The giant Tengiz oilfield in Kazakhstan has returned 60% of its peak production and was pumping at a rate of 550,000 barrels per day as of Sunday, following a forced shutdown for half of January due to a fire, anonymous sources told Reuters on Monday. Tengiz, which is operated by a consortium led by U.S. supermajor Chevron, is expected to reach peak levels of oil output of about 950,000 bpd by February 23, according to the sources familiar with the production data. The Tengiz oilfield was forced into a temporary shutdown on…