A Temperature- and Pressure-Coupled Model for Surge Pressure in High-Temperature, High-Pressure Wells

Summary In high-temperature, high-pressure (HTHP) wells with a limited safety margin during tripping operations, modifications in the properties of drilling fluid within the well are substantial. Accurate prediction of surge and swab pressures is crucial for secure drilling operations. With this research, we introduce a method for improving surge pressure calculations through a predictive model for drilling fluid rheological parameters. The research investigates the actual condition of the opened-ended pipe (OEP) drillstring configuration beneath a 5-in. drillpipe, considering different yield stress, annular ratios, and tripping velocities. Findings indicate that when the annular ratio is below 0.55 or above 0.65, the drillstring configuration consistently results in either internal pipe blockage or annular blockage, regardless of the yield stress or annular ratio. This method can be extended to various drilling tool combinations through extensive data analysis, facilitating field assessment of drillstring conditions. Additionally, a systematic investigation was simultaneously done on the impact of sensitive parameters, including tripping speed, pump displacement, and annular size, on the surge pressure at the drill bit. The results suggest that accounting for temperature and pressure effects on drilling fluid characteristics may lead to an underestimation of computed surge pressure. In an OEP configuration, higher tripping speeds are feasible; in contrast, in a closed-ended pipe (CEP) configuration, activating the pump during tripping may reduce swab pressure. This study provides both theoretical and operational guidance for managing wellbore surge pressure across different drillstring configurations in HTHP wells, along with a novel approach for accurately predicting wellbore surge pressure.