The pipe shall be immediately worked and jarred in the opposite direction to that when it became stuck. That is, if stuck when POOH jar down, if stuck when drilling or RIH jar up.
Notes: Pipe shall be pulled to the maximum safe limit previously specified. If the first attempts to free the pipe are unsuccessful, the pipe shall be worked in both directions until alternative action can be taken.
Prior to using any lubricating pill, the effect on the hydrostatic pressure in relation to the pore and fracture pressures shall be taken into account. If circulation is not possible and the drillpipe is pressured in an attempt to initiate circulation, the pressure applied shall not exceed the MAASP.
Jarring Theory
There are two types of jars, mechanical and hydraulic.
Mechanical jars are pre-set at the surface.
Some hydraulic jars are adjustable for overpull downhole. In general, an increase in jar stroke length increases both impact and impulse. With these obvious advantages, a long stroke hydraulic jar shall be used where possible.
Two phenomena have to be considered when jarring:
- impact
- impulse
The impact force must be high enough to break the binding forces causing the pipe to stick and that force must act long enough to move the fish. This is termed the impulse force. Both forces are influenced by the amount of drill collars placed above the jar.
The smaller the quantity of drill collars placed above the jar, the higher the impact force. Conversely, the larger the quantity of drill collars above the jar, the greater the impulse. A compromise has to be reached where impact and impulse are operating together to reach the common objective.
Jar Placement
The standard used by Company, with respect to drilling jar placement, is to locate the jar on top of one joint of Hevi-weight drillpipe above the drill collars.
For potential H2S wells the jar shall be place above the Hevi-weight drill pipe. Do not drill with the jars at their neutral point in the string.
Jarring Practices
Ensure that all surface pulling equipment is in good working condition. Do not exceed the maximum allowable safe working rating of the weakest link in the pulling equipment.
Ensure that both the weight indicator and deadline anchor are correct and clear of debris.
Visually check the derrick for loose fittings. All personnel shall be kept clear of the derrick and drill floor while jarring.
Pull shall be limited on stuck pipe to 85 % of the minimum yield strength of the weakest member. When jarring, overpull to the maximum figure to trip the jar, wait for the jar to trip, then increase the overpull to that recommended for the pipe. If the string is overpulled to the maximum recommended for the pipe before the jar has tripped, severe overloading of the jar may occur causing catastrophic failure of the jar. The derrick shall be inspected after jarring operations.
Circulating While Jarring
When circulating, pump open forces greatly influence jarring performance and have to be carefully considered:
Jarring Up With a Hydraulic Jar
Circulating may make the jar harder to cock, but when the jar does trip, both impact and impulse forces are increased. To be confident that the jars are cocked, slack off more weight or stop circulating.
Jarring Up With a Mechanical Jar
The jar will trip with less overpull and is harder to cock.
Jarring Down With a Hydraulic or Mechanical Jar
The effects are less easily identified and circulating does not influence impact values. Cocking the jars is easier but the jar is harder to trip.
Accelerators
The use of accelerators are restricted to fishing assemblies after the string has become stuck.
Accelerators are normally run above the jar and are devices to maximise the impact force on the stuck position of the string.