Steam injection into hydrocarbon reservoirs involves significant heat exchange between the wellbore fluid and its surroundings. During injection, the hot fluid loses heat to the cold surroundings, continuously as it moves down the borehole. The heat transfer process impacts well-integrity and, in turn, the ability of the well to perform its required function effectively and efficiently with regard to safety and environmental factors. During the design phase of a steam injection well, it is necessary to avoid risks and uncertainties and accurately plan the life cycle of wellbore. The present study aims to investigate the nature and predict the natural convection heat transfer coefficient in the annulus. The approach to model the natural convection heat transfer in this study is by analytical and numerical techniques. The annular space between the tubing and the casing was treated as a finite space bounded by walls and filled with fluid media (enclosures). Correlations for vertical enclosures were employed in the work. The flow field was modeled and simulated for numerical analysis, using ANSYS-FLUENT software package. Some boundary parameters have been defined by the user and fed to the software. The predicted values of Nusselt numbers from both analytical and numerical approaches were compared with those of previous experimental investigations. The results of the present study can be used for preliminary design calculations of steam injection wells to estimate rate of heat transfer from wells. This study also provides a novel baseline assessment for temperature related well-integrity problems in steam injection wells.© Maxwell Scientific Organization, 2014.