Storms in the Black Sea and alerts of potential drone attacks at a key loading terminal are slowing the ramp up of crude oil production at Kazakhstan’s giant Tengiz oilfield, industry sources told Reuters on Wednesday. The huge field, capable of producing 950,000 barrels per day, was forced to shut down last month following a fire at the site that damaged critical power supply. Since then, the field, operated by a Chevron-led consortium, has resumed operations and has been gradually raising production. However, the pace…