U.S. patent application number 14/367937 was filed with the patent office on 2014-12-04 for cable telemetry synchronization system and method.
This patent application is currently assigned to Schlumberger Technology Corporation. The applicant listed for this patent is Schlumberger Holdings Limited, Schlumberger Technology Corporation, Services Petroliers Schlumberger. Invention is credited to Yasumasa Fujisawa, Yuichi Kobayashi, Milos Milosevic, Takeaki Nakayama, Thi Huong Lien Nguyen, David Santoso, Tsubasa Tanaka, Kun Wang, Nalin Weerasinghe.
Application Number | 20140354446 14/367937 |
Document ID | / |
Family ID | 48698531 |
Filed Date | 2014-12-04 |
United States Patent
Application |
20140354446 |
Kind Code |
A1 |
Nakayama; Takeaki ; et
al. |
December 4, 2014 |
Cable Telemetry Synchronization System and Method
Abstract
Cable telemetry synchronization systems and methods. The
synchronization can involve positioning downhole equipment into a
wellbore via a cable operatively coupled to a surface module that
can include a telemetry system master clock. The downhole equipment
can include a toolbus master node and at least one slave node
module having a node clock operatively coupled to the toolbus
master node. The synchronization can also involve sending a frame
start command to the at least one slave node module from the
toolbus master node at predetermined intervals, receiving a clock
value from each of the at least one slave node module, calculating
a clock offset for each of the at least one slave node module, and
sending an absolute clock value and the calculated clock offset for
each of the at least one slave node module via a downlink
synchronization command to the at least one slave node module.
Inventors: |
Nakayama; Takeaki;
(Machida-Shi, JP) ; Kobayashi; Yuichi;
(Machida-shi, JP) ; Wang; Kun; (West Windsor,
NJ) ; Weerasinghe; Nalin; (Imbulgoda, LK) ;
Milosevic; Milos; (Houston, TX) ; Santoso; David;
(Sugar Land, TX) ; Fujisawa; Yasumasa;
(Sagamihara-shi, JP) ; Nguyen; Thi Huong Lien;
(Yokohama-shi, JP) ; Tanaka; Tsubasa;
(Yokosuka-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Schlumberger Technology Corporation
Services Petroliers Schlumberger
Schlumberger Holdings Limited |
Sugar Land
Paris
Tortola |
TX |
US
FR
VG |
|
|
Assignee: |
Schlumberger Technology
Corporation
Sugar Land,
TX
|
Family ID: |
48698531 |
Appl. No.: |
14/367937 |
Filed: |
December 19, 2012 |
PCT Filed: |
December 19, 2012 |
PCT NO: |
PCT/US12/70437 |
371 Date: |
June 23, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61581091 |
Dec 29, 2011 |
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|
61581093 |
Dec 29, 2011 |
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61581096 |
Dec 29, 2011 |
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Current U.S.
Class: |
340/854.9 |
Current CPC
Class: |
G06F 1/14 20130101; E21B
47/12 20130101 |
Class at
Publication: |
340/854.9 |
International
Class: |
E21B 47/12 20060101
E21B047/12 |
Claims
1. A cable telemetry synchronization system for a wellsite having a
rig positionable about a borehole penetrating a subterranean
formation, comprising: a surface module comprising a telemetry
system clock; downhole equipment deployable into a wellbore via a
cable operatively coupled to the surface module, the downhole
equipment comprising: at least one slave node module, each of the
at least one slave node module having a node clock and interface
packet; and a downhole master node module comprising a toolbus
master node clock synchronized to the telemetry system clock, and
the downhole master node module sends a frame start command to each
of the at least one slave node module to synchronize the node
clock(s) to the toolbus master node clock.
2. The cable telemetry synchronization system according to claim 1,
further comprising a global positioning system (GPS) clock; wherein
the telemetry system clock and the toolbus master node clock
further synchronize to the GPS clock.
3. The cable telemetry synchronization system according to claim 1,
wherein the downhole master node module determines, for each of the
at least one slave node module, a clock offset based on a function
of an arrival time for the frame start command and a response time
for a return uplink packet from each of the at least one slave node
module in response to the frame start command.
4. The cable telemetry synchronization system according to claim 3,
wherein, upon determining the clock offset for each of the at least
one slave node module, the downhole master node module sends an
absolute clock value and the clock offset for each of the at least
one slave node module to a relevant one of the at least one slave
node module, and each relevant one updates the node clock based on
the absolute clock value and the clock offset for the relevant
one.
5. The cable telemetry synchronization system according to claim 3,
wherein the interface packet for each of the at least one slave
node module, upon receipt of the absolute clock value and a clock
offset time, time stamps slave node event data based on the
absolute clock value and the clock offset time for the at least one
slave node module; and wherein the slave node event data is
obtained by at least one downhole tool coupled to the at least one
slave node module.
6. The cable telemetry synchronization system according to claim 1,
wherein each of the at least one slave node module further
comprises a clock and data recovery (CDR) module that, upon receipt
of an uplink message at the at least one slave node module, detects
a preamble of the uplink message indicative of a coding scheme used
by at least one lower node of the at least one slave node module
for the uplink message, and locks the at least one slave node
module to the detected coding scheme of the preamble.
7. The cable telemetry synchronization system according to claim 1,
wherein each of the at least one slave node module further
comprises a clock recovery (CR) module that, upon receipt of a
downlink message, detects the frame start command.
8. The cable telemetry synchronization system according to claim 1,
further comprising a numerically controlled oscillator, the toolbus
master node clock being driven by the numerically controlled
oscillator.
9. A method for synchronizing a cable telemetry synchronization
system of a wellsite having a rig positionable about a wellbore
penetrating a subterranean formation, comprising: positioning
downhole equipment into the wellbore via a cable, the downhole
equipment comprising a toolbus master node and at least one slave
node module operatively coupled to the toolbus master node, each of
the at least one slave node module having a node clock; sending a
frame start command to the at least one slave node module from the
toolbus master node at predetermined intervals; receiving a clock
value from each of the at least one slave node module; calculating
a clock offset for each of the at least one slave node module; and
sending an absolute clock value and the calculated clock offset for
each of the at least one slave node module via a downlink
synchronization command to the at least one slave node module.
10. The synchronization method according to claim 9, wherein
calculating the clock offset further comprises determining, for
each of the at least one slave node module, the clock offset based
on a function of an arrival time for the frame start command and a
response time for a return uplink packet from each of the at least
one slave node module in response to the frame start command.
11. The synchronization method according to claim 9, further
comprising: obtaining slave node event data by at least one
downhole tool coupled to the at least one slave node module; and
upon receipt of the absolute clock value and a clock offset time,
time stamping the slave node event data based on the absolute clock
value and the clock offset time for the at least one slave node
module.
12. The synchronization method according to claim 9, further
comprising updating the node clock of a relevant one of the at
least one slave node module based on the absolute clock value and
the clock offset for the relevant one slave node.
13. The synchronization method according to claim 9, further
comprising determining, for each of the at least one slave node
module, a phase-lock adjustment based on a function of an arrival
time for the frame start command.
14. The synchronization method according to claim 9, further
comprising synchronizing the toolbus master node and the at least
one slave node module to a global positioning system (GPS) clock.
Description
BACKGROUND
[0001] The following descriptions and examples are not admitted to
be prior art by virtue of their inclusion in this section.
