Note: Descriptions are shown in the official language in which they were submitted.
1
DOVVNHOLE LOW RATE LINEAR REPEATER RELAY NETWORK TIMING
SYSTEM AND METHOD
[0001] BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The present invention relates generally to telemetry apparatuses
and methods,
and more particularly to acoustic telemetry relay network timing for
exploration, completion
and production wells for hydrocarbons and other resources, and for other
telemetry
applications.
2. Description of the Related Art
[0003] Acoustic telemetry is a method of communication used in the well
drilling,
completion and production industries. In a typical drilling environment,
acoustic extensional
.. carrier waves from an acoustic telemetry device are modulated in order to
carry information
via the drillpipe as the transmission medium to the surface. Upon arrival at
the surface, the
waves are detected, decoded and displayed in order that drillers, geologists
and others helping
steer or control the well are provided with drilling and formation data. In
production wells,
downhole information can similarly be transmitted via the well casings.
Acoustic telemetry
.. transmits data to the surface in real-time and is independent of fluid
flow, depth, well
trajectory and other drilling parameters.
[0004] The theory of acoustic telemetry as applied to communication
along
drillstrings and well casings has a long history, and a comprehensive
theoretical
understanding has generally been backed up by accurate measurements. It is now
generally
.. recognized that the nearly regular periodic structure of drillpipe and well
casings imposes a
passband/stopband structure on the frequency response, similar to that of a
comb filter.
Dispersion, phase non-linearity and frequency-dependent attenuation make
drillpipe a
challenging medium for telemetry, the situation being made even more
challenging by the
significant surface and downhole noise generally experienced.
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100051 When exploring for oil or gas, in coal mine drilling and in
other drilling
applications, an acoustic transmitter is preferentially placed near the BHA,
typically near the
drill bit where the transmitter can gather certain drilling and geological
formation data,
process this data, and then convert the data into a signal to be transmitted
up-hole to an
appropriate receiving and decoding node. In some systems, the transmitter is
designed to
produce elastic extensional stress waves that propagate through the
drillstring to the surface,
where the waves are detected by sensors, such as accelerometers, attached to
the drill string
or associated drilling rig equipment. These waves carry information of value
to the drillers
and others who are responsible for steering the well. Examples of such systems
and their
components are shown in: Drumheller U.S. Patent No. 5,128,901 for Acoustic
Data
Transmission through a Drillstring; Drumheller U.S. Patent No. 6,791,470 for
Reducing
Injection Loss in Drill Strings; Camwell et al. U.S. Patent No. 7,928,861 for
Telemetry Wave
Detection Apparatus and Method; and Camwell et al. U.S. Patent No. 8,115,651
for Drill
String Telemetry Methods and Apparatus.
[0006] Acoustic communication through drilling and production strings
(collectively
"drillstrings") is generally limited by available frequency spectra and signal
attenuation.
Consequently, transmission data rates tend to be relatively low, e.g., in the
range of tens of
bits per second, and multiple repeater nodes have previously been used to
boost the telemetry
signals and overcome the problem of acoustic signal attenuation and associated
range
limitations. The inclusion of multiple acoustic transceiver nodes within a
drillstring forms a
low rate linear repeater dam network. As used herein "nodes" are defined as
receivers (Rx),
transmitters or transceivers (Tx) for telemetry signals traveling between
adjacent pairs of
nodes. Alternatively, the nodes could be associated with and referred to as
"stations" (e.g.,
STO, ST1. STn) located along the drillstring. The low data rate linear
repeater networks
suffer from high latency (time for data to propagate through the network) due
to the time it
takes for each node to receive data packets and relay data onward. An
objective of repeater
networks is to relay data as quickly as possible after initial receipt, in
order to minimize
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latency of data delivered to the surface (or other destination) and to
maximize data
throughput.
100071 The latency of delivered measurement data translates into a
potentially large
time difference between the time at which a downhole sensor measurement is
made and when
that value is delivered to the surface, obscuring potentially valuable
correlation between
downhole and upholc events. Additionally, as sensor acquisition at each node
within the
network occurs at different points in time, the accuracy of inter-node
differential
measurements is limited, impairing the ability to discern transient events
traversing the string.
[00081 A possible solution to drillstring acoustic communication latency-
associated
problems is to include time-of-measurement information with transmitted
information from
each node. However, bandwidth limitations make the inclusion of time-of-
measurement
(e.g., sensor acquisition time) information overhead in the acoustic packets
undesirable, and
require all downhole clocks to be very accurately aligned, which can be
problematic given
the significant temperature differentials across the networks (e.g., 150 C or
more) and the
.. long periods of continuous network operation.
