U.S. patent application number 12/999892 was filed with the patent office on 2011-07-07 for flow line electric impedance generation.
This patent application is currently assigned to EXPRO NORTH SEA LIMITED. Invention is credited to Steven Martin Hudson.
Application Number | 20110163830 12/999892 |
Document ID | / |
Family ID | 41202745 |
Filed Date | 2011-07-07 |
United States Patent
Application |
20110163830 |
Kind Code |
A1 |
Hudson; Steven Martin |
July 7, 2011 |
FLOW LINE ELECTRIC IMPEDANCE GENERATION
Abstract
A flowline electrical impedance generation apparatus for
generating a local electrical impedance in a metallic tubing
portion of a flowline may be used in place of insulation joints in
various systems. The impedance generation apparatus is tuned or
tuneable to achieve maximum impedance at chosen frequencies, i.e.,
frequencies which it is desired to block.
Inventors: |
Hudson; Steven Martin;
(Dorset, GB) |
Assignee: |
EXPRO NORTH SEA LIMITED
Berkshire
GB
|
Family ID: |
41202745 |
Appl. No.: |
12/999892 |
Filed: |
June 16, 2009 |
PCT Filed: |
June 16, 2009 |
PCT NO: |
PCT/GB09/01501 |
371 Date: |
March 2, 2011 |
Current U.S.
Class: |
334/17 |
Current CPC
Class: |
E21B 47/12 20130101;
G01V 11/002 20130101; E21B 34/066 20130101 |
Class at
Publication: |
334/17 |
International
Class: |
H03J 3/20 20060101
H03J003/20 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 18, 2008 |
GB |
0811223.7 |
Jun 18, 2008 |
GB |
0811224.5 |
Claims
1. Flowline electrical impedance generation apparatus for
electromagnetically generating a local electrical impedance in a
metallic tubing portion of a flowline, wherein the impedance
generation apparatus is one of tuned and tuneable to generate a
maximum impedance to signals at a chosen frequency.
2. Flowline electrical impedance generation apparatus according to
claim 1 which comprises a generally toroidal portion of magnetic
material for surrounding the tubing portion.
3. Flowline electrical impedance generation apparatus according to
claim 2 in which a winding is provided on the toroidal portion of
magnetic material.
4. Flowline electrical impedance generation apparatus according to
claim 3 in which the winding is connected to at least one impedance
component which is chosen so that the impedance seen in a tubing
portion passing through the toroidal portion of magnetic material
varies with frequency.
5. Flowline electrical impedance generation apparatus according to
claim 4 in which the impedance component comprises a capacitor
connected in series with the winding.
6. Flowline electrical impedance generation apparatus according to
claim 4, in which the impedance generation apparatus comprises a
plurality of impedance components which are selectively
electrically connectable with the winding to alter a resonant
frequency of the system and hence tune the local electrical
impedance.
7. Flowline electrical impedance generation apparatus according to
claim 1 which is arranged to be mounted on the tubing portion such
that tubing may run uninterruptedly through or past the impedance
generation apparatus when installed and in use.
8. Flowline electrical impedance generation means according to
claim 1 which comprises a control unit for controlling the
generation of the local electrical impedance.
9. Flowline communication apparatus for use where metallic tubing
of a flowline system is used in a signal path, the apparatus
comprising: impedance generation apparatus for electromagnetically
generating a local electrical impedance in a metallic tubing
portion of a flowline in the flowline system, wherein the impedance
generation apparatus is one of tuned and tuneable to generate a
maximum impedance to signals at a chosen frequency; and a
communications unit comprising at least one of a transmitter for
transmitting signals into the tubing portion across the local
electrical impedance and a receiver for receiving signals across
the local impedance from the tubing.
10. Flowline communication apparatus according to claim 9, which
comprises a control unit for controlling the impedance generation
apparatus to control the local electrical impedance.
11. Flowline electrical impedance generation means according to
claim 8, in which the control unit is arranged to tune the
impedance to the frequency of signals being sent and/or
received.
12. Flowline electrical impedance generation means according to
claim 8, in which the control unit is arranged to selectively
enable and disable the impedance generation apparatus to control
whether a local electrical impedance is generated.
13. Flowline communication apparatus according to claim 11 in which
the impedance generation apparatus is arranged to generate an
impedance which is tuned or tuneable to the frequency of the
signals to be transmitted and/or received across the local
impedance.
14. Flowline communication apparatus according to claim 10, in
which the control unit is arranged to measure one of: received
signal strength from the tubing and the local electrical impedance
in the tubing, and arranged to control the impedance generation
apparatus so that at the signalling frequency, the signal strength
or impedance respectively tends towards a maximum.
15. Flowline communication apparatus according to claim 9
comprising a spaced pair of electrical contacts for contacting with
tubing so as to connect the transmitter and/or receiver across the
local impedance.
16. A flowline arrangement comprising a metallic tubing portion and
impedance generation apparatus as claimed in claim 1.
17. A flowline communication arrangement comprising flowline
communication apparatus as claimed in claim 9 and a length of
tubing.
18. A flowline arrangement according to claim 16, in which the
impedance generating apparatus is mounted on or around tubing, and
insulation is provided on the outer surface of the tubing in
regions on both sides of the impedance generating apparatus or
where the tubing on which the impedance generating apparatus is
mounted is itself provided within a second length of tubing,
insulation is provided between the two lengths of tubing in regions
on both sides of the impedance generating apparatus.
