دیکشنری تخصصی مهندسی نفت - نسخه آنلاین

n: 1. a hole in the rig floor, some 30 to 40 feet (9 to 12 metres) deep, which is lined with casing that projects above the floor, into which the kelly and the swivel are placed when hoisting operations are in progress. 2. a hole of a diameter smaller than the main hole and drilled in the bottom of the main hole. v: to reduce the size of the wellbore and drill ahead.