U.S. patent application number 10/275421 was filed with the patent office on 2003-06-05 for control cable.
Invention is credited to Grimseth, Tom.
Application Number | 20030103811 10/275421 |
Document ID | / |
Family ID | 19911111 |
Filed Date | 2003-06-05 |
United States Patent
Application |
20030103811 |
Kind Code |
A1 |
Grimseth, Tom |
June 5, 2003 |
Control cable
Abstract
The present invention relates to a cable for supplying chemicals
to, and for the control of, a sub-sea hydrocarbon well comprising
an external pressure pipe enclosing a number of smaller pipes, the
cable having the special features that the external enclosing pipe
forms a channel for the hydration inhibiting agent and in addition
forms an element that takes up mechanical tension in the cable,
protects the internal pipes against radial forces and forms a
nearly corrosion free environment protecting the smaller, internal
pipes.
Inventors: |
Grimseth, Tom; (Oslo,
NO) |
Correspondence
Address: |
WILDMAN, HARROLD, ALLEN & DIXON
225 WEST WACKER DRIVE
CHICAGO
IL
60606
US
|
Family ID: |
19911111 |
Appl. No.: |
10/275421 |
Filed: |
November 5, 2002 |
PCT Filed: |
May 7, 2001 |
PCT NO: |
PCT/NO01/00190 |
Current U.S.
Class: |
405/157 |
Current CPC
Class: |
E21B 34/16 20130101;
E21B 17/206 20130101; F16L 9/19 20130101 |
Class at
Publication: |
405/157 |
International
Class: |
E03B 007/10 |
Foreign Application Data
Date |
Code |
Application Number |
May 5, 2000 |
NO |
20002382 |
Claims
1. A method for supplying chemicals, such as hydrate inhibitor, to
a sub-sea hydrocarbon well and controlling the same, characterised
in that an outer pipe (31) is sufficiently strong enough to be led
through the same J-pipe, and possibly the same ditch along the
seabed, as a flowline, the hydrate inhibitor being led through an
open space between the inside of the outer pipe (31) and the
internal control lines (32, 33, 34).
2. A method according to claim 1, characterised in that said outer
pipe (31) is provided with a complete set of pipelines that provide
channels (32, 33) for electric cables (33) and/or hydraulic pipes,
as well as channels for chemical injection fluids.
3. A method according to claim 1 or 2, characterised in that said
outer pipe (31) forms a nearly corrosion free environment,
permanently protecting the smaller internal channels (32, 33).
4. A method according to one of the previous claims, characterised
in that said outer pipe (31) is provided with an external
protective sheath and/or a central element (35) able to take up
tensional forces, said central element (35) being provided with
said channels (32, 33).
5. Use of a per se known coiled tubing (31) as a control cable,
said coiled tubing being provided with a complete set of pipelines
that provide channels (32, 33), such as channels for electric
cables (33), hydraulic pipes and chemical injection fluids as well
as an open space for chemicals, such as hydrate inhibitors, between
the inside of the coiled tubing and the set of channels, said
coiled tubing (31) being strong enough to be led through the same
J-pipe, and possibly the same ditch along the sea bed, as a
flow-line.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a control cable (umbilical
cord) for sub sea field developments producing hydrocarbons,
especially sub sea installations tied back to a central production
platform by means of a flow line and an umbilical cord, where the
umbilical cord supplies the sub-sea production installation with
chemicals and control/monitoring functions.
STATE-OF-THE-ART
[0002] During the 25 years of developing sub sea petroleum
technology 2 types of sub sea control/service umbilical have become
commonplace.
[0003] I. So called bundled design, where a relatively large tube,
typically a 2" tube for hydrate inhibitor, is strapped to a cable
consisting of a number of small bore tubes and electrical
conductors, which are laid up in a helically twisted pattern, and
protected by an outer sleeve. Armour may be added as required.
[0004] This design is characterised by relatively moderate
material-and construction costs. The laying process is slowed down
by the requirement for strapping of several elements on deck during
deployment. Fig. I illustrates a typical design as described. The
design includes a tube for hydrate inhibitor Il, a saddle 12, on
outer sleeve 13, typically of polyethylene, an inner sleeve 13',
small bore tubes 14 for a variety of chemicals/hydraulic power,
separated from each other by means of saddles 18, an electrical
centre section 15 containing a quad 16, a strap 17 holding the
hydrate inhibitor Tube 11 with the cable containing the tubes 14
and centre section 15 and armour 19.
