Abstract: To optimize injection parameters of non-condensing gas and overheated steam (steam/gas mixture) in offshore heavy oil reservoirs,a mathematical model of non-isothermal flow in wellbore was established following the conservation equations of mass,energy and momentum.Taking into account the heat-transfer model for seawater and transient thermal conductivity model in reservoir formation,an integral heat transfer model in wellbore with steam/gas mixture was established.By using finite difference method and iterative method,pressure and temperature distributions within the wellbore were obtained.Research results show seawater flow results in significant heat losses in the wellbore and reduces temperatures of steam/gas mixture.When the amount of non-condensing gases increases,the temperature and overheat degrees of the mixed steam/gas may decrease.Likewise,with the increase of steam injection pressure,the overheat degrees may decrease.The heat transfer model for wellbores with mixed steam/gas may provide a theoretical basis for optimizing the parameters of steam injection and creating an effective analysis of seawater on heat losses in wellbores.