U.S. patent application number 14/079139 was filed with the patent office on 2014-06-05 for tractor communication/control and select fire perforating switch simulations.
This patent application is currently assigned to Hunting Titan, Ltd.. The applicant listed for this patent is Hunting Titan, Ltd.. Invention is credited to James E. Brooks, Jesper Oluf Larsen, Kasper Juul Larsen, Nolan C. Lerche, Brian Thomsen.
Application Number | 20140151018 14/079139 |
Document ID | / |
Family ID | 39690662 |
Filed Date | 2014-06-05 |
United States Patent
Application |
20140151018 |
Kind Code |
A1 |
Lerche; Nolan C. ; et
al. |
June 5, 2014 |
Tractor Communication/Control and Select Fire Perforating Switch
Simulations
Abstract
Apparatus and methods for controlling and communicating with one
or more tools in a downhole tool string including a tractor, an
auxiliary tractor tool, a logging tool, a safety sub, a release
mechanism, a unit containing sensors for monitoring downhole
conditions, a setting tool, and a perforating gun. Control and
communication are accomplished by sending signals from the surface
to control switches in the control units on the tool, with
redundant switches for safety, to state machines in the respective
control units, each state machine returning a signal verifying
switch status to the surface. The state machine need not return a
signal including a unique identifier.
Inventors: |
Lerche; Nolan C.; (Stafford,
TX) ; Brooks; James E.; (Manvel, TX) ; Larsen;
Jesper Oluf; (Vallensbaek Strand, DK) ; Thomsen;
Brian; (Fredrikssund, DK) ; Larsen; Kasper Juul;
(Valby, DK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hunting Titan, Ltd. |
Pampa |
TX |
US |
|
|
Assignee: |
Hunting Titan, Ltd.
Pampa
TX
|
Family ID: |
39690662 |
Appl. No.: |
14/079139 |
Filed: |
November 13, 2013 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12451913 |
May 3, 2010 |
8689868 |
|
|
PCT/US08/00200 |
Jan 7, 2008 |
|
|
|
14079139 |
|
|
|
|
60879169 |
Jan 6, 2007 |
|
|
|
Current U.S.
Class: |
166/53 ;
102/202.5 |
Current CPC
Class: |
E21B 43/11857 20130101;
E21B 43/116 20130101; E21B 47/13 20200501; E21B 47/12 20130101;
E21B 47/024 20130101; E21B 44/00 20130101; E21B 23/001
20200501 |
Class at
Publication: |
166/53 ;
102/202.5 |
International
Class: |
E21B 47/12 20060101
E21B047/12 |
Claims
1. Apparatus for controlling one or more devices in a wellbore
comprising: a surface computer; a surface controller; one or more
control units connected to one or more devices, the control units
being adapted for bi-directional communication with said surface
controller over a cable, each said control unit comprising a state
machine for identifying the status of the control unit, the surface
controller being adapted to send commands to the control units;
characterized in that; the state machine of each control unit is
adapted to identify one or more valid commands for each status of
the control unit; the control units each being adapted to verify
whether a command is valid for the status of the control unit, send
an error message to the surface controller if the command is not
valid for the status of the control unit, perform the command and
send an uplink message to the surface controller comprising the
status of the control unit if the command is valid for the status
of the control unit; and the surface controller being adapted to
identify the relative position of the devices within the tool
string by tracking the commands and uplink messages and remove
power to the control units if it receives an error message or if
does not receive an uplink message after the command is sent.
2. The apparatus of claim 1 wherein said surface computer
communicates with the surface controller via wireless
connection.
3. The apparatus of claim 1 wherein said surface computer and said
surface controller selectively controls said control units using a
sequence of commands.
4. The apparatus of claim 1 wherein each said control unit is
adapted for communicating status information to said surface
computer over-a cable.
5. The apparatus of claim 1 wherein the control units are
electrically connected in series.
6. The apparatus of claim 1 wherein said control units access one
or more than one of the following: a tractor motor; sensors for
monitoring one or more of the parameters of tractor RPM,
temperature, voltage, and/or current either at the surface or at
the surface while tractoring; a mechanism for releasing a tractor
from said cable; a mechanism for releasing one or more tools in a
tool string; a unit containing sensors for monitoring downhole
conditions including temperature, pressure, voltage, current,
inclination, rotation, and/or acceleration; a well logging tool; an
auxiliary tractor tool; a device for blocking voltage; an explosive
initiator; a perforating gun including an explosive initiator;
and/or a setting tool including an explosive initiator.
7. The apparatus of claim 1 wherein said control unit comprises one
or more transistor switches, form-C switches, latching relays, or
motorized piston switches.
8. The apparatus of claim 1 additionally comprising
voltage-protected circuitry for controlling one or more switches in
said control unit.
9. The apparatus of claim 8 wherein said voltage-protected
circuitry comprises a shunting device and a fuse element.
10. The apparatus of claim 8 further comprising a circuit
containing a transformer or one or more diodes, Zener diodes,
triacs, or P- or N-channel FETs.
11. The apparatus of claim 1 wherein the state machine of each of
said control units is provided with a pre-assigned identifier for
each said control unit.
12. The apparatus of claim 11 wherein the pre-assigned identifier
is contained in either a downlink, an uplink, or both downlink and
uplink communications.
13. An explosive initiator integrated with a control unit
comprising: means for receiving a signal from a cable to which the
explosive initiator is electrically connected; characterized in
that the initiator further comprises: a microcontroller including a
state machine for validating a signal from said signal receiving
means; a switch responsive to an output from said microcontroller
when a signal is validated by the state machine; and an explosive
initiator connected to said switch.
14. The explosive initiator of claim 13 additionally comprising a
switch for passing power, communication signals, or power and
communication signals, to a device connected to the cable.
15. The explosive initiator of claim 13 wherein said switch is
comprised of an explosive initiator switch and a wireline
switch.
16. The explosive initiator of claim 13 wherein the state machine
is provided with a pre-assigned identifier.
17. An apparatus for checking the function of one or more downhole
tools before lowering the tools into a wellbore comprising: a
pre-check controller; electrical connections between said pre-check
controller and one or more downhole tools to be lowered into a
wellbore; and one or more control units mounted on each downhole
tool adapted for bi-directional communication with said pre-check
controller, each said control unit comprising a state machine for
identifying the status of each said control unit, said pre-check
controller being adapted to send a plurality of commands to the
respective control units; characterized in that; the state machine
of each control unit is adapted to identify one or more valid
commands for each state of the control unit; the control units each
being adapted to verify whether a command is valid for the state of
the control unit, send an error message to the pre-check controller
if the command is not valid for the state of the control unit,
perform the command and send an uplink message to the pre-check
controller comprising the state of the control unit if the command
is valid for the state of the control unit; and the pre-check
controller being adapted to identify the relative position of the
devices within the tool string by tracking the commands and uplink
messages and remove power to the control units if it receives an
error message or if it does not receive an uplink message after the
command is sent.
18. The apparatus of claim 17 additionally comprising a surface
computer, said surface computer communicating with said pre-check
controller via either a cable, a wireless connection, or a
combination of cable and wireless connection.
19. The apparatus of claim 17 wherein the state machine of each of
said control units is provided with a pre-assigned identifier for
each said control unit.
20. The apparatus of claim 19 wherein the pre-assigned identifier
is contained in either a downlink, an uplink, or both downlink and
uplink communications.
21. The apparatus of claim 17 wherein the switches controlled by
the state machine are located on either a perforating gun or
setting tool.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. Non-Provisional
application Ser. No. 12/451,913, filed May 3, 2010, which is the
national phase application of PCT/US08/00200, filed Jan. 7, 2008,
which claims the benefit of U.S. Provisional Application No.
60/879,169, filed Jan. 6, 2007, which related patent application is
hereby incorporated in its entirety by this specific reference
thereto.
BACKGROUND OF THE INVENTION
[0002] Perforating guns are used in operations to complete an oil
or gas well by creating a series of tunnels through the casing into
the formation, allowing hydrocarbons to flow into the wellbore.
Such operations can involve multiple guns that create separate
perforations in multiple producing zones where each gun is fired
separately. Operations can also involve single or multiple guns in
conjunction with setting a plug. The guns are typically conveyed by
wireline, tubing or downhole tractors.
[0003] Switches are typically coupled to each detonator or igniter
in a string of guns to determine the sequence of firing. One simple
type of switch uses a diode that allows two guns (or a gun and a
plug) to be fired, one with positive voltage and the other with
negative voltage. Percussion switches are typically used to
selectively fire three or more guns. Percussion switches are
mechanical devices that use the force of the detonation of one gun
to connect electrically to the next one, starting with the bottom
gun and working up. The devices also disconnect from the gun just
fired, preventing the wireline from shorting out electrically. One
problem with percussion switches is that if any one switch in the
gun string fails to actuate, the firing sequence cannot continue,
and the gun string has to be pulled out of the wellbore, redressed
and run again.
[0004] More recently, electronic switches have been used in
select-fire guns. Unlike the percussion actuated mechanical
switches, selective firing of guns can continue in the event of a
misfired gun or a gun that cannot be fired because it is flooded
with wellbore fluid. One commercial switch of this type has
downlink communication but is limited in the number of individual
guns that can be fired in one run. As with the percussion switches,
the system relies on detecting changes in current at the surface to
identify gun position, which may not be a reliable method to
identify gun position in a changing environment.
[0005] Another type of electronic switch has both downlink and
uplink communication, is not as limited in total number of guns
that can be fired in a run, but is somewhat slow to fire because of
the long bidirectional bit sequence required for communication.
Both downlink and uplink communications use a unique address
associated with each switch to identify correct gun position prior
to firing.