[0002] Hydrocarbon fluids, such as oil and natural gas, may be
obtained from a subterranean geologic formation, referred to as a
reservoir, by drilling a well that penetrates a hydrocarbon-bearing
formation. A variety of downhole tools may be used in various areas
of oil and natural gas services. In some cases, downhole tools may
be used in a well for surveying, drilling, and production of
hydrocarbons. The downhole tools may communicate with the surface
via various telemetry systems. In some cases, the downhole tools
may comprise one or more individual modules in operative
communication with one another, such as a master module and
multiple slave modules. Examples of communication systems are
provided in U.S. Pat. Nos. 6,628,992, 7,181,515, and Application
20020178295.
[0003] With the increased precision of downhole tools and sensors,
relatively shorter time may be available to send increasingly
larger amounts of data. In addition to new modules and assemblies
being developed for downhole use on a continuing basis, tool bus
systems may facilitate communication between older and newer
generation modules in order to obtain the maximum service life from
existing modules.
[0004] Applications of disclosed embodiments of the present
disclosure are not limited to these illustrated examples, different
industrial applications may benefit from implementations of the
following disclosure.
SUMMARY
[0005] In at least one aspect, the disclosure relates to a cable
telemetry synchronization system for a wellsite having a rig
positionable about a borehole penetrating a subterranean formation.
The system can include a surface module including a telemetry
system clock. The system can also include downhole equipment
deployable into the wellbore via a cable operatively coupled to the
surface module. The downhole equipment can include at least one
slave node module, each of the slave node modules having a node
clock and an interface packet. The downhole equipment can also
include a downhole master node module including a toolbus master
node clock synchronized to the telemetry system clock. The downhole
master node module can send a frame start command to each of the
slave node modules to synchronize the node clocks to the toolbus
master node clock.
[0006] In at least another aspect, the disclosure relates to a
method for synchronizing a cable telemetry synchronization system
of a wellsite having a rig positionable about a wellbore
penetrating a subterranean formation. The method can include
positioning downhole equipment into the wellbore via a cable. The
downhole equipment can include a toolbus master node and at least
one slave node module operatively coupled to the toolbus master
node. Each of the slave node modules has a node clock. The method
can include sending a frame start command to the at least one slave
node module from the toolbus master node at predetermined
intervals, receiving a clock value from each of the slave node
modules, calculating a clock offset for each of the slave node
modules, and sending an absolute clock value and a calculated clock
offset for each of the slave node modules via a downlink
synchronization command to the slave node modules.
[0007] This summary is provided to introduce a selection of
concepts that are further described below in the detailed
description. This summary is not intended to identify key or
essential features of the claimed subject matter, nor is it
intended to be used as an aid in limiting the scope of the claimed
subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Embodiments of systems, apparatuses, and methods for cable
telemetry synchronization are described with reference to the
following figures. Like numbers are used throughout the figures to
reference like features and components.
[0009] FIG. 1 is a schematic representation illustrating a wellsite
with a borehole traversing a subsurface formation and having a
toolstring with a cable telemetry system deployed therein in
accordance with an embodiment of the present disclosure.
[0010] FIG. 2 shows a block diagram illustrating an example cable
telemetry synchronization system in accordance with an embodiment
of the present disclosure.
[0011] FIG. 3-1 is a block diagram illustrating a synchronization
sub-system in accordance with an embodiment of the present
disclosure.
[0012] FIG. 3-2 is a block diagram illustrating a tool bus
communication system in accordance with an embodiment of the
present disclosure.
[0013] FIG. 3-3 is a schematic illustration of a data timing
communications scheme in accordance with an embodiment of the
present disclosure.
[0014] FIG. 3-4 is a schematic diagram illustrating a tool bus
synchronization scheme in accordance with an embodiment of the
present disclosure.
[0015] FIG. 3-5 is a schematic diagram illustrating a GPS-master
clock synchronization system in accordance with an embodiment of
the present disclosure.
[0016] FIG. 4 is a flowchart illustrating a method for
synchronizing the cable telemetry system in accordance with an
embodiment of the present disclosure.
[0017] FIG. 5-1 is a schematic diagram illustrating an example
timing diagram for synchronizing the cable telemetry system in
accordance with an embodiment of the present disclosure.
[0018] FIG. 5-2 is a schematic diagram illustrating time stamping
in accordance with an embodiment of the present disclosure.
[0019] FIG. 5-3 is a schematic diagram illustrating communication
flow between master and slave nodes in accordance with an
embodiment of the present disclosure.
[0020] FIG. 5-4 is a schematic diagram illustrating time stamping
using external interface packet (IP) clock time in accordance with
an embodiment of the present disclosure.
[0021] FIG. 5-5 is a schematic diagram illustrating synchronization
using a phase lock loop (PLL) system in accordance with an
embodiment of the present disclosure.
[0022] FIG. 5-6 is a schematic diagram illustrating an example
cable telemetry tool string in accordance with an embodiment of the
present disclosure.
[0023] FIG. 6 is a schematic diagram illustrating an automatic
coding scheme selection in accordance with an embodiment of the
present disclosure.
[0024] FIG. 7 is a schematic diagram illustrating a downlink scheme
in accordance with an embodiment of the present disclosure.
[0025] FIG. 8 is a schematic diagram illustrating timeline of
synchronization events in accordance with an embodiment of the
present disclosure.
DETAILED DESCRIPTION
[0026] In the following description, numerous details are set forth
to provide an understanding of the present disclosure. However, it
will be understood by those skilled in the art that the present
disclosure may be practiced without these details and that numerous
variations or modifications from the described embodiments are
possible.
[0027] The disclosure relates to a cable telemetry synchronization
system and method involving synchronization between surface and
downhole equipment operatively coupled by a cable. The surface
equipment includes a surface telemetry clock linked to a downhole
master node module, a toolbus master node clock and a plurality of
slave node clocks of the downhole equipment. Compared to
conventional telemetry systems, the present disclosure extends the
synchronization of the clocks all the way to each of the downhole
tool nodes. Embodiments of the present disclosure may achieve a
synchronization accuracy of +/-10 .mu.sec between a global
positioning system (GPS) time at surface and downhole clock times
across temperature and cable length ranges encountered in various
logging operations.
[0028] A frame start command may be downlinked from the downhole
master node module to each of the slave nodes, and at least one of
a clock offset (based on time for a responsive uplink to return
from each of the slave nodes) and a phase-lock adjustment based on
arrival time for the frame start command may be determined by the
downhole master node module, and applied to the slave node clocks.
Further synchronization with the surface telemetry clock may be
added with GPS information.
[0029] Each slave node may include a clock recovery module that,
upon receipt of a downlink message from the nodes relatively
uphole, detects the frame start command. Each slave node may also
include a clock and a data recovery module that, upon receipt of an
uplink message indicative of the coding scheme for the uplink
message used by at least one node relatively downhole, locks the
slave node to that coding scheme.
[0030] "Uplink" may be used to generally refer to any communication
transferring data from a downhole tool to the surface, while
"downlink" may be used to generally refer to any communication of a
command or data from the surface to one or more downhole tools.
Communication between downhole tools is termed "inter-tool"
communication herein and includes communication between downhole
tools without traveling to and from a surface module. Uplinking
data may include passing to a CDR (clock and data recovery) module
to lock the receiving node to the sending (i.e., lower) node a data
transmission phase; the CDR is configured to detect the coding
scheme by sensing the preamble (i.e., a prefix portion of the data
indicating the time frame or coding scheme of the remainder of the
data). Downlinking data may include passing to a clock recovery
(CR) module to lock to the tool bus master clock by detecting a
frame start command.
[0031] Examples of aspects of features usable with the present
disclosure are provided in U.S. Provisional Patent Application Nos.
