Note: Descriptions are shown in the official language in which they were submitted.
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DOWNHOLE SYSTEM
Field of the invention
The present invention relates to a downhole system for completing a well,
comprising a downhole well tubular structure having a wall and being
configured
to be arranged in a borehole of the well; a first annular barrier for being
expanded in an annulus between the downhole well tubular structure and a wall
of the borehole; and a first aperture in the wall of the downhole well tubular
structure. Furthermore, the invention relates to a completion method for
completing a downhole system.
Background art
Hydrocarbon-containing wells may be completed in very different manners and
with very different designs, and the design used depends on the geological
structure and composition of the formation in which the well is formed. In sub-
salt fields that experience high losses during drilling and completion, it is
very
important that the well tubular structure is closed off until the annular
barriers
are expanded so that a zone experiencing a high pressure loss can be closed
off
after opening for production from that zone.
Also, when using expandable annular barriers where the well tubular structure
is
pressurised to expand several annular barriers in one run, the well tubular
structure needs to be sealed off so that the well tubular structure can be
pressurised to a certain pressure. Subsequently, the well tubular structure
needs
to be opened to let hydrocarbon-containing fluid from the formation into the
well
tubular structure. For this reason, well tubular structures are often opened
for
production by perforating the well tubular structure by means of perforation
guns
after the expansion of the annular barriers. However, such detonation entails
a
risk of the well tubular structure leaking in unintended areas, and sliding
sleeves
are therefore often preferred. However, operating such sliding sleeves by
intervening the well with a tool takes time and cannot be done remotely as
demanded by oil companies nowadays.
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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 downhole system having annular barriers configured to be
expanded by pressurising the well tubular structure, in which system opening
for
production may be done remotely and easily.
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 a downhole system
for
completing a well, comprising:
- a downhole well tubular structure having a wall and being configured to
be
arranged in a borehole of the well,
- a first annular barrier for being expanded in an annulus between the
downhole
well tubular structure and a wall of the borehole, the first annular barrier
comprising:
- a tubular part for mounting as part of the downhole well tubular
structure, the tubular part having a first expansion opening and an outer
face,
- an expandable metal sleeve surrounding the tubular part and having an
inner face facing the tubular part and an outer face facing the wall of the
borehole,
- a first connection part and a second connection part configured to
connect a first end and a second end, respectively, of the expandable
metal sleeve with the tubular part, and
- an annular space between the inner face of the expandable metal
sleeve and the tubular part, the expandable metal sleeve being
expanded by pressurising the annular space to an expansion pressure by
pressurising the tubular part opposite the expansion opening, and
- a first aperture in the wall of the downhole well tubular structure,
wherein the aperture is at least partly plugged with an acid-soluble material.
The downhole well tubular structure may have a first end nearest a top of the
well and a second end, the second end may be configured to be closed or may be
closed when inserting the downhole well tubular structure into the well, and
the
second end may comprise a second aperture in which a burstable element is
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arranged for closing the second end. By having a burstable element in the
second
end, the annular barrier can be expanded in that the downhole well tubular
structure is closed, and subsequently the well tubular structure is
pressurised to
a pressure above the expansion pressure to burst the burstable element so that
acid can be circulated down past the acid-soluble material to dissolve the
plug.
In an embodiment, the material may comprise aluminium.
Moreover, the first aperture plugged with a plug of the material may be
configured to withstand a first pressure higher than the expansion pressure.
Further, the plug may have a body part and a flange, the body part extending
into the aperture and the flange abutting an inner face of the well tubular
structure.
Also, the body part of the plug may have a bore. By having a hollow body part,
fluid communication between the inside of the well tubular structure and the
annulus can be established by the bore.
The body part may have a notch for initiating separation between the body part
and the flange.
Furthermore, the first aperture plugged with the material may be configured to
withstand a first pressure being higher than the expansion pressure.
Moreover, the burstable element may be configured to burst at a burst
pressure.
The first aperture plugged with the material may be configured to withstand a
first pressure higher than the burst pressure.
The downhole system may further comprise a second annular barrier, and the
aperture may be arranged between the first annular barrier and the second
annular barrier.
Furthermore, the downhole system may further comprise a sliding sleeve
arranged opposite the aperture and having a first initial position uncovering
the
aperture.
