U.S. patent application number 10/278556 was filed with the patent office on 2003-03-27 for power and signal transmission using insulated conduit for permanent downhole installations.
This patent application is currently assigned to SCHLUMBERGER TECHNOLOGY CORPORATION. Invention is credited to Babour, Kamal, Chouzenoux, Christian, Rossi, David.
Application Number | 20030058127 10/278556 |
Document ID | / |
Family ID | 10833736 |
Filed Date | 2003-03-27 |
United States Patent
Application |
20030058127 |
Kind Code |
A1 |
Babour, Kamal ; et
al. |
March 27, 2003 |
Power and signal transmission using insulated conduit for permanent
downhole installations
Abstract
An apparatus and method is presented for establishing electrical
connection to permanent downhole oilfield installations using an
electrically insulated conducting casing. Current is caused to flow
in the casing by a source on the surface connected to the casing.
One or more permanent downhole installations are electrically
connected to the casing, and the electrical connection to the
casing is used to power the downhole installations. The downhole
installations also inject a signal into the insulated casing that
passes via the casing to a surface readout which detects and
records the downhole signals.
Inventors: |
Babour, Kamal; (Bures sur
Yvette, FR) ; Chouzenoux, Christian; (Saint Cloud,
FR) ; Rossi, David; (Houston, TX) |
Correspondence
Address: |
Office of Patent Counsel
Schlumberger Oilfield Services
P.O. Box 2175
Houston
TX
77252-2175
US
|
Assignee: |
SCHLUMBERGER TECHNOLOGY
CORPORATION
|
Family ID: |
10833736 |
Appl. No.: |
10/278556 |
Filed: |
October 23, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
10278556 |
Oct 23, 2002 |
|
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|
09329543 |
Jun 10, 1999 |
|
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6515592 |
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Current U.S.
Class: |
340/854.3 ;
175/40; 340/854.6 |
Current CPC
Class: |
E21B 47/12 20130101;
E21B 17/028 20130101; E21B 47/13 20200501; G01V 11/002
20130101 |
Class at
Publication: |
340/854.3 ;
340/854.6; 175/40 |
International
Class: |
G01V 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 12, 1998 |
GB |
9812812.7 |
Claims
We claim:
1. A method for transmitting at least one electrical signal to or
from at least one downhole device in a well, the method comprising
the steps of: providing an electrically conductive conduit in the
well; electrically insulating a section of the conduit by
encapsulating a section of the conduit with an insulative layer and
insulating the encapsulated section of conduit from an adjoining
section of the conduit by a conduit gap; introducing the electrical
signal within the insulated section of conduit; providing a return
path for the electrical signal; and coupling the downhole device to
the insulated section.
2. The method of claim 1 wherein the step of introducing the
electrical signal is performed via inductive coupling.
3. The method of claim 1 wherein the step of introducing the
electrical signal is performed via direct coupling.
4. The method of claim 1 wherein the electrical signal includes
power signals.
5. The method of claim 1 wherein the electrical signal includes
communication signals.
6. The method of claim 5 wherein the step of introducing the
electrical signal is performed by one of the downhole devices.
7. The method of claim 5 wherein the step of introducing the
electrical signal is performed by a surface device.
8. The method of claim 7 further including the step of inductively
coupling the surface device to the insulated section of
conduit.
9. The method of claim 7 further including the step of directly
coupling the surface device to the insulated section of
conduit.
10. The method of claim 1 wherein the step of electrically
insulating a section of conduit further comprises the step of
disposing a second conduit gap to form a completely electrically
insulated conduit section.
11. The method of claim 10 further including the step of
inductively coupling the surface device to the insulated section of
conduit.
12. The method of claim 10 further including the step of directly
coupling the surface device to the insulated section of
conduit.
13. The method of claim 10 further including the step of
inductively coupling at least one of the downhole device to the
insulated section of conduit.
14. The method of claim 10 further including the step of directly
coupling at least one of the downhole devices to the insulated
section of conduit.
15. The method of any one of claims 1-14 wherein the return path
for the electrical signal is provided through the earth formation
surrounding the well.
16. The method of any one of claims 1-14 wherein the step of
providing a conductive conduit comprises providing electrically
conductive casing permanently installed in the well via
cementation.
17. The method of claim 16 wherein the cement is of a highly
conductive formulation.
18. The method of claim 16 or 17 wherein the return path for the
electrical signal is provided through the cement.
19. The method of claim 18 further including the step of retrieving
the electric signal from the insulated section of conduit.
20. The method of claim 19 wherein the step of retrieving is
performed by inductive coupling.
21. The method of claim 19 wherein the step of retrieving is
performed by direct coupling.
22. The method of claim 1 wherein the step of introducing the
electrical signal within the insulated section of conduit is
performed via coupling through a second conductive conduit.
23. The method of any one of claims 1-14 further including the step
of providing an outer electrically conductive layer on the
insulated conduit.
24. The method of claim 23 wherein the return path for the
electrical signal is through the outer conductive layer.
25. The method of any one of claims 1-24 wherein the conduit gap is
disposed within the insulative layer.
26. An apparatus for transmitting at least one electrical signal to
or from at least one downhole device in a well, the apparatus
comprising: an electrically conductive conduit installed in the
well; insulation means for electrically insulating a section of the
conduit, the insulation means comprising an insulative
encapsulation layer around the section of the conduit and a conduit
gap insulating the insulated section of the conduit from an
adjoining section of the conduit; means for introducing the
electrical signal within the insulated section of the conduit;
means for providing a return path for the electrical signal; and
means for electrically connecting the downhole device to the
insulated section of the conduit.
27. The apparatus of claim 26 wherein the means for introducing the
signal employs inductive coupling.
28. The apparatus of claim 26 wherein the means for introducing the
signal employs direct coupling.
29. The apparatus of claim 26 wherein the electrical signal
includes power signals.
30. The apparatus of claim 26 wherein the electrical signal
includes communication signals.