61/581,091 (filed on 29 Dec. 2011 entitled "A System and Method for
Manipulation of Node Synchronization in a Multi-Scheme Tool Bus");
61/581,093 (filed on 29 Dec. 2011 entitled "A Method for Numerical
Controlled Oscillator Based Clock Synchronization in a Telemetry
System"); and 61/581,096 (filed on 29 Dec. 2011 entitled "A Method
and System for Node Synchronization in a Telemetry Bus"), the
entire contents of each are incorporated herein by reference in
their entireties.
Cable Telemetry Synchronization Overview
[0032] Referring to FIG. 1, an example wireline logging operation
is illustrated with respect to the wellsite system 100 employed in
a wellbore 102 traversing a subsurface formation 104. A downhole
telemetry cartridge 110 is connected to a toolstring 116. In a
well-logging operation, a plurality of tools (e.g., 230, 230', etc.
of FIG. 2) may be connected in the toolstring 116. The tools of the
toolstring 116 communicate with the downhole telemetry circuits of
downhole telemetry cartridge 110 via a bi-directional electrical
interface.
[0033] In some embodiments, the tools of the toolstring 116 may be
connected to the telemetry cartridge 110 over a common data bus. In
some embodiments, each tool of the toolstring 116 may be
individually, directly connected to the telemetry cartridge 110. In
one embodiment, the telemetry cartridge 110 may be a separate unit,
which is mechanically and electrically connected to the tools in
the toolstring 116. In one embodiment, the telemetry cartridge 110
may be integrated into a housing of one of the well-logging tools
116.
[0034] The telemetry cartridge 110 is operatively coupled to a
wireline cable 114. The tools of the toolstring 116, including the
telemetry cartridge 110, may be lowered into the wellbore 102 on
the wireline cable 114.
[0035] A surface data acquisition computer 118 is located at the
surface end of the wireline cable 114. The surface data acquisition
computer 118 includes or couples to an uphole telemetry unit 112.
The data acquisition computer 118 may provide control of the
components in the toolstring 116 and process and store the data
acquired downhole. The acquisition computer 118 may communicate
with the uphole telemetry unit 112 via a bi-directional electrical
interface.
[0036] The uphole telemetry unit 112 may modulate downlink commands
from the acquisition computer 118 for transmission down the cable
114 to the toolstring 116, and demodulates uplink data from the
toolstring 116 for processing and storage by the surface data
acquisition computer 118.
[0037] The downhole telemetry cartridge 110 contains circuitry to
modulate uplink data from the tools of the toolstring 116 for
transmission up the wireline cable 114 to the surface data
acquisition computer 118 and to demodulate downlink commands or
data from the surface data acquisition computer 118 for the tools
of the toolstring 116.
[0038] A more detailed schematic view of an example cable telemetry
system 200 is shown in FIG. 2. The cable telemetry system 200 shown
includes a surface acquisition module/surface modem (DTM) 220
having a telemetry interface module (TIM) 222, which can be located
at the surface as a portion of or operatively coupled to the
surface data acquisition front end 119 (a component of surface data
acquisition computer 118 of FIG. 1). The front end 119 may be, for
example, eWAFE.TM. commercially available from SCHLUMBERGER.TM.
(see: www.slb.com).
[0039] The surface data acquisition front end 119 is coupled to the
wireline cable 114, and a downhole modem (DTC) 226 (as a portion of
the downhole telemetry cartridge 110 at the head of the toolstring
116 of FIG. 1). The tool string 116 includes a number of downhole
tools, 230, 230', 230'', 230''', etc. The downhole tools 230, 230',
etc., each containing a respective interface packet, 232, 232',
232'', 232'', etc., through which they are in communication with
the DTC 226 via a tool bus 228. The downhole tools 230, 230',
230'', 230''', etc. may also have tool node controllers 233, 233',
233'', 233''', etc., respectively.
[0040] The cable telemetry system 200 may handle data flows in
opposite directions (i.e., from the tools 230, 230', etc.) via the
respective node and the tool bus 228. The flow extends to the DTC
226 to the DTM 220 over the cable 114 ("uplink"), and the reverse
direction from the DTM 220 to the DTC 226 and tools 230, 230',
etc., over the same path ("downlink"). The cable telemetry system
200 provides a communication path from the tools, 230, 230', etc.,
to the DTM 220 of the data acquisition computer 118 so that data
acquired by sensors 231, 231', 231'', 231''', etc. of the downhole
tools, 230, 230', etc., can be processed and analyzed at the
surface, as well as communication between tools 230, 230', etc.
[0041] Each individual tool (230, 230', etc.) may include a node
command buffer (not shown) at the interface packet 232, 232', etc.,
as well as a logic controller of its own (not shown). The surface
acquisition front-end unit 119 may also include various additional
components, such as a power module 221, a depth and tension module
223, and a flow controller software module (FEPC) 224.
[0042] The downhole telemetry cartridge 226 can include a downhole
master node controller 227 that may examine packets sent by each
respective tool 230, 230', etc. Data communicated in either
direction may be copied and buffered at the master node controller
227, and sent to the recipient.
[0043] A surface computer 234 can store and execute a surface data
dispatcher module 236 (which may be, in an embodiment, a software
data routing module, such as SCHLUMBERGER's.TM. MAXWELL.TM.
framework). The surface computer 234 can also store and execute a
plurality of surface tool-specific applications 238, 238', 238'',
238''', etc. that analyze and use data obtained, respectively, by
tools 230, 230', etc.
[0044] Referring to FIGS. 2 and 3-1, block diagrams are shown for
the synchronization sub-system 300 for a cable telemetry system,
such as the system 200 illustrated in FIG. 2. A (optional) GPS
clock 340 (maintained at the surface, for example, in the surface
acquisition front-end unit 119 or surface computer 234) is
operatively coupled to the telemetry system master clock 342
(maintained at the surface by the DTM 220 or TIM 222, for example).
The telemetry system master clock 342 is operatively coupled to a
tool bus clock 344 (maintained downhole, for example, by the DTC
226), which in turn couples to each tool node clock 346, 346', etc.
of each respective tool 230, 230', etc. via the toolbus 228.
Generally, each slave node (i.e., individual tool(s) 230, 230',
etc.) can include the interface packet(s) 232, 232', etc. to
control the tool node clock(s) 346, 346', etc. thereof, while the
DTC 226 maintains the tool bus clock 344, the DTM 220 maintains the
telemetry system master clock 342, and other surface equipment may
maintain an optional GPS clock 340.
[0045] The GPS clock 340 may be used in some embodiments. In
continuous and checkshot seismic surveys, synchronizing surface,
downhole, and tool node clocks with GPS time permits sharing a
common time reference between wave emission and reception clocks,
and acquiring data at precise time intervals. In logging
operations, synchronizing surface, downhole, and tool node clocks
with GPS time permits sharing a common time reference between the
downhole clock, used to time stamp the downhole tool measurement,
and the surface clock, used to time stamp the downhole tool depth,
and correlating measurements with depth.
[0046] The telemetry system master clock 342 value at the time the
GPS signal is detected may be communicated to the surface data
dispatcher module 236. The surface data dispatcher module 236 may
continuously realign the telemetry system master clock 342 with GPS
clock 340 time by assuming that the drift evolved smoothly between
detections of the GPS signal. In an embodiment, after realignment,
the telemetry system master clock 342 tracks the GPS clock 340
within about +/-1.4 .mu.s.
[0047] The surface data acquisition front end 119 may use an
Ethernet network to synchronize a depth and tension module 223 to
the TIM 222. In an embodiment, each second, the TIM 222 transmits a
single broadcast packet onto the local Ethernet network containing
the current value for the telemetry system master clock 342
maintained by the TIM 222.
