Technical Field
[0001] The present invention relates to a sealing method for sealing off a production zone
where a casing having a circumference and perforations is situated in a borehole downhole,
but with a distance to an inner wall of the borehole, creating an intervening space
there between. Furthermore, the invention relates to a sealing arrangement.
Background
[0002] Casings are placed in boreholes in the formation mainly for preventing a collapse
of the boreholes. The borehole may have a number of casings situated within one another
so that a production casing is situated within an intermediate casing which again
is situated within a surface casing and a conductor pipe.
[0003] When the production casing is placed in the borehole, it is subsequently perforated
in a certain zone where oil is present. The oil fluid is then able to enter the production
casing, and oil production is initiated. During the oil production phase, the oil
fluid may be mixed with water as the zone with oil may shift when emptying the oil
reservoir for oil.
[0004] In the event that the zone with oil has shifted, it is necessary to make new perforations
in the production casing and to seal off the previous perforations. In order to seal
off the previous perforations, a new production casing is inserted within the first
production casing, and packers are placed on both sides of the zone. Subsequently,
new perforations are made in the new production casing.
[0005] By inserting a new production casing into the previous production casing, the production
rate is substantially diminished due to the increase in friction and the velocity
is likewise decreased causing a variety of related problems.
[0006] Another way to seal off the zone with water is to insert a cement plug above the
zone for plugging the underlying casing. Subsequently, the production casing is perforated
in a new area above the cement plug where oil is present. Hereby, the underlying casing
is shut off more permanently and it is very difficult, if not impossible, to resume
the production in the production casing beneath the plug without having to insert
a new production casing.
Description of the Invention
[0007] An aspect of the present invention is, at least partly, to overcome the disadvantages
of the known solutions to sealing off a production zone mentioned by providing a method
for sealing off a production zone which does not entail plugging part of the production
casing or inserting a new production casing diminishing the production rate substantially.
[0008] This aspect and the advantages becoming evident from the description below are obtained
by a sealing method for sealing off a leak in a casing or a production zone where
the casing having a circumference and perforations is situated in a borehole downhole,
but with a distance to the inner wall of the borehole, creating an intervening space
there between, comprising the steps of:
- injecting a composition for making a first circumferential seal in the intervening
space at a first position of the casing in one end of the production zone through
holes situated along a first circular or oval line around the casing,
- filling the intervening space at a first position in a radial direction of the casing,
- injecting a composition for making a second circumferential seal in the intervening
space at a second position of the casing in another end of the production zone through
holes situated along a second circular or oval line around the casing,
- filling the intervening space at a second position in a radial direction of the casing,
- inserting a liner into the casing opposite the perforations and extending within both
the first and the second circumferential seal, and
- expanding the liner until the liner is pressing against the casing whereby the liner
together with the first and the second circumferential seal isolate the production
zone.
[0009] Injecting a composition for making two separate circumferential seals in the intervening
space in a predetermined distance from one another and subsequently expanding a liner
between the two seals makes it possible to seal off a production zone without having
to block the lowest part of the casing or seal every perforation hole one by one.
[0010] In one embodiment, the composition may comprise a compound which is able to harden,
expand, swell or paste once injected into the intervening space.
[0011] In another embodiment, the holes through which the composition is injected may be
positioned directly opposite each other in the casing.
[0012] Moreover, the holes may be some of the perforations.
[0013] In addition, the method may also comprise the step of making the holes prior to at
least one of the injection steps.
[0014] In one embodiment, the sealing method may moreover comprise a third injection step
where composition is injected for making a third circumferential seal in the intervening
space through holes made at a distance from the perforations.
[0015] Furthermore, the sealing method may comprise the step of making new perforations
in the casing for letting oil fluid flow into the casing from a new and second production
zone.
[0016] In some embodiments, the composition may be expanded for making the circumferential
seals.
[0017] In addition, the sealing method may comprise a further step of injecting an intermediate
circumferential seal between the first and the second circumferential seal.
