8-Drilling Jar and Jar placement - (ELC)

IPM Stuck Pipe Prevention 8- Introduction of Drilling Jar & Jar Placement
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STUCK PIPE
Learning Objectives
• • • • • Have a basic understanding of jar physic Know the different types of jar Understand the importance of jar placement Know general guidelines about jar placement Know why the jar is not firing
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STUCK PIPE
Drilling Jars and Comparison
Comparison of Mechanical and Hydraulic Drilling Jars Capabilities Overpull setting variability. Mechanical One setting made at surface of 10,000 lb to 180,000 lb, depending on jar size Hydraulic Continuously variable down hole, between 10,000 and 135,000 lbs.
STUCK PIPE
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Drilling Jars and Comparison
3. Hydro mechanical
• Are a hybrid of both designs, usually hydraulic up and mechanical down
Easier passage with larger OD tools. Passage difficult or impossible in high inclination wells. Dailey and similar designs can Change by 10 -15%
Typically has a larger ID than mechanical jar with the same OD, which is an advantage up to an OD of about 6 ¼”. Yes 400ºF bottom hole static is approximate limit. As temperature increases, tool may release sooner and without reaching full tension.
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STUCK PIPE
Schlumberger PrivateΒιβλιοθήκη Drilling Jars
Jarring Objectives
Kinetic Energy = ½ MV2 M= Mass (weight) of BHA above the jar. V= Velocity (speed) at which the mass is moving when the jar fires (hammer strikes anvil) in feet/second ,
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Ease of admitting wireline cable for surveying equipment and string shots. Ability to increase or decrease tension setting from surface.
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STUCK PIPE
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Drilling Jars
• Are immediately available to apply jarring action and release the stuck portion of the string • Designed to apply an intensified force in either upward or a downward direction. • Must apply the force or overpull in addition to the load already supported by the rig and the DP Jarring Objective • To transfer the potential energy stored in the stretched drill pipe to kinetic energy in the BHA above the jars. • The magnitude of the stress wave is related to the velocity of the accelerated BHA • The duration of the wave is related to the length of the BHA
• Consists of two reservoirs of hydraulic fluid separated by a valve. When tension or compression is applied to the tool in the cocked position, fluid from one chamber is compressed and passes through the valve at high flow resistance into the second chamber. When the strokes reaches certain point, the compressed fluid is allowed to suddenly bypass the valve The valve trips as the fluids rushes into the second chamber, instantly equalizing pressures between the two chambers The greater the force on the jar, the greater the compression of the fluid and the sooner and more forceful the release. Does not trip at preselected threshold The jar trip is determined by the magnitude of the applied tension or compression.
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STUCK PIPE
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Drilling Jars
There are three types of drilling jars: 1. Mechanical Jars
• • • • • • Operate using a series of spring, lock and release mechanisms Trips up at a preselected tensile force, and trips down at a preselected compressional force The position of the mechanical jar while drilling is either cocked (neutral) or extended. Drilling is never conducted with jars tripped down as unnecessary jarring might damage the bit and BHA components. Delivered to the rig with specific up and down tripping load settings. Can be varied down hole 10% - 15% by applying torque to the drill string
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STUCK PIPE
Drilling Jars
1. Mechanical Jar (Cont…)
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Mechanical Jar Mechanism
STUCK PIPE
Drilling Jars
2. Hydraulic Jar
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STUCK PIPE
Basic Jar Schematic
Impact and Impulse
Impact is defined as the magnitude of the force delivered to the stuck spot in the BHA. The impact force is generated at the drilling jar and it travels down the BHA to the stuck spot. The impact force must be stronger than the sticking force at the stuck spot. If the impact force exceeds the sticking force, the BHA slides for a short distance. The distance that the BHA slides is determined by the impulse delivered to the stuck spot. Impulse determines how long the impact lasts. The larger the impulse, the more that the BHA slides per jarring cycle and the sooner the string is freed. Both impact and impulse are required for effective jarring. In all cases, it is necessary for the impact force to exceed the sticking force or the BHA will not slide, no matter how great an impulse is available. Maximize Impact for Mechanically stuck and Packed off Strings Maximize Impulse for Differential Sticking (more mass to free the drill string)