Note: Descriptions are shown in the official language in which they were submitted.
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WIRELESS COMMUNICATION USING WELL CASING
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates in general to petroleum wells, and in particular
to a
petroleum well having a casing which is used as a conductive path to transmit
wireless spread
spectrum communications between surface equipment and a downhole module used
to measure
physical characteristics of a petroleum formation or condition of well
structures.
Description of Related Art
Several methods have been devised to place electronics, sensors, or
controllable valves
downhole along an oil production tubing string, but all such known devices
typically use an
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internal or external cable along the tubing string to provide power and
communications
downhole. It is, of course, highly undesirable and in practice difficult to
use a cable along the
tubing string either integral to the tubing string or spaced in the annulus
between the tubing
string and the casing. The use of a cable presents difficulties for well
operators while
assembling and inserting the tubing string into a borehole. Additionally, the
cable is subjected
to corrosion and heavy wear due to movement of the tubing string within the
borehole. An
example of a downhole communication system using a cable is shown in
PCT/EP97/01621.
U. S. Patent No. 4,839,644 describes a method and system for wireless two-way
communications in a cased borehole having a tubing string. However, this
system describes a
communication scheme for coupling electromagnetic energy in a TEM mode using
the annulus
between the casing and the tubing. This inductive coupling requires a
substantially
nonconductive fluid such as crude oil in the annulus between the casing and
the tubing.
Therefore, the invention described in U. S. Patent No. 4,839,644 has not been
widely adopted as
a practical scheme for downhole two-way communication. Another system for
downhole
communication using mud pulse telemetry is described in U. S. Patent Nos.
4,648,471 and
5,887,657. Although mud pulse telemetry can be successful at low data rates,
it is of limited
usefulness where high data rates are required or where it is undesirable to
have complex, mud
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pulse telemetry equipment downhole. Other methods of eommunicating within a
borehole are
described in U.S. Patent Nos. 4,468,665; 4,578,675; 4,739,325; 5,130,706;
5,467,083;
5,493,288; 5,576,703; 5,574,374; and 5,883,516. Similarly, several permanent
downhole
sensors and control systems have been described in U.S. Pat. Nos. 4,972,704;
5,001,675;
5,134,285; 5,278,758; 5,662,165; 5,730,219; 5,934,371; and 5,941,307.
Due to the limited success of wireless communication within a borehole, the
current use
of downhole measurement and control equipment is minimal. A lack of downhole
measurement
and control restricts the ability to maximize economic return by optimizing
production of the
well.
It would, therefore, be a significant advance in the operation of petroleuni
wells if an
alternate means for providing communications within a well were provided. More
specifically,
it would be advantageous if downhole physical characteristics of the formation
could be easily
communicated to the surface of the well. This information could then be used
to increase the
aggregate recovery of formation reserves, and would thereby optimize
production of the well.
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BRIEF SUMMARY OF THE INVENTION
The problems associated with communicating in the borehole of a petroleum well
are
solved by the present invention. The metal well casing is used as a power and
communications
path between the surface and downhole modules, with a formation ground used as
the return
path to complete the electrical circuit. Communications are implemented using
spread-spectrum
transceivers at the wellhead and at the downhole modules. The communications
enable
tra nsmission of measurements from downhole sensors to the surface and control
of downhole
devices.
A petroleum well according to the present invention includes a downhole module
and a
communications system: The downhole module is positioned on an exterior
surface of a piping
structure, the piping structure being positioned within a borehole of the
petroleum well that
extends into a formation. The downhole module collects formation data from the
formation and
communicates the data by using the communication system. The signals
transmitted by the
communication system are passed along the piping structure.
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A method for assessing a formation according to
the present invention is applied to a petroleum well having
a borehole that extends into the formation. The petroleum
well also includes a piping structure that is positioned
within the borehole. The method includes the step of
sensing a formation characteristic within the formation and
then communicating information about the formation
characteristic along the piping structure of the well.
