Shock subs, also known as vibration dampeners, are used to absorb vibrations and bit shock loads in drill collar strings. They usually feature long integral elastomeric elements, which serve to transmit torque and weight to the bit simultaneously. When drilling is being carried out at shallow depths, intermittent hard and soft streaks, along with broken formations, can transmit vibrations to the surface, where they are easily detected. With greater depths, though, these vibrations might not be detected because the drill string cushions them. However, they will still cause damage to the bit, as well as bottom hole assembly components and the drill string.
Some advantages of using a shock sub include:
- Offering faster drilling rates, since optimum bit weight and rotary speed may be used on the bit constantly.
- Increasing the bit length by reducing shock loads.
- Cutting damage to drill collars, drill pipe, and downhole tools by reducing bouncing.
- Reduced connection damage, because the elastomeric element absorbs both torsional and axial loads, so that connections are not at risk if the bit stalls.
- Reduced damage to surface equipment, including swivels, blocks, and wirelines.