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Numerical Simulation of Supercritical-Water Flow in Concentric-Dual-Tubing Wells


 Much work has been performed on the modeling of saturated/superheated-steam flow in wellbores. At present, the study on supercritical-water (SCW) flow in wellbores, especially concentric-dual-tubing wells (CDTWs), is very limited.
 In this paper, work was performed on modeling of SCW flow in CDTWs. First, a comprehensive mathematical model comprising a pipe-flow model, supercritical-fluid model, and heat-transfer model is established. In the model, the heat exchange between the integral joint tubing (IJT) and annuli is taken into consideration. Numerical solutions of SCW flow in CDTWs were obtained with a straightforward numerical method. Then, sensitivity analysis was conducted. The following results were found:
 SCW in annuli (with a higher temperature) releases thermal energy to SCW in the IJT, which causes increase of temperature in IJT. As a result, SCW density in the IJT has a decrease. The density gradient near the wellhead increases with increasing of injection rate. When the injection temperature in the IJT is larger than that in annuli, SCW density increases with well depth near the wellhead.