Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD AND APPARATUS FOR HEAVE COMPENSATED
DRILLING WITH COILED TUBING
This application claims the benefit of U.S. application no. 09/179,586, filed
October 27, 1998, which application is incorporated herein by reference.
FIELD OF INVENTION
The invention pertains generally to the use of coiled tubing injectors on
floating
offshore platforms and specifically to methods for drilling using coiled
tubing injectors
on floating platforms.
BACKGROUND OF INVENTION
Continuous pipe, generally known within the industry as coiled tubing since it
is
stored on a large reel, has been used for many years. It is much faster to run
into and out
of a well bore than conventional jointed straight pipe since there is no need
to join or
disconnect short segments of straight pipe. Coiled tubing "injectors" are used
to run
continuous strings of tubing into and out of well bores. The name "injector"
was derived
from the fact that, in preexisting well bores, the tubing must be literally
forced or
"injected" into the well through a sliding seal while overcoming the force
produced by
the well pressure a'~ting on the cross-sectional area of the end of the
tubing. Once a
2o sufficient length of tubing has been injected into the well the weight of
the tubing
eventually exceeds the force produced by the pressure acting against the cross-
sectional
area of the tubing. Once the weight of the tubing overcomes the pressure-
induced force,
it must be supported by the injector. The process is reversed as the tubing is
removed
from the well. One method by which a continuous length of tubing can be either
forced
against pressure into the well, and be raised and lowered in the well bore is
by
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continuously gripping a length of the tubing just before it enters the well
bore. This is
achieved in a tubing injector by arranging continuous chain loops on opposite
sides of
the tubing. The continuous chains carry a series of grippers that are pressed
against
opposite sides of the tubing. The chains are mounted on a frame, which sits on
the
drilling platform or is attached directly to the well head.
Coiled tubing has traditionally been used primarily for circulating fluids
into the
well and other work over operations, rather than drilling, because of its
relatively small
diameter and because it was not strong enough, especially for deep drilling.
However, in
recent years, the availability of larger, stronger coiled tubing has made
possible its use in
to drilling well bores and as permanent tubing in production wells. To drill,
a turbine motor
suspended at the end of the tubing and is driven by mud or drilling fluid
pumped down
the tubing.
The recent use of coiled tubing for drilling has brought about a new problem
when used in the offshore environment. This problem is controlling the motion
of the
end of the tubing string, including the attached drilling tools, while the
supporting vessel
of structure rises and falls in response to heaving seas. Maintaining a steady
load on the
drill bit is crucial to effective and efficient drilling.
Traditional methods for coping with the heaving problem have been to control
the
motion of the tubing through the tubing injector. This method has the tubing
cycling
2o back and forth through the injector's gripping zone in response to the
heaving. This
method produces substantial cold working of the tubing string as it is
plastically bent and
cycled back and forth across a guidance arch above the injector and onto and
off of a
tubing storage reel. Additionally, considerable energy is required to rapidly
change the
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direction of travel of the tubing storage reel, due to its high inertia, in
response to the
heave. Controlling the motion of the portion of the tubing between the
injector's tubing
guidance arch and the tubing storage reel, as the reel attempts to maintain
constant
tension on the tubing, can be difficult and dangerous.
SUMMARY OF INVENTION
One objective of the invention is to provide methods and apparatus for
reducing
stress on coiled tubing during offshore operations. In accordance with this
objective a
coiled tubing injector is supported on a floating platform using a heave
compensator.
l0 Coupling the coiled tubing injector through a heave compensator avoids
cyclical
spooling and unspooling coiled tubing from a reel to compensate for heaving
and thus
the excessive stress placed on the coiled tubing resulting therefrom.
Furthermore, it
avoids the difficulties in operating a relatively massive storage reel and
injector in a
manner to compensate for heaving.
Another objective of the invention is to provide methods and apparatus that
are able to be
adapted to existing drilling equipment for use in off shore drilling with
coiled tubing,
thereby minimizing capital investment and providing flexibility in choosing
which
drilling method to use, and easily switching between drilling methods. The
most cost-
effective method of drilling for a particular well can thus be chosen and
installed when
2o required, resulting in reduced operating costs. In accordance with this
objective, one
aspect of various disclosed embodiments of the invention includes suspending a
coiled
tubing injector from a derrick through a heave compensator. Depending on the
particular
type of heave compensator used, the heave compensator is coupled between the
coiled
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tubing injector and the dernck, between the top of the derrick and a draw
works assembly
that is supporting the injector, or between the top of the derrick and the
injector. The
draw works itself could, alternately, be heave compensated and connected
directly to the
injector. Coupling the coiled tubing injector through a heave compensator
avoids the
stress on the coiled tubing associated with cyclical spooling and unspooling
the coiled
tubing from the reel, and the operation of the relatively massive storage reel
and injector
to compensate for movement of a floating platform on which the derrick
located.
Furthermore, suspending the injector from a dernck allows the injector to be
raised in
order to attach bottom hole assemblies and other tubing end devices to the end
of the
to coiled tubing once it has been threaded through the injector and before it
is inserted into
the well bore. It also enables the injector to be utilized in conjunction with
tall lubricators
or risers.