[0006] A common problem in operating downhole devices is keeping
unwanted power from causing catastrophic actions. Some examples
include a perforating gun receiving voltage that accidentally fires
the gun downhole, a setting tool being activated prematurely, a
release device suddenly deploying and high voltage destroying
electronics in a well logging tool because its power rating is
exceeded. A solution is to stop unwanted power by inserting a
blocking mechanism between the power supply and the downhole device
that is to be protected. In a standard perforating job, the power
to log and to detonate the perforating gun is located at the
surface. Power can also be generated downhole using batteries.
Recently, there have been detonator designs that incorporate
electronics to block unwanted power from firing a gun.
[0007] The high voltage necessary to power a downhole tractor
presents particular problems in protecting the tool string it
conveys. The surface voltages powering a tractor are typically 1500
VDC or 1000 VAC. Tractors normally have an internal design that
prevents tractor power from being transmitted below the tractor,
but sometimes the circuitry fails or does not work properly,
allowing induced voltage or direct voltage to pass through the
tractor into the tool string below, which can include perforating
guns or logging tools. To protect the tool string, one or more
special safety subs are located between it and the tractor. Some of
the subs use electrical/mechanical relays to block accidental
tractor power. Others use electronic switches that are commanded to
turn off and on using communication messages from the surface that
contain a unique address.
[0008] More recently, the American Petroleum Institute has issued a
recommended practice for safe tractor operations, RP 67, which
includes a recommendation that the tractor be designed so that it
blocks unwanted voltage from passing through and that the design is
free of any single point failure. In addition, there must be an
independent, certified blocking device between the tractor and any
perforating gun to prevent unwanted power from being applied to a
gun.
BRIEF SUMMARY OF EXAMPLES OF THE INVENTION
[0009] It is, therefore, an object of the present invention to
provide a command and response system featuring fast bidirectional
communication while allowing a large number of guns to be fired
selectively. The system requires communication through a cable and
can include communications with a downhole tractor and safety sub.
Two embodiments are provided, both using a state machine as part of
the electrical switch to command and identify status within the
switch. In one, the gun position before firing is uniquely
identified by keeping track of the sequence of states. In the
other, correct gun position is established by state and an uplink
of a unique identifier. Unlike bidirectional communication
electronic switches, a returned downlink of the identifier is not
necessary.
[0010] Another object of the present invention is to provide a
system that prevents tractor power from migrating past the tractor.
Elements of this design are employed in a separate safety sub that
acts as a further safety barrier to block unwanted power to the
tool string.
[0011] Other objects of the present invention, and many advantages,
will be clear to those skilled in the art from the description of
the several embodiment(s) of the invention and the drawings
appended hereto. Those skilled in the art will also recognize that
the embodiment(s) described herein are only examples of specific
embodiment(s), set out for the purpose of describing the making and
using of the present invention.
[0012] The present invention provides a system for communicating
bi-directionally with a tractor that includes means for connecting
and disconnecting electrical power below the tractor. The system
also allows bidirectional communication to sensors contained in the
tractor for monitoring certain operational functions. The
communication and uplink data transmission can occur with tractor
power either off or on. A separate safety sub uses common elements
of the bidirectional communication and switching to block unwanted
voltage and to pass allowable voltage. In addition, methods are
disclosed for disconnecting a shorted wireline below the tractor or
below the safety sub.
[0013] Also provided is a system for bi-directional communication
with other devices such as selectively fired perforating guns,
setting tool, release devices and downhole sensors. According to
described embodiments, the invention features a system to select
and fire specific guns in a perforating string. In one embodiment
each switch unit is interrogated and returns a unique address that
is retrieved under system control from the surface. Each location
within the gun string is identified with a particular address.
[0014] In another aspect, the present invention provides an
embodiment in which every switch unit is identical without an
identifying address. Each switch unit's sequential position in the
gun string is identified by keeping proper track of the number of
surface commands along with the uplink status from an embedded
state machine. This predetermined chain of events provides surface
information for determining the unique location of each switch unit
in a given gun string. These enhancements allow for faster
communication, initialization and firing time. As an added feature,
all switches are exactly the same with no unique embedded address
to program and manage.
[0015] Also provided is a method for controlling one or more
devices on a tool string in a wellbore with a surface computer and
a surface controller comprising the steps of sending a signal down
a cable extending into the wellbore to one or more control units
located on the devices in the tool string, each said control unit
comprising a state machine for identifying the status of each said
control unit, processing the signal with the state machine,
controlling the position of one or more switches located on the
device in the tool string when the state machine for that device
processes a valid signal, and returning a signal validating switch
action to the surface computer.
[0016] In another aspect, a method of switching wireline voltage
between a tractor motor or the tractor output in a downhole tool
string including a tractor is provided. The method comprises the
steps of sending a signal to a control unit on the tractor from the
surface, processing the signal with a state machine on board the
tractor for controlling the position of one or more switches
located in one or more circuits connecting the wireline to either
the tractor motor or a through wire that connects to the tool
string; and returning a signal validating switch action to the
surface. In another aspect, a method of switching between a safe
mode for tractoring and a perforating mode for perforating in a
tool string including a tractor and a perforating gun that has been
lowered into a well on a wireline is provided. The method comprises
the steps of sending a signal to a control unit on the tractor from
the surface, processing the signal with a state machine for
controlling the position of one or more switches located in one or
more circuits for connecting the wireline to either the tractor
motor or a through wire connecting to the perforating gun, and
returning a signal validating switch action to the surface.
[0017] Also provided is an explosive initiator that is integrated
with a control unit comprising means for receiving a signal from a
cable to which the explosive initiator is electrically connected, a
microcontroller including a state machine for validating a signal
from the signal receiving means, a switch responsive to an output
from the microcontroller when a signal is validated by the state
machine; and an explosive initiator that is connected to the
switch.
[0018] In yet another aspect, the present invention provides an
apparatus for checking the function of one or more downhole tools
before lowering the tools into a wellbore comprising a pre-check
controller, electrical connections between the pre-check controller
and one or more downhole tools to be lowered into a wellbore, and
one or more control units mounted on each downhold tool that are
adapted for bi-directional communication with the pre-check
controller, each control unit comprising a state machine for
identifying the status of each control unit, the pre-check
controller being adapted to send a plurality of commands to the
respective control units.
[0019] Also provided is a method for checking one or more devices
in a tool string before lowering the tool string into a wellbore
comprising the steps of sending a signal to one or more control
units located on the devices in the tool string, each control unit
comprising a state machine for identifying the status of each
control unit; and processing the signal with the state machine. The
position of one or more switches located on the device in the tool
string is controlled when the state machine for that device
processes a valid signal and a signal validating switch action is
returned from the control unit.
[0020] Also provided is a communication system than allows both
serial and parallel control of downhole devices including tractors,
auxiliary tractor tools, well logging tools, release mechanisms,
and sensors. The advantage of parallel control is that individual
devices can be interrogated without going through a series path,
thereby being more accessible. Each tool in the parallel
arrangement has a control unit that carries a tool identifier as
part of its uplink communication. A detonator that contains an
integral switch unit is also provided.
[0021] Also provided is a system including several components, a
tractor, surface controller, surface computer, and safety sub as
follows:
[0022] Tractor [0023] 1. Use of dual processors, each controlling a
set of switches for connecting a W/L to either a tractor motor or a
tool below for directing the wireline for powering the tractor
power or providing a direct through wire mode. [0024] 2. A Zener
diode in series with the final output to decouple the wireline in
case of a short, thereby allowing communication to the micro in
order to actuate a switch to disconnect a shorted circuit to regain
tractor functions. [0025] 3. An inline series transformer on the
output of the tractor with one end of the primary winding
connecting directly to the tractor output while the other end
connecting to tools below. In addition, the output end of the
transformer primary is capacitive coupled to ground. In the event
of a shorted W/L, a high frequency signal can be sent down the
wireline and produce power on the transformer secondary for
actuating a switch such as a motorized piston switch or a form C
switch, thereby clearing the shorted wireline. [0026] 4.
Pre-selecting W/L switches within a tractor and remaining in a
fixed or latched position for further use by another service
operation. [0027] 5. Provide real time status for temperature.
[0028] 6. Provide real time status for downhole voltage. [0029] 7.
Gang switch for control and status in a piston contact geometry.
[0030] 8. Design applies to both AC or DC driven tractors. [0031]
9. Supports 2-way communication. [0032] 10. Receives downlink
commands. [0033] 11. Transmits switch status. [0034] 12. Transmits
sensor data (Temp, V, RPM, etc.). [0035] 13. No single point
failures in Tractor itself [0036] 14. Complies with RP67.
[0037] Surface Controller [0038] 1. Wireless interface for sending
and receiving data between a laptop computer and a Surface
Controller. [0039] 2. Laptop provides: [0040] Control and human
interface via special program [0041] Monitor System Status [0042]
Archives data [0043] Job History [0044] Bluetooth between Laptop
and Surface Controller. [0045] 3. Interfaces between laptop and
Tractor. [0046] 4. Sends commands and solicits data.
[0047] Surface Computer [0048] 1. Wireless connection to a surface
controller. [0049] 2. Monitor which power supply is connected
between tractor or perforating and run appropriate program. [0050]
3. Surface computer for controlling tractor pre-check, tractor
operations including communications and sending commands, and power
for perforating. [0051] 4. Communicate using a power line carrier
during tractor operation with either AC or DC power. [0052] 5.
Correlation (CCL) during tractor operation.
[0053] Safety Sub [0054] 1. Use of dual processors, each
controlling a set of switches for connecting a perforating gun
string to either ground or to a downhole W/L. [0055] 2. A Zener
diode in series with the final output to decouple the wireline in
case of a short thereby allowing communication to the micro in
order to actuate a switch to disconnect a shorted circuit in order
to regain tractor functions. [0056] 3. Provide an inline
transformer on the output of the Safety Sub having the output
capacitive coupled to ground. In the event of a shorted W/L, a high
frequency signal can be sent down the wireline and produce power on
the transformer secondary for actuating a switch such as a
motorized piston switch or a form C switch, thereby clearing the
shorted wireline, and produce power on the transformer secondary
for actuating a piston switch and clearing the shorted wireline in
the same way as with the tractor. [0057] 4. A wireless interface
for sending and receiving data between a laptop computer and a
Surface Controller. [0058] 5. Pre-selecting Safe Sub W/L switches
and remain in a fixed position for further use by another service
operation. [0059] 6. Supports two-way communication. [0060] 7.
