Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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APPARATUS AND METHOD FOR COMMUNICATING INFORMATION
BETWEEN A WELLBORE AND SURFACE
Inventors: ZAEPER, Ralf, MACPHERSON, John, MENGE, Mathias
BACKGROUND OF THE DISCLOSURE
1. Field of the Disclosure
[0001] This disclosure relates to apparatus and methods that provide data
communication between a surface location and downhole tools during drilling of
the wellbore
2. Description of the Related Art
[0002] Wellbores or boreholes are drilled in the earth's subsurface formations
for the production of hydrocarbons (such as oil and gas) utilizing a rig (land
or
offshore) and a drill string that includes a tubing (jointed pipe or a coiled
tubing)
and a drilling assembly (also referred to as a bottom hole assembly or "BHA").
The drilling assembly carries a drill bit that is rotated by a motor at the
surface
and/or a drilling motor (also referred to as mud motor) carried by the
drilling
assembly. The drilling assembly typically carries a variety of downhole tools,
usually referred to as the measurement-while-drilling ("MWD") tools. Drilling
fluid or mud is pumped by mud pumps at the surface into the drill string.
After
discharging at the drill bit bottom, the drilling fluid returns to the surface
via an
annulus between the drill string and the wellbore walls. The MWD tools may
include a resistivity sensor, acoustic sensor, nuclear-magnetic-resonance
sensor,
nuclear sensors, formation testing tools, etc. for providing information about
various properties of the formation surrounding the wellbore. The drilling
assembly may also include tools and sensors that are useful in drilling the
wellbore along a desired trajectory. Additional sensors, such as pressure
sensors,
temperature sensors and flow rate sensors are used to determine pressure,
temperature and fluid flow rates in the wellbore.
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[00031 The MWD tools and sensors are capable of providing a large amount
of data that is useful for drilling the wellbore along a desired trajectory
and for
estimating the properties of the formations surrounding the wellbore. It is
therefore
desirable to send large amounts of data to the surface during drilling of the
wellbore.
Also, it is desirable to send data from the surface to the downhole MWD tools
to
cause the tools to cause the tools to perform in a desired manner. Wired-pipe
and
mud pulse telemetry have been used to transmit data between the downhole tools
and the surface. Wired-pipes provide wide band data communication, while mud
pulse telemetry sends a few bits per second.
[00041 The present disclosure provides an improved apparatus and methods
for communicating data between the downhole tools and the surface using both
the
wired-pipe and the mud pulse telemetry.
SUMMARY OF THE DISCLOSURE
[00051 Accordingly, in one aspect there is provided a method of
communicating data between a wellbore and the surface, comprising: receiving
data
from at least one tool in the wellbore at a control circuit in the wellbore;
transmitting
the data from the control circuit to the surface at a first data rate via a
communication link in a tubing that supplies fluid to the wellbore; detecting
when a
quality level of the communication link is below a selected value from a
condition of
the transmitted data; transmitting a selected portion of the data from the
control
circuit to the surface over a mud pulse telemetry unit that generates pressure
pulses
through the fluid in the tubing at a second data rate; and instructing the at
least one
tool to change an amount of data sent to the control circuit when the detected
quality
level is below the selected value.
[00061 According to another aspect there is provided a wellbore telemetry
system, comprising: a drillstring in a wellbore having a tubing that carries a
data
communication link and supplies fluid under pressure during drilling of the
wellbore; at least one tool conveyed by the tubing into the wellbore; a first
data
transmission device that transmits data to the surface via the data
communication
link at a first data rate; a downhole pulser configured to send data to the
surface by
producing pressure pulses in the fluid at a second data rate that is lower
than the first
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data rate; and a control circuit configured to: receive the data from the at
least one
tool; detect when a quality level of the data communication link is below a
selected
value; select a portion of the data to be sent to the surface via the downhole
pulser;
activate the downhole pulser to transmit the selected portion of the data; and
instruct
the at least one tool to change an amount of data sent to the control circuit
when the
detected quality level is below the selected value.
