Note: Descriptions are shown in the official language in which they were submitted.
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OFFSHORE METHOD
Description
The present invention relates to an offshore method for preparing a well for
production of hydrocarbon-containing fluids from a wellbore. The invention
also
relates to a downhole system derived from the method according to the present
invention.
The Deepwater Horizon oil spill, also referred to as the oil spill in the Gulf
of
Mexico or the Macondo blowout, is an oil spill which flowed unabated for three
months in 2010. This blowout is considered one of the largest accidental
marine
oil spills in the history of the petroleum industry, and the spill stemmed
from a
sea-floor oil gush which was a result of the 20 April 2010 explosion of the
Deepwater Horizon rig which drilled on the Macondo Prospect. It is believed
that
one of the primary reasons for the cause of the blowout was a defective cement
job during completion of the well. Cement is used to seal between a first
tubular
and a borehole wall and between the first tubular and the next tubular. The
cement is injected, and for some reason, the cement settles in the intended
space. During this process, unwanted pockets are formed in the cement, or the
cement disappears in an unexpected fracture in the formation. If the cement
does not sufficiently fill the annular space, e.g. between the first tubular
and the
borehole wall, the oil may leak during production and gush through the cement
or along the tubular, and an oil spill disaster may be a consequence of this.
After the Macondo blowout, ensuring well integrity has been an increased focus
of
governments around the world, and thus also of the oil industry. To this
effect,
the downhole barrier systems incorporated in the well completion designs have
been brought into focus to improve the well integrity.
Due to the low price on an oil barrel, the recent focus has been on costs and
how
the wells can be completed at a lower cost, in order that the oil production
can
give return on investment at an earlier stage.
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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 offshore method providing a less expensive way of drilling
and completing a well without jeopardising the safety and thus still ensuring
well
integrity.
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 offshore method
for
preparing a well for production of hydrocarbon-containing fluids from a
wellbore,
comprising:
- installation of a drilling rig for drilling at least part of the
wellbore,
- drilling a first part of the wellbore,
- installation of a surface casing,
- connecting a drilling blowout preventer with a top of the surface casing,
e.g. via
a wellhead, i.e. directly or indirectly via a wellhead,
- drilling a second part of the wellbore,
- installation of a production casing having a first end part being closest
to the
top of the surface casing and a second end part, the production casing
comprising a plurality of annular barriers, each annular barrier having a
tubular
metal part mounted as part of the production casing, an expandable metal
sleeve
surrounding the tubular metal part and having an inner face facing the tubular
metal part and an outer face facing an inner face of the wellbore of the well,
each
end of the expandable metal sleeve being connected with the tubular metal
part,
and an annular space between the inner face of the expandable metal sleeve and
the tubular metal part, the expandable metal sleeve being configured to
expand,
- expanding the expandable metal sleeves of the annular barriers in order
that
the expandable metal sleeves abut the inner face of the wellbore,
- installation of a plug in the first end part of the production casing
sealing off an
inside of the production casing,
- disconnecting the drilling blowout preventer from the top of the surface
casing,
- connecting a production tree with a wellhead,
- disconnecting the drilling rig from the well,
- removing the plug, and
- initiating production.
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In known completion methods, the drilling rig is maintained on top of the well
until production or at least early production is initiated. By installing the
plug
after the annular barriers have been expanded, the drilling can be
disconnected
earlier than in known solutions saving a lot of rig time and thereby
minimising
costs when making new wells. After the plug is installed, the BOP (blow-out
preventer) is disconnected and the production tree or Christmas tree is
connected, and then the drilling rig is disconnected. Then, the production
testing
or production is initiated without having the drilling rig.
Furthermore, the drilling rig may be disconnected after the expandable metal
sleeves of the annular barriers have been expanded before production is
initiated.
The offshore method as described above may further comprise circulating
cleaning fluids.
The offshore method as described above may further comprise circulating
cleaning fluids before expansion of the expandable metal sleeves of the
annular
barriers for cleaning the wellbore from drilling mud.
Also, the installation of the production casing may be performed by means of a
drill pipe connected to the first end part of the production casing.
Moreover, the production casing may comprise at least one valve arranged
between two annular barriers, the valve being closed when disconnecting the
drilling rig.
In addition, the production casing may comprise at least one valve arranged
between two annular barriers, the valve being closed when disconnecting the
drilling rig, providing a well integrity barrier.
The offshore method as described above may further comprise installation of a
downhole safety valve which is closed when disconnecting the drilling rig.
Moreover, the offshore method as described above may further comprise
installation of a downhole safety valve which is closed when disconnecting the
drilling rig, providing a well integrity barrier.
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Additionally, the production casing below the plug may be filled with liquid
when
disconnecting the drilling rig.
Furthermore, the production casing below the plug may be filled with liquid
when
disconnecting the drilling rig, providing a well integrity barrier.
Also, the production casing above the plug may be filled with liquid when
disconnecting the drilling rig.
