ANNULAR BARRIER WITH SAFETY METAL SLEEVE
Field of the invention
The present invention relates to an annular barrier to be expanded in an annulus
between a well tubular structure and an inside wall of a borehole downhole for
providing zone isolation between a first zone and a second zone of the borehole.
Background art
In wellbores, annular barriers are used for different purposes, such as for
providing an isolation barrier. An annular barrier has a tubular part mounted as
part of the well tubular structure, such as the production casing, which is
surrounded by an annular expandable sleeve. The expandable sleeve is typically
made of an elastomeric material or metal. The sleeve is fastened at its ends to
the tubular part of the annular barrier.
In order to seal off a zone between a well tubular structure and the borehole or
an inner and an outer tubular structure, a second annular barrier is used. The
first annular barrier is expanded on one side of the zone to be sealed off, and the
second annular barrier is expanded on the other side of that zone, and in this
way, the zone is sealed off.
The pressure envelope of a well is governed by the burst rating of the tubular
and the well hardware etc. used within the well construction. In some
circumstances, the expandable sleeve of an annular barrier may be expanded by
increasing the pressure within the well, which is the most cost-efficient way of
expanding the sleeve.
Expanding the expandable sleeve by increasing the pressure within the well
requires a high expansion pressure. Using such a high expansion pressure applies
great stressing forces to the expandable sleeve, and the expandable sleeve may
rupture during expansion. The rupture of an expandable sleeve is very
undesirable since the outside of the well casing, i.e. the borehole environment,
becomes fluidly connected with the inside of the well casing, thereby polluting the
production fluid, e.g. crude oil, with fluids containing less oil, e.g. drilling mud.
Expanded annular barriers may be subjected to a continuous pressure or a
periodic high pressure from the outside, either in the form of hydraulic pressure
within the well environment or in the form of formation pressure. In some
circumstances, such pressure may cause the annular barrier to collapse, which
may have consequences for the area which is to be sealed off by the barrier as
the sealing properties are lost due to the collapse. Therefore, annular barriers are
designed to withstand large pressure to avoid collapse. The ability of the
expanded sleeve of an annular barrier to withstand the collapse pressure is
referred to as the collapse rating.
The ability of the expanded sleeve of an annular barrier to withstand both the
expansion pressure during expansion of the annular barrier and withstand the
collapse pressure during the lifetime of the annular barrier, which may easily
exceed 20 years, is thus affected by many variables, such as strength of
material, wall thickness, surface area exposed to the collapse pressure,
temperature, well fluids, etc. To increase resistance against rupture and collapse
of the annular barrier, expandable sleeves are therefore conventionally made
thicker and even braced with bracing elements to avoid collapse. However,
rupture of the expandable sleeve typically arises due to irregularities in the
material leading to a "weak area" on the expandable sleeve, and therefore even
the strongest expandable sleeves being expandable by an available expansion
pressure in the well may rupture due to these "weak areas". Producing a
"perfect" expandable sleeve without any "weak areas" is practically impossible
even with modern high standard material synthesis techniques, at least in a
scaled production facility producing bulk annular barriers for the oil producing
industry.
It is thus desirable to provide a solution wherein the annular barrier is improved
so that it does not rupture during expansion or collapse when expanded, without
having to increase the thickness of the expandable sleeve to levels where the
expandable sleeve cannot be inflated by the available expansion pressure in the
well.
Summary of the invention
It is an object of the present invention to wholly or partly overcome the above
disadvantages and drawbacks of the prior art. More specifically, it is an object to
provide an improved annular barrier solution which does not rupture during
expansion while still maintaining a required collapse rating.
