U.S. patent application number 16/479185 was filed with the patent office on 2019-11-28 for drilling unit comprising an electric heave-compensation system.
This patent application is currently assigned to National Oilwell Varco Norway AS. The applicant listed for this patent is National Oilwell Varco Norway AS. Invention is credited to Karsen BERGE MELING, Yngvar BOROY, Hans Anders ERIKSSON, Thor STRAND.
Application Number | 20190360282 16/479185 |
Document ID | / |
Family ID | 58098469 |
Filed Date | 2019-11-28 |
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United States Patent
Application |
20190360282 |
Kind Code |
A1 |
BERGE MELING; Karsen ; et
al. |
November 28, 2019 |
Drilling Unit Comprising an Electric Heave-Compensation System
Abstract
A drilling unit on a deck of a floating vessel, includes a drill
tower structure with a heave-compensation system, a winch mounted
at or near the deck, a crown block mounted at a top side of the
drill tower structure and at least one wire rope between the winch
and the crown block. The heave-compensation system includes a
slideable support frame configured to be moved in a direction
substantially parallel to the axial direction of the drill tower
structure. Either the winch or the crown block is positioned within
the slideable support frame such that a distance between the winch
and the crown block is controlled by at least one electric motor or
linear actuator. In an alternative embodiment in which a crown
block in not employed, the winch is placed in the slideable support
frame at the top side of the drill tower structure.
Inventors: |
BERGE MELING; Karsen;
(Kristiansand S, NO) ; ERIKSSON; Hans Anders;
(Fornebu, NO) ; BOROY; Yngvar; (Sogne, NO)
; STRAND; Thor; (Kristiansand, NO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
National Oilwell Varco Norway AS |
Kristiansand S |
|
NO |
|
|
Assignee: |
National Oilwell Varco Norway
AS
Kristiansand S
NO
|
Family ID: |
58098469 |
Appl. No.: |
16/479185 |
Filed: |
February 15, 2018 |
PCT Filed: |
February 15, 2018 |
PCT NO: |
PCT/NO2018/050041 |
371 Date: |
July 18, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21B 15/02 20130101;
E21B 19/008 20130101; E21B 19/09 20130101; E21B 19/006
20130101 |
International
Class: |
E21B 19/00 20060101
E21B019/00; E21B 15/02 20060101 E21B015/02; E21B 19/09 20060101
E21B019/09 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 16, 2017 |
EP |
17156406.5 |
Claims
1. Drilling unit for mounting on a deck of a floating vessel, the
drilling unit comprising: a drill tower structure with a
heave-compensation system for compensating vertical movements of
the floating vessel due to waves, wherein the drilling unit further
comprises: a winch, a crown block mounted at a top side of the
drill tower structure and at least one wire rope provided between
the winch and the crown block, wherein the heave-compensation
system comprises a slideable support frame configured to be moved
relative to the drill tower structure in a direction substantially
parallel to the axial direction of the drill tower structure, and
wherein either the winch or the crown block is provided within the
slideable support frame such that a distance between the winch and
the crown block is controllable, and wherein the position of the
slideable support frame with respect to the drill tower structure
is controlled by at least one electric motor or linear
actuator.
2. The drilling unit according to claim 1, wherein the slideable
support frame is provided with at least one friction track, and
wherein the drill tower structure is provided with at least one
rotatable friction wheel that is driven by the at least one
electric motor or linear actuator, the at least one rotatable
friction wheel being configured for rolling over the at least one
friction track for controlling the position of the slideable
support frame.
3. The drilling unit according to claim 1, wherein the drill tower
structure is provided with at least one friction track, and wherein
the slideable support frame is provided with at least one rotatable
friction wheel that is driven by the at least one electric motor or
linear actuator, the at least one rotatable friction wheel being
configured for rolling over the at least one friction track for
controlling the position of the slideable support frame.
4. The drilling unit according to claim 2, wherein the at least one
friction wheel is directly driven by the at least one electric
motor or linear actuator.
5. The drilling unit according to claim 2, comprising one or more
respective gearing systems in between the at least one electric
motor or linear actuator and the at least one friction wheel.