[0048] The depth and tension module 223 compares the received
telemetry system master clock 342 value to its own free-running
counter to determine a slowly evolving correction value, updated at
a frequency of about 62.5 Hz. The depth and tension module 223
adjusted time may be computed by adding the correction value to the
free-running counter. In an embodiment, the synchronization error
may be not exceeding about +/-2 milliseconds (ms).
[0049] The DTC 226 may synchronize its internal clock (the toolbus
clock 344) to the telemetry system master clock 342 via messages
sent onto the wireline cable 114. The messages may be sent one-way
by downlink or uplink. The messages may also be sent round trip
including uplink plus downlink time. A round trip delay, including
uplink time plus downlink time plus an inserted guard time, is the
time difference between the transmission of an uplink frame and the
reception of the next downlink frame by the DTC 226. Internally,
the DTC 226 records the tool node clock 346 value upon the
transmission of each uplink frame. Each following downlink
maintenance packet contains the telemetry system master clock 342
timestamp recorded at the reception of the uplink frame. The DTC
226 also records the toolbus clock 344 at the reception of each
downlink frame.
[0050] Since downlink and uplink share the same mode, the one-way
trip propagation time may be determined as half of the round trip
propagation time. Thus, with these clock values, and the knowledge
of the inserted guard time, a propagation time can be estimated.
The DTC 226 may adjust the toolbus clock 344 during each downlink
frame based on the timestamp from the telemetry system master clock
342. In an embodiment, the synchronization described herein may
also compensate for computational delays.
[0051] In an embodiment, the present disclosure may increase the
accuracy of the calculation of cable telemetry systems in that the
slave clock synchronization is increased to about 15 Hz (for
example, about every 67 milliseconds), thereby reducing the
duration of time the downhole (slave) clock is allowed to drift
between updates and the amount of drift may be reduced by almost
half (for example, from about 2.2 is compared to about 4.4 .mu.s).
The frequency of the telemetry system master clock can be
increased, for example, to about 2.048 MHz from about 256 kHz, thus
reducing the update uncertainty to about 0.49 .mu.s.
[0052] In an example where both uplinks and downlinks occur on the
same mode (propagation mode T5), the uplink trip time will be half
the round-trip time. This change reduces the propagation time
uncertainty by about 2.6 is (assuming about 2 .mu.s/ft (0.61
.mu.s/m) propagation speed, about 10% error in the propagation mode
T5 to propagation mode T7 speed ratio estimate, and about 35,000 ft
(10,668 m) cable length). Thus, the uncertainty in the
master--slave clock synchronization is about 2.2 .mu.s (the amount
of drift allowed between updates as noted above)+about 0.49 .mu.s
(update uncertainty)=about 2.69 .mu.s.
[0053] In order to provide synchronous timing for surface equipment
and downhole equipment, including the slave nodes, a frame pulse
(FP) can be used for periodic timing synchronization to a telemetry
system time basis. The individual slave node clocks may be
controlled so as to be synchronous to the toolbus master node
clock, which is in turn synchronized to the telemetry system clock.
The individual node clock synchronization may be done by downlink
transmission delay measurement and/or individual node clock
adjustment to be phase-locked to the toolbus master node clock. The
two processes may be repeated continuously to establish and
maintain the individual node clock synchronization with the
telemetry system clock, the toolbus master node clock, and,
optionally, the GPS.
[0054] In an example, each tool event time is time-stamped when the
tool data arrives at the interface packet of a tool bus slave with
the slave node clock. Due to individual node synchronization, the
stamped time may be an absolute time immediately on a telemetry
system time basis, and accordingly, the time-stamp accuracy may be
increased beyond the accuracy of free running clocks. The DTM 220
monitors uplink and downlink transmission delays, and if clock
offset values for the various nodes fluctuate by more than a
threshold number of clock cycles, an error may be reported.
[0055] Referring now to the examples of FIG. 3-2, an illustrative
embodiment is provided of a tool bus communication system including
a master slave module and one or more tool slave modules (only one
is shown in this example). In the downhole telemetry bus coupling
the master slave module and the tool slave module, an event in a
node (such as a tool slave module) may be time-stamped. However,
problems may exist when the node's clock in the tool bus is not
synchronized to the rest of the system.
[0056] In order to synchronize the clocks of the various nodes, a
method following the tool bus communication system of FIG. 3-2 may
be used. FIG. 3-2 shows an example tool bus configuration including
a master slave module EDTC-H, a tool bus EFTB, and slave modules
EIP 2.0. This figure also depicts the data flow through the
system.
[0057] According to FIG. 3-2, a master slave module EDTC-H (e.g.,
DTC 226 of FIG. 2 or SCHLUMBERGER's.TM. Enhanced Digital Telemetry
Cartridge-H) may include a master tool bus clock. For example, the
master tool bus clock may be a Numerically Controlled Oscillator
(NCO) operating at about 40.96 MHz. The master tool bus clock acts
as the Job Time Counter. In some embodiments as described herein,
the master tool bus clock may further be synchronized with a
surface system.
[0058] In an embodiment, the EDTC-H may send a clock value to all
of the lower nodes via the EFTB telemetry bus (such as
SCHLUMBERGER's.TM. EFTB Enhanced Fast Tool Bus) using a downlink
packet command (e.g., command A) about every 16 ms. The downlink
packet may contain a frame start pulse (FSP), used synonymously
with Frame Start Command (FSC). In some embodiments, each of the
lower node's clocks may be driven by a Numerically Controlled
Oscillator (NCO) operating at a frequency of approximately 40.96
MHz. A delay, based in hardware and/or software, is introduced by
the EFTB bus as the clock value propagates across the EFTB.
[0059] In the interface packet of each node, the follow may occur
to synchronize each node to the master tool bus clock. The delayed
FSP (delayed by transmission across the EFTB bus) is passed to the
tool slave module's Clock and Data Recovery (CDR) module. Each node
then sends their clock values (SLVCLK-slave clock) after receiving
the downlink packet command (command A). The DTC 226 may use the
individual clock values of the particular tool slave modules (e.g.,
SCHLUMBERGER's.TM. EIP 2.0--Enhanced Interface packet 2.0) to
determine each tool slave module's (i.e., node's) clock offset
(DLTD-delta d). The frame start command may be delayed, based on
various hardware or software factors, upon processing by the EFTB
tool bus. The delayed frame start command may be sent through the
tool slave module's Clock and Data Recovery (CDR) module.
[0060] The output of the CDR inputs the slave clock current time,
the current delayed time for the master tool bus clock, as well as
the previous most recent delayed time for the master tool bus clock
into an adder, the result of which is latched in a clock register.
The output of the latch reflective of the changed in delayed time
is added to a period constant (i.e., 16 ms in this example), and
the previous most recent clock value for the slave node. The output
of the second adder is the reference slave node clock value (shown
as Reference EIP2.0 clock value), which is latched to the clock
register.
[0061] A second output of the CDR module is also latched, adding a
16 ms period constant from a second FSP to update the latch timing.
The latched value may be passed to a scaler low pass filter (LPF),
the result of which is latched, and used to adjust the dispersion
up or down on the actual clock value shown for the slave node
(i.e., actual EIP2.0 clock value).
[0062] Each latch register holds the most recent value until the
next update FSP command is sent, which starts the slave node clock
update process of FIG. 3-2 over again.
[0063] After the EDTC-H calculates the clock offset for each of the
tool slave modules, the EDTC-H sends the initial value and the
offset value of the clock via a second FSP command (e.g., command
B). Each node then sets the initial value with the offset for that
particular node's clock. Periodically (e.g., about every 16 ms),
the previous steps may be repeated. In addition, the CDR module in
a particular node may decode and latch the running clock, and
compare this result to the clock signal sent from the EDTC-H.
