CALGARY, Alberta, Aug 7 (Reuters) - Alliance Pipeline shut down its 1.6 billion cubic feet per day (bcf/d) natural gas mainline in Western Canada on Friday after poisonous hydrogen-sulphide gas got into the system, forcing at least one shipper to suspend production.
The 3,848-kilometre (2,391-mile) Alliance Pipeline delivers natural gas from Western Canada and North Dakota's Williston Basin to the Chicago market hub.
The company, a limited partnership owned by affiliates of Enbridge Income Fund Holdings and Veresen Inc, did not give any estimate of when the pipeline would restart.
"In order to correct the situation, Alliance is commencing mitigation activities which are expected to result in a zero-flow condition on the pipeline," the company said in a statement.
Hydrogen sulphide, a flammable, extremely hazardous gas with a rotten egg smell, entered the mainline pipeline system as a result of complications experienced by an unnamed upstream operator, the company added.
Seven Generations Energy Ltd, a shipper on the Alliance system, said the pipeline company had called for all natural gas suppliers to suspend pipeline injections for an indeterminate period, starting on Friday morning.
Seven Generations, a Calgary-based light oil producer, has been forced to shut in 55,000 barrels of oil equivalent per day, its entire production, as a result.
"This suspension will result in a deferral of essentially all of Seven Generations' production until the situation is resolved. 7G intends to use this temporary event to conduct maintenance of its production and processing facilities," the company said.
Alliance spokesman Rob Gray could not give details of exactly how the hydrogen sulphide gas entered the system and said the company's first priority was to manage the situation safely.
Alliance plans to get rid of the natural gas that has been affected by flaring it at its Alameda compressor station in Saskatchewan.
Daniel Sutherland, Alliance's vice president of commercial Operations, apologized to customers and said the company was working with partners and regulators to determine the cause. (Editing by Peter Galloway)