19. A flowline communication arrangement according to claim 17
disposed for communicating between metallic tubing in a main bore
hole and metallic tubing in a lateral which is not electrically
connected to the metallic tubing in the main bore.
20. A flowline communication arrangement according to claim 17
disposed for use in drill stem testing.
21. A flowline arrangement according to claim 16, in which the
impedance generation apparatus is provided in a well installation
including a communication system arranged to transmit signals at a
predetermined frequency and having a riser leading away from a well
head, the impedance generation apparatus being disposed around the
riser.
22. A flowline power transmission apparatus set comprising a master
unit arranged for applying power to metallic tubing of a flowline
system and at least one other unit arranged to extract power from
metallic tubing of a flowline system, the at least one other unit
comprising an impedance generation apparatus for
electromagnetically generating a local electrical impedance in a
metallic tubing portion of a flowline, wherein the impedance
generation means is tuned or tuneable to generate a maximum
impedance to signals at a chosen frequency and is arranged to
generate an impedance across which power can be extracted in
use.
23. A flowline power transmission apparatus according to claim 22
in which the master unit is arranged to selectively apply power
signals having one of a plurality of predefined frequencies.
24. A flowline power transmission apparatus according to claim 23
in which there is a plurality of said other units each of which has
an assigned predefined frequency and each being arranged to extract
power only when a signal having the respective predefined frequency
is detected at that unit.
25. A flowline power transmission apparatus according to claim 23
in which each other unit is arranged to activate the impedance
generation apparatus to allow the extraction of power on detection
of a signal having a respective predefined frequency.
26. A flowline power transmission apparatus according to claim 22,
in which the master unit comprises a power generation source.
27. A flowline power transmission system comprising a flowline
power transmission apparatus set according to claim 22 and a
flowline on which the apparatus set is installed.
28. Flowline communication apparatus for use where metallic tubing
of a flowline system is used in a signal path, the apparatus
comprising a toroidal portion of magnetic material for location
around a length of metallic tubing and a winding wound around the
toroidal portion of magnetic material and connected to at least one
impedance component chosen so that an impedance seen in a metallic
tubing portion passing through the toroidal portion of magnetic
material varies with frequency and a communications unit comprising
at least one of a transmitter for transmitting signals into the
length of metallic tubing across a portion of the tubing passing
through the toroidal portion of magnetic material and a receiver
for receiving signals, from the length of metallic tubing, across a
portion of the tubing passing through the toroidal portion of
magnetic material.
29. A downhole communication system for communicating between
metallic tubing in a main bore hole and metallic tubing in a
lateral bore hole which is not electrically connected to the
metallic tubing in the main bore, comprising a transmitter for
applying signals to the metallic tubing in the main bore so that
signals pass into the surrounding formation and towards the lateral
bore and flowline communication apparatus according to claim 28
provided in the lateral bore for extracting signals from the tubing
in the lateral bore, the signals in the tubing in the lateral bore
having been generated by the signals passing through the
surrounding formation.
30. A drill stem testing system comprising, a length of metallic
tubing supporting a drill bit, a downhole sensor for sensing a
downhole parameter, and a communication system for transmitting
data from the downhole sensor to the surface, the communication
system comprising flowline communication apparatus according to
claim 28 for injecting signals representing said data into the
drill supporting metallic tubing for transmission towards the
surface.
31. Flowline electrical impedance generation means for
electromagnetically generating a local electrical impedance in a
metallic tubing portion of a flowline, wherein the impedance
generation means is tuned or tuneable to generate a maximum
impedance to signals at a chosen frequency.
32. A downhole communication system for communicating between
metallic tubing in a main bore hole and metallic tubing in a
lateral bore hole which is not electrically connected to the
metallic tubing in the main bore, comprising transmitting means for
applying signals to the metallic tubing in the main bore so that
signals pass into the surrounding formation and towards the lateral
bore and flowline communication apparatus according to claim 28
provided in the lateral bore for extracting signals from the tubing
in the lateral bore, the signals in the tubing in the lateral bore
having been generated by the signals passing through the
surrounding formation.
Description
[0001] This invention relates to flow line electrical impedance
generation, in particular to devices for generating electrical
impedance in flow lines and communication apparatus and systems for
communicating in flow line structures where tubing portions of the
flow line structure are used as part of a signal path.
[0002] The present methods and apparatus are of particular interest
in the oil and gas industry where flow lines are used for
transporting product (oil and/or gas) up out of wells and away from
wells either along, for example, a sea bed or along the land
surface. In each situation metallic tubing is provided through
which the product flows, be this, for example, "casing", "lining",
or "production tubing" down hole in a well or a "pipeline" along a
seabed or the earth's surface. In this specification the word
"tubing" is used to cover all such metallic tubing.
[0003] In various situations it can be desirable to provide an
insulation joint between two lengths of tubing so that a first of
the lengths of tubing is electrically isolated from a second of the
lengths of tubing. As a particular example, there are various
existing systems for communicating in flow line systems where the
metallic structure of the flow line, that is to say the tubing, is
used as a signal channel for carrying electrical signals. Such
communication systems are useful in allowing the transmission of
data from, for example, down hole in a well to the surface. Such
data may relate to parameters which are measured in the well such
as pressure and/or temperature.
[0004] Insulation joints can be used in such communication systems
to provide a mechanism for applying signals onto the metallic
structure within the well or extracting signals from within the
metallic structure within the well. In particular some form of
transmitter or receiver may be connected across the insulation
joint.
