Note: Descriptions are shown in the official language in which they were submitted.
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SEALING OF A WELLBORE DEVICE IN A
TUBULAR ELEMENT
The present invention relates to a method of
operating a wellbore formed in an earth formation, the
wellbore being provided with a tubular element in which a
wellbore device is to be arranged such that the wellbore
device is sealed to the inner surface of the tubular
element, and whereby an elongate member is to be extended
through the tubular element for carrying out a wellbore
operation.
In the production of hydrocarbon fluid from a
wellbore it is common practice that the produced
hydrocarbon fluid flows from the producing zone in a
lower part of the well via a conduit, referred to as the
production tubing, to surface. The production tubing can
be provided with one or more devices, such as surface-
controlled subsurface safety valves, tubing hangers,
landing nipples, packers and sliding side-doors. Some of
= these devices are retrievable and are sealingly installed
in the string. The production tubing string is assembled
from a plurality of tubular sections, whereby one or more
landing nipples are incorporated in the string at each
location in the string where such retrievable device is
to be installed. To ensure that each retrievable device
is arranged at the desired depth in the tubing string,
each landing nipple corresponds to the dimensions of a
respective one of the retrievable devices. Sealing of the
retrievable device to the inner surface of the landing
nipple is achieved by suitable seal elements, such as
chevron type seals. In order to achieve adequate sealing,
the seal surface portions of the landing nipples are
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often polished so as to provide a very smooth seal
surface.
Another example of a wellbore device which is
sealingly received in a tubular element, is a seal
assembly of a production tubing. The seal assembly is
formed by the lower end part of the production tubing and
is received in a polished bore receptacle (PBR) of a
production packer arranged near the producing zone of the
wellbore. The seal assembly is axially movable relative
to the PBR to allow for thermal expansion/contraction of
the production tubing.
Tubular elements, like production tubings and PBR's,
are also used to convey equipment for conducting downhole
operations. For example in a wireline-conveyed operation
the downhole equipment can be lowered on a wireline
through the production tubing or through the PBR. Such
operation involves movement of the wireline (which can be
of several kilometres length) at high speed through the
production tubing or PBR whereby the wireline scratches
along the polished seal surfaces. As a result, the seal
surfaces may become damaged so that adequate sealing of
the device in the tubular element can no longer be
guaranteed. In many instances such situation leads to
serious limitations in operating the well, and may even
compromise the safety of the well. In the special case of
seal surfaces for a surface-controlled subsurface safety
valve, damage to the seal surfaces can imply that the
well needs to be shut-in. Such situation occurs
frequently since the seal surfaces of the safety valve
landing nipple are often unprotected during well entries
when the safety valve is pulled to allow lowering of
maximum-size tools into the well.
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Thus, there is a need to provide an improved method
of operating a wellbore which overcomes the aforementioned
drawbacks.
In accordance with an aspect of the invention there
is provided a method of operating a wellbore formed in an earth
formation, the wellbore being provided with a tubular element
in which a wellbore device is to be arranged such that the
wellbore device is sealed to the inner surface of the tubular
element, the method comprising: providing the wellbore device
at the outer surface thereof with a swelleable seal susceptible
of swelling upon contact with a selected fluid, and installing
the wellbore device in the tubular element; inducing the
swelleable seal to swell by virtue of contact of the swelleable
seal with the selected fluid; wherein the tubular element is a
production tubing for transporting hydrocarbon fluid produced
from the earth formation to surface; extending an elongate
member through the tubular element to carry out a wellbore
operation; and removing the elongate member from the tubular
element; wherein the tubular element includes a landing nipple
for receiving said wellbore device, and wherein the step of
installing the wellbore device in the tubular element comprises
installing the wellbore device in the landing nipple.
It is thereby achieved that, by virtue of swelling of
the swelleable seal upon contact with the selected fluid, the
seal expands into any irregularities in the seal surfaces of
the tubular element which are attributable to damage caused by
the wellbore operations carried out through the tubular
element.
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Another aspect of the invention relates to a
wellbore device for use in a wellbore formed in an earth
formation whereby the wellbore is provided with a tubular
element in which the wellbore device is arranged in a manner
that the wellbore device is sealed to the inner surface of the
tubular element, the wellbore device being provided at the
outer surface thereof with a swelleable seal susceptible of
swelling upon contact with a selected fluid, wherein the
tubular element is a production tubing for transporting
hydrocarbon fluid produced from the earth formation to surface,
wherein the tubular element includes a landing nipple for
receiving the wellbore device, and that the wellbore device is
installed in the landing nipple.
