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An Apache Corp. pipeline spill in June in northwestern Alberta, 20 kilometres north of Zama City, Alta. In a separate leak in the oil sands, Canadian Natural Resources Ltd. said faulty engineering on old wells at its Primrose project is responsible for bitumen leaking to the surface of an oil-sands project, and the company did some of the work itself. CNRL believes steam-softened bitumen reached the surface up old vertical wells, escaping when it hit defective spots in the casing or cement. Under pressure, the bitumen squirted into natural cracks in the rock layers and moved upward.

Dene Tha First Nation

Canadian Natural Resources Ltd. said faulty engineering on old wells is responsible for bitumen leaking to the surface of an oil-sands project, and the company did some of the work itself.

CNRL believes bitumen made softer through steaming reached the surface unintentionally by travelling up old vertical wells and escaping when it hit defective spots in the casing or cement. Under pressure, the bitumen squirted into natural cracks in the rock layers and moved upward. Casing and cement are used to prevent hydrocarbons from spilling out of well bores. Bitumen is leaking at four sites on CNRL's Primrose project, and one leak has killed beavers, frogs, tadpoles, shrews and birds.

The leaks underscore how newer oil-sands technology, which the energy industry touts as key to carbon reduction and a smaller physical footprint in the oil patch, can cause unanticipated problems. While CNRL has collected 6,300 barrels of bitumen emulsion in its cleanup effort, the four leaks are still releasing a combined 20 barrels of oil per day.

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Now experts are wondering whether Alberta's current extraction methods could lead to more leaks.

"Throughout Alberta there are many old wells, which were drilled, which were not completed for thermal operation," said Ian Gates, a professor in the department of chemical and petroleum engineering at the Schulich School of Engineering at the University of Calgary. "That is – thermal cement was not used and thus, when an operation steams where these wells are located, there could be a failure of the non-thermally completed wells and thus flow to surface behind the casing of these wells."

Steve Laut, CNRL's president, said while the investigation is ongoing, his Calgary-based company may have cemented and cased the wells that are now leaking. CNRL in investigating a handful of potentially problematic wells, including former gas and water-source wells, Mr. Laut said Wednesday.

"We're pretty confident we know it is a well-bore failure, but just exactly what the mechanism within that failure is, it is too early for me to give that detail," he said. "Some of them will be our wells. Some of them will be other operators in the area before."

Amoco Corp. is one of the companies in the area prior to CNRL, Mr. Laut said. "In over 30 years of using the current steaming and extraction method in the Primrose area, there have been few bitumen emulsion seepages to surface," the company said in a statement.

Two leaks started on May 20, one on June 8, and the final on June 24, according to Alberta Energy Regulator spokeswoman Cara Tobin. The regulator did not issue news releases on the first three spills because they were "small" and had "no public impact," she said. They were disclosed on the incident reporting section of the regulator's website. The fourth leak was announced in July in an AER press release because it involved water. The other three were mentioned in that statement because they were "related," Ms. Tobin said, adding the AER encourages companies to inform the public. CNRL, which did not address the spills until after the AER issued its release in July, said it believed the regulator was keeping citizens informed.

"In hindsight, we should have come out with more information sooner, but we thought that the regulator was providing that information" Mr. Laut said.

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