6. The drilling unit according to any one of claims 2, wherein the
at least one friction track comprises a toothed rack.
7. The drilling unit according to any one of claims 2, wherein the
at least one rotatable friction wheel comprises a pinion.
8. The drilling unit according to claim 1, wherein the winch is
also configured for compensating vertical movements of the floating
vessel due to waves.
9. The drilling unit according to claim 1, further comprising an
energy recovery system connected to the at least one electric motor
or linear actuator, wherein the energy recovery system is
configured for storing energy generated by a load when the load is
being lowered and for supplying it to the at least one electric
motor or linear actuator when the load is being hoisted.
10. The drilling unit according to claim 1 wherein the winch is
provided within the slideable support frame.
11. The drilling unit according to claim 1, wherein the crown block
provided within the slideable support frame.
12. The drilling unit according to claim 1, wherein the winch
located at a drill floor or deck (200).
13. The drilling unit according to claim 1, wherein the winch is
located outside the drill tower structure (130).
14. The drilling unit according to claim 1, wherein the winch is
located inside the drill tower structure (130).
15. The drilling unit according to claim 1, wherein the slideable
support frame is configured for being lockable relative the drill
tower structure.
16. Drilling unit for mounting on a deck of a floating vessel, the
drilling unit comprising: a drill tower structure with a
heave-compensation system for compensating vertical movements of
the floating vessel due to waves, wherein the drilling unit further
comprises a winch and at least one wire rope coupled to the winch,
wherein the heave-compensation system comprises a slideable support
frame provided at a top side of the drill tower structure, and
wherein the slideable support frame is configured to be moved
relative to the drill tower structure in a direction substantially
parallel to the axial direction of the drill tower structure, and
wherein the winch is provided within the slideable support frame,
and wherein the position of the slideable support frame with
respect to the drill tower structure is controlled by at least one
electric motor or linear actuator.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a 35 U.S.C. .sctn. 371 national state
application of PCT/NO2018/050041 filed Feb. 15, 2018 and entitled
"Drilling Unit Comprising an Electric Heave-Compensation System",
which claims priority to European Patent Application No. 17156406.5
filed Feb. 16, 2017, each of which is incorporated herein by
reference in their entirety for all purposes.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable.
FIELD OF THE INVENTION
[0003] The present disclosure relates to a drilling unit for
mounting on a deck of a floating vessel, the drilling unit
comprising a drill tower structure with a heave-compensation system
for compensating vertical movements of the floating vessel due to
waves.
BACKGROUND
[0004] Floating drilling and intervention vessels must have a
heave-compensation system to compensate for the vertical movements
transferred from the wave surge to the vessel. Such a
heave-compensation system can be mounted at the top side of the
derrick or drill tower or anywhere in the load path if a stationary
sheave is used.
[0005] Traditional heave-compensation systems are located at
various places at the vessel to stabilize the vessel movements
during operation. Reference is made to Frank Langlo's master
thesis, entitled: "Application of reliability centered maintenance
on a drilling system" from the Department of Mechanical and
Structural engineering and Material Science, Faculty of Science and
Technology, of the University of Stavanger, published June 2014.
This publication is incorporated by reference herein and shows that
known compensators typically are often characterized by a guided
system mounted between a drilling tower (derrick) structure and a
drilling machine, having the ability to store energy generated by
the forces and speed from the waves. Traditional derrick
compensator system may be placed at the top side of a derrick,
using a hydraulic system for transferring the power. The energy
storage is normally kept close to the actuators to minimize the
loss, hence there will be a large amount of energy at the top side
of the derrick, with a consistent risk, high cost and low
serviceability.
SUMMARY OF THE DISCLOSURE
[0006] In view of the above, there is a need for a drilling unit
having an improved heave-compensation system, which does not suffer
from the drawbacks mentioned above, or at least to a much lesser
extent.
[0007] The disclosure addresses at least one of the drawbacks of
the prior art, or at least provide a useful alternative to prior
art, and offers an improved and overall more compact design of a
compensation system.