SUMMARY OF THE INVENTION
100091 In the practice of the present invention, a repeater network is
provided with
highly controlled and predictable timing. This is achieved by reconfiguring
the network with
constants, which are known to all nodes: guard time, allocated time between
receipt and
transmission (relay), thus allowing for processing time, acquisition of sensor
data and
subsiding of channel delay spread (echoes, e.g., 0.5-5 seconds); and data
packet transmission
time, a function of the internodc data rate and the packet bit length (for
example, a 100-bit
packet transmitted at a 20 bits-per-second (bps) link rate would have a data
packet
transmission time of 5 seconds). The sensor acquisition time is typically
negligible, and is
.. determined by the time between the acquisition of a measurement from a
sensor to
transmission of the corresponding data through the telemetry network. Based on
the network
time constants, a surface time-of-measurement for the relative timing offsets
of all relay
transmissions within the network can be computed from variables including: the
packet
received times, packet types, and guard and sensor acquisition times.
Propagation delays can
either be neglected or included in the time-of-measurement computation based
on node
4
separations and depth from surface, i.e., node depths. The advantages of the
repeater network
timing control include, without limitation:
= No costly overhead associated with time-of-measurement within acoustic
packets.
= No network synchronization signal is required.
= Variable inter-node propagation delays do not impact.
= Agility, timing can change from frame-to-frame (packet type-to-packet
type).
1009a] In a broad aspect, moreover, the present invention relates to a
downhole linear
repeater relay network timing control system for a drilling rig including a
drillstring extending
subsurface downwardly from a surface and terminating at a drillstring end, the
linear repeater
relay network timing control system comprising: a primary node located near
said drillstring
end and including a sensor configured to output signal data corresponding to
downhole
conditions; a surface node; and multiple nodes located between the primary
node and the
surface node and associated with the drillstring, the multiple nodes
configured to receive and
retransmit the signal data to form a telemetry relay network, wherein linear
repeater relay
network timing control system is configured to control one or more variables
within a relay
frame according to a plurality of preconfigured network constants that are
known to all of the
nodes, wherein the preconfigured network constants include at least guard
times allocated
between receipt and re-transmission of the signal data and packet transmission
duration;
wherein said multiple nodes are configured to individually derive transmission
timing offsets
relative to each other based on point in time of receipt of the signal data
and the network
constants known to all of the nodes, wherein the multiple nodes are configured
to select
measurement data for transmission with the signal data, and wherein selection
of the
measurement data at the multiple nodes is time-synchronized; and a signal
receiver configured
to calculate an originating node sensor data acquisition point in time from
the point in time of
receipt of the signal data for use as an accurate time-of-measurement.
1009b] In another broad aspect, the present invention relates to a downhole
linear repeater
relay network timing control system for a drilling rig including a drillstring
extending
subsurface downwardly from a surface and terminating at a drillshing end, the
downhole
linear repeater relay network timing control system comprising: multiple nodes
located
downhole between said drillstring end and said surface and associated with
said drillstring, at
least one node located at the surface, two or more of said nodes including a
sensor adapted for
providing signal data output corresponding to downhole conditions, and said
nodes receiving
and re-transmitting said signal data output to form a telemetry relay network;
said relay
network system being adapted for controlling one or more variables within a
relay frame
according to a plurality of preconfigured constants that are known to all
nodes, wherein the
Date Recue/Date Received 2022-10-07
4a
preconfigured network constants include at least guard times allocated between
receipt and re-
transmission of the signal data and packet transmission duration; said nodes
being individually
adapted to derive timing offsets relative to each other based on said network
constants and
signal reception points in time; two or more of said nodes selecting current
or buffered past
sensor data, such that sensor data acquisitions at said nodes are time-
synchronized with each
other; and said nodes sending said selected sensor data to a destination node
located downhole
or at surface, directly or via said telemetry relay network.
[0009c] In another broad aspect, the present invention relates to a downhole
linear repeater
relay network timing method for acoustic telemetry, the method comprises the
steps of:
providing an originating node near a downhole end of a drillstring and having
a sensor
configured to transmit signal data corresponding to downhole conditions;
providing
intennediate nodes along the drillstring configured to receive and retransmit
the signal data to
form a telemetry relay network, wherein each intermediate node has a sensor
configured to
acquire measurement data, and wherein the signal data is relayed between the
nodes as data
packets; determining with said relay timing system, transmission times based
on signal data
received times from said intermediate nodes according to a plurality of
preconfigured network
constants that are known to all nodes, wherein the preconfigured network
constants include at
least guard times allocated between receipt and re-transmission of the signal
data and packet
transmission duration; synchronizing sensor acquisition within the linear
repeater relay
network; configuring data packets received at a surface node with network
synchronized
payload data; adjusting timestamps of said synchronized payload data according
to that of the
originating node; providing all nodes with the same acquisition timestamp; and
acquiring
sensor measurement data at all intermediate nodes at the same point in time as
the originating
node.
