U.S. patent application number 15/825577 was filed with the patent office on 2018-06-07 for method of drilling a borehole in an earth formation.
The applicant listed for this patent is SHELL OIL COMPANY. Invention is credited to Ernesto Rafael FONSECA OCAMPOS.
Application Number | 20180155988 15/825577 |
Document ID | / |
Family ID | 62239996 |
Filed Date | 2018-06-07 |
United States Patent
Application |
20180155988 |
Kind Code |
A1 |
FONSECA OCAMPOS; Ernesto
Rafael |
June 7, 2018 |
METHOD OF DRILLING A BOREHOLE IN AN EARTH FORMATION
Abstract
A borehole is drilled in an earth formation using consecutive
steps of: (a) drilling a first open hole section of a borehole,
employing a first drill string extending into the borehole from a
surface on the earth, to a casing setting depth; (b) retrieving the
first drill string from the borehole to the surface; (c) everting a
tubular element in the open hole section, wherein axially advancing
an inner tube section of the tubular element into the borehole
through and in relative axial movement to an outer tube section of
the same tubular element; (d) creating an annular seal between the
outer tube section and an inward facing wall of the borehole; (e)
inserting a second drill string through the inner tube section into
the borehole; and (f) further deepening the borehole by drilling a
second open hole section of the borehole.
Inventors: |
FONSECA OCAMPOS; Ernesto
Rafael; (Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SHELL OIL COMPANY |
Houston |
TX |
US |
|
|
Family ID: |
62239996 |
Appl. No.: |
15/825577 |
Filed: |
November 29, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62430075 |
Dec 5, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21B 17/18 20130101;
E21B 7/00 20130101; E21B 33/14 20130101; E21B 43/103 20130101; E21B
33/13 20130101; E21B 7/20 20130101; E21B 17/08 20130101 |
International
Class: |
E21B 7/20 20060101
E21B007/20; E21B 17/18 20060101 E21B017/18; E21B 17/08 20060101
E21B017/08 |
Claims
1. A method of drilling a borehole in an earth formation,
comprising consecutive steps of: (a) drilling a first open hole
section of a borehole, employing a first drill string extending
into the borehole from a surface on the earth, to a casing setting
depth; (b) retrieving the first drill string from the borehole to
the surface; (c) everting a tubular element in the open hole
section, which tubular element comprises an inner tube section and
an outer tube section connected to each other in a lower bending
zone, wherein the inner tube section runs through the outer tube
section and wherein a wall of the tubular element is, in said lower
bending zone at a lower end of the inner tube section, induced to
bend radially outward and in axially reversed direction so as to
form the outer tube section which thereby is everted compared to
the inner tube section, wherein said everting comprises axially
advancing the inner tube section into the borehole through the
outer tube section in relative axial movement compared to the outer
tube section; (d) creating an annular seal between the outer tube
section and an inward facing wall of the borehole; (e) inserting a
second drill string through the inner tube section into the
borehole; (f) further deepening the borehole by drilling a second
open hole section of the borehole, employing the second drill
string, to a second depth that is deeper than the casing setting
depth.
2. The method of claim 1, wherein during step (f) the second drill
string is advanced into the borehole as the borehole is being
drilled, whereas the tubular element is kept stationary whereby
keeping the lower bending zone at a fixed depth.
3. The method of claim 2, wherein the inner tube is temporarily
secured at or near the surface for at least the duration of step
(f).
4. The method of claim 1, wherein step (f) is continued until
reaching a further case setting depth; and subsequently carrying
out step (b) again with respect to the second drill string, after
which further everting the tubular element into the second open
hole section, comprising axially further advancing the inner tube
section into the borehole through the outer tube section in
relative axial movement with the outer tube section.
5. The method of claim 1, wherein the tubular element is a seamless
tubular element.
6. The method of claim 4, wherein said further everting comprises
extending the inner tube section with an extension tube by
sealingly abutting the extension tube to a top rim of the inner
tube.