[0005] 2. A so-called integrated design characterised by a
requirement for lying of only one single element. This design is
based on the hydrate inhibitor tube being located in the centre of
the umbilical cord with small bore tubes and electrical cables
twisted around the centre tube in a symmetrical and helical
pattern. There is an industrial practice for using 25% Cr steel for
all tubes in order to resist corrosion caused by sea water
penetrating the interior of the umbilical cord. Particularly lines
for supply of hydraulic power fluid require high cleanliness
standards and consequently often leads to requirement for high
quality alloy steel.
[0006] A mixture of dissimilar metals may be disadvantageous in a
marine environment. This has often resulted in selection of high
quality expensive alloys for all tubulars in a sub sea control
umbilical. FIG. 2 illustrates a typical design. This design
includes centre tube 21 for hydrate inhibitor, small bore tubes 22
for chemicals/hydraulic fluid as well as quads 24, separated by
spacers 23, and an outer sleeve 25, typically made for
polyethylene.
[0007] Both the referred main types of design have been extensively
and successfully used for field development projects. For large
robust field developments the costs associated with construction
and installation are normally acceptable. However, in the tailing
end of the life of an oil province there will be a large number of
small hydrocarbon deposits to be developed by tie-back to existing
infra-structure. Such field developments may be viable but require
more cost effective designs than the developments of larger fields.
For development of marginal fields the referred techniques may be
associated with undesirable costs. The following patents are
referred to as representative of this technique:
[0008] NO 160389, GB 2246410 A, US 4709730, NO 304533. The referred
methods are considered of little relevance to control
cables/umbilical cords.
PURPOSE OF THE INVENTION
[0009] The objective of the present invention is to achieve tubes
and electrical optic cables accommodated inside of an outer carrier
pipe. Such design (bundled pipe) is common for flow line systems
for the purpose achieving temperature control of fluids in a flow
line. Separate pipes for heating water is added to one or more flow
lines accommodated inside an outer carrier pipe. Such bundles
cannot be reeled on to a lay barge, but are towed to the final
destination by several tugs.
[0010] It is the objective of the present invention to eliminate
the disadvantages identified for the referred techniques and it is
aimed at combining low construction cost with cost effective
installation techniques. The invention has probably an economical
limit related to the number of wells operated by means of a single
cable of the proposed
[0011] Design. It may typically be suitable for fields with 1-4
wells connected to a flow line and controlled by means of a single
cable (umbilical cord).
[0012] The invention is aimed at saving material cost, as only
lower and less costly steel quality is required due to the novel
design. For some scenarios significant costs may be saved
associated with installation of the cable. A further objective is
to achieve a well control module, which requires fewer control
lines (hydraulic) of lower capacity. This may be achieved by means
of a modification of the hydraulic circuitry of the well control
module.
BRIEF DESCRIPTIONS OF THE INVENTION
[0013] The objectives referred above are achieved by means of an
arrangement characterised by the features included in the
characterising part of claim 1. Further features are described in
the dependent claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] In the following there is a detailed description of the
invention with references to the enclosed drawings, where
[0015] FIG. 1 shows a service umbilical cord according to
state-of-the-art
[0016] FIG. 2 shows another service umbilical cord according to
state-of-the-art.
[0017] FIG. 3 shows a design of an integrated service umbilical
cord according to the present invention
[0018] FIG. 4 shows the principle for conventional hydraulic
control of a down hole safety valve, and
[0019] FIG. 5 shows a schematic of the hydraulic control circuits
of a control module according to the invention
DETAILED DESCRIPTION
[0020] The concept is based on use of a regular 2-4" pipe in carbon
steel as carrier pipe and conduit for hydrate inhibitor 31. This
pipe also provides mechanical protection, stress relief and
corrosion protection for all the internal components. All small
bore tubing such as conduits for supply of chemicals 32, conduits
for hydraulic power fluid (control system) and electrical
conductors 33 are accommodated inside the outer carrier 31. The
concept is illustrated in FIG. 3, where the carrier pipe 31
(hydrate inhibitor conduit) contains a conduit for low capacity
supply of chemicals, e.g. scale inhibitor or wax inhibitor, and an
electrical cable 33, e.g. a quad, metal clad. Additionally there is
provided a wire or a fibre rope 34 as well as a clamp/strap or
other form of bundling mechanism 35.
