Engineering Assessment of Dynamic Thermophysical Property Effects on Wellbore Temperature and Pressure Prediction under Lost Circulation

Abstract

During drilling in deep, high-temperature, high-pressure (HTHP) wells, lost circulation can significantly alter annular flow distribution, wellbore heat transfer balance, and pressure response, making conventional constant-property models inadequate for accurate wellbore temperature and pressure prediction. In this study, we develop a transient wellbore-formation temperature-pressure (T-P) coupling model for known lost circulation conditions. The model accounts for flow redistribution caused by fluid loss, transient wellbore-formation heat transfer, wellbore pressure response, and the dynamic evolution of thermophysical properties within a unified computational framework. The governing equations are solved using a fully implicit finite-difference scheme, in which temperature, pressure, and fluid properties are iteratively updated. Because the loss scenarios are constrained by field-measured loss data, recorded loss volumes, or prescribed operating conditions, the model is intended as an engineering-scale tool for evaluating post-loss redistribution of wellbore temperature and pressure. The model is validated against classical models and field temperature and pressure measurements under normal and lost circulation conditions. The results show that dynamic thermophysical properties significantly affect wellbore temperature and pressure predictions during lost circulation. Compared with the constant-property model, the dynamic-property model reduces the bottomhole temperature (BHT) prediction error to 1.06%, provides a conservative upper-bound estimate of BHT, and avoids systematic overestimation of bottomhole pressure (BHP). Lost circulation reduces annular flow rate and disturbs the wellbore heat transfer balance, leading to nonlinear redistribution of temperature and pressure. Sensitivity analysis indicates that BHT is mainly controlled by density and specific heat capacity, with relative contributions of 42.89% and 39.11%, respectively, whereas BHP is dominated by density, with a contribution of 96.59%. Full-factorial interaction analysis further shows that the interaction between density and specific heat capacity is the key coupled factor affecting BHT, and higher specific heat capacity reduces the sensitivity of BHT to density variation by approximately 28%. Extended sensitivity analyses of inclination angle, drillstring eccentricity, high equivalent circulating density (ECD) conditions, and loss rate show that the model can characterize temperature and pressure response differences under complex wellbore configurations and operating conditions. The results provide engineering support for post-loss T-P assessment, loss-zone diagnosis, well-control safety-margin evaluation, and circulation-parameter optimization under lost circulation.