Mechanism and Energy Efficiency Evaluation of Superheated Steam Assisted Gravity Drainage Technique

The superheated steam is defined as the steam with a higher temperature than saturated steam at saturation pressure, and the temperature difference is called superheated degree. The superheated-SAGD technique injects superheated steam rather than saturated steam, which was considered more efficient than conventional SAGD. However, the main recovery mechanisms and whether superheated steam has energy efficiency advantage compared with saturated steam is worthier of attention and answer. The OSR is often used as a key economic indicator for the steam recovery process. However, it cannot reflect the actual energy efficiency when it comes to the superheated steam. Although superheated steam recovers more oil than saturated steam, the energy consumption required to produce superheated steam is also higher. In this paper, the numerical simulation method is used to study the mechanisms of superheated-SAGD. The results show that the superheated steam can significantly improve the oil recovery efficiency of SAGD due to higher enthalpy and steam quality. Also, the aquathermolysis reaction has considerable impact on the SAGD performance, especially when superheated steam is used. The NCGs could add pressure and energy to the reservoir and decrease the heat loss between the steam chamber and the overburden layer. However, it will also influence the heat transfer between the steam chamber to the surrounding oil reservoir, thus limit the steam chamber lateral development. Moreover, the energy efficiency indicator is proposed, which can better evaluate the energy efficiency of a SAGD project. The optimal superheated degree is determined and the energy efficiency chart of SAGD projects are presented based on the proposed energy efficiency indicator. It shows that although the superheated steam can significantly increase the energy efficiency and OSR of SAGD, there is an optimal superheated degree under different steam saturation pressure. The superheated steam is more suitable for improving oil recovery efficiency at relatively low operating pressure SAGD projects.