7. The method of claim 6, wherein said sealingly abutting comprises
welding a bottom rim of said extension tube to the top rim of the
inner tube.
8. The method of claim 6, wherein the tubular element and the
extension tube are both seamless.
9. The method of claim 4, wherein creating a second annular seal
between the outer tube section and an inward facing wall of the
borehole in the second open hole section.
10. The method of claim 1, wherein the tubular element is provided
in the form of coiled tubing, and wherein the inner tube section
extends to a coiled-up portion of the coiled tubing, and wherein
step (c) comprises supplying the inner tube by uncoiling the coiled
tubing from the coiled-up portion while axially advancing the inner
tube section into the borehole.
11. The method of claim 1, wherein after completing step (c) and
prior to step (e) the inner tube section is circumferentially cut
off whereby removing at least a part of the tubular element that is
exposed at the earth surface and retaining a part of the inner tube
section below a cut rim.
12. The method of claim 1, wherein after completing step (a) and
prior to step (d) a hardening liquid substance is introduced into
the borehole, and wherein step (d) comprises allowing hardening of
the liquid substance while at least the lower bending zone is
submerged into the hardening liquid substance.
13. The method of claim 12, wherein the hardening liquid substance
is retarded to allow time to complete step (c) before hardening of
the liquid substance is completed.
14. The method of claim 1, wherein the second drill string
comprises an under-reamer having a gauge diameter larger than an
inside bore diameter of the inner tube section to drill the second
open hole section to a bore diameter that is larger than the inside
bore diameter of the inner tube section.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of US Provisional
Application No. 62/430,075 filed, Dec. 5, 2016.
FIELD OF THE INVENTION
[0002] In a first aspect, the present invention relates to a method
of drilling a borehole in an earth formation, wherein drilling a
first open hole section of the borehole, employing a first drill
string extending into the borehole from a surface on the earth, to
a casing setting depth.
BACKGROUND OF THE INVENTION
[0003] Traditionally, particularly in the oil and gas industry,
casing is set during drilling of a borehole in the earth. Such
casing may aid the drilling and well completion process in one or
more of several ways: [0004] preventing contamination of fresh
water well zones; [0005] preventing unstable upper formations from
caving in and sticking the drill string or forming large caverns;
[0006] providing a strong upper foundation to use high-density
drilling fluid to continue drilling deeper; [0007] isolating
different zones, that may have different pressures or fluids,
sometimes referred to as zonal isolation, in the drilled formations
from one another; [0008] sealing off high pressure zones from the
surface, avoiding potential for a blowout; [0009] preventing fluid
loss into or contamination of production zones; and [0010]
providing a smooth internal bore for installing production
equipment.
[0011] In the planning stages of a well, a well engineer may pick
strategic depths at casing will be set in order for drilling to
reach the desired total depth. The casing setting depths may for
example be based on subsurface data such as formation pressures,
strengths, and makeup, and may preferably be balanced against the
cost objectives and desired drilling strategy.
[0012] With the casing set depths determined, hole sizes and casing
sizes follow. The borehole is drilled in intervals whereby a casing
which is to be installed in a lower borehole interval is lowered
through a previously installed casing of an upper borehole
interval. As a consequence of this procedure the casing of the
lower interval is of smaller diameter than the casing of the upper
interval. Thus, the casings are in a nested arrangement with casing
diameters decreasing in downward direction. As a consequence of
this nested arrangement, a relatively large borehole diameter is
required at the upper part of the borehole. Such a large borehole
diameter involves increased costs due to heavy casing handling
equipment, large drill bits and increased volumes of drilling fluid
and drill cuttings. This is a major drawback of traditional
drilling method using casing as described above.
[0013] In some instances, the well design may include liners
instead of casing, the difference being that casing typically
extends all the way up to surface, while liner is hung off at the
bottom of a preceding casing or other liner. For the purpose of the
present disclosure, liner and casing are relevant in the same way
and the terms are interchangeable.