[0064] In an embodiment, the compared results may be low-pass
filtered and scaled so that a change to the clock is relatively
small. The scaled value is then used to adjust the clock's
NCOs.
[0065] By repeating the most recent two steps several times, a
node's clock becomes synchronized to the clock of the EDTC-H, and
in turn, to the clock on the surface. Additionally or
alternatively, the clock signal from the NCO can be provided to the
controller connected to the tool slave module (e.g., EIP 2.0). The
clock signal may be synchronized to the EDTC-H.
[0066] FIG. 3-3 is a schematic illustration of a data timing
communications scheme. In an illustrative embodiment of a tool bus
communication system including a tool bus slave master and one or
more tool bus slaves, such as the system of FIG. 3-2, a high data
rate may be achieved to allow for real time decision making on the
surface or downhole relating to measurements made by the sensors.
In addition, in some embodiments, older and newer modules may be
combined without regard to tool generation, to maximize the service
life of older modules while introducing newer modules.
[0067] As shown in FIG. 3-3, an 8b10b encoding/decoding scheme is
introduced by the first (and in this case, newer) tool bus slave,
labeled EIP 2.0, identifying the interface packet (e.g., 232, 232',
etc. of FIG. 2). An older, or more conventional tool bus slave
(labeled IP/EIP) using a bi-phase scheme, is also in communication
with the tool bus slave master.
[0068] An embodiment of a communication system may be configured to
communicate with the modules making up a particular tool string,
sometimes known as backwards compatibility. The first tool bus
slave may use a new generation communication scheme (such as
SCHLUMBERGER's.TM. EFTB 2.0--Enhanced Fast Tool Bus version EIP
2.0). This first tool bus slave may be communicatively coupled to a
second tool bus slave using a different communication scheme (such
as SCHLUMBERGER's.TM. FTB or EFTB version IP or EIP (Interface
Packet or Enhanced Interface Packet)). The system may support, for
example, a 2 Mbps bi-phase (5.12 MHz) and an 8 Mbps 8b10b (10.24
MHz) encoding/communication schemes.
[0069] FIG. 3-4 is a schematic illustration of an embodiment of a
tool bus synchronization scheme including both synchronous and
coarsely synchronous modules according to aspects of the present
disclosure. This scheme may be used to establish tool bus node
synchronization across the entire tool and the various modules. In
FIG. 3-4, both synchronous and coarsely synchronous downhole
modules are included in the system.
[0070] In the illustrated embodiment, a telemetry system may
include a master clock (telemetry system clock) at the surface. The
master clock includes a data acquisition front end (e.g., 119 of
FIG. 2), such as SCHLUMBERGER's eWAFE.TM. Enhanced Wireline
Acquisition Front End. In some cases, the data acquisition front
end may be based on Ethernet architecture and operate with
Universal Power Supply (UPM) modules that are versatile and
interchangeable. Other embodiments may have alternative or
completely different configurations.
[0071] The front end may be communicatively coupled to a slave
master module (e.g., 226 of FIG. 2), such as SCHLUMBERGER's.TM.
EDTC--Enhanced Digital Telemetry Cartridge. The slave master module
may include a slave clock (tool bus master clock) that is
synchronous to the master clock. The tool bus master clock
establishes the synchronization with the surface for the rest of
the downhole tool modules (sometimes referred to herein as nodes).
The first of multiple slave modules (two are shown in this example)
may also include a clock, and is synchronously coupled to the
master module. Another of the slave modules may only be coarsely
synchronously coupled to the master module.
[0072] In the embodiment shown in FIG. 3-4, the lower portion of
the first slave module is configured to be backwards compatible
with the lowermost slave module (for example, communicating via a
bi-phase communication scheme as discussed previously). The upper
portion of the first slave module may be configured to be
synchronized to the slave master module and therefore synchronized
to the master module located at the surface. As a result, the
lowermost slave module is only coarsely synchronous to the master
slave module while the intermediate slave module is synchronous to
the master slave module.
[0073] FIG. 3-5 shows a block diagram of GPS-Master Clock
Synchronization combining the schematic of FIG. 2 with detail from
FIG. 3-1. The system depicts a surface computer with software
(i.e., MAXWELL application), applications and MAXWELL framework
coupled to a surface acquisition system (eWAFE). The surface
acquisition system includes a surface telemetry module (having the
JTC clock 3) as well as a depth module. The surface acquisition
system is linked by a logging cable to a downhole telemetry
cartridge. The downhole telemetry cartridge is coupled by a tool
bus to downhole tools EFTB 2.0 tool 1 and EFTB 2.0 Tool 2. A GPS
clock 4 may optionally be included in the system of FIG. 3-5 for
synchronization between the master and slave nodes.
[0074] The downhole telemetry cartridge includes the tool bus
master clock 2 (labeled EFTB 2.0 master), as well as cable
telemetry firmware. EFTB 2.0 Tool 1 includes, as detailed above, an
interface packet EIP 2.0, a node tool controller, and a plurality
of sensors. The EFTB 2.0 Tool 1 includes a slave clock 1. Likewise,
EFTB Tool 2 includes, an interface packet EIP 2.0, and a node tool
controller.
[0075] In an embodiment, a telemetry system master clock is
implemented as a Job-Time-Counter 3 (JTC) incremented in cycles
(e.g., every 8 cycles). The master clock may be an oscillator
(e.g., NCO) having a nominal frequency (e.g., of about 16.384 MHz).
The telemetry system master clock is incremented about every 0.488
ms, or at a frequency of about 2.048 Mhz. The GPS clock 4 generates
an external signal at about 1 pulse-per-second (PPS) that may be
regularly detected by the surface software (e.g., by TIM 222 of
FIG. 2). As shown in FIG. 3-5, an arrow between two clocks shows
that the clock having the end of the arrow is synchronized to the
clock where the arrow points.
[0076] The telemetry system master clock 342 increments between
consecutive detections of the GPS signal may be indicative of drift
in the telemetry system master clock relative to the GPS reference
time measured in multiple of about 0.488 .mu.s. In an embodiment,
without accounting for drift of the oscillator, the GPS clock 340
signal may be detected every 1,024.times.2,000=2,048,000 increments
of the telemetry system master clock. In an embodiment, the node
clocks may be derived from oscillators rated at about 40.96 MHz
with about +/-250 pules per minute (ppm). The JTC serves as the
time for the master clock of the telemetry module (TIM) 222.
[0077] Turning now to FIG. 4, a flowchart is shown for a method 400
for synchronizing a cable telemetry synchronization system. The
method 400 can begin with sending 450 a downlink frame start
command. The sending may involve, for example, sending from the DTC
226 to one or more slave modules at predetermined intervals via the
toolbus 228 (which may be, for example, SCHLUMBERGER.TM.'s EFTB
(Enhanced Fast Tool Bus)). In an example embodiment, the
predetermined interval may be about 16 ms.
[0078] The downlink frame start command may be delayed during
processing by the toolbus 228 due to, for example, hardware
limitations. The delayed downlink frame start command may be
processed at each individual node in a clock recovery module that,
upon receipt of a downlink message from nodes relatively uphole,
detects the frame start command (i.e., an arrival time).
[0079] The method can continue with receiving 452 a clock value
uplinked from each of the one or more slave modules, in response to
the downlink frame start command. In an embodiment, the toolbus
master node clock 344 may be driven by an oscillator (NCO), at a
frequency of, for example, about 40.96 MHz.
