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.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
18 June 2007
- Meeting paper published:
12 June 2007
- Revised manuscript received:
23 November 2009
- Manuscript approved:
9 December 2009
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