Drilling Jar Manual
Written by Jim Borthwick Technical and Simulator Instructor For DART Drilling and Advanced Rig Training KCA DEUTAG Drilling Limited Copyright Notice © KCA DEUTAG Drilling Limited No part of this document shall be reproduced in any materials, including photocopying or storing it by electronic means without the prior written permission of KCA DEUTAG Drilling Ltd, Training and Development department, except as permitted by the Copyright, Designs and Patents Act 1988.
Forward This manual and the course it accompanies are designed to show the basic principles of how drilling jars and accelerators work. Drillers seldom get the opportunity to use jars and often they are in doubt about the mechanisms associated with what is happening down hole when forces are applied to the string.
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Drilling Jar Manual Introduction During the drilling process the possibility of getting the drill string stuck in the hole exists. Well construction teams do try to design the well with the least possible chance of this happening. However drill strings do get stuck despite all the prevention efforts, to allow the Driller the opportunity to get the string free a drilling jar can be included in the bottom hole assembly (BHA). There is a fairly large range of drilling jars available to the industry. Several different types exist such as mechanical jars, hydraulic jars and hydro-mechanical (hybrid) jars. The various mechanisms which allow the jar to be operated may differ but the principle behind how they transmit forces remains the same. The manual will discuss all the basic jar principles and one particular hydraulic jar, the operation of most jars is basic, but one particular jar is often thought to have failed to operate. Often it has simply not been given long enough to complete its metering stroke. This manual will give information to clarify and educate, it should never be used in place of the manufacturers operating manual. Never operate any jar or associated equipment outside the manufacturers recommended envelope. Always use and follow manufacturers instructions. As stated previously the manual is designed to familiarise drilling teams in the use of jars. Do not use the information within as an operations manual. Another genre of jar exists in the industry, this is the fishing jar. A fishing jar may be used for a whole plethora of reasons. This manual will not cover fishing jars. Jim Borthwick Simulator and Technical Instructor
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Drilling Jar Manual Contents Sectio Sectio n 1 – The The Basic Princ ipl e
• •
What is a jar The most basic jar
Secti Secti on 2 – Mechanical Mechanical J ars
Secti Secti on 3 – Hydraulic Jars
Secti Secti on 4 - Hydro-mechanical Jars
Secti Secti on 5 – Jar Positi on
• •
Placement programmes Stress wave theory
Section 6 –
Section 7 – Ap pendi pen di ces
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Drilling Jar Manual Section 1 The basic Principles What is a Jar? A Jar is a device which can deliver an impact force to a drill string which is stuck, if it is operated correctly. Purposes Drilling Jars can be included in the string prior to drilling or work-over operations. Fishing Jars are usually used as part of a string placed in the hole to recover broken drill strings and drill string components, but they can be included in drill strings recovering sections of casing or liner. Types There are three basic types, Mechanical J ars Most mechanical Jars are designed to trigger when a particular magnitude of force has been applied, only this amount of force can be used. The force to trigger them is set by the manufacturer in the workshop based on experience or client requirements. Some mechanical Jars can be reset to a different value by rotating the drill string a certain number of turns, these are fairly uncommon. Hydraulic Jars Hydraulic Jars use hydraulic oil to delay the firing mechanism long enough for the Driller to apply a force to the string. The time delay can vary greatly between different makes of Jar. One Jar in particular can take up to 7 minutes to fire in the desired direction. Hybrid Jars Hybrid Jars are also called Hydro-mechanical Jars; this is because they use a combination of both mechanical and hydraulic principles to operate. Sometimes the Jar is designed to operate hydraulically up but also mechanically down. Other types use the mechanical latch simply to keep the Jar in the centre latch position during tripping and drilling operations, this means that the Jar can be fired up or down immediately without the need to cock them. The following discussion will cover the basic principles of how all jars work and how pressure, tension and compression affect them.
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Drilling Jar Manual The Basic Jar The most basic type of Jar is simply a sliding hammer; this device is used in warehouses every day to remove nails from wooden packing crates or pallets. A similar device is used in drilling to remove stubborn float valves from float sub recesses or bit jets which may be stuck.
