BACKGROUND OF INVENTION

1. Field of the Invention

This invention relates to a release mechanism for a jarring device used in conjunction with the drilling and/or completion of oil or gas wells. Jarring devices are typically used in conjunction with drilling or completion tubular strings positioned within a well to impart an upward or downward force on a tool carried by the string should the tool or string become lodged within the well.

2. Description of Related Art

U.S. Pat. No. 5,139,086 discloses a double acting jar having a first end for connection to a work string and a second end 2 for connection to the tool which may become struck in the wellbore. The jar includes accumulator springs 4 and 5 which act to accumulate energy in two directions. Also disclosed are latch bars, bias spring 13 and bushings 12. The amount of force necessary to release jarring mandrel 2 is determined by the adjustment of bias spring 13 which acts on latch bars 11 via bushings 12. Latch bars 11 include ridges 17 which are positioned in a groove 16 on the jarring mandrel. The more compressive force applied to latch bars 11, more force is required to displace ridges 17 out of groove 16 thereby enabling the jarring mandrel to be released.

U.S. Pat. No. 5,330,018 discloses a similar latch mechanism including latch bars 160, ridges 170 and 182 and grooves 100 and 118 located in mandrel 100.

The release mechanisms of the prior art have the disadvantage of excessive wear and increased friction which reduces the effectiveness and reliability of the jar.

BRIEF SUMMARY OF THE INVENTION

The present invention overcomes the deficiencies of the prior art as discussed above by providing a predetermined release mechanism for a jar that reduces drag and wear to a minimum. Springs such as Belleville springs are compressed within a split housing. A collet is positioned between a jarring mandrel and a trigger sleeve. The trigger sleeve surrounds the collet and the mandrel. A force sufficient to overcome the force exerted by the springs is required before the mandrel is released thereby allowing the jar to operate.

