Drill Collar
Drill Collars are heavy wall rigid pipes that are used as part of the bottom hole assembly above the drill bit. Drill Collars are stiff tubular, which are added in the drilling assembly so that more weight on the bit can be applied at the bottom for drilling without the risk of buckling the drill string. Drill collars can be either plain or spiral. Spiral drill collars have spiral grooves machined on their outer surface. This reduces the contact area of the drill collar with the hole, reducing the chances of differential sticking.