In downhole drilling operations, whether it be when drilling for oil, gas, or water, or for civil, geological or mining engineering purposes, typically a drill string is used to connect the surface rig to the downhole bit or motor. The drill string is usually comprised of a number of tubular sections that are threaded together such that its length can be varied as needed.
During the drilling operation the drill string can sometimes become wedged against the wall of the well casing or bore hole, often requiring the application of a high impact tensile load in order to free the wedged string. In other instances high impact tensile loading may be necessary to retrieve downhole tools that have been "set" within the well, or that otherwise have become lodged within the casing. To provide the application of high impact tensile loading for such purposes, others have developed mechanical or hydraulic jars that are capable of "jarring" or impacting the drill string in an upward or downward direction. In the case of an upwardly operating jar, a high impact load is directed upwardly to retrieve tools or dislodge a wedged drilling string. In the case of a downwardly directed jar, the impact loading is typically utilized to "set" a variety of different downhole tools with the well.
Unfortunately, such existing jars generally tend to be relatively complex mechanical and hydraulic devices that add significant capital expense to the drilling operation, and that are more prone to becoming jammed and to failure.