In a preferred embodiment the tubular element is a
production tubing for transporting hydrocarbon fluid produced
from the earth formation to surface, or a part thereof such as
a landing nipple for the wellbore device. In such application
the wellbore device is, for example, a safety valve assembly
for selectively controlling flow of hydrocarbon fluid through
the production tubing.
Alternatively the tubular element is a polished bore
receptacle (PBR), and the wellbore device is a seal assembly of
a production tubing for transporting hydrocarbon fluid produced
from the earth formation, to surface.
Preferably the swelleable seal swells upon contact
with hydrocarbon fluid, and includes a material selected from
natural rubber, nitrile rubber, hydrogenated nitrile rubber,
acrylate butadiene rubber, poly acrylate rubber, butyl rubber,
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brominated butyl rubber, chlorinated butyl rubber,
chlorinated polyethylene, neoprene rubber, styrene
butadiene copolymer rubber, sulphonated polyethylene,
ethylene acrylate rubber, epichlorohydrin ethylene oxide
copolymer, ethylene-propylene-copolymer (peroxide crosslinked),
ethylene-propylene-copolymer (sulphur crosslinked),
ethylene-propylene-diene terpolymer rubber, ethylene vinyl
acetate copolymer, fluoro rubbers, fluoro silicone rubber, and
silicone rubbers.
Said material is suitably selected from EP(D)M rubber
(ethylene-propylene-copolymer, either peroxide or sulphur
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crosslinked), EPT rubber (ethylene-propylene-diene
terpolymer rubber), butyl rubber, brominated butyl
rubber, chlorinated butyl rubber, and chlorinated
polyethylene.
Instead of, or in addition to, the swelleable seal
swelling upon contact with hydrocarbon fluid, the
swelleable seal suitably swells upon contact with water,
and includes a material selected from NBR, HNBR, XNBR,
FKM, FFKM, TFE/P or EPDM base rubber. In order to enhance
the swelling capacity of the swelleable member, even for
saline water conditions, said material suitably is a
matrix material wherein a compound soluble in water is
incorporated in the matrix material in a manner that the
matrix material substantially prevents or restricts
migration of the compound out of the swelleable seal and
allows migration of water into the swelleable seal by
osmosis so as to induce swelling of the swelleable seal
upon migration of said water into the swelleable seal.
Said compound suitably comprises a salt, for example at
least 20 weight% salt based on the combined weight of the
matrix material and the salt, preferably at least
35 weight% salt based on the combined weight of the
matrix material and the salt. In order to prevent, or
reduce, leaching of the compound out of the matrix
material, it is preferred that the matrix material is
substantially impermeable to said compound or to ions of
said compound. The compound can be present in the matrix
material, for example, in the form of a plurality of
compound particles dispersed in the matrix material.
The invention will be described hereinafter in more
detail and by way of example, with reference to the
accompanying drawings in which:
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Fig. 1 schematically shows an embodiment of the
wellbore device according to the invention;
Fig. 2 schematically shows detail A of the wellbore
device of Fig. 1;
Fig. 3 schematically shows a longitudinal section of
a tubular element to be used in conjunction with the
wellbore device of Fig. 1;
Fig. 4 schematically shows the wellbore device of
Fig. 1 when arranged in the tubular element of Fig. 3.
In the Figures, like reference numerals relate to
like components.
Referring to Fig. 1 there is shown a surface-
controlled subsurface safety valve assembly 1
(hereinafter: safety valve assembly 1) for selectively
controlling flow of fluid through a wellbore (not shown)
for the production of hydrocarbon fluid. The safety valve
assembly 1 includes a tubular conduit 2 having a
passage 4 for produced hydrocarbon fluid, the passage 4
being provided with valve 6 for selectively closing the
passage 4. The valve 6 is controlled by a hydraulic
control system of which only hydraulic control lines 8, 9
and plunger system 10 are schematically shown. The
hydraulic lines 8, 9 are in fluid communication with the
exterior of the safety valve assembly 1 via a port 11
provided in the wall of the tubular conduit 2. A locking
mandrel 12 is provided at an upper portion of the safety
valve assembly 1 for supporting and locking the safety
valve assembly 1 in a production tubing referred to
hereinafter.
