Note: Descriptions are shown in the official language in which they were submitted.
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COMMUNICATING MEASUREMENT DATA FROM A WELL
TECHNICAL FIELD
[0001] The invention relates generally to communicating measurement data
from a
well.
BACKGROUND
[0002] To produce fluids from or to inject fluids into a well, various
completion
equipment can be provided into the well, such as tubings, packers, flow
control devices,
sensors, and so forth. The sensors deployed in a well are used to measure
various
parameters associated with fluids in the well or with the surrounding
reservoir.
[0003] The measurement data is then communicated over some type of a
telemetry
system to surface equipment. The telemetry system can be especially
complicated in a
subsea environment, where data transmission has to pass through a subsea tree
to be
routed to surface equipment. In many cases, a lossy telemetry stage is used at
the subsea
interface, wherein data is discarded if it satisfies certain parameters. For
example if a
change of pressure is less than some predetermined threshold then the new
pressure data
might not be transmitted but instead discarded. Conventionally, presence of
such a lossy
telemetry stage prevents use of encryption and compression. In implementations
that
involve a relatively large number of sensors, the amount of measurement data
can be
relatively large, and consequently more data may be discarded at the subsea
interface.
Bandwidth constraints on conventional telemetry systems can prevent timely
communication of measurement data to surface equipment, which leads to a
desire to
compress the data before it is transmitted. Also, in some scenarios,
maintaining security
of measurement data can be a concern, in which case an encryption algorithm
may be
employed. Conventionally, however, use of a lossy telemetry stage will prevent
application of compression or encryption as discussed above.
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SUMMARY
[0004] In general, a method of communicating measurement data from a
well includes
applying transformation to measurement data collected by sensors in the well,
transmitting the
transformed data through a subsea telemetry system that applies a lossy
compression
algorithm and then retransforming the data back into meaningful values. The
applied
transformation may include data compression or encryption.
[0004a] According to one aspect of the present invention, there is
provided a method
for communicating measurement data from a well, comprising: applying a
downhole
transformation to measurement data collected by sensors in the well, wherein
applying the
downhole transformation comprises converting the measurement data collected by
the sensors
into blocks, where at least one of the blocks contains portions of the
measurement data that
are expected to vary more than portions of the measurement data contained in
at least another
of the blocks; passing the transformed measurement data through an
intermediate
communications device that applies a lossy compression algorithm on the
blocks;
transforming data received from the intermediate communications device based
on application
of the lossy compression algorithm on the blocks so as to produce meaningful
data at a
destination communications device; wherein: applying the lossy compression
algorithm
comprises forwarding only blocks of the transformed measurement data that have
changed by
at least a predetermined threshold amount with respect to the prior
corresponding versions of
the blocks containing respective portions of prior measurement data from
sensors; and
transforming the received data comprises identifying blocks of the measurement
data not
transmitted by the intermediate communications device; and using prior
versions of the
identified blocks already present at the destination communications device to
produce the
meaningful data.
[0004b] According to another aspect of the present invention, there is
provided a
system comprising: sensors for deployment in a well; a first module to receive
measurement
data from the sensors and to transform first portions of the measurement data
from the sensors
into a first block and to transform second portions of the measurement data
from the sensors
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into a second block; an intermediate communications device to receive the
first and second
blocks from the first module and to apply a lossy compression algorithm on the
blocks,
wherein the lossy compression algorithm selects one of the blocks to not send
to a destination
communications device, wherein the first block has data that is expected to
vary at a slower
rate than data in the second block, wherein the selected one of the first and
second blocks that
is not sent to the destination communications device is the block where the
data has varied
from a previous version of the block by less than a threshold amount; and the
destination
communications device, wherein the destination communications device is
configured to:
receive data from the intermediate communications device based on application
of the lossy
compression algorithm, wherein the received data includes one of the first and
second blocks
sent by the intermediate communications device; and identify the one of the
first and second
blocks not sent by the intermediate communications device due to application
of the lossy
compression algorithm; and use a prior version of the identified block already
present at the
destination communications device to produce meaningful data for use at the
destination
communications device, wherein the prior version of the identified block is
combined with the
one of the first and second blocks contained in the received data to produce
the meaningful
data.