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In another embodiment, the annular barrier may have only one or no connection
parts.
In addition, the downhole system may further comprise:
- an inner well tubular structure arranged inside the downhole well tubular
structure, the inner well tubular structure comprising a wall,
- a first inner annular barrier and a second inner annular barrier, each
inner
annular barrier comprising:
- a tubular part for mounting as part of the inner well tubular structure,
the tubular part having an inner expansion opening,
- an expandable metal sleeve surrounding the tubular part and having an
inner face facing the tubular part and an outer face facing the wall of the
downhole well tubular structure,
- a first connection part and a second connection part configured to
connect a first end and a second end, respectively, of the expandable
metal sleeve with the tubular part, and
- an annular space between the inner face of the expandable metal
sleeve and the tubular part, the expandable metal sleeve being
expanded by pressurising the annular space to an inner expansion
pressure by pressurising the tubular part opposite the inner expansion
opening, and
- a second aperture in the wall of the inner well tubular structure.
In an embodiment, a burst disc may be arranged in the second aperture and be
configured to burst at a burst pressure higher than the inner expansion
pressure.
Moreover, the inner well tubular structure may comprise a sliding sleeve
arranged opposite the second aperture.
Also, the downhole well tubular structure may comprise other annular barriers.
In addition, the inner well tubular structure may comprise other inner annular
barriers.
Furthermore, the downhole well tubular structure may comprise other first
apertures arranged between two annular barriers.
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Additionally, the inner well tubular structure may comprise other second
apertures arranged between two inner annular barriers.
The downhole system may further comprise a tool configured to close and/or
5 open the sliding sleeves.
In an embodiment, the tool may be arranged at the bottom of the well or be
inserted when needed.
Furthermore, the downhole system may further comprise a dart tool having
projecting elements for engaging a groove in the sliding sleeve and an
inflatable
element.
The present invention furthermore relates to a completion method for
completing
a downhole system as described above comprising the steps of:
- inserting the downhole well tubular structure into the borehole,
- pressurising the downhole well tubular structure to expand the annular
barriers,
and
- acidising the acid-soluble material to clear the first aperture.
Said completion method as described above may, before the step of acidising
the
acid-soluble material, further comprise the step of pressurising the well
tubular
structure to a pressure above the expansion pressure to burst a burstable
element in a second end of the well tubular structure below the annular
barrier.
Also, the well tubular structure may comprise a sliding sleeve which is run in
hole
in an open position, uncovering the first aperture.
In an embodiment, the completion method may, before the step of acidising the
acid-soluble material, further comprise the step of inserting an inner well
tubular
structure.
Furthermore, the completion method may, before the step of acidising the acid-
soluble material and after the step of inserting the inner well tubular
structure,
further comprise the step of pressurising the inner well tubular structure to
the
inner expansion pressure to expand inner annular barriers connected with the
inner well tubular structure.
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In addition, the completion method may, before the step of acidising the acid-
soluble material and after the step of pressurising the inner well tubular
structure
to the inner expansion pressure, further comprise the step of pressurising the
inner well tubular structure to the burst pressure to burst a burst disc.
Finally, the completion method may, after the step of pressurising the inner
well
tubular structure to the burst pressure to burst the burst disc, let acid
through a
second aperture into a second annulus between the inner well tubular
structure,
the downhole well tubular structure and the inner annular barriers to acidise
the
acid-soluble material.
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 partially cross-sectional view of a downhole system having a
downhole well tubular structure connected with unexpanded annular barriers,
Fig. 2 shows a partially cross-sectional view of the downhole system of Fig. 1
where the annular barriers are in the expanded position,
Fig. 3 shows a partially cross-sectional view of another downhole system
having
an inner well tubular structure arranged within the downhole well tubular
structure, before the inner annular barriers connected with the inner well
tubular
structure are expanded,
Fig. 4 shows a partially cross-sectional view of the downhole system of Fig. 1
where the inner annular barriers are in the expanded position,
Fig. 5 shows a partially cross-sectional view of another downhole system
having
a tool inserted for operating sliding sleeves covering/uncovering the second
apertures in the inner well tubular structure,
Fig. 6 shows a partially cross-sectional view of yet another downhole system
having a dart tool for sequentially operating the sliding sleeves,
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Fig. 7 shows a partially cross-sectional view of yet another downhole system
having a burst disc in the second end of the well tubular structure,
Fig. 8 shows a cross-sectional view of part of the downhole system having a
plug
and a sliding sleeve in its open position,
Fig. 8A shows a partial view of Fig. 8, and
Fig. 9 shows a cross-sectional view of part of the downhole system of Fig. 8
in
which the sliding sleeve has released the flange from the bode part.