Hammer
The sliding hammer slides freely between an upper and lower stop. The claw at the bottom is hinged in such a way that whenever an upward blow is delivered it closes gripping what ever it is applied to. The claw is placed in a position suitable for grabbing the nail head. A downward blow is applied by sliding the hammer down and striking the lower stop with a force. This embeds the claw into the wood at a sufficient depth to put it below the level of the head of the nail. The hammer is then slid up rapidly and the hammer impacts the upper stop with a force, this closes the claw and moves the nail up a little. Repeating this process will eventually move the nail up until it is completely removed.
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Drilling Jar Manual Jars Although Jars may be much bigger than the device for removing nails, they still work on the same basic principles. The sliding hammer is comprised of an inner mandrel attached to the upper portion of the drill string and an outer barrel attached to the lower portion of the string.
Inner Mandrel
Outer Barrel
The inner mandrel is not fixed to the outer barrel; it uses mechanical stops or shoulders to prevent it sliding all the way out. The distance that the mandrel can slide relative to the outer barrel is referred to as the stroke. The total stroke can vary with make and size, it can range from 12 inches to 28 inches, although these values are not absolute, some types of Jar can have smaller or longer strokes.
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Drilling Jar Manual Forces Jars are subjected to a variety of forces; the Jar is designed to transmit those forces from the upper portion of the string to the lower portion of the string. Not only forces applied to a stuck drill string are expected to be transmitted. The primary function of a drill string is to drill a hole, it is those forces which are most often required to be transmitted. The three forces that are required are,
• Tension • Compression • Torque There is also another force which has to be taken into account, it is,
• Pressure The tension and compression forces are transmitted mechanically by shoulders, mechanical stops or knockers. The torsional forces are usually transmitted mechanically be a spline drive mechanism. Spline Drive A spline drive is a mating mechanism which allows a drive shaft to transmit rotational forces to a housing via teeth called splines.
A shaft is attached to the inner mandrel of the Jar
A Bush is attached to the outer barrel of the Jar
The spline allows the mandrel and barrel to move independently up and down while still being capable of transmitting torque.
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Drilling Jar Manual
Shoulders
Knocker
Spline
The inner mandrel can slide in and out of the outer barrel and still be able to transmit rotational forces.
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Drilling Jar Manual What is Moving When calculations are performed to establish cocking or jarring forces; the weight of the string below the Jar has to be taken into account for the following reason, when the string is stuck part of the string may still be capable of some movement. If the sticking point is below the Jar the string above the Jar will be able to move as far as the stroke of the Jar. If the string is stuck above the Jar; the Jar will not be capable of transmitting forces required to free the string. When the BHA is made up the Driller should record the weight below the Jar as recorded on his weight indicator, this is used as a general guideline to establish what the weight indicator should read at various points in the Jar cycle. There is also the Jar friction to take into account; this is the friction that all the seals and mechanical parts inside the Jar have to overcome to start opening or closing. The example below shows how the calculations are performed to establish surface weight readings for the different phases of the Jar cycle. Pressure There is also pressure to be taken into account, because pumping forces and trapped pressure in the string act to force the Jar to open. This will be discussed in detail later in this section of the manual. Example Up weight Dn weight WBJ Jar Friction POF
= 350,000 lbs = 250,000 lbs = 30,000 lbs = 10,000 lbs = 32,000 lbs
To cock jars down for firing up = 250,000 – (30,000 + 10,000 +32,000) In this case a set down weight of 178,000 lbs is required to cock the jar To fire the Jars down = 250,000 – (30,000 + 10,000 +32,000 + X) X = the load that is being applied for jarring If X = 80,000 a set down weight of 98,000 lbs is required. Calculations for all the phases are in the Appendix section of the manual.