[0005] An example of such a communication system using this type of
mechanism to extract signals from and inject signals into a subsea
oil pipeline installation is described in one of the inventor's
earlier patents U.S. Pat. No. 5,587,707.
[0006] Whilst transmitting or receiving signals across an
insulation joint can work well in many circumstances there are
situations where it is not possible to introduce an insulation
joint into such tubing. It will be appreciated that in at least
some circumstances there can be significant pressures or other
loads which will be experienced by the tubing in flow lines used in
the oil and gas industry and therefore the introduction of an
insulation joint can be undesirable or impossible. The introduction
of such a joint may degrade the structural integrity of the
metallic tubing.
[0007] It is an aim of the present invention to provide a way to
avoid the introduction of a physical insulation joint whilst still
giving at least some of the functionality that may be given by a
physical insulation joint.
[0008] According to the present invention there is provided
flowline electrical impedance generation means for generating a
local electrical impedance in a metallic tubing portion of a
flowline.
[0009] There may be a flow line arrangement comprising a metallic
tubing portion and impedance generation means as defined above.
[0010] The impedance generation means may be arranged to
electromagnetically generate the local electrical impedance. The
impedance generation means may be arranged so as to not impair the
structural integrity of the tubing with which it is used. The
impedance generation means may be structurally distinct from the
tubing with which it is used. The impedance generation means may be
arranged to generate the local electrical impedance in the tubing
without modifying the dimensions or materials of the tubing in that
region.
[0011] The impedance generation means may be arranged to be mounted
on the tubing portion. The impedance generation means may be
arranged to be mounted around the tubing portion. The impedance
generation means may be arranged so that tubing may run
uninterruptedly through or past the impedance generation means when
the apparatus is installed and in use.
[0012] The impedance generation means may be arranged so that the
value of the local electrical impedance is dependent on frequency.
The impedance generation means may be arranged so that the value of
the local electrical impedance is dependent on frequency and will
exhibit a maximum within a predetermined range of frequencies. This
means that the impedance generation means may be constructed so as
to generate a relatively high impedance to signals within a chosen
frequency range and a lower impedance to signals outside this
range.
[0013] Preferably the impedance generation means is arranged to
generate an impedance which is tuned or tuneable to a chosen
frequency of signals to be seen by the local impedance.
[0014] The impedance generation means may comprise a generally
toroidal portion of magnetic material for surrounding the tubing
portion. A winding may be provided on the toroidal portion of
magnetic material. This can allow the tubing portion to act as a
single turn winding in a transformer also comprising the toroidal
portion of magnetic material and said winding provided on the
toroidal portion of magnetic material.
[0015] Here it is to be understood that word toroidal is used in a
broad way to refer to any ring like shape that can encircle a
length of tubing--it is not relevant what shape the ring adopts nor
is it relevant what shape a cross-section through the material of
the ring has.
[0016] The winding may be connected to at least one impedance
component. The at least one impedance component may be chosen so
that the impedance seen in a tubing portion passing through the
toroidal portion of magnetic material varies with frequency. The
impedance component may comprise a capacitor connected in series
with the winding.
[0017] According to another aspect of the present invention there
is provided flowline communication apparatus for use where metallic
tubing of a flowline system is used in a signal path, the apparatus
comprising impedance generation means as defined above for
generating a local electrical impedance in a metallic tubing
portion and a communications unit comprising at least one of a
transmitter for transmitting signals into the tubing portion across
the local electrical impedance and a receiver for receiving signals
across the local impedance from the tubing.
[0018] According to another aspect of the present invention there
is provided a flowline communication arrangement comprising
flowline communication apparatus as defined above and a length of
tubing.
[0019] Preferably the impedance generation means is arranged to
generate an impedance which is tuned or tuneable to the frequency
of the signals to be transmitted and/or received across the local
impedance. Here the idea of tuning the impedance relates to
providing a maximum impedance at the signalling frequency to help
in the application and/or extraction of signals across the
impedance.
[0020] The flowline communication apparatus may comprise a control
unit for controlling the impedance generation means to control the
local electrical impedance. Where there is no communication
apparatus, the impedance generation means may have an associated
control unit. The impedance generation means may comprise a control
unit. The control unit may be arranged to tune the impedance to the
frequency of signals being sent and/or received. The control unit
may be arranged to selectively enable and disable the impedance
generation means to control whether a local electrical impedance is
generated.
[0021] Where the impedance generation means comprises a toroidal
portion of magnetic material carrying a winding, the impedance
generation means may further comprise a plurality of impedance
components which are selectively electrically connectable, for
example under control of the control unit, with the winding to
alter a resonant frequency of the system and hence tune the local
electrical impedance. There may be a plurality of capacitors
selectively connectable in series with the winding. The capacitors
may be connected in parallel relative to each other. The capacitors
may be connected such that each, or each of a subset of the
capacitors, can be selectively and independently switched into
series connection with the winding. The capacitors may be arranged
in a ladder network.
[0022] The impedance generation means may comprise active and/or
passive components.
[0023] The control unit may be arranged to measure one of: received
signal strength from the tubing and the local electrical impedance
in the tubing, and arranged to control the impedance generation
means so that at the signalling frequency, the signal strength or
impedance respectively tends towards a maximum.