The above objects, together with numerous other objects, advantages, and
features, which will become evident from the below description, are accomplished
by a solution in accordance with the present invention by an annular barrier to be
expanded in an annulus between a well tubular structure and an inside wall of a
borehole downhole for providing zone isolation between a first zone and a second
zone of the borehole, comprising
- a tubular part for mounting as part of the well tubular structure,
- an expandable metal sleeve surrounding the tubular part and having an
inner face facing the tubular part and an outer face facing towards the
inside wall of the borehole, each end of the expandable metal sleeve being
connected with a connection part which is connected with the tubular part,
- a space between the inner face of the expandable metal sleeve and the
tubular part, and
- an expansion opening in the tubular part through which fluid may enter
into the space in order to expand the expandable metal sleeve,
wherein the annular barrier further comprises a first safety metal sleeve
surrounding the tubular part and abutting the expandable metal sleeve and said
first safety metal sleeve having a first inner face abutting the face of the
expandable metal sleeve, each end of the first safety metal sleeve being
connected with the connection part which is connected with the tubular part.
In one embodiment, the sleeves may have a length, and the first face of the first
safety metal sleeve may abut the face of the expandable metal sleeve along the
whole length of the expandable metal sleeve.
Moreover, the first safety metal sleeve may have a first inner face abutting the
outer face of the expandable metal sleeve.
The annular barrier as described above may further comprise a second safety
metal sleeve surrounding the tubular part, the expandable metal sleeve and said
second safety metal sleeve having a second inner face facing the safety metal
sleeve, each end of the second safety metal sleeve being connected with the
connection part which is connected with the tubular part.
Also, the annular barrier as described above may comprise a third safety metal
sleeve, said third safety metal sleeve having a third inner face facing the second
outer face of the second safety metal sleeve, each end of the third safety metal
sleeve being connected with the connection part which is connected with the
tubular part.
Further, the annular barrier as described above may comprise a plurality of
additional safety metal sleeves surrounding the tubular part and the safety metal
sleeves being the first and second safety metal sleeves and being connected with
the connection part which is connected with the tubular part.
In addition, the expandable metal sleeve and safety metal sleeve may have
different required expansion pressures, i.e. the pressure required to expand one
sleeve may be different from sleeve to sleeve.
Moreover, the expandable metal sleeve and safety metal sleeve may be made
from different materials.
Said sleeves may have a thickness and the thickness of the expandable metal
sleeve may be greater than the thickness of the safety metal sleeve.
Also, the sleeves may have a thickness, the thickness of the first safety metal
sleeve being smaller than the thickness of the expandable metal sleeve and
greater than the thickness of the second safety sleeve.
Additionally, the sleeves may have a thickness, the thickness of the first safety
metal sleeve being smaller than the thickness of the expandable metal sleeve
and smaller than the thickness of the second safety sleeve.
Furthermore, the safety metal sleeve may have a higher ductility than the
expandable metal sleeve.
The expandable metal sleeve may have a higher yield strength than the safety
metal sleeve.
More specifically, the thickness of the expandable metal sleeve may be at least
10% greater than the thickness of the safety metal sleeve(s), preferably at least
15% greater than the thickness of the safety metal sleeve(s), and more
preferably at least 20% greater than the thickness of the safety metal sleeve(s).
In an embodiment, the first safety metal sleeve may be made of a material
having an elongation of more than 10% of an elongation of the material of the
expandable metal sleeve.
Also, one of the safety metal sleeves may be made of a material more ductile
than a material of the expandable metal sleeve.
Said expandable metal sleeve may have a length being substantially equal to a
length of the first and second sleeves in an unexpanded condition of the annular
barrier.
Further, the expandable metal sleeve may be made of a material having a yield
strength which is higher than a yield strength of a material of the first and/or
second safety metal sleeve.
In addition, the expandable metal sleeve may be made of a material having a
yield strength which is at least 10% higher than a yield strength of a material of
the first and/or second sleeve, preferably at least 15% higher and more
preferably at least 20% higher than a yield strength of the material of the first
and/or second sleeve.
Moreover, the expandable metal sleeve may have an unexpanded outside
diameter and an expanded outside diameter, the expanded diameter of the
expandable metal sleeve being at least 10% larger than the unexpanded
diameter, preferably at least 15% larger than the unexpanded diameter, more
preferably at least 30% larger than the unexpanded diameter.