[0005] Other or alternative features will become apparent from the
following
description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] Fig. 1 illustrates an example arrangement that includes
sensors and a telemetry
system, according to an embodiment.
[0007] Fig. 2 illustrates an encryption algorithm, according to an
embodiment;
[0008] Fig. 3 illustrates an example arrangement that includes
sensors and a telemetry
system, according to another embodiment.
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DETAILED DESCRIPTION
[0009] In the following description, numerous details are set forth to
provide an
understanding of the present invention. However, it will be understood by
those skilled in the
art that the present invention may be practiced without these details and that
numerous
variations or modifications from the described embodiments are possible.
[0010] As used here, the terms "above" and "below;" "up" and "down;"
"upper" and
"lower;" "upwardly" and "downwardly;" and other like terms indicating relative
positions
above or below a given point or element are used in this description to more
clearly describe
some embodiments of the invention. However, when applied to
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equipment and methods for use in wells that are deviated or horizontal, such
terms may
refer to a left to right, right to left, or diagonal relationship as
appropriate.
[0011] In accordance with some embodiments, transformed data is sent from
downhole sensors in a well to an intermediate communications device. The
transformation may be compression of the data from a sensor, joint compression
of data
from multiple sensors, or encryption of the data. The intermediate
communications
device has a lossy compression stage that employs a lossy compression
algorithm in
which not all of the received measurement data is forwarded to a destination
communications device. The lossy compression algorithm allows for more
efficient use
of bandwidth between the intermediate communications device and the
destination
communications device. The intermediate communications device has the
characteristic,
however, that because not all of the data received by the intermediate
communications
device is forwarded, it is generally not possible to retransform the data back
to
meaningful or interpretable values at the destination (e.g., at surface
equipment) using
conventional techniques.
[0012] In one embodiment, the transformation applied is encryption. This is
of
benefit because the proprietary nature of the measurement data can be
maintained, which
is desirable if the intermediate communications device is being managed by a
different
entity than the entity that is operating the downhole sensors and destination
communications device. For example, a first company may be the provider of the
downhole sensors and the destination communications device, while a second
company
(different from the first company) is the provider of the intermediate
communications
device. The lossy characteristic of the intermediate communications device
might cause
the loss of sufficiently many bits of data that conventional
encryption/decryption
techniques cannot be used.
[0013] To protect the proprietary nature of the measurement data as it
passes
through the intermediate communications device, the measurement data is
encrypted.
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However, even though the measurement data is encrypted, the intermediate
communications device still has to be able to apply its lossy compression
algorithm. In
accordance with some embodiments, the encryption of the measurement data is
according
to an algorithm that allows for the application of such lossy compression
algorithm at the
intermediate communications device.
[0014] In another embodiment, the transformation applied is data
compression. In
the case that a large number of sensors are deployed across a wellbore, then
there will be
much similarity between the data from one sensor to the next. This provides
significant
opportunities for data compression. For example, in the case that each sensor
uses 32 bits
of data, it may be possible to instead use 32 bits to send the average value
of the sensors,
and use only 8 bits of data to send the difference between each sensor and the
average. Or
more sophisticated transformations may be used, in which the Fourier transform
of the
array data is taken, and a certain number of bits are assigned to each of the
transformed
variables, with fewer bits used for the highest order Fourier transforms. Such
compression can be done in a lossless fashion.
[0015] Fig. 1 illustrates an example arrangement that includes sensors
provided in
multiple wellbores, where two wellbores 100 and 102 are depicted in Fig. 1. In
other
examples, sensors can be provided in just one wellbore, or in more than two
wellbores.
Sensors 104 are provided in the first wellbore 100, and sensors 106 are
provided in the
second wellbore 102. The sensors 104, 106 may be provided in a sand face
completion.
Alternatively, sensors can be arranged as an array along a reservoir section
of the well.