[0024] The flowline communication apparatus may have a spaced pair
of electrical contacts for contacting with tubing so as to connect
the transmitter and/or receiver across the local impedance. The
apparatus may have one electrical contact disposed on a first side
of the toroidal portion of magnetic material and another electrical
contact disposed on a second side of the toroidal portion of
magnetic material.
[0025] The tubing may be used in the signal path as a transmission
medium and/or as an antenna.
[0026] Where the impedance generating means is mounted on or around
tubing, insulation may be provided on the outer surface of the
tubing in regions on both sides of the impedance generating means.
Where tubing on which the impedance generating means is mounted is
itself provided within a second length of tubing, insulation may be
provided between the two lengths of tubing in regions on both sides
of the impedance generating means.
[0027] Typically the tubing will be downhole tubing or pipeline
tubing as used in the oil and gas industry. Typically the tubing
will be for carrying fluid, generally oil and/or gas.
[0028] The flowline communication apparatus may be used in
communicating between metallic tubing in a main bore hole and
metallic tubing in a lateral which is not electrically connected to
the metallic tubing in the main bore. The communications apparatus
may pick up signals transmitted through the formation in which the
communications apparatus is disposed.
[0029] The flowline communication apparatus may be used as a relay
station for both receiving signals from and transmitting signals
into tubing.
[0030] The flowline communication apparatus may be used in drill
stem testing.
[0031] The impedance generation means may be used to block or
impede signals in a riser. The impedance generation means may be
provided in a well installation including a communication system
arranged to transmit signals at a predetermined frequency and
having a riser leading away from a well head, the impedance
generation means being disposed and arranged so as offer impedance
to transmission of signals of said predetermined frequency from the
well head into the riser. The impedance generation means may be
disposed around the riser. The impedance generation means may be
tuned to said predetermined frequency.
[0032] According to another aspect of the present invention there
is provided a flowline power transmission apparatus set comprising
a master unit arranged for applying power to metallic tubing of a
flowline system and at least one other unit arranged to extract
power from metallic tubing of a flowline system, the at least one
other unit comprising an impedance generation means as defined
above to generate an impedance across which power can be extracted
in use.
[0033] The master unit may be a master communications unit.
[0034] The at least one other unit may be a communications unit.
The communications unit may have one or more of the respective
optional features defined above.
[0035] The master unit may be arranged to apply power signals
having a predefined frequency. The master unit may be arranged to
selectively apply power signals having one of a plurality of
predefined frequencies.
[0036] The at least one other unit may be arranged to extract power
only when a signal having a predefined frequency is detected at
said other unit.
[0037] There may be a plurality of said other units each of which
has an assigned predefined frequency and each being arranged to
extract power only when a signal having the respective predefined
frequency is detected at that unit.
[0038] The or each other unit may be arranged to activate the
impedance generation means to allow the extraction of power under
predetermined conditions. The predetermined conditions may be the
detection of a signal having a respective predefined frequency.
[0039] The impedance generation means in the or each other unit may
be tuned or tuneable to said respective predefined frequency, so as
to provide high impedance to signals having that frequency.
[0040] The master unit may comprise power generation means. The
power generation means may comprise a turbine. The master unit may
comprise impedance generation means for generating an impedance
across which power can be applied in use.
[0041] According to another aspect of the invention there is
provided a flowline power transmission system comprising a flowline
power transmission apparatus set as defined above and a flowline on
which the apparatus set is installed.
[0042] The flowline may comprise a horizontal completion in an oil
and/or gas well.
[0043] According to another aspect of the present invention there
is provided flowline communication apparatus for use where metallic
tubing of a flowline system is used in a signal path, the apparatus
comprising a toroidal portion of magnetic material for location
around a length of metallic tubing and a winding wound around the
toroidal portion of magnetic material and connected to at least one
impedance component chosen so that an impedance seen in a metallic
tubing portion passing through the toroidal portion of magnetic
material varies with frequency and a communications unit comprising
at least one of a transmitter for transmitting signals into the
length of metallic tubing across a portion of the tubing passing
through the toroidal portion of magnetic material and a receiver
for receiving signals, from the length of metallic tubing, across a
portion of the tubing passing through the toroidal portion of
magnetic material.
[0044] According to another aspect of the present invention there
is provided a flowline communication system comprising a length of
tubing and flowline communication apparatus as defined above with
the communications unit disposed for transmitting signals into the
tubing and/or receiving signals from the tubing at a first location
and comprising another communications means for transmitting
signals into the tubing and/or receiving signals from the tubing at
a second location.
[0045] According to another aspect of the present invention there
is provided a well installation comprising metallic structure
including a length of tubing and flowline impedance generation
means as defined above.
[0046] According to another aspect of the present invention there
is provided a downhole communication system for communicating
between metallic tubing in a main bore hole and metallic tubing in
a lateral bore hole which is not electrically connected to the
metallic tubing in the main bore, comprising transmitting means for
applying signals to the metallic tubing in the main bore so that
signals pass into the surrounding formation and towards the lateral
bore and flowline communication apparatus as defined above provided
in the lateral bore for extracting signals from the tubing in the
lateral bore, the signals in the tubing in the lateral bore having
been generated by the signals passing through the surrounding
formation.
[0047] According to another aspect of the present invention there
is provided a drill stem testing system comprising, a length of
metallic tubing supporting a drill bit, a downhole sensor for
sensing a downhole parameter, and a communication system for
transmitting data from the downhole sensor to the surface, the
communication system comprising flowline communication apparatus as
defined above for injecting signals representing said data into the
drill supporting metallic tubing for transmission towards the
surface.