Receives Safe and Perf commands from surface. [0061] 8. Transmits
switch status. [0062] 9. Independent Unit with no single point
failures. [0063] 10. Uses same design as portion of tractor
electronics. [0064] 11. Complies with RP67.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0065] Referring now to the figures, FIG. 1 is a diagram of a tool
string that includes a perforating gun string, downhole Sensors and
Release Device, a Safety Sub for preventing unwanted voltages from
getting to the gun string, a Casing Collar Locator (CCL) or other
positioning device for locating the gun string within a cased well
bore, a Tractor Unit for pushing tools along a horizontal well
bore, and a wireline unit containing a wireline wench, Surface
Controller, computers and power supplies. A wireline collector
provides a method for selecting either the Surface Controller or
the Tractor Power Unit.
[0066] FIG. 2 is a block diagram of a Surface Controller that
integrates perforating, tractor operations, logging and other well
services, including pre-checks for tools at the surface. This
pre-check would include, but is not limited to, Tractor and Safety
Sub operations, select fire switches, sensors, release devices and
communication links associated with logging and perforating
operations and tractoring. The Surface Controller also supports
receiving and transmitting signals to a Tractor, Safety Sub,
Release Device, Sensors and Switch Unit. Controlling power supplies
archiving job data, program control and safety barriers are also
functions of the Surface Controller.
[0067] FIGS. 3A, 3B and 3C show tool strings being prepared for
downhole service. In FIG. 3A, a Surface Controller interfaces to a
Tractor for providing power and communications. Typical pre-checks
and set-ups for the Tractor would be to set all switches to an
initial condition for safe operation and to check communication
functions. Communications and functions are also checked for the
Sensors, Release Devices and select switches within the perforating
gun. FIG. 3B shows a Surface Controller for checking Tractor
functions only. FIG. 3C shows a surface check of only the Release
Device, Sensors and select switches. Any combination of tools can
be tested at the surface. A laptop computer provides program
control to the Surface Controller through a wireless
connection.
[0068] FIG. 4 is a Pre-check Controller block diagram used in the
surface pre-check shown in FIG. 3.
[0069] FIG. 5 is a flow chart describing program control for
performing a pre-check on the gun string containing selective
Switch Units prior to running in hole. This embodiment does not use
any addressing between the Switch Units and surface computer.
[0070] FIG. 6 is a block diagram of the Tractor Controller
electronics for sending and receiving commands and controlling
switches for tractor operation or perforating events.
[0071] FIGS. 7A, 7B, 7C and 7D show the combination of position for
two sets of form C switches. No single switch can be positioned
such that the tractor would be unsafe for perforating.
[0072] FIG. 8 is a block diagram of various sensors within the
tractor electronics.
[0073] FIGS. 9A and 9B are a block diagram of a Safety Sub that
resides on top of a perforating gun string and a detail diagram of
a motorized piston switch suitable for use in the circuits of the
Safety Sub, respectively.
[0074] FIG. 10 is a flow chart for a Tractor Controller single
State Machine for controlling either tractor electronics, shown in
FIG. 6, or Safety Sub, shown in FIG. 9.
[0075] FIG. 11 is a State Diagram for a single State Machine which
can control either the electronics of the Tractor, shown in FIG. 6,
or the Safety Sub, shown in FIG. 9.
[0076] FIG. 12 is a block diagram for a Power Line Carrier
Communication (PLCC) interface to the wireline. The interface could
be the same at the surface and at the tractor.
[0077] FIG. 13 shows a tool string that includes Switch Units in a
gun string for firing selected guns, a wireline, a logging truck
equipped with a power supply and a surface computer for controlling
job events such as communication with the Switch Units, data
storage, power supplies current and voltages, all following
standard safety procedures.
[0078] FIG. 14 is a block diagram of a perforating Switch Unit
according to an embodiment shown in FIG. 13. The Switch Unit shown
is adapted for a positive voltage on the wireline conductor with
the wireline armor being at ground potential.
[0079] FIG. 15 is a block diagram showing a Switch Unit integrated
into a detonator.
[0080] FIGS. 16A and 16B are a flow chart describing the program
control sequence for initializing a three gun string and firing the
bottom gun. This embodiment does not use any addressing between the
Switch Units and surface computer.
[0081] FIG. 17 is a state diagram for the state machine within a
Switch Unit and defines the predetermined logical flow for
selectively firing detonators in a gun string. This embodiment does
not use any addressing between the Switch Units and surface
computer.
[0082] FIGS. 18A and 18B a flow chart describing the program
control and sequence for initializing a two gun string and firing
the bottom gun using common downlink commands for all Switch Units
that solicits a unique address from each Switch Unit.
[0083] FIG. 19A is a diagram of a generalized perforating tool
string that includes a setting tool and auxiliary devices such as
sensors and cable release mechanisms. The diagram illustrates both
series and parallel communication paths. FIG. 19B shows a tool
string including multiple auxiliary tractor and logging tools. The
auxiliary and logging tools shown in FIG. 19B are powered by
positive DC voltage from the surface as shown in FIG. 19C.
[0084] FIG. 20 is a flow chart describing the program control
sequence for communicating with devices that are connected in a
tool string in parallel and in series.
[0085] FIG. 21 is a state diagram defining the predetermined
logical flow for selecting various devices that are connected in a
tool string in parallel and in series.
DETAILED DESCRIPTION OF EXAMPLES OF THE INVENTION
[0086] In more detail, and referring to FIG. 1, a tractor system is
shown equipped with a tractor 10, casing collar locator (CCL) 12
(or any correlation device for depth association), Safety Sub 14
for preventing tractor voltages from migrating to the gun system,
and set of sensors for monitoring downhole events/Release Device 18
for separating the gun string from tractor 10 and perforating gun
18. Tractor 10 functions to push perforating gun 18 along
horizontal or nearly horizontal sections of an oil well. A logging
truck 20 typically houses power supplies and computers for
performing required logging and perforating operations. A separate
power supply 22 is typically used for supplying tractor power. The
tractor is powered through a wireline 24 using high voltage in the
range of 1000 Volts AC or DC.
[0087] Perforating power supply 26 and Tractor Power Unit 22 are
not connected to the Wireline Collector 28 at the same time.
Wireline Collector 28 provides a means for selecting a plurality of
different signals or power for a specific operation. In all cases,
only one signal and/or power source 22, 26 is connected to wireline
collector 28 at a time.
[0088] Referring now also to FIG. 2, the supporting peripherals
used during a tractor and perforating interval are shown. The
Surface Controller 30 interfaces with all power supplies, commands
ON/OFF sequences, and controls and delivers voltage and current to
the tool string. In addition, surface computer 32 runs software for
controlling and recording all communication events during a
perforating job, such as position of the Switch Unit within the gun
string. Computer 32 is also provided with a monitor (not shown) for
displaying a visual tool string and events during a job. On many
wells, the tractor operator does not have the capability of running
additional services because of equipment differences or for lack of
integrated support hardware. The embodiment shown illustrates a
Surface Computer 32 and peripherals for supporting both perforating
and tractor operation, which provides more reliable and safer
operation. The more common arrangement has separate responsibility
for controlling tractor and perforating operations.
[0089] Surface Controller 30 runs such events as pre-check and
initialization of tractor 10, controlling tractor power supply 22
during tractor operation, running embedded software for logging
during tractor operations, controlling sequences during a
perforating job, communicating with and controlling other tools in
a string such as drop-off joints (to disconnect in case of being
stuck in the hole), safety sub functions, and operating parameters
of tractor 10 such as temperature, RPM, voltage and/or current,
etc. A Downlink Driver 34 typically interfaces to wireline 24
through transformer 36 to send signals down wireline 24 while
powering the tools below. Uplink signals are monitored across a
Signal Transformer/current-viewing-resistor (CVR) 38 and decoded
for message integrity by uplink 40. Series wireline switch 42 turns
power ON or OFF under computer control and also by means of using a
manual removable safety key 44.
[0090] Surface Computer 32 is also equipped with a wireless or
cable, or combination of wireless and cable, interface 46 to
Pre-Check Controller 48. Pre-Check Controller could include a
laptop, PDA or any preprogrammed device that controls predetermined
events, a laptop computer being shown in FIG. 2. Pre-Check
Controller 48 is connected to the tractor or gun string as shown in
FIG. 3 while at the surface for pre-check procedures during which
wireline safety switch/key 44 is in the OFF position with the key
removed. Also due to a low power RF restriction during perforating,
it may be necessary to have the Surface Computer 32 equipped with
an extension cable having a receiver/transmitter attached to one
end to allow the wireless path to be a shorter distance and in line
of sight.
[0091] As described above, Surface Controller 30 is equipped with
power supplies 22, 26, one for perforating and another for tractor
operations, in separate compartments for safety reasons, and only
one is connected to wireline 24 at a time through a Perf/Tractor
switch in wireline collector 28. The switch could also be a
physical connector that allows only one connector to be installed
at a time. Those skilled in the art will also recognize that
computer 32 can be configured to sense whichever power supply is
connected and only allow the programs to run that are associated
with a particular power supply.