[0080] The method can continue calculating 454 a clock offset for
each of the slave modules (i.e., the individual tools 230, 230',
etc.), for example, using the DTC 226 to calculate based on a
function of the arrival time for the downlink frame start command
and the response time for the response uplinked from each slave
node in response to the downlink frame start command.
Telemetry Synchronization Explanation
[0081] FIG. 5-1 depicts a timing diagram 500 plotting signal
amplitude over time for a toolbus master and two slave nodes,
depicted as Tool 1 and Tool 2. The toolbus master node clock sends
a frame start command 564 at a time t.sub.r0. As can be seen, there
is a delay in transmission to Tool 1 as well as a delay in
transmission to Tool 2 (due to toolbus processing), such that the
frame start command 564 arrives at Tool 2 at a time t.sub.r2 and
arrives at Tool 1 at a time t.sub.r1.
[0082] Each slave node (at Tool 1 and Tool 2) latches the toolbus
master node clock value at the time of receiving the frame start
command 564 (at time t.sub.rn where n=tool number in the
toolstring). Each slave node also latches the toolbus master node
clock value at the time of sending an uplink (which can include a
frame time length 568, an uplink time 570, and packet data 572) in
response (at a time t.sub.sn where n=tool number in the
toolstring). Over time, the values latched by each slave node can
be sent to the toolbus master node controller (e.g., 227 of FIG. 2)
as uplink packets.
[0083] At time t.sub.s2 an uplink, including the time frame
preamble 568, the uplink time 570 and the packet data 572, is sent
from Tool 2 at t.sub.s2 to Tool 1 and passed on at time t.sub.s1.
Another uplink at t.sub.s4, including a time frame preamble 574, an
uplink time 576, and packet data 578 is sent from Tool 1 at
t.sub.s3 to Tool 2 until each slave node has received the frame
start command 564 and sends a response uplink. The toolbus master
node controller 227 may also latch the toolbus master node clock
value t.sub.s0 at the time of receiving the uplink packets from
Tool 1 and Tool 2, and may calculate the clock offset according to
a function of the form:
Clock offset=(t.sub.s0+t.sub.r0)/2-(t.sub.sn+t.sub.rn)/2 Eq.
(1)
where t.sub.r0=time of sending frame start command from the toolbus
master, t.sub.so=time of sending first packet of data from toolbus
master, t.sub.rn=time of receiving the frame start command at Tool
n, where n=the Nth tool in the toolstring, and t.sub.sn=time of
sending first packet of data from Tool n. The toolbus master node
controller may generate and send still another uplink, shown in
FIG. 5-1 as sending at time t.sub.s5 including the frame time 580
for the master, the uplink time 582 for the master clock, and
packet data 584, which is sent to the DTM (e.g., 220 for
synchronizing with the telemetry system master clock).
[0084] Referring back to FIG. 4, the method can continue with
sending 456 an absolute clock value (from the toolbus master node
clock) and the calculated offset value for each of the slave node
via a downlink synchronization command to the one or more slave
modules. Each node can then set the initial value for its own clock
with the clock offset for that particular node's clock. The
compared result may be low-pass filtered and scaled so that the
change to the clock is small. The scaled value may be used to
adjust each node clock's NCO.
[0085] The method can optionally continue with determining 460, for
each slave node module, a phase-lock adjustment based on a function
of an arrival time for the frame start command, as determined by
the clock and data recovery (CDR) module (i.e., logic circuit)
implemented in each tool node controller (e.g., 233, 233', etc. of
FIG. 2). Upon receipt of an uplink message at the slave node from
any tool located relatively downhole thereof, the node controller
detects a preamble of the uplink message indicative of the coding
scheme used by the lower node or nodes for the uplink message, and
locks the slave node to the detected coding scheme of the preamble.
A first in-first out (FIFO) buffer at each node may be implemented
for this purpose.
[0086] Each node clock may be controlled (speeded up or slowed
down) to phase lock to the timing of the downlink frame start
command arrival time. Each slave node may also implement a clock
recovery (CR) module (i.e., logic circuit) that, upon receipt of a
downlink message, detects the frame start command, which can be
used in the previous blocks as well as in the phase-lock mechanism
of block 460.
[0087] The method can continue with each relevant slave node
updating 462 its node clock based on the absolute clock value
(i.e., the telemetry system master clock value) and the clock
offset for the particular slave node, as well as the phase-lock
adjustment. Periodically, part or all of the method may be repeated
to maintain synchronization between the system components.
[0088] Accordingly, the tool node controller (e.g., 233, 233',
etc.) for each individual node can latch event data from the tool
(e.g., 230, 230', etc.) by means of the telemetry system's time
(i.e., from the toolbus master node clock 344). In an example
involving individual node clocks synchronized to the telemetry
system's time, a tool node controller(s) (e.g., 233, 233', etc.)
for individual tool enables an external IP clock mode. A value
EIP_LATCH may be asserted at input at the timing of a tool event so
that the interface packet 232, 232', etc. for the tool 230, 230',
etc. latches the node clock value to the appropriate register. The
tool node controller 233, 233', etc. gathers the data sensing tool
event and also reads the latched node clock from the interface
packet 232, 232', etc. register. The tool node controller 233,
233', etc. may create an uplink message that is time-stamped with
the latched node clock value in the register. The tool node
controller 233, 233', etc. may write the tool message to the
interface packet 232, 232', etc. to send to the surface via the
tool bus 228.
[0089] The method may be performed in any order and repeated as
desired, for example, until the desired degree of synchronization
is achieved.
[0090] In an embodiment, the frame start command may be issued
about every 16 ms when the lower 15 bits of slave clock rolls over,
and the master (e.g., EFTB 2.0) latches the slave clock counter
value at the time of sending (t.sub.r0). In an embodiment, each
interface packet 232, 232', etc. of each node 230, 230', etc.
latches its clock at the time of receiving the frame start command
(t.sub.r1, t.sub.r2, . . . ).
[0091] In an embodiment, each interface packet 232, 232', etc. of
each node 230, 230', etc. latches its own clock at the time of
first uplink packet sending (t.sub.s1, t.sub.s2, . . . ). The clock
values latched most previously, that is (frame time 1, frame time
2, . . . ) and (uplink time 1, uplink time 2, . . . ), are sent to
the master (e.g., EFTB 2.0), in the tool packet header.
[0092] The master (e.g., EFTB 2.0) latches the slave clock counter
value at the time of receiving the first uplink packet (t.sub.s0).
The master calculates the transmission delay and the clock offsets
as described herein. The uplink and downlink transmission delays
are monitored at the master. If the offset values fluctuate more
than several clock ticks (TBD at the implementation), an error is
reported.
[0093] During initial synchronizations of the interface packet 232,
232', etc. of each node 230, 230', etc. clock, after the link
(e.g., EFTB 2.0) is established, the transmission delay measurement
may be performed. If the node uplinks and downlinks are confirmed
as acceptable, the master (e.g., EFTB 2.0) may calculate each
interface packet clock offset from the slave clock. The master may
send a clock correction value obtained from the offset to each
interface packet. The master sends frame pulse generation time
value to each interface packet.
[0094] The present disclosure may reduce the uncertainty of the
"absolute" acquisition time of data as well as "relative"
acquisition time between nodes by introducing measurements of
transmission delay. The downlink transmission delay may be handled
by using a fixed value. This value may be only an approximation as
the delays may not be unique among various IP/EIP implementations
and setting a fixed delay according to tool location may not be
done at all.
[0095] The uncertainty of the "absolute" acquisition time of data
as well as "relative" acquisition time between nodes may be reduced
by introducing synchronization between the slave clock in the
telemetry cartridge clock and the clocks of each interface packet
232, 232', etc. of each node 230, 230', etc. based on the measured
transmission delay.
