Permanent Packer Failure Causes
Factors causing failures
Permanent Packer Performance
Hoppman and Walker, PEI, May 1995
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Rating envelope - regions of stress
catastrophic failure - packer no longer able
to maintain seal integrity
non-catastrophic - limit the ability of the
packer to function as designed
Packer Failure Causes
Body Collapse
ID of seal bore contacts OD of seal assembly
Caused by differential pressure above or below
the packer, or by packer and tubing forces; or
by a combination of the two.
Virtually all of the pressure and forces exerted
on the packer are locked in by the slip system.
The body remains collapsed even after the
forces are removed.
Packer Failure Causes
Body Collapse (continued)
Since pressures and forces are dependent on the crosssectional area of the packing element, they are
dependent on the casing ID.
Each size packer is used in a range of casing IDs
(weights)
As casing ID increases, the expansion of the packing
element must
be greater - adversely
affects packer rating.
Consequences of Body Collapse
Not a catastrophic failure (sealing not
compromised)
often cannot remove seals from packer bore
Safe Operating Region - 3 on envelope
Packer Failure Causes
Packing Element System Failure
failure of the element occurs when the element
extrudes through the back-up system
Packer Failure Causes
Causes of packing element failure
temperature of seal material exceeded
excess pressure on element causes extrusion
chemical attack (breakdown or softening)
gas permeation and sudden decompression causing
blisters and seal ruptures
backup system failures
seal bore corrosion or erosion leaves sealing surface
rough
Consequences of Seal Failure
Catastrophic failure (sealing compromised)
seal is lost - leaks may cause other problems
often cannot remove seals from packer bore
(baked, hardened, fused, etc.)
Safe Operating Region - 4 on envelope
Packer Failure Causes
Pin collapse at the body/guide connection
like a body collapse, collapse of the pin connection at
the lower connection with maximum deflection at the
middel of the lower thread.
Differential pressure can occur when the seals are in a
seal bore extension below packer or if a wireline plug is
set in a nipple in the tailpipe.
Consequences - non-catastrophic
Region - 5 on envelope
Packer Failure Causes
Body to Guide Failure
fails at thread relief or in thread itself.
Thread relief failure occurs when the yield
strength of the body is exceeded.
Thread failure occurs when the tensile loads
exceed the shear or bearing strength of the
threads.
Packer Failure Causes
Body to Guide Failure (continued)
Sources of the loads are pressure differential below the
packer, packer-to-tubing tensile forces or a combination
of the two.
If both forces are present, their effects are additive.
Failure is catastrophic - body becomes free to moveupward
through the packer and the guide is free to fall downhole.
Safe Operating Region - 2
Packer Failure Causes
Anchor Attachment Failure (failure of left
hand square thread)
can occur only when a tubing anchor seal
assembly is used. Tread can fail in the tread
relief, in the tread, or due to swelling of box.
Thread relief fails when body tensile exceeded
Threads fail when bearing strength exceeded
Swelling occurs when elastic burst limit of the
wall is exceeded
Packer Failure Causes
Anchor Attachment Failure (continued)
Consequences Failure in thread relief or threads is catastrophic anchor seal pulls out of the packer - pressure integrity is
lost.
Most likely effect of a box swelling failure is loss of
contact area between anchor and packer. If box swells
to the point where anchor can pull out - the failure will
be catastrophic.
Safe Operating Region - 1
Packer Failure Causes
Body Lock Ring System Failure
The body lock ring fails when the stresses in the threads
exceed the material shear or bearing strength in the ring
or its supporting elements.
Consequences - body is free to float, even though slips
continue to trap the packoff force. When pressure
cycles - leads to reciprocation and wear on packing
element - produces a leak.
No pressure cycle - no serious consequences.
Safe operating Limit - region 6.
Packer Failure Causes
Bearing Failure
occurs with locator and anchor seal assemblies.
Bearing failure at contact of anchor/locator and
packer occurs when compressive stress exceeds
bearing strength of the material.
An added force may be stress in body and seal
sub generated by radial component of the
contact forces (this is caused strictly by
compressive packer-to-tubing forces).
Bearing Failure
Consequences
Generally, only result is deformation of the
contact surface of each part.
In cases of extreme, high set-down loads, the
seal assembly can be swaged into the bore or
body of the packer.
Bearing failure is represented in the
envelope as region 6
Using The Packer Envelope in
Well Design
Plot data from tubing movement and stress
programs on a packer envelope to determine
if the loads fall in the safe area during initial
setting, production, stimulation and kill
operations.
Using The Packer Envelope in
Well Design
The envelope can be used to determine optimum
material for packer construction.
Check outer limits of the packer for its casing
weight range.
All future operations must be accounted for in a
permanent packer design.
Failure rate for permanent packers is less than 1%.