[0007] According to yet another aspect there is provided a drilling assembly
for use during drilling of a wellbore, comprising: a data connection
configured to
connect to a data communication link carried by a tubing that supplies fluid
under
pressure to the drilling assembly during drilling of the wellbore; at least
one tool in
the drilling assembly configured to provide data to be transmitted to a
surface
location during drilling of the wellbore; a first data transmission device
that
transmits data received from the at least one tool to the data communication
link via
the data connection at a first data rate; a downhole pulser that is configured
to
produce pressure pulses in the fluid at a second data rate that is lower than
the first
data rate during drilling of the wellbore; and a control circuit configured
to: detect
when a quality level of the data communication link is below a selected value;
select
a portion of the data to be sent to the surface via the downhole pulser;
control the
downhole pulser to transmit the selected portion of the data at the second
data rate;
and instruct the at least one tool to change an amount of data sent to the
control
circuit when the detected quality level is below the selected value.
[0007a] According to still yet another aspect there is provided a method of
communicating data between a wellbore and the surface, comprising:
transmitting
data between at least one tool in the wellbore and the surface at a first data
rate via a
first wired-communication link; detecting when a quality level of the first
wired-data
communication link is below a selected value; selecting a portion of the data
to be
sent over a second telemetry link that sends data at a second data rate that
is lower
than the first data rate; sending the selected portion of the data to the
surface via the
second telemetry link; and instructing the at least one tool to change an
amount of
data for transmitting when the detected quality level is below the selected
value.
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[00081 Examples of the more important features of the invention have been
summarized (albeit rather broadly) in order that the detailed description
thereof that
follows may be better understood and in order that the contributions they
represent
to the art may be appreciated. There are, of course, additional features of
the
invention that will be described hereinafter and which will form the subject
of the
claims appended hereto.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] For detailed understanding of the present invention, reference should
be made to the following detailed description of the embodiments, taken in
conjunction with the accompanying drawing in which like elements sometimes
have
been assigned like numerals and; wherein:
[0010] FIG. 1 shows a schematic illustration of a drilling system that
utilizes
one embodiment of the present invention; and
[0011] FIG. 2 shows a functional block diagram of a telemetry system
according to one embodiment of the present disclosure.
DETAILED DESCRIPTION OF THE DISCLOSURE
[00121 FIG. 1 shows a schematic diagram of a drilling system 10 in which a
drill string 20 carrying a drilling assembly 90 or CHA is shown conveyed in a
wellbore 26. The drilling system 10 may include a conventional derrick 11
erected on a platform or floor 12 which supports a rotary table 14 that is
rotated by
a prime mover, such as an electric motor (not shown), at a desired rotational
speed. The rotary table is coupled to and rotates the drill string 20. The
drill string
20 includes a tubing 22 (which may be made by joining metallic pipe sections
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(drill pipe sections) or a metallic or composite coiled-tubing. A drill bit 50
attached to the end of the drilling assembly 90 is rotated to disintegrate the
geological formations to form the wellbore 26. The drill string 20 is coupled
to a
draw works 30 via a Kelly joint 21, swivel 28, and line 29 through a pulley
23.
The draw works 30 controls the weight on bit, which is a parameter that
affects
the rate of penetration.
[0013] To drill the wellbore 26, a suitable drilling fluid 31 (also known as
"mud") from a mud pit 32 (source) is circulated under pressure through the
tubing
22 by one or more mud pumps 34. The drilling fluid 31 passes from the mud
pumps 34 into the drill string 20, fluid line 38 and Kelly joint 21. The
drilling
fluid 31 discharges at the bottom of the wellbore 20 through openings in the
drill
bit 50. The drilling fluid 31 lubricates the drill bit 50 and carries rock
cuttings.
The drilling fluid 31 then returns to the surface via an annular space 27
("annulus") between the drill string 20 and the wellbore 26. The rocks in the
returning fluid are removed at the surface and the clean fluid is discharged
in the
pit 32 via a return line 35.