A downhole module according to the present
invention is adapted for coupling to a piping structure of a
petroleum well. The module includes a sensor that is used
to sense a physical characteristic of a formation
surrounding the piping structure. A downhole modem is used
to transmit data representing the physical characteristic
along the piping structure of the well.
According to one aspect of the present invention,
there is provided a petroleum well comprising: a borehole
extending into a formation; a piping structure including a
casing positioned within the borehole; a downhole module
positioned on the outside of the casing for collecting
formation characteristic data of the formation; a
communication system operably coupled to the piping
structure and module such that the formation characteristic
data can be communicated along the piping structure as a
time-varying signal; an upper induction choke positioned
concentrically around the piping structure; a lower
induction choke positioned concentrically around the piping
structure; wherein the formation characteristic data is
communicated along the piping structure between the upper
induction choke and the lower induction choke.
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According to another aspect of the present
invention, there is provided in a petroleum well having a
borehole extending into a formation and having a piping
structure positioned within the borehole, a method for
assessing the formation comprising the steps of: sensing a
formation characteristic of the formation using sensors
external to the piping structure; and communicating the
formation characteristic along the piping structure as a
time varying signal applied to the piping structure, wherein
the communicating step further comprises: providing an upper
induction choke positioned concentrically around the piping
structure; providing a lower induction choke positioned
concentrically around the piping structure; and
communicating the formation characteristic along the piping
structure between the upper induction choke and the lower
induction choke.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1A is a schematic of a petroleum well
having a downhole module attached to a casing, the downhole
module being configured to measure formation characteristics
according to the present invention.
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DESCRIPTION OF THE PREFERRED EMBODIMENTS
As used in the present application, a "piping structure" can be one single
pipe, a tubing
string, a well casing, a pumping rod, a series of interconnected pipes, rods,
rails, trusses, lattices,
supports, a branch or lateral extension of a well, a network of interconnected
pipes, or other
structures known to one of ordinary skill in the art. The preferred embodiment
makes use of the
invention in the context of an oil well where the piping structure comprises
tubular, metallic,
electrically-conductive pipe or tubing strings, but the invention is not so
limited. For the present
invention, at least a portion of the piping structure needs to be electrically
conductive, such
electrically conductive portion may be the entire piping structure (e.g.,
steel pipes, copper pipes)
or a longitudinal extending electrically conductive portion combined with a
longitudinally
extending non-conductive portion. In other words, an electrically conductive
piping structure is
one that provides an electrical conducting path from one location where a
power source is
electrically connected to another location where a device and/or electrical
return is electrically
connected. The piping structure will typically be conventional round metal
tubing, but the cross-
sectional geometry of the piping structure, or any portion thereof, can vary
in shape (e.g., round,
rectangular, square, oval) and size (e.g., length, diameter, wall thickness)
along any portion of
the piping structure.
A "valve" is any device that functions to regulate the flow of a fluid.
Examples of valves
include, but are not limited to, sub-surface safety valves used to control
fluid flow in well
tubulars, and bellows-type gas-lift valves and controllable gas-lift valves
each of which may be
used to regulate the flow of lift gas into a tubing string of a well. The
internal workings of
valves can vary greatly, and in the present application, it is not intended to
limit the valves
described to any particular configuration, so long as the valve functions to
regulate flow. Some
of the various types of flow regulating mechanisms include, but are not
limited to, ball valve
configurations, needle valve configurations, gate valve configurations, and
cage valve
configurations. Valves can be mounted downhole in a well in many different
ways, some of
which include tubing conveyed mounting configurations, side-pocket mandrel
configurations, or
permanent mounting configurations such as mounting the valve in an enlarged
tubing pod.