[0021] The reason for this design is that the carrier pipe may be
constructed from low cost carbon steel and protected against sea
water based corrosion by means of coating and anodes, typically
from zinc or aluminium as per standard sub sea design. The carrier
and small bore tubes require no protection against common hydrate
preventing chemicals, which are typically methanol or glycol.
Neither of the chemicals are good electrical insulators nor
function as electrolytes thus facilitating corrosion.
[0022] In such a medium a mixture of different metals may be
pursued without risk of corrosion thus facilitating selection of
material for each small bore tube according to service condition.
Control lines, for instance, are subject to extreme cleanliness
requirements, this has often resulted in selection of 22% Cr or 25%
Cr alloys for such service.
[0023] It may happen occasionally that there is a requirement for
bleeding back live hydrocarbons from the flow line through the
hydrate inhibitor line, such that the inner surface of the carrier
31 is exposed to corrosive well fluids. Such occurrences are rare
and mostly of short duration and does not involve corrosion of any
significance. Many operators do not include this facility at
all.
[0024] A key feature in this methodology is the choice of electric
conductors 33 and shielding against hydrate inhibitors, especially
methanol. It is known that methanol acts aggressively on some
isolators. It is therefore a requirement on control cables that all
materials are compatible with methanol. The production of electric
cable terminator penetrations in order to keep methanol away from
other electrical parts is also problematic. According to the
present invention, the electric conductors 33, preferably arranged
as quads, are laid down in welded diffusion resistant pipes with
welded connections at both ends. This entails that the methanol
only encounters extruded, rolled or welded metal surfaces along the
entire length of the service pipeline, including the
termination.
[0025] Such metal clad cables 33 are common in oil wells. They are
in particular used for down-hole instrumentation and are designed
for durable use in wells encountering high temperatures up to
150.degree. C., and are commonly available. Typical voltages are
2-3 kV, i.e. voltages above the normal choice for control systems
in sub-sea wells.
[0026] In the design practice followed in the North Sea, where the
multiphase transport usually is protected against hydrates in the
steady state by means of isolation and the maintenance of high
temperatures through the entire transport distance, the diameter of
the service pipeline only varies marginally for large or small
fields, since only one well is injected with hydrate inhibitors at
the time (Other oil fields may have may have other requirements and
needs for methanol).
[0027] However, the dimensions of all the other pipes and electric
conductors are dependent of the number of wells, e.g. the flow
capacity requirement for a small number of wells is smaller than
for a field with many wells being served by the same control cable.
Small fields only require pipes with small cross-sections as
compared to the length of the control cable. Since these pipes and
electric conductors occupy space in the external pipeline for
hydrate inhibitors and contribute to the reduction of the flow
capacity, the arrangement according to the present invention will
be especially suited for smaller fields. A larger number of larger
pipes placed in the external pipeline will lead to a
disproportionately large diameter of the external pipeline, driving
up the price of this pipe even if the applied material is
comparatively cheap.
[0028] A pipe-based design with the same pipe specifications as for
all other small pipes is usually applied for a control cable, in
order to maintain symmetry in design and of mechanic forces. This
often results in the guiding of low-dose chemicals, such as deposit
and wax inhibitors, through over-sized and thereby unnecessarily
expensive pipes (the dimension usually is decided by the largest
user, most often the low pressure supply to the control
system).
[0029] For high-pressure fields, the requirements for a relatively
large wall thickness of the external pipe increases, in addition to
the increased requirements for the small, internal pipes for
withstanding larger collapsing pressures. However, the requirement
for the internal pressure capacity will increase correspondingly
for all internal pipes (This also applies for the control system
described in this specification. Note that for a traditional supply
system with a separate pipes for control of the XMT-actuators, also
known as the 207 bar system, the requirements for internal pressure
will not increase. The system described here does not utilize a
separate 207 bar pipe). Therefore, it may be concluded, as also may
be shown by simple calculations, that the positioning of small
pipes in the hydrate inhibitor does not increase the requirements
for their wall thickness. The internal pressure is the deciding
factor. Small pipes usually have a higher capacity for external
pressures than for internal pressures. It is only the number and
the cross-sections of the internal pipelines that drive up the
dimension of the external pipeline in regard to a conventional
concept as shown in FIGS. 1 and 2.
[0030] The most important consideration in regard to a practical
implementation of a control cable of this kind is the fabrication
of the pipeline. Two methods may be used:
[0031] 1. Pulling the center element trough an already welded
external pipeline, or
[0032] 2. Fabrication of an external pipeline around the center
element.