[0014] A sensor or device S1, such as a flow meter typically placed in the
line
38, provides information about the fluid flow rate. A surface torque sensor S2
and
a sensor S3 associated with the drill string 20 respectively provide
information
about the torque and the rotational speed of the drill string. Additionally, a
sensor
(not shown) associated with line 29 is used to provide the hook load of the
drill
string 20. The drill bit 50 may be rotated by rotating the drill pipe 22 or a
downhole motor 55 (mud motor) disposed in the drilling assembly 90 or both.
[0015] In the exemplary embodiment of FIG. 1, the mud motor 55 is shown
coupled to the drill bit 50 via a drive shaft (not shown) disposed in a
bearing
assembly 57. The mud motor 55 rotates the drill bit 50 when the drilling fluid
31
passes through the mud motor 55 under pressure. The bearing assembly 57
provides support to the drilling assembly from the radial and axial forces of
the
drill bit. One or more stabilizers 58 coupled to the drilling assembly 90
maintain
the drilling assembly in the center of the wellbore.
[0016] A surface control unit 40 (also referred to as the "surface
controller")
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may be used to control various operations of the drilling system 10, including
controlling the pumps 34, draw works 30, rotation of the rotary table 14 and
operation of the various tools and sensors contained in drilling assembly 90.
In
one aspect, the control unit 40 is in data communication with drilling
assembly 90
via at least two separate communication channels. One such channel may provide
a wide data band width and may be formed by a direct data communication link
45 that runs in or along the tubing 22. The direct data communication link 45
may
include one or more electrical conductors and/or optical fibers that run in or
along
the tubing 22, as described in more detail later. A coupler 46 at the surface
transfers the data to and from the stationary control unit to the rotating
drill string
22. A rotating coupler may not be needed when coiled tubing is used. The
coupler
46 may be any suitable coupler, including one that provides a radio (wireless)
link. The other data communication channel may utilize a relatively low data
rate
and may use the mud in the drill string 20 as the communication channel.
[00171 A pulser 49 may be used to generate pressure pulses in the fluid in the
line 38 to send coded signals to the drilling assembly. Alternatively, the mud
pumps may be used to generate pressure pulses in the mud in line 38. The
pulser
may be a positive pressure pulser, such a "poppet pulser," an oscillating disc-
type
pulser, a "rotary pulser" (also referred to as a "siren pulser") or any other
suitable
pulser. The coded signals also mat be sent to the downhole tools by varying
the
flow rate of the drilling fluid or by momentarily diverting the drilling
fluid. A
bypass or venting-type device or pulser, wherein the fluid in line 38 is
bypassed at
selected rates for selected time periods, may be utilized to change the fluid
flow
rate to generate pressure pulses in the fluid in line 38. A sensor 43, such a
pressure
sensor or a flow meter, provides measurements indicative of the surface-
generated
pressure pulses to the controller 40. The sensor 43 or another sensor detects
pressure pulses sent from the drilling assembly 90 and provides such
information
to the surface controller 40. Other sensors, such as sensors S1, S2, S3,
provide to
the surface controller 40 information about hook load, rotational speed of the
drill
string, fluid flow rate, rate of penetration and any other desired parameter
measured at the surface relating to the drilling of the wellbore 20.
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[0018] The surface control unit 40 may be a computer-based system that
utilizes programs, models and algorithms to process information received from
various tools, sensors and a remote unit to effect the drilling of the
wellbore 26.
The surface control unit 40 may include one or more processors, such as
microprocessors, suitable data storage media, including solid state memory,
tapes,
discs, disc drives, etc., and one or more displays 42. The surface control
unit 40
may communicate with one or more remote locations 5 via any suitable link,
including but not limited to an Ethernet connection, a wireless connection or
the
Internet. The surface control unit 40 also may display any desired drilling
parameters and other information on a display/monitor 42 for use an operator
to
control the drilling operations. The surface control unit 40 also may be
configured
to activate alarms 44 when certain unsafe or undesirable operating conditions
are
detected or determined. The rig I1 is shown as a surface rig that utilizes a
rotary
table to rotate the drill pipe only as an example of a rig and a drive
mechanism.
