U.S. patent application number 11/596762 was filed with the patent office on 2008-11-06 for device in connection with heave compensation.
This patent application is currently assigned to FMC Kongsberg Subsea AS. Invention is credited to Hans-Paul Carlsen, Olav Inderberg, Anthony D. Muff.
Application Number | 20080271896 11/596762 |
Document ID | / |
Family ID | 35005875 |
Filed Date | 2008-11-06 |
United States Patent
Application |
20080271896 |
Kind Code |
A1 |
Inderberg; Olav ; et
al. |
November 6, 2008 |
Device in Connection with Heave Compensation
Abstract
The present invention relates to a heave compensator for a
riser, particularly a working riser (9), comprising a telescopic
connection (10) with a first chamber (60) which is in fluid
connection with the interior of the riser and a second chamber (62)
which is connected with a source of pressure fluid. By varying the
pressure in the second chamber in response to the movements of the
platform, the telescopic connection can be arranged to move in
correspondence with the platform's movements, thereby permitting
access to the riser during working operations.
Inventors: |
Inderberg; Olav; (Kongsberg,
NO) ; Carlsen; Hans-Paul; (Notodden, NO) ;
Muff; Anthony D.; (Kongsberg, NO) |
Correspondence
Address: |
Henry C. Query, Jr.
504 S. Pierce Avenue
Wheaton
IL
60187
US
|
Assignee: |
FMC Kongsberg Subsea AS
Kongsberg
NO
|
Family ID: |
35005875 |
Appl. No.: |
11/596762 |
Filed: |
May 23, 2005 |
PCT Filed: |
May 23, 2005 |
PCT NO: |
PCT/NO2005/000169 |
371 Date: |
June 18, 2008 |
Current U.S.
Class: |
166/355 |
Current CPC
Class: |
E21B 17/07 20130101;
E21B 19/006 20130101 |
Class at
Publication: |
166/355 |
International
Class: |
E21B 43/01 20060101
E21B043/01 |
Foreign Application Data
Date |
Code |
Application Number |
May 21, 2004 |
NO |
20042096 |
Claims
1: In combination with a heave compensation device for a
pressurized riser which extends between a subsea installation and a
floating unit, the riser comprising at least two tubular parts
which are connected by a telescopic connection that includes a
first tubular member which is connected to the first part, a second
tubular member which is connected to the second part and a first
chamber which is formed between the first and second members and is
connected with the interior of the riser and, the improvement
comprising a control system which includes: a second chamber which
is formed between the first and second members and is connected
with a source of pressure fluid; wherein the source of pressure
fluid includes means for adjusting at least one of the pressure and
the volume of the fluid in the second chamber to thereby control
the movement of the first member relative to the second member.
2: The combination of claim 1, wherein one of the parts of the
riser is an upper part which is connected to at least one of a dry
Christmas tree, an adaptor connection and a surface BOP.
3: The combination of claim 1, wherein one of the parts of the
riser is a lower part which comprises a second heave compensation
device that maintains the lower part of the riser under
substantially constant tension.
4: The combination of claim 1, wherein the adjusting means
comprises a pressure-regulating device.
5: The combination of claim 1, wherein the adjusting means
comprises a pump.
6: The combination of claim 4, wherein the adjusting means
comprises an intelligent control unit for controlling the
pressure-regulating device.
7: The combination of claim 1, wherein the first and second members
of the telescopic connection overlap at least partially to thereby
form an annulus between them within which the first and second
chambers are located.
8: A method for controlling the movement of an upper part of a
pressurized riser which is connected to a floating unit and which
comprises at least a lower part that is heave compensated by means
of tension relative to the floating unit, the lower part and the
upper part being connected by a telescopic connection which
includes a first chamber in connection with the interior of the
riser, the method comprising: providing the telescopic connection
with a second chamber in connection with a pressure fluid source;
and regulating the supply of pressure fluid to the second chamber
in response to at least one of the heave motion of the floating
unit and the desired positioning of the upper part relative to the
floating unit.
9: The method according to claim 8, wherein the step of regulating
the supply of pressure fluid to the second chamber includes
regulating the pressure in the second chamber with a pressure
regulation device.
10: The method according to claim 9, wherein the pressure
regulation device is controlled on the basis of signals received by
a data processing unit.
11: The method according to claim 10, wherein the signals comprise
data from sensors which measure at least one of the movement of the
floating unit and the pressure in the riser.
Description
[0001] The present invention relates to a device in connection with
heave compensation of a pressurised riser extending between a
subsea installation and a floating unit, particularly a working
riser, comprising a telescopic connection with a first chamber
which is in fluid connection with the interior of the riser and a
second chamber.