[0033] 1. Pulling the Center Element Trough an Already Welded
External Pipeline
[0034] Several kinds of pipes suited as an external pipeline
according to the present invention are offered on the marked.
Industrial pipes, suited for a large number of umbilical operations
and high degrees of deformation without becoming oval, are offered
for umbilical applications. Such pipes are suitable for external
pipeline applications. 12 meter long pipes, typically seamless
pipes, are also delivered for butt welding from most of the larger
steelworks.
[0035] For pulling the center element 36 through the external pipe
one can envisage a pipe section of limited length being rolled out
on a flat surface, i.e. on shallow waters from a barge or from a
vehicle on land, e.g. a shut down railway or airport, such that the
pipe 31 rests perfectly straight and level. It will then be
possible to pull a center element trough an external pipeline
length 31. Typically, the external pipeline 31 is filled with
inhibited water, while the internal pipelines 32, 33 are filled
with air in order to reduce frictional forces.
[0036] The pulling wire 34 may be shot hydraulically through the
external pipeline 31 with the aid of a plug, while the external
pipeline 31 is filled with for example inhibited water. When the
central element 36 is pulled though the external pipeline 31, a
production length is completed. The assembly of the external
pipeline 31 and the central element 36 can be stored in a straight
configuration or coiled on a carousel or reel. The internal
friction in the coiled state will prevent large displacements of
the central element 36 with respect to the external pipeline 31.
Finally, the cable sections are joined together and the entire
cable is coiled up on a carousel or reel for later unrolling to an
installation carousel or reel on a laying vessel, alternatively the
entire cable is coiled up directly on an installation reel,
whereupon the latter is transferred to a laying vessel.
[0037] It is also possible to guide the bundle of internal pipes
32, 33 through a vertically positioned external pipeline 31, e.g.
on a barge. In this case, the pulling wire 34 probably may be
omitted entirely.
[0038] The joining of small pipes and metal clad, electric
conductors is a standard practice in the industry.
[0039] In an alternate embodiment, it would be advantageous to
fabricate an external pipeline 31 around the central element 36.
This will cut down the number of operation steps, but will also
require substantial capital investment for suitable equipment for
the production of suitable pipes and their welding. The welding of
pipes is known per se and will not be further elaborated.
[0040] The described concept implies a risk for tensioning the
central element 36 when the external pipeline is reeled, as it is
impossible to control that the that all the smaller pipes are
centered in the middle, even if the purpose of the shown radial
spacers is to center the smaller pipelines. This may be solved by
giving the central element 36, i.e. the small pipes 32 and electric
conductors 33, an undulating--or spiral configuration in the
lengthwise direction as compared to the middle point of the
external pipeline 31. Thereby the pipelines 32, 33 may be both
compressed and tensioned without imposing unnecessary stress and
strain.
[0041] A horizontally oriented pulling operation will automatically
result in some slack of the internal pipes 32 as a result of the
catinary suspension between the spacers 35(?).
[0042] The central element 36 may be arranged with a number of
parallel pipelines or as a spiral-configured bundle.
[0043] The described configuration is cost saving in regard
materials as compared to the established alternatives, shown in
FIGS. 1 and 2, in the following respects.
[0044] Hydrate inhibiting pipes of carbon steel without the need
for expensive alloys are used. This is shown in FIG. 2.
[0045] Only one cable has to be laid. No strapping operations
requiring stops are necessary. This is shown in FIG. 1.
[0046] Only a few small pipes and electric cables are necessary.
This is described above in regard with the rationalization of the
control system.
[0047] Robust outer surfaces on the cable are provided, typically
3.5-4 mm steel, that are well suited for the pulling in J-pipes.
This feature, together with electric conductors that are designed
for high temperatures, e.g. 150.degree. C., makes it possible to
lay down the cable in the same trench as the flow line, thereby
saving costs in regard to trenching, surveying and inspection,
which are the same activities as for the flow line (The laying time
does however increase somewhat as a result of the strapping
operation).
[0048] It is noted that it for conventional operations has not been
possible to install flow lines and control cables in the same
trench because the control cable has been prone to be damaged by
the flow line as a result of temperature effects, e.g. buckling,
and the fact that the outer surface of a conventional control cable
has a far weaker structure than the presently proposed embodiment.
Also, the most usual material used for electric isolation
(polyethylene) does not withstand high temperatures. However,
several projects have installed umbilicals that are strapped to the
flow line with good results.
[0049] As described above, a main feature of the present invention
is to keep the number of internal pipelines and their
cross-sections down. This is achieved by means of a minor
modification in the control module of each well, and is described
in the following.