31. The apparatus of claim 30 wherein the electrical signal is
sourced by the downhole device.
32. The apparatus of claim 30 wherein the electrical signal is
sourced by a surface device.
33. The apparatus of claim 31 wherein the surface device is
connected to the insulated section via inductive coupling
34. The apparatus of claim 31 wherein the surface device is
directly coupled to the insulated section.
35. The apparatus of claim 26 wherein the insulation means further
comprises a second conduit gap disposed to form a completely
electrically insulated conduit section.
36. The apparatus of claim 35 wherein the surface device is
inductively coupled to the insulated section.
37. The apparatus of claim 35 wherein the surface device is
directly coupled to the insulated section.
38. The apparatus of claim 35 wherein the downhole device is
inductively coupled to the insulated section.
39. The apparatus of claim 35 wherein the downhole device is
directly coupled to the insulated section.
40. The apparatus of any one of claims 26-39 wherein the return
path for the electrical signal is through the earth formation
surrounding the well.
41. The apparatus of any one of claims 26-39 wherein the conductive
conduit comprises electrically conductive casing permanently
installed in the well via cementation.
42. The apparatus of claim 41 wherein the cement is of a highly
conductive formulation.
43. The apparatus of claim 41 or 42 wherein the return path for the
electrical signal is through the cement.
44. The apparatus of claim 43 further comprising means for
retrieving the electric signal from the insulated section of
conduit.
45. The apparatus of claim 44 wherein the means for retrieving
comprises inductive coupling.
46. The apparatus of claim 44 wherein the means for retrieving
comprises direct coupling.
47. The apparatus of any one of claims 26-46 wherein the means for
introducing the electrical signal within the insulated section of
conduit comprises a second conductive conduit.
48. The apparatus of any one of claims 26-39 wherein the conductive
conduit further comprises an outer electrically conductive
layer.
49. The apparatus of claim 48 wherein the return path for the
electrical signal is through the outer conductive layer.
50. The apparatus of any one of claims 26-49 wherein the conduit
gap is disposed within the insulative layer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] The present invention relates to monitoring and control of
subsurface installations located in one or more reservoirs of
fluids such as hydrocarbons, and more particularly to methods and
installations for providing wireless transmission of power and
communication signals to, and receiving communication signals from,
those subsurface installations.
[0003] 2. Related Background Art
[0004] Reservoir monitoring includes the process of acquiring
reservoir data for purposes of reservoir management. Permanent
monitoring techniques are frequently used for long-term reservoir
management. In permanent monitoring, sensors are often permanently
implanted in direct contact with the reservoir to be managed.
Permanent installations have the benefit of allowing continuous
monitoring of the reservoir without interrupting production from
the reservoir and providing data when well re-entry is difficult,
e.g. subsea completions. Permanent downhole sensors are used in the
oil industry for several applications. For example, in one
application, sensors are permanently situated inside the casing to
measure phenomenon inside the well such as fluid flow rates or
pressure.
[0005] Another application is in combination with so-called smart
or instrumented wells with downhole flow control. An exemplary
smart or instrumented well system combines downhole pressure
gauges, flow rate sensors and flow controlling devices placed
within the casing to measure and record pressure and flow rate
inside the well and adjust fluid flow rate to optimize well
performance and reservoir behavior.
[0006] Other applications call for using sensors permanently
situated in the cement annulus surrounding the well casing. In
these applications, formation pressure is measured using cemented
pressure gauges; distribution of water saturation away from the
well using resistivity sensors in the cement annulus; and seismic
or acoustic earth properties using cemented geophones. Appropriate
instrumentation allows other parameters to be measured.
[0007] These systems utilize cables to provide power and/or signal
connection between the downhole devices and the surface. The use of
a cable extending from the surface to provide a direct to
connection to the downhole devices presents a number of well known
advantages.
[0008] There are however, a number of disadvantages associated with
the use of a cable in the cement annulus connecting the downhole
devices to the surface including: a cable outside the casing
complicates casing installation; reliability problems are
associated with connectors currently in use; there is a risk of the
cable breaking; the cable needs to be regularly anchored to the
casing with cable protectors; the presence of a cable in the cement
annulus may increase the risk of an inadequate hydraulic seal
between zones that must be isolated; added expense of modifications
to the wellhead to accommodate the feed-through of large diameter
multi-conductor cables; the cables can be damaged if they pass
through a zone that is perforated and it is difficult to pass the
cable across the connection of two casings of different
diameters.
[0009] In efforts to alleviate these and other disadvantages of
downhole cable use, so-called "wireless systems" have been
developed.
[0010] Bottom electromagnetic telemetry allows for electrical
signals to be injected into conductive casings to create an
electrical dipole source at the bottom of the well in order to
telemeter measurement data from the subsurface to the surface. A
related idea uses currents in a casing segment downhole to
establish a magnetic field in the earth, the latter used to steer
another well being drilled.
[0011] Bottom switching as telemetry via casing and tubing or
wireline utilizes various arrangements of an electrical switch
downhole between casing and tubing, between casing and a wireline
tool, or between two electrically isolated segments of casing to
send downhole measurement data to a surface detection and recording
system.
[0012] Tubing-Casing transmission ("TUCAS"), a wireless two-way
communication system, developed and patented by Schlumberger (U.S.
Pat. No. 4,839,644 which is incorporated herein by reference), in
which an insulated system of tubing and casing serve as a coaxial
line as illustrated in FIG. 1. Both power and two-way signal
(communication) transmission are possible in the TUCAS system.
Because the system uses an inductive coupling technique to inject
or retrieve power and signal from the system, only on the order of
several tens of watts of power can be sent to the downhole sensor
devices, which is adequate for commercial pressure gauge sensors.
Additionally, electrical insulation between the tubing and casing
must be maintained.