Top drives are often used to rotate the drill pipe. Such and other mechanisms
may
be equally utilized for the purpose of this disclosure. Also, for offshore
drilling, an
offshore platform or vessel may be utilized to implement any of the
embodiments
and methods described herein.
[0019] Still referring to FIG. 1, the BHA 90 may contain a variety of MWD
tools, sensors and other devices that are configured to provide a variety of
measurements for estimating or determining various parameters of the formation
surrounding the wellbore 97, downhole drilling parameters, parameters relating
to
the behavior of the drilling assembly 90 and devices for drilling the wellbore
26
along a desired path. Such devices may include a device for measuring the
formation resistivity near and/or in front of the drill bit, a gamma ray
device for
measuring the formation gamma ray intensity and devices for determining the
inclination and azimuth of the drilling assembly, acoustic tool for estimating
the
porosity and permeability of the formation, nuclear toll for estimating the
composition and nuclear porosity of the formation and nuclear resonance tool
for
estimating the composition of the formation. Formation evaluation tools may be
used to take formation fluid samples and to perform PVT (pressure, volume and
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temperature) tests.
[0020] The MWD tools and sensors may be placed in any desirable order and
some of the sensors may be placed on a common drilling assembly housing. For
example, the formation resistivity measuring tool 64 may be coupled above a
lower kick-off subassembly 6 that provides signals from which resistivity of
the
formation near or in front of the drill bit 50 may be determined. An
inclinometer
74 and gamma ray device 76 may be suitably placed along the BHA for
respectively determining the inclination of the BHA and the formation gamma
ray
intensity. In addition, an azimuth device (not shown), such as a magnetometer
or a
gyroscopic device, may be utilized to determine the drill string azimuth.
Other
tools, which are collectively designated by numeral 77, are shown placed above
(uphole) the resistivity tool, as an example. Additionally, a drilling sensor
module
59 is placed near the drill bit 50. The drilling sensor module 59 contains
sensors,
circuitry and processing software and algorithms relating to the dynamic
drilling
parameters. Such parameters may include bending moment, vibration, bit bounce,
stick-slip, backward rotation, torque, shock, borehole and annulus pressure,
acceleration and any other desired drilling assembly and drill bit parameter.
[0021] In the exemplary configuration of FIG. 1, the mud motor 55 transfers
power to the drill bit 50 via a hollow shaft that also enables the drilling
fluid to
pass from the mud motor 55 to the drill bit 50. In an alternate embodiment of
the
drill string 20, the mud motor 55 may be coupled below resistivity measuring
device 64 or at any other suitable place. Each of these tools and devices may
include its own processing circuits that provide the results and/or provide
raw
data. Some or all such data may be recorded in downhole storage media and/or
transmitted to the surface control unit 40 during drilling of the wellbore 26.
A
downhole telemetry system or unit 99 carried by the drilling assembly 90
provides
two-way communication between the drilling assembly 90 and the surface. The
downhole telemetry system 99 receives data from the various MWD tools and
other sensors and devices and transmits the received data as coded signals to
the
surface via the data communication link 45. The downhole telemetry system 99
also receives signals and data from the surface control unit 40 and transmits
such
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received signals and data to the appropriate downhole devices. The downhole
telemetry system 99 also is configured to transmit and receive data using the
mud
pulse telemetry in parallel with the data communication link 45 or to the
exclusion
of such link when a fault with the link 45 is detected or when the data
communication quality level over the link 45 is below a selected value or
threshold.
[0022] FIG. 2 shows a functional block diagram of a system 200 for
communicating data between a drilling assembly and the surface for a drilling
system, such as shown in FIG.1. The system 200 is shown to include the drill
bit
50 at one end of the drilling assembly 90. A steering unit 57 is shown to
carry a
plurality of force application members or "ribs" 202a-202n, etc., wherein each
rib
is independently controlled to apply force on the inside of the wellbore 26 to
guide
the drill bit in a desired drilling direction. The steering unit may include
multiple
sensors 59 configured to provide measurements relating to the various physical
conditions of the drilling assembly 90, such as bending moment, vibration,
stick-
slip, pressure, temperature, weight-on-bit, etc. Additional sensors may be
provided on the mud motor 55 housing, which may include resistivity sensors. A
number of MWD tools, designated as 210a through 210n are shown placed above
the mud motor 55. For the purpose of this disclosure, any tool or sensor may
be
placed anywhere in the drilling assembly 90. Each MWD tool may include a
separate processor for processing the data and may store some or all such data
and
results in a downhole memory and/or send some or all such data and results to
the
surface.
