Prediction of transient wellbore cement circulating temperature distribution using CFD simulation

Abstract Accurate prediction of the cement slurry temperature while being circulated downhole is critical for a successful cement job. Failure to predict the cement slurry temperature correctly may result in premature or delayed cement setting. Due to the practical limitations of using temperature sensors for direct measurement and the complexity of the bottomhole circulating conditions, it is difficult to gather accurate information about how the temperature of cement slurry changes as it is being circulated through the well. To overcome these challenges and help with designing a cement system more accurately, a computational fluid dynamics (CFD) model is developed. The model simulates the balanced-plug cementing operation, which considers the continuous displacement of the drilling fluid by the cement slurry and the cement slurry by water. The CFD model predicts the transient changes in the temperatures of the cement slurry and near wellbore formation during this displacement process involving three different fluids. A new dynamic mesh method was developed to effectively handle the interface mixing of different fluids, and thus model the three-fluid displacement process in the annulus more realistically. The CFD model can also deal with complex well conditions such as deviated wellbores, variable geothermal gradients and formation rock properties. Most importantly, in the absence of the measurements allowing direct monitoring of the downhole conditions, the new CFD model allows for continuous monitoring of downhole transient fluid and formation temperature at any position along the wellbore. The results of CFD transient simulations indicate that the bottomhole circulation temperature (BHCT) values predicted by using API method are significantly overestimated. The highest cement slurry temperature in the annulus was observed at some distance above the bottom of the well. Results also confirmed the existence of an equilibrium plane (extending horizontally) into the formation across which a temperature reversal was observed. The formations above and below the equilibrium plane have opposite heat transfer patterns. The depth of the equilibrium plane rises steadily while its temperature gradually decreases as the circulation continues. The change of the cement/drilling fluid interface temperature is traced dynamically. CFD simulation is proven to be a realistic and reliable approach for prediction of the cement circulating temperature and can be easily used in combination with real time operational data. Practical guidelines and solutions derived from the simulation results can be useful for improved cement job design in field applications.