Typical thermal processes involve sophisticated wellbore configurations, complex fluid flow, and heat transfer in tubing, annulus, wellbore completion, and surrounding formation. Despite notable advancements made in wellbore modeling, accurate heat-loss modeling is still a challenge by use of the existing wellbore simulators. This challenge becomes even greater when complex but common wellbore configurations, such as multiparallel or multiconcentric tubings, are used in thermal processes such as steam-assisted gravity drainage (SAGD).
To improve heat-loss estimation, a standalone fully implicit thermal wellbore simulator is developed that can handle several different wellbore configurations and completions. This simulator uses a fully implicit method to model heat loss from tubing walls to the surrounding formation. Instead of implementing the common Ramey (1962) method for heat-loss calculations, which has been shown to be a source of large errors, a series of computational-fluid-dynamics (CFD) models are run for the buoyancy-driven flow for different annulus sizes and lengths and numbers of tubings. On the basis of these CFD models, correlations are derived that can conveniently be used for the more-accurate heat-loss estimation from the wellbore to the surrounding formation for SAGD injection wells with single or multiple tubing strings. These correlations are embedded in the developed wellbore simulator, and results are compared with other heat-loss-modeling methods to demonstrate its improvements. A series of validations against commercial simulators and field data are presented in this paper.