[0023] In the system configuration of FIG.2, the data from each tool and
sensor that is to be sent to the surface is passed on a common bus 280
associated
with a master control unit 220, also referred to as the MWD master. The MWD
master, in aspect, may include one or more processors 222, a data storage
device
224, such as a solid-state memory, programs and models 226, and other
electronic
circuits 228 useful for receiving, transmitting and processing the data. The
MWD
master 220 provides the data to be sent to the surface via an interface 230.
The
interface 230 transfers the received data to the data communication link 45 in
the
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tubing 205 via a coupler or coupling device 206. The interface 230 may include
a
processor, memory,, programs and other electrical circuitry. A battery 237 may
be provided to supply electrical power to the interface 230 so that data
communication may be maintained and to ensure certain sensors (such as
pressure
sensors) remain powered when drilling fluid flow is interrupted or halted and
power is unavailable from the power unit 242. As discussed above, the data
communication link 45 may be run through each section of the drilling pipe 205
via suitable electrical or optical couplers. The interface 230 communicates
data
with the data link 45 via a suitable coupler 206, which in the case of an
electrical
conductor is an electrical connection device and in the case of an optical
fiber is a
suitable optical coupler. The same connection scheme may be used when the data
link 45' is in coiled-tubing. The coupling unit 206 may be the same as the
coupler
271. The data communication link 45 connects to the surface control unit 40
via a
suitable coupler 273, thereby establishing a high data rate or wide band data
connection between the drilling assembly 90 and the surface control unit 40.
100241 Still referring to FIG. 2, the system 200 also is shown to include a
mud-pulse telemetry system. The mud pulse telemetry system includes a pulser
240 and a power unit 242. The pulser 247 produces pressure pulses in the
drilling
fluid 31 flowing in the tubing 205 in response to the commands provided by the
MWD master 220 and or the surface control unit 40 or instructions programmed
in a memory for the pulser 240. As noted above, any suitable pulser may be
used
as the downhole pulser 240, including but not limited to, an oscillating-type
pulser, a rotary pulser and a poppet-type pulser. A detector 275, such as a
pressure
transducer, detects the mud pulses and sends electrical signals representative
of
the pulses to the surface controller 40 via link 275' for analysis. The data
from
the surface is transmitted by using a surface pulser 274 in the fluid line 38,
which
sends coded signals in the form of pressure pulses in the fluid 32 flowing
downhole. A detector 247 detects the pressure pulses sent from the surface and
provides corresponding electrical signals to the MWD master 220 for further
processing. The characteristics of the downhole generated pulses, such as
amplitude, pulse width, pulse shape, pulse phase and pulse frequency are
normally
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controlled by the MWD master 220 or another downhole controller. The coded
signals may also be detected by measuring the flow rate of the drilling fluid
when,
such as by a flow meter, when mud pulse telemetry is used. The coded signals
may be detected by determining the drill string rotation when the drill pipe
rotation is used to send the coded pulses. The same characteristics of the
surface-
generated pressure pulses are normally controlled by the surface control unit
40 or
another suitable controller. The surface control unit 40 and the MWD master
220
communicate with each other via one or both of the telemetry schemes to
coordinate transfer of the data between the drilling assembly and the surface.