[0008] In a first aspect, the disclosure relates to a drilling unit
for mounting on a deck of a floating vessel. The drilling unit
comprises a drill tower structure with a heave-compensation system
for compensating vertical movements of the floating vessel due to
waves. The drilling unit further comprises a winch, a crown block
mounted at a top side of the drill tower structure and at least one
wire rope provided between the winch and the crown block. The
heave-compensation system comprises a slideable support frame
configured to be moved relative to the drill tower structure in a
direction substantially parallel to the axial direction (in
practise this is a vertical direction) of the drill tower
structure, wherein either the winch or the crown block is provided
within the slideable support frame such that a distance between the
winch and the crown block is controllable. Furthermore, the
position of the slideable support frame with respect to the drill
tower structure is controlled by at least one electric motor or
linear actuator.
[0009] The effects of the drilling unit in accordance with the
disclosure are as follows. By providing a slideable support frame,
which comprises either the crown block or the winch, the distance
between the winch and the crown block may be made controllable.
This opens up the way to compensate vertical movements of the
floating vessel due to waves by simply moving the slideable support
frame. The slideable support frame is actuated by at least one
electric motor or linear actuator. That feature by itself is quite
revolutionary as the prior art systems are all based on hydraulic
systems. Switching the system towards the electrical domain leads
to significant advantages. For instance, the heave-compensation
system may now be fed by the same power supply as the winch system
(which is often electrically driven). This renders the design of
the whole drilling unit less complex. Furthermore, the
heave-compensation system may, in certain embodiments, be combined
with electrical energy recovery systems, i.e. the electrical energy
recovery systems may be used to supply power to the
heave-compensation system of the disclosure.
[0010] The winch itself may also heave-compensated, in that the
actuation of the winch is done such that vertical movements of the
floating vessel due to waves are compensated for. In such cases,
the disclosure thus provides for an extra heave-compensation
system, which either may support the other heave-compensation
system or be used as a back-up system in case the other system
fails. Both scenarios are very effective and advantageous for the
oil industry.
[0011] In summary, the disclosure provides for accurate
compensation, at reduced weight and volume and allows for energy
storage in a safe and controlled area placed anywhere on the rig.
Electric cabling of such heave-compensation system may be run to
so-called VFD cabinets stored inside or below the deck. In this
context, "safe" means non-hazardous/non-explosive. Serviceability
may also be severely improved due to these factors and efficiency
of electric systems are considerable better than traditional
hydraulic systems.
[0012] In order to facilitate a fuller understanding of the
disclosure, one or more expressions are further defined. Wherever
in this description the wording "drill tower structure" is used,
this must be interpreted as including hoisting towers, derricks and
any other type of drilling structure. Wherever in this description
the wording "crown block" is used, this must be interpreted as that
part at the top side of the drill tower structure, which houses or
holds at least one top sheave for guiding the at least one wire
rope.
[0013] In an embodiment of the drilling unit in accordance with the
disclosure, the slideable support frame is provided with at least
one friction track, and the drill tower structure is provided with
at least one rotatable friction wheel that is driven by the at
least one electric motor or linear actuator. The at least one
rotatable friction wheel is configured for rolling over the at
least one friction track for controlling the position of the
slideable support frame. This embodiment constitutes a first main
variant of providing for a slideable support frame which position
is controlled by an electric motor or linear actuator.
[0014] In an embodiment of the drilling unit in accordance with the
disclosure, the drill tower structure is provided with at least one
friction track, and the slideable support frame is provided with at
least one rotatable friction wheel that is driven by the at least
one electric motor or linear actuator. The at least one rotatable
friction wheel is configured for rolling over the at least one
friction track for controlling the position of the slideable
support frame. This embodiment constitutes a second main variant of
providing for a slideable support frame which position is
controlled by an electric motor or linear actuator.
[0015] In an embodiment of the drilling unit in accordance with the
disclosure, the at least one friction wheel is directly driven by
the at least one electric motor or linear actuator. In this
embodiment the electric motor or linear actuator may have a driving
axle that is directly coupled to an axle of the friction wheel.
[0016] An embodiment of the drilling unit in accordance with the
disclosure, further comprises one or more respective gearing
systems in between the at least one electric motor or linear
actuator and the at least one friction wheel. This embodiment is a
variant of the previous-mentioned embodiment in that the electric
motor or linear actuator now drives a gearing system, which on its
turn drives the friction wheel.
