Insights on Heat Transfer at the Top of Steam Chambers in SAGD

Steam-assisted gravity drainage (SAGD) is the method of choice for producing oil from oil sands reservoirs. In this method, steam is injected into the formation and the oil, upon heating, is mobilized and driven under gravity to a production well. The accumulation of steam within the reservoir is referred to as the steam chamber. One of the critical issues confronting SAGD operators is the thermal efficiency, measured by the steam-to-oil ratio, of their operations since it directly ties to process costs. Using thermocouple profiles from observation wells on three SAGD fields in Alberta, we use error function fits to estimate the thermal conductivity of the shale above the oil formation (found to be from 0.33 to 3.81 W/mK), heat flux at the top of the steam chamber, vertical height of the steam/gas zone above the steam chamber, and accumulated gas volume present. A gas material balance is then derived to estimate the volume of gas that might be generated through in situ chemical processes. The results of the heat transfer analysis performed on the thermocouple data reveal that the gas co-injection during SAGD operations studied did not directly affect the heat transfer rate at the top of the steam chamber since the gas volume added was small. The results also show that a sufficiently large accumulation of gas at the top of the chamber lowers the heat flux at the edge of the chamber.