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Drilling Jar Manual Drilling Jars Several types of drilling jars exist, too many to discuss in one manual. The types of Jars we will discuss in any detail are,
•
Mechanical Jar
•
Hydraulic Jar
•
Hybrid Jar
The only specific make of Jars we will discuss is the Hydrajar™ and the Dailey® Hydraulic Drilling Jar. Dual Act ing Dual acting means that they are capable of jarring up and down. The Blow The blow or hit comes from shoulders or knockers striking each other when the Jar becomes fully open or fully closed. These parts are often referred to as the hammer and the anvil. The discussions on specific makes of Jar will highlight how the blow is transmitted on that particular Jar
In some Jars the impact can be between the top of the outer barrel and the bottom of the large diameter portion of the inner mandrel.
In others the impact can be between Knockers or shoulders inside the Jar
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Drilling Jar Manual Pump Forces When the pumps are on the pressure losses between the Jar and bit nozzles act on the Jar. This force pushes the Jar open. The name for this force can vary; they are usually called “pump open force” or “Jar extension force”. Regardless of the name the effect is the same. Seals All Jars have seals, this is to,
• • •
Separate well bore fluids from affecting mechanical parts. Act as a barrier between the fluids and pressures inside and outside the Jar. Prevent hydraulic fluid leaking or becoming contaminated by mud, cuttings or other undesirable fluids.
Ports Some Jars have ports in the outer barrel to allow pressure equalisation between fluid in the Jar and the well bore as the Jar is run deeper in the hole. The pumping forces act differently on different makes of Jar, however it acts on all Jars to some degree. Trapped pressure also acts in a similar manner to the pressure losses between the Jar and the bit nozzles; this pressure is the pressure as read on the stand pipe pressure gauge. The following pages describe how pressure acts on two types of popular Jars made by two different manufacturers. The first is the Smith Services HE Group Hydrajar™ and the second is the Dailey® Hydraulic Drilling Jar. These Jars are discussed in particular because of their popularity, reliability and ease of use. The author and the company make no marketing comparisons or express a preference of any particular make of Jar.
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Drilling Jar Manual The Hydrajar™ As the jar is run deeper in the hole the fluid in the well bore enters ports in the outer barrel. Seals which are floating (not attached to the inner mandrel or the outer barrel) are pushed by the fluid pressure in the well bore, this equalises the pressure in the hydraulic chambers with the hydrostatic of the well. Pumping Forces When the pumps are on the pressure in the drill string causes the Jar to extend. This pumping pressure acts on the bottom of the mandrel wash-pipe area. It is a simple calculation using the pressure loss in psi multiplied by the area in square inches of the wash-pipe.
For example the wash-pipe area of an 8" Hydrajar ™ is approximately 16² inches. Therefore if the pressure losses between the Jar and bit nozzles are 2,000 psi. The pump open force or Jar extension force is approximately 32,000 lbs. This means that a weight of 32,000 lbs will need to be applied to move the Jar closed, there are other considerations which also need to be taken into account, see example on the next page.
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Drilling Jar Manual • • • •
Down weight Weight below jar Pump open force Friction of seals and mechanical parts
= 300,000 lbs = 30,000 lbs = 32,000 lbs = 10,000 lbs
•
300,000 – (30,000 + 32,000 +10,000) = 228,000 lbs
A fully open jar will start to close at this point. A mechanical jar will stop closing when the latch re-engages and the jar is cocked. • A hydraulic jar such as a Hydrajar™ will start metering on the down stroke and fire down if the driller continues to move the string down. • The driller can observe the jars closing on his weight indicator. • •
Each manufacturer of Jars provides tables to determine what the pump open force is. These tables should come with the other Jar paperwork, if not contact the vendor; they will usually make reference to their website which sometimes allows free downloading of the tables in PDF format.
This is an example of the Hydrajar™ extension force table. Contact Smith Services HE Group for further information or clarification, the table above is for demonstration purposes only and should not be used to replace the Hydrajar™ operating manual supplied by the manufacturer.
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Drilling Jar Manual The Dailey® hydraulic Drilling Jar The Dailey Jar has seals which are fixed to the inner mandrel, this results in a greater area being affected by the pressure. An 8" Dailey Jar has a pump open area of 28.3" this means that with 2000 psi pressure losses the pump open force is 56,600 lbs. There are no ports in a Dailey Jar and the mandrel or inner workings are never exposed to well bore fluids such as mud or contaminants such as cuttings.
