U.S. drillers this week added oil rigs for an 11th week in the past 12, according to a closely followed report on Friday, although the rate of increases has slowed as crude prices remain below the key $50 a barrel level that spurs a return to the well pad. That is, however, the longest streak of not cutting rigs since 2011 with the rig count increasing or holding steady every week so far this quarter. Drillers added two oil rigs in the week to Sept. 16, bringing the total rig count up to 416, the most since February but still below the 644 rigs seen a year ago, energy services firm Baker Hughes Inc said. The oil rig count plunged from a record high of 1…