[0013] Likewise, shortcomings are evident in known systems where a
toroid is used for current injection in casing or a drill string
which is in contact with a surrounding cement annulus or earth
formation. In addition to the limitations on the level of power
which can be inductively coupled, the current loop will be local as
the current return will seek the shortest electrical path through
the formation to return to casing, as illustrated in FIG. 2.
[0014] Another system using casing conductivity injects current for
locally heating the formation to help move viscous hydrocarbon
fluids. This system, as illustrated in FIG. 3, concentrates a large
current into a minimal area resulting in localized high current
density in the resistive earth, thereby generating heat. High
current density is seen in heated zone H while very low current
density is seen at surface return electrode R.
[0015] A simple surface return is utilized as there is no concern
with overall system efficiency as far as electrical circulation is
concerned. This type of system does not use the casing in
conjunction with downhole electronics, i.e. for communication with
or direct power transfer to downhole electronics, but rather
focuses on the generation of heat in the formation via
concentration of a large current flux at the end of the casing in
zone H. Insulation is employed for current concentration in zone H
by preventing injected current from flowing out of the casing to
the surrounding formation except where desired--i.e., at the bottom
of the well where the casing is exposed in zone H.
[0016] Several practical disadvantages are evident in such a system
as that of FIG. 3. One primary, and potentially dangerous
disadvantage is that the wellhead is necessarily maintained at a
very high potential in order to achieve the desired current density
at well bottom to generate sufficient formation heating for their
desired purposes. This can pose significant danger to the crew at
the well site.
SUMMARY OF THE INVENTION
[0017] Limitations of the prior art are overcome by the method and
apparatus of the present invention of power and signal transmission
using insulated casing for permanent downhole installations as
described hereinbelow.
[0018] The present invention is directed to various methods and
apparatus for transmitting at least one electrical signal to or
from at least one downhole device in a well. The method comprises
providing an electrically conductive conduit in the well,
electrically insulating a section of the conduit by encapsulating a
section of the conduit with an insulative layer and insulating the
encapsulated section of conduit from an adjoining section of the
conduit by using a conduit gap, introducing the electrical signal
within the insulated section of conduit, providing a return path
for the electrical signal, and connecting the downhole device to
the insulated section.
[0019] In alternative embodiments, the method includes introducing
the electrical signal is performed via inductive coupling and/or
direct coupling. The electrical signal includes power or
communication signals.
[0020] The electrical signals can be introduced by one of the
downhole devices or by a surface device, directly or inductively
coupled to the insulated section of conduit.
[0021] The method may also include use of a second conduit gap to
form a completely electrically insulated conduit section.
[0022] In the various embodiments, single or multiple devices may
be coupled to the insulated section of conduit.
[0023] The return path for the electrical signal may be provided
through the earth formation surrounding the well, through the
cement annulus or through an outer conductive layer of the
conductive conduit.
[0024] An apparatus is also disclosed for transmitting at least one
electrical signal to or from at least one downhole device in a
well. In various embodiments, the apparatus comprises an
electrically conductive conduit installed in the well, insulation
means for electrically insulating a section of the conduit, the
insulation means comprising an insulative encapsulation layer
around the section of the conduit and a conduit gap insulating the
insulated section of the conduit from an adjoining section of the
conduit, means for introducing the electrical signal within the
insulated section of the conduit, means for providing a return path
for the electrical signal, and means for electrically connecting
the downhole device to the insulated section of the conduit.
[0025] In alternative embodiments, the apparatus comprises
inductive coupling and/or direct coupling for introducing the
electrical power or communication signals.
[0026] The electrical signals can be introduced by one of the
downhole devices or by a surface device, directly or inductively
coupled to the insulated section of conduit.
[0027] The apparatus may also comprise a second conduit gap to form
a completely electrically insulated conduit section.
[0028] In the various embodiments, single or multiple devices may
be coupled to the insulated section of conduit.
[0029] The return path for the electrical signal may be provided
through the earth formation surrounding the well, through the
cement annulus or through an outer conductive layer of the
conductive conduit. The foregoing and other features and advantages
of the present invention will become more apparent in light of the
following detailed description of exemplary embodiments thereof, as
illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0030] The following drawings are referenced in the detailed
description which follows and are provided to facilitate a better
understanding of the invention disclosed herein.
[0031] FIG. 1 illustrates a known wireless transmission
apparatus.
[0032] FIG. 2 illustrates known behavior of induced current. FIG. 3
illustrates a known apparatus for earth formation heating.
[0033] FIG. 4 illustrates one embodiment of the present invention
using an insulated casing with direct uphole and inductive downhole
coupling.
[0034] FIG. 5A illustrates an alternative embodiment of the present
invention using an insulated casing with direct uphole and downhole
coupling. FIG. 5B illustrates the current path through the downhole
device of FIG. 5A.
[0035] FIG. 6 illustrates an alternative embodiment of the present
invention using insulated casing and production tubing with direct
uphole and downhole coupling.
[0036] FIG. 7 illustrates an alternative embodiment of the present
invention implemented with casing and/or tubing of different
diameters.
[0037] FIG. 8 illustrates an alternative embodiment of the present
invention implemented in a well having a lateral well and casing
and/or tubing of different diameters.
[0038] FIG. 9 illustrates one embodiment of the present invention
using an insulated casing with inductive uphole and downhole
coupling.
[0039] FIG. 10 illustrates one embodiment of the present invention
where downhole devices are connected in series downhole through use
of conduit gaps in the production tubing.
[0040] FIG. 11 illustrates an alternative embodiment of the present
invention where multiple downhole devices are connected in parallel
through use of conduit gaps in the production tubing.
[0041] FIG. 12A illustrates one embodiment of the present invention
where multiple downhole devices are connected in series downhole
through use of the conduit gap in the production tubing.
[0042] FIG. 12B illustrates the current path through the downhole
device of FIG. 12A.
[0043] FIG. 13 illustrates one embodiment of the present invention
where multiple downhole devices are connected in series downhole
through use of conduit gaps in the insulated casing.