These are only 2 examples, the other makes of Jar will have different pump open areas because of the difference in design, it is important that you use the correct table for the Jar in use.
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Drilling Jar Manual Latch or Trigger Mechanism All types of Jar need a latch mechanism or trigger mechanism to allow potential energy from the Drillstring to be suddenly released as kinetic energy. For instance when the Driller needs to Jar up or down he needs time to apply a force before the Jar trips or fires. Mechanical Jar A mechanical Jar is named for obvious reasons; the latch mechanism is purely mechanical. Below is a description of a basic type of mechanical latch.
Spring loaded buttons keep the Jar in the centre latched position
Inner mandrel Outer barrel
•The The jar will not fire until enough force has been applied to compress the spring • The Jar will then move in the desired direction • This Jar is in the process of being fired Up
Jar up and down trip settings are usually different, the up trip setting is usually higher than the down trip setting. Ensure that the value for the Jar in use is known.
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Drilling Jar Manual Hydraulic Jars The Hydrajar™ The latch mechanism comprises of,
• • •
A piston which slides freely up and down between two stop shoulders. A detent area which acts as a cylinder for the piston, it forms a seal that will not allow hydraulic oil to pass. A metering port, this is a small communication port which will allow oil to pass from one chamber to the other very slowly
1
2
3
4
5
6
7
The seven illustrations above show how the hydraulic up-latch in the Hydrajar™ works. 1. 2. 3. 4. 5.
The Jar is fully open. The Jar has started to close The piston comes into contact with the detent. The Jar is still closing but the piston is sliding up to the upper piston stop. The piston is on the upper stop and the by-pass valve is fully open, the hydraulic oil can now pass freely from the lower chamber to the upper chamber. 6. The piston is about to leave the detent. 7. The Jar is fully closed now. The Haydrajar™ has two of these mechanisms. One is for jarring up; and the other is for jarring down. One is simply a mirror image of the other. The lower latch would have tripped and the Jar will have fired down in the long stroke.
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Drilling Jar Manual The Long Stroke Down Below is a series of illustrations which show both latches going through the long stroke to fire down.
1
2 3 4
5 6
The Hydrajar™ may take up to 7 minutes to fire when it moves from fully open to fully closed, this is because the piston needs to travel all the way through the detent. 1. 2. 3. 4.
The Jar is fully open, both pistons are on the lower stops. The Jar starts to close and the pistons make contact with the detents. The pistons slide up towards the upper stops. The pistons are now on the upper stops, the top latch has opened the bypass allowing oil to pass freely from the lower chamber to the upper chamber. The lower piston has closed the by-pass and the oil can now only meter through the metering port slowly. 5. The Jar is being lowered further and string weight is being applied to fire the Jar down. 6. The Pistons exit the detents and the drill collars and heavy weight drill pipe accelerate, the shoulders on the mandrel and outer barrel collide providing an impact to the string.
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Drilling Jar Manual The Long Stro ke Up Below a series of illustrations show the Jar going through the long stroke up, the Jar is going from the fully closed position to the fully open position.
1 2
3
4
5
6
Again the Jar may take up to 7 minutes to fire in the long stroke. 1. The Jar is fully closed. 2. The Jar starts to open and the pistons make contact with the detent. 3. The Jar continues to open and the pistons slide from the upper stop to the lower stop, the lower piston has opened the by-pass port and the upper piston has closed the by-pass port. 4. The Driller has applied a force to fire the Jar up, the lower piston moves unrestricted through the lower detent, the upper piston can only move through slowly in its metering cycle. 5. The Driller has been waiting for up to 7 minutes and the pistons are about to exit the detent. 6. The pistons exit the detent and the Jar opens very quickly as the potential energy in the stretched string is turned into kinetic energy.
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Drilling Jar Manual The Short Strok e After the Jar has been fired up, the Jar need only be cocked to fire up again. To cock it the pistons simply need to be slid back into the detents. The Driller lowers the string until he sees 10,000 to 15,000 below his down weight minus his weight below the Jar.
