Note: Descriptions are shown in the official language in which they were submitted.
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Liner hanger
BACKGROUND
Field of the invention
This invention concerns a liner hanger for use in wellbores.
Related and prior art
For retrieving oil and/or gas, hydro carbons, from subterranean formations, a
borehole is drilled to a predetermined depth. Then the drill bit is retrieved,
and a
section of pipes is assembled from pipes that are threaded together at their
ends.
The section, known as a casing, is inserted into the borehole and typically
cemented to the formation by pumping cement into the annular space between the
casing and the formation. The cement is allowed to cure, and a smaller
diameter
drill bit is inserted through the casing to drill a new section through the
formation to
a second predetermined depth. The next section of pipes, called a `liner', is
inserted through the casing to a depth where the top of the liner overlaps the
lower
part of the existing casing. In this position, the liner is suspended from the
casing
using a liner hanger. The liner may in turn be cemented to the formation, and
the
process may be repeated until the wellbore has reached its intended depth. For
practical reasons, the term 'casing' as used herein refers to an upper section
of
pipes, usually cemented to the formation, and the term `liner' as used herein
refers
to a lower section of pipes. However, there is no clear distinction between a
'casing' and a 'liner' as both comprise strings of pipes, and as the liner of
one
section will be the casing of the next.
The liner hanger is mounted at the top of the new string of pipes, and will
have to
carry the weight of it, which often is several tens of tons. It is usual to
dimension
the elements for a weight of 150 tons.
The problem to be solved by the present invention is to provide a liner hanger
that
can be attached to an existing casing for a shorter or longer period of time,
without
it necessarily being cemented.
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Another objective of the invention is to provide a liner hanger that can be
set
without rotating the entire section of pipes that is suspended from it.
Yet another purpose of the invention is to avoid leakage to occur in the
annular
space between existing and new casing as the rubber becomes old.
SUMMARY OF THE INVENTION
According to the invention, this is solved by a liner hanger to be placed in
an
existing casing with a flexible expansion seal and a metallic gripping element
disposed on inclined surfaces such that they are moved radially when a
leadscrew
nut is moved axially relative to an inner, hollow shaft,
the lead screw nut being moved axially when a lead screw is rotated therein,
and
the lead screw being disposed around the inner, hollow shaft 150.
When the new section is suspended from the inner shaft 150, which does not
rotate, it is still simple to rotate the sleeve 110.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be disclosed in greater detail in the following with
reference to
the accompanying drawings, where similar reference numerals refer to similar
elements, and where:
Figure 1 is a partial cross section through a liner hanger according to the
invention.
DETAILED DESCRIIPTION OF A PREFERRED EMBODIMENT
Figure 1 is a partial cross section through a liner hanger according to the
invention. The liner hanger has an inner, hollow shaft 150 disposed within an
outer
housing. The shaft 150 is at one of its ends, to the left on figure 1,
connected to a
lead screw having outer threads on a torque transmitting sleeve 110. The lead
screw can have conventional Acme-threading, and is disposed within a lead
screw
nut 130 having corresponding internal threading. The lead screw is part of the
outer housing of the liner hanger. The lead screw is rotated in the nut 130 by
an
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external drive shaft 120 which is rotation locked using first latching dogs
121 in the
sleeve 110, while second latching dogs 141 are rotation locked to the lead
screw
nut 130. The external drive shaft rotates the first latching dogs 121 relative
to the
second latching dogs 141, and thus the lead screw on the sleeve 110 relative
to
the lead screw nut 130.
The lead screw nut 130 is axially slidably disposed around the inner shaft
150.
Thus, when the lead screw is rotated in the lead screw nut 130, the nut 130
will be
moved axially along the shaft 150. When the liner hanger is set, the drive
shaft is
rotated such that the lead screw nut 130 is moved downward relative to the
inner,
hollow shaft 150, i.e. to the right in Fig. 1.
Thereby, the lead screw nut 130 will push against the other parts of the outer
shell,
which, starting from the lead screw nut, are in order: Belleville springs 160,
expandable seal 180, Belleville springs 170 and a slip section having slips
190.
The slips 190 are disposed on inclined surfaces that are pulled closer to each
other by the axial displacement. Thereby, the slips will be moved radially
outward
and be the first elements to engage the wall of the well. When the lead screw
is
rotated further, the seal 180 will expand radially until it engages the wall
of the well
and seals the annular space between the shaft 150 and the existing casing (not
shown).
When the seal 180, which conventionally is made from a rubber blend, has been
disposed in the well for a while, its characteristics are expected to change,
and it is
expected to seal less well. The purpose of the Belleville springs 160 and 170
is to
preload the seal 180, such that it continues to seal after this occurs. The
Belleville
springs can e.g. be preloaded with a force around 200kN. Depending on the
rubber blend and well conditions, it is expected that the force from (the less
compressed) Belleville springs is half of the original force after a while.
However,
the seal will still seal. If the seal was not compressed by the Belleville
springs, a
leak would have been expected at this point in time.
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The inner, hollow shaft 150 is in one of its ends connected to the external
drive
shaft through milled out grooves and the second latching dogs 141. In its
other
end, the shaft 150 is preferably provided with pipe threads. Thereby, the
liner
hanger can be threaded to the upper part of a new section of pipes before the
entire assembly is lowered into the well. The shaft 150 thereby becomes part
of
the new section of pipes.
When the hanger is to be attached to the lower or outer end of the existing
casing,
the entire weight of a section of pipes, possibly in the order of hundreds of
tons,
will thereby be suspended from the second dogs 141 and the shaft 150, while
the
sleeve 110 with the lead screw is rotated around the shaft 150. Hence, it is
not
necessary to rotate a mass of several tens of tons to set the liner hanger.
When the slips 190 has a firm grip in the casing and the seal 180 engages the
inner surface of the casing, the new section of pipes is suspended from the
shaft
150, and the weight is removed from the second dogs 141. When the external
drive shaft is to be removed, the part 140 can be used to release the latching
dogs
in different ways, e.g. by moving a ring over inclined faces of the dogs to
retract
them from their latching position.
The first latching dogs 121 are not subject to any substantial axial load in
the
above description. As long as they provide the required rotational locking,
nothing
prevents them from being pulled axially out from the sleeve 110 when the liner
hanger is attached to the existing casing.
When the drive shaft is pulled back and the new section of pipes is suspended
from the liner hanger, the new section of pipes can optionally be cemented to
the
formation, be penetrated and/or be treated like other steel pipes in the well.
