A torsional damping system includes a housing having an interior space. An inertia ring is located in the interior space, and a torsion fluid is located between the inertia ring and the housing. The inertia ring is rotatably installed relative to the housing. As the housing oscillates, the inertia ring damps at least a portion of the oscillation. The torsional damping system may be included in a downhole tool or bottomhole assembly, and used to damp oscillations along a drill string or along the bottomhole assembly, including between a downhole motor and a cutting tool.

An active system is provided that changes the mechanical stiffness of a BHA during drilling to prevent/reduce damage to a BHA due to vibrations. The active system uses a combination of mechanical and electronic systems to change the physical characteristics of a BHA that govern the natural frequencies thereof. The active system can change the mechanical stiffness of a BHA by switching between two different coupling modes for connecting sections or portions of the BHA. An active torsional isolator and damper (ATID) can be used to switch between the different coupling modes. In one example, the ATID includes: (1) a dynamic coupler configured to connect a first portion of a BHA to a second portion of the BHA according to different coupling modes, and (2) a processor configured to control switching of the dynamic coupler between the different coupling modes during a drilling operation of a drill bit.

A vibration mitigation tool may include a mandrel portion, a sleeve portion arranged about the mandrel portion and configured to move longitudinally and rotationally relative to the mandrel portion. The tool may also include a spring stack configured to control compression on the vibration mitigation tool through compression of the spring stack and to control tension on the vibration mitigation tool through compression of the spring stack. A helical engagement between the mandrel portion and the sleeve portion may also be provided.

An apparatus may include a connector sub rigidly securable to a conveyance for running the connector sub along a wellbore and a spool mandrel coupled to a downhole end of the connector sub. The spool mandrel is rotatable with respect to the connector sub. Further, the apparatus may include a control line extending between the connector sub and the spool mandrel. The control line is displaceable to permit rotation of the spool mandrel with respect to the connector sub. Additionally, the apparatus may include at least one biasing member for biasing the spool mandrel to a neutral position with respect to the connector sub.

An embodiment of a coupling device is configured to be disposed in a borehole string in a borehole in a subterranean region. The coupling device includes a coupler body having a longitudinal axis, the coupler body including an elongated shaft extending along the longitudinal axis and configured to carry loads through the coupling device, a stiffness control device connected to the elongated shaft, the stiffness control device configured to adjust a bending stiffness of the coupler body, and an actuator configured to cause the stiffness control device to adjust the bending stiffness of the coupler body.

A rotary glide system for a downhole tool includes a ball bearing sleeve comprising a first plurality of helical grooves formed into an inner surface of the ball bearing sleeve, a shaft comprising a bearing section having a second plurality of helical grooves formed into an outer surface of the shaft, the shaft configured to extend through the ball bearing sleeve, and a plurality of ball bearings disposed within a plurality of channels formed by the first and second pluralities of helical grooves.

An embodiment of a coupling device includes an elongated coupler body configured to be deployed at a borehole string and connected to a downhole component of a borehole string. The coupler body has a longitudinal axis, and the coupler body has a torsional stiffness sufficient to transmit rotational motion to the connected downhole component. The coupling device also includes at least one recess formed in a wall of the coupler body, the at least one recess extending along a periphery of the coupler body in a direction generally perpendicular to the longitudinal axis. The at least one recess is configured to impart a bending stiffness that is less than or equal to a reference bending stiffness, and the torsional stiffness and the bending stiffness are selected to modify a mode shape of an undesired torsional oscillation.

A vibration mitigation tool may include a mandrel portion, a sleeve portion arranged about the mandrel portion and configured to move longitudinally and rotationally relative to the mandrel portion. The tool may also include a spring stack configured to control compression on the vibration mitigation tool through compression of the spring stack and to control tension on the vibration mitigation tool through compression of the spring stack. A helical engagement between the mandrel portion and the sleeve portion may also be provided.

An offshore method includes providing an elongate support string for extending between a mobile offshore drilling unit and a seabed location. The string has an upper portion and a lower portion, and an articulated joint is provided between the upper portion and the lower portion. The provision of the articulated joint maintains the lower portion of the elongate support string in a substantially vertical orientation and increases the safe operating radius of the mobile offshore drilling unit or increases the speed at which the unit may transit through the sea with objects suspended via the elongate support string.

A downhole shock absorbing sub which includes a tubular main stem extending through a sub housing and a lateral shock absorbing assembly positioned within the sub housing. The lateral shock absorbing assembly includes an activator ring positioned around the main stem, the activator ring including a plurality of wedge inserts positioned around a perimeter of the activator ring. A reaction collar is positioned on each side of the activator ring with the reaction collars including ramp surfaces engaged by the wedge inserts. A spring system is positioned to resist movement of the reaction collars away from the activator ring, whereby lateral movement of the main stem causes the wedge inserts to move the reaction collars against the spring system.