The second sleeve may have circumferential elements restricting a free
expansion of at least the second safety sleeve.
In an embodiment, the additional sealing element surrounding an outermost
safety sleeve may comprise an intermediate layer of elastomer, rubber or
polymer arranged between the outermost safety metal sleeve and a sealing
element sleeve.
Furthermore, the safety metal sleeve closest to the inside wall of the borehole
may be made from a sealing metal material.
Also, the safety metal sleeve closest to the inside wall of the borehole may
comprise at least one sealing element.
Finally, the annular barrier according to the present invention may further
comprise a protective layer of lames on the outer face of the safety metal sleeve
closest to the inside wall of the borehole.
Brief description of the drawings
The invention and its many advantages will be described in more detail below
with reference to the accompanying schematic drawings, which for the purpose of
illustration show some non-limiting embodiments and in which
Fig. 1 shows a cross-sectional view along a longitudinal extension of an annular
barrier in its unexpanded condition,
Fig. 2 shows the annular barrier of Fig. 1 in its expanded condition,
Fig. 3 shows a cross-sectional view along a longitudinal extension of another
embodiment of the annular barrier in its unexpanded condition comprising a
second safety metal sleeve,
Fig. 4 shows the annular barrier of Fig. 3 in its expanded condition,
Fig. 5 shows a cross-sectional view along a longitudinal extension of another
embodiment of the annular barrier in its unexpanded condition further comprising
a third safety metal sleeve,
Fig. 6a shows a cross-sectional view along a longitudinal extension of a known
annular barrier comprising one expandable metal sleeve in its unexpanded
condition,
Fig. 6b shows the known annular barrier of Fig. 6a in an intermediate condition
during expansion of the annular barrier,
Fig. 6c shows the known annular barrier of Figs. 6a and 6b in an expanded
condition comprising a ruptured expandable metal sleeve,
Fig. 7a shows a cross-sectional view along a longitudinal extension of another
embodiment of the annular barrier comprising an expandable metal sleeve and a
first safety sleeve in its unexpanded condition,
Fig. 7b shows the annular barrier of Fig. 7a in an intermediate condition during
expansion of the annular barrier,
Fig. 7c shows the annular barrier of Figs. 7a and 7b in an expanded condition,
Fig. 8a shows a cross-sectional view along a longitudinal extension of another
embodiment of the annular barrier comprising an expandable metal sleeve, a first
safety sleeve and a second safety metal sleeve in its unexpanded condition,
Fig. 8b shows the annular barrier of Fig. 8a in an intermediate condition during
expansion of the annular barrier,
Fig. 8c shows the annular barrier of Figs. 8a and 8b in an expanded condition,
and
Fig. 9 shows a known annular barrier comprising a sealing element.
All the figures are highly schematic and not necessarily to scale, and they show
only those parts which are necessary in order to elucidate the invention, other
parts being omitted or merely suggested.
Detailed description of the invention
Fig. 1 shows a cross-sectional view along a longitudinal extension of an annular
barrier 1 in its unexpanded condition. The annular barrier 1 is rotationally
symmetric around a centre axis of rotation 18. The annular barrier is to be
expanded in an annulus 2 between a well tubular structure 3 and an inside wall 4
of a borehole 5 downhole. Fig. 2 shows the annular barrier of Fig. 1 in its
expanded condition, providing zone isolation between a first zone 200 and a
second zone 300 of the borehole 5. The annular barrier 1 comprises a tubular
part 6 for mounting as part of the well tubular structure and an expandable metal
sleeve 7 surrounding the tubular part 6. The expandable metal sleeve has an
inner face 7a facing the tubular part, and each end 71, 72 of the expandable
metal sleeve is connected with a connection part 12 which is connected with the
tubular part, thereby defining a space 13 between the inner face of the
expandable metal sleeve 7 and the tubular part. The space 13 is defined by the
expandable metal sleeve, the connection parts 12 and the tubular part 6. The
annular barrier further comprises a first safety metal sleeve 8 surrounding the
tubular part and abutting the expandable metal sleeve 7. The first safety metal
sleeve has a first inner face 8a abutting an outer face 7b of the expandable metal
sleeve, and each end 81, 82 of the first safety metal sleeve is connected with the
connection part 12 which is connected with the tubular part. The tubular part 6
comprises an expansion opening 11 for allowing fluid to enter the space 13
during expansion of the annular barrier 1. The inner face of the first safety metal
sleeve 8 abuts and contacts the face of the expandable metal sleeve along the
whole length of the expandable metal sleeve in its unexpanded condition. In the
expanded condition and the unexpanded condition, the outer face 8b of the first
safety metal sleeve abuts the inner wall of the borehole and during expansion,
the safety metal sleeve limits the free movement of the expandable metal sleeve.