Also, the production casing above the plug may be filled with liquid when
disconnecting the drilling rig, providing a well integrity barrier.
The liquid may be sea water or brine.
The offshore method as described above may further comprise cementing an
annulus between the production casing and an inner face of the wellbore.
Moreover, the installation of the production casing may comprise a rotation of
the
production casing.
In addition, cleaning fluid, such as acid, may be circulated out of the second
end
part of the production casing while installing the production casing.
Further, cleaning fluid, such as acid, may be circulated out of the second end
part
of the production casing while installing the production casing for cleaning
the
wellbore from drilling mud.
A dart may be circulated to the second end of the production casing, landing
and
closing the second end part before expansion of the expandable metal sleeves
of
the annular barriers.
The offshore method as described above may further comprise hanging off the
production casing in a liner hanger or in a wellhead.
Also, the production casing may have a receptacle at the first end.
Furthermore, the production casing may comprise gas lift valves.
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Moreover, the liquid above the plug may be brine.
The plug may be a glass plug.
5 Finally, the present invention also relates to a downhole system derived
from the
offshore method as described above.
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 partly cross-sectional view of an initial part of an offshore
wellsite
having a well being made by means of a drilling rig which has its legs founded
in
the seafloor adjacent to the well to be completed,
Fig. 2 shows the offshore wellsite of Fig. 1 where a drilling blowout
preventer has
been installed in the top of the well and a second part of the wellbore is
being
drilled,
Fig. 3 shows the offshore wellsite of Fig. 2 where a production casing is
being
installed,
Fig. 4 shows the offshore wellsite of Fig. 3 where expandable metal sleeves of
annular barriers of the production casing are expanded to create zonal
isolation,
Fig. 5 shows the offshore wellsite of Fig. 4 where an upper production casing
is
installed,
Fig. 6 shows the offshore wellsite of Fig. 5 where a plug is set in the
production
casing,
Fig. 7 shows the offshore wellsite of Fig. 6 where the drilling blowout
preventer
has been replaced with a production tree and the drilling rig has been
disconnected,
Fig. 8 shows the well where the production has been initiated, and
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Fig. 9 shows another offshore wellsite in which cement is displaced into the
annulus before the annular barriers are expanded.
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.
Fig. 1 shows a wellsite 100 where legs of a drilling rig 4 are mounted into a
seabed 14 adjacent an offshore well 2 which is being prepared, i.e. drilled
and
completed for production of hydrocarbon-containing fluids from a wellbore 3.
First, the drilling rig 4 is installed and a first part 5 of the wellbore is
drilled, and
then a conductor pipe 15 is arranged and after that, a surface casing 6 is
arranged in the first part of the wellbore and both are cemented in place.
In Fig. 2, a drilling blowout preventer 7 has been connected with a top 8 of
the
surface casing, e.g. via a wellhead (not shown). Thus, the drilling blowout
preventer 7 may be connected directly to or via a wellhead as shown in Fig. 9.
Then, a second part 9 of the wellbore has been drilled by a drill string 41
and a
drilling head 42.
Then, a production casing 10 is installed, as shown in Fig. 3. The production
casing 10 has a first end part 11 which is closest to the top 8 of the surface
casing, and the production casing further has a second end part 12 arranged
low
in the wellbore. The production casing 10 comprises a plurality of annular
barriers
20. Each annular barrier has a tubular metal part 21 mounted as part of the
production casing and an expandable metal sleeve 22 surrounding the tubular
metal part. The expandable metal sleeve has an inner face 23 facing the
tubular
metal part and an outer face 24 facing an inner face 25 of the wellbore of the
well. Each end 26 of the expandable metal sleeve is connected with the tubular
metal part providing an annular space 27 (shown in Fig. 4) between the inner
face of the expandable metal sleeve and the tubular metal part. The production
casing is inserted into the wellbore by means of drill pipe 52 connected to
the
first end part 11, e.g. by means of a running tool 17 or a similar connection
unit.
The expandable metal sleeve 22 is configured to expand, e.g. by pressurised
fluid
from within the production casing 10, as shown in Fig. 4, where the expandable
metal sleeves 22 of the annular barriers 20 have been expanded in order that
the
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outer face 24 of the expandable metal sleeves 22 abut the inner face 25 of the
wellbore. The expandable metal sleeve 22 may be expanded by pressurising both
the drill pipe and the production casing. The second end part 12 of the
production
casing 10 is closed by inserting a dart 56, which is circulated to the second
end
part 12 of the production casing 10 landing and closing the second end 18 of
the
production casing before expansion of the expandable metal sleeves 22 of the
annular barriers 20.
In Fig. 5, a second and upper production casing 10A is installed in the first
part of
the wellbore overlapping the lower production casing 10, 10B by docking into a
receptacle 58 at the first end part 11 of the lower production casing 10.