[0044] FIG. 14 depicts an illustrative embodiment of the conduit
gap of present invention.
[0045] FIG. 15 illustrates an alternative embodiment of the present
invention using an outer conductive layer on the insulated casing
and inductive downhole coupling.
[0046] FIG. 16 illustrates an alternative embodiment of the present
invention using an outer conductive layer on the insulated casing
and direct (parallel) downhole coupling.
[0047] FIG. 17 illustrates an alternative embodiment of the present
invention using a highly conductive cement layer as the outer
conductive layer on the insulated casing and direct (parallel)
downhole coupling.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0048] Shown in FIG. 4 is an illustrative embodiment of the present
invention.
[0049] A well 1 (with direction of production flow in well
indicated by arrow) is drilled into earth formation 10 and
completed with an insulated conductive conduit 20 secured by a
cement annulus 40. While in this exemplary embodiment a production
well is shown, the invention is equally applicable to other types
of wells.
[0050] Conduit gap 11 is disposed within the conductive conduit so
as to provide 2 electrical zones of the conduit I and II, above and
below the gap, respectively.
[0051] In this embodiment, the conductive conduit is implemented as
a casing string 22 including casing segments 22A and 22B, region A
of the string 22 being insulated by insulative layer 30. The 2
electrical zones are effected by providing an electrical "gap"
between casing segments 22A and 22B where casing segment 22A is
electrically insulated from segment 22B by the gap. To fully effect
the electrical zones, insulative layer 30 should extend along
casing segment 22B beyond the gap 11 (i.e. to overlap segment 22A)
so as to electrically isolate adjacent casing segments 22A and 22B
from each other at the point of joining and throughout region A.
Details concerning conduit gap 11 follow in the discussion
associated with FIG. 14.
[0052] Above and below the electrically insulated region A of
segment 22B are exposed portions of casing, which form top and
bottom electrode portions, 70, 72 respectively. These portions are
exposed to allow electrical contact between these limited electrode
portions of the casing and surrounding annulus 40 and earth 10.
[0053] Surface equipment (including voltage source 24 and
encoder/decoder 25) is connected to casing string 22 via lines 60
and 61 on either side of conduit gap 11. The current is injected
via line 60 directly into casing segment 22B with a return
connection on line 61 connected to casing segment 22A. The injected
current will flow along illustrative current lines 12 through
casing segment 22B, leaking into annulus 40 and earth formation 10
via bottom electrode 72 and seek a return path to casing segment
22A through top (return) electrode 70 back to casing segment 22A
and to surface equipment via line 61.
[0054] At an appropriate depth in the well, measurement devices are
installed inside or outside the casing. Measurement devices,
typically sensors, measure a signal, related to a physical property
of the earth formation, well or reservoir, on either the interior
or exterior of the casing. For illustrative purposes, measurement
device 28 in FIG. 4 is shown installed outside casing 22.
[0055] The downhole electronics in device 28 receive electrical
power via induction from a toroidal transformer ("toroid") 26 on
the outside of the casing 22, specifically casing segment 22B. The
aforementioned injected current flowing through the casing segment
22B (here injected via line 60 as described above) inductively
generates a voltage in the toroid 26 by known electromagnetic
principles, used to power and communicate with the sensor. As is
known, various signals (including power and communication) can be
modulated on a single carrier current for transmission downhole via
injection. Toroid 26 can be fitted and installed on a segment of
casing 22 during casing manufacture, as can various measurement
devices intended for permanent installation.
[0056] For communication to surface, the signal sensed by device 28
is encoded into a second alternating voltage in toroid 26 by
downhole encoder circuit 27, at a frequency distinct from that of
the injected current. This second voltage induces a second current
in casing segment 22B, which also flows along illustrative current
lines 12 and is detected by a surface electronic detector 25 where
it is recorded, stored or otherwise processed as required.
[0057] Although not shown, multiple measurement devices (of the
same or different type) with encoding/decoding circuits, and/or
multiple toroids may be placed at various points (vertically) along
the insulated casing (i.e., throughout region A). This allows a
multitude of measurement devices to be distributed along the length
of the well to accomplish diverse measurements. The encoder/decoder
circuit 27 of each measurement device may additionally be equipped
with an addressable circuit that allows instructions to be sent to,
and measurement signals received from, individually controllable
measurement devices.
[0058] While a typical cement annulus 40 has conductive properties,
special highly conductive formulations of cement can be used to
increase the conductivity of the cement so as to provide a more
conductive path for currents. The use of highly conductive cement
formulations has the advantage of providing a return path with
controllable electrical characteristics. Use of specially
formulated highly conductive cement will aid in performance and
efficiency but is not critical and typical cement can none-the-less
be used.
[0059] As for all embodiments described herein, the permanently
installed conductive conduit includes at least an inner conductive
member and an outer insulative layer. The conductive member can be
either: 1) traditional metallic, preferable non-magnetic,
conductive casing; 2) conductive production tubing; or, 3) other
conductive liner installed permanently (usually via cementing)
downhole (such as those described with respect to FIGS. 15-17
hereinbelow). The conduit is circumferentially encapsulated by an
insulating layer over a specified region. For illustrative purposes
and without the intent of imposing limitation, the various
embodiments discussed herein utilize conductive casing or a
combination of casing and tubing as the conduit conductive member.
The insulating layer can be ceramic, plastic, fiberglass or other
material pre-applied to each casing section before it is shipped to
the wellsite for installation or, alternatively, the insulating
layer may be a coating, paint or wrapping pre-applied or to be
applied on-site at the wellsite. A current source and return path
are also provided as discussed with respect to the various
embodiments herein. In the various embodiments herein, top and
bottom electrode portions of the insulated conduit are exposed so
as to allow the conductive conduit to electrically contact the
surrounding cement annulus to provide a current source and return
path. The principle of operation of the present invention remains
unchanged regardless of the physical structure chosen as the
conduit, the implementation of the insulating layer, the current
source or return path.
