Offset Housing

I. Adjust The Main Functions And Roles of The Offset Housing

1. Core function: connection and transition.

It serves as a "bridge" connecting the upper stator/rotor and the lower drive shaft assembly of the downhole motor. It smoothly transmits the low-speed and high-torque transmitted from the universal joint to the drive shaft, ultimately driving the drill bit to rotate.

2. Key function: adjust length and match specification.

There may be minor manufacturing tolerances or length differences among stator and drive shaft assemblies of different models. By using offset housings of different specific lengths, it can be ensured that the total length of the entire downhole motor and the preload force of the internal components meet the design requirements.

3. Provide internal space and protection.

Adjusting the internal cavity of the shell provides space for the universal joint (usually a flexible shaft or hinged universal joint) to accommodate and operate, and allows the drilling fluid to pass through smoothly. As a robust shell, it protects the internal universal joint components from direct impact and wear by external drilling fluid and the wellbore wall.

4. Transmit torque and bear loads.

As a link in the power transmission path, the offset housing needs to withstand and transmit the counter-torque of the drilling tool. Meanwhile, it also helps to bear part of the axial and radial loads.

II. Characteristics and Requirements of Offset Housing

Due to its significant role, the offset housing has strict requirements in design and manufacture:

• High-strength materials: They are usually forged from high-strength alloy steels (such as AISI 4140, 4340, etc.) to ensure their mechanical properties.

• Precision threads: The connecting threads at both ends must be precisely machined, featuring high strength and wear resistance to ensure no puncturing or disengagement occurs under high pressure and high torque.

• Strict dimensional control: There are strict tolerance requirements for its length, inner and outer diameters, concentricity, etc., to ensure the straightness of the entire drill tool and the smoothness of power transmission.

• Excellent corrosion and wear resistance: The inner and outer surfaces usually need to undergo heat treatment (such as quenching and tempering) or surface treatment (such as chromium plating, nitriding) to resist the corrosion of drilling fluid and the erosion of abrasive particles.

III. Precautions in Actual Use of Offset Housing

• Thread maintenance and inspection: After each drill is lifted, the threads at both ends of the housing must be carefully inspected and cleaned for adjustment. When fastening, it must be tightened in accordance with the standard torque value.
  

• Visual inspection: Check whether the shell body has obvious wear, pits or cracks. Especially the outer surface in contact with the well wall, if it wears out excessively, its strength will be weakened.

• Pay attention to internal erosion: Long-term operation in high-flow, sand-containing drilling fluid may cause the inner wall to be eroded and thinned, and regular wall thickness detection is required.