Is a Paradigm Shift in Produced Water Treatment Technology Occurring at SAGD Facilities?

Over the past few years, a paradigm shift has occurred in the treatment of produced water for steam-assisted gravity drainage (SAGD) heavy oil recovery facilities. The shift has been away from the use of warm lime softening (WLS), filtration and weak acid cation (WAC) ion exchange to pretreat de-oiled produced water to an approach using falling film, mechanical vapour compression (MVC) evaporation to produce steam generator feedwater. Today, approximately 16 such evaporators are operating, under construction or in various stages of delivery in Alberta and overseas. Many new SAGD facilities are evaluating MVC evaporation as the baseline approach with the traditional WLS/WAC system being treated as a secondary alternative, along with other alternative approaches. This shift in methodology is because of a combination of technical and economic factors, increased reliability and availability associated with MVC evaporation and, perhaps most significantly, because of the potential to use standard drum boilers and alternative fuels for steam generation [as opposed to the use of once-through steam generators (OTSGs) required with the traditional approach]. Requirements for increased water recovery at SAGD facilities, which are made possible by MVC evaporation, also play a significant role in the shift towards produced water evaporation. This paper presents a technical and economic evaluation of the shift towards produced water evaporation, increased water reuse and recovery, use of standard drum boilers and the use of alternate fuels at SAGD heavy oil recovery facilities.