[0048] Embodiments of the present invention will now be described,
by way of example only, with reference to the accompanying drawings
in which:
[0049] FIG. 1 schematically shows a well installation including a
lateral bore and a communication system for communicating between
the main bore and the lateral bore;
[0050] FIG. 2 schematically shows part of the communication system
of the well installation shown in FIG. 1; and
[0051] FIG. 3 shows part of the arrangement shown in FIG. 2 in a
schematic circuit diagram form;
[0052] FIG. 4 shows one particular implementation of the circuit
components shown in FIG. 3;
[0053] FIG. 5 shows another particular implementation of the
circuit components shown in FIG. 3;
[0054] FIG. 6 shows a drill testing system comprising a
communication system;
[0055] FIG. 7 schematically shows a subsea well installation with a
communication system;
[0056] FIG. 8 schematically shows another well with a communication
system; and
[0057] FIG. 9 shows a communications unit of the system shown in
FIG. 8.
[0058] FIG. 1 schematically shows a well installation which well
has a main bore 1 and a lateral bore 2. As is well known in the oil
and gas industry when a well is drilled, holes are drilled into the
formation and these are lined with metallic tubing in one form or
another to form a flow line through which product from the well may
pass up the well to the surface.
[0059] The metallic tubing provided within the well may take
various forms. It may for example, be an outer casing and within it
an inner production tubing or drill stem tubing. In other
circumstances there may simply be a liner tubing which is provided
in the bore hole with no further tubing within it. All of these
different possible configurations might be used with the ideas of
the present invention and the details of such configurations is not
of particular interest in the present application. The present
invention is of interest in any of these situations where there is
metallic tubing be that "casing", "lining", "production tubing",
"drill stem tubing" or so on. Thus, whilst the word "tubing" can
sometimes have a special meaning within the oil and gas industry,
within this specification it is used generically to refer to any
tubular like length of metallic material.
[0060] In the well installation shown in FIG. 1, tubing in the form
of a casing 11 is provided in the main bore hole 1 and tubing in
the form of a liner 21 is provided in the lateral bore 2. Where the
lateral bore 2 joins into the main bore hole 1, there is an opening
or breakout in the casing 11 of the main bore 1. This opening is,
of course, there to allow product from the lateral liner 21 to pass
into the casing 11 for upwards transport to the surface. In the
present case and in general, there is no metal to metal contact
between the casing 11 in the main bore hole and the liner 21 in the
lateral. Rather the flow path for the product is completed by
cementing in the end of the liner 21 in the region where it meets
the casing 11. Such portions of cement 3 are schematically shown in
FIG. 1.
[0061] Thus there is a continuous conduit for product to flow from
the lateral bore 2 into the main bore 1, i.e. within the liner 21
and casing 11, but there is no metal to metal contact between the
liner 21 and the casing 11. Thus, there is no ready path for
electrical signals between the liner 21 and casing 11. This can
present difficulties when using communication systems which rely on
the transmission of electrical signals through the metallic
structure of the well. This is because there may be a desire to
transmit signals between equipment located in the lateral bore 2
and equipment located in the main bore 1 and/or the surface.
[0062] A potential solution to this problem is to look to detect
signals passing out into the formation F surrounding the bore holes
due to signals being transmitted into the metallic structure 11,
21. In this example, we considered a case where signals are
injected into the casing 11 at a region near where the lateral bore
2 joins the main bore 1 and from there (amongst other things)
propagate out into the formation F.
[0063] In the installation shown in FIG. 1, a downhole
communication tool 4 is provided in the casing 11 at a location
near to where the lateral bore 2 joins the main bore 1. This
downhole communication tool 4 is arranged for applying high
current, very low frequency, signals into the casing 11 via spaced
contacts 41. Such downhole tools are commercially available from
the Applicant. In a normal mode of operation, such a tool is used
to inject high current, very low frequency, signals into the
metallic structure 11 from where they propagate along the metallic
structure to another location where they may be detected by a
similar tool or at the surface. However, as this process occurs,
electro-magnetic signals E (which are only highly schematically
represented in the drawings) will also travel away from the tool 4
into the formation F surrounding the tool 4. (Of course, other
techniques may be used to inject signals into the formation F in
the region of the meeting point between the main bore 1 and the
natural bore 2.) This brings another possibility of using the
portion of the liner 21 close to the main bore 1 as an antenna for
picking up these signals.
[0064] A natural way to do this would be to introduce an insulation
joint in the length of tubing 21 near the main bore 1 so that there
are two portions of metallic tubing which are electrically
insulated/isolated from one another. In such a circumstance a
receiver (or a transmitter) may be connected across the insulation
joint to allow the reception (or transmission) of signals. However,
this is a circumstance where including an insulation joint in the
tubing is highly undesirable or impossible. This is due to the high
loads which will be exerted on the tubing 21 as it is pushed into
the lateral bore 2 to form the liner 21.
[0065] In the present communication system as shown in FIG. 1
rather than including an insulation joint in the liner 21, flow
line impedance generation means 5 is provided for generating a
local electrical impedance in the liner 21 which is much higher
than the impedance of the tubing alone. This gives rise to the
possibility of receiving signals across this local electrical
impedance created in the liner 21 (and also transmitting signals
across that impedance).