[0016] Examples of sensors 104 and 106 include temperature sensors,
pressure
sensors, flow rate sensors, and/or sensors to measure various other parameters
associated
with the wellbores 100, 102, and/or surrounding reservoirs.
[0017] The sensors 104 are interconnected over a cable 108 (e.g.,
electrical cable or
fiber optic cable) to an inductive coupler 110 that has a first inductive
coupler portion
112 for mating with a second inductive coupler portion 114. Use of the
inductive coupler
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110 allows for the inductive coupler portion 114 and sensors 104 to be first
deployed as
part of a lower completion system, with an upper completion system including
the mating
inductive coupler portion 112 to be lowered at a later time. The inductive
coupler
portions 112 and 114 allow for electrical communication between different
completion
systems installed at different times. In alternative implementations, other
types of
communications mechanisms can be used, including electromagnetic communication
mechanisms, acoustic communication mechanisms, pressure pulse communication
mechanisms, wired communication mechanisms, optical communication mechanisms,
and so forth.
[0018] The inductive coupler portion 112 is electrically connected to a
downhole
control module 116, which can include a telemetry interface for communicating
over an
electrical cable 118 to an earth surface location. In one example, the
electrical cable 118
is a twisted pair cable. In other examples, other types of electrical cables
can be used. In
yet further examples, the cable 118 can be a fiber optic cable rather than an
electrical
cable.
[0019] The cable 118 is connected to a converter 120, which can be located
at an
earth surface location. In a subsea environment, the converter 120 can be part
of subsea
wellhead equipment provided at a sea floor. The converter 120 converts between
the
communications protocol used on the cable 118 (which can be any type of
communications protocol, including proprietary communications protocols used
by
different well operators), and an open communications protocol used on a
communications channel 122 between the converter 120 and a communications
module
124. One example of such an open communications protocol is a Transmission
Control
Protocol/Internet Protocol (TCP/IP). Other communications protocols can be
used in
other embodiments. An "open" communications protocol is a protocol that is not
a
proprietary protocol.
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[0020] In a subsea application, the communications module 124 can be a
subsea
communications module that is deployed somewhere in a body of water or at the
sea
floor. Note that although reference is made to subsea applications, it is
noted that
techniques according to some embodiments can also be applied to land-based
communications arrangements.
[0021] The subsea communications module 124 can receive data from other
sources, including a second converter 126 that is electrically coupled to the
sensors 106
in the second wellbore 102 through a downhole control module 127 and inductive
coupler 129. The subsea communications module 124 receives measurement data
from
multiple sources and assembles the measurement data for communication over
another
communications channel 130 to a destination communications device 132. In one
example, the communications channel 130 can be part of an umbilical provided
between
subsea equipment and sea surface equipment.
[0022] In a subsea application, the destination communications device 132
is a
surface (e.g., sea surface) controller, such as a surface controller provided
on a sea vessel
or a sea platform. Alternatively, the destination communications device 132
can be
remotely located on land, where transmission from the subsea communications
module
124 to the destination communications device can include communications over a
wireless link, such as a satellite link, cellular link, and so forth.
[0023] The communications module 124, or a combination of the
communications
module 124 and converter 120, can be considered an example of the
"intermediate
communications device" mentioned above. The intermediate communications device
may be operated by a third party such that security associated with
communication of
measurement data from the sensors (104, 106) that pass through the
intermediate
communications device to the destination communications device 132 would be
desirable.
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[0024] As further depicted in Fig. 1, the destination communications device
132 is
coupled to a computer 134 to allow for a user to access data that is received
by the
destination communications device 132. A user at the computer 134 can also
configure
various components along the chain of the communications arrangement in Fig.
1.
[0025] The subsea communications module 124 can apply a lossy compression
algorithm in which less than all of the received measurement data is
communicated over
the communications channel 130 to the destination communications device 132.
