Powered Slip Actuation

Abstract

A system for pushing and pulling rod strings through the ground or an underground pipe. The apparatus has a downhole tool attached to the distal end of the rod string. The push/pull machine has a stationary frame that is placed against the ground to provide a reaction surface. The stationary frame has an opening for the rod string to pass through. A grip assembly is supported on the stationary frame and moveable relative to the stationary frame. The grip assembly has a slip bowl, a plurality of slips, and an actuator. The actuator does not engage the internal surface of any slip and powers relative axial movement between the slip bowl and the slips. A positioning assembly carries the grip assembly and powers its reciprocating and straight-line movement to urge the grip assembly in either a first or second direction.

What is claimed is: 
     
         1 . A system, comprising:
 a grip assembly comprising:
 a slip bowl having a tapering internal passage; 
 a plurality of slips, each slip having an external surface conformable with the internal passage of the slip bowl; and 
 an actuator that does not engage the internal surface of any slip and powers relative axial movement between the slip bowl and the slips; and 
   a positioning assembly that carries the grip assembly and powers its reciprocating and straight-line movement.   
     
     
         2 . The system of  claim 1  in which the slip bowl is symmetric about an axis and in which the positioning assembly moves the grip assembly such that the slip bowl moves along that axis. 
     
     
         3 . The system of  claim 2  in which the actuator comprises a piston that is coaxial with the axis about which the slip bowl is symmetric. 
     
     
         4 . The system of  claim 1  in which the tapering internal passage of the slip bowl terminates at a narrow end and the actuator, in a powered state, urges the slips toward the narrow end of the slip bowl. 
     
     
         5 . The system of  claim 4  in which the actuator is a hydraulic cylinder having an extendable piston and in which the piston in a powered state urges the slips toward the narrow end of the slip bowl. 
     
     
         6 . The system of  claim 5  in which the piston is hollow and coaxial with the slip bowl. 
     
     
         7 . A method of using the system of  claim 1 , comprising:
 positioning a portion of a rod string section within the slip bowl;   powering the actuator to urge the slips in a first direction within the slip bowl toward a narrow end of the slip bowl and into a gripping relationship with the rod string section; and   powering the positioning assembly to urge the grip assembly and gripped rod string section in the first direction.   
     
     
         8 . The method of  claim 7  further comprising positioning a portion of the rod string section within the actuator before powering the actuator to urge the slips in a first direction. 
     
     
         9 . The method of  claim 7  further comprising:
 powering the actuator to urge the slips in a second direction, opposite the first direction, away from the narrow end of the slip bowl and into an ungripped relationship with the rod string section. 
 
     
     
         10 . The method of  claim 9  further comprising:
 powering the positioning assembly to move the grip assembly, without the formerly gripped rod string section, in the second direction. 
 
     
     
         11 . The method of  claim 10  further comprising:
 after moving the grip assembly in the second direction, powering the actuator to urge the slips in the first direction within the slip bowl toward the narrow end of the slip bowl and into the gripping relationship with the rod string section; and 
 thereafter, powering the positioning assembly to urge the grip assembly and gripped rod string section in the first direction. 
 
     
     
         12 . The method of  claim 7  in which urging the slips in the first direction comprises pushing the plurality of slips toward a borehole.