Top Western oil companies face a hit to revenue as disruptions at a Russian Black Sea port force producers to curtail output from Kazakhstan’s giant oil fields, highlighting the growing global supply risk after Moscow's invasion of Ukraine.

Chevron Corp., Exxon Mobil Corp., Shell Plc, TotalEnergies SE and Italy’s Eni SpA are among international companies with stakes in Kazakhstan’s oil fields.

More than 80% of the central Asian country’s crude is exported via the Caspian Pipeline Consortium (CPC) pipeline to the port of Novorossiisk, supplying around 1.2% of global oil demand.

The port’s operator shut down two of the three berths at the CPC export terminal on March 23, blaming damage from a recent storm, although loadings were partially resuming from one on March 24.

Chevron, the operator of Kazakhstan’s largest oil venture Tengizchevroil (TCO), on March 24 said it was reducing output owing to the unscheduled repair work at Novorossiisk.

The company would not provide details on the size of the output cuts.

And storage at the CPC terminal was nearing full capacity, traders said.

Sources with knowledge of the terminal said they believed it was unlikely the site’s berths were significantly damaged by the storms, which have been built to withstand severe weather, pointing instead to Russian politics in the face of heavy Western sanctions.

Russian energy officials do not usually comment on the CPC pipeline, which is run by an international consortium. A spokesperson for Chevron, which operates the CPC pipeline, earlier declined to comment on the reason for the shutdowns.

The 1,511 km-long pipeline exports around 1.1 million bbl/d, the equivalent of around $140 million based on current oil prices. Its owners also include Exxon Mobil, Eni, Shell, domestic energy company KazMunayGas and Russian pipeline operator Transneft.

The barrels include the roughly 700,000 bbl/d produced from TCO, in which operator Chevron holds a 50% stake while Exxon Mobil holds 25%.

CPC is also the main export route for the Kashagan oil field with production of about 400,000 bbl/d.

It was unclear if output was reduced at the Kashagan and Karachaganak oil fields.

TCO accounted for more than 10% of Chevron's production last year at 338,000 bbl/d. For Exxon Mobil, Kazakhstan accounted for 210,000 bbl/d in 2020, almost 10% of the company’s total oil output.

Shell declined to comment. Exxon Mobil, Eni and TotalEnergies did not respond to a request for comment.