Note
that because the subsea communications module 124 is coupled to multiple
sources of
measurement data, the amount of measurement data that is received at the
subsea
communications module 124 can be relatively large. The communications channel
130
can have bandwidth constraints that may prevent timely communication of all
received
measurement data from the subsea communications module 124 to the destination
communications device 132. The lossy compression algorithm conserves the
bandwidth
of the communications channel 130 by communicating just a portion of all
received
measurement data to the destination communications device 132.
[0026] In some embodiments, for security purposes, the measurement data
received
at the subsea communications module 124 may include encrypted measurement
data. As
noted above, the subsea communications module 124 can actually be operated by
an
entity that is different from the entity that operates the components in the
wellbores 100
and 102, as well as the destination communications device 132. To prevent the
operator
of the subsea communications module 124 from understanding the proprietary
measurement data, the measurement data is encrypted, such as by the downhole
control
module 116 or 127 provided in the wellbore 100 or 102. However, in accordance
with
some embodiments, the encryption applied by the downhole control module 116 or
127
(or by the converter 120 or 126) does not prevent the application of the lossy
compression algorithm by the subsea communications module 124.
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[0027] The lossy compression algorithm applied by the subsea communications
module 124 can include an algorithm in which data is communicated only if the
data has
changed from a prior version of the data by at least some threshold amount
(i.e., the
current version of the measurement data is less than or greater than the prior
version of
the measurement data by more than the threshold amount). For example, if the
measurement data includes temperature data, then a current version of the
temperature
data is transmitted by the subsea communications module 124 over the
communications
channel 130 to the destination communications device 132 only if the current
version of
the temperature data differs from the prior version of the temperature data by
more than a
threshold temperature difference. By applying such lossy compression
algorithm, the
amount of traffic that is communicated over the communications channel 130
from the
subsea communications module 124 to the destination communications device 132
is
reduced.
[0028] As noted above, an open communications protocol, such as TCP/IP, is
used
over the channel 122, 123 between the converter 120, 126 and the subsea
communications module 124. An issue associated with the open communications
protocol employed over the channel 122, 123 is that protocol headers have to
be added to
each packet communicated between the converter 120, 126 and subsea
communications
module 124. If the open communications protocol is the TCP/IP protocol, then
the
headers added include TCP and IP headers, as well as any headers from higher
level
layers of the communications protocol. Thus, if the measurement data from
individual
sensors is sent in individual packets, the overhead can be quite large, since
there would
be many packets with corresponding overhead headers communicating traffic from
individual sensors over each communications channel 122, 123.
[0029] Although the converters 120, 126 are provided in the depicted
implementation, note that the converters 120, 126 can be omitted in other
implementations. In such other implementations, the downhole control modules
116, 127
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can communicate packets according to an open communications protocol to the
subsea
communications module 124.
[0030] To reduce the amount of overhead in the form of packet headers,
measurement data from multiple sensors can be assembled into larger blocks,
such that
each block can include measurement data from multiple sensors. Thus, rather
than
assemble measurement data from individual sensors in packets, the blocks
representing
measurement data of multiple sensors are assembled into packets. However, an
issue
associated with communicating measurement data from different sensors in large
blocks
is that the lossy compression algorithm applied by the subsea communications
module
124 may be made less effective.
[0031] To address this issue, in accordance with some embodiments, sensors
in a
well can be divided into banks (or other groups), with measurement data from
each bank
forming a data block. Thus, each bank includes N sensors, where N 2. The
number of
sensors in a bank can be selected by a well operator based on analyzing the
overhead
burden versus effective application of the lossy compression algorithm by the
subsea
communications module 124.
[0032] It is noted that one or more banks can be disabled, such as when
some fault
(e.g., an electrical short or a current surge) is present in the bank. The
converter 120 or
126 can stop polling for data from a particular bank if the converter senses
that the bank
has been disabled. Alternatively, the converter can continue to poll disabled
banks, with
the downhole control module 116 transmitting zeros for such disabled bank.