[0017] In an embodiment of the drilling unit in accordance with the
disclosure, the at least one friction track comprises a toothed
rack. A toothed rack is able to provide a very large friction,
particularly when a pinion (or wheel gear) is used to cooperate
with it.
[0018] In an embodiment of the drilling unit in accordance with the
disclosure, the at least one rotatable friction wheel comprises a
pinion. A pinion is able to provide a very large friction,
particularly when a toothed rack is used to cooperate with it.
[0019] In an embodiment of the drilling unit in accordance with the
disclosure, the winch is also configured for compensating vertical
movements of the floating vessel due to waves. As already
mentioned, the disclosure may provide for a heave-compensation
system that comes in addition to an already existing
heave-compensation system (for example on the winch as is the case
in this embodiment). Then the heave-compensation system of the
disclosure may be used to either support the other
heave-compensation system, or be used as a back-up in case that
system fails.
[0020] An embodiment of the drilling unit in accordance with the
disclosure, further comprises an energy recovery system connected
to the at least one electric motor or linear actuator. The energy
recovery system is configured for storing energy generated by a
load when the load is being lowered and for supplying it to the at
least one electric motor or linear actuator when the load is being
hoisted. This embodiment makes the heave-compensation system of the
disclosure more self-supporting, i.e. it does not or hardly
requires power from a rig to be able to operate. More information
on the implementation of an energy recovery system may be found in
U.S. Pat. No. 7,923,946, for example, the disclosure of which is
incorporated herein by this reference.
[0021] In the embodiments discussed hereinafter various variations
with regards to the placement of the different parts of the
disclosure are discussed.
[0022] In an embodiment of the drilling unit in accordance with the
disclosure, the winch is provided within the slideable support
frame. This embodiment concerns a first main group of embodiments
of the disclosure.
[0023] In an embodiment of the drilling unit in accordance with the
disclosure, the crown block is provided within the slideable
support frame. This embodiment concerns a second main group of
embodiment of the disclosure.
[0024] In an embodiment of the drilling unit in accordance with the
disclosure, the winch is located at a drill floor or deck. In
another embodiment, the winch is located outside the drill tower
structure. In yet another embodiment, the winch is located inside
the drill tower structure.
[0025] In an embodiment of the drilling unit in accordance with the
disclosure, the slideable support frame is configured for being
lockable relative the drill tower structure. This embodiment is
advantageous in that the heave-compensation system of the
disclosure can be effectively deactivated by the locking of the
slideable support frame. Such feature may be convenient in case the
hoisting activities of the drilling unit are not critical (i.e. not
near the sea bottom) or when service is to be carried out on the
drilling unit.
[0026] In a second aspect, the disclosure relates to a drilling
unit for mounting on a deck of a floating vessel. The drilling unit
comprises a drill tower structure with a heave-compensation system
for compensating vertical movements of the floating vessel due to
waves, wherein the drilling unit further comprises a winch and at
least one wire rope coupled to the winch. The heave-compensation
system comprises a slideable support frame provided at a top side
of the drill tower structure, wherein the slideable support frame
is configured to be moved relative to the drill tower structure in
a direction substantially parallel to the axial direction of the
drill tower structure, wherein the winch is provided within the
slideable support frame, and wherein the position of the slideable
support frame with respect to the drill tower structure is
controlled by at least one electric motor or linear actuator.
[0027] The second aspect of the disclosure actually does not
deviate much from the first aspect, and it includes similar
embodiments as the further embodiments discussed with regards to
the first aspect. The main difference is that the crown block is
missing and that the winch actually takes over the role of the
crown block. Thus, this embodiment concerns a third main group of
embodiments of the disclosure.