SUMMARY OF THE INVENTION
[0014] In a first aspect, there is provided a method of drilling a
borehole in an earth formation, comprising consecutive steps of:
[0015] (a) drilling a first open hole section of a borehole,
employing a first drill string extending into the borehole from a
surface on the earth, to a casing setting depth; [0016] (b)
retrieving the first drill string from the borehole to the surface;
[0017] (c) everting a tubular element in the open hole section,
which tubular element comprises an inner tube section and an outer
tube section connected to each other in a lower bending zone,
wherein the inner tube section runs through the outer tube section
and wherein a wall of the tubular element is, in said lower bending
zone at a lower end of the inner tube section, induced to bend
radially outward and in axially reversed direction so as to form
the outer tube section which thereby is everted compared to the
inner tube section, wherein said everting comprises axially
advancing the inner tube section into the borehole through the
outer tube section in relative axial movement compared to the outer
tube section; [0018] (d) creating an annular seal between the outer
tube section and an inward facing wall of the borehole; [0019] (e)
inserting a second drill string through the inner tube section into
the borehole; [0020] (f) further deepening the borehole by drilling
a second open hole section of the borehole, employing the second
drill string, to a second depth that is deeper than the casing
setting depth.
BRIEF DESCRIPTION OF THE DRAWING
[0021] The appended drawing, which is non-limiting, comprises the
following figures:
[0022] FIG. 1 schematically shows drilling of a first open hole
section of a borehole;
[0023] FIG. 2 schematically shows a quantity of a hardening liquid
in the first open hole section of FIG. 1;
[0024] FIG. 3 schematically shows the first borehole section of
FIG. 1 having an everted tubular element of which a lower bending
zone is submerged into the hardening liquid substance of FIG.
2;
[0025] FIG. 4 schematically shows further drilling of the borehole
by drilling a second open hole section;
[0026] FIG. 5 schematically illustrates a close up of the annular
seal and the lower bending zone from FIG. 4;
[0027] FIG. 6 schematically illustrates extending of the inner tube
section of the everted tubular element of FIG. 3; and
[0028] FIG. 7 schematically shows coiled tubing used for creating
the everted tubular element of FIG. 3.
[0029] The figures are schematic of nature, and not to scale. Like
reference numbers are used for like features.
DETAILED DESCRIPTION OF THE INVENTION
[0030] The invention will be further illustrated hereinafter by way
of example only, and with reference to the non-limiting drawing.
The person skilled in the art will readily understand that, while
the invention is illustrated making reference to one or more
specific combinations of features and measures, many of those
features and measures are functionally independent from other
features and measures such that they can be equally or similarly
applied independently in other embodiments or combinations.
[0031] A method is presently proposed wherein a first open hole
section is drilled to a casing setting depth. The drill string is
retrieved, and instead of setting a casing in the traditional way a
tubular element is everted in the open hole section, wherein an
inner tube section of the tubular element is axially advanced into
the borehole through and in relative axial movement to an outer
tube section of the same tubular element. After creating an annular
seal between the outer wall section and the inward facing wall of
the borehole, the inverted tubular element functions as a
traditional casing.
[0032] A second open hole section can be drilled with a drill
string extending through the inner tube section of the tubular
element. However, as the tubular element is expanded radially
outward when being everted, the second borehole section does not
have to be smaller than the first borehole section. Instead, the
second borehole section may be cased by further everting the same
tubular element as before.
[0033] Compared to drilling and setting traditional casing, the
presently proposed method becomes more advantageous for each casing
setting depth that is needed to reach the final destination
depth.
[0034] It is remarked that drilling a mono-diameter well and
everting a tubular element in such well is known and described in
numerous publications including U.S. Pat. No. 7,946,349 and U.S.
Pat. No. 9,482,070, and European patent application EP 3034189, the
contents of each of which is incorporated herein by reference.