[0060] FIG. 5A illustrates an alternative embodiment of the present
invention where direct coupling is used for both current injection
and connection to the downhole measurement device. Similar to the
embodiment of FIG. 4, the conduit is implemented as a casing string
22 including casing segments 22A, 22B and 22C. Conduit gap 11 is
placed within the casing string to provide electrical isolation
between adjoining casing segments 22A and 22B. Second conduit gap
110 is located between adjoining casing segments 22B and 22C to
provide electric zones I, II and III. The electric zones result
from the electrical "gap" between casing segments 22A and 22B, and
that between 22B and 22C, where casing segment 22A is electrically
insulated from segment 22B by gap 11 and 22B electrically insulated
from 22C by second gap 110. The insulative layer 30 extends beyond
each gap 11, 110 to completely electrically insulate casing segment
22B. Current will flow through the conductive cement annulus 40
(and surrounding earth formation 10) between zone III and zone I
(i.e., casing segments 22C and 22A) external to the insulated
conductive conduit of region A.
[0061] Surface equipment (including voltage source 24 and
encoder/decoder 25) is connected to the casing string 22 via a
lines 60 and 61. The current is injected via line 60 into casing
segment 22B with a return connection via line 61 connected to
casing segment 22A.
[0062] Communications with and power to device 28 are provided via
direct connection of downhole device 28 to casing 22 as illustrated
in FIG. 5B. Device 28 and casing segments 22B and 22C are connected
in series, with independent connections via leads 28A and 28B on
either side of gap 110 to casing segments 22B and 22C,
respectively. Current from casing segment 22B will flow through
device 28 to casing segment 22C.
[0063] Referring again to FIG. 5A, the injected current will flow
along illustrative current lines 12 through casing segment 22B,
through device 28 to 22C, leaking into annulus 40 via bottom
electrode 72 and seeking a return path to casing segment 22A
through top (return) electrode 70. The current injection
connection, via line 60 to casing segment 22B in both FIGS. 4 and
5A is achieved downhole locally within the insulated region A,
below gap 11. The return connection (via line 61 and casing segment
22A in both FIGS. 4 and 5A), on the other hand, can be achieved
downhole or alternatively near the surface without any diminished
performance as all casing segments above gap 11 back to the surface
are electrically connected. Direct downhole casing connections such
as discussed with respect to the embodiments of FIGS. 4 and 5A can
be achieved in any suitable manner to assure good (i.e., low loss,
efficient) electrical contact. One known technique is the use of
landing devices.
[0064] FIG. 6 shows an alternative embodiment of the present
invention where electrical connection for current injection is
achieved via direct connection to the conductive conduit and
production tubing.
[0065] Similar to the embodiment of FIG. 5A, the conductive conduit
is implemented as a casing string 22 which includes casing segments
22A, 22B and 22C. Conduit gap 11 is placed within the casing string
to provide electrical isolation between adjoining casing segments
22A and 22B. Second conduit gap 110 is disposed between adjoining
casing segments 22B and 22C providing electrical zones I, II and
III. The electric zones result because of the electrical "gap"
between casing segments 22A and 22B, and 22B and 22C, where casing
segment 22A is electrically insulated from segment 22B by gap 11
and 22B electrically insulated from 22C by second gap 110. The
insulative layer 30 extends beyond each gap 11, 110 to completely
electrically insulate casing segment 22B. Current will flow through
the conductive cement annulus 40 (and surrounding earth formation
10) between zone III and zone I (i.e., casing segments 22C and 22A)
external to the insulated conductive conduit of region A.
[0066] Tubing 18 is electrically isolated from the zone I and III
casing (i.e., the casing segments from surface down through and
including 22A and from and including 22C down to well bottom) by
any of several known techniques such as providing an insulative
layer around the tubing or an insulative layer on the inside of the
casing or non-conductive centralizers (not shown) can be deployed
in zones I and III. Tubing 18 is electrically connected to zone II
casing via appropriate means such as conductive packer 71. Where
insulated tubing is used the insulative layer must be traversed or
removed at conductive packer 71 to allow for electrical contact
with the casing (i.e., in the illustration, casing segment
22B).
[0067] Surface equipment (including voltage source 24 and
encoder/decoder 25) is connected to the tubing 18 via line 60 and
to zone I casing string via line 61. The current is injected via
line 60 into tubing 18 with the return connection on line 61
connected to the zone I casing segment (22A). Electrical connection
from tubing 18 to zone II casing segment 22B is achieved in this
embodiment through conductive packer 71.
[0068] Communication with and power transmission to device 28 are
achieved by direct connection of downhole device 28. Device 28 and
the casing segments 22B and 22C are connected in series, with
independent connections via leads 28A and 28B on either side of gap
110 to casing segments 22B and 22C, respectively. Current from
casing segment 22B will flow through device 28 on lead 28A to
casing segment 22C on lead 28B. The series connection is as
illustrated in FIG. 5B, discussed supra.
[0069] The injected current will flow along illustrative current
lines 12 in tubing 18 through conductive packer 71 to zone II
casing segment 22B, through device 28 to zone III casing segment
22C, leaking into annulus 40 via bottom electrode 72 and seeking a
return path to zone I casing segment 22A through top (return)
electrode 70.
[0070] The embodiment of FIG. 7 illustrates implementation of the
present invention across two conductive conduits of varying
diameter.
[0071] For illustrative purposes, an upper conduit section
comprising a casing string 22 with an insulative layer 30, is
connected electrically to a lower conduit section comprising
smaller diameter production tubing 221 with an insulative layer
301. Insulative layers 30 and 301 form an insulated region A. Note
that while it may be desirable to implement layers 30 and 301 as
one continuous layer, a minimal break B between the layers 30 and
301 is acceptable because leakage through this exposed area would
be negligible and not appreciably affect overall efficiency or
operation of the present invention. Casing/casing and tubing/tubing
conduit combinations are also possible as will be understood by one
of skill in the art.
