Prediction of thermophysical properties of saturated steam and wellbore heat losses in concentric dual-tubing steam injection wells

Concentric dual-tubing steam injection is important in the process of thermal recovery for heavy oils. This paper firstly presented a mathematical model to predict thermophysical properties of saturated steam (i.e. steam pressure, temperature and quality) and wellbore heat losses in CDTSIW (concentric dual-tubing steam injection wells). More importantly, a semi-analytical model for estimating pressure gradient for steam/water flow in annuli was developed. Then the mathematical model is solved using an iterative technique. Predicted results were compared with measured field data to verify the accuracy of the model. The results indicate that the direction of heat transfer between fluids in the integral joint tubing and in the annulus depends not only on wellhead injection conditions but on temperature drop in each tubing. In addition, the steam qualities in CDTSIW are significantly influenced by heat exchange between fluids in dual tubing, which can cause steam boiling or condensation. Moreover, the paper shows that to effectively reduce the wellbore heat losses and to ensure high bottomhole steam qualities in Well Xing 67 of Liaohe Oilfield, the thermal conductivity of insulation materials should be less than 0.7 W/(m K).