Numerical simulation of superheated steam flow in dual-tubing wells

In this paper, a novel model is presented to estimate the thermophysical properties of superheated steam (SHS) in dual-tubing wells (DTW). Firstly, a mathematical model comprised of the mass conservation equation, momentum balance equation and energy balance equation in the integral joint tubing (IJT) and annuli is proposed for concentric dual-tubing wells (CDTW), and in the main tubing (MT) and auxiliary tubing (AT) for parallel dual-tubing wells (PDTW). Secondly, the distribution of temperature, pressure and superheat degree along the wellbores are obtained by finite difference method on space and solved with iteration technique. Finally, based upon the validated model, sensitivity analysis of injection temperature is conducted. The results show that: (1) effect of injection temperature difference between MT and AT on temperature profiles is weak compared with that between the IJT and annuli. (2) Temperature gradient in IJT and annuli near wellhead is larger than that in MT and AT. (3) Superheat degree in both CDTW and PDTW increases with the increase in injection temperature in IJT and MT, respectively. (4) Superheat degree in IJT and MT decreases rapidly near wellhead, but the superheat degree in annuli and AT has an increase. (5) Thermal radiation and convection are the main ways of heat exchange between MT and AT. This paper gives engineers a novel insight into what is the flow and heat transfer characteristics of SHS in DTW, and provides an optimization method of injection parameters for oilfield.