[0072] Operation of this embodiment is similar to that of the FIG.
4 embodiment where current is injected via direct coupling on line
60 and downhole device 28 is inductively coupled to the conduit via
toroid 26. As in FIG. 4, injection (i.e., connection of line 60)
and toroid 26 must be disposed within insulated region A so as to
inject a current which is confined to flow in the conduit within
region A to inductively couple to toroid 26 also placed within
region A.
[0073] The embodiment of FIG. 8 illustrates the utility of the
present invention in a lateral (or "side-track") well.
[0074] As discussed with regard to FIG. 7, implementation can be
across conductive conduits of varying diameter. The illustrative
embodiment of FIG. 8 shows an upper conduit section comprising a
casing string 22 with an insulative layer 30 connected electrically
to a lower conduit section comprising smaller diameter production
tubing 221 with an insulative layer 301 (as in FIG. 7), and casing
222 and insulative layer 302 of a lateral well 2. Insulative layers
30, 301 and 302 form insulated region A as shown. Note that, as in
FIG. 7, while it may be desirable to have layers 30, 301 and 302 be
continuous, small breaks B between the layers is acceptable because
leakage through this exposed area would be minimal and not
appreciably affect overall efficiency or operation of the present
invention. Casing strings 22, 221 and 222 should be electrically
connected.
[0075] Operation of this embodiment is similar to that of the FIG.
7 embodiment where current is injected via direct coupling on lines
60 and 61 (above and below gap 11) and downhole devices 28 and 28'
are inductively coupled to the conduit via toroids 26 and 26'. As
in FIG. 7, injection (i.e., connection of line 60) must be within
insulated region A so as to inject a current which will flow in the
conduit within region A and likewise toroids 26 and 26' must be
placed within region A to capture the injected current.
[0076] Although not shown, addressable circuitry can be added to
the encoder/decoder circuit 25 of surface equipment and 27, 27' of
downhole devices 28 and 28' to effect independent communication and
control of the individual downhole devices.
[0077] Additional various combinations including direct downhole
device coupling and/or inductive injection coupling connections
will also be understood.
[0078] FIG. 9 illustrates one embodiment of the present invention
in which insulated casing and inductive coupling is used for
downhole power and two-way signal transmission.
[0079] Toroid 23 is used for current injection where a current is
induced in casing 22 within insulated region A. Toroid 23 is linked
to surface by a cable 60. Conduit gap 11 is used to form electrical
zones I and II as previously discussed.
[0080] At the surface, electrical current is injected into toroid
23 via source 24 through cable 60, thereby inducing a current in
casing 22 (by known electromagnetic principles). The induced casing
current flows along illustrative current paths 12 through the
casing 22 where, at the bottom of the casing, via bottom electrode
72, the current leaks into the cement annulus 40 and flows through
the annulus to the top (source and return) electrode 70.
[0081] Measurement device 28 receives electrical power from a
toroid 26 on the outside of the casing 22 via induction where the
aforementioned current flowing through the casing (here induced by
toroid 23 as described above) inductively generates a voltage in
the toroid 26 that is used to power the sensor. The toroid 26 can
be fitted and installed on segments of casing 22 during casing
manufacture, as can various measurement devices intended for
permanent installation.
[0082] The signal sensed by measurement device 28 is encoded into a
second alternating voltage in the toroid 26 by downhole encoder
circuit 27, at a distinct frequency from that of the first injected
current. This second voltage creates a second current in the casing
22, which also flows along illustrative current lines 12 and is
detected by a surface electronic detector 25 where it is recorded,
stored or otherwise processed.
[0083] Although not shown, multiple measurement devices (of the
same or different type) with encoding/decoding circuits, and
multiple toroids may be placed at various points along the
insulated casing. This allows a multitude of measurement devices to
be distributed along the length of the well to accomplish diverse
measurements.
[0084] The encoder/decoder circuit 27 of each measurement device
may additionally be equipped with an addressable circuit that
allows instructions to be sent to, and measurement signals received
from, individually controllable measurement devices.
[0085] Illustrated in FIG. 10 is an alternative embodiment of the
present invention where production tubing 18 is utilized as the
conductive conduit and conventional (uninsulated) casing 22 is used
as a return path for both communication with and power transmission
to a downhole device 28.
[0086] Operationally similar to the embodiments of FIGS. 5A and 6,
the conduit is implemented as production tubing string 18 including
tubing segments 118A, 18B and 18C. Conduit gap 111 is placed within
the tubing string to provide electrical isolation between tubing
segments 18A and 18B. Second conduit gap 112 is located between
tubing segments 18B and 18C to provide electrical zones I, II and
III. The electrical zones result from the electrical "gap" between
tubing segments 18A and 18B and 18B and 18C where tubing segment
18A is electrically insulated from segment 18B by gap 111 and 18B
electrically insulated from 18C by gap 112. Zone II tubing (i.e.,
tubing segment 18B) is maintained in electrical isolation from
casing 22 and is thus completely insulated electrically. This can
be achieved in any of several known techniques such as providing an
insulative layer around the tubing with the layer traversed or
removed at connection to device 28, or by using, for example
nonconductive centralizers (not shown) or non-conductive fluid in
the interior annulus (i.e., the space between the tubing and
casing) (not shown). Electrical connection is established between
tubing segment 18C and casing 22 through conductive packer 71 for
the current return path.
[0087] Surface equipment (including voltage source 24 and
encoder/decoder 25) is connected to the tubing segment 18B and
casing 22 via a lines 60 and 61, respectively. The current is
injected via line 60 into tubing segment 18B with a return
connection on line 61 connected to casing 22.