[0018] Finally, the invention also relates to a sealing arrangement for sealing off a leak
in a casing or a production zone where the casing having a circumference and perforations
is situated in a borehole downhole, but with a distance to the inner wall of borehole,
creating an intervening space between casing and the borehole, comprising:
- a first circumferential seal of composition in the intervening space at a first position
of the casing in a first end of the production zone,
- a second circumferential seal of composition in the intervening space at a second
position of the casing in a second end of the production zone, and
- an expanded liner in between the first and the second circumferential seal, for isolation
of the production zone.
Brief Description of the Drawings
[0019] The invention is explained in detail below with reference to the drawings, in which
Fig. 1 shows a sectional view of a casing within a borehole,
Fig. 2 shows a sectional view of the casing of Fig. 1 during a first injection step,
Fig. 3 shows a sectional view of the casing of Fig. 1 with a first circumferentially
seal;
Fig. 4 shows a sectional view of the casing of Fig. 1 during a second injecting step,
Fig. 5 shows a sectional view of the casing of Fig. 1 with a second circumferentially
seal,
Fig. 6 shows a cross-sectional view the casing of Fig. 5,
Fig. 7 shows the cross-sectional view the casing of Fig. 5 during the performance
of an expansion step of the present method,
Fig. 8 shows a cross-sectional view of the casing of Fig. 5 with a fully expanded
liner,
Fig. 9 shows a sectional view into the borehole with a plurality of circumferentially
seals and a new production zone, and
[0020] Fig. 10 shows a sectional view into the borehole with a production casing, intermediate
casings, a surface casing, and a conductor pipe.
[0021] The drawings are merely schematic and shown for an illustrative purpose.
Detailed description of the invention
[0022] The present invention finds it use in a situation where a perforated casing is used
in a borehole and where an oil production zone 1 for some reason has shifted or become
emptied of oil. Perforations 3 are situated facing the production zone 1, enabling
oil to flow into the casing 2 and in this way be brought up from downhole. When the
oil has become too emulsified with water or the reservoir has been emptied for oil,
the perforations 3 of the casing 2 must be sealed so that a new production zone 14
can be made in another place along the extension of the casing 2.
[0023] The borehole can be made in a formation of limestone or in sand. The oil fluid seeps
from the formation or sand into the casing 2 through the perforations 3 in the casing.
The seepage of oil fluid is illustrated by arrows in Fig. 1. Due to the fact that
the casing 2 is not cemented in order to fixate the casing in relation to the borehole,
a space occurs between the outside wall of the casing 2 and the inside wall of the
borehole. Thus, the oil fluid is able to flow along the longitudinal extension of
the casing 2 and into the perforations 3 of the casing. When the amount of oil present
in a production zone 1 is no longer sufficient and/or oil fluid has become too diluted,
the production zone 1 needs to be sealed off. Subsequently, new perforations are made
at a certain distance from the previous production zone so that a new production zone
14 can be created. The distance depends on how far the water is able to flow within
the formation or the sand towards the casing 2 and along the casing so that the diluted
fluid from the previous production zone is not mixed with the oil fluid from the new
production zone 14.
[0024] In Fig. 1 a casing 2 situated in a borehole is shown. The casing 2 has perforations
3 in the area facing the production zone 1 in order for the oil fluid to flow into
the casing. As can be seen, the diameter of the borehole may vary, and the intervening
space 4 between the casing 3 and the inside of the borehole thus vary accordingly.
When sealing off the production zone 1, the intervening space 4 is locally filled
with a composition 5 that is able to harden upon injection into the space for making
a circumferential seal 6, 9 around the outside wall of the casing 2.
[0025] A circumferential seal 6, 9 in the intervening space 4 around the outside wall of
the casing 2 is made by injecting a composition 5 through holes situated along a first
circular line 8 as shown with a broken line in Fig. 1. The intersecting line 8 is
shown as a first plane perpendicular to the longitudinal extension of the casing and
intersecting with the circumference of the casing. Thus, the circumferential seal
6, 9 has an extension around the outside of the casing 2 substantially perpendicular
to the longitudinal extension of the casing.
