Definition
Weight on Bit — Weight on bit (WOB) is the downward axial force applied to the drill bit at the bottom of the hole, supplied by the weight of the drill collars and BHA, that drives the cutting structure into the formation to make hole.
Also known as: weight on bit, WOB
What WOB is
Weight on bit is the compressive load pressing the bit against the rock. It comes not from pushing the drill pipe from surface but from the buoyed weight of the drill collars and heavy components in the bottomhole assembly. The driller controls WOB by slacking off a portion of the string’s weight through the brake while the rest keeps the drill pipe in tension. The dividing line between the collars in compression and the pipe in tension is the neutral point.
Balancing WOB
Too little WOB gives slow penetration; too much causes bit damage, excess torque, buckling, and directional problems. Optimal WOB is balanced against rotary speed (RPM) and hydraulics to maximize rate of penetration while protecting the bit and controlling deviation. Only the collars and heavy-weight pipe should ever be in compression — running standard drill pipe below the neutral point invites fatigue and failure.
Why it matters for rentals
Delivering the right WOB means carrying enough collar weight for the bit and hole size, which varies by well.
Rent the drill collars and BHA components you need to build proper weight, or contact us for help sizing collar weight to your bit and hole program.