UP-HOLE OVERSHOT AND SAFETY DRILLING APPARATUS

摘要

The drilling apparatus includes a safety sub mountable to the drill stri ng outer end to retain the combination of an overshot assembly and an overshot adaptor extending within the drill string outer end during a drilling operation and preventing the drilling tool moving out of the drill string until the sub is removed. The overshot assembly has a fluid seal between the overshot tube and the dri ll string and a fluid bypass channel with valve means for blocking axial outwar d flow through the channel when the overshot adaptor is separated from the overshot assembly and when connected thereto, retaining the valve means in a n open condition. When the overshot adaptor is removed from the overshot assembly, the overshot assembly is fluidly propellable to the bit end. A disconnect tool facilitates the removal of the adaptor from the sub.