World's First SAGD Facility Using Evaporators, Drum Boilers, and Zero Discharge Crystallizers to Treat Produced Water
Authors: Heins W.F. , McNeill R. , Albion S. 
Published: March 2010

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.