However, the methods described in these publications use a
complicated machine wherein the tubular element is continuously
formed on-site from a band of flat metal strip wound on a reel. The
flat metal sheet is unwound from the reel, fed to the drill string
and bent around the drill string by means of a bending device after
which the adjoining long edges of the bent metal sheet are
continuously welded together to form a tubular element with a
longitudinal welded seam. Accordingly, the tubular element is
advanced into the borehole simultaneously with the drill
string.
[0035] Such complicated machine is not needed in the present
proposal, as the drill string is retrieved from the borehole prior
to everting the tubular element. Thus, the present proposal can
enjoy at least some of the benefits of the known pipe eversion
drilling technology, without having to endure some of its
drawbacks. Apart from not needing the complicated machine, the
proposed approach has many other advantages, including that the
tubular element can be seamless and in particular the tubular
element can be brought on site as coiled tubing. Moreover, the
drilling operation can be carried out with a standard (vertical)
drilling rig and standard drill string.
[0036] It is further remarked that fabricating a mono-diameter well
using expandable tubulars that are expanded by advancing an
expansion tool, such as an expansion cone, through the tubulars to
expand their diameter is known and described in numerous
publications including for example U.S. Pat. No. 7,100,685 and U.S.
Pat. No. 7,357,188. However, these methods typically take longer to
complete and require more complex and heavy tools compared to the
method presently proposed herein.
[0037] It is estimated that expandable tubular technologies may be
better suited for wells having larger casing sizes and/or where the
formation pressures are higher than average. Today, the theoretical
limit of the pipe eversion technology is estimated to be somewhere
between 7 to 9 inch outer diameter (OD) of the (unexpanded) inner
tube section. As a typical rule of thumb, for typical tubing/CT the
resulting OD of the outer tube section is about one inch larger
than the OD of the inner tube section, this number being merely an
indication as it may vary from case to case and tube to tube.
[0038] The presently proposed method may thus be competitive for
open hole inner diameters of up to about 10 inch, and/or using an
inner tube section having OD of up to 7 to 9 inch, specifically in
the range of 4 to 9 inch or 4 to 7 inch. It is currently envisaged
that the present proposal may be most competitive against competing
technologies for somewhat smaller sizes of up to about 5.5 or 6
inch OD (for instance, in the range of 4 to 6 inch or in the range
of 4 to 5.5 inch and/or medium to low pressure wells.
[0039] FIGS. 1 to 5 illustrate steps of one way of carrying out the
proposed method. FIG. 1 schematically shows drilling a first open
hole section 10 of a borehole 1 in an earth formation 2. A first
drill string 5 is employed, which extends into the borehole 1 from
a surface 6 of the earth. Any desired type of drill string may be
used, including traditional jointed string or coiled tubing (CT). A
bottom hole assembly includes a drill bit 22, which in this
instance comprises a pilot bit 24 and an under-reamer 26.
Alternatives may be employed, as desired. The first open hole
section 10 extends to a casing setting depth D .sub.1.
[0040] Upon reaching the casing setting depth D.sub.1, the first
drill string 5 is retrieved to the surface 6. Furthermore, a
hardening liquid substance 12 may be introduced into the borehole
1. FIG. 2 schematically shows the borehole 1 with the hardening
liquid substance 12, after the drill string 5 has been retrieved.
The hardening substance will be employed to create an annular seal
as will be explained below.
[0041] Suitably, the hardening liquid substance is a cement, such
as a concrete-based cement or a neat cement. Nonetheless
alternatives exist in the market which may be used instead of or in
addition to concrete or neat cements, such as resin-based
substances (see, for example, "Resin emerging as alternative to
cement" an article by Sally Charpiot and Paul Jones from OffShore
Magazine May 2013 and/or GB2480546A). Resin-based substances for
wellbore use are commercially available under the name
WellLock.RTM. Resin from Halliburton. Suitable resins may be based
on scorch-inhibited crosslinkable polymers using a
tetrahydrocarbylpiperidin-1-oxyl or alkyloxy (TEMPO) compound or of
a derivative, preferably an ether, ester or urethane derivative, of
a TEMPO compound. There are also non-cementing substances that can
be used to accomplish the seal in the context of the present
disclosure, such as for instance a clay seal (e.g. bentonite).