[0002] During operations on a subsea well, a floating platform is
employed which is held in position by means of anchors or dynamic
positioning (DP). Such a platform has to be compensated for
movements caused by waves, current and wind. During drilling a
heave compensator is employed which keeps the riser under tension
during the vessel's movements. In the upper part a telescopic
connection is inserted with one part attached to the riser and the
other part attached to the platform. The riser is open, with the
result that drilling mud that returns up through the riser runs
over into a tank. Any volume changes due to the platform's
movements are compensated for by the tank having sufficient volume
to receive the mud.
[0003] When work has to be carried out in a producing well, the
riser cannot be open, since the interior of the riser is under
pressure, corresponding to the pressure in the well. Thus it has
not been common practice to equip working risers with telescopic
joints, since the high internal pressure in the riser will attempt
to force the telescopic joint into its extreme position, thereby
neutralizing the function of the telescopic joint. Moreover, since
there is well-pressure in the riser, a pressure safety element,
called a surface-mounted wellhead Christmas tree, must be mounted
on the top of the riser. It is therefore common practice to suspend
the Christmas tree from the platform's derrick and mount the heave
compensator for the riser in connection therewith.
[0004] Since the Christmas tree is attached to the riser, on
account of the wave movements the platform will move relative to
the Christmas tree, thereby impeding work on the Christmas tree.
Necessary operations, such as the insertion of equipment through
the Christmas tree have therefore been performed by personnel being
suspended from the derrick in a working harness, which is a
hazardous operation that has resulted in many accidents.
[0005] In NO patent no. 315 807 a method is described for avoiding
such dangerous situations. There the riser is equipped with a
telescopic joint. During operations this is locked in one position,
with the result that the Christmas tree will move relative to the
platform deck. When equipment has to be inserted in the riser, it
is firstly lowered until it rests against the seabed. The lock is
released and the telescopic joint brought into its central
position. The upper part can then be caused to stand still relative
to the platform, thereby enabling personnel to perform work in
connection with the Christmas tree. The disadvantage of this method
is that all work in the well must be interrupted when the
telescopic joint is placed in this operating position.
[0006] Another disadvantage is that the riser has to be supported
at the bottom, which may result in unacceptable bending
stresses.
[0007] The present invention is based on a principle known from US
patent publication no. 2 373 280 wherein a telescopic joint, which
is intended to absorb changes in the length of a pipe carrying
fluids under pressure, is equipped with oppositely-directed piston
surfaces that provide a resultant pressure equal to zero, thus
preventing the pressure from causing changes in the length of the
pipe.
[0008] In NO patent no. 169 027 the use of this principle is
proposed in a riser, thereby permitting a telescopic joint to be
employed in a working riser with an internal pressure. However, it
does not solve the real problem, which is to get the surface tree
to stand still relative to the platform while work is in
progress.
[0009] An object of the present invention is to provide a system
that solves at least some of the above-mentioned problems.
[0010] A further object is to provide a system where the surface
tree can stand still relative to the platform while work is in
progress, while at the same time maintaining a substantially
constant tension in a main part of the riser.
[0011] This is achieved by a device and a method as defined in the
attached claims. By means of a solution according to the invention
the above-mentioned problems are solved by the second chamber being
connected to a source of pressurised fluid with pressure and volume
being varied so that heave is actively compensated for the upper
part of the riser. The upper part of the riser can thereby be
actively regulated relative to the other part of the riser in order
to keep the other part under constant tension and/or the upper part
can be actively regulated relative to the floating unit during work
that requires the surface tree to be stationary relative to the
floating unit or other equipment employed for performing the work.
The upper part of the riser and the Christmas tree can thereby be
accessible under all conditions, including when the tool is located
down in the well and can be optimised with regard to their movement
in order to avoid unnecessary stresses on the riser system and
related equipment.
[0012] An advantage of the invention is that it can also be
employed for active heave compensation of the riser, thereby
avoiding the use of the known tension rods and accumulators for
heave compensation.
[0013] According to a second aspect of the invention the upper part
of the riser may be actively controlled as required with regard to
heave and the lower part of the riser may comprise a separate
device for heave compensation of this part independent of the upper
part of the riser.
[0014] A device according to the invention will also comprise, or
alternatively be connected with, related equipment that can provide
automatic control as a consequence of signals received from one or
more sensors, or an arrangement for manual control and/or a
combination thereof.
[0015] The invention will now be described in greater detail with
reference to the accompanying drawings, in which:
[0016] FIG. 1 is a schematic view of a typical working riser,
and
[0017] FIG. 2 illustrates a telescopic joint with a diagram for
controlling the telescopic joint.