[0010] Other objects and advantages of the present invention will be
apparent from
the following description. Detailed descriptions of exemplary embodiments are
provided in
the following sections. However, the invention is not limited to such
embodiments.
Date Recue/Date Received 2022-10-07
4b
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. I is a diagram of a typical drilling rig, including an
acoustic telemetry
system, which can be provided with a downhole linear repeater relay network
timing system
embodying an aspect of the present invention.
[0012] FIG. 2 is a fragmentary, side-elevational and cross-sectional
view of a typical
drillstring, which can provide the medium for acoustic telemetry transmissions
for relaying,
repeating and timing with the present invention.
[0013] FIG. 3 is a schematic diagram of the repeater relay network
timing system of
the present invention, particularly showing accurate surface time-of-
measurement.
[0014] FIG. 4 is another schematic diagram of the repeater relay network
timing
system, particularly showing how a surface decode time-of-receipt of telemetry
signal can be
related back to the sensor acquisition time of any network node.
[0015] FIG. 5 is another schematic diagram of the repeater relay network
timing
system, particularly showing how a surface decode time-of-receipt of telemetry
signal of a
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packet containing synchronized data is related to synchronized sensor
acquisition across the
network.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
100161 In the following description, reference is made to -up" and
"down" waves, but
5 this is merely for convenience and clarity. It is to be understood that
the present invention is
not to be limited in this manner to conceptually simple applications in
acoustic
communication from the downhole end of the drillstring to the surface. It will
be readily
apparent to one skilled in the art that the present invention applies equally,
for example, to
subsurface nodes, such as would be found in telemetry repeaters.
I. Drilling Rig, Drillstring and Well Environment
100171 Referring to the drawings in more detail, the reference numeral 2
generally
designates a downhole low rate linear repeater relay network timing or control
system
embodying an aspect of the present invention. Without limitation on the
generality of useful
applications of the system 2, an exemplary application is in a drilling rig 4
(FIG. 1). For
example, the rig 4 can include a derrick 6 suspending a traveling block 8
mounting a kelly
swivel 10, which receives drilling mud via a kelly hose 11 for pumping
downhole into a
drillstring 12. The drillstring 12 is rotated by a kelly spinner 14 connected
to a kelly pipe 16,
which in turn connects to multiple drill pipe sections 18, which are
interconnected by tool
joints 19, thus forming a drillstring of considerable length, e.g., several
kilometers, which can
be guided downwardly and/or laterally using well-known techniques.
100181 The drillstring 12 terminates at a bottom-hole assembly (BHA) 20
at acoustic
transceiver node (STO). Other rig configurations can likewise employ the
present invention,
including top-drive, coiled tubing, etc. Moreover, additional applications
include completion
rigs, completion strings, casing strings, gravel packs, frac packs and other
applications.
Without limitation on the generality of useful applications of the present
invention, acoustic
telemetry systems in general can utilize the repeater network timing control
system and
method of the present invention. FIG. I also shows the components of the
drillstring 12 just
above the BHA 20, which can include, without limitation, a repeater
transceiver node 26 ST1
and an additional repeater transceiver node 22, ST2. An upper, adjacent
drillpipe section I 8a
is connected to the repeater 22 and the transmitter 26. A downhole adjacent
drillpipe section
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I fib is connected to the transmitter 26 and the BHA 20. A surface receiver
(node) 2] can be
provided at or near the upper end of the drillstring 12.
[0019] FIG. 2 shows the internal construction of the drillstring 12,
e.g., an inner
drillpipe 30 within an outer casing 32. Interfaces 28a, 28b are provided for
connecting
drillpipe sections to each other and to the other drillpipe components, as
described above.
W.1 illustrates an acoustic, electromagnetic or other energy waveform
transmitted along the
drillstring 12, either upwardly or downwardly. The drillstring 12 can include
multiple
additional repeaters 22 at intervals determined by operating parameters such
as optimizing
signal transmissions with minimal delays and errors. The drillstring 12 can
also include
multiple sensors along its length for producing output signals corresponding
to various
downhole conditions.
II. Acoustic Network: Operation
[0020] FIG. 3 shows the operation of a downhole low rate linear repeater
acoustic
network timing control system. Other applications of the present invention
include
electromagnetic signal telemetry systems and systems transmitting signaLs
through other
media, such as drilling mud, ground, water, air, etc.
100211 Telemetry data packets contain sensor or tool status data and are
transmitted
fi U111 the ptioraty itodc(STO, typically the deepest node) and relayed from
node-to-node to
the surface receiver 21 (Surface Rx), which is generally located at or near
the wellhead. The
telemetry data packets include sensor measurements from the BHA 20 and other
sensors
along the drillstring 12. Such data packet sensor measurements can include,
without
limitation, wellbore conditions (e.g., annular/bore/differential pressure,
fluid flow, vibration,
rotation, etc.). Local sensor data can be added to the data packet being
relayed at each sensor
node, thus providing along-string-measurements (ASMs).