Another, separate objective met by other aspects of another disclosed
embodiment is to provide an extra semi-relaxed length of tubing between the
tubing
~5 storage reel and the injector. The extra semi-relaxed tubing length between
the tubing
storage reel and injector allows the injector and tubing storage reels to move
relative to
one another without the need to spool tubing onto and off of the storage reel,
or through
the injector in response to heave as is done using conventional methods. The
tubing
storage reel has a tensioning injector mounted directly on its framework that
provides the
2o necessary tension to maintain proper spooling of the tubing on the reel.
The two injectors
thus move the tubing in unison to maintain the same length of tubing between
the tubing
storage reel and the injector mounted in the derrick. This means the length of
tubing
between the storage reel and injector remains constant. The extra length of
tubing allows
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the injector to move relative to the storage reel with less stress in the
coiled tubing string
as compared to the conventional methods, in which Cyclical stressing and
straining of
the tubing string can lead to premature fatigue in the wall of the coiled
tubing.
These and other aspects of various embodiments incorporating the invention,
and
their respective advantages, are described below in reference to the appended
drawings,
in which:
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic illustration of a dernck used for drilling well bores,
having
an injector hanging from the derrick, through a heave compensator, for running
coiled
1o tubing wound on a reel located on a drilling platform;
FIG. 2 is a schematic illustration of a derrick used for drilling well bores,
having
an injector hanging from the derrick, through a heave compensator, for running
coiled
tubing wound on a reel located on a boat floating beside a floating platform
on which the
derrick is located;
~ 5 FIG. 3 is a schematic illustration of an alternate embodiment to FIG. 2;
FIG. 4 is a schematic illustration of a floating platform with a derrick for
drilling
well bores having a coiled tubing injector and a reel wound with coiled tubing
hanging
from the derrick, through a heave compensator; and
FIG. 5 is a schematic illustration of an alternate embodiment to FIG. 1.
DETAILED DESCRIPTION
In the following description, like numbers refer to like elements.
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Referring to FIGS 1, 2, 3, 4 and 5, suspended from mast or derrick 10 is a
coiled
tubing injector 14. The coiled tubing injector lowers and raises coiled tubing
16 into a
well bore (not shown) for drilling or other down-hole operations. The coiled
tubing is
wound on a storage reel 18. The derrick as shown is of a type that can also be
used for
drilling well bores or performing down-hole operations using jointed pipe.
Furthermore,
derrick 10 is operating offshore, and is thus shown atop floating drilling
platform 12.
However, the tubing injector 14 can also be operated from other types of
floating
structures, including for example semi-submersible platforms, ships and boats.
The term
"floating platform," as used herein, refers to any sort of floating structure,
including
those that are semi-submersible, that are affected by heaving in offshore
environments.
Coiled tubing injector is mounted within a travelling frame 20 (Figs. 1, 2, 3
and 5) or 52
(Fig. 4), which in turn is hung from derrick 10. The travelling frame is
preferably
constrained against movement in all directions except along a vertical axis
21. In an
offshore environment, horizontal movement might be caused by waves on the
surface of
water 28. The travelling frame 20 cooperates with one or more vertical guides.
In the
illustrated embodiments, vertical members 22 and 24 of dernck act as rails
that constrain
movement of the travelling frame 20. However, any number of different
configurations
of vertical rails or tracks can be used to form guides to achieve the result
of confining the
frame to movement along the vertical axis during down-hole operations. On
drilling rigs
2o incorporating top drives, existing top drive guide rails can be used. This
means the top
drive can be removed and the drilling injector framework installed with the
minimal of
effort.
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Heaving caused by waves can subject floating platform 12 to considerable
vertical movement. Vertical movement of a drill string during drilling
operations is not
desirable since it is advantageous to maintain a near-constant weight on the
drill bit.
Maintaining constant weight on the drill bit promotes more efficient drilling
and thus
higher penetration rates. A variety of methods have been employed to
compensate for
vertical movement of drilling platforms at sea and thus, in effect, isolate a
conventional
jointed, drill string from the effects of heaving. These methods typically use
a
mechanical or hydraulic (or combination thereof) system known as motion or
heave
compensator. There are many types of heave compensators. They can be passive,
semi-
active or active.
In each embodiment respectively illustrated in Figs. I-5, a heave compensator
is
coupled between the coiled tubing injector 14 and derrick 10. Alternately, a
heave
compensator can be mounted on the floor of the floating platform, and the
coiled tubing
injector mounted on top of the heave compensator. By supporting the coiled
tubing
Is injector 14 on the floating platform with a heave compenstor, such as by
coupling the
derrick 10 and the coiled tubing injector 14 through a heave compensator or
mounting
the coiled tubing injector on top of a heave compenstor mounted on the floor
of the
floating platform, the heave compensator is able to maintain the coiled tubing
injector in
a substantially fixed position relative to the well bore. As floating platform
12, heaves or
otherwise moves relative to the well bore, the heave compensator will move the
coiled
tubing injector along the vertical axis, relative to derrick 10, to compensate
for the
movement of the derrick caused by the heaving. In the illustrated embodiments,
travelling frame 20, in which the coiled tubing injector is mounted, will move
up and
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down within the derrick 10 along the derrick's vertical axis, which is
designated in Fig. 1
by axis line 21.
