Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF CREATING A WELD IN A WELLBORE
The present invention relates to a method of creating
a weld to connect a first element to a second element.
For a variety of applications it would be desirable to
provide a method of creating a weld in a wellbore formed
in an earth formation, the wellbore containing a wellbore
fluid. Such applications include, for example, forming of
metal-to-metal seals, providing structural integrity to
welibore components or repairing corrosion damage.
However welding in a liquid environment (the wellbore
fluid) at high pressures generally encountered in
wellbores, is not feasible. An analogous situation exists
for underwater welding, e.g. at offshore platforms,
whereby the depth at which such welding is feasible is
limited by the hydrostatic pressure of the water.
It is an object of the invention to provide a method
of creating a weld to connect a first element to a second
element, said elements being arranged in a wellbore
containing a wellbore fluid.
The method according to the invention comprises
a) selecting a welding path along which the weld is to
be created;
b) selecting a volume portion of the wellbore, in which
volume portion said path is located, and sealing said
selected volume portion from the remainder of the
wellbore volume;
c) providing pressure control means for controlling the
fluid pressure in said selected volume portion;
d) operating the pressure control means so as to reduce
the fluid pressure in said selected volume portion to a
selected pressure at which the weld can be created; and
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e) creating the weld along the selected welding path.
By sealing the volume portion in which the weld is to
be created from the remainder of the wellbore, and
subsequently reducing the pressure in the volume portion,
the fluid pressure no longer prevents the creation of the
weld.
Suitably the first element is an upper wellbore
casing and the second element is a lower weilbore casing
having an upper part extending into a lower part of the
upper wellbore casing. In this manner metal-to-metal
sealed casings are obtained allowing gas at high pressure
to be produced through the wellbore casing rather than
through a conventional production tube extending through
the wellbore casing.
In a preferred embodiment said upper part has an
outer diameter substantially equal to the inner diameter
of said lower part, and step e) comprises welding the
upper edge of the lower casing to the upper casing.
In another preferred embodiment said upper part has
an outer diameter smaller than the inner diameter of the
lower part, and wherein the method further comprises
inserting a filler tube in the annular space between said
upper part and said lower part, and wherein step e)
comprises welding the upper edge of the lower casing to
the filler tube and welding the upper edge of the filler
tube to the upper casing.
To allow high pressure gas production from a
multilateral wellbore system, suitably the wellbore is a
main wellbore provided with a branch wellbore, said first
element being a branch of a branch casing member which
connects a main casing extending through the main
wellbore to a branch casing extending through the branch
welibore, said second element being the branch casing.
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The invention will be described hereinafter in more
detail and by way of example with reference to the
accompanying drawings in which
Fig. 1 schematically shows a longitudinal cross-
section of a system used in conjunction with a first
embodiment of the method of the invention;
Fig. 2 schematically shows a longitudinal cross-
section of a system used in conjunction with a second
embodiment of the method of the invention;
Fig. 3 schematically shows detail A of Fig. 2.
In the Figures like reference numerals relate to like
components.
The system shown in Fig. 1 includes a wellbore 1
formed in an earth formation 3, the wellbore being
provided with a first element in the form of upper
wellbore casing 5 extending in an upper part la of the
wellbore and a second element in the form of lower
wellbore casing 7 extending in a lower part lb of the
welibore 1. The lower casing 7 has an outer diameter
substantially equal to the inner diameter of the upper
casing 5 and extends partly into the upper casing 5. A
layer of cement 9 is arranged in the annular space
between the two casings on one hand and the wellbore wall
on the other hand.
A welding system 10 is arranged in the wellbore 1,
the welding system comprising a radially expandable upper
packer 12 arranged in the upper casing 5 above the upper
edge 14 of the lower casing 7 and a radially expandable
lower packer 16 arranged in the lower casing 7. The
packer 12, 16 are interconnected by a tubular element 18
provided with a plurality of openings 20 in the wall
thereof. Each packer 12, 16 is internally provided with
an contractible memory metal element (not shown) for
radially expanding the packer against the respective
casing 5, 7 and with an electric heating coil (not shown)
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for activating the memory metal element. The packers 12,
16 are provided with suitable seals 21 for sealing the
packers 12, 16 in their expanded position against the
respective casing 5, 7.
The upper packer 12 is internally provided with a
remotely controlled welding unit 22 (shown in dotted
lines) having a welding electrode 24 and a tube 25. The
electrode 24 and tube 25 are movable between a retracted
position and an expanded position. In the retracted
position the electrode 24 and tube 25 are located in a
chamber (not shown) arranged within the upper packer 12,
which chamber is sealed by a removable annular sealing
member 26 fitting in a corresponding annular recess 28
(shown in dotted lines) provided in the upper packer 12
at the side facing the lower packer 16. The annular
sealing member 26 is removable from the upper packer by
the operation of a solenoid coil (not shown) which is
capable of inducing the sealing member to drop down from
the packer 12. In Fig. 1 the annular sealing member is
shown removed from the upper packer 12. In the expanded
position the electrode 24 and tube 25 extend through
annular recess 28 into a volume portion 30 of the
wellbore 1 defined by the space enclosed by the
packers 12, 16 and the casings 5, 7. The welding unit is
furthermore provided with means (not shown) for moving
the electrode 24 and tube 25 in circumferential direction
along the corner formed by the upper edge 14 of the lower
casing 7 and the inner surface of the upper casing 5.