[0092] FIGS. 3A, 3B and 3C show various tool string configurations
being tested at the surface before running in the hole. The support
equipment for setup and test operations is Pre-Check Controller 48
that connects to the wireline input of the tool string, provides
power and communications to the tractor input, and receives program
control from a laptop through a wireless or cable connection, or
from a Surface Controller as shown in FIG. 2. Radio frequency power
must remain low in a perforating environment and therefore
communication links are not limited to a single RF link. The
communication link could be implemented using RF repeaters to get
around steel buildings and remain in the line of sight, use RF
receiver/transmitters on an extension cable, or a simple cable
connection.
[0093] FIG. 3A shows typical pre-check functions for a tractor
system equipped with a Tractor 10, CCL 12, Safety Sub 14, Release
Sub and Sensor Unit 16, and perforating gun 18 containing selective
Control Units as described below. Types of tests performed for
Tractor 10 and Safety Sub 14 include, but are not limited to,
verifying communications, setting up switches to safe positions to
perform tractor operations, soliciting status from the Tractor and
Safety Sub switches, and other tractor functions such as verifying
sensor data transmissions. Tests for the Sensors and Release Device
16 include communications and function tests. Tests for perforating
gun 18 include sending wireline ON commands to the series string of
Control Units, verifying communication to all Control Units, along
with correlating a Control Unit to a specific gun. These checks are
normally performed without perforating gun 18 attached, although
with the Pre-Check Controller 48 described herein, it is possible
to leave perforating gun 18 attached because the Surface Controller
30 in one embodiment is designed to limit its current output in
compliance with the above-described API RP67. FIG. 3B shows a
pre-check for a tool string that includes only a Tractor 10 and
Safety Sub 14. In this embodiment, the perforating gun string is
equipped with other type of select fire devices and would not be
tested by Pre-Check Controller 48. FIG. 3C shows a pre-check for a
Sensor Unit and Release Device 16 and perforating gun string
equipped with selective Control Units tested as shown in FIG. 3A.
The Surface Controller 30 or laptop also stores pre-check and setup
data for conformation of proper operation. Using a Surface
Controller located in logging truck 20 instead of a laptop, all
functions, including pre-check, tractor operation, depth
correlation, and perforating, can be performed inside the wireline
unit, reducing total operational rig time.
[0094] The purpose of the pre-check is to verify proper function of
all control units connected to the wireline. Tractor Control Units,
Safety Sub Control Units, Sensors, and Release Devices are tested.
An additional reduced current and voltage power supply is utilized
for testing Switch Units within a gun string. These tests verify
that the Control Units are communicating and functioning correctly
before running the perforating gun in the hole, and for safety
reasons, are typically not done with the same power supply used to
fire the gun downhole. As described above, a special power supply
is used that generates communication power signals with limited
current output in accordance with API RP 67. Pre-Check Controller
48 commands a special internal power supply and sends power along
with signals to the Control Units in the gun string through a
connecting cable. Pre-Check Controller 48 receives wireless
commands from a laptop; alternatively, Surface Controller 30
communicates wirelessly using communication protocols such as
BlueTooth which limits the wireless output power according to
established commercial standards.
[0095] FIG. 4 illustrates the Pre-Check Controller 48 and
functional blocks required for conducting a tractor pre-check.
Pre-Check Controller 48 is a self-contained, battery operated
device that communicates on one side through a wireless or cable
link to a laptop or Surface Controller 30 (FIG. 2) and connects
directly on the other side to the tractor input. A State Machine,
implemented within the microprocessor, controls all events based on
commands received and is recommended for most solutions where there
are non time-critical tasks to perform. In this embodiment and
throughout the following descriptions, a State Machine is
implemented within the structure of a microprocessor. In addition,
the microprocessor is provided with additional functions such as
signal conditioning, analog-to-digital inputs, digital inputs,
driver outputs, watch dog timers, etc., all as known in the art. As
described herein, a state machine is as an algorithm that can be in
one of a small number of states. A state is a condition that causes
a prescribed relationship of inputs to outputs and of inputs to
next states. Those skilled in the art will recognize that the state
machine described is a Mealy machine, which is a state machine
where the outputs are a function of both present state and input,
as opposed to a Moore machine in which outputs are a function only
of state. The state machine as defined above can also be
implemented using an Application Specific Integrated Circuit
(ASIC), programmable logic array (PLA), or any other logical
elements conforming to a predefined algorithm.
[0096] A Downlink Driver 50 provides an interface link between the
Microprocessor and a Signal Transformer 52 that is capacitor
coupled to the wireline. Induced signals from transformer 52 are
received by the Tractor or Safety Sub (not shown in FIG. 4). An
Uplink Detector 54 provides signal interfaces between the
Microprocessor and a Current Viewing Resistor (CVR) 56 or Signal
Transformer 52. The components of Uplink Detector sense and
condition signals received from either the Tractor Unit or Safety
Sub. Power for the surface controller is derived from on-board
batteries 58 that can be turned ON and OFF 60. Power supplies 62
convert the battery power for proper operation of electronics and
tractor communication. A current limiting element 64 in series with
the power output limits the current level in compliance with API RP
67. A series wireline switch provides a means for turning the power
ON or OFF under computer control.
[0097] As an example, the following describes a pre-check event for
a plurality of Switch Units. FIG. 5 is a flow chart describing a
first embodiment of the program control for performing the
pre-check. Unlike the second embodiment described below, in this
embodiment, no unique address(es) is/are used in the uplink
communications. The position of each Switch Unit in the perforating
string is determined by recognition of the status of the respective
State Machine and the proper sequencing of messages.
[0098] The default or initial condition of the Deto Switch, see
FIG. 14, is the OFF position, thereby disallowing power to all
detonators. The default condition for each W/L switch is also in
the OFF position so that there is no wireline connection beyond the
input of the top Switch Unit. Pre-Check Controller 48 commands a
power supply to apply a power signal to the gun string through a
connecting cable. Power energizes the microprocessor or State
Machine in the top Switch Unit. Pre-Check Controller 48 then
interrogates the top Switch Unit and sends a State (0) command (see
FIG. 17 for a state machine diagram). After receiving the first
message, the top Switch Unit validates the message. Upon receiving
a valid message, the State Machine in the top Switch Unit advances
and uplinks a message containing switch status, state machine
status, and a security check word. Upon receiving an invalid
address, the Switch Unit uplinks an invalid message response. Upon
receiving the first uplink message, the surface computer validates
the message, verifies the state machine status, and downlinks a W/L
ON command. If the Switch Unit sent an error message or the uplink
message was invalid in any way, the power to the gun string would
be removed and the process restarted. After receiving the second
downlink message, the top Switch Unit validates the message. If a
valid message was received, the Switch Unit advances the State
Machine of the top Switch Unit, turns the W/L Switch ON, and
uplinks a message containing switch status, state machine status
and a security check word. The top Switch Unit then goes into
hibernation. This process is then repeated for each and every
Switch Unit in the gun string
[0099] There are several variations on this sequence. One variation
is for the top Switch Unit to send an automatic uplink message
after being powered up containing a State (0) status, State Machine
status, and security check word. The surface computer records and
validates the message and returns a downlink command to advance the
State Machine to (1), which turns the W/L Switch ON. The top Switch
Unit then sends a second uplink message that contains a State (1)
status. Applying power to the next Switch Unit wakes it up and
triggers an automatic uplink message of its current State (0)
status. The uplink is delayed to allow the second uplink message to
be received first at the surface. The second Switch Unit is then
commanded from the surface to advance to State (1), and so forth.
By recognizing the change in state of each Switch Unit as it is
communicated with, the surface computer can uniquely identify each
Switch Unit in the perforating gun string.
[0100] A tractor has two basic operation modes, Tractor Mode or
Logging Mode. In Tractor Mode, high power is delivered to the
tractor motor for pushing tools along a horizontal section of a
well. In Logging Mode, the tractor provides only a through-wire
connection to tools connected below the tractor. FIG. 6 illustrates
a control function for directing the wireline voltages to either
the tractor motor, Tractor Mode, or directing the wireline to the
tractor output, Logging Mode. Voltages for powering the tractor
must never be present at the tractor output. After the tractor has
pushed the tool string into location, a redirection to Logging Mode
is required. The wireline must first be disconnected from the
tractor motor and then reconnected to the tractor output.
[0101] The process of switching the wireline is accomplished using
small voltage and low current signals. The following disclosure
describes a control system within the tractor that safely
disconnects the wireline from the tractor motor and connects it to
the output of the tractor. The system only allows connection to the
Logging Mode when certain criteria are met and verified, and
contains redundancy so that no single point failure can cause
unwanted voltage below the tractor. Referring to FIG. 6, the system
comprises two similar circuits 66 connected in series. First
circuit 66A provides control for a set of switches 68A that
connects the wireline to either the tractor motor or to the second
set of switches 68B within the second circuit 66B. Second circuit
66B provides control for a set of switches 68B that connects the
output of the tractor to either ground or to the first set of
switches. Each set of single-pole-double-pole (SPDT/form C)
switches is ganged together with another like pair of contacts in
order to obtain status of the combined pair. The switches 68A, 68B
shown in FIG. 6 are generic and can be one or more of many
different types such as latching relays, latching solenoid piston
switches, bidirectional solid state switches in the form of N and P
channel Field Effect Transistors (FET), insolated gate bipolar
transistor (IGBT) with high side drivers, etc. The Switch Control
70A, 70B between the respective microprocessors 72A, 72B and
switches 68A, 68B is designed for the appropriate action as known
to those skilled in the art. Switches 68A, 68B are controlled from
the surface by sending signals to the control units that are
decoded by onboard microprocessor 72A, 72B, processed by the
respective state machine, and used to control the position of the
switches. In addition, switch status is returned to the surface,
validating switch action. Each control unit is also provided with
an onboard power supply 74A, 74B and transmit 76A, 76B and receive
78A, 78B circuits for communication.
