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By Lauren Krugel

CALGARY — Excessive steaming was one of the factors that caused more than a million litres of oily water to ooze to the surface at an eastern Alberta oilsands site nearly three years ago, an investigation by the Alberta Energy Regulator has concluded.

The AER's report released Monday also said the bitumen-water emulsion was able to travel from deep underground through old unused wellbores, natural fractures and faults as well as man-made cracks in the rock.

"This is one of the most complex investigations we've ever undertaken," said Kirk Bailey, executive vice-president of operations at the provincial energy watchdog.

Canadian Natural Resources Ltd. (TSX:CNQ) had been using an extraction method at its Primrose oilsands property called high-pressure cyclic steam stimulation, the safety of which has been questioned by environmental groups.

That technique involves injecting steam deep into a reservoir through a well, letting it soak so that the thick bitumen is liquefied, and drawing the oil up to the surface through the same well.

Pressure restrictions imposed at Primrose following the leaks discovered in May and June of 2013 have been made permanent to avoid a similar event from happening in future.

"The company will not be able to pursue its original operating strategy at Primrose," said Bailey.

Cyclic steaming is widely used in the oilsands. Bailey said the AER took a broader look at other operations and concluded that they are safe.

The geology at Primrose is particularly complicated because a layer of salt underlies the bitumen reservoir, said Bailey. As the salt has partially dissolved, rock formations closer to the surface have been weakened.

The AER said CNRL didn't break any rules with its steaming technique.

Both the company and the regulator say the amount of bitumen that can ultimately be recovered at Primrose is unchanged. But the AER said it may just take longer to do so.

The AER's final report on Primrose follows probes by the company and by an independent technical panel.

The AER didn't agree with CNRL's view on how big a role the wellbores played.

"I think the company's point of view is that they played a larger role," said Bailey. "We didn't agree with that point of view."

As a result, the restrictions the AER is imposing are "more conservative" than they would have been if the wellbores were the main factor.

CNRL spokeswoman Julie Woo said the company's own investigations were compiled in 4,000 pages of technical data and interpretation.

"As a result of extensive data gathering, investigation, analytical analysis and interpretation, Canadian Natural and the industry's understanding of cyclic steam processes has been enhanced. These learnings have been applied, and our operational practices and strategies have been modified to mitigate the risk of future seepages," she said in an emailed statement.

"Our enhanced operational practices and strategies — in place since July 2013 — includes modified steaming strategies, enhanced pressure monitoring and response strategies as well as remediation of wellbores to mitigate the risk of future seepages."