Water re-use treatment is a significant portion of the cost, complexity, and total footprint of the standard Oil Sands Steam Assisted Gravity Drainage (SAGD) facility. Water needs to be re-used and treated because bitumen production requires continuous well steaming, boilers require clean water to prevent scaling and failure, and the Alberta Energy Regulator (AER) limits fresh water usage and waste water disposal volumes.

With sustained lower oil prices and the increased attention on environmental issues there has been a growing need to improve on water treatment efficiencies and costs. It is a good time to reflect on the technology used in the SAGD water treatment process now, as there are difficulties economically justifying new projects, and existing plants are seeking to improve operating costs and uptime.

The first SAGD sites used a precipitation softening process. This involved using a warm lime softener (WLS) for silica removal, followed by filtration for suspended solids removal, and strong (SAC) or weak (WAC) acid cation exchange to remove dissolved calcium and magnesium ions. Some sites began using hot lime softeners (HLS), which operate at higher temperatures to improve silica removal, and have a reduced footprint. For ion removal, most sites have favoured the use of WACs over SACs due to their ability to self-clean during regeneration. Despite these improvements, this process remains difficult to operate, requires high capital cost, a large footprint, and produces a large amount of solid waste.

Recently, greenfield SAGD sites have been built with falling film and mechanical vapour compression (MVC) evaporators for water treatment. These produce a higher quality boiler feedwater and can be used with more standard drum boilers instead of once-through steam generators (OTSGs). Evaporation requires fewer pieces of equipment and less footprint and capital cost compared to the older SAGD softening process. The catch is that it requires much more power to operate the large compressors, increasing operating costs.
Despite the more apparent pros of evaporation over traditional lime softening, older, larger SAGD sites have continued to expand capacity by adding more of the old softening technology. This shows that there is value in maintaining consistency in a site, and that there is no single obvious treatment technology available yet.

The creation of Canada’s Oil Sands Innovation Alliance (COSIA) has increased collaboration for technology advancement in water treatment among other important areas. However, as COSIA has only existed since 2012, it will take some time to see results of their pilot tests of new technology. In the short term, it is expected that producers will mostly focus on improving uptime and efficiency of existing plants, due to the length of time required for development of better processes.

Ausenco has experience improving SAGD water treatment sites by identifying opportunities to improve equipment uptime and reduce waste volumes of water. We have provided direct onsite engineering support for the water treatment facilities in one of the oldest and largest SAGD sites in Alberta. Here, we were entrusted with day to day engineering support to the operations staff, and were responsible for continuous tracking and reporting on plant performance. We scoped out projects to reduce downtime in the softener’s chemical feed systems. These feed systems are critical for maintaining softener performance, and are often prone to clogging. We also saw success by helping operations maintain a recycle flow of boiler blowdown into their water treatment process. The client had not operated this way for long, and the engineering support we provided helped them address issues as they arose. Recycling blowdown water reduces disposal water volumes, and can increase total water throughput in the plant to create more boiler feedwater and steam. This improves plant efficiency and conformance with regulations.

Ausenco provides consulting services to sites that suffer from water treatment issues, such as poor uptime, inability to stay on treatment specs, and can identify opportunities to optimize the water balance.