[0102] To comply with safety standards for perforating while using
a tractor, it is necessary not to have single point failures that
cause unwanted voltages on the output of the tractor. The
embodiment in FIG. 6 shows the combinations positions for the Motor
switch and Log switch. Each switch has two positions, yielding a
total of four combinations, shown in FIGS. 7A, B, C, and D. In all
cases, the wireline voltage must pass through two separate switches
controlled by separate circuits before reaching the output,
satisfying the single point failure requirement.
[0103] It is sometimes important to solicit critical operating
parameters associated with operation of a well tractor including,
but are not limited to, temperature, head voltage and current
delivered to the tractor unit, as well as tractor motor RPM. These
and other operating parameters are retrieved in real time by
surface computer 32 using a power line carrier communications
(PLCC) that provide for both downlink and uplink communication
signals to be sent over a wireline in real time while the tractor
is powered. On the transmit side, communication signals are
injected onto the wireline and ride on top the power. On the
receiver side, signals are extracted using band pass filter
techniques, allowing commands to be sent to the tractor control
electronics as well as retrieving status from downhole events. FIG.
8 depicts a separate microcontroller using the same protocol as in
FIGS. 6 and 9. Input voltage 80 into tractor motor 82 is sensed
using a resistor voltage divider for DC tractors or a step-down
transformer followed by a bridge rectifier for an AC tractor. These
status signals are conditioned, scaled, and sent to an
analog-to-digital input of microprocessor 84. Monitoring the
current delivered to a tractor motor can reveal whether a motor has
lost traction, is in a lock rotor condition, or being over- or
under-loaded relative to well bore temperature. Tractor current is
monitored by sensing voltage across a current-viewing-resistor
(CVR) 86 using an operational amplifier 88 having sufficient gain
for reading by an analog-to-digital input. The scale factors used
depend on load ranges, analog to digital bits, and required
accuracy.
[0104] A plurality of temperature sensors, shown schematically at
reference numeral 90, may be used to monitor downhole temperature,
motor winding temperature, boring bit temperature, or any other
necessary tractor functions as known in the art. Implementation is
accomplished by a variety of sensors. Examples include a
resistor-thermal-device (RTD) associated with a reference voltage,
thermocouples, junction voltages of semiconductors, and
voltage-to-frequency converter associated with an RTD. In all of
the examples, a calibration and scale factor is part of an overall
design as known to persons practicing the art. The sensor outputs
mentioned are represented by either a voltage or frequency and
monitored by either an analog-to-digital input or time domain
counter and converted to temperature. The revolutions-per-minute
(RPM) of various motors within a tractor is important for milling
operations as well as pushing pay loads to location. The RPM sensor
91 accumulates pulses generated as a function of motor shaft
rotation. Various sensors may be used including, but not limited
to, magnetic field coupling, optical, infrared, switch contacts,
and brush encoders. Pulses generated are counted over a selected
time frame for RPM derivation.
[0105] As part of the safety requirements for perforating with a
tractor system, a separate independent device, typically the
above-described Safety Sub 14 (FIG. 1), must be placed between the
output from tractor 10 and the input to perforating gun 18. In
addition, the Safety Sub must not have any single point failures
and is typically certified by an outside authority. The Safety Sub
has two modes of operation, Safe Mode during all tractor operations
and Perf Mode only when perforating. Switching between modes is
done only after tractor power has been disconnected at the
surface.
[0106] The block diagram in FIG. 9A describes a system that has no
single point failures. This is accomplished by placing two similar
circuits 92A, 92B connected in series for redundancy. For example,
when the first (bottom) circuit 92A is in Safe Mode, switch K1
disconnects from the wireline and connects the entire second (top)
circuit to ground. The Safety Sub output is also grounded either
through switch K1 or switch K2. If the first (bottom) circuit 92A
is in the Perf Mode, switch K1 connects the second (top) circuit
92B to the wireline. The output is again protected by the second
switch K2. In order for the wireline voltages to pass to the Safe
Sub output, two sets of switches, K1 and K2, must be commanded and
set to the Perf Mode. The second circuit 92B provides control to a
set of switches identified as K2. The switch K2 connects the output
of the Safety Sub to either ground or to the center contact of
switch K1. Whenever switch K2 is connected to ground, the Safety
Sub also provides a ground to the perforating gun input. Whenever
switch K2 is connected to the center contact of switch K1, the
Safety Sub output may be connected to ground or the wireline input.
The logic that follows shows that both control circuits must fail
in a Perf Mode before the Safety Sub would pass unwanted
voltage.
[0107] Each set 94A, 94B of single-pole-double-pole (SPDT/form C)
switches are ganged together with another like pair of contacts to
obtain true status of the existing pair. The switches shown are
generic and can be one or more of many different types such as
latching relays, latching solenoid piston switches, bidirectional
solid state switches in the form of N and P channel FETs, and IGBT
with high side drivers, all as known in the art. The switch control
96A, 96B between microprocessor 98A, 98B and the switch element is
designed for appropriate action as known in the art. Switches
within the Safety Sub are controlled from the surface by sending
signals to the Control Units that are decoded by onboard
microprocessor 98A, 98B and used to control the position of
switches 94A, 94B. In addition, switch status is returned to the
surface, thereby providing validation of switching action. Each
control unit also has an onboard power supply 100A, 100B along with
circuits that transmit 102A, 102B and receive 104A, 104B
communication signals.
[0108] A motorized piston switch as shown in FIG. 9B has the
advantage of a construction that is easily adapted to round tubing
geometry and provides a rugged and reliable switch for the high
shock perforating environment. In addition, the position of the
contact make-up, either open or closed, remains in position after
removal of all power. The latching feature of the piston switch
allows the tractor operator to set the switch to a desired position
and then turn the wireline operations over to another company for
logging or perforating services. The piston switch is comprised of
the following functions. A microcontroller 106 controls the signal
for turning motor 1080N and OFF and selects the direction of the
motor rotation (either clockwise or counter clockwise).
Additionally, the microcontroller 106 monitors the position of the
Piston Switch to determine if the contacts are in either the SAFE
or PERF positions. An H-Bridge 110 receives commands from
microcontroller 106 and changes polarity to DC motor 108, thereby
allowing the motor to turn in either direction. Motor 108 is
connected to a planetary gear reduction box equipped with a
threaded screw section. The threaded screw section, having an
embedded set of contacts, shuttles back and forth to make up to
mating contacts. This action forms either a single pole single
throw (Wireline to Gun contact) or single pole double throw (as
Perf and Safe Status to the micro). The switch shown on top of FIG.
9B is in an open position (SAFE) and the switch on the bottom is in
a closed position (PERF).
[0109] A wireline can short to ground when the perforating gun
fires and communication can be interrupted, particularly with a
form-C switch. Without communication, the switches in both the
Tractor and the Safety Sub cannot be changed. FIG. 9A shows two
methods for resolving the shorted wireline situation. The first
solution is to place the primary of a transformer 112 in series
with the output of the Safety Sub. The output side of transformer
112 is also shunted to ground through a small capacitor. The value
of the capacitor is chosen such that it only provides a shunt to
ground at frequencies much higher than the communication
frequencies and therefore does not interfere with normal
communications and perforating operations. A W/L Disconnect Control
114 is connected to the secondary of transformer 112. W/L
Disconnect Control 114 encompasses a bridge rectifier and is
filtered in order to produce DC voltage and a path to route the
developed voltage to release the switch from the Safety Sub output.
When a shorted wireline exists on the output of the Safety Sub, a
high frequency signal is sent from the surface through the
transformer and capacitor. The result is that a voltage is
developed on the secondary of transformer to actuate the Safety Sub
switch K2 and clear the short.
[0110] A second method of preventing a short on the output of the
Safety Sub is to place a diode in series with the output of the
Safety Sub. Those skilled in the art will recognize that the diode
could be a normal diode of chosen polarity, a single Zener diode of
chosen polarity, or a back-to-back Zener having a predetermined
breakdown voltage in both directions. Using a normal diode as an
example, perforating is done in one polarity and communication in
the opposite polarity. With a simple diode, only one polarity would
be shorted to ground thereby allowing communication by using the
opposite polarity.
[0111] A Zener provides the same results as a normal diode along
with a selected breakdown voltage in one polarity. With a properly
selected Zener voltage, communication continues at signal levels
below breakdown voltage with the advantage that shooting of the
perforating gun can be done selectively in both polarities. The
voltage delivered to the gun system in one polarity would be less
by the Zener breakdown value and generally has no effect on
perforating. A back-to-back Zener has all the features of a single
Zener diode except that standoff voltage is the same for both
polarities. The voltage delivered to the gun system would be less
by the Zener breakdown value for both polarities of shooting
voltage. Again, no detrimental effect is seen during selective
perforating. Voltage blocks between the Safety Sub can also be
accomplished using a Triac that triggers at a predetermined voltage
that is either positive or negative and is above the operating
voltages of the Safety Sub. The Triac blocks all voltages until
triggered and after being triggered, only a small voltage drop is
seen across the device, which is desirable for shooting selectively
(plus and minus polarities). Another method for creating a voltage
block is implemented with a set of FET transistors. One P-Channel
FET controls or switches the high side and the other N-Channel FET
controls or switches the low side, allowing both polarities to pass
for selective shooting. Again, predetermined switch voltages (turn
ON) can be implemented using zeners, diacs, thyristors, etc.
[0112] FIG. 10 illustrates a method for communicating with a
microprocessor/state machine without sending a downlink address for
an identifier. Typically when two or more remote devices are on a
common buss, an identifying address is embedded in the host message
to prevent coincident response signals from multiple remote
responding devices. In accordance with the present invention, each
state machine or device has a plurality of its own set of legal
commands. Upon receiving a message, the controller decodes the
embedded command. Only if the command is legal is the receiving
controller allowed to generate an uplink message, thereby
preventing buss contention or collision of data when two or more
remote units are on a buss or party line connection. In addition,
before an uplink transmission can occur, the logical position of
the state machine is also compared and must be in sync with the
expected state position transmitted by the host. This comparison
further discriminates which messages are legal and which
controllers are allowed to return an uplink message. In another
embodiment, a unique identifier is attached to each uplink or
returned message to further distinguish or identify one control
unit from another. In another embodiment, unique identifiers are
attached to both uplink and downlink messages. These methods apply
to each controller within the Tractor Electronics (FIG. 6) and to
each control unit within the Safety Sub (FIG. 9).