[0050] Control Module
[0051] In a conventional control system it is usual to have two
supply lines (see FIG. 4 which shows one of them), one for high
pressure to the down-hole safety valve 47 and one for the 207 bar
pressure supply to the actuators 55 on the wellhead Christmas tree.
The high-pressure system 40 is characterized by a near zero fluid
flow. In principle, a high pressure may be generated by the
low-pressure system by means of a booster, and a low pressure may
be generated by the high-pressure system by means of a reduction
valve 50. Boosters are known to have been installed in new fields,
but are not very common. Pressure reduction valves are usually
avoided in the design of sub-sea control systems for hydrocarbon
installations, because they are considered to be unreliable.
[0052] However, a special valve 51 of the on/off-kind only used to
control a flow between two accumulators 42, 52 has been build and
tested. The valve 51 is developed by others and does not constitute
a part of the present invention. It comprises of a shear seal,
which is common in this kind of system and has proven to be
reliable, and two pilot steps for turning on and off the hydraulic
flow in the main unit. This kind of valve 51 has not been
implemented yet, probably because it requires a unusually large
accumulator 42 on the high pressure side 40 if it is to provide a
satisfactory control of the pressures in a larger installation, in
addition to that a series of error modes makes it unsuited for
larger installations. However, for marginal fields with small or no
interaction between the pressure supplies of the various wells,
this will not present large problems.
[0053] A marginal field will probably be allowed to spill smaller
amounts of water-based hydraulic fluids. This entails that the
entire well may be controlled by only one hydraulic pipeline.
[0054] It will therefore be possible to provide a supply system for
a marginal field that comprises one pipeline 32 for chemicals
(there may be need for more than one), one pipeline as a backup for
the two first, and a quad 33. A quad 33 provides a redundant
control for one well, and depending on the configuration it may
also provide some redundancy for more that one well. In addition,
metal clad optical fibers withstanding high temperatures may be
installed in the quad-unit 33 if real-time broadband instruments
are required. Optical fibers installed between the electric
conductors 33 will not increase the cross-section.
[0055] FIG. 4 shows the principle of a conventional hydraulic
control unit for a down-hole safety valve 47. The supply line 41
(innermost pipeline) with a connected accumulator 42, leads to a
control valve 45, which in turn is connected to the valve 49. The
circuit (somewhat simplified) is used by most suppliers.
[0056] FIG. 5 shows a schematic of the suggested hydraulic control
system of the control system. A fixed restriction 50 reduces the
flow between the high-pressure accumulator 42 and the low-pressure
accumulator 52 to practical values. The valve 51 is the one
referred to as two pilot steps controlled by the pressure in the
accumulator 42 and the accumulator 52 in the off or on mode. A
control valve 53 controls the valve 56 via the actuator 55, the
low-pressure accumulator 57 providing a stable pressure in the
spring chamber of the actuator. A non-return valve 54 allows
dumping of the used fluid to the sea. A pressure relief system 58
is similarly provided with a non-return valve 59 that dumps used
fluid to the sea.
[0057] The circuit functions in the following manner: The
high-pressure accumulator loads the low-pressure accumulator 52
when it has the capacity to do so, i.e. almost always. The pilots
in the valve 52 are loaded when the pressure falls bellow a certain
value. The loading stops when the pressure reaches its highest
allowed value, typically 207 bar.
[0058] A circuit like this will not be accepted for larger
installations, one of the reasons being that the high pressure may
propagate into the low-pressure system and harm its components in
case of accidents. This may be avoided by means of security
measures, e.g. the pressure relief system 58, but in larger
installations this measure is probably not sufficient in total
(i.e. production regularity). For 1-3 wells the risks may be
accepted by the operators under certain production conditions if
the capital cost is sufficiently reduced.
[0059] Conventional control cables often has a copper content that
is significantly higher than required in regard to the electric
losses in the system. This is due to the concerns like mechanic
strength and line control, the latter often being connected to
complex supply systems of both effect and control signals to wells
that are geographically spread out. The electric conductors 33
according to the present invention are metal clad and exhibit
extreme mechanic properties (even if these features primarily are
meant for protection against aggressive chemicals). If the actual
copper requirement (for an electric system) is to be the deciding
factor for the dimensioning of the supply system for 1-3
satellites, a considerable reduction of the copper content in, and
thereby also the cross-section of, the conductors will be
achieved.
* * * * *