Furthermore, the force applied to the expandable metal sleeve 7 is transferred to
the safety metal sleeve 8 by means of the expandable metal sleeve, resulting in a
more even distribution of the force applied on the safety metal sleeve than when
applied on the expandable metal sleeve.
Fig. 3 shows a cross-sectional view along a longitudinal extension of an annular
barrier 1 condition further comprising a second safety metal sleeve 9 surrounding
the tubular part, the expandable metal sleeve 7 and the first safety metal sleeve
8. The second safety metal sleeve 9 has a second inner face 9a facing the first
safety metal sleeve 8, and each end 91, 92 of the second safety metal sleeve 9 is
connected with the connection part 12 which again is connected with the tubular
part. The tubular part 6 comprises an expansion opening 11 for allowing fluid to
enter the space 13 during expansion of the annular barrier 1. Fig. 4 shows the
annular barrier of Fig. 3 in its expanded condition, providing zone isolation
between a first zone 200 and a second zone 300 of the borehole 5.
Fig. 5 shows an annular barrier further comprising an additional safety metal
sleeve 10. The annular barrier 1 shown in Fig. 5 comprises one additional safety
metal sleeve 10, the first and second safety metal sleeve 8, 9 and the
expandable metal sleeve 7, but even more additional safety metal sleeves may
be added to avoid ruptures of the annular barrier.
When using several additional safety metal sleeves such as shown in Fig. 5, the
annular barrier may be optimised by using safety metal sleeves with different
required expansion pressures, so that peripheral sleeves have lower required
expansion pressures than more central sleeves. If the safety metal sleeves have
lower required expansion pressures, e.g. because they are thinner than the
expandable metal sleeve such as shown in Figs. 1 and 2, the pressure required to
expand the annular barrier may be lowered. Instead of changing the thickness of
the safety metal sleeves and the expandable metal sleeve, the sleeves may be
made from different materials to provide a difference in required expansion
pressure, e.g. one sleeve may be designed to require a smaller expansion
pressure than another sleeve by using two different materials. Furthermore, the
use of different materials may be used to provide a very ductile material in the
outermost sleeves to inhibit necking in the outermost sleeves during expansion.
On the other hand, the innermost sleeves, such as the expandable metal sleeve
and the first safety metal sleeve, may be be made from a less ductile material,
which may resist a larger external pressure from the outside of the annular
barrier, e.g. sudden changes in the borehole pressure. Since the outermost
sleeves are supported by the innermost sleeves when a pressure is applied from
the outside, the ability of the innermost sleeves to resist such pressures are
important when requiring an annular barrier with a high collapse pressure.
The thickness of the expandable metal sleeve shown in Fig. 5 is substantially
reduced compared to the expandable metal sleeves shown in Figs. 1-4. When the
number of safety metal sleeves is increased, the overall strength of the annular
barrier is increased, and the thickness of the expandable metal sleeve 7 may be
decreased in order to reduce the total thickness of the sleeves.
An annular barrier may comprise several additional safety metal sleeves 10, such
as three additional safety metal sleeves 10, such as four additional safety metal
sleeves 10, such as five additional safety metal sleeves 10, or even more
additional safety metal sleeves.