[0113] Referring to FIG. 10, the Surface Unit first applies power
to the wireline, causing all control units on the communication
buss to initiate a power-up reset and enter state "0" waiting for a
downlink message. The surface unit then sends a downlink message
containing a plurality of commands specific to only one controller
along with a state "0" status. Every downhole controller then
receives and verifies the message for errors. If an error is
detected, the downhole controller goes back to state "0" with no
further action. If the message is error free, the state machine
advances and the command bits within the message are decoded. If
the command is illegal, the downhole device reverts to state "0."
If the command is legal for a particular device, the state machine
again advances, uplinks a message and waits for a second response.
The Surface Unit then receives and validates the first uplink
message. If the message is in error, the surface controller goes
into a restart mode by turning power OFF and then back ON. If the
message is error free, the Surface Controller transmits a second
message containing the same control command along with the state
machine expected position. Again, all remote control units receive
the second message and only the one controller matching the
downlink state position and having received a legal command is
allowed to advance and process the message. If the message is
verified and an error exists, a bad message status will be returned
and the downhole device must be powered down to continue. If the
message is verified to be free of errors, the command is processed
and a return (uplink) confirmation message is transmitted. The
surface unit receives and validates the message. If the message
contains errors, the surface controller restarts the entire
process. If the message is error free, the surface controller
accepts the data and continues to the next downhole controller.
[0114] FIG. 11 illustrates a predefined sequence of events for
controlling each downhole device (such as the Tractor Control Unit
or a Safety Sub) containing one or more microprocessors or state
machines. Upon power-up, the state machine enters state "0" and
waits for a downlink message. Upon receiving a message from the
surface, the state machine advances to state "1." While in state
"1," the message is validated for proper state position,
cyclic-redundancy-check, and message length. An invalid message
decoded by the microprocessor causes the state machine to revert to
state "0." If a valid message is decoded the state machine advances
to state "2." While in state "2," the command bits are decoded. If
an illegal command is decoded for that particular controller, the
state machine again goes back to state "0." If a legal command is
decoded, the device returns a message containing state "3," the
decoded command, switch status, embedded address (if used) and
cyclic-redundancy-check and the device waits for a second downlink
message. Upon receiving a second downlink message, the state
machine advances to state "4." While in state "4," the downhole
controller verifies receiving the proper state position from the
surface controller, again compares the command bits with the
previous command bits, cyclic-redundancy-check, and message length.
If the message is invalid in any way, the state machine advances to
state "6" and the downhole controller transmits an uplink message
confirming an invalid message. At this point, the controller must
be powered down in order to restart. If the message is valid, the
state machine advances to state "5." While in state "5," the device
processes the command. For the last event, the downhole controller
transmits an uplink message including state "5" position, switch
status, embedded address (if used), and cyclic-redundancy-check.
The microprocessor/state machine now enters a sleep mode while
maintaining its present logic state and will not listen to any more
messages until a complete restart.
[0115] The block diagram in FIG. 12 is but one example for
interfacing a Power Line Carrier Communication (PLCC) scheme onto a
wireline and could be the same at the Surface Controller in FIG. 2
and the Tractor Controller FIG. 6. For those skilled in the art,
there are many ways to interface a power cable for PLCC operations.
A capacitive coupled transformer taps across the wireline (power
line), providing a route for injecting high frequency communication
signals onto the wireline and for extracting signals from the
wireline during power operations. The receiver section also
includes a Receiver Filter and Amplifier for conditioning the
signal for use by the microprocessor. The transmitter section also
includes an amplifier of sufficient power for signal generation.
Communicate using half-duplex, master/slave party line, and
complies to interrogation/response only (no unsolicited uplinks).
Signals:
[0116] a. Downlink--FSK (mark/space frequencies TBD)
[0117] b. Uplink--Current Loop, modified NRZ
[0118] Baud Rate--300 Baud or higher (for example).
[0119] FIG. 13 shows a perforating gun system having a series of
three guns attached to a wireline, or more generally, to any
electrical conductor, that is conveyed into a wellbore to a first
formation zone to be perforated using a truck and winch. A Surface
Controller and associated power supply is typically located in a
logging truck. The firing sequence begins on the bottom (Gun 1) and
progresses upward until the top gun (Gun 3) is shot, completing the
firing sequence. The system is initialized starting with Gun 3,
followed by Gun 2 and Gun 1.
[0120] Initialization of the Switch Units (FIG. 14) occurs by
sending power and a sequence of signals to the gun string. In one
embodiment, the first command signal is sent to the top gun,
thereby validating its presence and position followed by turning
its wireline (W/L) Switch to ON. The second gun (middle) is
initialized in the same manner. Successive messages are sent to the
first gun (bottom) and validated before turning on the ARM Switch
and Fire Switch, respectively. The wireline is prevented from
shorting to ground because the W/L Switch of Switch Unit (1)
remains OFF during firing. Shooting voltage is then applied to the
wireline and the bottom gun is the first gun fired, destroying
Switch Unit (1). The remaining Switch Units disconnect
automatically from the wireline when power is turned off. Following
relocation to the second perforating zone, the initialization
sequence is repeated, except only two guns remain in the string.
The bottom gun is now Gun 2. The signal is sent to the top gun,
thereby validating its presence and position, followed by turning
its W/L Switch to ON. Successive messages are sent to the second
gun (bottom) and validated before turning on the ARM Switch and
Fire Switch, respectively. Shooting voltage is then applied to the
wireline and Gun 2 is fired. Following relocation to the third
perforating zone, the initialization sequence is repeated except
only one gun remains in the string. The bottom gun is now Gun 3.
Successive messages are sent to the third gun (bottom) and
validated before turning on the ARM Switch and Fire Switch,
respectively. Shooting voltage is then applied to the wireline and
the bottom Gun 3 is fired, completing the shooting sequence for a
three gun string. If the gun string has more or fewer guns, the
same sequence of initialization and shooting follows the basic
example presented here.
[0121] If one of the guns fails to fire for some reason, the
operator can communicate and control the remaining guns. Given that
misfires can occur frequently, an extra gun(s) can be attached to
the gun string and fired in place of a misfired gun, saving an
additional trip in the hole. Accidental application of voltage on
the wireline will not cause a detonation because proper
communication must be established before the Switch Unit will
connect to the detonator. As an added safety element, a top switch
may be added that is not connected to a detonator, giving a safety
redundancy that prevents an accidental detonation should a Switch
Unit be defective.
[0122] FIG. 14 is a block diagram of a perforating Switch Unit. The
embodiment shows the wireline input voltage to be positive with the
wireline armor being at ground potential. The Power Supply 116
input connects the Switch Unit to the wireline and regulates the
voltage for the power circuitry within the Switch Unit. The State
Machine 118 receives downlink messages, provides uplink states,
traces command-sequence status and controls the W/L and Deto
Switches 120, 122. State Machine 118 can be a specially programmed
microprocessor or separate circuitry that is functionally
equivalent to a microprocessor. The Receiver 124 interfaces to the
wireline to capture data from downlink signals. The Xmit
transmitter 126 induces a signal current onto the wireline that is
decoded at the surface. A Deto Switch 122, controlled by State
Machine/microprocessor 118, provides switching between wireline
power and the detonator. Deto Switch 122 may be a single switch or
two switches in series (for additional safety). During any
perforating sequence, only the Deto Switch 122 in the bottom gun is
selectively turned ON to apply power to the detonator. The W/L
switch 120 controls both firing power and communication signals
through the gun string. In one embodiment, W/L and Deto switches
120, 122 include transistors such as field effect transistors (FET)
or integrated gate bipolar transistors (IGBT), but can be any type
of switch that allows power to be connected by command. This type
of switch has the advantage of disconnecting when powered down,
preventing the wireline from seeing a short during the next command
sequence. As shown in the FIG. 14, a High Side Driver 128 is used
to interface State Machine 118 to W/L Switch 120. Shooting power is
shown as positive, which requires a High Side Driver to interface
State Machine 118 to W/L Switch 120. If the shooting power is
negative, a High Side Driver would not be necessary provided the
W/L Switch is in series with the W/L Armor input and the W/L In is
powered with negative voltage.
[0123] Detonators can include all types, such as hot wire
detonators, exploding foil initiators, exploding bridge wire
detonators, and semiconductor bridge detonators. In addition, the
Switch Units described herein can be integrated into the body of
such detonators as shown in FIG. 15 for safer handling at the
surface because application of accidental power will not cause the
detonator to fire. Also, an integrated detonator needs only three
wires compared to five wires for a separate Switch Unit connected
to a detonator. Power can only be applied to the detonators after
the proper communication sequence is established. The embodiment in
FIG. 15 shows a Switch Unit that is integrated with a detonator
having a negative shooting polarity (as compared to a positive
shooting polarity shown in FIG. 14). The integrated components
include all parts of the Switch Unit along with whatever parts are
required for the detonator of choice.
[0124] In an alternative embodiment, the interrogation-response
communications system of the present invention does not use
addressing between the surface computer and the downhole Switch
Units. In this alternative embodiment, the surface computer and
power supply are typically the same as used in ordinary perforating
jobs, but different software is used for the communication protocol
that tracks the number of uplink and downlink messages and the
state machine position within each Switch Unit. FIGS. 16A and 16B
are a flow chart describing the program control sequence for
initializing a three gun string and firing the bottom gun in
accordance with this alternative embodiment of the present
invention.
