Chevron Corp. affiliate Tengizchevroil LLP has started up the first phase of an expansion at Tengiz Field in Kazakhstan. The addition of 90,000 barrels a day brings total capacity to 400,000 barrels a day.

A major segment of the expansion was the start of a gas injection project, which injects sour gas into the reservoir at high pressures to improve production. Another component was front-end construction of a plant to process sour gas into useable products.

Later this year, when facilities are at full capacity, Chevron will be able to produce 540,000 barrels of crude a day from Tengiz. Plans call for injection of one-third of the field’s sour-gas production and processing of the remaining two-thirds.

Interests in supergiant Tengiz are held 50% by Chevron, 20% by KazMunaiGas, 25% by ExxonMobil and 5% by LUKArco.