The term "modem" is used generically herein to refer to any communications
device for
transmitting and/or receiving electrical communication signals via an
electrical conductor (e.g.,
metal). Hence, the term is not limited to the acronym for a modulator (device
that converts a
voice or data signal into a form that can be transmitted)/demodulator (a
device that recovers an
original signal after it has modulated a high frequency carrier). Also, the
term "modem" as used
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herein is not limited to conventional computer modems that convert digital
signals to analog
signals and vice versa (e.g., to send digital data signals over the analog
Public Switched
Telephone Network). For example, if a sensor outputs measurements in an analog
format, then
such measurements may only need to be modulated (e.g., spread spectrum
modulation) and
transmitted-hence no analog-to-digital conversion is needed. As another
example, a
relay/slave modem or communication device may only need to identify, filter,
amplify, and/or
retransmit a signal received.
The term "processor" is used in the present application to denote any device
that is
capable of performing arithmetic and/or logic operations. The processor may
optionally include
a control unit, a memory unit, and an arithmetic and logic unit.
The term "sensor" as used in the present application refers to any device that
detects,
determines, monitors, records, or otherwise senses the absolute value of or a
change in a physical
quantity. Sensors as described in the present application can be used to
measure temperature,
pressure (both absolute and differential), flow rate, seismic data, acoustic
data, pH level, salinity
levels, valve positions, or almost any other physical data.
As used in the present application, "wireless" means the absence of a
conventional,
insulated wire conductor e.g. extending from a downhole device to the surface.
Using the tubing
and/or casing as a conductor is considered "wireless."
The term "electronics module" in the present application refers to a control
device.
Electronics modules can exist in many configurations and can be mounted
downhole in many
different ways. In one mounting configuration, the electronics module is
actually located within
a valve and provides control for the operation of a motor within the valve.
Electronics modules
can also be mounted external to any particular valve. Some electronics modules
will be
mounted within side pocket mandrels or enlarged tubing pockets, while others
may be
permanently attached to the tubing string. Electronics modules often are
electrically connected
to sensors and assist in relaying sensor information to the surface of the
well. It is conceivable
that the sensors associated with a particular electronics module may even be
packaged within the
electronics module. Finally, the electronics module is often closely
associated with, and may
actually contain, a modem for receiving, sending, and relaying communications
from and to the
surface of the well. Signals that are received from the surface by the
electronics module are
often used to effect changes within downhole controllable devices, such as
valves. Signals sent
or relayed to the surface by the electronics module generally contain
information about
downhole physical conditions supplied by the sensors.
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In accordance with conventional terminology of oilfield practice, the
descriptors "upper,"
"lower," "uphole," and "downhole" as used herein are relative and refer to
distance along hole
depth from the surface, which in deviated or horizontal wells may or may not
accord with
vertical elevation measured with respect to a survey datum.
The term "formation" as used in the present application refers to a bed or
deposit
composed throughout of substantially the same kinds of rock. A formation may
or may not
contain petroleum products.
Referring to FIG. 1 in the drawings, a petroleum well 10 having a wireless
smart well
casing 12 is illustrated. Petroleum well 10 includes a borehole 14 extending
into a formation
from a surface 16 to a production zone 18 that is located downhole. The casing
12 is disposed in
borehole 14 and includes a structure of the type conventionally employed in
the oil and gas
industry. The casing 12 is typically installed in sections and is secured in
borehole 14 during
well completion with cement 34. A tubing string, or production tubing, 26 is
generally
conventional comprising a plurality of elongated tubular pipe sections joined
by threaded
couplings at each end of the pipe sections. Oil or gas produced by petroleum
well 10 is typically
delivered to surface 16 by tubing string 26.
A production platform 27 is located at surface 16 and includes a tubing hanger
28.
Tubing hanger 28 supports tubing string 26 such that the tubing string 26 is
concentrically
positioned within casing 12. As illustrated in FIG. 1 production platform 27
also includes a gas
input throttle 30 to permit the input of compressed gas into an annular space
31 between casing
12 and tubing string 26. Conversely, an output valve 32 permits the expulsion
of oil and gas
bubbles from an interior of tubing string 26 during oil production. While FIG.