[0018] The riser system illustrated in FIG. 1 is of a type that is
normally called an intervention riser or working riser, i.e. it is
arranged to be employed during operations in a well after the well
is completed and put into production. This may involve, for
example, operations for lowering or retrieving equipment to and
from the well, stimulating the well with chemical or mechanical
agents, etc. A riser of this kind is arranged to withstand high
pressure but is normally smaller than the riser employed in
drilling operations and usually has an external diameter of
14''.
[0019] The configuration illustrated in FIG. 1 is only intended as
an example of such types of risers and it will be appreciated that
it may comprise more parts, or that other parts may replace those
illustrated. The riser is shown attached to the upper part of a
subsea Christmas tree 1, which in turn is connected to a wellhead 2
which is fixed in a guide-base 3. The latter forms the foundation
of the well 4 and rests on the seabed 5.
[0020] From the bottom up the riser system comprises a lower riser
package (LRP) 6, an emergency quick disconnect piece (EQDP) 7, a
bending joint 8, the pipe 9 and a telescopic joint 10. The riser
pipe 9 consists of a number of pipes that are screwed together or
interconnected in some other way to form an elongate column. In the
telescopic joint 10 there may be provided attachment means for
wires 24, which in turn are attached to a tension-based heave
compensating system. This is a commonly known arrangement for
keeping the riser under tension and implemented in order to avoid
excessive loading stresses on the well.
[0021] The vessel has a main deck or drill floor 13, which is the
primary working area on the vessel and a moon pool 14 through which
equipment is lowered to the seabed.
[0022] The upper parts of the riser system comprise an adapter
connection 15, which forms a transition between the riser 9 and a
tension frame 16, which in turn is suspended in the rig's drive
gear 17. Inside the tension frame 16 are mounted a surface
Christmas tree 18, a surface BOP 19 and a coil pipe injector 20. In
the drill floor 13 is mounted a sliding or wear joint 21 through
which the pipe 9 is passed in order to avoid damage to the pipe. An
umbilical (not shown) leads down to the lower parts of the riser
and comprises hydraulic and electrical lines for control of the
systems on the seabed.
[0023] The vessel further comprises non-illustrated derricks,
cranes and other equipment normally found on a vessel. On the
vessel there is also located an operations centre with an operator
who supervises the operations in the well. In the operations centre
there is provided an intelligent control unit that receives and
processes data, and is employed for controlling the heave
compensating system, as will be described in greater detail in the
following section.
[0024] According to the invention a number of critical components
are provided with meters for measuring their condition. The result
of the measurements is transmitted, preferably in real time, to the
control unit in the operations centre where the signals are
received and processed in the computer.
[0025] The critical parameters that require to be measured are
primarily the vessel's position, either by measuring the vessel's
geographical position by means of a GPS system or by measuring the
angle of the riser, or possibly both. Even though the riser's
angular deviation from the vertical can be calculated on the basis
of the vessel's position, it is desirable to measure it as well,
since it provides a verification of the DP system's reliability. In
addition, a number of parameters in the heave compensating system
are measured, such as the riser's height above the drill floor, the
so-called "stick-up" and the change rate for stick-up. In the heave
compensating system the piston's position in the cylinder requires
to be measured, particularly if it is located near the extreme
points of the stroke, together with the change rate, i.e. how fast
the piston is moving. In addition, meters are provided in the
actual heave compensation.
[0026] According to the invention the telescopic joint is designed
in such a manner that it can function as active heave compensation,
as a replacement for, or in addition to, the standard tension-based
heave compensation illustrated in FIG. 1. As illustrated in FIG. 2
the telescopic joint consists in the known manner of an internal
telescopic pipe 30 attached to the riser 9 and an external pipe 40
attached to the adapter connector 15 (in FIG. 1). The telescopic
pipe 30, and possibly the riser 9, may be equipped with a flange
that forms an attachment point for the tension wires 24 (in FIG.
1).
[0027] The telescopic pipe 30 has an additional protruding flange
with a lower surface 33, an upper surface 34 and an external
surface 35. The surface 34 has an area A.sub.5 and the surface 33
has an area A.sub.2. One or more seals 36 are mounted in the
surface 35. The telescopic pipe 30 has an internal diameter equal
to the riser's 9 internal diameter and has an inner surface 37 and
an outer surface 38. One or more holes 39 through the pipe wall are
provided in the pipe 30.
[0028] The outer part 40 of the telescopic joint comprises an upper
part 42 with an inner surface 43 arranged to slide towards the
outer surface 38 of the internal telescopic joint. From the upper
part 42 there is attached a pipe 44 with an inner surface 45
arranged to slide towards the outer surface 35 of the protruding
flange. At the bottom (as viewed in the figure) the pipe 44 is
provided with an inwardly directed flange 48 with an inner surface
49 arranged to slide towards the pipe's 30 outer surface 38. The
transition between the upper part 42 and the pipe 44 forms a
shoulder with a downwardly-facing surface 52 with an area A.sub.4.