1
2 3 5 4
A full description of the calculations for cocking and firing the Jar is in the appendix section of the manual. 1. The Jar is fully open. 2. The Driller lowers the string and the pistons contact the detent sliding them to the upper stops. 3. The pistons are now inside the detents. 4. The Driller picks up and applies his desired firing force. 5. The pistons only need to slide approximately 50mm to exit the detents; the waiting time is only 2 minutes with low over-pulls. The Jar fires up again.
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Drilling Jar Manual Hydrajar™ Delay The long stroke is only used to fire the Jar up when it is fully closed. It is only used to fire the Jar down when the Jar is fully open. If the Jar is already open it can be cocked and fired up in the short stroke. If it is closed it can be cocked and fired down in the short stroke. Below is a table which shows the expected delay time in seconds in both the long and the short stroke.
This chart is for demonstration purposes only; contact Smith Services HE Group for information on the delay time of the Hydrajar ™.
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Drilling Jar Manual Jar Limits Detent Li mit The Hydrajar ™ has a maximum limit of force which can be applied to it when it has been cocked; this limit is determined by the amount of hydraulic pressure the mechanical parts, seals etc can withstand. This limit is called the detent limit. This is the same for all hydraulic Jars not just the Hydrajar™. The limits are clearly stated in the manufacturer’s tables of operating limits. Below is an example of the Hydrajar ™ limits.
This table is for demonstration purposes only, contact Smith Services HE Group for information on the detent limits of the Hydrajar ™. Exceeding the limits of the detent will damage or even destroy the Jar. Tong and slip die notches in the detent area can cause the Jar to fail at a value under the stated detent limit. Do not use slips or tongs on the Jar outer barrel. The manufacturer will simply charge the user for any damage caused by misuse. When the Jar is fully open the limit is determined by the tensile limit of the material, this may be steel or other materials such as vanadium. Since Jars are in the BHA they are under less tension than the drill pipe. The drill pipe which will be under most tension will be the joint immediately under the top drive or Kelly. The detent limit should be compared to the margin of over-pull (MOP). If the detent limit is greater than the MOP, the limit is the drill pipe strength. If the detent limit is less than the MOP the limit of tension is determined by the Jar detent limitations.
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Drilling Jar Manual Other Limit s Because Jars are manufactured from high tensile materials it can make the prone to certain types of failure. One of these is fatigue; this is because fatigue cracks propagate more quickly in hard materials. This is the reason why we record the rotating hours for the Jar and limit its rotating hours.
Notice that the rotating limit for milling is 50 hours in all cases. Milling produces particularly high rotational vibrations; this accelerates fatigue in high strength materials. Jars should only be included in a string for milling after very careful consideration. Contact the Manufacturer of the Jar for information and advice when milling with Jars. Never exceed the recommended rotating hours. If the Jars have been used to mill for a period prior to drilling, contact the manufacturer for advice on the limit for drilling rotating hours, they will have to be reduced due to the time spent milling. High strength materials can be prone to stress corrosion cracking in high chloride or sulphide environments. The Hydrajar oil can get hot when jarring for long periods, this is due to friction. The Jar may fire before sufficient tension has been applied; in this case the Jars have to be left to cool down.
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Drilling Jar Manual
Dailey® Hydraulic Drilling Jar The Dailey® hydraulic drilling jar works on the same principle for using hydraulic oil metering through valves or ports to delay the firing. However the Dailey® Jar delay mechanism itself is vastly different to the Hydrajar™, the differences are,
• • • • • •
The Dailey has a single mechanism for up and down metering. There is no long and short stroke. The length of time to trip is shorter. The knockers and impact surfaces are all contained within the Jar body. There are no equalisation ports. There is virtually no internal friction so the Jar does not overheat.
The similarities are,
• • • • •
The Jar will fire down if the driller continues to go down after it is cocked. They are subject to Jar extension forces. They have detent limits. They have rotating hour limits. They are prone to the same failure mechanisms as any other high strength material.