1 illustrates a gas
lift well, the present invention is not so limited, and the gas input throttle
valve 30 and its
associated input tubing is therefore optional.
Well 10 includes a communication system 44 for providing power and two-way
communication signals downhole in well 10. Casing 12 acts as an electrical
conductor for
communication system 44. In accordance with the present invention, an
induction choke 42 is
positioned concentrically around casing 12 prior to securing the casing 12
within cement 34.
Induction choke 42 serves as a series impedance to electric current flow along
the casing 12.
The size and material of lower induction choke 42 can be altered to vary the
series impedance
value; however, the lower induction choke 42 is made of a ferromagnetic
material. Induction
choke 42 is mounted concentric and external to casing 12, and is typically
hardened with epoxy
to withstand rqugh handling.
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A means is provided to electrically insulate casing 12 and tubing string 26
from ground
connection tluough surface ancillary tubing connected to valves 30 and 32.
Insulators 40
provide this function as shown in FIG. 1, but alternative methods exist and
will be clear to those
of average skill in the art, such as the use of an insulated tubing hanger
(not shown) in
combination with an electrical isolation tubing joint (not shown). In
alternative, another
induction choke (not shown) can be placed about the casing above the
electrical point of
connection 49 of the surface power and communication equipment 44, or two such
chokes may
be placed individually about the production fluids tubing and the lift gas
supply pipe.
Inductive chokes such as 42 external to the casing act to impede
current flow on both casing and tubing at the points where these pass through
such inductive
chokes.
By electrically isolating a section of casing 12, power and communications
signals can
be supplied liownhole along the casing 12 and tubing 26. While it is not an
ideal electrical
insulator, the cement 20 can be of low electrical conductivity and provides.a
degree of electrical,
isolation between casing 12 and the formation surrounding the well. Induction
choke 42 further
impedes current flow along casing 12 and tubing 26, thereby allowing the
signals to be passed
between induction choke 42 and the surface of the well. It is important to
note that electrical
contact between casing 12 and tubing string 26 does not short circuit the
signals travelling along
casing 12. Since tubing string 26 is also located within the annulus of
induction choke 42, the
choke 42 has the same electrical impedance effect on tubing string 26 as on
casing 12. More
specifically, current travelling down tubing string 26 is effectively blocked
from travelling
further downhole to a potential ground. Similar protection is provided at the
top of tubing string
26 by insulating tubing joints 40. In practice the majority of the current
conveyed into the well
by the embodinient illustrated in FIG. I is carried on the casing, and the
tubing contributes
negligibly to the conveyance of power to depth in the well.
A computer and power source 44 including a power supply 46 and a spread
spectrum
communications device (e.g. modem) 48 is disposed outside of borehole 14 at
surface 16. The
computer and power source 44 is electrically connected to casing 12 at a
current supply point 49
for supplying time varying current to the casing 12. Computer and power source
44 is grounded
to surface 16.1In operation the use of casing 12 as a conductor is lossy
because of the imperfect
electrical isolation provided by the cement 20. However, the spread-spectntm
communications
technique is tolerant of noise and low signal levels, and can operate
effectively even with losses
as high as -100db.
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As shown in FIG. 1, downhole electronics module 50 is positioned proximate to
an
exterior surface of the casing 12 prior to completion of the well. Downhole
module 50 includes
a plurality of sensors 70, 72, 74, for assessing formation characteristics
(i.e. physical
characteristics) about the formation that surrounds the well. These sensors
could include
resistivity sensors, pressure sensors, temperature sensors, flow rate sensors,
corrosion sensors, or
geophones. Each of these sensors can be used to obtain information about the
characteristics of
the formation. Additionally, hydrophones could be used to measure acoustic
waves in well
fluids within casing 12.