100221 A single node functions as the master node (e.g., STO) and is
typically an edge
node at the top or bottom of the drillstring l2. The master node monitors well
conditions and
sends data packets of varying types and intervals accordingly. In addition to
the long
transmission/reception times associated with low data rate links, the
asynchronous nature of
wellbore variation tends to cause latency in an ASM operating mode because
data-receiving
nodes must await incoming packets before determining what sensor measurements
must be
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acquired for inclusion in the packets being relayed. Such latency in a low-
throughput
repeater network translates into a potentially large time difference between
the point when a
downhole sensor measurement is made and when that value is delivered to the
surface.
Although including time-of-measurement (i.e., telemetry signal receive time)
information
within each acoustic packet with measurement data delivered to the surface can
partly
address this problem, additional problems can arise based on prohibitively
large bandwidth
requirements necessitated by the network low data rates, and the necessity of
highly accurate
alignment (synchronization) of downhole and surface clocks, which can be
problematic due
to relatively wide temperature differentials across the network (e.g., 150 C
+), and long
periods of network operation.
Ill. Acoustic Network: Relay Timing and Control
100231 According to the system and method of the present invention, all
time
constraints are controlled based on pre-configured constants, which are input
to all nodes.
The pre-configured constants can include:
= Civard Times: time allocated between receipt and transmission (relay) to
allow for
processing time, acquisition of sensor data and channel delay spread (echoes)
subsiding. Typically about 0.5 to 5.0 seconds.
= Packet Transmission Time: a function of the internode data rate and
packet bit length.
For example, transmitting 100 bits (c4 20 bps link rate = 5 seconds.
= Sensor Acquisition Time: time between the acquisition and measurement from a
sensor to transmission of data through the telemetry network. Typically
negligible,
e.g. about 5-100 ms.
100241 With all time controlled within such a frame, the surface
receiver can calculate
the relative timing offsets of all relay transmissions within the network
based on the telemetry
signal received time (e.g., time-of-measurement) of any packet and its type.
With the
additional information of sensor acquisition time, an exact time of sensor
measurement can
be calculated from the received time and used as an accurate time-of-
measurement as
follows:
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N : Decoded Packet STID
o :Originating Station ID
Packet Time :# payload bits (link bit rate)
Time of measurement =
Surface DecodeTime[N] - E Packet Time[n]- Guard Timex (N - o) - Ac Time[o]
n-o
100251 Wave propagation delays tend to minor relative to the above
delays, and can
be neglected, or can be easily accounted for with an additional subtraction
based on
originating node separation from the surface and group velocity of the packet
signal (i.e.
propagation delay = node depth x group velocity). In this way, a surface
decode time-of-
measurement can be related back to the signal receive time of any network
node, as shown in
FIGS. 4 and 5.
100261 In eases requiring quality differential measurements between
nodes, all nodes
must acquire sensor measurement data at the same point in time, and add the
data to the
appropriate relay packet such that the packet delivered to the surface
contains time-
synchronized sensor data acquisition. This can be accomplished with controlled
network
timing, if, based upon receipt time and type of a packet, all nodes can
calculate the relative
point in time at which the primary node (e.g. STO, deepest node) acquired its
measurement
data, and acquire sensor data at that same point in time.
[00271 From the perspective of the receiver node(s), the primary node
sensor
acquisition point occurred in the past. Sensor acquisition must therefore
occur regularly and
be buffered such that past measurement values are accessible. Buffer capacity
and sampling
rate are determined by the greatest possible frame length of all configurable
modes, and the
required alignment accuracy in the data of the network synchronized
measurement. At the
surface, the packets that arc configured with network synchronized payload
data will have
their times-of-measurement adjusted according to that of the primary node.
[00281 In the practice of the method of the present invention, all nodes
acquire sensor
measurement value at the same point in time as the primary node. All nodes
have the same
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acquisition time. A surface decode time-of-receipt of telemetry signal can be
related back to
the sensor acquisition time of STO, as shown in FIG. 5.
IV. Extensions and Additional Applications
100291 Without limitation on the generality of useful applications of
the present
invention, the network timing control system and method described above can bc
extended
and applied to a wide range of additional applications, including:
= Applicable to electromagnetic pulse systems as well as acoustic.
= Applicable to downlink, uplink and bi-directional networks.
= The network synchronized sensor acquisition could be aligned with any
node within
the network, or any point in time within a frame.
[0030] It is to be understood that the invention can be embodied in
various forms, and
is not to be limited to the examples discussed above. The range of components
and
configurations which can be utilized in the practice of the present invention
is virtually
unlimited.
