The heat efficiency of steam during SAGD process is vital for the SAGD economic performance. In deposits with buried depth more than 400 meters, the in-situ steam quality is basically less than 85% by injecting the saturated steam on the wellhead. Less steam quality means less specific heat enthalpy and less effect of oil viscosity reduction by steam and lower oil drainage rate. The super-heated steam injection was proposed in this paper in which the key mechanisms of oil drainage rate enhancement were investigated for a typical SAGD project in Athabasca oil sands.
The experimental and numerical simulation approaches were chosen to integrally study the key mechanisms. A serial of two dimensional scaled physical modeling were performed to simulate the characteristics of steam chamber evolution, to compare the dynamics of SAGD production by different steam temperatures, and to determine the potential of SAGD by super-heated steam. In addition, the field scale numerical simulation model was built based on the geologic modeling, and the relationship between steam temperature and steam chamber growth behaviors were studied.
The two dimensional scaled physical modeling results indicated that the steam needed was reduced by elevating the steam temperature, and less time was required to reach the plateau oil production rate. Super-heated steam with higher temperature speeded up the steam chamber growth rate more evidently, while when the super-heated value was more than 300°C, further enhancing the temperature would result in less incremental oil drainage rate and higher risk of caprock failure. The numerical simulation of typical SAGD wellpair required that the overall temperature of super-heated steam should be not above 300°C considering the lifting requirements and hydrothermal reaction. 7.67% of less steam injection for the whole life cycle of SAGD, 13.5% of reduced SCOR would be achieved by steam with super-heated degree of 40°C.
The results from this paper have been used to guide the field operation, and the encouraging performance was expected.