[0026] In another embodiment, the intersecting line 8 occurs when a plane intersects with
the circumference of the casing and has an angle of 60°-85° to the longitudinal extension
of the casing 2. Thus, the circumferential seal 6, 9 will also have an angle of 60°-85°
to the longitudinal extension of the casing 2.
[0027] The injection of composition 5 is performed in some of the perforations by an injection
tool 13 as shown in Fig. 2. The injection tool 13 is submerged into the casing 2 and
an injection tip 16 is subsequently moved outwards and out of some of the perforations
3 in a radial direction of the casing.
[0028] To seal off a production zone 1, at least two seals 6, 9 must to be made, one in
each end of the production zone 1, and a liner 12 must be inserted covering the perforations
3 from inside the casing and overlapping the first 6 and the second 9 seal. In this
way, fluid seeping from the formation is not able to flow along the casing 2 and into
other perforations of the casing.
[0029] Firstly, a first circumferential seal 6 is made at a first position 7 of the casing
in one end of the production zone 1 as shown in Figs. 2 and 3. Secondly, a second
circumferential seal 9 is made at a second position of the casing in a second opposing
end of the production zone 1 as shown in Figs. 4 and 5. As can be seen, the intervening
space 4 is filled with composition 5 until a circumferential seal 6, 9 has been created.
[0030] Fig. 6 shows a cross-section of a casing with a surrounding first 6 and second 9
seal and perforations 3. Subsequent to the injection steps, a liner 12 must be expanded
so as to cover the perforations 3 from within the casing 2 and to overlap both the
first and the second seal. As shown in Fig. 7, a liner 12 is submerged into the casing
2 and placed outside the perforations 3 by an expansion tool. Then, the liner 12 is
expanded until it abuts and is sealed against the inside wall of the casing 2 as shown
in Fig. 8. The expanded liner 12 at least partly overlaps each seal 6, 9 so that the
sealing arrangement - i.e. the first 6 and the second 9 seal, the expanded liner 12,
and the intermediate casing wall - hinders a fluid connection between the production
zone 1 and the inside of the casing 2.
[0031] The perforations 3 through which the composition 5 has been injected may be filled
with composition 5 during the expansion process of the composition 5. However, due
to the fluid pressure from the production zone 1, it is sometimes recommendable that
the liner 12 also overlaps the perforations through which the composition 5 has been
injected, as shown in Fig. 8.
[0032] The liner 12 may be expanded in many ways using a variety of expansion tools in addition
to the one shown in Fig. 7. Furthermore, the liner 12 may be a tube of an expandable
material such as metal. In another embodiment, the liner 12 may in have circumferential
groves with a sealing ring, such as an O-ring.
[0033] Occasionally, the production zone 1 extends beyond the extension of the perforations
3. In this case, new holes have to be made before injecting the composition 5. Alternatively,
a third seal 15 can be placed at a distance between the sealing arrangement and the
new perforations facing the new production zone 14 in order to hinder fluid seeping
from the former production zone 1 along the outside of the casing 2 and to the new
production zone 14 as shown in Fig. 9.
[0034] Additionally, the casing 2 may have several perforation sections within the range
of the same production zone 1. In that case each perforation section has to be sealed
off by a first 6 and a second 9 seal followed by an expanded liner 12 within the casing
2.
[0035] In some events, it may not be possible for one liner 12 to overlap both the first
6 and the second 9 seal since it may not be possible the expand a sufficiently long
liner 12 or the casing may bend, demanding a use of several liners in order to fit
the bend of the casing. In these events, intermediate seals can be made between the
first 6 and the second 9 seal, and liners 12 can be expanded so that each liner at
least partly covers two adjacent seals.
[0036] Furthermore, the perforations 3 may be too small for the injection tip 16 to inject
the composition 5 into the intervening space 4. In this event, the perforations 3
need to be widened before the injections step can take place.