The Dailey® hydraulic drilling Jar is manufactured by Weatherford Drilling & Intervention Services. Contact them for specific information and advice when using the Dailey® Jar.
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Drilling Jar Manual Trigger Mechanism The trigger mechanism on the Dailey Jar consists of two pistons on the inner mandrel which seal on the outer barrel; there is a hydraulic valve between the two pistons. When the Jar is cocked and in the centre latch position the valve is closed. When the mandrel is pulled through further a shoulder on the outer barrel prevents the lower half of the valve from moving any more with the inner mandrel. The Jar is now metering, When a enough force is applied the two halves of the valve are forced apart which allows the oil to by-pass the metering ports and the Jar opens rapidly causing the hammer to strike the anvil.
in
ton
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Drilling Jar Manual Energy The energy for jarring up is the stretch in the drill string and the energy for jarring down is the weight of the drill string above the Jar pushing down. It is usually easier to get en impact up than it is to get an impact down, especially in a deviated well bore. In a horizontal well it may be impossible to get an impct down because of the drag. The Jarring Trade Off The position of the Jar in the string will determine how effective they are. A combination of impact and impulse is required. The proportions of impact and impulse depends on many variables. Impact force Impact force is defined as “ A high force or shock applied over a short period ot time” High impacts are achieved by light weights moving very fast. For example a squash ball can travel at fairly high velocitey, however th impact force when it strikes the wall is not enough to deform or break the wall. This is because the ball is made of rubber and air, it has a small mass. If the rubber and air ball was replaced by a solid lead ball travelling at the same velocity it would deform or break the wall easily. This is because we have increased its mass. However the energy required to accelerate it to the same velocity as the rubber ball would also have to be greatly increased. If we simply hit it with the squash racquet it would not travel fast enogh to reach the wall, and may in fact burst the racquet. Impulse Impulse is defined as the integral of a force with respect to time. In the technical sense, impulse is a physical quantity not an event or force. In the example of the squash ball the ball made of rubber produced a high impact, the ball made of lead travelling at the same speed produced a high impact and a high impulse. With respect to Jars, a high impact is how hard the blow is and impulse is how long the blow lasts or how far the string moves when blow is struck. The Trade Off To effectively place the Jar in the string we have to make certain assumptions, • Where will the stuck point be? • What will the sticking mechanism be? If the string is stuck at the bit by a piece of junk, the string will not have to be moved a great distance to become free. If however it is differentially stuck it will have to be moved a considerable distance to become free. When the impact and impulse forces are generated by the drillstring, the shock wave travels in all directions at the speed of sound, these waves are called stress waves. Page 25 of 33
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Drilling Jar Manual Stress Waves Once generated stress waves will travel along the string at the speed of sound through steel, this is approximately 5000 metres per second. The waves do not conveniently travel to the stuck point. They travel all along the string, the waves have to pass through many different cross sectional changes in the string, this is due to the geometry of the components, tools, connections and cross overs. As they encounter these changes in geometry the waves can be transmitted or reflected. Transmitted waves continue on their journey, reflected waves are disipated into the mud, formation and well bore. To effectively calculate Jar placement special software is required, rule of thumb is not accurate enough when a bottom hole assembly may cost several million dollars. Jar manufacturers have such software and they provide a service that gives advice on Jar placement. The software is usually modelled using stress wave theory. Neutral p oint The neutral point is the transition point in the string where it changes from being in tension to being in compression, placing the Jar at this point may cause them to inadvertantly cock or fire due to bouyancy effects. Jars should be placed with consideration to the neutral point when drilling with maximum weight on bit. The Jar should be placed above this point because the buckling neatral point is always below this point. In vertical wells the Jar should be placed above the buckling neutral point when maximum weight on bit is being applied and 2 drill collars should be placed above the Jar as a minimum. In deviated wells up to 45 degrees they should never be run below the buckling neutral point, this is very difficult to calculate so design software is usually used to determine this. In horizontal wells the force of gravity pulls the string into the curve of the low side of the hole. This force resists the string bending sideways sinusoidally. This means that there is little chance of the Jars ever becoming buckled.
