A device for damping vibrations of a rotary drill string in motion in a wellbore, a related method, drill string and drill string sub or section, where at least one component of motion of the drill string is communicated to the device, and brake means counter the vibrations, resisting the motion in dependence upon the speed of motion. The device may have an outer sleeve arranged on an inner, tubular body which is rotatably arranged within the outer sleeve. Roller wheels support the sleeve on the wellbore wall and facilitate longitudinal movement of the device and prevent rotational slipping of the outer sleeve relative to the wall upon rotating the tubular body and drill string. One brake part of the brake means on the outer sleeve and another on the tubular body operate to resist rotational vibration components.

A high frequency torsional oscillation mitigation tool for use in a downhole drilling assembly. The tool has a first end, a second end, and a one-way coupling therebetween. The one-way coupling has a first part connected to rotate with the first end and a second part connected to rotate with the second end. The one-way coupling has an engaged condition in which the first part and the second part can rotate together in a first rotational direction whereby drill string rotation can be communicated to the drill bit. The one-way coupling has a disengaged condition in which the first part can rotate relative to the second part in a second rotational direction. The one-way coupling can have multiple sets of driving elements along its longitudinal axis. The tool can include a locking mechanism to override the one-way coupling for recovering a stuck downhole assembly.

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.

A downhole tool has a main body that is cylindrical and includes a top coupling that couples to a drill string. A second body that is cylindrical is positioned at least partially within the main body. The second body has a bottom coupling that couples to a drill bit. Springs are positioned within the downhole tool and transmit an axial force to the drill bit. A first set of grooves is formed on an interior of the main body, and a second set of grooves is formed on an exterior of the second body. Balls travel within the first and second sets of grooves. At least some of the balls simultaneously engage the main body and the second body.

A high frequency torsional oscillation mitigation tool for use in a downhole drilling assembly. The tool has a first end, a second end, and a one-way coupling therebetween. The one-way coupling has a first part connected to rotate with the first end and a second part connected to rotate with the second end. The one-way coupling has an engaged condition in which the first part and the second part can rotate together in a first rotational direction whereby drill string rotation can be communicated to the drill bit. The one-way coupling has a disengaged condition in which the first part can rotate relative to the second part in a second rotational direction. The one-way coupling can have multiple sets of driving elements along its longitudinal axis. The tool can include a locking mechanism to override the one-way coupling for recovering a stuck downhole assembly.

A sub-assembly, rock drilling rig and method of absorbing vibrations in rotary and DTH drilling. The sub-assembly is for transmitting torque and axial forces between a rotating head and a drilling tool. There is an axial floating arrangement for providing an allowed limited axial relative movement between coupling elements of the sub-assembly. The arrangement comprises several axial drive pins for transmitting the torque. First ends of the drive pins are mounted immovably and second ends are mounted with clearances, whereby the drive pins can bend under torsional shocks. Thus, the drive pins serve as torsional dampening elements.