[0037] As shown in Fig. 10, the sealing method may also be used for sealing a leak 21 in
a production casing 2 which is partly surrounded by an intermediate casing 20. The
intermediate casing 20 is partly surrounded by a surface casing 17, which again is
partly surrounded by a conductor pipe 18. The production casing 2 is fixated in the
intermediate casing 20 by means of packers 19, and the intermediate casing 20 is fixated
within the surface casing 17 by means of cement as is the surface casing 17 to the
conductor pipe 18.
[0038] The first 6 and second 9 circumferential seals are made in the same manner as mentioned
above followed by insertion of a liner 12. The first 6 and the second 9 seals are
placed on each side of the leak 21 in the casing 2, and the liner 12 overlaps both
of the seals 6, 9 and the leak 21 as shown in Fig. 10.
[0039] The injection tool 13 has at least one chamber comprising the composition 5 to be
injected. In one embodiment, the tool 13 has one chamber with composition 5 and, in
another embodiment, the tool may have two chambers, each comprising enough composition
to make one circumferential seal. Due to the fact that the composition 5 expands subsequent
to being injected into the intervening space 4, the chamber does not need to be of
the same volume as the final seal or seals.
[0040] In one embodiment, the injection tool may be part of a system which also comprises
a drilling tool able to drill holes in the casing 2 prior to the injection steps.
The drilling tool may also be a separate tool which is submerged into the casing 2
prior to the injection tool 13 so that the drilling operation and the injection operation
is performed in two separate runs. Following the injection step, the injection tool
13 is retracted from the casing 2 and, subsequently, an expansion tool for expanding
the liner 12 is submerged into the casing.
[0041] The composition 5 to be injected may be any kind of expandable composition. In one
embodiment, the composition is thus a two-part glue where the parts when mixed expand
and harden. In another embodiment, the composition 5 expands when subjected to the
water in the emulsified fluid seeping from the formation and/or when subjected to
the heat of the fluid. Additionally, the composition 5 may be of the type which does
not expand, but only hardens when subjected to the water in the emulsified fluid or
the heat of the fluid seeping from the formation. Thus, the composition 5 may be a
two-component polyurethane glue or another suitable polymer able to harden in one
of the mentioned ways.
[0042] In one embodiment, a network is comprised in the composition after injection. The
composition can be in the form of a compound or in the form of separate units.
[0043] When the composition is in form of a compound, the compound is injected in its liquid
phase, and while the compound hardens it needs to be held in place in a certain position,
which is accomplished by a network.
[0044] In one embodiment, the composition 5 is melted before being injected and hardens/stiffens
when injected. In another embodiment, the composition 5 consists of one base part
in its liquid form, or at least in a partly liquid form, which is mixed with another
part such as a hardener prior to being injected in order to make the compound harden.
By a partly liquid form is meant an injectable base part which is partly liquid and
partly solid.
[0045] In another embodiment, the composition 5 expands or swells while hardening. The composition
5 may be any kind of expandable or swellable composition. Thus, the composition 5
may be a two-part polyurethane glue, or another suitable polymer able to harden in
one of the ways mentioned above.
[0046] Furthermore, the composition 5 may comprise a resin and a catalyst reacting under
pressure whereby the composition hardens. Thus, the composition 5 reacts when exposed
to a certain pressure which may be applied by the injection tool 13 just before injecting
the composition. Alternatively, the reaction may come from the high pressure within
the borehole 22 when the composition has been injected.
[0047] In another embodiment, the composition comprises separate units in the form of balls,
beads, or the like objects. Each unit has an external layer of a compound enabling
the units to paste together after injection and thereby form a network.
[0048] The sealing arrangement 100 comprises a composition 5 which is in its liquid or partially
liquid phase when injected. In this embodiment, the network 30 is a plurality of interlacing
lines 29 in the form of a woven wire, a wire netting, a web, a grid, a lattice 27,
a grating, or the like networks. The network 30 is compressed during storage in the
injection tool 13 and is discharged either before the composition 5 or simultaneously
with the composition.