[0096] The present disclosure may reduce the uncertainty of the
"absolute" acquisition time of data as well as "relative"
acquisition time between nodes by introducing a higher node clock
frequency (e.g., at 2.048 MHz instead of 256 kHz). Thus, the update
uncertainty may be reduced from about +/-3.9 .mu.s to about +/-0.49
.mu.s.
[0097] The present disclosure may also reduce the uncertainty of
the "absolute" acquisition time of data as well as "relative"
acquisition time between nodes by introducing digital Phase Lock
Loop (PLL) in the downlink data transmission to maintain clock
drift within about 9 clk for every frame from the upper node. The
clock drift between adjacent nodes may be reduced to about 14 ppm
(i.e. (9/40.96 MHz)/16 ms) or 220 ns.
[0098] Total synchronization accuracy may be shown in Chart 1
below. The total represents the overall accuracy between the GPS
receiver and the timestamp derived from the tool messages at that
instant.
TABLE-US-00001 CHART 1 Link Accuracy GPS-Master Clock
Synchronization 1.4 .mu.s Master Clock (TIM) - Slave Clock (e.g.,
2.7 .mu.s EDTC) Synchronization Slave Clock (e.g., EDTC) - Tool
Node 2.1 .mu.s (worst-case within Clock Synchronization at bottom
node Gaussian distribution) number (Total number of slave nodes is
31) Total 6.2 .mu.s
[0099] FIG. 5-2 is a schematic illustration of time stamping
according to an embodiment of the present disclosure. The time
stamping depicted is a normal time stamp illustrating a tool event
that is sensed by a tool controller, and a message is sent via EIC
to an EIP 2.0. A tool event time is time-stamped when the tool data
sensed arrives at an interface packet labeled EIP 2.0 (e.g., 232,
232', etc. of each node 230, 230', etc.), having passed through the
tool controller 233, 233', etc., collectively contributing to a
software delay, with the value from the tool node clock of the
particular node. Due to the individual node synchronization, the
stamped time may be an absolute time on a telemetry system time
basis. Accordingly, the time-stamp accuracy may provide a
relatively higher accuracy than the accuracy achieved using free
running clocks for measuring relative time.
[0100] FIG. 5-3 is a schematic illustration showing the
communication flow between the master and slave nodes according to
an embodiment of the present disclosure. A master is shown in
communication with an EIP 2.0 of node 1 and EIP 2.0 of a node 2.
The master has a master oscillator (EFTB 2.0 Master's Clock, in
this case labeled as a master oscillator 343), and slave CLK that
communicates with an EIP 2.0 CLK of node 1 and an EIP 2.0 CLK of
node 2.
[0101] During interface packet CLK adjustment, the clocks can be
derived from oscillators 345 rated at about 40.96 MHz with about
+/-250 ppm. The digital Phase Lock Loop (PLL) method may be used in
downlink data transmission at every frame received from the upper
node. FIG. 5-3 shows the EFTB 2.0 clock and data flow. Slave CLK is
driven from about a 40.96 MHz oscillator. The frame start command
may be issued about every 16 ms measured at the slave CLK.
[0102] The interface packet for node 1 receives the frame start
command at the CDR (Clock and Data Recovery) module. The command is
passed to the CR (Clock Recovery) module. In the CR module, the
difference between slave CLK and tool node CLK based on TX CLK are
measured compensating the propagation delay. TX_CLK can be adjusted
so that the interface packet (e.g., 232, 232', etc. for node 230,
230', etc. clock) matches to the slave CLK.
[0103] The TX CLK is used to drive tool node CLK, and also the
modulator. The downlink bit stream frequency clocks out to the
interface packet of node 2 from the interface packet of node 1 to
match with the downlink bit stream frequency from the master.
[0104] The time needed for downlink commands to pass the CDR module
may be made constant. The interval of the frame start command for
the interface packet for node 2 may be the same as the interface
packet for node 1. The interface packet for node 2 may perform the
same process as the interface packet for node 1. The TX_CLK of the
interface packet for node 2 and the downlink bit stream frequency
to the node below may be roughly the same as for the interface
packet for node 1.
[0105] Still referring to FIG. 5-3, the slave master clock may be
driven from a slave oscillator, which may be synchronized to the
master clock (telemetry system clock) in a similar way as in a
conventional tool bus. The frame start command may be issued
periodically by the master. As shown in the schematic, the various
signals can be modulated (MOD) or demodulated (DEMOD) depending on
the direction of the data flow.
[0106] Each of the interface packets of the nodes receives a frame
start command from a clock and data recovery (CDR) module. The
frame start command is passed directly to the clock recovery (CR)
module. The frame start command generation timing is synchronous to
the slave master clock. Accordingly, the EIP2.0 clock is controlled
(speeded up or slowed down) to phase lock to the timing of the
frame start command arrival.
[0107] By setting each of the individual nodes EIP 2.0 clock's
delay from the frame start command arrival, an event in the nodes
can be synchronized to each other. As shown in FIG. 5-1, the
synchronized event can be a frame pulse (FP), such as frame pulses
566.
[0108] FIG. 5-4 is a schematic illustration of time stamping using
external interface packet (IP) clock time, according to an
embodiment of the present disclosure. This figure shows an external
IP clock time stamp where a tool event is sensed by the tool
controller, and a message is passed from the tool controller to the
EIP 2.0. A clock value is returned from the EIP 2.0 to the tool
controller.
[0109] The EIP 2.0 clock's (slave clock or tool bus clock) value is
synchronized to the slave master clock (tool bus master clock),
which is in turn synchronized to the master clock (telemetry system
clock). The interface to notice the EIP 2.0 clock value is added to
the EIP 2.0. Accordingly, the tool controller for each of the
individual nodes can latch its own events by means of the telemetry
system time from the master clock.
[0110] A method can be used for situations in which the individual
node clocks are synchronized to the telemetry system's time, such
as when a tool controller enables an external IP clock mode, when
EIP_LATCH (input pin in EIP2.0) is asserted at the timing of a tool
event so that EIP 2.0 latches the EIP 2.0 clock value to the
appropriate register, when a tool controller gathers the data
sensing tool event and also reads the latched EIP 2.0 clock from
the EIP 2.0 register (and the tool controller then creates a tool
message filled with data, the message being time-stamped with the
latched EIP 2.0 clock), and when a tool controller writes the tool
message to EIP 2.0 to send to the surface via the tool bus.
[0111] Through the procedure, the accuracy of tool event time
stamping may depend on hardware delay from the tool event
occurrence to the EIP 2.0 clock latch. In a conventional system,
the accuracy of the tool event time stamping may be relatively
larger due to the software process delay. The extent that the
software delay is reduced is still under investigation.
[0112] FIG. 5-5 is a schematic illustration of synchronization
using a phase lock loop (PLL) system, according to an embodiment of
the present disclosure. FIG. 5-5 shows a tool application coupled
to an EIP 2.0. The tool application receives a clock-out signal
from the EIP 2.0 clock.
[0113] The EIP 2.0 clock-out gets synchronized to the telemetry
system clock (master clock) via the slave master clock. The
interface to provide EIP 2.0 clock-out is added to the EIP 2.0. The
tool application can generate a tool system clock synchronous to
the telemetry system clock by using an appropriate stabilizer and a
PLL mechanism. This method can be used for situations in which an
individual node clock is synchronized to the telemetry system's
time.
