An R-K-S Equation-Based Study on the Heat Transmission Features of Multi- Component Thermal Fluid Injection through Concentric Dual-Tubing

A mathematic model for heat transfer in wellbores when injecting multi-component thermal fluid through concentric dual-tubing was constructed with the goal of better understanding the heat transmission characteristics of multi-component thermal fluid injection through concentric dual-tubing and determine the optimum bottom hole steam parameters.The study involved modeling wellbore behaviors in response to the injection of superheated multi-component thermal fluid through concentric dual-tubing.To establish the model,the actual gas based R-K-S equation of state,the mass,energy and momentum conservation equation and the transient heat transfer model in classical stratum were used.After verification with the model,the typical heat transfer features of the mixed steam/gases within the wellbore were analyzed,and the analysis indicated that a small temperature difference between the integral joint tubing and the inner tubing annulus near the wellhead may lead to dramatic changes in the fluid thermo-physical parameters,but the temperature gradients converge quickly.The content of non-condensing gases and the steam injection temperature were optimized with the model,and the results showed that the downhole superheat degree decreased as the content of the non-condensing gases increased.However,the downhole superheat degree increased as the steam injection temperature in the integral joint tubing increased.The results of the study demonstrated that the steam injection parameters had a significant influence on the distribution of the thermal parameters within the wellbore.The way steam was injected affected wellbore temperatures.Therefore,it was suggested to optimize the steam injection parameters based on the actual boreholes used during field operations.