Patent ID: 9097086
Filing Date: 2015-08-04
Classification: E21B

Abstract:
1. A tractor assembly for use with a downhole tool, the tractor assembly comprising: an actuator comprising a cylinder, a piston in the cylinder that is selectively moveable in the cylinder between a deployed position and a stowed position, and a piston rod coupled to a side of the piston; a gripper coupled to an end of the piston rod distal from the piston, and selectively moveable between a retracted position substantially contained within a body of the downhole tool and an extended position in contact with a wellbore wall; fluid in the cylinder that is retained in the cylinder on a side of the piston distal from the piston rod and isolated from the piston rod; magnetically responsive particles in the fluid; and a magnetic field source for selectively generating a magnetic field that intersects the fluid, so that a viscosity of the fluid increases when the magnetic field is applied to the fluid and dampens vibration in the tractor assembly, so that an urging force is selective transferred from the fluid to the piston.