“This is a project every company would like to have if they could,” said J. Robinson West, the managing director of the BCG Center for Energy Impact, a consulting firm .

The expansion is about three years from completion, but the Tengiz oil field already provides nearly a quarter of Kazakhstan’s national revenue, and about a quarter of Chevron’s profits. Chevron approved the project in 2016 at what may have seemed like an inopportune time: The world was awash in oil, and the industry was still reeling from a price collapse that had begun in 2014. Expanding the Tengiz operation appeared to be a good bet because the field had performed so well in the past and because Chevron places a high value on its relationship with Kazakhstan.

“When we looked at this, it was the major capital project that we felt was worthy,” said Todd Levy, Chevron’s exploration and production president for Europe, Eurasia and the Middle East.

Still, the expansion remains a calculated gamble.

It begins with the weather. Ice on the Caspian can halt shipments of equipment, idling thousands of workers. Chevron has had good luck so far, officials said, and the project is more than half finished.

Making progress at Tengiz also requires maintaining good relations with Moscow, which has not forgotten that Kazakhstan was a Soviet republic until the early 1990s. Russia looms over its neighbor along the 4,200-mile border they share, with equipment bound for Tengiz moving through Russia’s waterways and crude oil from Tengiz shipped through a Russian port on the Black Sea. It helps that the Russian company Lukoil is a partner in the joint venture, known as Tengizchevroil .