[0114] FIG. 5-6 is a block diagram illustrating an example cable
telemetry tool string in accordance with an embodiment of the
present disclosure. The block diagram shows a downhole modem (e.g.,
DTC 226) including a tool bus master and a cable modem interface.
The tool bus master (e.g., EFTB 2.0) includes a master controller,
a transceiver and an interface. The master is coupled to a cable
modem.
[0115] The downhole modem (e.g., EFTB 2.0) includes a telemetry
tool (e.g., EDTC-H) with a tool bus slave, a transceiver, and a
slave controller. The telemetry tool is coupled to next most
proximate tool bus slave in the tool string.
[0116] Turning now to FIG. 6, an embodiment of a configuration for
uplink data reception is shown for multiple downhole tools of a
toolstring. The toolstring is shown as having three tools, with two
using synchronously coupled slave modules and one using a
conventional slave module. Specifically, as shown in FIG. 6, Tool
#1 uses EIP2.0, Tool#2 uses EIP2.0 and Tool#3 uses IP/EIP. A master
(e.g., EFTB 2.0) coupled to a cable modem is shown in detail.
[0117] When receiving the uplink data by one of the multiple slave
tool modules, a CDR module (i.e., logic unit) can be employed to
lock to the lower nodes data transmission phase. In an embodiment
including a multi-coding scheme, the CDR may be used to detect a
particular coding scheme by sensing a preamble (i.e., a prefix
portion of the data indicating the time frame or coding scheme of
the remainder of the data).
[0118] In the example illustrated by FIG. 6, a FIFO (First In,
First Out) CDR module has the responsibility to absorb the clock
difference between the sending node and the receiving node. This
may be provided such that the received data is not transmitted on
to the upper node (or master module) on the recovered clock and
instead is temporarily stopped by a NG (No Go). In more detail, an
uplink data signal as shown in the bottom right of the FIG. 6 shows
an uplink packet, followed by a guard band, followed by a preamble,
followed by the next uplink packet. The uplink data signal enters
the CDR module of Tool #1, where a bi-phase decoder and 8B/10B
decoder analyzes the uplink data signal to identify the preamble
separately from the uplink data. The preamble information can be
used in the upper portion of the Tool #1 node to lock the
transmission to the same modulation scheme used by the lower node
(i.e., Tool #2 or Tool #3, where the uplink data signal
originated).
[0119] FIG. 7 shows a schematic of an embodiment of a configuration
for downlink data transmission. In an embodiment, the downlink
transmission also has a multi-scheme modulation similar to the
uplink data reception described with respect to FIG. 6, employing a
Clock Recovery (CR) module in the downlink embodiment analogous to
the CDR module described with respect to FIG. 6. The CR module may
synchronize the clocks whereas the CDR module may synchronize the
clocks and sample data.
[0120] In an embodiment, the CR module may synchronize the
telemetry system clock (located at the surface in the master
module) to the master slave clock (i.e., the tool bus master clock)
by detecting the frame start command. Further down the tool string,
the synchronous clock from CR module at the master slave module may
be applied to the data transmission and the slave clock counter via
the CDR in the slave modules, thereby locking the downlinked data
to the tool bus master clock.
[0121] By transmitting the data based on the synchronous clock and
generating the synchronous slave clock, EFTB 2.0 tool bus master
(labeled EFTB 2.0 master) and EFTB 2.0 tool bus slaves (labeled EIP
2.0) can exchange data according to a common synchronized
clock.
[0122] The synchronized clock is applied to the EIP 2.0 clock. In
an embodiment, the recovered clock from CDR is not applied to a
given tool node clock, otherwise the tool node clock is synchronous
to the lower node (not the tool bus master as it should be).
[0123] FIG. 8 shows an example timeline of synchronization events,
in accordance with an embodiment of the present disclosure. The
timeline extends from times t1 through t5, and includes a recorded
round trip time plus guard time from times t1-t4 which includes an
uplink propagation delay from times t1 through t2, a guard time
from times t2 through t3, a downlink propagation delay a from times
t3 through t4, and a slave clock loaded at time t5.
[0124] The DTC 226 may synchronize its internal clock (the toolbus
clock) to the telemetry system master clock via messages sent by
uplink onto the wireline cable (e.g., 114 of FIGS. 1 and 2). A
round trip delay (uplink time plus downlink time plus an inserted
guard time) is the time difference between the transmission of an
uplink frame and the reception of the next downlink frame by the
DTC 226. Internally, the DTC 226 records the tool node clock value
upon the transmission of each uplink frame. Each following downlink
maintenance packet contains the telemetry system master clock
timestamp recorded at the reception of the uplink frame. The DTC
226 also records the toolbus clock at the reception of each
downlink frame.
[0125] In a given example, at time t1 the DTC 226 starts an uplink
transmission in mode T5. At time t2, the TIM 222 receives the last
uplinked frame, and the value of the master clock is time stamped
onto the uplinked data. A guard time is inserted between the uplink
transmission and downlink transmission. At time t3, the TIM 222
starts a downlink transmission. At time t4, the DTC 226 receives
the first downlinked frame, and at time t5 the value for the slave
clock is loaded. The uplink propagation delay may be time t2-time
t1. The downlink propagation delay may be time t4-time t3.
[0126] Since downlink and uplink share the same mode, the one-way
trip propagation time may be determined as half of the round trip
propagation time. With these clock values and the knowledge of the
inserted guard time, a propagation time may be estimated. The DTC
226 may adjust the toolbus clock during each downlink frame based
on the timestamp from the telemetry system master clock. In an
embodiment, the synchronization described here may also compensate
for computational delays.
[0127] The various techniques disclosed herein may be utilized to
facilitate and improve data acquisition and analysis in downhole
tools and systems. In this, downhole tools and systems are provided
that utilize arrays of sensing devices that are configured or
designed for easy attachment and detachment in downhole sensor
tools or modules that are deployed for purposes of sensing data
relating to environmental and tool parameters downhole, within a
borehole. The tools and sensing systems disclosed herein may
effectively sense and store characteristics relating to components
of downhole tools as well as formation parameters at elevated
temperatures and pressures. Chemicals and chemical properties of
interest in oilfield exploration and development may also be
measured and stored by the sensing systems contemplated by the
present disclosure.
[0128] The sensing systems herein may be incorporated in tool
systems such as wireline logging tools, measurement-while-drilling
and logging-while-drilling tools, permanent monitoring systems,
drill bits, drill collars, sondes, among others. For the purposes
of this disclosure, when any one of the terms wireline, cable line,
slickline or coiled tubing or conveyance is used it is understood
that any of the referenced deployment means, or any other suitable
equivalent means, may be used with the present disclosure without
departing from the spirit and scope of the disclosure.
[0129] While the disclosure has been described 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 there from. It is intended that the appended claims
cover such modifications and variations as fall within the true
spirit and scope of the disclosure.
[0130] Although a few example embodiments have been described in
detail above, those skilled in the art will readily appreciate that
many modifications are possible in the example embodiments without
materially departing from this disclosure. Accordingly, such
modifications are intended to be included within the scope of this
disclosure as defined in the following claims. In the claims,
means-plus-function clauses are intended to cover the structures
described herein as performing the recited function and not simply
structural equivalents, but also equivalent structures. Thus,
although a nail and a screw may not be structural equivalents in
that a nail employs a cylindrical surface to secure wooden parts
together, whereas a screw employs a helical surface, in the
environment of fastening wooden parts, a nail and a screw may be
equivalent structures. It is the express intention of the applicant
not to invoke 35 U.S.C. .sctn.112, paragraph 6 for any limitations
of any of the claims herein, except for those in which the claim
expressly uses the words `means for` together with an associated
function.
* * * * *
References