Figs. 6a-6c show a known annular barrier comprising an expandable metal sleeve
7 with no safety metal sleeves. The expandable metal sleeve 7 has a weak area
17a, e.g. a thinning, an area with one or more fractures, an area with reduced
strength due to material composition, and/or an area with impurities. When the
annular barrier having such a weak area is expanded, the expandable metal
sleeve starts to deform more rapidly around the weak area 17a and bulge due to
the reduced strength in this weak area, as shown in Fig. 6b. The more rapid
expansion of the material around the weak area leads to the creation of a
"bubble" on the expandable metal sleeve 7 near the weak area. Since the
material around the weak area expands more rapidly than the rest of the
material of the expandable metal sleeve, the expandable metal sleeve thins in
this area and is more likely to have a fracture 20 near the weak area 17a, leading
to at least a local rupture if not a circumferential rupture of the annular barrier as
illustrated in Fig. 6c.
Figs. 7a-7c show an annular barrier comprising an expandable metal sleeve 7 and
a first safety metal sleeve 8. As shown in Fig. 7a, the expandable metal sleeve 7
has a weak area 17a, which is most likely to occur during the manufacturing
process of making the expandable metal sleeve. Even though the first safety
metal sleeve also has a weak area 17b, it is not likely to be arranged opposite
the weak area of the expandable metal sleeve. When the annular barrier shown
in Fig. 7a is expanded as shown in Fig. 7b, the safety metal sleeve 8 braces and
supports the weak area 17a of the expandable metal sleeve so that it cannot
bulge and form a bubble 21, such as the one shown in Fig. 6b. In this way, the
safety metal sleeve prevents the expandable metal sleeve from moving freely but
controls the expansion process of the expandable metal sleeve to occur more
evenly. Furthermore, the force from the expansion fluid in the space 13 will be
applied on the inner face 7a of the expandable metal sleeve 7, and since the
safety metal sleeve abuts the expandable metal sleeve, the force on the safety
metal sleeve will be applied by the expandable metal sleeve directly. Therefore,
should the safety metal sleeve 8 comprise a weak area 17b, the part of the
expandable metal sleeve close to the weak area will brace the weak area 17b of
the safety metal sleeve so that a bubble is not formed on the safety metal sleeve
as well. The force on the safety metal sleeve is distributed evenly to the safety
metal sleeve by means of the expandable metal sleeve, and thus no force will be
applied to a part of the safety metal sleeve which is not in contact with the
expandable metal sleeve until the expandable metal sleeve is once again in
contact with that part of the safety metal sleeve. Thus, no bulging of the safety
metal sleeve can occur as no force will be applied to the somewhat bulging part,
resulting in a subsequent burst of the safety metal sleeve.
The safety metal sleeve of Figs. 7a-7b is thinner than the expandable metal
sleeve, e.g. the safety metal sleeve may be 0.5-1.0 mm and the expandable
metal sleeve may be 5-10 mm and thus, by adding only a thin outer sleeve, the
risk of fracturing the expandable metal sleeve during expansion is substantially
reduced without substantially increasing the overall thickness of the annular
barrier.
Figs. 8a-8c show an annular barrier comprising an expandable metal sleeve 7, a
first safety metal sleeve 8 and a second safety metal sleeve 9. As shown in Fig.
8a, the expandable metal sleeve 7 has a weak area 17a, and the first safety
metal sleeve 8 has a weak area 17b and the second safety metal sleeve 9 has a
weak area 17c. Increasing the number of safety metal sleeves reduces the risk of
all sleeves having a weak area close to each other. If all sleeves have a weak
area close to each other, the situation resembles the situation shown in Fig. 6a
where only one sleeve comprising a weak area constitutes the expandable part of
the annular barrier. Therefore, providing a safety metal sleeve substantially
reduces the risk of rupturing the expandable metal sleeve during expansion, and
the addition of more safety metal sleeves even further minimises this risk.
