Activating mechanism for hydraulically operable downhole tool

Abstract

An activating mechanism for a hydraulically operable downhole tool provided in a drill string, in which the mechanism is incorporated in the drill string and has a tubular housing, a pressure piston mounted for linear reciprocating movement in the housing between first and second end positions, a mandrel coupled with the piston for movement therewith between an activating position and a non-activating position to control the supply of hydraulic pressure fluid to operate the downhole tool when the mandrel is in the activating position, a cam arrangement for controlling the linear movement of the piston, and a cam follower to permit linear indexing movement of the piston, communication means for applying drill string pressure to the piston, and means biasing the piston in a direction from the second end position to the first end position so that, when drill string pressure is released, the activating mechanism is indexed.

1 . An activating mechanism for a hydraulically operable downhole tool provided in a drill sting, in which the mechanism is adapted to be incorporated in the drill string and comprises: 
 a tubular housing;    a pressure piston mounted for linear reciprocating movement in the housing between first and second end positions    a mandrel coupled with the piston for movement therewith between an activating position ( FIG. 1   c ) and a non activating position ( FIG. 1   a ), in which the mandrel controls the supply of hydraulic pressure fluid to operate the downhole tool when the mandrel is in the activating position;    a cam arrangement for controlling the linear movement of the piston and having a cylindrical cam with a cam profile, and a cam follower engageable with the cam profile such that, upon relative rotation taking place between the cam and the cam follower, linear indexing movement of the piston is permitted between the first and second end positions;    communication means for applying drill string pressure to the piston to move the piston from the first end position to the second end position when permitted by the cam arrangement; and    means biassing the piston in a direction from the second end position to the first end position so that, when drill string pressure is released, the activating mechanism is indexed whereby, upon subsequent pressurisation of the drill string, the cam arrangement does not undergo relative rotation and linear movement of the piston from the first end position is prevented.    
   
   
       2 . A mechanism according to  claim 1 , in which the cam arrangement comprises a cylindrical body having at least one inwardly extending indexing pin forming said cam follower, and a cylindrical barrel rotatable within said cylindrical body and provided on its outer surface with said cam profile which is engageable by said indexing pin.  
   
   
       3 . A mechanism according to  claim 1 , in which the cam profile is a wavy profile undulating laterally of the direction of linear reciprocation of the piston.  
   
   
       4 . A mechanism according to  claim 3 , in which two axially spaced indexing pins are provided, engaging a common cam profile at axially spaced locations.  
   
   
       5 . A mechanism according to  claim 1 , in which the biassing means comprises a compression spring acting on a lower end of the mandrel.  
   
   
       6 . A drill string incorporating a downhole tool and a mechanism according to  claim 1.