Patent ID: 7493967
Filing Date: 2009-02-24
Classification: E21B

Abstract:
1. A tractor for moving equipment through a borehole, comprising: an elongate body having an internal passage extending longitudinally therethrough, the internal passage being adapted for receiving pressurized operating fluid from a supply line; aft and forward gripper assemblies longitudinally movably engaged with the body, the aft and forward gripper assemblies each being hydraulically actuated and defining engagement surfaces configured to selectively engage an inner surface of the borehole; aft and forward propulsion assemblies configured to advance the body through the borehole relative to the aft and forward gripper assemblies, respectively; a valve system housed within the elongate body, the valve system being configured for directing a portion of the pressurized fluid from the internal passage to the aft and forward gripper assemblies in a desired sequence for effecting movement of the tractor through the borehole; a tractor isolation apparatus configured to prevent fluid in the internal passage of the body from flowing into the valve system, to thereby prevent longitudinal movement of the body within the borehole; and a pressure relief valve that regulates the pressure of fluid that flows from the internal passage of the body to one or more components connected downhole of the tractor; wherein when the isolation apparatus prevents fluid in the internal passage of the body from flowing into the valve system, the fluid in the internal passage can flow to the one or more components connected downhole of the tractor, the isolation apparatus comprising a start/stop valve having an open position in which the start/stop valve prevents fluid flow from the internal passage of the body into the valve system, the start/stop valve having a closed position in which the start/stop valve allows fluid flow from the internal passage into the valve system, the start/stop valve being configured to toggle between its open and closed positions when a differential fluid pressure between the internal passage of the body and an exterior of the tractor drops from a predefined high pressure threshold to a predefined low pressure threshold and then rises back to the high pressure threshold.