It is not obvious that sensors 70 - 74 would be able to measure formation
characteristics
such as pressure or resistivity, since they are embedded within cement 34 and
not in direct
connection with formation 18. However, while the permeability of cement 34 is
low, it does not
provide an absolute hydraulic seal. Since the flow of formation fluids through
the cement is
prevented by the casing 12, the pressure of fluids in the pore spaces of the
cement 34
equilibrates witli the pressure in the formation. Rapid changes in formation
pressure cannot be
measured, but slow changes can be measured, and it is data from slow changes
as the reservoir is
depleted that are valuable as an indication of reservoir condition.
The same considerations apply to other physical characteristics of the
formation 18, such
as fluid composition, which would be reflected in resistivity changes. The
interpretation of such
resistivity data differs from that for a conventional resistivity log of a
well as measured by open-
hole logging tools. Open-hole resistivity logs reveal the spatial variation of
resistivity over the
logged section of the formation, measured at essentially a single instant of
time. The resistivity
log acquired by the methods of the present invention is derived from a
locationally static single
sensor, but over an extended period of time. In both cases, changes in the
resistivity are the
features which reveal the condition of the formation: in the open-hole log,
these are spatial
changes, in the present invention, the changes are a function of time rather
than spatial
variations.
Downhole module 50 is configured to be mechanically connected to the casing 12
either
above or below induction choke 42. Electrical connections to the downhole
module 50 are
provided by jumpers. Power is received at the downhole module 50 by a jumper
connected to
casing 12 above the induction choke 42. A ground return jumper is provided
that connects
downhole module 50 to casing 12 below induction choke 42.
Downhole module 50 also includes a spread spectrum transceiver (not shown) for
communicating with modem 48 at the surface of the well 10. The transceiver
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data representing the formation characteristics to be transmitted to the
surface of the well 10 for
use in optimizing production of the well 10. If multiple downhole modules 50
are positioned on
the casing 12, the transceiver in each downhole module is able to communicate
with transceivers
in the other downhole modules, thereby allowingtransceivers to relay signals
and providing
redundancy in the event of a failure of one of the downhole modules 50.
After positioning induction choke 42 and downhole module 50 on casing 12, the
casing
12 is run into borehole 14. Cement 34 is injected into the annulus between the
borehole and
casing 12 to secure the casing within the borehole 14. The cement 34 also
further secures the
positioning of the induction choke 42 and the downhole module 50 relative to
casing 12
Even though many of the examples discussed herein are applications of the
present
invention in petroleum wells, the present invention also can be applied to
other types of wells,
including but not limited to water wells and natural gas wells. I
One skilled in the art will see that the present invention can be applied in
many areas
where there is a need to provide a communication system within a borehole,
well, or any other
area that is difficult to access. Also, one skilled in the art will see that
the present invention can
be applied in many areas where there is an already existing conductive piping
structure and a
need to route power and communications to a location on the piping structure.
A water sprinkler
system or network in a building for extinguishing fires is an exainple of a
piping structure that
may be already existing and may have a same or similar path as that desired
for routing power
and communications. In such case another piping structure or another portion
of the same
piping structure may be used as the electrical return. The steel structure of
a building may also
be used as a piping structure and/or electrical return for transmitting power
and communications
in accordance with the present invention. The steel rebar in a concrete dam or
a street may be
used as a piping structure and/or electrical return for transmitting power and
communications in
accordance with the present invention. The transmission lines and network of
piping between
wells or across large stretches of land may be used as a piping structure
and/or electrical return
for transmitting power and communications in accordance with the present
invention. Surface
refinery production pipe networks may be used as a piping structure and/or
electrical return for
transmitting power and communications in accordance with the present
invention. Thus, there
are numerous applications of the present invention in many different areas or
fields of use.
It should be apparent from the foregoing that an invention having significant
advantages
has been provided. While the invention is shown in only a few of its forms, it
is not just limited
but is susceptible to various changes and modifications without departing from
the spirit thereof.
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