Having an annular barrier, where the expandable metal sleeve 7 has a weak area
17a close to or even spot on a weak area 17b on the first safety metal sleeve,
the two inner sleeves, i.e. the expandable metal sleeve and the first safety metal
sleeve, are still braced by the second safety metal sleeve to ensure that a
"bubble" is not formed. Since the annular barrier has a large surface area and the
weak areas of the sleeves with modern production techniques are typically very
small and widely spread on this large surface area, the risk of two overlapping
weak areas is very small. However, adding one more safety metal sleeves as
shown in Figs. 8a-8c or even a third safety metal sleeve as shown in Fig. 5
almost eliminates the risk of overlapping weak areas, since the probability may
typically be lowered by several orders of magnitude for every additional safety
metal sleeve.
Fig. 9 shows a known barrier 400 comprising an expandable metal sleeve
member 40 surrounding a tubular section 4 1 and a further outer sleeve member
42 partially surrounding the expandable metal sleeve member 40 and enclosing a
space 43 filled with a sealing material 44 such as a polymeric material. This is a
known solution thought to provide better sealing between the inside wall 4 of the
borehole and an inside of the production casing 46. However, as shown in Fig. 9,
if the expandable metal sleeve member comprises a weak area 45, the
expandable metal sleeve member 40 may still rupture during expansion, since a
bubble or bulging may start to form within the space 43 and displace the
polymeric material and eventually lead to a fracture in the sealing expandable
metal sleeve member 40. The collapse strength of the expandable metal sleeve
member is thus substantially reduced. As the polymeric material leaves the space
43 through the opening in the further outer sleeve member, the barrier leaks
since the pressurised fluid expanding the expandable metal sleeve member will
force its way through the polymeric material and out through the opening, and a
seal will never be formed.
The annular barrier of the present invention may be improved with respect to
sealing properties towards the inside wall 4 of the borehole by adding an
additional sealing element surrounding an outermost safety sleeve, which
comprises an intermediate layer of elastomer, rubber or polymer arranged
between the outermost safety metal sleeve and a sealing element sleeve. Also,
other known sealing elements may be added to the annular barrier surrounding
the outermost safety sleeve to improve sealing properties of the annular barrier.
Also, the outermost safety metal sleeve may be made from or comprise a sealing
metal material. If additional sealing elements surrounding the outermost safety
metal sleeve are inappropriate for other reasons such as limited space in the
annulus, the outermost safety metal sleeve may be made from a material having
good sealing properties such as high ductility.
Also, the annular barrier may comprise restricting a free expansion of the
sleeves.
The expandable metal sleeve 7 and the additional safety metal sleeves 8, 9, 10
may be made from different materials, one having a higher strength and thereby
lower ductility than the other material having a lower strength but higher
ductility. Hereby, the annular barrier may comprise the materials adapted to
provide high strength or high ductility in a preferred combination. Once
expanded, the overall effect is an annular barrier with a higher collapse
resistance and higher resistance towards rupture during expansion.
Also, the metal used for the sleeves may have an elongation of 10-35%,
preferably 25-35%. The metal may have a yield strength (cold worked) of 500-
1000 MPa, preferably 500-700 MPa. The sleeves may be a cold-drawn or hotdrawn
tubular structure.
The thickness of the expandable metal sleeve may preferably be at least 10%
greater than the thickness of the safety metal sleeves, and more preferably at
least 15% greater than the thickness of the safety metal sleeves, and even more
preferably at least 20% greater than the thickness of the safety metal sleeves.
The thickness of the safety metal sleeve may be 0.5 mm to 5 mm, and the
thickness of the expandable metal sleeve may be 5 mm to 20 mm.
Furthermore, the safety metal sleeves may preferably be made from a material
having an elongation of more than 10% of an elongation of the material of the
expandable metal sleeve.
The annular barrier may preferably comprise an expandable metal sleeve made
from a material having a yield strength which is at least 10% higher than a yield
strength of a material of the first and/or second safety metal sleeve, or more
preferably at least 15% higher and even more preferably at least 20% higher
than a yield strength of the material of the first and/or second safety metal
sleeve.