Referring further to Fig. 2, the safety valve
assembly 1 is provided with two annular seals 14, 16
arranged at an axial distance from each other, whereby
the port 11 is located between the annular seals 14, 16.
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Each annular seal 14, 16 includes a plurality of chevron
type seals 18 and a swelleable seal 20 made of EPDM
rubber which is susceptible of swelling upon contact with
hydraulic oil to be used in the hydraulic control system
for controlling the valve 6.
Referring further to Fig. 3, there is shown a tubular
element in the form of a landing nipple 22 incorporated
in a production tubing (not shown) for transporting
produced hydrocarbon fluid through the wellbore to
surface. The inner diameter of the landing nipple 22 is
slightly larger than the outer diameter of the safety
valve assembly 1 so as to allow axial movement of the
safety valve assembly 1 through the landing nipple 22.
The landing nipple 22 is internally provided with a
locking profile 24 which is complementary to, and
cooperates with, the profile of the locking mandrel 12 so
as to allow the safety valve assembly 1 to be supported
and locked in the landing nipple 22. Furthermore, the
inner surface of the landing nipple 22 is provided with
two polished annular surface portions 26, 28 of slightly
smaller diameter than the remainder of the inner surface
of the landing nipple 22. The polished surface
portions 26, 28 are arranged such that annular seal 14 is
located opposite polished surface portion 26, and annular
seal 16 is located opposite polished surface portion 28
when the safety valve assembly 1 is locked in the landing
nipple 22 by the cooperating locking mandrel 12 and
locking profile 24.
A port 30 is provided in the wall of the landing
nipple 22 at a location between the polished surface
portions 26, 28, the port 30 being in fluid communication
with a hydraulic control unit (not shown) at surface via
a hydraulic control line 32 extending along the outer
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surface of the production tubing. It is to be understood
that the hydraulic control unit at surface, the control
line 32, the port 30, the port 11, the hydraulic control
lines 8, 9, and the plunger system 10 are all part of the
hydraulic control system for controlling the valve 6.
Referring further to Fig. 4, during normal use the
safety valve assembly 1 is arranged in the landing
nipple 22 of the production tubing. Hydrocarbon fluid is
produced from the earth formation surrounding the
wellbore and transported to surface via the production
tubing. The produced hydrocarbon fluid thereby flows
through the passage 4 of the safety valve assembly 1. If
it is required to shut the well in, for example in case
of an emergency situation, the valve 6 is induced to
close under control of the hydraulic control system
operated at surface. Leakage of hydrocarbon fluid along
the outside of the safety valve assembly 1 is prevented
by the annular seals 14, 16 which seal against the
polished surface portions 26, 28 of the production
tubing 22.
After some time of continued hydrocarbon fluid
production from the wellbore it may be required to
suspend the wellbore and to remove the safety valve
assembly 1 from the production tubing in order to conduct
a downhole workover operation using a wireline (not
shown) extending from surface through the production
tubing. During such workover operation, the wireline
moves at high speed through the production tubing, and
hence through the landing nipple 22. The wireline thereby
scratches against the protruding polished surface
portion 26, 28 of the landing nipple 22. As a result the
polished surface portions 26, 28 can easily become
damaged so that the chevron type seals 18 of the annular
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seals 14, 16 no longer adequately seal against these
surface portions after the safety valve assembly 1 has
been reinstalled in the landing nipple 22. However, the
sealing function of the annular seals 14, 16 is still
guaranteed by the swelleable seals 20 which swell by
virtue of contact with the hydraulic oil present in the
annular chamber defined by the outer surface of the
safety valve assembly 1, the inner surface of the landing
nipple 22, and the annular seals 14, 16. Thus, the
seals 20, after swelling, extend into the irregularities
formed at the damaged surface portions 26, 28 and thereby
adequately seal the safety valve assembly 1 against the
landing nipple 22.
It is to be understood that the invention is not
limited to applications whereby the tubular element is a
production tubing or a portion thereof, such as a landing
nipple. Other useful applications include, for example,
tubing hangers, packers, polished bore receptacles and
sliding side-doors.