[0049] The network 30 can be made of coiled metal wires 28 or threads which are compressed
in the tool 13 by stacking the windings of each coiled wire 28 onto each other forming
a coil or a helically spring. The network 30 can also be made of wire, core, polymer
thread, glass fibre threads, or a like elongated component being tangled up into a
network during injection.
[0050] In another embodiment, the network 30 is an expandable lattice 27 in which first
interlacing lines 29 cross second interlacing lines 29, the interlacing lines being
twisted so that each first interlacing lines abut other adjacent first interlacing
lines and each second interlacing lines abut other adjacent second interlacing lines.
Thus, the compressed lattice 27 has the form of an elongated member and the expanded
lattice has the form of a sheet. In yet another embodiment, the network 30 is in the
form of a grid made of a slit plate which, when expanded, forms a perforated plate.
Such networks 30 can be discharged prior to the injection of the composition 5 in
order to retain the composition and form the sealing arrangement 100.
[0051] The network 30 can also be comprised in the composition 5 and be formed during hardening
of the composition. In this case, the network 30 is formed from elements pasting together
during hardening of the injected composition 5. The elements may be in the form of
beads or small balls 25 or in the form of fibres 36 or threads. The elements may be
made from ceramics, polymer, glass fibre, cellulose, or pulpwood.
[0052] The composition 5 may be injected so that it hits the inside wall of the borehole
22. In order to hold the composition 5 in position outside the leak 21 in the casing
2, a network 30 is discharged together with the composition. As mentioned above, the
network 30 can also be discharged prior to the injection of the composition 5. The
network 30 helps the composition bridge he gap between the outside of the leak in
the casing 2 and the inside wall of the borehole 22.
[0053] In some embodiments, the composition 5 is a compound comprising cement, polymer,
synthetic rubber, natural rubber, and/or silicone. When using rubber or silicone,
the compound is typically melted prior to the injection. The melting process is performed
in the injection tool 13 or prior to loading the compound into the tool.
[0054] The polymer may be any suitable elastomer or a thermoplastic polymer. The elastomer
may comprise nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), carboxyl nitrile
rubber (XNBR), silicone rubber, ethylene-propylene-diene copolymer (EPDM), fluoroelastomer
(FKM, FEPM), and perfluoroelastomer (FFKM), or other suitable polymers. Thermoplastic
polymer may comprise Teflon, polyetheretherketone, polypropylene, polystyrene, and
polyphenylene sulphide, or other suitable polymers.
[0055] In order to absorb water from the emulsified fluid seeping from the formation, the
polymer may comprise any water-soluble polymer able to absorb water, thus enabling
a hardening of the compound. Such water-soluble polymer may be methylcellulose, cellulose
acetate phthalate, and hydroxypropyl methylcellulose polymers, poly (ethylene oxide)
polymers, guar and its derivatives, polyacrylamide, polyvinylpyrolidone, polyacrylic
acid, polyvinylpyrolidone, oligo maleinate copolymers, oligo maleinate oligomers,
allyl maleate oligomers, silicon-based materials, and flouro-silicone based materials.
[0056] As mentioned, the compound can comprise a hardener or a curing agent when the compound
is stored in a two-part form and mixed just before injection of the compound. In order
for the elements to paste together, the compound may comprise a binding agent. The
binding agent can also be added to the composition 5 in order for the compound to
bind to the metal wire or other elongated components. The process of stiffening or
hardening must take place immediately after the composition 5 has been injected so
that the highly pressurised fluid in the well does not interfere with the forming
of a sealing arrangement 100 in a predetermined position, and the compound may therefore
be provided with an accelerator.
[0057] When using a network 30 of metal - such as coiled wire 28, threads, woven wire, wire
netting, a web, a grid, a lattice 27, or a grating - the network can be used to provide
heat to the compound thereby accelerating the hardening process. Electricity is led
through the metal and transformed into heat, which again is ejected into the compound
from within the compound.
