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Jars
1. WHAT IS JARRING
Jarring is a process of transferring stored strain energy
(drill pipe stretch) in to Kinetic energy by releasing the
detent (delay mechanism) in the jar.
• Kinetic Energy = ½ M x V2
• M is the mass of weight members above jar
• V is the velocity
• When the jar trips, the energy is released providing a
sudden Impact
3. HYDRAULIC UP JAR
• STRAIGHT PULL OPERATED JAR, NO PRIOR SETTING
• VARIABLE IMPACT, OPERATES IN A CLOSED HYDRAULIC ENVELOP
• USED DURING FISHING, DST & CORING
4. HYDRAULIC JARS
• Hydraulic jars use a hydraulic fluid to delay the firing of the jar
until the driller can apply appropriate load to the string to
give a high impact
• Time delay is provided by hydraulic fluid being forced
through small ports or series of jets
• Hydraulic jar firing delay is dependent upon combination of
load & time
MECHANICAL JARS
• Mechanical jars have a preset load that causes the jar to trip
•Thus they are sensitive to load & not to time
5. HYDRAULIC/MECHANICAL DRILLING JARS (NOV)
• HYDRAULIC DELAY UPSTROKE & MECHANICAL DOWN STROKE
• FEATURES A MECHANICAL LATCH
• JET TYPE METERING DEVICE FOR HYDRAULIC DELAY
• JAR PLACEMENT CAN BE IN TENSION OR COMPRESSION
DOUBLE ACTING HYDRAULIC/MECHANICAL
DRILLING JARS (NOV)
• HYDRAULIC DELAY UPSTROKE & DOWN STROKE
• FEATURES A MECHANICAL LATCH
• JET TYPE METERING DEVICE FOR HYDRAULIC DELAY
• JAR PLACEMENT CAN BE IN TENSION OR COMPRESSION
6. POWER STROKE HYDRAULIC DRILLING JARS (NOV)
• HYDRAULIC DELAY UPSTROKE & DOWN STROKE
• NO MECHANICAL LATCH
• SEAL CONE TYPE METERING SYSTEM FOR HYDRAULIC DELAY
• JAR PLACEMENT CAN BE IN TENSION OR COMPRESSION
JAR PLACEMENT IN TENSION
•The weight of BHA below jar plus the ‘pump open force’ tends to keep the jar
in open position
JAR PLACEMENT IN COMPRESSION
•The jar will normally be in tension when the bit reaches bottom. Jar needs to
be triggered down with a light blow in order to avoid any damage to bit
•Jar will cock to neutral position whenever string is lifted off bottom. Therefore
above procedure of triggering down with light blow shall be repeated every
time a connection is made
7. DRILLING JAR OPERATIONS
FOLLOWING INFO SHOULD BE AVAILBALE PRIOR TO
MAKING CALCULATIONS FOR JARRING
• Normal pick-up weight
• Normal set down weight
• Free rotating weight
• BHA weight below jar
• Jar Internal Friction
• Pump Open Force
• Maximum jar load
• Up latch setting (hydraulic/mechanical jars)
• Down latch setting (hydraulic /mechanical jars)
JARRING SHOULD START IN THE OPPOSITE DIRECTION TO
THAT WHICH GOT THE STRING STUCK