[0088] Direct connection of downhole device 28 to tubing 18 is used
to communicate and provide power to device 28. Device 28 and the
tubing segments 18B and 18C are connected in series, with
independent connections via leads 28A and 28B on either side of gap
112 to tubing segments 18B and 18C, respectively. Current from
tubing segment 18B will flow through device 28 to tubing segment
18C. The series connection is similar to that illustrated in FIG.
5B.
[0089] The injected current will flow along illustrative current
lines 12 through tubing segment 18B, through device 28 to tubing
segment 18C, through conductive packer 71 along a return path in
casing 22.
[0090] Direct downhole tubing connections such as discussed with
respect to the embodiments of FIG. 10 can be achieved in any
suitable manner to assure good (i.e., low loss, efficient)
electrical contact. One known technique is via landing devices. The
injection connection, via line 60 to tubing segment 18B must be
achieved downhole locally within zone II tubing. The return
connection (via line 61 and casing 22), on the other hand, can be
achieved downhole or alternatively near the surface without any
diminished performance.
[0091] Illustrated in FIG. 11 is an alternative embodiment of the
present invention as shown in FIG. 10 useful for connecting
multiple downhole devices. Here production tubing 18 is utilized as
the conductive conduit and conventional casing 22 are used for
communication with a downhole device 28 within the well.
[0092] The conduit is implemented as a production tubing string 18
including tubing segments 18A, 18B and 118C. Conduit gap 111 is
placed within the tubing string to provide electrical isolation
between tubing segments 118A and 18B. Second conduit gap 112 is
disposed between tubing segments 18B and 18C to provide electric
zones I, II and III. The electric zones result from the electrical
"gap" between tubing segments 18A and 18B and 11B and 18C where
tubing segment 18A is electrically insulated from segment 18B by
gap 111 and 18B electrically insulated from 18C by gap 112 to
completely insulate electrically tubing segment 18B.
[0093] Surface equipment (including voltage source 24 and
encoder/decoder 25) is connected to the tubing segment 18B and
casing 22 via a lines 60 and 61, respectively. A voltage is applied
via-line 60 into casing segment 18B with a return connection on
line 61 connected to casing 22. A differential voltage is thus
established between tubing segment 18B and casing 22.
[0094] Direct connection of downhole device 28 is used to
communicate with and provide power to device 28. Device 28 is
connected in parallel between the tubing segment 18B and casing 22.
Current from tubing segment 18B will flow through device 28 to
casing 22.
[0095] The current path will thus be along illustrative current
lines 12 through tubing segment 18B, through device 28 to a return
path along casing 22.
[0096] Direct downhole tubing-connections such as discussed with
respect to the embodiments of FIG. 11 can be achieved in any
suitable manner to assure good (i.e., low loss, efficient)
electrical contact. The voltage application connection, via line 60
to tubing segment 18B must be achieved downhole locally within the
zone II tubing (i.e., segment 18B). The return connection (via line
61 and casing 22), on the other hand, can be achieved downhole or
alternatively near the surface without any diminished
performance.
[0097] As in FIG. 10, the zone II tubing (i.e., segment 18B) should
be kept electrically isolated from the casing string 22.
[0098] FIG. 12A is an alternative embodiment of that of FIG. 10
useful for connection of multiple downhole devices.
[0099] This configuration allows for device-independent connection
to maintain integrity of the series connection in case of fault at
any one of the multiple devices.
[0100] The embodiment of FIG. 12A avoids direct connection of the
downhole device to the tubing 18 by implementation of an
intermediate transformer coil 128 across the two electrical zones
on either side of the conduit gaps. Here several gaps are used to
implement electrical zones I, II, III and IV, as shown. The coil
128 will allow current to flow freely around gap 112 through
consecutive tubing segments 18n+1 and 18n+2 or 18n+2 and 18n+3,
independent of the type of device deployed.
[0101] A representative current path is illustrated in FIG. 12B via
leads 128A and 128B.
[0102] Zone IV tubing is electrically connected to casing 22 via
appropriate means such as conductive packer 71. Where insulated
tubing is used the insulative layer must be traversed or removed at
conductive packer 71 to allow for electrical contact with the
casing. Conductive packer 71 will thus close the electrical circuit
between tubing 18 and casing 22. Zone II and III segments should
remain in electrical isolation from casing 22.
[0103] Downhole device 28 is then inductively coupled to coil 128
by a mating coil 228. Addressable circuitry can be included in
encoder decoder 27 to allow for independent control of individual
devices. Although only 2 such downhole devices 28 are shown, any
number can be deployed in this fashion, each in conjunction with a
conduit gap as shown.
[0104] FIG. 13 is an alternative embodiment of the present
invention as shown in FIG. 12A, illustrating application of the
present invention across casing segments.
[0105] Principles of operation of the embodiment illustrated in
FIG. 13 are similar to those described with respect to the
embodiment of FIG. 12A as will be understood by one skilled in the
art.
[0106] FIG. 14 depicts an illustrative embodiment of the conduit
gap of the present invention.
[0107] For illustrative purposes, the various conduit gaps as
discussed herein (with respect to FIGS. 4-13) are implemented as a
threaded sleeve 32 of insulative material such as resin, ceramic or
plastic, fitted between mating threaded conduit sections. In this
illustration, the conduit is casing string with the threaded sleeve
32 fitted between adjoining threaded casing sections 22n and 22n+1.
An outer insulative layer 30 is also provided in this embodiment
external to the conduit to overlap the joined sections 22n and
22n+1 to prevent electrical connection between the two conduit
sections via an external path, such as the surrounding cement or
earth formation.
[0108] Where direct connection is utilized for current injection
(such as illustrated in FIG. 14) and it is expected that conductive
fluids (such as salt water) may be produced in the well, insulation
on the interior of the conduit may be desirable to prevent a short
circuit path between the contact points (60a and 61a in FIG. 14)
through the conductive fluid. An inner insulative layer 303 around
the inner circumference of the conduit (shown as casing 22 in the
figure) is desirable. A minimum length 1.sub.c of layer 303 can be
calculated based on factors including the distance d.sub.c between
contact points 60a, 61a, the expected conductivity of the fluid and
the level of current to be injected (i.e., the potential expected
between points 60a and 61a). A maximum length is not critical
because a longer (than minimum) insulative layer 303 will result in
a gain in efficiency.