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 downhole system 100 for completing a well 2, comprising a
downhole well tubular structure 1 having a wall la and being configured to be
arranged in a borehole 3 of the well. The downhole system 100 comprises a
first
annular barrier 10, 10a configured to be expanded in an annulus 4 between the
downhole well tubular structure 1 and a wall 5 of the borehole 3, as shown in
Fig.
2. The first annular barrier 10, 10a comprises a tubular part 11 configured to
be
mounted as part of the downhole well tubular structure 1. The tubular part 11
has a first expansion opening 12 and an outer face 14. The first annular
barrier
10, 10a further comprises an expandable metal sleeve 15 surrounding the
tubular part 11 and having an inner face 16 facing the outer face 14 of the
tubular part, the expandable metal sleeve further having an outer face 17
facing
the wall of the borehole 3. A first connection part 18 is configured to
connect a
first end 20 of the expandable metal sleeve 15 with the tubular part 11, and a
second connection part 19 is configured to connect a second end 21 of the
expandable metal sleeve with the tubular part. An annular space 22 (as shown
in
Fig. 2) is defined between the inner face of the expandable metal sleeve 15
and
the outer face 14 of the tubular part 11. The first annular barrier 10, 10a is
set
and thus expanded by the expandable metal sleeve 15 being expanded by
pressurising the annular space 22 with fluid to an expansion pressure by
pressurising the fluid inside the tubular part 11 opposite the first expansion
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opening. The wall of the downhole well tubular structure 1 has a first
aperture 23
which is at least partly plugged with an acid-soluble material 24 so that the
aperture is configured to withstand a first pressure being higher than the
expansion pressure. The material 24 mainly comprises aluminium so that acid
can dissolve the material and clear the aperture 23.
When having well tubular structures with annular barriers which are expanded
by
pressurising fluid inside the well tubular structure and letting the
pressurised fluid
in through the expansion opening and into the annular space, the apertures for
the subsequent production of hydrocarbon-containing fluid need to be sealed
off
to be able to pressurise the well tubular structure. After the pressurisation
and
the expansion, the production apertures in known completions need to be opened
by sliding sleeves arranged opposite the apertures. However, this has to be
done
in a separate run and with the risk of not being able to slide the sleeve and
thus
not being able to open for production in one or more production zones. For
this
and other reasons, well tubular structures are often opened for production by
perforating the well tubular structure by means of perforation guns after the
expansion of the annular barriers. However, such detonation entails a risk of
the
well tubular structure leaking in unintended areas, and sliding sleeves are
therefore preferred. After sliding the sliding sleeves and thereby uncovering
the
apertures, the well tubular structure is pressurised with acid to acidise the
formation and increase the production contact area and thus increase formation
contact.
By having the first aperture at least partly plugged with an acid-soluble
material,
the step or run of intervening the well in order to slide the sliding sleeves
can be
avoided since the acid provides access through the aperture to the formation.
In
the event that one production zone opposite one of the first apertures 23
produces too much water, that zone can be shut off by sliding the sliding
sleeve
to close off the flow through the first aperture opposite that zone. Thus, the
sliding sleeve 26 is run in hole in its open position.
As can be seen in Fig. 2, the downhole system 100 further comprises a second
annular barrier 10, 10b for isolating a first production zone 101, and the
first
aperture 23 is arranged between the first and second annular barriers 10, 10a,
10b. The downhole system 100 further comprises a third annular barrier 10, 10c
for isolating a second production zone 102 between the second and third
annular
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barriers 10, 10b, 10c. The downhole well tubular structure 1 is closed at the
bottom by a ball 46 fitting into a ball seat 47. In this way, the entire well
tubular
structure 1 can be pressurised from its top to expand the annular barriers 10.
The well tubular structure 1 may also be closed, e.g. by a plug or the like.
The downhole system 100 further comprises a sliding sleeve 26 arranged
opposite the first aperture 23 and having a first initial position uncovering
the
first aperture so that a second run is not necessary to open the first
apertures.