[0066] In the present communications system, a communications unit
6 is provided which comprises the flow line impedance generation
means 5 and a transceiver 61 for transmitting and receiving signals
across the impedance which can be generated by the impedance
generating means 5. The communication unit 6 also comprises spaced
contacts 62 for contacting with the metallic tubing 21 on either
side of the impedance generating means 5 and thus on either side of
the local impedance generated by the impedance generating means 5
in use.
[0067] FIG. 2 schematically shows the communication unit 6 in more
detail. In the present embodiment the transceiver 61 and impedance
generation means 5 are controlled by a control unit 63. This
control unit 63 is used in the present embodiment to control the
transmission and reception of signals from and to the communication
unit and might for example, also receive data from local sensors to
be included in messages to be transmitted.
[0068] Further, in the present embodiment the control unit 63
controls the behaviour of the impedance generation means 5. In
particular, it is arranged to control the frequency at which the
impedance generated by the impedance generation means is maximum.
This is done so that the local electrical impedance generated by
the impedance generation means 5 is most effective at the frequency
of the signals which are to be transmitted and/or received.
[0069] During reception of signals, maximisation of the signals
received may be achieved by monitoring the received signal
strength, varying the characteristics of the impedance generation
means 5 across a range and choosing the characteristics of the
impedance generation means 5 which give rise to the largest
received signal strength. As an alternative, the characteristics of
the impedance generation means 5 may be directly controlled in
response to a known or determined frequency of the signals to be
transmitted/received. As a yet further alternative, the impedance
actually generated in the portion of tubing passing through the
impedance generation means 5 might be measured and the
characteristics of the impedance generation means 5 varied until
this value is maximised.
[0070] It should also be said that in other alternatives the
impedance generation means 5 may not have this element of control
and rather just be designed and arranged to give a maximum
impedance at a pre-chosen frequency. To put this another way, it is
possible to either have the impedance generation means 5 pre-tuned
to give its best effect at a pre-chosen frequency or it is possible
to have the impedance generation means 5 "tuneable" so that it may
be actively "tuned" in use.
[0071] In the present embodiment, the impedance generation means 5
comprises a toroidal portion of magnetic material 51 which is
located around the tubing 21 in which the impedance is to be
generated. In practice this portion of magnetic material 51 may
have any shape which is suitable for surrounding the tubing 21. It
is shown only in highly schematic form in FIG. 2. There is no
requirement for the portion of magnetic material 51 to have an
overall circular shape or to have any particular cross section.
Moreover, the toroidal portion of magnetic material 51 may be
originally two half annular pieces of material which are joined
together around the tubing 21 or any other number of pieces which
are joined together around the tubing 21.
[0072] Furthermore, there may in fact be a multiple number of
toroidal pieces of magnetic material which are arranged axially
next to one another along the tubing 21.
[0073] In this embodiment a multi-turn winding 52 is wound around
the portion of magnetic material 51 and connected in series with at
least one impedance component 53. With this arrangement the winding
52, magnetic material 51 and tubing portion 21 passing through the
magnetic material portion 51 act as a transformer with the tubing
21 acting as a single turn.
[0074] Whilst the winding 52 could have a single turn as well, it
is generally found beneficial for this to be a multi-turn winding
in the present preferred uses, where very low frequencies are to be
used for transmission and reception. This is because the impedance
components 53 used to allow generation of impedance in the tubing
portion 21 will typically comprise capacitors and the capacitance
value of these capacitors necessary to tune the impedance
generation means 5 to the required frequency will be smaller where
a multi-turn winding 52 is used.
[0075] FIG. 3 schematically shows, in circuit diagram form, the
impedance generation means 5 and the transformer like arrangement
between the tubing portion 21 and the impedance components 53.
[0076] FIG. 4 schematically shows in circuit diagram form more
detail of the impedance generation means 5 of the present
embodiment where the impedance generation means 5 is tuneable. Here
the impedance components 53 comprise three capacitors 53a, 53b and
53c which are arranged in parallel with one another and are
connected to the winding 52. A first of the capacitors 53 is
connected in series with the winding 52 and is so connected at all
times. On the other hand the other two capacitors 53b, 53c are
connectable in parallel across the first capacitor 53a, but such
connection is controlled by respective switches 53d, 53e. Thus the
impedance generation means 5 is tuneable by the control unit 63
selectively operating the switches 53d, 53e to switch the second
and third capacitors 53b, 53c into and out of the circuit.
[0077] Such an arrangement may be used where it is known that a
number of predetermined different frequencies will be used for
transmission at different times or to allow tuning to obtain the
best possible signal in a particular implementation at a particular
time. Of course, in reality, a larger number of capacitive elements
may be provided as part of the impedance components 53 to give more
granular control. Furthermore, rather than using purely passive
components, active components can be used to provide similar
effects as part of the impedance components 53 in the impedance
generation means 5.
[0078] It will be appreciated that here what is being done is that
the impedance generation means 5 is being used in place of an
insulation joint to provide a block or at least significant
impedance against signals passing from one portion of the tubing 21
to the other portion of the tubing 21. Of course, in practical
terms, using such an impedance generation means 5, it is unlikely
to be possible to completely block the signal path between the two
portions of tubing 21 on either side of the impedance generation
means 51. However, such a complete block is not necessary to give
useful results. For example, in the present embodiment a
significant enough impedance may be generated in the tubing 21 to
allow the sending and receiving of signals.