Also, the expandable metal sleeve may have an unexpanded outside diameter
and an expanded outside diameter, the expanded diameter of the expandable
metal sleeve being at least 10% larger than the unexpanded diameter, preferably
at least 15% larger than the unexpanded diameter, and more preferably at least
30% larger than the unexpanded diameter.
Although the invention has been described in the above in connection with
preferred embodiments of the invention, it will be evident for a person skilled in
the art that several modifications are conceivable without departing from the
invention as defined by the following claims.
Claims
1. An annular barrier (1) to be expanded in an annulus (2) between a well
tubular structure (3) and an inside wall (4) of a borehole (5) downhole for
providing zone isolation between a first zone (200) and a second zone (300) of
the borehole, comprising
- a tubular part (6) for mounting as part of the well tubular structure,
- an expandable metal sleeve (7) surrounding the tubular part and having
an inner face (7a) facing the tubular part and an outer face (7b) facing
towards the inside wall of the borehole, each end (71, 72) of the
expandable metal sleeve being connected with a connection part (12) which
is connected with the tubular part,
- a space (13) between the inner face of the expandable metal sleeve and
the tubular part, and
- an expansion opening (11) in the tubular part (6) through which fluid may
enter into the space (13) in order to expand the expandable metal sleeve
(7),
wherein the annular barrier further comprises a first safety metal sleeve (8)
surrounding the tubular part and abutting the expandable metal sleeve and said
first safety metal sleeve having a first inner face (8a) abutting the face of the
expandable metal sleeve, each end (81, 82) of the first safety metal sleeve being
connected with the connection part (12) which is connected with the tubular part.
2. An annular barrier according to claim 1, wherein the first safety metal
sleeve has a first inner face (8a) abutting the outer face of the expandable metal
sleeve.
3. An annular barrier according to claim 1 or 2, further comprising a second
safety metal sleeve (9) surrounding the tubular part, the expandable metal
sleeve and said second safety metal sleeve having a second inner face (9a)
facing the safety metal sleeve, each end (91, 92) of the second safety metal
sleeve being connected with the connection part (12) which is connected with the
tubular part.
4. An annular barrier according to claim 3, further comprising a third safety
metal sleeve (10), said third safety metal sleeve having a third inner face (10a)
facing the second outer face (9b) of the second safety metal sleeve, each end
(101, 102) of the third safety metal sleeve being connected with the connection
part (12) which is connected with the tubular part.
5. An annular barrier according to claim 1, further comprising a plurality of
additional safety metal sleeves surrounding the tubular part and the safety metal
sleeves being the first and second safety metal sleeves, and being connected
with the connection part (12) which is connected with the tubular part.
6. An annular barrier according to any of the preceding claims, wherein the
expandable metal sleeve and safety metal sleeve have different required
expansion pressures.
7. An annular barrier according to any of the preceding claims, wherein the
expandable metal sleeve and safety metal sleeve are made from different
materials.
8. An annular barrier according to any of the preceding claims, wherein the
sleeves have a thickness and the thickness of the expandable metal sleeve is
greater than the thickness of the safety metal sleeve.
9. An annular barrier according to any of the preceding claims, wherein the
safety metal sleeve has a higher ductility than the expandable metal sleeve.
10. An annular barrier according to any of the preceding claims, wherein the
expandable metal sleeve has a higher yield strength than the safety metal
sleeve.
11. An annular barrier according to claim 9, wherein the first safety metal
sleeve is made of a material having an elongation of more than 10% of an
elongation of the material of the expandable metal sleeve.
12. An annular barrier according to claim 5, wherein an additional sealing
element surrounding an outermost safety sleeve comprises an intermediate layer
of elastomer, rubber or polymer arranged between the outermost safety metal
sleeve and a sealing element sleeve.
13. An annular barrier according to claim 5, wherein the safety metal sleeve
closest to the inside wall (4) of the borehole is made from a sealing metal
material.
14. An annular barrier according to claim 5, wherein the safety metal sleeve
closest to the inside wall (4) of the borehole comprises at least one sealing
element.