In a similar manner, the end flange 48 has an upwardly-directed
surface 54 with an area A.sub.3. Below the shoulder 52 an opening
56 is provided in the pipe 44. Packers 51 and 53 mounted in the end
flange 48 and the upper part respectively provide a seal against
the pipe's outer surface 38.
[0029] The surfaces 33, 38, 45 and 54 define a first piston chamber
60, which via the holes 39 is connected with the interior of the
riser. When the upper part of the telescopic joint moves relative
to the lower part, the volume changes in the riser will be
compensated for in the chamber 60. The surfaces 38, 34, 45 and 52
define a second piston chamber 62, which via the hole 56 is
connected with a line 70, which in turn connects the chamber 62
with a device for regulating pressure and volume in the piston
chamber 62. The fluid line 70 leads to a reversible valve 72, which
can be regulated between two positions. In the valve's first
position the line 70 is connected with a fluid reservoir 80 via a
line 74. A controlled throttle valve 75 is advantageously mounted
in the line 74. Since the fluid reservoir is at atmospheric
pressure, in the said first position the chamber 62 with the valve
can thereby be vented to the environment and the heave compensator
is in its passive mode.
[0030] In the second position the line 70 is connected with a
circuit comprising a first line 76 that is connected with the fluid
reservoir 80. A controlled pressure-regulating valve, for example a
throttle valve 77, is mounted in the line 76. In the second line 78
a pump 82 is mounted. The pump 82 is driven by a motor 83. The pump
82 is supplied with fluid from the reservoir 80 via the line 84. An
accumulator 83 is advantageously provided in the line 78 for
equalising minor pressure pulses during start-up and stopping of
the pump 74. A pressure-controlled check valve 85 is advantageously
mounted in the line 78.
[0031] A number of sensors are mounted in connection with the heave
compensating system. These comprise a pressure sensor 91 in
connection with the chamber 60 and a flow meter 92 in the line 70.
Furthermore, the control unit 90 receives signals from the DP
system 93 and from a heave sensor 94 as previously mentioned. The
heave sensor 94 may be an accelerometer, a length meter or a
position sensor. The values from these measurements are transmitted
to the control unit 90. As previously mentioned, the control unit
comprises a programmable unit that processes the said signals and
in response thereto controls the pump 82, the control valve 72 and
the throttle valves 75 and 77.
[0032] The telescopic joint is so designed that it is volume and
force-compensated. This is achieved by designing the chamber 60 in
such a way that the area A.sub.3 is approximately equal to the area
A.sub.1 corresponding to the pipe's 10 internal cross sectional
area, which in turn is the theoretical area that is formed by the
closed top of the riser, indicated in FIG. 2 by the line 27. Since
the riser is at all times under well pressure, it must be closed at
the upper end in order to avoid blow-out; in reality this is in the
area of the surface Christmas tree, but for the sake of clarity it
is illustrated by the dotted line 27.
[0033] Changes in fluid volume in the riser are compensated for by
the ability of fluid to flow in and out of the chamber 60. The
riser is thereby pressure balanced, thus preventing the occurrence
of pressure pulses as a result of the volume changes caused by
heave movements. When ventilated to the environment, the chamber 62
can act as passive length compensation. In the case of active
compensation, fluid is pumped into the chamber in response to the
movements in the platform and controlled in the control unit.
[0034] In addition, in the event of emergency disconnection or
fracture of the riser, the chamber 42 can be controlled so as to
cushion a recoil caused by the upwardly-directed force in the
riser, thereby preventing the telescopic joint from touching the
bottom and causing damage to the platform.
[0035] When the system is placed in passive mode, i.e. when the
chamber 62 is ventilated to the environment, the heave compensator
behaves like a standard type of heave compensator, as is also known
from NO 169 027. When the system is run in active mode, it will be
possible to choose between synchronising the top of the riser with
the platform deck or controlling it so that a tool in the well can
stand still in one position, thus permitting operations that
require this to be performed in the well. The control system for
the telescopic joint may also be programmed to keep the surface
Christmas tree at a predetermined height above deck, thus enabling
operations to be carried out while the operator is in a safe
position. The system may be provided with an alarm that gives a
warning when there is a risk of the Christmas tree moving outside
of fixed limits.
[0036] A further function of the invention is that the traditional
tension-based heave compensating system can either be replaced by
or combined with the active control of the pressure in the chamber
62. An increase in the pressure in the chamber 62 will give an
increased tension in the riser and this can be employed as an
alternative heave compensating system.
* * * * *