bent sub

bent sub

[′bent ‚səb]
(petroleum engineering)
A short cylinder installed in the drill stem between the lowest drill collar and the downhole turbodrill to deflect the turbodrill from vertical in order to drill a directional hole.
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Like its predecessors, the 3-inch RockEye hammer system comes complete with two bits, bent sub, transmitter housing, shock dampening transmitter assembly, portable break out kit and a drill pipe adapter.
In this method, the drill string does not rotate and precise control of directional drilling is effected by using a bent sub close to the head of the drill string.
The forward steering surface is located on the bit, while the second is located on the bent sub. The dual steering surfaces work in tandem to provide predictable steering, regardless of soil condition.
This is achieved by using either a downhole motor with a bent sub between the drill bit and the downhole motor, or by use of a combination of standard barrel, stiff barrel, impregnated bits and surface set bits.
At 70 inches in length, which includes the transmitter housing, 2-degree bent sub, bearing housing and drill bit, the R.A.T.T.
The probe is located in a non-magnetic bottom hole assembly that typically includes a collar, orientation sub and a bent sub with a bit when jetting or a mud motor.
A 2-degree bent sub allows the operator to make quicker direction changes for more rotating time and increased penetration.
Before the bore progressed, the Island Mechanical crew stopped drilling, read the orientation of the downhole bent sub, and marked it on the drill pipe.
Compressed air passes through the transmitter boring via the bent sub to operate the percussive device impacting the drill bit and rock that needs to be broken.
The inner shaft powers a high-torque rock bit; the outer pipe provides directional control with a bent sub and high-torque for backreaming.
A mud motor achieves steering in rock with a bent sub - a slight (1 1/2 to 3 percent) bend in the motor's housing.
The system employs a patented dual pipe system: the inner pipe powers a high-torque rock bit, and the outer pipe provides directional control with a bent sub.