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

Abstract

Abstract 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. Introduction Over the past few years, water treatment and steam generation methods for heavy oil recovery processes have rapidly evolved. Traditionally, especially for cyclic steam operations, OTSGs, driven by natural gas, have been used to produce about 80% quality steam (80% vapour, 20% liquid) for injection into the well to fluidize the heavy oil. However, the relatively new heavy oil recovery method, referred to as SAGD, requires 100% quality steam for injection. To allow the continued use of OTSG for SAGD applications, a series of vapour/liquid separators is required to produce the required steam quality. For both SAGD and non-SAGD applications, pretreatment of the OTSG feedwater has consisted of silica reduction in a hot lime softener (HLS) or WLS, filtration and hardness removal by WAC ion exchange.