However, the sliding sleeves 26 can be closed later, e.g. if one of the
production
zones starts producing water, that zone can be closed by sliding the sliding
sleeve arranged opposite that aperture through which the water flows from that
zone.
In order to expand the expandable metal sleeves 15 of the annular barriers 10,
10a, 10b, 10c, the inside of the well tubular structure 1 is pressurised so
that
several annular barriers 10 are set in one pressurising step. The first
apertures
23 between the annular barriers 10a, 10b, 10c are plugged by a plug 9 of an
acid-soluble material 24 and the plugs 9 are configured to withstand a first
pressure being higher than the expansion pressure. The downhole well tubular
structure 1 has a first end 6 and a second end 7 as shown in Fig. 7. The first
end
6 is nearest a top of the well and the second end 7 is closed when inserting
the
downhole well tubular structure 1 into the borehole of the well. The second
end 7
comprises a second aperture 52 in which a burstable element 8 is arranged, and
the second aperture 52 is also arranged below all the annular barriers 10. By
having a burstable element 8 in the second end 7, the annular barriers 10 can
be
expanded in that the downhole well tubular structure 1 is closed by the
burstable
element 8, and subsequently the well tubular structure 1 is pressurised to a
pressure above the expansion pressure to burst the burstable element 8 so that
acid can be circulated down past the acid-soluble material 24 to dissolve the
plug
9. In known solutions, the ball dropped for closing the well tubular metal
structure in order to be able to pressurise it has to be drilled out before
fluid can
be circulated in the well tubular metal structure. By the present solution,
the
combination of the burstable element 8 in the second aperture 52 in the second
end 7 for closing the well tubular structure 1 and plugs 9 of acid-dissoluble
material 24 in the first apertures 23 between the annular barriers 10a, 10b,
10c
allows the annular barriers to be expanded, and then the burstable element 8
is
burst to open the second aperture 52 of the second end 7, and acid can be
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circulated to dissolve the plugs 9, and the well tubular structure 1 is thus
open
for production without having to intervene the well by tools. A burstable
element
8, such as a burst disc, is set to burst at a certain pressure, meaning within
a
certain pressure range. If all first apertures were plugged with burst discs,
the
5 first burst disc bursting would cause the pressure to drop and the
remaining burst
discs would not burst, and then a tool isolating a zone opposite each of the
burst
discs has to be inserted into the well. The present invention thus presents a
downhole system 100 in which annular barriers 10 can be expanded and no
intervention is needed to open for production subsequently.
In Fig. 8, the plug 9 has a body part 27 and a flange 28, the body part
extending
into the aperture and the flange abutting an inner face 44 of a groove 43 in
the
well tubular structure 1. The flange 28 has a sealing means 48 in order to
seal
against the inner face 44. The body part has a bore 51 closed by the flange
28.
The body part has on its outer face a notch 25, also shown in Fig. 8A, so that
if
the plug is not dissolved when acidising, a tool 50 as shown in Fig. 9 can
intervene the well and a projectable part 55 of the tool 50 can slide the
sleeve
and separate by force the flange 28 from the body part 27. When separating the
flange 28 from the body part 27, as shown in Fig. 9, the bore 51 in the body
part
27 provides access to the production zone and the production can begin as
indicated by arrows.
In Fig. 3, the downhole system 100 further comprises an inner well tubular
structure 29 arranged inside the downhole well tubular structure 1. The inner
well
tubular structure 29 comprises a first inner annular barrier 30, 30a and a
second
inner annular barrier 30, 30b. Each inner annular barrier 30 comprises a
tubular
part 31 for mounting as part of the inner well tubular structure 29. The
tubular
part 31 has an inner expansion opening 32 through which pressurised fluid
enters
to expand an expandable metal sleeve 33 surrounding the tubular part and
having an inner face 34 facing the tubular part and an outer face facing the
wall
of the downhole well tubular structure 1. A first connection part 35 is
configured
to connect a first end 37 of the expandable metal sleeve 33 with the tubular
part
31, and a second connection part 36 is configured to connect a second end 38
of
the expandable metal sleeve with the tubular part. An annular space 39 is
formed
between the inner face 34 of the expandable metal sleeve 33 and the tubular
part 31. The expandable metal sleeve 33 of the inner annular barriers 30, 30a,
30b is expanded by pressurising the annular space to an inner expansion
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pressure by pressurising the tubular part 31 and letting the pressurised fluid
in
through the inner expansion opening 32. The wall of the inner well tubular
structure 29 comprises a second aperture 40 through which acid is let into a
second annulus 45 between the inner well tubular structure 29, the downhole
well tubular structure 1 and the inner annular barriers 30 to acidise the acid-
soluble material in the first aperture 23 in the wall of the downhole well
tubular
structure 1.