[0109] The manner in which electrical isolation of the conduit
sections is achieved is not essential and the implementation shown
in the illustrative embodiment is not intended to be restrictive.
It is important only to achieve the desired result of electrically
isolating two joined (i.e., consecutive) sections of conduit on
either side of the gap from each other.
[0110] FIG. 15 shows an alternative embodiment of the present
invention where the return circuit is provided by means of an
additional conductive layer 140 applied to the outside of the
insulating layer 130 on the conductive conduit, casing 122, forming
a three-layer conductor-insulator-conductor "sandwich". The
conductive layer 140 may be any conductive metal suitable for
downhole use which applied to the outside of each insulated casing
section before it is shipped to the wellsite; alternatively it
could be in the form of a coating, paint or wrapping applied at the
wellsite.
[0111] As shown in the drawing, insulative layer 130 is formed with
an "overhanging" section 130a which will effect the conduit gap of
the present invention.
[0112] The inner and outer conductors are electrically connected at
some point during the run of the well so that current injected at
the surface by source 24 via lines 60 and 61, through
encoder/decoder 25, has a closed path within which to flow along
illustrative current line 12. In this embodiment, the connection
between inner and outer conductors is accomplished at the bottom of
the well by shunt 150. A toroid 126 is disposed in the insulating
layer 130, i.e., "sandwiched" between the inner conductive casing
122 and the outer conductive layer 140.
[0113] As in the earlier embodiments such as FIG. 4, measurement
device 28 is installed on the casing 122 along with encoder/decoder
27. Device 28 receives electrical power from toroid 126 where the
current flowing through the casing 122 inductively generates a
voltage in the toroid that is used to power the sensor. The device
is connected to the toroid 126 via a lead through feed through
nonconductive seal 160.
[0114] The signal sensed by measurement device 28 is encoded into a
second alternating current in the toroid 126, at a frequency
distinct from that of the current injected at the surface, thus
creating a second current in casing 122 and conductive layer 140,
which is decoded by surface electronic encoder/decoder 25 and
recorded or otherwise processed.
[0115] FIG. 16 illustrates another which utilizes direct downhole
coupling. Like the embodiment of FIG. 15, a three-layer "sandwich",
comprising conductive casing 122, insulating layer 130 and a second
conductive layer 140, is used
[0116] The two conductive elements 122 and 140 are insulated from
each other by extending insulating layer 130 beyond the length of
conductive casing 122 and into region 180, effecting a first
conduit gap. As for the embodiment of FIG. 15, an "overhanging"
section 130a effects a second conduit gap.
[0117] An electrical power source 24, typically at surface and
equipped with encoder/decoder 25, establishes a voltage potential
across the two conductive elements 140 and 122 via lines 60 and 61.
At various points along the well, measurement devices 28 measuring
properties either inside or outside the well are connected across
the two conductive elements as shown where insulating feed throughs
160 insulate and seal the area of the casing 122 through which a
connection between measuring device 28 and the outer conductive
layer 140 is made. The measurement devices 28 can be fitted and
installed on segments of three-layer casing during casing
manufacture to assure a reliable connection to the two conductive
elements. Current flow will be through device 28 from casing 122 to
outer conductive layer 140.
[0118] The principle of operation of the alternative embodiment
illustrated in FIG. 17 is similar to that of the embodiment
illustrated in FIG. 16, with the conductive outer layer (140 of
FIG. 16) replaced by an annulus of conductive cement 40. The
conductive casing 122 is covered with an insulating layer 130 which
is surrounded by conductive cement annulus 40. The two conductive
elements (casing 122 and cement annulus 40) are insulated from each
other, by extending insulating layer 130 beyond the length of
conductive casing 122 and into region 180 forming a first conduit
gap and "overhanging" section 130a effecting a second conduit
gap.
[0119] At the surface, a voltage generator 24, through
encoder/decoder 25, electrically connected to the casing 122 and
cement annulus 40 (by electrode 266) via lines 60 and 61, applies
an electric potential across the casing 122 and the conductive
cement 40. At various points along the well, measurement devices 28
are placed to measure physical properties either inside or outside
the casing. Such devices derive their electrical input power from
the potential difference between the casing 122 and the conductive
cement 40 in a manner similar to that of the FIG. 16 embodiment. In
particular, the device 28 would have one power cable attached to
the casing 122, and the other would pass via an insulating feed
through 160 to an electrode 267 situated in the conductive cement
40. Current flow will be through device 28 from casing 122 to
electrodes 267, through conductive cement 40 to electrode 266 as
shown by illustrative current lines 12.
[0120] Electrodes 266 and 267 are illustrated as outer conductive
layers or bands on limited segments of three-layer casing. These
electrodes could also be implemented as mechanically separate
electrodes disposed within the cement. However, compared to
separate electrodes, implementation of the electrodes as shown in
FIG. 17 as a section or band of casing would offer the advantage of
increased surface area through which currents flow to power the
measurement device(s).
[0121] In the illustrative embodiments described with respect to
FIGS. 15-17, alternative methods of effecting the conduit gap can
also be arranged as will be understood by one skilled in the
art.
[0122] The present invention has been illustrated and described
with respect to specific embodiments thereof. It is to be
understood, however, that the above-described embodiments are
merely illustrative of the principles of the invention and are not
intended to be exclusive embodiments.
[0123] Alternative embodiments capturing variations in the
embodiments disclosed herein can be implemented to achieve the
benefits of the present invention.
[0124] It should further be understood that the foregoing and many
various modifications, omissions and additions may be devised by
one skilled in the art without departing from the spirit and scope
of the invention.
* * * * *