General Description
Hydraulic Jars are run in conjunction with, or in combination with, other fishing tools.
The Hydraulic Jars was specially designed for oil well fishing operations.
The Hydraulic Jar is simple and easy to operate. No presetting is required and no adjustments are necessary during its use. Only straight pull is required to operate the tool. The operator is always in complete control and may strike forceful blows as often and rapidly as he can operate the rig. In addition, varying the stretch applied to the fishing string can control the intensity of each blow.
Full torque may be applied in either direction and in any position of stroke during operation. Full fluid circulation may be maintained at all times.
Use
The Hydraulic Jars is used for fishing, testing, reaming, washover, coring, and directional or straight drilling.
Construction
Since the manufacturer maintains them, we will not discuss the parts too deeply. We will name the basic parts and terms used when we discuss jars.
The Hydraulic Jar has a top sub and a mandrel. These pieces are usually one piece and are referred to as an Integral Mandrel Jar. There is a middle body and a bottom sub. The middle body is usually made in two parts. This makes two connections on the middle body that has to be tightened (with rotary tongs) before running in the hole. Both connections are fine thread and this should be considered when tightening them.
Operation
Hydraulic Jars are used to jar up on a fish. The closer you have them to the stuck point, the more effective they will be. Also, the more concentrated weight you run immediately above them, like drill collars or heave weight drill pipe, the more effective the jarring action will be. Hydraulic Jars are most always run in conjunction with bumper jars. A typical combination of tools would be an overshot to catch the fish, bumper jars, hydraulic jars, and six drill collars with the work string above.
To use Hydraulic Jars, you should pick up the weight you want to jar and hold it for a few seconds. The jars will hit or go off. When the jars hit, lower the string until you have a slight weight down on the jars. This will close the jar or recock them. Then pull them again to the desired weight for another lick. Sometimes after prolonged jarring, the jars will hit much sooner or before you can reach the desired weight. When this happens, close the jars and let them set for a few minutes.
All Hydraulic Jars have a maximum pull load and a maximum jar load. Always refer to the manufacturer’s books before jarring to determine the maximum weight you can jar.
Different jars will differ in the time they hit. Sometimes you may have to work them up and down a few times to make them hit the first time. Sometimes in a well, where you have a lot of drag, the friction on the wall of the hole will prevent you from getting enough pull on the jars to make them work. This will have to be determined by the well conditions.
You should never jar with the pipe on elevators, be sure they are secured where they cannot snap open.
Always be sure that the derrick is clear of people and objects that could be dislodged while jarring. Do not let people stand on the rotary or the rig floor while jarring. Do not allow crews to gang up in one place and block the passageways where you cannot move out of the way if necessary.
Remember: Always keep safety in mind!