[0058] As mentioned, the composition 5 may comprise a plurality of separate units each having
a core enclosed by a compound. The compound may be the same as mentioned above and
enable the units to paste together after being ejected into the intervening space.
Thus, the network is made from the separate units pasting together during hardening
of the compound and thereby forming the network.
[0059] The composition may comprise a plurality of separate units. Each unit has a core
31 enclosed within an intermediate substance 32 which again is enclosed within an
external layer 33 of compound. When ejecting the units into the intervening space
to make a circumferential seal, the units paste together as a seal in that the compound
layer of one unit pastes to the compound layer of another unit. In this embodiment,
the compound becomes sticky when reacting with the water in the space.
[0060] In one embodiment, the elements, the core, or the intermediate substance are made
from ceramics, metal, polymer, glass fibre, cellulose, or pulpwood.
[0061] In another embodiment, the core of each separate unit is made of a magnetic material
making the separate units paste together. Thus, the units will be drawn towards one
another when injected and since the casing through which the composition is injected
is of metal, the units will also stick to the casing. In this way, a leak is easily
sealed without filling up the whole intervening space.
[0062] In the event that the system is not submergible all the way into the casing 2, a
downhole tractor can be used to push the system all the way into position in the well.
A downhole tool is any kind of driving tool capable of pushing or pulling tools in
a well downhole, such as a Well Tractor®.
1. Sealing method for sealing off a leak in a casing (2) or for sealing off a production
zone (1) where the casing (2) having a circumference and perforations (3) is situated
in a borehole downhole, but with a distance to an inner wall of the borehole, creating
an intervening space (4) there between, comprising the steps of:
- injecting a composition (5) for making a first circumferential seal (6) in the intervening
space (4) at a first position (7) of the casing in one end of the production zone
through holes situated along a first intersecting line (8) where a first plane intersects
the circumference of the casing,
- filling the intervening space at a first position in a radial direction of the casing,
- injecting a composition (5) for making a second circumferential seal (9) in the
intervening space (4) at a second position (10) of the casing in another end of the
production zone through holes situated along a second intersecting line (11) where
a second plane intersects the circumference of the casing,
- filling the intervening space at a second position in a radial direction of the
casing,
- inserting a liner (12) into the casing (2) covering the holes (3) and extending
between and at least partly covering both the first and the second circumferential
seal, and
- expanding the liner until the liner is pressing against the casing whereby the liner
together with the first and the second circumferential seal isolate the production
zone.
2. Sealing method according to claim 1, wherein the composition comprises a compound
which is able to harden, expand, swell or paste once injected into the intervening
space.
3. Sealing method according to claim 1 or 2, wherein the holes through which the composition
is injected are positioned directly opposite each other in the casing.
4. Sealing method according to any one of claims 1-3, wherein the holes are some of the
perforations.
5. Sealing method according to any one of claims 1-4, further comprising the step of
making the holes prior to at least one of the injection steps.
6. Sealing method according to claim 5, comprising a third injection step where composition
is injected for making a third circumferential seal (15) in the intervening space
(4) through holes made at a distance from the perforations.
7. Sealing method according to any of the preceding claims, further comprising the step
of making new perforations in the casing for letting oil fluid flow into the casing
from a new and second production zone (14).
8. Sealing method according to any of the preceding claims, wherein the composition is
expanded for making the circumferential seals.
9. Sealing method according to any of the preceding claims, comprising a further step
of injecting an intermediate circumferential seal between the first and the second
circumferential seal.
10. Sealing arrangement for sealing off a leak in a casing or for sealing off a production
zone where the casing having a circumference and perforations is situated in a borehole
downhole, but with a distance to an inner wall of borehole, creating an intervening
space between casing and the borehole, comprising:
- a first circumferential seal of composition in the intervening space at a first
position of the casing in a first end of the production zone,
- a second circumferential seal of composition in the intervening space at a second
position of the casing in a second end of the production zone, and
- an expanded liner in between the first and the second circumferential seal, for
isolation of the production zone.