Patent ID: 8323115
Filing Date: 2012-12-04
Classification: E21B

Abstract:
1. A cushion sub-assembly for connection to a drill string to absorb vibrations in the drill string, the cushion sub-assembly including: a main body defining a chamber therein; a piston member disposed within the chamber capable of axial movement at least partially within the chamber between a first and second position; at least one axially extending piston rod disposed inside a respective axial bore of the piston member, the at least one piston rod preventing relative rotation between the piston member and the main body while permitting axial movement of the piston member between the first and second positions; and a vibration absorbing means at opposite ends of the chamber for engagement by the piston member when in either of the first or second positions for absorbing axial vibrations; the configuration of the at least one piston rod inside the piston member, and engagement of the piston member with the vibration absorbing means serving to minimize transmission of axial vibrations between the piston member and the main body, wherein the upper end of the at least one axially extending piston rod is constrained by a cap to prevent movement thereof, wherein the vibration absorbing means at the upper end of the chamber comprises three pads of elastomeric material, each one of the three pads of elastomeric material having a different grade strength, and wherein the lower-most pad of elastomeric material has a first thickness and has a first, grade strength, the middle pad has a second thickness substantially equal to the first thickness and a second grade strength substantially greater than the first grade strength, and the upper-most pad of elastomeric material has a third thickness substantially thinner than the first thickness and has a third grade strength substantially greater than the second grade strength.