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Drilling Jar Manual Neutr al Point Neutral point in a vertical string can be calculated using Archimedes principle. This states that a body immersed in a fluid is bouyed up force equal to the weight of the displaced fluid. It applies to both floating and submerged objects. For example if a person were to pick up a rock weighing 60 lbs and walk into a lake with it until it was completely submerged, it would no longer feel as if it weighed 60 lbs, a bouyancy force acting on the surface area of the rock would appear to weigh less by the exact weight of the fluid it displaced, so if the rock displaced 2 gallons of water it would appear to weigh less by the weight of 2 gallons of water, aproximately 16.6 lbs, the rock would feel as if it had lost this weight even though it still contained the same mass. The neutral point in a vertical drill string cam be calculated using this principle, the exaples are in the appendix section.
The bouyancy force would be acting this area at the bottom of an open ended drill collar.
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Drilling Jar Manual Helpi ng The Jar What if the stretch in the available drill pipe is not enough to overcome the stroke of the Jar? What if the drag in the well bore is preventing string contraction or impeding the mass above the Jar in some way due to friction? How can we increase the force provided by the Jar without exceeding our limitations? Ac cel erat or s Accelerators also have an inner mandrel sliding in and out of an outer barrel, however there is no trigger or latch mechanism. The device is kept in midstroke by a spring or pressure vessal and pistons. The energy from the tension applied at surface forces the accelerator open and the energy is stored in the spring. The spring can be made from a solid material,a fluid or a gas. Fluid spring types are usually called intensifiers. Regardless of the name they do the same thing. Short String If the Driller was drilling top hole and there was HWDP to surface, there would be insufficient stretch in the string to overcome the stroke of the Jar. The Jar would not fire regardless of how much over-pull was applied. An accelerator compensates for the stretch by storing it in the spring. When the Jar fires the energy of the extra tension is delivered by the spring contracting. The accelerator should should not shoulder out fully open, or fully closed even when the maximum force is applied at the Jar. Otherwise it is not being allowed to function correctly. High Drag Conditio ns When the Jar fires the whole length of stretched drill pipe needs to contract to deliver the blow. If high drag conditions exist the string may be restricted in movement and contraction may be slowed. An accelerator stores the stretch in the spring eliminating the need for the whole s tring to contract. Ab so rb in g Shock The impact force from the Jar blow tries to travel all the way up the drill string. In some cases this has damaged top drive units. By seperating the string above the accelerator from the shock it acts as a shock absorber. This has the effect of transmitting more of the impact force to the stuck point. The force can easily be double the original blow.
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Drilling Jar Manual Ap pen di ces Calculate the neutral point of 3 stands of 6 inch DC’s in a vertical well with 12.2 ppg mud in the hole.
⎛ M GR × L × X Area ⎞ ⎟ S WT ⎝ ⎠
NP = L − ⎜
Where, SWT L MGR XArea Stand NP
= String weight (lb/ft) = Length of string (ft) = Mud gradient (psi/ft) = Cross sectional area of the string at the bottom (in2) = 93ft = Depth of neutral point from surface
Example
⎛ 0.6344 × 279 × 28.274328 ⎞ ⎟ 96 ⎝ ⎠ ⎛ 5004.5 ⎞ NP = 279 − ⎜ ⎟ 96 ⎝ ⎠ NP = 279 − (52.13) NP = 279 − ⎜
NP = 226.87 The neutral point can only be calculated this way for a vertical well, deviated wells require the use of software to accurately determine the neutral point
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Drilling Jar Manual Jarring Calculations To cock the jar down for firing up = DW – (WBJ + JF + POF) To cock the jar up for firing down = UW – (WBJ + POF) + JF To fire the jar up = UW – (WBJ + POF) + JF + X To fire the jar down = DW – (WBJ + JF + POF + X)
Where DW UW WBJ JF POF
= = = = =
Down weight lbs Up weight lbs Weight below jar lbs Jar friction lbs Pump open force lbs
Example UW DW WBJ JF POF X
= = = = = =
350,000lbs 250,000lbs 40,000lbs 10,000lbs 20,000lbs Desired firing force
For example purposes X = 100,000lbs To Cock down for firing up 250,000lbs – (40,000lbs+10,000lbs+20,000lbs) = 180,000lbs To cock up for firing down 350,000lbs – (40,000lbs + 20,000lbs) + 10,000lbs = 300,000lbs To fire up 350,000lbs – (40,000lbs + 20,000lbs) + 10,000lbs + 100,000lbs = 400,000lbs To fire down 250,000lbs – (40,000lbs+10,000lbs+20,000lbs + 100,000lbs) = 80,000lbs The Jarring Worksheet on the next page keeps a good record of Jarring operations.