[0042] Suitably, the borehole 1 also contains a non-hardening
wellbore fluid 13, commonly used to contain the well. The wellbore
fluid 13 may suitably be a drilling mud. The density of the
hardening liquid substance may be higher than that of the wellbore
fluid 13, so that the hardening liquid substance accumulates in the
bottom of the first open hole section 10 around the casing setting
depth D.sub.1. The hardening liquid substance 12 is conveniently
introduced into the borehole by spotting a quantity of the
hardening liquid substance through the drill string 5, prior to, or
while retrieving the drill string 5 to the surface 6, or during an
interruption of retrieving the drill string 5 when is has partly
been retrieved to the surface 6. Alternatively, the hardening
liquid substance 12 may be cast into the borehole 1 after the first
drill string 5 has been fully retrieved from the borehole 1. In
some instances, it may be more convenient if the hardening liquid
substance is introduced in the annular space between the outer tube
section 9 and the inward facing wall of the borehole by spotting a
quantity of the hardening liquid substance through such annular
space from the surface 6. This may be accomplished using an
appropriate side valve (not shown). The latter option may be an
advantageous option in zones that have a very stable hole size that
does not interfere in the hardening liquid getting to the bottom of
the hole.
[0043] The next step is everting a tubular element 4 in the open
hole section. This is illustrated in FIG. 3. The tubular element 4
comprises an inner tube section 8 and an outer tube section 9
connected to each other in a lower bending zone 14. The inner tube
section 8 runs through the outer tube section 9. A wall of the
tubular element is, in said lower bending zone 14 at a lower end of
the inner tube section 8, induced to bend radially outward and in
axially reversed direction, so as to form the outer tube section 9,
which thereby is everted compared to the inner tube section 8. As
seen in cross section, the lower end of the tubular element 4 has a
shape that can be described by two U's (UU) wherein the wall shows
a curve 15. A so-called blind annulus 44 is formed between the
inner tube section 8 and the outer tube section 9. The blind
annulus 44 is an annular space that is closed in the lower bending
zone 14 by the curved wall 15.
[0044] An upper end of the outer tube section 9 may be suitably
landed on a wellhead device 50. This wellhead device 50 may form
part of or be integrated into a blowout preventer (BOP). The outer
tubular section 9 may be axially fixed to prevent axial movement.
For instance, it may be connected to a ring or flange 59, for
instance by welding and/or screwing, on in the wellhead device 50
or any other suitable structure at surface. Optionally, the outer
tube section 10 may be fixed to the borehole wall, for instance by
virtue of frictional forces between the outer tube section 9 and
the borehole wall as a result of the eversion operation.
Alternatively, or in addition, the outer tube section 9 may be
anchored, for instance to the borehole wall.
[0045] Suitably, an upper end of the inner tube section 8 may pass
through one, two or more annular seals 56, 58 provided in the
wellhead device 50. The annular seals 56, 58 engage with the
outside of the inner tube section 8 and allow sliding movement of
the inner tube section 8 in its axial direction, and close off the
blind annulus 44. The wellhead device 50 suitably comprises a
conduit 52 which may be connected to a pump (not shown) for pumping
a fluid into or out of the blind annulus 44.