Seals are
provided therebetween. Thus, the production casing 10 in Fig. 5 comprises an
upper production casing 10A and a lower production casing 10B. In another
embodiment, the production casing 10 extends all the way to the seabed.
In Fig. 6, a plug 28 is installed inside the production casing in the first
end part
11 of the production casing 10 sealing off an inside 29 of the production
casing.
The plug is set in the upper production casing 10A in Fig. 6, but it may also
be
set in the lower production casing 10B in another embodiment.
When having the plug installed, the wellbore is sealed off, and the drilling
blowout preventer can safely be disconnected from the top 8 of the surface
casing 6, as shown in Fig. 7, where also a production tree 19 has been
connected
with a wellhead 50 at the top 8 of the surface casing 6. Then, the drilling
rig is
disconnected from the well 2, as shown in Fig. 7. A downhole safety valve 54
may be installed, as shown in Fig. 8. In known solutions, the drilling rig is
disconnected after initiating production and thus by the present method many
days of rig time is saved minimising costs when making a new well.
After disconnecting the drilling blowout preventer and the drilling rig 4 and
after
connecting the production tree 19, the plug is removed and production of
hydrocarbon-containing fluid is initiated, e.g. early production or straight
to
production, as shown in Fig. 8. Thus, the drilling rig 4 is disconnected after
the
expandable metal sleeves 22 of the annular barriers 20 have been expanded and
before production is initiated. In this way, the annular barriers 20 provide a
first
well integrity barrier between the wall of the wellbore and the production
casing
10. The plug, shown in Figs. 6 and 7, provides a second well integrity barrier
in
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the production casing 10. The cement 44 between the first part of the wellbore
and the conductor pipe and the cement between the conductor pipe and the
surface casing provides a third well integrity barrier. If a downhole safety
valve
54 (shown in Fig. 8) is installed before disconnecting the drilling rig, the
closed
downhole safety valve provides a fourth well integrity barrier and thus
creates a
well integrity barrier when disconnecting the rig. The production casing 10
below
the plug is filled with liquid when disconnecting the drilling rig which
provides a
well integrity barrier and thus a fifth well integrity barrier. The production
casing
above the plug is filled with liquid when disconnecting the drilling rig which
10 provides a well integrity barrier and thus a sixth well integrity
barrier. In the first
end part 11 of the production casing 10, an annular barrier 20 is expanded
providing a well integrity barrier between the surface casing and the
production
casing, providing a seventh well integrity barrier. Thus, providing a plug and
having expanded all the annular barriers, it is safe to disconnect the
drilling rig
before initiating production, and thus, approximately 45 days of rig time can
be
saved, minimising costs by at least 30-50 million US dollars. The many well
integrity barriers provide even further safety if the authority requires.
Before expanding the expandable metal sleeves of the annular barriers,
cleaning
fluid, such as acid, is circulated out of the second end 12 of the production
casing
10, e.g. while installing the production casing, to clean the wellbore from
drilling
mud. When inserting the production casing, a rotation of the production casing
may be performed to ease the insertion of the production casing into the
wellbore. The plug may be a glass plug or a similar plug.
In Fig. 8, the production casing comprises at least one valve 53 arranged
between two annular barriers 20. The valve is closed when disconnecting the
drilling rig, providing a well integrity barrier being an eighth well
integrity barrier.
The production casing also comprises gas lift valves 59 in order to provide a
gas
lift if needed later on.
The liquid below or above the plug may be sea water or well fluid, and the
liquid
may also be brine so that the liquid can always be circulated if needed before
production.
The offshore method as described in relation to describing the above figures
may
also comprise cementing an annulus 55 between the production casing and an
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inner face of the wellbore, as shown in Fig. 9. The cement 44 is displaced
down in
the production casing 10, and it is arranged in front of the dart in order
that the
cement is forced out of the second end 18 by forcing the dart downwards by a
pressurised fluid upstream of the dart. When the dart seats in the seat in the
second end of the production casing 10, the production casing is pressurised
and
the expandable metal sleeves of the annular barriers are expanded by the
pressurised fluid entering through openings in the tubular metal part of the
production casing, allowing the pressurised fluid to enter the space of the
annular
barriers and thus forcing the expandable metal sleeves radially outwards. The
method may further comprise hanging off the production casing in a liner
hanger
57 or in a wellhead 50, as shown in Fig. 9. The invention further relates to
the
downhole system 101 derived from the above described method.
The valves of the production casing 10 may be opened e.g. by applying acid to
dissolve an acid-dissolvable plug or they may be opened by an intervention
tool,
such as a key tool engaging e.g. grooves in a sliding sleeve.
By 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 an annular barrier is meant an annular barrier comprising a tubular metal
part
mounted as part of the well tubular metal structure and an expandable metal
sleeve surrounding and connected to the tubular part defining an annular
barrier
space.
By a production casing, intermediate casing, surface casing or well tubular
metal
structure 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
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the tool forwards 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
.
Although the invention has been described in the above in connection with
5 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.
