Modeling of lifting heavy oil assisted by enclosed thermal fluid circulation in hollow rod

Enclosed thermal fluid circulation is a kind of economic and effective technology for viscosity reducing in wellbore. It forms a flow channel using insulated tube and hollow rod. Heat is transferred from thermal fluid to produced fluid to reduce viscosity of heavy oil. Compared to other technologies, it can save energy, and does not affect measuring of produced fluid. A mathematical model for the process was established, and solved by the numerical method. Temperature and pressure distributions for thermal fluid and produced fluid in wellbore were given. Sensitivity factor analysis was made. This technology mainly improves the produced fluid temperature of the upper part of wellbore, reducing the viscosity of crude oil. Compared to heat transfer oil, water carries more heat under the same condition. The temperature of produced fluid heated by water is higher and viscous load is relatively lower. The increase of hot water flow rate, insulated tube depth, liquid production rate and production time can improve the temperature of produced fluid, and reduce the viscous force. An insulated tube with a lower thermal conductivity can reduce heat loss in the wellbore, and enhance viscosity reducing effect. Decrease of gas pressure in tubing casing annular can reduce free convection and radiation heat transfer, and improve heating effect. The site applications verify the practicability of the technology and the validation of the mathematical model.