Reservoir heating in cyclic steam stimulation for heavy oil recovery

Cyclic steam stimulation (CSS) is one of the most successful heavy oil production methods. Heating the reservoir and reducing oil viscosity through steam condensation is a key mechanism. This study develops a mathematical model to investigate the cumulative heat and heating rate in reservoir throughout a CSS process. Results show that: First, during the steam injection stage, the heating rate remains stable if the temperature and pressure continue to rise, and decreases rapidly if the pressure and temperature stay constant or stable. This suggests that the heating efficiency is rather low under constant-pressure injection stage. Second, during the soaking stage, the temperature and pressure of the heating chamber gradually level off. Accordingly, the corresponding heat transfer rate quickly decreases to zero. Therefore, it is recommended that the soak time should not be long. Third, in the early production stage, the temperature and pressure near the wellbore rapidly decline, conduction and convection work in opposite directions, and cumulative heat falls sharply with the drop of temperature in the transition zone. Later on, when the pressure is depleted, conduction dominates heat transfer, and the cumulative heat in the reservoir keeps growing at a small rate. Finally, the incremental of heat cumulation becomes insignificant after six cycles, which suggests that follow-up processes be considered to improve oil production.