Since the
data block associated with a disabled bank would include just zeros, it is
noted that when
the subsea communications module 124 decides whether or not to send a
particular data
block associated with the disabled bank, the subsea communications module 124
will
detect that the current version of the data block (which contains zeros) will
not have
changed from a previous version of the data block (which also contains zeros);
as a result,
according to the lossy compression algorithm, the subsea communications module
124
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would not forward the data block of the disabled bank to the destination
communications
device 132.
[0033] Also, in accordance with some embodiments, encryption of the
measurement data associated with each bank of sensors can be performed in the
following manner. The encryption can be performed by the downhole control
module
116, 127, or by the converter 120, 126. Assume there are N sensors in a bank,
where
each measurement data from a particular sensor has M bits, A/11 . Then, the
most
significant bits of corresponding measurement data from the N sensors of the
bank can be
collected into a first block. The next most significant bits of the respective
measurement
data from the N sensors are collected into a second block. This process
continues for
each bit of measurement data from respective sensors. Effectively, according
to the
encryption algorithm of one embodiment, the measurement data of each sensor in
a bank
is divided into individual bits, with different individual bits of the
measurement data of
each sensor provided into different corresponding blocks. Each block includes
a group of
bits from multiple sensors of the bank.
[0034] Fig. 2 shows an example implementation, where each measurement data
is
assumed to be a byte that includes eight bits: b0, bl, b2, b3, b4, b5, b6, and
b7, where b0
is the least significant bit and b7 is the most significant bit. Also, Fig. 2
shows N
measurement data bytes from N sensors (sensor 1, sensor 2, ... sensor /V). The
encryption
algorithm takes the most significant bits b7 from the N measurement data bytes
and
collects them into a block, referred to as B7. Thus, bit b7 from sensor 1, bit
b7 from
sensor 2, and so forth up to bit b7 from sensor N, is collected into the block
B7.
Similarly, the encryption algorithm collects the b6 bits from the measurement
data bytes
of the N sensors into a block B6. The same is repeated for the other bits of
the
measurement data bytes from the N sensors for collection into blocks B5, B4,
B3, B2, Bl,
and BO. These are the blocks that are communicated to the subsea
communications
module 124.
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[0035] In the lossy compression algorithm applied by the subsea
communications
module 124, it is noted that it is generally unlikely for a current version of
block B7
(containing the most significant bits of measurement data from multiple
sensors) to differ
from a prior version of the block B7, since it is unlikely for measurement
data to differ
significantly, particularly if the measurement data is being communicated at
relatively
short time intervals. Consequently, it is unlikely that the subsea
communications module
124 will detect that the most significant block B7 will differ from a previous
version by
more than the threshold amount; therefore, the subsea communications module
124, in
applying its lossy compression algorithm, will usually not forward block B7 to
the
destination communications device 132 over the communications channel 130
(Fig. 1).
On the other hand, it is likely that block BO (the block containing the least
significant bits
of measurement data from the N sensors) will differ by greater than the
threshold amount
from a previous version; therefore, it is likely that block BO will be
forwarded to the
destination communications device 132.
[0036] Since the encryption of the measurement data is achieved by
communicating
individual bits from corresponding measurement data of respective sensors in
different
blocks, from the perspective of the subsea communications module 124, the data
is
practically meaningless (since the subsea communications module 124 is unaware
of the
specific encryption algorithm used). Each block B0-B7 does not include any
meaningful
data from any individual sensor. However, even though the data is encrypted,
the subsea
communications module 127 is still able to apply its lossy compression
algorithm.
[0037] At the receiving end (e.g., destination communications device 132 or
computer 134), the blocks received from the subsea communications module 124
can be
re-assembled into meaningful measurement data bytes for analysis. "Meaningful"
data
refers to data that can be understood by a user or a software program. Note
that the blocks
not transmitted by the subsea communications module 124 due to application of
the lossy
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compression algorithm are present at the destination communications device 132
since
such blocks have not changed.
[0038] In a different embodiment, instead of collecting individual bits
into
respective blocks, it is noted that two or more bits of measurement data from
each sensor
can be collected into corresponding blocks. In another example, two bits from
each
measurement data byte of the multiple sensors can be collected into blocks.