[0025] Still referring to FIG. 2, during drilling of the wellbore 26, the MWD
master 220 or another suitable processor transmits the data from the downhole
tools and sensors to the surface control unit 40 via the direct data
communication
link 45. When a wired-pipe is used to include the data link 45, whether an
electrical conductor or optical fibres, a new drill pipe section, typically
about 30
meters in length, is installed after drilling such a distance, which may occur
every
few minutes to an hour or longer. The connection joints between pipe sections
sometimes become damaged or out of alignment, due to the severe downhole
drilling conditions and may not function properly to communicate data at the
intended high data rate. The MWD master 220 and/or the surface controller 40
may determine the condition of the data being transmitted/and or received and
determine, using a selected criterion the degradation in the performance of
the
data communication link 45. The surface controller and/or the MWD master then
may initiate transmission of the data using the relatively slow mud pulse
telemetry. The initiation of the mud pulse telemetry system may be
automatically
activated by either the MWD master 220 or the surface control unit 40, without
human intervention. As noted above, the mud pulse telemetry is a relatively
low
rate data transmission system (typically between 2-60 bits per second, based
on
the puller used and the wellbore depth) compared to the direct communication
link that may transmit data at several thousand or million bits per second.
[0026] The MWD master may act as a gateway and determine the type,
amount and timing of the data that will be sent from each downhole tool and
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device using the mud pulse telemetry. The MWD master also may receive
commands from the surface control unit 40 and transmit data using the mud
pulse
telemetry according to the received commands. In another aspect, if it is
determined that some data can be safely sent over the data link 45, then the
MWD
master may send some selected data over this link and send some other data via
the mud pulse telemetry. Also, optionally, the system 200 may utilize both
telemetry methods simultaneously, i.e., in parallel.
[0027] In one aspect, the MWD master 220 may communicate with each tool
210a-210n and other devices and change the amount and type of each tool's
respective data to be sent to the MWD master and/or the sequence in which such
data is sent. In another aspect, the MWD master 220 may cause one or more of
the downhole tools 210a-210n to stop sending data until a later time or reduce
the
number of bits sent over a certain period of time or the type of information
that is
to be sent, For example, the MWD master 220 may limit data transmission to
selected results from the tools when such results are outside a norm. The MWD
master 220 then may send the received data to the pulser which generates the
pressure pulses according a preselected pulse sequence. The MWD master 220
may control the characteristics of the pressure pulses generated by the pulser
230,
such as shape, phase, amplitude, frequency, time between the pulses, etc. Any
suitable transmission scheme may be employed, including but not limited to,
gain
or amplitude modulation, frequency modulation, time duration modulation or any
combination of such schemes to transmit coded pulses to the surface. Fault
detection, reprogramming, etc. may be accomplished by the downhole master or a
separate control unit. The functions performed by the downhole master and the
separate control unit may be changed over time to accomplish any desired
telemetry control scheme. Also, in one mode, the mud pulse or low data rate
telemetry may be run in a background mode and the control unit may switch
decidable mode as desired.
[0028] Still referring to FIG. 2, the surface control unit 40 includes or has
access to various computer programs 262, model 264, data storage devices 266
and data base 268 and utilizes such computer programs, models and data base to
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interact with the MWD master 220 to provide effective data communication
between the drilling assembly 90 and the surface. The surface control unit 40
may
communicate with any remote computer-based systems via any suitable link, such
as the Ethernet, Internet, wirelessly or direct connection and operate the
telemetry
systems described herein in response to any instructions received from the
remote
unit 5. The control unit 40 also displays the results relating to the drilling
of the
wellbore 26 on one or more displays 269 at the rig site for the use of the
operator.
The MWD master and/or surface control unit 40 may be configured to
automatically switch and/or allocate data transfer between the high data
transmission rate communication link 45 and the mud pulse telemetry channel in
response to the condition of the data link 45. The parallel telemetry system
described herein may achieve higher reliability compared to a single telemetry
system. For example, assuming a mud pulse telemetry system has a mean time
between failure (MTBF) of 500 hours and a wired pipe system has an MTBF of
200 hours, then the parallel telemetry system will have an MTBF of 10,000
hours.