[0028] In embodiments, there may be further sheaves added to the
winch in order to guide the at least one wire rope. Even though all
"intelligence" in these embodiments is located at the top side of
the drill tower structure, still the same principle of the
disclosure is used, namely that the heave-compensation is carried
out by controlling the position of the slideable support frame
using an electric motor or linear actuator in order to vary the
distance, measured along the at least one wire rope, between the
winch and the sea (as is indirectly also the case for the other two
embodiments). Therefore, these embodiments concern the same
disclosure as the embodiments of the first aspect.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Exemplary embodiments of this disclosure are illustrated in
the accompanying drawings, wherein:
[0030] FIG. 1 shows a perspective view of a first main embodiment
of the drilling unit in accordance with the disclosure;
[0031] FIG. 2 shows a perspective view of a slightly modified
version of the embodiment of FIG. 1;
[0032] FIG. 3 shows the embodiment of FIG. 2, seen from a different
view point;
[0033] FIG. 4 shows a side view of the embodiment of FIG. 2;
[0034] FIG. 5 shows a front view of the embodiment of FIG. 2;
[0035] FIG. 6 shows a top view of the embodiment of FIG. 2;
[0036] FIG. 7 shows a slideable support frame in accordance with
the embodiment of FIG. 2;
[0037] FIG. 8 shows an enlarged view of part of FIG. 6 illustrated
by AA;
[0038] FIG. 9 shows an enlarged view of the drives foundation and
the drives assembly of the embodiment of FIG. 2;
[0039] FIG. 10 shows a perspective view of a second main embodiment
of the drilling unit in accordance with the disclosure, and
[0040] FIG. 11 shows a perspective view of a third main embodiment
of the drilling unit in accordance with the disclosure.
DETAILED DESCRIPTION OF THE DISCLOSED EXEMPLARY EMBODIMENTS
[0041] Various illustrative embodiments of the present subject
matter are described below. In the interest of clarity, not all
features of an actual implementation are described in this
specification. It will of course be appreciated that in the
development of any such actual embodiment, numerous
implementation-specific decisions must be made to achieve the
developers' specific goals, such as compliance with system-related
and business-related constraints, which will vary from one
implementation to another. Moreover, it will be appreciated that
such a development effort might be complex and time-consuming, but
would nevertheless be a routine undertaking for those of ordinary
skill in the art once they have had the benefit of this
disclosure.
[0042] The present subject matter will now be described with
reference to the attached figures. Various systems, structures and
devices are schematically depicted in the drawings for purposes of
explanation only and so as to not obscure the present disclosure
with details that are well known to those skilled in the art.
Nevertheless, the attached drawings are included to describe and
explain illustrative examples of the present disclosure. The words
and phrases used herein should be understood and interpreted to
have a meaning consistent with the understanding of those words and
phrases by those skilled in the relevant art. No special definition
of a term or phrase, i.e., a definition that is different from the
ordinary and customary meaning as understood by those skilled in
the art, is intended to be implied by consistent usage of the term
or phrase herein. To the extent that a term or phrase is intended
to have a special meaning, i.e., a meaning other than that
understood by skilled artisans, such a special definition will be
expressly set forth in the specification in a definitional manner
that directly and unequivocally provides the special definition for
the term or phrase.
[0043] The heave-compensation system of the disclosure may be
mounted on floating drilling units where an unintended
stop/emergency stop of the heave compensation function may cause
severe damage to environment and material. For a floating rig to be
able to keep the drill bit (or other equipment depending of
operation) in position and at proper weight on seabed the drill
string needs to compensate for the heave that is moving the rig up
and down. For some critical operations normally referred to as
locked/fixed to bottom operation it is required for the rig to have
a passive heave compensation function. Passive heave compensation
means that the heave compensation function is self-supporting and
does not require power from the rig to operate. In an embodiment, a
Kinetic Energy Recovery System (KERS) or energy recovery system may
be employed in which the KERS will store the energy generated, when
the load is being lowered and supply it to the motors when the load
needs to be hoisted. Further details on power regeneration can be
found in U.S. Pat. No. 7,923,946, for example.
[0044] The drilling unit may work together with the winch
heave-compensation system or it may perform only heave compensation
while the winch is setting position up or down, for example during
landing of an object on the seabed or during a drilling operation.
The disclosed heave-compensation system may also work as a back-up
system for the winch only, provided that the winch also has
heave-compensation possibility. In this way of using the disclosed
system, the winch will be performing both hoisting/lowering and
heave compensation at the same time. If for any reason the winch
needs to stop during this operation the electric top compensator
will instantly take over the heave compensation work from the
winch. The result is that the drill bit (or other equipment) will
stay in position at sea bed without damaging equipment or
environment. The electric top compensator if connected to a KERS
will then heave compensate self-supported until winch is again
restarted and hoisting again can begin.
