The Jarring Assembly

Fishing Oil Jars

Hydraulic (Oil) Jars

General Description

Hydraulic (Oil) 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!

Accelerator Jars

General Description
The Accelerator Jar was developed to run in conjunction with any hydraulic rotary jar.  The function of the Accelerator Jar is to supply extra acceleration to the upper portion of the hydraulic jar and drill collars during the jarring (free) stroke of the hydraulic jar.

When pull is applied to the fishing string, fluid, or gas in the Accelerator is compressed storing high-intensity energy.  At the free stroke of the jar, this energy is released, giving up this stored energy to accelerate the upward travel of the hydraulic jars and drill collars, resulting in a high-impact blow, delivered directly to the fish where it is most effective.

Use
The Accelerator Jar is, in a sense, a spring that should be run with the proper tension.  Effectiveness of the jarring action of a hydraulic jar is proportional to the upward acceleration produced at the drill collars and lower end of the fishing string during the free stroke of the jar.  This acceleration is produced, in turn, by the rebound of the running string having been stretched and suddenly released.  It is clear, then, that any condition that diminishes this available stretch will diminish the effectiveness of the jarring action.  Such conditions exist in very deep or very crooked holes where much of the stretch is given up to drag in the hole or “doglegs.”  Also, at very shallow depths, very little stretch is available in the running string due to the inherent lack of stretchable length.

The great value of the Accelerator Jar or Booster Jar is that it stores energy at the point of greatest effectiveness.

An important secondary benefit is that after jarring, the Accelerator cushions the downward rebound of the fishing string.  This reduced the shock to the string, tools, and rig, minimizing shock damage.

Construction
The tool utilizes the Mandrel Piston assembly within the fluid chamber, but has no tripping mechanism and no free-stroke.  The Fluid chamber is filled with gas or hydraulic fluid under low pre-compression.  During the pull stroke, this fluid is highly compressed, absorbing and storing the energy that is suddenly released by the tripping of the jar below it.

The Seals have Teflon anti-extrusion rings to assure long life even in hot hole conditions.  Accelerator Jars and Booster Jars are available in all drill pipe sizes from 1 13/16” through 6 5/8” A.P.I. regular.

Operation
They are run above the Hydraulic Jars and the amount of weight run between them and the Hydraulic Jars determine the tension.  When you pick up on the work string to begin jarring, the additional pull will completely open the Accelerator Jar (putting it in full tension).  When the Hydraulic jars move upward to hit, the tension on the Accelerator Jars will increase the speed that the mass between the jars travel; therefore, it will increase the impact of the Hydraulic Jars.

There is a chart available to figure the weight that should be run between the jars.  If you don’t have a chart, a good rule to follow is one drill collar per O.D. inch of the jars, as long as the O.D. of the jars and drill collars are close.  If they are not, then you will have to make allowances for them.

Accelerator Jars are very helpful in deep crooked holes where drag is a problem.  They will allow the lower part of the string to move much faster.

They are good to run when jarring shallow, where you have no stretch in the drill pipe.  Regardless of where you run them, they reduce the shock on surface equipment.

Bumper Jars
 
General Description
Bumper Jars are probably the most simple of all fishing tools, but also one of the most useful to a fishing tool supervisor.

Any properly made up fishing string will necessarily include a dependable Bumper Jar.  The Fishing Bumper Jar will provide sustained bumping action, either upward or downward.  It is rugged and dependable.  Full circulation may be maintained through the tool at al times and in any position of stroke.  The tool will transmit full torque in either direction and in any position of strike; open, close, or during stroke.

Use
The Fishing Bumper Jar is used in all types of fishing operations.  It is usually made up in the string immediately above the fishing tool or safety joint (or both), enabling the operator to deliver forceful downward blows or upward blows at will.  The Fishing Bumper Jar is used to break the “freeze” of engagement of fishing tools, to shear pins, to dislodge a stuck string, or to use as a “feed-off” tool in pipe cutting operations.

Fishing Bumper Subs are suited for all fishing operations; they will bump down, jar up, or help disengage a fish after retrieval.  Their rugged simplicity makes them simple to operate and very easy to maintain.  They are available in sizes to match all sizes of fishing strings, drill pipe, or tubing.

Construction
The Bumper Jar is a telescopic or slip jarring action.  You determine exactly where the jar closes on the downward stroke and mark the pipe or Kelly at the top of the rotary.  Then pick up until the jar is extended open, plus about 10,000 lbs. strain.  At this time, drop the string as rapidly as possible, catching it will the mark three or four inches above the rotary.  The stretch in the pipe will cause the jars to snap closed very rapidly.  It is like slapping your hands together very rapidly.
The Bumper Jar is a good tool to have in the string to give you a neutral weight point.  It also permits you to move the work string up and down to prevent sticking when in open hole.  It can be used to run a predetermined amount of weight on the bottom when there is a need to.  I am sure you can find other uses for them when the need arises.

Images Courtesy of Logan Oil Tools.