[0125] The process begins at the time the Surface Unit sends power
down the wireline. The Surface Unit then sends a State (0) command
to the top Switch Unit (3). After receiving the first message, the
top Switch Unit (3) validates the message. Upon receiving a valid
message, the State Machine advances within the top Switch Unit (3).
If the message validation is error free, Switch Unit (3) uplinks a
message containing switch status, State Machine status, and a
security check word. If an invalid message is received, the Switch
Unit uplinks an invalid response message. Upon receiving the first
uplink message from Switch Unit (3), the surface computer validates
the message, verifies the status of the State Machine, and switches
and downlinks a W/L ON command. If the Switch Unit sends an error
message or the uplink message was invalid in any way, the power to
the gun string is removed and the process restarted.
[0126] Upon receiving the second downlink message, the State
Machine advances within the top Switch Unit (3). If the message
validation is error free, the Switch Unit (3) turns the W/L Switch
ON, uplinks a message containing switch status, State Machine
status, and a security check word and then goes into hibernation.
The action of turning W/L Switch ON within Switch Unit (3) allows
wireline power to be applied to Switch Unit (2). If an invalid
message was receive, the Switch Unit uplinks an invalid message
response with no other action. Upon receiving the second uplink
message from Switch Unit (3), the surface computer validates the
message and verifies the status of the State Machine and the
switches, completing the communication to Switch Unit (3). Switch
Unit (3) then goes into hibernation.
[0127] The following process begins a first time communication to
Switch Unit (2). The surface computer sends the first message, a
State (0) command to the middle Switch Unit (2). Switch Unit (2)
now receives and validates its first message. Upon receiving a
valid message, the State Machine advances within the middle Switch
Unit (2). If the message validation is error free, Switch Unit (2)
uplinks a message containing switch status, State Machine status,
and a security check word. If an invalid message is received, the
Switch Unit uplinks an invalid response message. Upon receiving the
first uplink message from Switch Unit (2), the surface computer
validates the message, verifies the status of the State Machine and
then switches and downlinks a W/L ON command. If the Switch Unit
sends an error message or the uplink message was invalid in any
way, the power to the gun string is removed and the process
restarted.
[0128] The middle Switch Unit (2) receives and validates the second
downlink message. Upon receiving a valid message, the State Machine
advances within middle Switch Unit (2). If the message validation
is error free, the Switch Unit (2) turns the W/L Switch ON, uplinks
a message containing switch status, State Machine status, and a
security check word and then goes into hibernation. With the action
of turning W/L Switch ON with Switch Unit (2), wireline power is
applied to Switch Unit (1). If an invalid message is received, the
Switch Unit uplinks an invalid message response. Upon receiving the
second uplink message from Switch Unit (2), the surface computer
validates the message, verifies the status of the State Machine and
the switches, completing the communication to Switch Unit (2).
Switch Unit (2) then goes into hibernation.
[0129] The following process begins a first time communication with
Switch Unit (1). The Surface Unit sends the first message, a State
(0) command to the bottom Switch Unit (1), which receives and
validates its first message. Upon receiving a valid message, the
State Machine advances within bottom Switch Unit (1). If the
message validation is error free, Switch Unit (1) uplinks a message
containing switch status, State Machine status, and a security
check word. If an invalid message is received, Switch Unit (1)
uplinks an invalid response message. Upon receiving the first
uplink message from Switch Unit (1), the surface computer validates
the message, verifies the status of the State Machine, and switches
and downlinks an ARM ON command. If an error message was sent or
the uplink message was invalid, power to the gun string is removed
and the process restarted.
[0130] Upon receiving the second downlink message, the state
machine advances within the bottom Switch Unit (1). If the message
validation is error free, the Switch Unit (1) turns the ARM Switch
ON, uplinks a message containing switch status, State Machine
status, and a security check. If an invalid message is received,
the Switch Unit uplinks an invalid message response. Upon receiving
the second uplink message from Switch Unit (1), the surface
computer validates the message, verifies status of the State
Machine and the switches and downlinks a FIRE ON command. If an
error message was sent or the uplink message was invalid in any
way, power to the gun string is removed and the process
restarted.
[0131] Upon receiving the third downlink message, the state machine
advances within the bottom Switch Unit (1). If the message
validation is error free, the Switch Unit (1) turns the FIRE Switch
ON, uplinks a message containing switch status, State Machine
status, and a security check. If an invalid message is received,
the Switch Unit uplinks an invalid message response. Upon receiving
the third uplink message from Switch Unit (1), the surface computer
validates the message, verifies the status of the State Machine and
the switches. All conditions are now met to send power for
detonation of the bottom gun. Following detonation, power is
removed from the wireline and the gun string is repositioned for
firing gun (2), which is now the bottom gun. On a gun string of (n)
guns, the process is repeated for each gun. Again, no addressing is
required.
[0132] Those skilled in the art will recognize that there are
several variations on this method. One variation is for the top
Switch Unit to send an automatic uplink message after being powered
up containing a State (0) status, State Machine status, and a
security check word. The surface computer records and validates the
message and returns a downlink command to advance the State Machine
to State (1), which turns the W/L Switch ON. The top Switch Unit
then sends a second uplink message containing a State (1) status
that is verified at the surface. Applying power to the next Switch
Unit wakes it up and triggers an automatic uplink message of its
current State (0) status. The uplink is delayed to allow the second
uplink message to be received first at the surface. The second
Switch Unit is then commanded from the surface to advance to State
(1), and so forth until the bottom Switch Unit is located and power
sent to detonate the bottom perforating gun. By recognizing the
change in state of each Switch Unit as it is communicated, the
surface computer uniquely identifies each Switch Unit in the
perforating gun string.
[0133] FIG. 17 describes an embedded State Machine within each
Switch Unit along with its pre defined sequence of events. Upon
power-up, the State Machine begins in State (0). When in State (0)
the Switch Unit waits for the first downlink message. After
receiving the first message, the State Machine advances from State
(0) to State (1) and tests the message sent for correct bit count,
content and cyclic-redundancy-check (CRC). If the first message is
invalid, the State Machine advances from State (1) to State (8) and
uplinks an invalid message status. The results of this action alert
the surface computer and cause the Switch Unit to progress to a
permanent hold state waiting for power to be removed. If the first
message is valid, the State Machine advances from State (1) to
State (2) and uplinks a message containing valid message status.
The State Machine now waits in State (2) for the second downlink
message.
[0134] After receiving the second downlink message the State
Machine advances from State (2) to State (3) and tests the second
message sent for correct bit count, content and
cyclic-redundancy-check (CRC). If the second message is invalid,
the State Machine advances from State (3) to State (9) and uplinks
an invalid message status. The results of this action alert the
surface computer and cause the Switch Unit to progress to a
permanent hold state waiting for power to be removed. If the second
message is verified, the received command bits must be decoded. The
two legal commands for the second downlink message are a W/L ON
command or an ARM ON command. If the Switch Unit decodes a W/L ON
command, the State Machine advances from State (3) to State (4).
While in State (4), the Switch Unit turns the W/L Switch ON,
uplinks a valid status message and then goes into hibernation. The
Switch Unit is not allowed to receive any further commands. If the
Switch Unit decodes an ARM ON command, the State Machine advances
from State (3) to State (5) and turns the ARM Switch ON, uplinks a
valid status message and waits for a third downlink message.
[0135] After receiving the third downlink message, the State
Machine advances from State (5) to State (6) and again the message
is validated for content. If an error is detected in the third
downlink message, the State Machine advances from State (6) to
State (10) and uplinks an invalid message status. The results of
this action alert the surface computer and cause the Switch Unit to
progress to a permanent hold state waiting for power to be removed.
If a valid third downlink message is decoded along with a valid
FIRE ON command, the State Machine advances from State (6) to State
(7). While the State Machine is in State (7), the switch unit sets
the FIRE Switch to ON, uplinks a valid status message, and waits
for the firing voltage to be applied to the wireline. Application
of the firing voltage causes the detonator to fire. Other error
trapping as known to those skilled in the art may also be used in
accordance with the method of the present invention.
[0136] Another alternative embodiment follows the same logic except
that any uplink message also contains a unique address specific to
a particular Switch Unit. The address is pre-programmed into the
State Machine during manufacturing of the circuit, providing
additional confirmation of the position of an individual Switch
Unit within the tool string.
[0137] In the following paragraphs, an interrogation-response
communication between the surface computer and the downhole Switch
Units is described that uses common commands for all downlink
interrogations. The surface computer and power supply are typically
the same as used in ordinary perforating jobs and the communication
protocol is implemented with appropriate software. All Switch Units
respond to a common specific protocol for the downlink
interrogation. A unique address is retrieved from each individual
switch unit as a result of a downlink interrogation and is
transmitted back up to the surface computer. In this embodiment,
downlink commands do not contain the address of the switch, making
the commands shorter and quicker than if they did.
[0138] FIGS. 18A and 18B show a flow chart describing a sequence of
events for shooting two guns in a string. The first event occurs
when the surface controller sends power down the wireline. The
second event occurs when the surface computer interrogates the top
switch using a common sequence. The first downlink transmission
includes a State (0) command in order to sync the surface computer
with the Switch Unit. The embedded state machine within each Switch
Unit allows the surface computer to track the sequence of commands
to all Switch Units in the entire string.
[0139] After receiving the first message, the top Switch Unit
validates the message. If the downlink message is free of errors,
the top Switch Unit advances the State Machine, loads its embedded
unique address, and uplinks a message containing switch status,
state machine status, address information and a security check
word. If the downlink message contains errors, the Switch Unit
advances the state machine and uplinks an invalid message response
identifying the detected error. This error trapping is repeated for
any invalid receive message for a switch unit. For clarity, this
routine will not be repeated in the remaining paragraphs of this
description of this embodiment of the communication/control
protocol of the present invention. The surface computer receives
and validates the first uplink message from the top Switch Unit.