[0045] FIG. 1 shows a perspective view of a first main embodiment
of the drilling unit 100a in accordance with the disclosure. The
drilling unit 100a comprises a drill tower structure 130, which may
be a derrick, a drill tower, or another type of drill structure.
The drill tower structure 130 holds at a top side 140 thereof a
slideable support frame 150 that can be moved up and down (slide)
within the drill tower structure 130. At the other end (at the
lower side) of the drill tower structure 130 there is provided a
winch 110. The slideable support frame 150 comprises a
sheave-cluster assembly, which is explained later in this
description. The winch 110 is connected to the sheave-cluster
assembly via wire ropes 120 (at least one, but in practise often a
plurality). As a matter of fact, the wire ropes 120 are guided over
sheaves in said sheave-cluster assembly and then run down towards
the top drive 180, possibly via a travelling block (not shown in
this embodiment). All parts except the slideable support frame 150
are well-known as such within the technical field of drilling. The
drilling unit 100a further comprises a drives foundation 160 that
forms an interface between the top side 140 of the drill tower
structure 130 and the slideable support frame 150. The drilling
unit 100a also comprises a drives assembly 170 which is configured
for driving (actuating) the slideable support frame 150. The
heave-compensation system of this embodiment of the disclosure
resides in the provision of the sheave-cluster assembly (also
referred to as crown block) in the slideable support frame 150,
such that the distance between the winch 110 and the sheave-cluster
assembly (crown block) is controllable. All details with regards to
the heave-compensation control system are considered to be
well-known and not discussed in detail in this specification (i.e.
a control system is required having sensors, and a control loop
system).
[0046] FIG. 2 shows a perspective view of a slightly modified
version of the embodiment of FIG. 1. FIG. 3 shows the embodiment of
FIG. 2, seen from a different view point. The figures serve to
illustrate some further details of implementing a slideable support
frame 150 within the drill tower structure 130. First of all, the
figures show that the slideable support frame 150 comprises a crown
block (sheave-cluster assembly) 151, which comprises at least one
top sheave 152. Furthermore, the drives foundation 160 comprises a
drives foundation interface 162 and a track 164 for receiving
guiding wheels (discussed below). The drives assembly 170 comprises
a plurality of electric motors 171 (but this may also be electric
linear actuators) that are connected to respective friction wheels
173 (pinions or wheel gears) via respective gearing systems 172.
This is further explained with reference to other figures. FIGS. 2
and 3 further illustrate that the drilling unit 100a is placed on a
deck 200 of a floating vessel (not shown) or on drill floor 200 of
a rig (not shown).
[0047] FIG. 4 shows a side view of the embodiment of FIG. 2. FIG. 5
shows a front view of the embodiment of FIG. 2. FIG. 6 shows a top
view of the embodiment of FIG. 2. FIG. 6 shows also the guiding
wheels 163 that are configured for cooperating with the
earlier-mentioned track 164 in the drives foundation 160. This
figure also shows the friction tracks 153 on the slideable support
frame 150. The rack-and-pinion system as illustrated in the
embodiment of FIGS. 1 to 9 is just an example of creating a
controllable slideable support frame 150, yet the advantage of
rack-and-pinion is that the friction is extremely high, i.e. it is
a very robust system, the position is well-determined, especially
when the pinions are not rotating (and maybe even locked).
[0048] FIG. 7 shows a slideable support frame 150 in accordance
with the embodiment of FIG. 2. The toothed racks 153 as well as the
guided wheels 163 on the outside of the slideable support frame 150
are clearly illustrated.
[0049] FIG. 8 shows an enlarged view of part of FIG. 6 illustrated
by AA. FIG. 9 shows an enlarged view of the drives foundation (of
which there is one on each side of the drill tower structure 130)
and the drives assembly of the embodiment of FIG. 2. These figure
show in more detail how the electric motor 171 drive the friction
wheels 173 via the gearing systems 172. The figure also illustrates
how the guiding wheels 173 run within the track 164 of the drives
foundation interface 162.
