Daily Oil Bulletin: May 17, 2012
More Water Recycling Can Mean More Toxic Waste, More Greenhouse Gases: Study
Thermal oil projects could reuse more than 90 per cent of their produced water, but water recycling can increase greenhouse gas emissions and solid and liquid waste generation, a study found.
Replacing fresh water with saline water can also have adverse environmental impacts, suggests the study by JACOBS Consultancy.
The study was done for Alberta Innovates - Energy and Environment Solutions (an Alberta government research entity) in collaboration with Alberta's Energy Resources Conservation Board, Alberta Environment and nine oil producers.
The participating producers -- all of which have or are planning thermal oil projects in Alberta -- were BP Canada, Canadian Natural Resources Limited, Cenovus Energy Inc., ConocoPhillips Canada, Nexen Inc., PennWest Petroleum Ltd., Statoil Canada, Suncor Energy Inc. and Total E&P Canada Ltd.
SAGD and cyclic steam projects use massive amounts of water to generate steam injected into the reservoir to reduce oil viscosity. A SAGD project with a steam/oil ratio of three, for example, uses three bbls of water to produce a bbl of bitumen.
However, overall water consumption is hugely reduced because roughly 70 to 90 per cent is recycled, depending on the quality of the water returned from the reservoir with the oil. (The proportion of produced water that can be effectively recycled can depend heavily on such factors as salinity.) So the amount of new, or "makeup," water needed ranges from roughly 10 to 30 per cent of the total requirement.
"Produced water recycle rates can surpass 90 per cent with the use of commercially available technologies," says the study's summary report released on Wednesday
But while technology can increase the percentage of produced water reused at thermal oil projects, there is a tradeoff between water recycling, greenhouse gas emissions and waste generation -- and this tradeoff becomes more pronounced as the quality of produced water deteriorates, the report says.
"Technology options are impacted by the relative value of water, the amount of waste generated and the value of [greenhouse gas] emissions," the report said.
In its evaluation of water treatment technologies, the study found that warm lime softening and hot lime softening had the lowest greenhouse gas emissions.
Using these technologies, the produced water recycle rate was 87 per cent with the use of fresh makeup water, but it "quickly deteriorated" when the total dissolved solids of the makeup water exceeded 7,000 parts per million, the report says.
On the other hand, produced water evaporation was estimated to have a produced water recycle rate of more than 90 per cent even with total dissolved solids of more than 24,000 parts per million in the makeup water.
However, the greenhouse gas emissions from produced-water evaporation were seven to eight per cent higher than from warm lime softening.
The report says the best overall balance of produced water recycle rate versus greenhouse gas emissions may be achieved by using warm lime softening of the produced and makeup water, and evaporation treatment of the boiler blowdown (known as blowdown evaporation).
Blowdown evaporation had greenhouse gas emissions only three per cent higher than warm lime softening, and had a produced water recycle rate on par with produced water evaporation, the report says.
Among the study's other conclusions:
Improved reliability and operability could potentially be bigger drivers for water-treating technology selection than reductions in greenhouse gas emissions and water use, especially for producers using zero liquids discharge, the report said.
"We understand that water conservation comes at a price," Clyde Fulton of Statoil said at Wednesday's release of the summary report.
Fulton said producers are simultaneously striving to reduce greenhouse gas emissions, waste generation and land disturbance.
"And as this study has shown, some of the water treatment technologies available today -- that are most efficient with respect to water conservation -- [also] have higher greenhouse gas production and generate greater quantities of byproducts that are more difficult to manage than some of the traditional water-recycling processes we use today," he said.
Replacing fresh water with saline water is often touted as a key way to reduce the industry's fresh water consumption.
But Fulton noted this can also increase greenhouse gas emissions, result in more solid waste (particularly as more saline water sources are tapped) and actually increase the total amount of water consumed.
"Although not considered in this study, some site-specific conditions can also create greater land disturbance when longer pipelines are required to access distant sources of saline water preferentially over more locally available sources of lower-salinity water," he added.
What it boils down to for industry and regulators, Fulton said, is finding the appropriate balance between the goals of water conservation, greenhouse gas mitigation, waste reduction, minimizing land disturbance and favourable economics.
He concluded the study is "a useful tool for all parties involved in this endeavour to use in meeting this challenge," as it quantifies the tradeoffs and provides a methodology for developing policies and strategies to ensure the sustainable development of Alberta's bitumen resources.
The study's summary report can be downloaded here.