The flow and heat transfer characteristics of superheated steam in concentric dual-tubing wells

In this paper, a numerical model is presented to estimate the thermophysical propertes of superheated steam (SHS) in concentric dual-tubing wells (CDTW). Firstly, a model comprised of mass, momentum and energy balance equations in the integral joint tubing (IJT) and annuli is proposed for CDTW. Secondly, distributions of temperature, pressure and superheat degree along the wellbores are obtained by finite difference method on space and solved by iteration technique. Finally, based upon the validated model, sensitivity analysis is conducted. The calculated results show that: (1) In CDTW, the difference of injection temperature between the IJT and annuli has a strong influence on the profiles of temperature and superheat degree in wellbores. (2) Temperature in the UT and annuli rapidly tends to be consistent. (3) SHS temperature in each tubing increases with increasing of injection temperature in UT. (4) Superheat degree in UT decreases rapidly near the wellhead, but the superheat degree in annuli has an increase. This study unravels some intrinsic flow characteristics of SHS in CDTW, which has a significant impact on the optimization of SHS injection parameters and analysis of heat transfer law in CDTW. (C) 2017 Elsevier Ltd. All rights reserved.