Thus, in this
example, the b0 and bl bits from the measurement data of the N sensors can be
collected
into one block, the b2 and b3 bits of the measurement data of the N sensors
can be
collected into another block, and so forth. Thus, generally, the encryption
performed
according some embodiments is to divide each measurement data of a particular
sensor
into multiple portions (where each portion includes one bit or multiple bits),
and to
provide individual portions from respective measurement data of the N sensors
into a
corresponding block.
[0039] In other embodiments, other types of transformation algorithms can
be
applied by the converters 120, 126, or by downhole control modules 116, 127,
or even by
the sensors. For example, the transformation can be based on Haar
transformation, which
is a particular type of wavelet transformation. The transformation takes an
array of data
and converts the data into the part that changes the most frequently and the
part that
changes less frequently. The part that changes most frequently is provided in
one block,
and the part that changes less frequently is provided in another block. As
noted above, the
transformation applied can alternatively be a compression algorithm applied on
measurement data from the sensors.
[0040] In general, such a transformation algorithm performed seeks to keep
slowly
varying data together in blocks and to keep more rapidly varying data in other
blocks,
such that the lossy compression algorithm applied by the intermediate
communications
device can be enhanced.
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[0041] In yet further embodiments, to reduce the amount of data
that is actually
communicated to the subsea communications module, the sensors can omit to send
some
number of the most significant bits of each measurement data. The most
significant bits
of data may be irrelevant when the well operator is interested in detecting
drift of
temperature measurements. Also, some number of the least significant bits may
be
irrelevant for drift analysis. Multiple measurement data from the same sensor
can be
averaged over some time interval, which effectively removes the need to save
the lowest
order bits. By removing some number of the most significant bits and some
number of
the least significant bits, the amount of data that is actually sent can be
further reduced.
,
[0042] Fig. 3 shows an alternative arrangement according to
another embodiment to
allow for communication of measurement data to a destination communications
device.
In the Fig. 3 arrangement, measurement data' frcim sensors 300 and sensors 302
in
different wells are provided through respective converters 304, µ306 to
respective subsea
communications modules 308, 310. Note that the data from sensors 300 are
provided
through a downhole control module 303 to the converter 304. The converters 304
and
306 can apply an encryption as discussed above, and the subsea communications
modules
308 and 310 can apply the lossy compression algorithm discussed above.
[0043] Data from the subsea communications modules 308 and 310
are passed to a
subsea module (SM) 322, which can also receive data from other sources. The SM
322
can pass data to another electronic module 314, which can receive data from
other SMs
316 and 318. The electronic module 314 is connected to a surface control unit
320,
which can be considered the destination communications device in this
implementation.
The surface control unit 320 can be connected to other devices over a network
324, such
as an Ethernet network or some other type of network.
[0044] The transformation and lossy compression algorithms
discussed above can
be performed by hardware or by a combination of software and hardware.
Instructions of
the software can be loaded for execution on a processor. The processor can
include
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microprocessors, microcontrollers, processor modules or subsystems (including
one or
more microprocessors or microcontrollers), or other control or computing
devices. A
"processor" can refer to a single component or to plural components.
[0045] Data and instructions (of the software) can be stored in
respective storage
devices, which are implemented as one or more computer-readable or computer-
usable
storage media. The storage media include different forms of memory including
semiconductor memory devices such as dynamic or static random access memories
(DRAMs or SRAMs), erasable and programmable read-only memories (EPROMs),
electrically erasable and programmable read-only memories (EEPROMs) and flash
memories; magnetic disks such as fixed, floppy and removable disks; other
magnetic
media including tape; and optical media such as compact disks (CDs) or digital
video
disks (DVDs).
[0046] While the invention has been disclosed with respect to a limited
number of
embodiments, those skilled in the art, having the benefit of this disclosure,
will appreciate
numerous modifications and variations therefrom. It is intended that the
appended claims
cover such modifications and variations as fall within the scope of the
claims.
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