[00291 Thus, in one aspect, a method for communicating data between a
wellbore and the surface during drilling of the wellbore is provided. The
method
may include the features of. (i) transmitting data from a plurality of tools
in the
wellbore to the surface at a first data rate via a data communication link in
a
tubing that supplies fluid under pressure; (ii) detecting occurrence of a
fault
relating to the data communication link; and (iii) in response to the
detection of
the fault, switching transmission of selected tool data to a mud pulse
telemetry
unit that sends the data to the surface by generating pressure pulses through
the
fluid in the tubing at a second data rate that is lower than the first data
rate. The
method may further include the feature of sending command signals to the
downhole tools to cause them to send data in a manner that is compatible with
transmitting the data at the second data rate through the fluid. The data
communication link may be any suitable hard link, such as an electrical
conductor
or an optical fiber that runs the length of the drill string. The method may
automatically switch sending data between the communication link and the
fluid.
It also may automatically cease to transmit data using the pressure pulses
when
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the fault has been corrected or cease sending data via the communication link
when a fault or unacceptable condition for the link has been determined. The
method also provides for activating a pulser downhole to generate the pressure
pulses upon detecting the fault. The pressure pulses to the surface may be
sent by
any suitable pulsing scheme, such as amplitude, phase, frequency, duration and
timing between pulses modulation schemes or a combination thereof. The method
also may include the feature of controlling flow of data from the various
downhole tools and devices upon the detection of the fault. The data
communication link may be any suitable link, including but not limited to one
or
more electrical conductors, one or more optical fibers, one or more conductors
containing carbon nano-tubes that are aligned in a direction along the
longitudinal
axis of the conductor. The pulses downhole may be generated by any suitable
pressure pulser, including but not limited to a rotary pulser, poppet pulser,
piezoelectric device or an oscillating shear-valve pulser
[0030] The disclosure in another aspect provides a wellbore telemetry system
in which a tubing of the drill string carries a data communication link along
the
length of the tubing to a drilling assembly that carries a plurality of tools.
A first
data transmission device in the drilling assembly transmits data received from
the
downhole tools to the surface via the data communication link at a first data
rate.
The wellbore telemetry system further includes a downhole pulser that is
configured to send data to the surface by producing pressure pulses in the
fluid at
a second data rate that is lower than the first data rate. A control circuit
in the
drilling assembly activates the downhole pulser to transmit at least some of
the
data from the tools at the second data rate when a fault is detected with the
data
communication link. A control unit in the drilling assembly may send commands
to the downhole tools to cause them to send data at a data rate that is
compatible
with the transmission of the data by the pulser. In one aspect, the control
unit may
include a processor that utilizes one or more programs, models and database
stored in suitable data storage medium to determine when data from a
particular
tool is below a standard and then may control the flow of data from that tool
for
further transmission to the surface. An interface circuit may be used to
receive the
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CA 02705511 2010-05-12
WO 2009/064758 PCT/US2008/083188
data from the downhole control unit, such as a MWD master, to transfer the
data
to the data communication link. The wellbore telemetry system may further
include a surface mud pulse telemetry unit that is activated when the downhole
pulser is activated to establish two-way mud pulse telemetry. A detector
downhole
detects pressure pulses downhole that correspond to the surface sent signals
and
generates electrical signals responsive to the detected pressure pulses. A
processor
downhole processes the electrical signals generated by the detector to
ascertain the
surface signals.
[0031] In another aspect, a downhole drilling assembly is provided that is
configured to connect to a data communication link carried by a wired-pipe. A
control circuit is configured to transmit tool data via the communication link
during normal operations. The control circuit switches the transmission of at
least
some of the data via a mud pulse telemetry unit when the data communication
link
fails or when the data transmission is below a selected standard.
[0032] The data communication link may be any direct communication link,
including but not limited to an electrical conductor, an optical fiber or a
conductor
using aligned carbon nano-particles. The downhole tools may include any
combination of the tools, such as a resistivity tool, an imaging tool, a
nuclear tool,
a nuclear magnetic resonance tool, an acoustic tool, a formation testing tool
and a
directional drilling tool.
[0033] While the foregoing disclosure is directed to certain disclosed
embodiments and methods, various modifications will be apparent to those
skilled
in the art. It is intended that all modifications that fall within the scopes
of the
claims relating to this disclosure are deemed to be a part of the foregoing
disclosure.
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