Posted May 19, 2017 20:59:10

Photo: Woodside Petroleum said it reported a leak from an oil well in April last year. (ABC)

Woodside Petroleum says an oil spill off the coast of Western Australia, which was kept secret by the offshore regulator for more than a year, has not caused lasting damage to the environment.

The oil and gas giant said it reported the leak from a well in the Cossack field on the North West Shelf to the National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA) in April 2016.

But the leak was not disclosed until this week when NOPSEMA referenced the 10,500-litre spill in its annual offshore performance report without naming the operator or location.

In a statement to the ABC, a spokesperson for Woodside said the company estimated the leak continued for 60 days at a maximum rate of about 175 litres per day, and was the result of a "seal degrading on a subsea hydraulic valve control line".

The company insisted no environmental damage was caused.

"Due to the composition of the fluid, small quantity released, water depth at release site and distance from environmentally sensitive areas, there was no lasting impact to the environment," the statement said.

"We remain a committed, responsible and prudent operator and continue to adhere to transparent reporting and high standards of operations that have characterised our history."

Topics: oil-and-gas, mining-environmental-issues, port-hedland-6721