Reduced flow rates on the 590,000 bbl/d Keystone pipeline are having only a slight impact on oil deliveries, analysts at consultancy Wood Mackenzie said on July 21, four days after operator TC Energy declared force majeure.

Calgary-based TC has not said when the pipeline, one of Canada's major export arteries to the United States, will return to full service.

One of the pipeline's pump stations in South Dakota was shut down on July 17 after damage to the pump's third-party power supply. Repairs are ongoing.

But analysts at Wood Mackenzie, which monitors pipeline volumes, said data shows the impact on flows has been limited.

"Keystone has continued operating since the incident began, as power consumption persisted at surrounding pump stations. Although a slight disruption did occur, our data shows that the impact on flows has been much less severe than what many expected," Wood Mackenzie analysts wrote in a note.

"We do not expect this disruption to have major, long-term impacts on Canadian crude prices and deliveries."

A spokeswoman for TC Energy said late on July 20 there was no material impact resulting from the reduced flow rate.

Crude traders in Calgary said there had been little impact on prices from the reduced rates. Benchmark Canadian heavy crude last settled around $20 a barrel below the WTI benchmark, according to brokers NE2 Group.