The Shock Sub impact and vibration reduction sub is a drillstring component that absorbs and dampens the variable axial dynamic loads produced by the drill bit during routine drilling and milling operations. The Shock Sub is most beneficial when drilling in hard rock, broken formations, and intermittent hard and soft streaks. Reducing the impact loads helps to increase ROP; improve borehole quality; and extend the life of the cutting structure, bearings, connections, and surface equipment—all translating to a lower cost of drilling per foot.
Advances in drilling technology have necessitated the redesign of shock tools to account for new parameters:
With enhanced reliability, better fatigue and corrosion resistance, large ID, significant reduction of vibrations, and the ability to operate with low or high weight on bit (WOB), the Shock Sub meets the challenges of modern drilling. It is made of high-quality, hardened steel. Seals isolate internal components from the drilling fluid and can withstand temperatures up to 400 degF.
The Shock Sub does not need to be activated in order to operate. During the drilling or milling operation, it is constantly working. As the cones of a roller cone bit traverse the pattern of “peaks and valleys” created on the bottom of the borehole, the Belleville spring assembly in the Shock Sub is compressed or allowed to relax, absorbing the shock load. Additionally, the load is dissipated by the mechanical friction resulting from the movement of the spring stack.
The axial movement of a hammer bit produces a similar compression and extension of the springs. These two combined actions isolate the axial loads present during the drilling operation and maintain a near constant WOB when the Shock Sub is run within its operational load limits.