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Drilling Jar Manual Jarring Work Sheet
Jar type Jar OD Up weight (UW) Down weight (DW) Jar detent limit (JDL) Jar tensile limit (JTL) Jar stroke Weight below jar (WBJ) Jar friction (JF) Maximum up weight (MUW) Margin of over-pull Maximum first pull Maximum total pull Weight to cock jar up Weight to Cock jar down Pump Open Force (POF) Rig Date
lbs lbs lbs lbs inch lbs lbs lbs lbs lbs lbs lbs lbs psi
Free up weight on weight indicator Free down weight on weight indicator Maximum limit when Jar is cocked Maximum limit when jar is fully open Full stroke of jar The recorded WBJ when BHA run The friction to start jar moving Maximum up weight of pipe in use MUW - UW Drillers limit prior to supervision MUW based on pipe strength UW – (WBJ + POF) + JF DW – (WBJ + JF + POF) Pressure differential inside and outside the jar Time Depth
Operation when string got stuck Bit Depth
M
Over-pull applied
Pressure
psi
Returns
lbs lbs
Ft/lbs
secs
Jar hit 3
lbs
Ft/lbs
secs
Jar hit 4
lbs
Ft/lbs
secs
Jar hit 5
lbs
Ft/lbs
secs
Jar hit 6
lbs
Ft/lbs
secs
Jar hit 7
lbs
Ft/lbs
secs
Jar hit 8
lbs
Ft/lbs
secs
Jar hit 9
lbs
Ft/lbs
secs
Jar hit 10
lbs
Ft/lbs
secs
Jar hit 11
lbs
Ft/lbs
secs
Jar hit 12
lbs
Ft/lbs
secs
Jar hit 13
lbs
Ft/lbs
secs
Jar hit 14
lbs
Ft/lbs
secs
Jar hit 15
lbs
Ft/lbs
secs
Jar hit 16
lbs
Ft/lbs
secs
Jar hit 17
lbs
Ft/lbs
secs
Jar hit 18
lbs
Ft/lbs
secs
Jar hit 19
lbs
Ft/lbs
secs
Jar hit 20
lbs
Ft/lbs
secs
Jar hit 21
lbs
Ft/lbs
secs
Jar hit 22
lbs
Ft/lbs
secs
Jar hit 23
lbs
Ft/lbs
secs
Jar hit 24
lbs
Ft/lbs
secs
Jar hit 25
lbs
Ft/lbs
secs
Page 31 of 33
lbs
gpm
Yes/No
Jar hit 1 Jar hit 2
As read on weight indicator
Pump rate Jar up or down
Packed off Return flow Delay Ft/lbs time Ft/lbs
Hit
Yes/No
lbs
Torque
% secs secs
Version 1.0
Drilling Jar Manual Length of Free Pipe
L =
735294
× W × e dP
ft
Where L e W dp
= = = =
Length of free pipe ft Stretch due to differential pulling inches Weight per foot of DP tube lb/ft Differential pull lbs
If the highest pull is 100,000lbs and the lowest pull is 50,000lbs L e W dp
= = = =
? 30 inches 19.5 lb/ft 50,000lbs
Constant is 735294
L =
735294 × 19 . 5 × 30 50000
ft = 8602 . 9 ft
L = 8602.9 ft
Page 32 of 33
Version 1.0
