Numerical calculation of bottom hole circulating temperature in wellbore cementing processes with multi-fluid and multi-step

In oil and gas well cementing processes, accurately predicting the bottom hole circulating temperature (BHCT) is critical to ensuring effective zonal isolation. Overestimating the temperature can lead to excessive retardation issues, while underestimation can cause cementing accidents. Current methods for calculating the BHCT of cement slurry typically simplify the cementing processes to a single-fluid circulation and ignore the impact of pre-cementing processes on temperature, leading to significant discrepancies between calculated and actual results. In this study, the wellbore and formation are simplified into a two-dimensional axisymmetric structure, and a mathematical model of the temperature field under multi-fluid and multi-step conditions is established based on the law of energy conservation. The finite volume method was used to discretize the model, and a transient temperature field solver for the entire cementing process was developed, which can numerically calculate the temperature of any fluid at any time, any location. For an actual well example, the temperature distribution of the wellbore and formation after casing running is taken as the initial condition. Numerical calculations were performed sequentially to calculate the temperature fields of circulation flushing, wellbore preparation, and cementing, as well as the BHCT of the cement slurry. The study reveals that during the circulation flushing stage, the maximum temperature point in the wellbore is located at a distance of about 366 m above the bottom of the well. In the wellbore preparation stage, due to static heat exchange, the maximum temperature point gradually shifts to the bottom of the well. The BHCT of cement slurry changes continuously under cementing processes with multi-fluid and multi-step, making it a transient value. The BHCT of the lead slurry and tail slurry are not equal, with the maximum BHCT of the tail slurry being 2.46 °C higher than that of the lead slurry. If circulation flushing and wellbore preparation are not considered, the calculated BHCT of the cement slurry will have errors of +6.8% and −1.9%. The study highlighted that considering thermal effects of all cementing stages, such as circulation flushing and wellbore preparation, in BHCT calculations can help improve prediction accuracy.