ASTANA, Oct 21 (Reuters) - Kazakhstan's Chevron ( CVX )-led

Tengiz oilfield, the country's largest, has been

undergoing maintenance which is due to be completed on October

24, Energy Minister Erlan Akkenzhenov told Reuters on Tuesday.

Tengizchevroil (TCO), Kazakhstan's largest producer, reached

record monthly output of 3.715 million metric tons, or around

953,000 barrels per day, in August at the field.

An industry source said the field had reduced oil production

in the first 19 days of October by around 27% from September's

average to 700,000 barrels per day.

TCO did not immediately reply to a request for comment.