The State Machine status is compared to expected results and the
unique address is recorded.
[0140] The surface computer sends a second downlink containing a
W/L ON command. If the Switch Unit sent an error message or the
uplink message was invalid in any way, the power to the gun string
would be removed and the process restarted. The top Switch Unit
receives and validates the second downlink message. If a valid
message was received, the Switch Unit advances the State Machine,
turns the W/L Switch ON, loads the embedded unique address for the
top Switch Unit, and uplinks a message containing switch status,
State Machine status, address information, and a security check
word. The top Switch Unit then goes into hibernation. With the W/L
switch turned ON, the second Switch Unit in the string is now
powered. The surface computer verifies the final uplink message
from the top Switch Unit, which includes State Machine and switch
status and the unique address of the Switch Unit, completing the
sequence for the top Switch Unit.
[0141] The surface computer now interrogates the second Switch
Unit. The first downlink interrogation to the second Switch Unit
includes a State (0) command. After receiving the first message,
the second Switch Unit validates the message. If the downlink
message is free of errors, the second Switch Unit advances the
State Machine, loads the embedded unique address, and uplinks a
message containing switch status, state machine status, address
information, and a security check word. If the downlink message
contains errors, the Switch Unit advances the State Machine and
uplinks an invalid message response identifying the detected error.
The surface computer receives and validates the first uplink
message from the second Switch Unit. The State Machine status is
compared to expected results and the unique address is recorded.
The surface computer sends a second downlink containing ARM ON
command. If the Switch Unit sent an error message or the uplink
message was invalid in any way, the power to the gun string is
removed and the process restarted.
[0142] The second (bottom) Switch Unit receives and validates the
second downlink message. If a valid message is received, the Switch
Unit advances the State Machine, turns the ARM Switch ON, loads the
embedded unique address for the second Switch Unit, and uplinks a
message containing switch status, state machine location, address
information and a security check word. The surface computer
receives and validates the second uplink message from the second
(bottom) Switch Unit. State Machine status and unique address are
compared to expected results and the surface computer sends a third
downlink message containing a FIRE ON command. If the Switch Unit
sent an error message or the uplink message was invalid in any way,
the power to the gun string would be removed and the process
restarted.
[0143] The second (bottom) Switch Unit receives and validates the
third downlink message. If a valid message is received, the Switch
Unit advances the State Machine, turns the FIRE Switch ON, loads
the embedded unique address for the second Switch Unit, and uplinks
a message containing switch status, state machine location, address
information, and a security check word. The surface computer
receives and validates the third uplink message from the second
(bottom) Switch Unit. State Machine status and unique address are
compared to expected results, and if all status and address data is
correct, the surface power supply is allowed to send shooting
voltage to the second switch and the bottom gun detonates.
[0144] Those skilled in the art will recognize that there are
several variations on this sequence. One variation is for the top
Switch Unit to send an automatic uplink message containing a State
(0) status, State Machine status, the unique embedded address for
the top Switch Unit, and a security check word after being powered
up. The surface computer records and validates the message and
returns a downlink command to advance the State Machine to State
(1), which turns the W/L Switch ON, which powers the next Switch
Unit, which then automatically uplinks a message containing a State
(0) status, State Machine status, the unique embedded address, and
a security check word, and so forth until the bottom Switch Unit is
reached and firing power applied to detonate the gun.
[0145] In the preceding paragraphs, selective perforating with
Switch Units controlling power access to detonators was described.
FIG. 19A shows a top level system having a combination of parallel
and serial control units for perforating. The difference is that
serial control units are electrically connected in any command
sequence that accesses a particular unit below them. Parallel units
need not be connected to access units below them. The parallel
units are shown on top of the string in FIG. 19A although they
could be located anywhere in the string, e.g. between series
control units, below the series units or any general placement. One
parallel Control Unit is used in conjunction with a Release Device.
Another parallel Control Unit is used for monitoring a plurality of
sensors. These sensors include, but are not limited to, such
functions as acceleration, downhole voltage, downhole current,
inclination and rotational positioning, temperature, and pressure.
Included in the serial string is a single control unit for
detonating a perforating gun. The actual number of serial control
units for perforating guns can be one or more. Another service uses
a serial control unit for igniting a Setting Tool.
[0146] Another version of the application of parallel/series
communication is for conveyance of well logging tools by a tractor
as shown in FIG. 19B. A Control Unit located at the tractor allows
electrical power to be selected by command to either power the
tractor or the logging tools. One or more auxiliary tractor tools
(millers, cleaners, strokers, for instance), each with their own
Control Unit and identified generically as "select ID1," "select
ID2," etc. at reference numeral 130A, 130B, etc. can be selected
and powered individually. The Control Units for the tractor and the
auxiliary tractor tools are connected electrically in parallel.
Those skilled in the art who have the benefit of this disclosure
will recognize that a particular auxiliary tractor tool 130A, 130B,
etc. may have two or more Control Units connected in series. FIG.
19B also shows two or more logging tools 132A, 132B connected
electrically in parallel that can be individually powered by either
positive or negative DC voltage from the surface, as detailed in
FIG. 19C. One or more safety subs are located below the tractor to
prevent accidental tractor power from reaching logging tools 132A,
132B. Each safety sub contains its own Control Unit that allows
electrical connection upon command from the surface.
[0147] FIG. 20 illustrates a method for communicating with a
microprocessor and state machines that have both parallel and
serial Control Units on the wireline as shown in FIGS. 19A and 19B.
Typically, whenever two or more remote devices are on a common
buss, an identifying address is embedded in the host message for
the purpose of preventing coincident response signals from more
that one remote responding device. In the method illustrated, each
state machine or device has a plurality of its own set of legal
commands. Upon receiving a message, the receiving controller
decodes the embedded command. Only if the command is legal is the
receiving controller allowed to generate an uplink message
preventing buss contention or collision of data whenever two or
more remote units are on a buss or party line connection.
[0148] In addition, before an uplink transmission can occur, the
logical position of the state machine is compared and must be in
sync with the expected state position transmitted by the host. This
comparison further discriminates which messages are legal and which
controllers are allowed to return an uplink message. In another
embodiment, to distinguish further or identify one type of tool
from the other, an identifier, either unique or common to that type
of tool is attached to each uplink or returned message. Those
skilled in the art will recognize that these methods apply to each
of the controllers within the parallel and serial systems shown in
FIGS. 19A and 19B.
[0149] Referring to FIG. 20, the Surface Unit first applies power
to the wireline, causing all control units on the communication
buss to initiate a power-up reset and enter state "0" waiting for a
downlink message. The Surface Unit then sends a downlink message
containing a plurality of commands specific to only one controller
along with a state "0" status. Every downhole controller then
receives and verifies the message for errors. If an error is
detected, the downhole controller goes back to state "0" with no
further action. If the message is error free, the state machine
advances and the command bits within the message are decoded. If
the command is illegal, the downhole device reverts to state "0."
If the command is legal for a particular device the state machine
again advances, uplinks a message, and waits for a second
response.
[0150] The Surface Unit then receives and validates the first
uplink message. If the message is in error, the Surface Controller
goes into a restart mode by turning power OFF and then back ON for
a fresh start. If the message is error free, the Surface Controller
transmits a second message containing the same control command
along with the state machine expected position. Again, all remote
control units receive the second message and only the one
controller matching the downlink state position and having received
a legal command is allowed to advance and process the message. If
the message is verified and an error exists, then a bad message
status is returned and the downhole device must be powered down to
continue. If the message is verified to free of errors, the command
is processed and a return (uplink) confirmation message is
transmitted. The Surface Controller receives and validates the
message, and if the message contains errors, the Surface Controller
restarts the entire process. If the message is error free, the
Surface Controller accepts the data and continues to the next
command or next control unit.
[0151] FIG. 21 illustrates a predefined sequence of events for each
control unit on the buss connected in either parallel or serial and
containing one or more microprocessors or state machines as
referred to in FIGS. 19A, 19B and 20. Upon power-up, the state
machine enters state "0" and waits for a downlink message. Upon
receiving a message from the surface, the state machine advances to
state "1". While in state "1," the message is validated for proper
state position, cyclic-redundancy-check, and message length. If an
invalid message is decoded by the microprocessor, the state machine
reverts to state "0." If a valid message is decoded, the state
machine advances to state "2."
[0152] While in state "2," the command bits are decoded. If an
illegal command is decoded for that particular controller, the
state machine again goes back to state "0." If a legal command is
decoded, the device returns a message containing state "3," the
decoded command, all status, embedded address (if used) and
cyclic-redundancy-check. The device now waits for a second downlink
message. Upon receiving a second downlink message the state machine
advances to state "4." While in state "4," the control unit
verifies receiving the proper state position from the surface
controller, again compares the command bits with the previous
command bits, cyclic-redundancy-check, and message length. If the
message is invalid in any way, the state machine advances to state
"6" and the downhole controller transmits an uplink message
confirming an invalid message. At this point, the control unit must
be powered down to restart. If the message is valid, the state
machine advances to state "5." While in state "5," the control unit
processes the command. For the last event, the control unit
transmits an uplink message including state "5" position, all
status, embedded address (if used), and cyclic-redundancy-check.
The State Diagram in FIG. 21 shows the microprocessor/state machine
entering a sleep mode following a command and will not listen to
any more messages until a complete restart as would be the case for
a serial connected control unit, but a parallel connected control
unit may wait for additional commands and may or may not enter the
sleep mode.
[0153] Those skilled in the art who have the benefit of this
disclosure will recognize that certain changes can be made to the
component parts and steps of the present invention without changing
the manner in which those parts/steps function and/or interact to
achieve their intended result. Several examples of such changes
have been described herein, and those skilled in the art will
recognize other such changes from this disclosure. All such changes
are intended to fall within the scope of the following,
non-limiting claims.
* * * * *