A novel model for dynamic temperature distribution in heavy oil reservoirs is derived from the principle of energy conservation.A difference equation of the model is firstly separated into radial and axial difference equations and then integrated.Taking into account the coupling of temperature and pressure in the reservoir and wellbore,models for calculating distributions of the reservoir temperature,reservoir pressure,and water saturation are also developed.The steam injected into the wellbore has a more significant effect on reservoir pressure than on reservoir temperature.Calculation results indicate that the reservoir temperature and pressure decrease exponentially with increasing distance from the horizontal wellbore.The radial variation range of the pressure field induced by steam is twice as wide as that of the temperature field,and both variation ranges decrease from the wellbore heel to the toe.Variation of water saturation induced by steam is similar to the temperature and pressure fields.The radial variation ranges of the reservoir temperature and pressure increase with steam injection time,but rate of increase diminishes gradually. A novel model for dynamic temperature distribution in heavy oil reservoirs is derived from the principle of energy conservation. A difference equation of the model is firstly separated into radial and axial difference equations and then integrated. .aking into account the coupling of temperature and pressure in the reservoir and wellbore, models for calculating distributions of the reservoir temperature, reservoir pressure, and water saturation are also developed. steam injected into the wellbore has a more significant effect on reservoir pressure than on reservoir temperature. Calculating results indicate that the reservoir temperature and pressure decrease exponentially with increasing distance from the horizontal wellbore. The radial variation range of the pressure field induced by steam is twice as wide as that of the temperature field, and both variation ranges decrease from the wellbore heel to the toe. Variation of water saturation induced by steam is similar to the temperature and pr essure fields. the radial variation ranges of the reservoir temperature and pressure increase with steam injection time, but rate of increase diminishes gradually.