Applying shock to pull stuck strings loose

The hydraulic jar tool is used if a packer or guns become stuck to provide an upward shock to help pull them loose—without tripping. To deliver repeated jarring as needed, the jar tool automatically resets through the application of string weight on the packer.

How it works

The tool comprises a housing connected to the free tools and a spline mandrel attached to the stuck tools. The housing can move up and down the mandrel.

The jar tool is initially closed (housing down). If the lower section becomes stuck, an overpull is put on the string to store energy in the drillpipe. This overpull causes the jar tool to begin metering oil through a flow restrictor in a chamber between the housing and mandrel. Once the seal ring reaches the undercut on the mandrel, the housing moves up quickly to produce an impact upward on the stuck tools.

Once the jar tool has been activated, the string is lowered, and the housing moves down. Oil flows through the one-way check valve back into the upper section of the chamber, and the tool is recocked, ready to jar again as many times as needed.