Jarring is the technique of applying high-impact forces to free stuck drillstring or fishing assemblies. Drilling jars—specialized tools in the BHA—store energy and release it suddenly to deliver hammer-like blows that break the sticking forces holding pipe against the formation.
Jar Types and Mechanics
Hydraulic jars use oil flow through a metering system to delay impact, allowing tension or compression to build before release. Typical delay times: 30 seconds for upward jarring, 60 seconds for downward jarring.
Mechanical jars use mechanical triggers that release at preset loads.
Hydraulic-mechanical combination jars provide the benefits of both systems with adjustable impact force.
Impact Force
Jars can multiply initial overpull up to 8× depending on configuration and conditions. Longer-stroke hydraulic jars maximize both impact force and impulse duration, improving stuck pipe recovery success.
Success Rates
Recovery success varies by stuck mechanism and pipe type. Vibration-assisted jarring technologies show 62% success on liners, 25% on drill pipe, and 19% on tubing across 70+ wells (SPE 14759). Time is critical—jarring should begin immediately when sticking is suspected.
Prevention vs. Cure
While jars remain essential BHA components, preventing stuck pipe is far more cost-effective than freeing it. Autonomous weight-on-bit control minimizes stationary time and maintains optimal loading across problematic zones, reducing the stuck pipe incidents that require jarring operations. The best jar is one that never needs to fire.