to 0.1346 W/(m·°C), an 80.8% reduction. These results identify mud-cake thermal resistance as an engineering-relevant boundary parameter for predicting and regulating the temperature field in deepwater open-hole sections.