[0046] Everting of the tubular element 4 comprises axially
advancing the inner tube section 8 into the borehole 1 through the
outer tube section 9 in relative axial movement compared to the
borehole and the outer tube section 9. As the inner tube section 8
is advanced downward, the wall 15 in the lower bending zone 14 is
radially bent over an angle of 180.degree. thereby everting the
tubular element 4. The everting operation is continued until the
lower bending zone 14 is submerged in the hardening liquid
substance 12. By allowing the liquid substance 12 to harden while
the lower bending zone 14 is submerged into the hardening liquid
substance 12, an annular seal 7 is created between the outer tube
section 9 and an inward facing wall of the borehole 1. FIG. 3
schematically shows the first borehole section of FIG. 1 after
having everted the tubular element 4 to the point that the lower
bending zone 14 is submerged into the hardening liquid substance
12. An inside bore diameter ID of the inner tube section 8 is also
indicated.
[0047] It is recognized that there are other technologies available
to create the annular seal. For instance, the inside of the inner
tube section 8 may locally be provided with a swellable material
which swells as it becomes exposed to a fluid in the borehole. The
eversion operation will eventually bring the swellable material to
the borehole facing side of the tubular element 4 after the lower
bending zone 14 has passed through the swellable material.
[0048] Preferably the hardening liquid substance 12 is retarded, to
allow time to complete the eversion operation before hardening of
the liquid substance is completed. Various technologies are
available to retard a hardening liquid. Retardation over a time
span of at least 4 hours, preferably at least 6 hours, more
preferably at least 8 hours and most preferably at least 12 hours
may be selected depending on the situation.
[0049] After the annular seal 7 has been created, a second drill
string 5', which may be the same drill string as previously used or
another drill string, may be inserted in the borehole 1 through the
inner tube section 8 of the tubular element 4. This is
schematically shown in FIG. 4. Before inserting the second drill
string 5', the inner tube section 8 may have to be cut off
circumferentially to remove at least a part of the tubular element
that is exposed at the earth surface. The part of the inner tube
section 8 below a cut rim is retained, and access into the borehole
1 is provided though the cut rim. Such cutting may be done while
the annular seal 7 is forming (e.g. while the liquid substance 12
is hardening).
[0050] A second open hole section 20 may then be drilled to deepen
the borehole 1 to a second depth that is deeper than the casing
setting depth D.sub.1. Any hardened cement that is left in the
lower part of the inner tube section may be drilled out and reamed.
A drilling annulus 32 is maintained between the inner tube section
8 and the second drill string 5', which may be employed for
circulation of a drilling fluid as is common in the art. As the
drilling progresses, the drilling annulus 32 extends into the
second open hole section 20.
[0051] Suitably, the second drill string 5' comprises a retractable
under-reamer 26 that has a gauge diameter larger than the inside
bore diameter ID of the inner tube section. This way the second
open hole section 20 can be drilled to a bore diameter that is
larger than the inside bore diameter ID of the inner tube section
8. Various types of retractable under-reamers are available in the
market.
[0052] During the drilling of the second open hole section 20, the
second drill string 5' is advanced into the borehole 1 as the
borehole 1 is being drilled, whereas the tubular element 4 is kept
stationary. Specifically, the lower bending zone 14 at a fixed
depth, similar to a traditional casing which is supported on a
casing shoe. If necessary, the inner tube section 8 may be
temporarily secured with slips 35 to the drilling floor 40, at
least for the duration needed to complete the drilling of the
second open hole section 20.
[0053] The drilling of the second open hole section 20 may be
continued until a further case setting depth D.sub.2 is reached.
The procedure may at that point be repeated, as many times as
required to reach the final destination depth. Accordingly, the
currently proposed method involves intermittently drilling, and
further everting of the tubular element 4 during the drilling
intermissions.
[0054] The annular seal 7 isolates any annular space that may exist
between the outer tube section 9 and the borehole wall from the
drilling annulus 32. By proper selection of the casing setting
depth, the proposed method can be employed to drill in formations
with different pressure-gradient regimes. FIG. 5 schematically
shows a close up of the annular seal 7 and the lower bending zone
from FIG. 4 after the hardened substance 12 has been drilled out.