A tubular conduit 33 is connected to the welding
unit 10 at upper packer 12 and extends through the
wellbore 1 to a control unit (not shown) at surface, the
conduit 33 being in fluid communication with the interior
of the tubular element 18 and being provided with a
control valve (not shown) at surface which, in open
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position, provides fluid communication of the conduit 33
to the atmosphere.
An electric cable 34 extends from the control unit
trough the tubular conduit 33 to the welding system 10
and from there to the heating coils and to the solenoid
coil. A fibre optical cable 35 extends from a monitoring
unit (not shown) at surface trough the tubular conduit 33
to the welding system 10 and from there into the tube 25
so as to provide optical signals to the monitoring unit.
The control unit is adapted to selectively provide
electric power and/or electric control signals via the
cable 34 to the welding system 10, the heating coils, the
solenoid coil and the camera.
An outlet conduit 36 extends from the lower packer 16
through the tubular element 18 and through the upper
packer 12, which outlet conduit provides fluid
communication between the volume portion 30 and the
interior of the welibore 1 above the welding unit 10. A
non-return valve 38 prevents flow of fluid from the
outlet conduit 36 into the volume portion 30.
During normal operation of the system used in the
first embodiment, the wellbore 1 contains a wellbore
fluid of selected density. The welding electrodes 24 are
in their retracted position and the annular sealing
member is located in the annular recess 28 so as to seal
the electrodes from the wellbore fluid. The welding
system 10 is suspended from the tubular conduit 33 and
lowered through the welibore to the location shown in
Fig. 1 whereby the upper edge 14 of the lower casing 7 is
located between the packers 12, 17. Electric power is
then provided by the control unit via the cable 34 to the
heating coils which thereby provide heat to the memory
metal elements. Upon reaching their transition
temperature the memory metal elements contract and
thereby radially expand the packers 12, 16 which become
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engaged to the respective casings 5, 7 in a sealing
manner.
The control valve at surface is closed and compressed
inert gas, for example nitrogen, is pumped from surface
trough the tubular conduit 33 and from there via the
tubular element 18 and the openings 20 into the volume
portion 30. By pumping the gas into the volume
portion 30, wellbore fluid is evacuated from the volume
portion 30 through the outlet conduit into the interior
of the wellbore 1 above the welding unit 10. When the
compressed gas has displaced substantially all wellbore
fluid from the volume portion 30 pumping is stopped. The
control valve is then opened to bleed off the gas
pressure in the volume portion 30 and the tubular
conduit 33 so that thereby the gas pressure is reduced to
substantially atmospheric pressure. The non-return-
valve 36 prevents return flow of wellbore fluid from the
outlet conduit 36 into the volume portion 30.
The control unit is induced to provide electric power
to the solenoid coil which thereby induces the annular
sealing member 26 to drop down from the upper packer 12
onto the lower packer 16 (as shown in Fig. 1). The
control unit is induced to provide electric power and
electric control signals to the welding system 10 so that
the welding electrodes 24 assume their expanded position
at which the tips of the welding electrodes are
positioned near the upper edge 14 of the lower casing 7.
The control unit then induces the electrodes 24 to create
a weld extending in circumferential direction along the
corner formed by the upper edge 14 of the lower casing 7
and the inner surface of the upper casing S. The weld
seals the lower casing 7 to the upper casing 5. During
the welding process the camera is operated by the control
unit in order to monitor the welding process at surface.
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When the welding process is completed the welding
system 10 is retrieved to surface by retrieval of the
tubular conduit 33 from the wellbore 1.
The system used in the second embodiment is shown in
Fig. 2, and includes a branch casing member 40 arranged
in a main wellbore (not shown) provided with a branch
wellbore (not shown), which branch casing member 40 is
located at the branch point of the two wellbores and
connects a main casing 42 extending through the main
wellbore to a branch casing 44 extending into the branch
wellbore. The branch casing 44 has an upper part 46
extending into a branch 48 of the branch casing
member 40, which upper part has an outer diameter smaller
than the inner diameter of the branch 48 and wherein a
filler tube 50 is arranged in the annular space between
said upper part 46 and said branch 48. The upper edge of
the branch casing 44 has been welded to the filler
tube 50 and the upper edge of the filler tube 50 has been
welded to the branch 48 using the method of the
invention.
Referring to Fig. 3, like reference numerals have
been used for like components indicated in Fig. 1,
therefore reference is made to Fig. 1 for a description
of such components in Fig. 3. The embodiment shown in
Fig. 3 differs from the embodiment of Fig. 1 in that the
first element is formed by branch casing 44 and the
second element is formed by branch casing 44. The outer
diameter of upper part 46 is smaller than the inner
diameter of branch 48.
Normal operation of the system of the second
embodiment is largely similar to normal operation of the
system of the first embodiment, except that the upper
edge of branch casing 44 is welded to the filler tube 50
by weld 52 using the welding system 10, and the upper
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edge of the filler tube 50 is welded to the branch 48 by
weld 54 using the welding system 10.
The second embodiment of the method of the invention
is of particular interest if during running of the branch
casing 46 into the branch wellbore the branch casing
becomes stuck in the branch wellbore before having
reached planned depth. The branch casing 46 is then cut
at a level such that the upper 46 part of the branch
casing remains in the branch 48, whereafter the filler
tube 50 is installed and the welds 52, 54 are created
using welding system 10. The cut upper section of the
branch casing is removed from the wellbore.
