Heating of heavy oil by circulating hot water in closed double casing in ultra-deep wells

In heavy oil production, the loss of energy to ambient surroundings decreases the temperature of the heavy oil flowing upwards in a vertical wellbore, which increases the oil viscosity and the oil may not flow normally in the wellbore. Therefore, it is necessary to lower the heavy oil viscosity by heating methods to allow it to be lifted easily. Heating of heavy oil in an oil well is achieved by circulating hot water in annuli in the well (tubing-casing annulus, casing-casing annulus). In this paper, based on heat transfer principles and fluid flow theory, a model is developed for produced fluids and hot water flowing in a vertical wellbore. The temperature and pressure of produced fluids and hot water in the wellbore are calculated and the effect of hot water on heavy oil temperature is analyzed. Calculated results show that the hot water circulating in the annuli may effectively heat the heavy oil in the tubing, so as to significantly reduce both oil viscosity and resistance to oil flow.