Referring now to only FIGS. l, 2, 3 and 4, the dernck 10 includes draw works
26.
The frame 20 is hung from the draw works. The draw works include a crown block
28
connected to the top of the derrick and a travelling block 30 coupled with the
travelling
frame 20. No particular type of coupling between the travelling frame and
travelling
block is required. An adaptor can be used, if necessary, to attach the
travelling frame to
existing draw works. The draw works also includes a cable having one end
wrapped
around the drum of winch 34. In the embodiments illustrated by Figs. 1 and 4,
the winch
to is part of, incorporates or includes (e.g. be controlled by) a heave
compensation system
or compensator. For example, the heave compensator operates the winch to lower
and
raise the coiled tubing injector to compensate for heaving. Although the winch
is shown
mounted on floor 36 of the floating platform 12, it could also be mounted on
top of the
dernck. Alternately, hydraulic heave compensator 38, which uses a piston and
cylinder to
generate forces that allow the derrick to move independently of a drill
string, can be
coupled between the between the derrick and crown block, as shown in Fig. 3;
between
the travelling block and coiled tubing injector 14 as shown in Fig. 2; or,
referring now to
FIG. 5, between the coiled tubing injector 14 to the derrick 10 without using
a draw
works, as shown therein.
2o Referring now to FIGS. l, 2, 3 and 5, as the coiled tubing injector 14
moves up
and down within dernck 10, it is also moving with respect to storage reel 18.
The reel is
tensioned to provide a bias that prevents uncoiling of the coiled tubing from
the reel.
However, in order to accommodate the movement of the coiled tubing injector 14
with
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respect to the reel 18 and avoid excessive bending of the tubing that would
place undue
stress on it, an extra amount of coiled tubing must be unwound. This extra
amount of
coiled tubing results in a "loop" being formed in a portion or segment of the
coiled
tubing extending between the reel 18 and the coiled tubing injector 14. A
tensioning
injector 40 is used to hold the coiled tubing so that tensioning on the reel
18 can be
transferred only to the portion of the coiled tubing wound on the reel and not
to the loop.
Two types of loops can be used: a sagging loop 42 (Figs. 1 and 2) and a
standing
loop (Figs. 3 and 5). Depending on the type of loop, a different type of
gooseneck is used
to provide the proper support for the coiled tubing as it transitions into the
coiled tubing
1o injector 14. Gooseneck support 46 (Figs. 1 and 2) is used with a sagging
loop; gooseneck
support 48 (Figs. 3 and 5) is used with a standing loop. Furthermore, as shown
in Figs. 1
and 2, the axis of the tensioning injector 40, which is defined by the portion
of the coiled
tubing passing through the injector, is oriented generally horizontally with
respect to axis
21 to establish sagging loop 42. As shown in Figs. 3 and 5, the axis of the
tensioning
is injector is oriented between a horizontal axis and a vertical axis, with
respect generally to
the axis 21 of the dernck, to establish standing loop 42. The tensioning
injector is
mounted on a support arm 48 that pivots about reel 18 so that the orientation
of the
tensioning injector can be easily adjusted in the field.
Furthermore, it is preferable that the axis of the tensioning injector 40 be
always
20 oriented with respect to the reel such that the coiled tubing, as it is
being taken off the
reel, remains relatively straight and does not bend before it enters the
tensioning injector.
The injector therefore pivots on the arm 48 as the outer diameter of the
tubing coil on the
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reel 18 changes, such that the axis of the injector remains tangential to an
outer
circumference of the coil of tubing.
The reel 18 can be placed either on the same floating platform as the derrick
or a
separate floating platform such as boat 50. Boat 50 can act as a tender,
bringing reels of
tubing out to the floating platform, as they are needed, without having to
unload the reel
on to the floating platform.
Referring now to FIG. 4, reel 18 is, alternatively, mounted with the coiled
tubing
injector 14 in a common frame 52. By placing the reel and coiled tubing
injector in a
common frame, the injector can be heave compensated without placing additional
stress
on the coiled tubing. However, due to the close proximity of the reel with the
coiled
tubing injector, the reel is preferably mounted within the frame 52 in a
manner that
avoids excessive bending of the coiled tubing after it has been unreeled.
Preferably, the
axis of the coiled tubing within the injector 14 should always remain
tangential to the
coiled tubing on the reel. A method and apparatus for reducing bending of
coiled tubing
as it is unreeled, and before it enters and injector, is disclosed in U.S.
Patent No.
5,660,235, of Sola, dated August 26, 1997, which is incorporated herein for
all purposes.
The forgoing embodiments are but examples incorporating use of the invention.
Modifications, omissions, rearrangements and other changes may be made to the
embodiments without departing from the invention as defined by the appended
claims.
2o What is claimed is:
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