By having an inner well tubular structure 29 arranged in the downhole well
tubular structure 1, the completion is double-skinned and the production fluid
flows from the first production zone 101 in through the first aperture 23,
into the
second annulus 45 and further into the inner well tubular structure 29 through
the second aperture 40.
As can be seen in Fig. 3, the inner well tubular structure 29 comprises a key
mechanism 49 at its toe at the bottom of the inner well tubular structure 29.
The
purpose of this is that when the inner well tubular structure 29 is recovered
for
recompletion or abandonment, the sliding sleeves of the valves of the downhole
well tubular structure 1 are closed as the inner well tubular structure is
retrieved
to surface. The key mechanism 49 slides along the downhole well tubular
structure 1 and engages a profile of the sliding sleeves 26 and slides the
sliding
sleeves into their closed position one by one as the inner well tubular
structure
29 is pulled out of the well. This prevents commingling of the zones or
significant
losses during work-over operations.
The inner well tubular structure 29 may be an intelligent completion with
surface
control of the inner valves, e.g. sliding sleeves 26 or other types of valves,
for
controlling the flow from the multiple zones. By using an acid-dissoluble
material
in the apertures in the downhole well tubular structure 1, the risk of losing
mud
out of the apertures when running the inner well tubular structure is
decreased,
while it is ensured that the zones are open for flow once the inner well
tubular
structure has landed in its position downhole.
In order to be able to expand the inner annular barriers 30 as shown in Fig.
4,
the second apertures 40 need to be sealed off, e.g. closed by a sliding sleeve
42
covering the second aperture 40. In order to move the sliding sleeves 42 to
open
the second aperture 40, an additional run is necessary. However, when a burst
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disc 41 is arranged in the second aperture 40 and configured to burst at a
burst
pressure higher than the inner expansion pressure, the inner well tubular
structure just needs to be pressurised to the burst pressure to open the
second
apertures. When supplying acid down the inner well tubular structure, the acid
fluid can be pressurised to a pressure above the burst pressure and can thus
burst the burst disc just before the acid is fed to the second annulus to
dissolve
the material 24 in the first aperture 23. Thus, the step of acidising entails
bursting the burst disc opening the second aperture, acidising the acid-
soluble
material in the first aperture 23 and acidising the formation to increase
formation
contact, all in one run without intervening the well.
Furthermore, when having an inner well tubular structure, it is not easy to
operate the sliding sleeves 42 covering/uncovering the first apertures 23 as
soon
as the inner well tubular structure has been inserted. Therefore, the
combination
of having a burst disc in the second apertures 40 in the inner well tubular
structure and having the acid-soluble material 24 in the downhole well tubular
structure 1 makes it possible to make a very operationally safe completion,
since
the first and second apertures are inserted in the uncovered position, but
"plugged" with acid-soluble material or a burst disc, respectively, so that
the
apertures can be opened in one run after expanding the inner annular barriers
30.
As shown in Figs. 3 and 4, the downhole well tubular structure 1 may be
connected with other annular barriers 10, and the inner well tubular structure
may be connected with other inner annular barriers 30. The downhole well
tubular structure 1 may comprise other first apertures 23 arranged between two
adjacent annular barriers 10, and the inner well tubular structure may
comprise
other second apertures 40 arranged between two adjacent inner annular barriers
30. The downhole system 100 may in this way have a plurality of production
zones other than the first and the second production zones.