[0050] FIG. 10 shows a perspective view of a second main embodiment
of the drilling unit 100b in accordance with the disclosure. This
embodiment will not be discussed in much detail, but only in as far
as it differs from the first embodiment (FIGS. 1 to 9). It was
already explained that the first embodiment was about varying the
distance between the winch 110 and the crown block 151. FIG. 10
shows a further way in which this effect is achieved. A further
frame structure 135 is provided underneath the drill tower
structure 130 for housing the slideable support frame 150. The
further frame structure 135 may also be integrated at a bottom side
of the drill tower structure 130 or be part of it. In this case,
however, such structure may be provided under the drill floor, for
example. In this embodiment it is the winch 110 that it provided
within the slideable support frame 150, while the crown block 151
is kept in a fixed position at the top side 140 of the drill tower
structure 130. Expressed differently, the heave-compensation system
of this embodiment resides in the provision of the winch 110 in the
slideable support frame 150, such that the distance between the
winch 110 and the sheave-cluster assembly (also referred to as
crown block 151) is controllable.
[0051] FIG. 11 shows a perspective view of a third main embodiment
of the drilling unit 100c in accordance with the disclosure. In
fact, this embodiment is less complex than the first and second
embodiments discussed with reference to FIGS. 1 and 10, in that the
crown block is left out (i.e. no crown block is employed). Instead,
the winch 110 is placed within the slideable support frame 150 and
placed in the top side 140 of the drill tower structure 130.
Similar to the other embodiments, the heave-compensation system of
this embodiment resides in the provision of the winch 110 in the
slideable support frame 150 at the top side 140 of the drill tower
structure 130, such that the distance between the winch 110 and the
drill floor is controllable.
[0052] The embodiments as illustrated in the figures are just one
of the many possible embodiments. There are many variations on the
embodiments possible, which has been extensively discussed in the
introduction of this specification. A few variations are discussed
hereinafter.
[0053] The heave-compensating system of the disclosure may be
mounted at the top side of the derrick/drill tower or anywhere in
the load path if stationary sheave are used. It may be used for
compensating the rig movements by means of a rack and pinion system
with electrical drive units (electric motors) connected to an
energy recovery system. The recovery system minimize energy supply
needed and hence reduce the power demand from the vessel generators
to provide less overall power consumption. In case of critical
failures that makes the winch stop, the disclosed embodiment can
single-handedly supply heave compensation to the drilling
machine/drill string without power provided from the vessel/rig
making it a fully-passive heave-compensation system. The embodiment
also makes it possible to keep the source of energy at a safe area,
remote from the derrick, more serviceability and space saving.
[0054] The heave-compensation system may be mounted between a winch
and a drilling machine, transferring the reaction forces from the
drilling operation into the derrick. The winch may be located above
or below the drill floor, having wire ropes routed via wire sheaves
that are mounted in the movable part (slideable support frame) of
the compensating system, to the drilling machine. Optionally, the
winch may be mounted directly, as a part of the compensator system,
at the top side of the derrick; and compensating by moving the
winch in a vertical linear direction. Optionally, the compensating
system is mounted on the outside or at the inside of the derrick;
as a foundation to support the winch, and compensating by moving
the winch in a linear direction with wires routed via sheaves to
the drilling machine.
[0055] The particular embodiments disclosed above are illustrative
only, as the disclosure may be modified and practiced in different
but equivalent manners apparent to those skilled in the art having
the benefit of the teachings herein. Furthermore, no limitations
are intended to the details of construction or design herein shown,
other than as described in the claims below. Accordingly, the
protection sought herein is as set forth in the claims below.
[0056] In the claims, any reference signs placed between
parentheses shall not be construed as limiting the claim. Use of
the verb "comprise" and its conjugations does not exclude the
presence of elements or steps other than those stated in a claim.
The article "a" or "an" preceding an element does not exclude the
presence of a plurality of such elements. The mere fact that
certain measures are recited in mutually different dependent claims
does not indicate that a combination of these measures cannot be
used to advantage. In the device claim enumerating several means,
several of these means may be embodied by one and the same item of
hardware.
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