[0079] It will be appreciated that in the bulk metal tubing of the
type used in the oil and gas industry then the impedance of a
length of tubing will be extremely low. Thus, the impedance which
is generated by the impedance generation means may, in absolute
terms, be quite low, but still be effective. For example, a
signalling circuit in these type of techniques where the metallic
flow line is used as a signal channel may have a circuit of
impedance of in the order of 5 milliOhms. It has been found that an
impedance generation means 5 of the type generally described with
respect to FIG. 2 can generate an impedance in the order of 50
milliOhms in the tubing in the region of the impedance generation
means. This then is massively higher than the impedance of the same
length of tubing 21 without the impedance generation means 5 in
place.
[0080] It may also be appreciated that even without the windings
52, or impedance components 51, the presence of a piece of magnetic
material 51 around the tubing 21 would cause some impedance in the
tubing 21. However, this impedance at the low frequencies generally
being used to transmit in such systems is generally too small to be
useful. The inclusion of suitable impedance components, for
example, even a single (correctly chosen) capacitor in series with
suitable windings 52 on the magnetic material 51 can dramatically
transform the impedance generated at the tuned frequency. Of
course, away from the tuned frequency the impedance generated may
be of no practical use, but this does not matter in a wide number
of circumstances.
[0081] FIG. 5 schematically shows, in circuit diagram form, a
simple form of impedance generation means 5 where the impedance
component 53 is a single capacitor 53f of a carefully chosen
capacitance value to match the frequency of signals which are to be
obstructed by the impedance generation means 5.
[0082] FIG. 6 schematically shows a drill stem testing system where
data concerning well parameters, for example, pressure are to be
transmitted from downhole to the surface. Here drill stem tubing
111 is provided in a main bore 101. A downhole mandrel tool 106 is
provided for collecting data readings concerning, for example,
pressure and transmitting this data towards the surface. The
downhole mandrel tool 106 comprises a communications unit 6 of the
same general type of that described above with reference to FIGS. 1
to 5. Thus again, an impedance generation means 5 is provided for
generating a local electrical impedance in the drill stem tubing
111 and a transceiver 61 is provided for transmitting and receiving
signals into and from the drill stem tubing 111 across the local
impedance generated by the impedance generation means 5. When
transmitting these signals are injected into the drill stem tubing
111 and travel up towards the surface.
[0083] However, in this circumstance due to the achievable signal
strength, repeater stations 107 are provided at locations along the
drill stem tubing 111 to receive the signals in the drill stem
tubing 111, amplify these and reapply them for onwards
transmission.
[0084] Each repeater station 107 comprises a communications unit 6
of a similar type to that described above. Here, however, in order
to increase the effectiveness of the reception and signalling
capabilities, a length of the drill stem tubing 111 is provided
with an outer insulating coating 111a for a region along either
side of the impedance generation means 5 and electrical contact to
the drill stem tubing 111 for the application and the reception of
signals is made at the remote ends of these insulated portions.
[0085] A surface transceiver 108 is provided for receiving the
signals transmitted by the downhole mandrel tool 106 after having
been passed up the drill stem 111 via the repeating stations 107.
The surface transceiver 108 has one terminal connected to the drill
stem tubing 111 and another terminal connected to ground.
[0086] FIG. 7 shows another situation where a impedance generation
means 5 of the type described above with reference to FIGS. 2 to 5
may be used. Here there is a subsea well 201 including a
communications system in which signals from downhole are
transmitted towards the surface along the metallic structure 211 of
the well 201. These signals are detected at the seabed by a seabed
transceiver 208 which has one connection to the metallic structure
211 of the well head/tubing near the surface and one connection to
earth. In isolation such a communication system has been proven to
work well.
[0087] However, this is a subsea well 201 where there is a metallic
riser 209 leading to a tethered vessel 291 at the surface. This
metallic riser 209 is provided to transport the extracted product
to the surface of the water at the tethered vessel 291 and,
together, the tethered vessel 291 and riser 209 have to accommodate
for changes in water level. At least partly because of this, the
riser 209 is generally a massive metal component. It may have a
wall thickness of three or four inches. This has the result that
signals in this riser 209, for example, environmental noise can
significantly effect the reception and transmission of signals
between the well 201 (and associated communication tools downhole)
and the sub-surface receiver 208. Electrically isolating the riser
209 from the well head would help to alleviate this problem.
However, this again is a circumstance where the provision of a
physical insulation joint is impractical.
[0088] Thus, in the present embodiment an impedance generation
means 5 of the same general type described above with reference to
FIGS. 2 to 5 is provided around the riser 209. This impedance
generation means 5 can be tuned to block, or at least significantly
attenuate, signals having frequencies which may interfere with the
well communication system. The impedance generation means 5 might
be tuned to block signals having a frequency where there is most
noise or alternatively, may be tuned to block the signals having
frequencies which correspond to transmission frequencies used in
the well communication system.
[0089] The impedance generation means 5 for use in such a situation
would most likely but not necessarily be statically tuned rather
than "tuneable".
[0090] FIG. 8 shows a further situation where impedance generation
means 5 of the type described above with reference to FIGS. 2 to 5
may be used. Here there is a well having a horizontal completion
301 and including a communications system in which signals are
transmitted along tubing 311 of the completion.
[0091] The present well also includes a power transmission system
for transmitting power from one location on the tubing 311 to
others. The power may be used for operating the communications
system and/or for other purposes.
