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Abstract There has been a shift away from the use of warm lime softening (WLS) and weak acid cation (WAC) ion exchange for produced water treatment to the use of mechanical vapour compression (MVC) evaporation followed by high pressure drum-type boilers. Approximately 18 steam assisted gravity drainage (SAGD) produced water evaporators are operating or are in various stages of construction in Alberta and overseas. Since the commissioning of the first such evaporators in 2002, many technical advancements have occurred which have resulted in reduced operating costs, improved reliability, reduced scaling and fouling potential, improved distillate quality and improved boiler feed quality for steam generation. This paper provides details of the technical advancements in evaporative produced water treatment based on full-scale operating data and lessons learned. It also presents improved evaporator configurations, discusses improvements in contaminant reduction and scale prevention systems, demonstrates how capital and operating costs can be drastically reduced as compared to earlier evaporator system designs, and provides recent advancements in modularization, evaporator disposal treatment, deoiling, membrane preconcentration, and zero discharge solids drying techniques. Introduction Over the past few years, there has been a rapid shift away from the use of traditional produced water treatment methods using WLS for silica reduction and WAC ion exchange for hardness removal, to the use of evaporative produced water treatment methods at SAGD facilities. With the use of evaporative produced water treatment, standard drum boilers are utilized for steam generation in lieu of once through steam generators (OTSG) and vapour liquid separators. This shift has occurred because of technical, economic and reliability factors, resulting in markedly improved life cycle costs for SAGD facilities. A simplified block flow diagram of the traditional approach to produced water treatment and steam generation is provided in Figure 1. A block flow diagram for the evaporative approach is provided in Figure 2.

Abstract Many new Steam-Assisted Gravity Drainage (SAGD) heavy oil recovery facilities have recently shifted from the use of warm or hot lime softening, filtration and weak acid cation (WAC) ion exchange to pretreat de-oiled produced water to an approach using falling film, mechanical vapour recompression evaporation to produce steam generator feedwater. This method of SAGD-produced water treatment is much simpler to operate, is more cost effective and results in significant increases in equipment reliability, on-stream availability and, ultimately, oil production. There are currently about 14 such evaporators operating, under construction, or in various stages of delivery in Alberta and overseas. Several of these evaporators produce feedwater for standard drum-type boilers rather than the traditional Once-Through Steam Generators (OTSG) due to the high level of water purity obtainable with the evaporative approach. This paper provides data from operational facilities, including evaporator distillate quality, heat transfer information, fouling rates, cleaning frequencies, energy and chemical consumption, and other technical and operational data. In conjunction with this evaporative produced water treatment process, some facilities have taken the additional step of recovering all liquid waste streams for re-use in the plant, resulting in zero liquid discharge (ZLD). Designing the facility for ZLD eliminates the need for deep well injection, minimizes make-up water requirements and simplifies the permitting process. Introduction The recovery of heavy oil from oil sands formations requires large volumes of water; sometimes three times the amount of water compared to the oil recovered. In steam-assisted gravity drainage (SAGD) facilities, 100% quality steam is injected into the well to heat up the formation and get the heavy oil to flow. Oil and condensed steam are brought to the surface where the oil is separated and the condensate, or produced water, is treated and recycled to produce the steam. This huge water demand and ultimate conversion to steam requires the maximum amount of recycle potential from the water. Produced water derived from oil recovery processes (SAGD and non-SAGD) can be characterized as predominantly sodium chloride brine with high silica and minimal amounts of hardness. High alkalinity is present as well. Overall concentration of the water can range from about 1,000 mg per litre TDS to over 10,000 mg per litre, and there is always some amount of organic material present. The method of converting this water to boiler feedwater must be carefully evaluated, both technically and economically. This paper discusses an evaporative method of deriving high quality boiler feedwater from produced water. A comparison is made to the 'traditional' method of warm (or hot) lime softening combined with weak acid cation exchange (WLS/WAC). A complete evaluation of these two approaches must also include the steam generation equipment. Having high quality boiler feedwater, as derived from an evaporative process, allows the use of drum boilers in lieu of once-through steam generators (OTSG). Since the WLS/WAC system does not produce a high quality water, OTSG must be used as these boilers are more tolerant of poorer quality feedwater.

Abstract Steam assisted gravity drainage (SAGD) heavy oil recovery facilities have traditionally used a combination of warm or hot lime softening, filtration, and weak acid cation (WAC) ion exchange to pretreat de-oiled produced water. The pretreated water is directed to "once-through" steam generators (OTSG) to produce 750–80% quality steam. The steam-water mixture goes through a series of vapour-liquid separators to produce the 100% quality steam required for injection into the oil well. The steam fluidizes the heavy oil and allows the oil/water mixture to be brought to the surface. The oil is recovered as product and the produced water is de-oiled and treated for reuse in the OTSG. An alternative method of produced water treatment and steam production, which has recently been implemented in Alberta by Deer Creek Energy, is mechanical vapour recompression evaporation followed by standard drum boilers. This method of SAGD steam production is much simpler to operate, is more cost effective, and results in significant increases in equipment reliability, on-stream availability, and ultimately in increased oil production. In conjunction with this process, Deer Creek Energy has taken the additional step of recovering all liquid waste streams for reuse in the plant, resulting in zero liquid discharge (ZLD). Designing the facility for ZLD eliminates the need for deep well injection, minimizes make-up water requirements, and simplifies the permitting process. Introduction Water treatment and steam generation methods for heavy oil recovery processes have rapidly evolved over the past few years. Traditionally, once-through steam generators (OTSG) 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 steam assisted gravity drainage (SAGD) requires 100% quality steam for injection. In order 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 or warm lime softener, filtration, and hardness removal by weak acid cation (WAC) ion exchange. In most cases, the OTSG blowdown is disposed of by deep well injection. A simplified block flow diagram of this traditional approach to produced water treatment and steam generation is provided in Figure 1. As the use of the SAGD process became increasingly common for heavy oil recovery in Alberta and worldwide, the traditional methods of produced water treatment and steam generation were re-evaluated to determine whether other alternative methods may provide more technically and economically viable solutions. This paper compares the use of traditional methods with an alternate method being implemented in Alberta the use of falling film, vertical tube vapour compression evaporation for produced water treatment, standard 100% quality drum boilers for steam production, and zero liquid discharge (ZLD) crystallizers to eliminate the need for deep well injection. Both technical and economic criteria are presented.