In Fig. 5, the downhole system 100 further comprises a tool 50 configured to
close the sliding sleeves 42 and reopen them when needed. The tool 50
comprises a flexible element (not shown) which is forced radially outwards,
but
when moving along the inner face 34 of the inner well tubular structure, it is
forced to retract, and when being opposite the groove 62 of the sliding sleeve
42,
the flexible element is allowed to project radially outwards and engage the
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groove 62, and as the tool 50 continues to move in one direction, the sliding
sleeve 42 is moved to either open or close the aperture 40. The tool 50 may be
arranged in the bottom of the well 2 and be engaged by a drill pipe inserted
in
the inner or downhole well tubular structure when the sliding sleeves 42 need
to
be closed, e.g. before the inner well tubular structure is retracted for
repair or
replacement.
As shown in Fig. 6, the downhole system 100 further comprises a dart tool 60
having projecting elements 61 configured to engage a groove 62 in the sliding
sleeve 42 and an inflatable element 63. The dart tool 60 can be used if the
inner
well tubular structure is inserted with the sliding sleeves 42 in a closed
position,
covering the second aperture 40, and the production zones need to be opened
and fractured sequentially. This is e.g. the case if only one zone is opened
and
treated with acid, and when that production zone produces water, the zone is
closed and another production zone is opened and treated with acid. The dart
tool 60 is then inserted into the inner well tubular structure, and when
detecting
the sliding sleeve 42 to be operated, the projecting elements 61 engage the
groove 62 of the sliding sleeve 42 and the inflatable element 63 is inflated.
Upon
further pressurisation of the fluid above the inflatable element 63, the dart
tool
60 is moved downwards and the sliding sleeve 42 is forced open, and the acid
is
let into the second annulus 45, the acid-soluble material 24 is dissolved and
the
acid enters the first aperture 23 and the formation. The dart tool 60 may be
used
to open and treat several zones with acid. When this is done, the sliding
sleeves
42 are self-closing.
The well 2 is completed by inserting the downhole well tubular structure 1
into
the borehole 3, by pressurising the downhole well tubular structure to expand
the
annular barriers 10, and by subsequently acidising the acid-soluble material
24 to
clear the first aperture 23 and allow the acid to enter the first aperture to
acidise
the formation as well.
When completing a double-cased completion as shown in Fig. 4, an inner well
tubular structure is inserted after the annular barriers 10 connected with the
downhole well tubular structure 1 are expanded and before the acid treatment.
After the step of inserting the inner well tubular structure, the inner well
tubular
structure is pressurised to the inner expansion pressure to expand the inner
annular barriers 30, 30a, 30b and thus isolate the second annulus 45 between
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the downhole well tubular structure 1 and the inner well tubular structure
into
several second annuluses 45. Then, the inner well tubular structure is
pressurised
to the burst pressure to burst the burst discs 41 and provide access to the
second annulus 45. The burst discs 41 may be burst one at a time and thus be
rated at different burst pressures so that e.g. the burst disc arranged
furthest
away from the top of the well is rated to the lowest burst pressure to ensure
that
it is burst before bursting the next burst disc closer to the top of the well.
In this
way, it is ensured that all burst discs 41 are burst to prevent that once the
first
burst disc arranged closest to the top is burst, all fluid is lost in that
zone so the
other burst discs are not burst.
The first apertures may also comprise a burst disc configured to burst at a
burst
pressure higher than the expansion pressure in order to expand the annular
barrier.
A flow control valve may be arranged in one of the apertures in the well
tubular
structures to control flow in or out of the well tubular structures.
By fluid or well fluid is meant any kind of fluid that may be present in oil
or gas
wells downhole, such as natural gas, oil, oil mud, crude oil, water, etc. By
gas is
meant any kind of gas composition present in a well, completion, or open hole,
and by oil is meant any kind of oil composition, such as crude oil, an oil-
containing fluid, etc. Gas, oil, and water fluids may thus all comprise other
elements or substances than gas, oil, and/or water, respectively.
By a casing, well tubular structure, downhole well tubular structure, inner
well
tubular structure, or production casing is meant any kind of pipe, tubing,
tubular,
liner, string etc. used downhole in relation to oil or natural gas production.
In the event that the tool is not submergible all the way into the casing, a
downhole tractor can be used to push the tool all the way into position in the
well. The downhole tractor may have projectable arms having wheels, wherein
the wheels contact the inner surface of the casing for propelling the tractor
and
the tool forward in the casing. A downhole tractor is any kind of driving tool
capable of pushing or pulling tools in a well downhole, such as a Well Tractor
.
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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.
5
