National
Oilwell's Griffith • Vector brand Shock Tool
effectively absorbs vibrations with any combination of weight
on bit, bit pressure drop, mud weight, and hole depth.
• Temperature
Compensated Shock Tool:
A floating piston and large expansion chamber are incorporated in this design to
compensate for lubricant expansion
at higher operating temperatures.
• Temperature and Pressure Compensated Shock Tool: Shock Tools 11-inch
and larger in diameter are designed to reduce the excessive pump open effect
inherent in larger diameter tools. This design permits a relatively low spring
rate, desirable when drilling large diameter holes, without fully extending the
tool at high pump pressures.
Advantages and Features
• Cost Effective: Reduces cost per foot drilled by increasing bit life,
reducing bit trips, allowing optimum rotary speed, increasing rate of
penetration, reducing vibration-induced drill string failures, and isolating
surface equipment from damaging vibrations transmitted through the drill string.
• Belleville Disc Springs: Provide a linear spring rate, high load
capacity, and low hysteresis.
• Sprung in Both Directions: Neutralizes the effect of pump open force.
• Hydrostatically Balanced: Not affected by hydrostatic head.
• Relatively Short: Eases handling and transportation.
• Fewer Body Connections: Reduces potential for connection failures.
• Safety Nut: Minimizes potential fishing jobs by preventing parts from
being -left in the hole if a connection is accidentally backed off.
• Lock Ring on Splined Mandrel: Provides positive stop during jarring.
Forces not transmitted through
Function
The
Shock Tool spring elements are arranged to function in both directions. The tool
will absorb deflections while either compressed through bit loading, or extended
by pump open forces. All National Oilwell Shock Tools will effectively absorb
vibrations with any combination of weight on bit, bit pressure drop, mud weight,
and hole depth.
Placement
For maximum effectiveness, the shock tool should be placed immediately above the
bit (Figure 1) to minimize the amount of unsprung mass below the tool.
Reduced service life and potentially severe damage to the shock tool can occur
if the tool is not properly located in the bottom hole assembly It is important
that the shock tool be located in a position where it is exposed to a minimum of
side loading or bending stress. Ideally the shock tool should have the same
degree of stabilization on either end. If it is stabilized at the lower
connection, there should be a stabilizer at the upper connection. There should
also be a third stabilizer thirty feet higher in the BHA.
Operation
Jarring
If it becomes necessary to jar through the shock tool, an over pull of 30,000 to
50,000 pounds (-13 300 to 22 300 daN) depending upon tool size (refer to the
Technical Specifications at right) brings the retaining ring on the mandrel into
contact with the pin on the splined housing, ensuring solid jarring.
Rotating Hours:
Maximum recommended rotating hours for shock tools are affected by the
following:
1. Size of the tool.
2. Bottom hole temperature.
3. Rotary speed.
4. Pressure differential at shock tool.
The following formulas should be used to calculate the maximum rotating hours:
Example:
An 8" shock tool is being used where the bottom hole temperature is 150°F, the
differential pressure at the tool is 1,200 psi and the rotary speed is 100 rpm.
Maintenance
and Storage
On each round trip the shock tool should be visually inspected for any
indication of damage, excessive wear or leakage.
If the shock tool isto be laid down and not used for a period of time, flush the
bore with fresh water to remove all drilling fluid. Wash external surfaces of
the tool and apply thread compound and protectors to the tool joint connections.
Protect the mandrel sealing surface from possible damage during handling or
storage. Never use tongs or slips on this surface. Never use this surface as a
lifting or tie-down point.
Griffith
• Vector is a licensed manufacturer under:
API Spec. 7 -License Number 7-0063
API Spec. 6A -License Number 6A-0490
API Spec. l6A - License Number 16A-0110
An
ISO registered firm: Certificate Number 93-20
Accredited by the Dutch Council for Certification