[0092] A plurality of communications units 306 one of which is
shown in FIG. 9 and each of which is similar to that described with
reference to FIGS. 1 to 5 are provided at selected locations in the
well installation. For the sake of brevity no detailed description
of the structure of each communications unit 306 is given
here--however it is noted that most aspects of the structure and
operation of the communications units 306 are the same as that of
the communications unit 6 shown in and described with reference to
FIG. 2. The following description will rely on the description of
the communications unit 6 above where the structure and operation
are the same and make use of the same reference numerals to refer
to the corresponding parts of the present communications units 306
and concentrate on the differences.
[0093] Each of the communications units 306 comprises an impedance
generation means 5 of the type described above to facilitate the
application of and/or extraction of signals to and/or from the
tubing 311. In this embodiment the locations for the communications
units 306 are selected to be ones where it is desired to take
measurements of pressure and/or temperature. In general terms the
communications units 306 may be located wherever it is on the
tubing 311 that there is a desire for data communication--this may
be, for example, to monitor a parameter or to remotely control an
item.
[0094] A master communications unit 307 is disposed on the tubing
311 at a location spaced from the communications units 306. The
master communications unit 307 is similar to the communications
units 306 but also comprises power generation means 308 for
generating power which may be used by the communications
system.
[0095] Significant power can be required for signalling and/or
other operations and providing power at downhole locations is
always an issue. The present system aids in this by the provision
of what might be termed an integral power transmission system.
[0096] In the present embodiment the power generation means 308
comprises a turbine which is driven by flow of product (i.e. oil
and/or gas) in the tubing 311. Such a device is preferably located
in a region of high flow rate. Furthermore, the provision of such a
device to extract energy from the flow of product is likely to be
intrusive--for example it may be a hindrance to access to the well
by wireline. Thus it is desirable to minimise such interference to
normal operating of the well by minimising the number of locations
at which a power generation means is located.
[0097] In the present embodiment there is a single power generation
means 308 provided at the master communications unit 307 and power
is fed from there along the tubing 311 to the other communications
units 306 as will be described below.
[0098] This power transmission system is particularly useful in a
well with a horizontal completion as this generally means that
there is a significant length of tubing passing through the
reservoir R where there is often relatively high resistivity, and
power may be efficiently transmitted along that length of
tubing.
[0099] In the present embodiment each of the communications units
306 has its own power source 361--this may include a back up
battery and a rechargeable charge storage unit or just comprise a
rechargeable charge storage unit--eg a rechargeable battery, or
capacitor based device. However each communications unit 306 is
arranged to harvest power from the tubing 311 which is transmitted
by the master communications unit 307 to charge this device 361 and
perform its main functions.
[0100] Each of the communications units 306 has a impedance
generation means 5 tuned to generate a high impedance at a selected
respective frequency--in this embodiment there are three
frequencies f.sub.1, f.sub.2, f.sub.3. Furthermore, the master
communications unit 307 is arranged to selectively apply power
signals to the tubing 311 at these three frequencies f.sub.1,
f.sub.2, f.sub.3.
[0101] The control unit 63 in each communications unit 306 is
arranged to periodically monitor signals on the tubing 311.
[0102] In the absence of a signal having the frequency f.sub.1,
f.sub.2, or f.sub.3 assigned to that communications unit 306, the
control unit 36 maintains a break in the circuit of the winding 52
and impedance means 53 so that the impedance generation means 5 is
non-resonant (i.e. just resistive) such that any power signals on
the tubing 311 will pass substantially unimpeded.
[0103] However, on detection of a signal having the frequency
f.sub.1, f.sub.2, or f.sub.3 assigned to that communications unit
306, the control unit 36 makes the circuit between the winding 52
and impedance means 53 so that the impedance generation means 5 is
resonant and offers high impedance to the transmitted signal such
that power may be extracted across the impedance generation means 5
by the communications unit 6.
[0104] The harvested energy may be then used in making measurements
and/or signalling.
[0105] The control unit 36 may be arranged to send a signal back to
the master communications unit 307 when its power requirements have
been satisfied.
[0106] In an alternative rather than signals being transmitted at
different frequencies for each communications unit 306, a different
mechanism may be used to control whether a particular
communications unit 306 should be harvesting power. For example
each communications unit 306 may extract power at a chosen time, in
response to a chosen signal (e.g. an address), on detecting that no
other unit is extracting power or so on.
[0107] The master communications unit 307 may apply signals to
and/or extract signals from the tubing 311 across an impedance
generation means 5, or in a different way--for example across a
conventional insulation joint.
[0108] Further it should be noted that a similar, but in most
circumstances less preferred, power transmission system might be
implemented without the use of any impedance generation means 5.
That is to say in an alternative there may be a master
communications unit 307 that transmits power along the tubing 311
which is selectively available to a plurality of communications
units 306 and one of the above techniques used to decide whether
this power can be harvested by a particular communications unit
306. Once such a determination is made, that communications unit
306 may connect in to extract the power. For this purpose each
communications unit may be located at a conventional insulation
joint which is usually electrically by-passed but can be put in to
operation by the respective communications unit 306, when it is
desired to signal and/or extract power.
[0109] It will be appreciated that the flow line impedance
generation means described above are arranged as resonant
devices.
[0110] As mentioned above the impedance generation means may be
arranged to be tuned or tuneable to particular frequencies. Another
way of expressing this is to say that the impedance generation
means may be arranged to resonate at a predetermined or a
selectively variable frequency. In, for example, FIG. 3 the winding
52 and impedance components 53 form a resonant circuit.
* * * * *