The borehole should be drilled clean enough such that any remaining
substance 12 will not pose a significant barrier to further
everting of the tubular element 4.
[0055] In order to further evert the tubular element 4, it may be
needed to extend the inner tube section 8 with an extension tube 18
as illustrated in FIG. 6. Particularly when employing a seamless
tubular element, extending may be necessary as during the drilling
of the second open hole section 20 the borehole needed to be
accessible for the second drill string 5' through the inner tube
section 8. Extension is suitably accomplished by sealingly abutting
a bottom rim 16 of the extension tube 18 to a top rim 17 of the
inner tube section 8 as indicated by arrows 19. There are various
techniques available to sealingly connect well tubulars in
abutment, including welding. A schematic welding head 21 is
included in FIG. 6. The extension tube 18 is preferentially
seamless, similar to the tubular element 4 that is already in the
borehole 1.
[0056] As illustrated in FIG. 7, the tubular element 4 may be
provided in the form of a coiled tubing 28. The inner tube section
extends to a coiled-up portion 29 of the coiled tubing 28. During
eversion, the inner tube section is supplied by uncoiling the
coiled tubing 28 from the coiled-up portion 29, while axially
advancing the inner tube section into the borehole 1. In order to
provide access to the borehole 1 for subsequent further drilling,
the coiled tubing 28 may have to be cut at or near the surface 6.
This is preferably done at a suitable location that allows the
coiled tubing (CT) to be re-abutted after drilling of the second
borehole section. There is a prejudice in the art that CT drilling
is unsuitable for drilling boreholes in formations with more than
one pressure regime. The presently proposed method breaks with this
prejudice. An important break-through is that the present proposal
does not require to move different CT sizes to the drilling site.
Neither does it require a customized tapering to accommodate
estimations of different length and OD's for the specific borehole
design. Today, CT is conveniently available in sizes ranging from 1
inch to about 5.5 inch OD maximum. Larger sizes exist but become
logistically more difficult to transport to site as the coils tend
to become larger.
[0057] To start the everting operation, it is recommended that a
starting section of the tubular element 4 (whether it is coiled
tubing or other tube material) has been pre-everted so that it can
be landed on the wellhead device 50 in a pre-everted condition. The
pre-eversion tool does not have to be on-site.
[0058] For purpose of interpretation of the present disclosure it
is remarked that the term "consecutive" is used only to identify an
order of steps relative to each other, but it is an open term in
any other sense. Accordingly the term should not be construed as
excluding the possibility of having any intermediate steps, or any
subsequent steps or preceding steps. Neither should the term be
interpreted as limiting the definition of any of the steps.
[0059] The terms "first" and "second" as such are not intended as
qualifying terms, but these terms are merely intended to provide a
unique nomenclature every feature in the claim for ease of
reference. Accordingly, the "first drill string" and "second drill
string" are not implied to be physically different drill strings;
while they may be physically drill strings the terms may also
represent the same physical drill string.
[0060] The term "surface" is may mean any surface above the
borehole. The term thus includes: land surface, ocean floor
surface, sea surface and other suitable surface above the borehole.
Suitably, the term "surface" may be characterized by the location
of the wellhead.
[0061] The term "casing setting depth" should be interpreted as
including a reasonable margin as common in the art of well
engineering. Casing setting depth is often determined at a depth
where a change in formation pressure gradient occurs. However, the
change is usually distributed over a certain depth range. Moreover,
an actual casing may be set somewhat, up to for instance about 10 m
(about 33 ft), above the actual bottom of the borehole section,
rather than in absolute abutment with the bottom of the borehole.
There may be various reasons for this, including the desire to have
the ability to extend wellbore tools in the borehole to below the
casing.
[0062] Ranges defined herein include the end values of the
range.
[0063] The person skilled in the art will understand that the
present invention can be carried out in many various ways without
departing from the scope of the appended claims.
* * * * *