DEVICES AND METHODS FOR DIGITAL SIGNAL PROCESSING I N MUD
PULSE TELEMETRY
BACKGROUND
[0001] I n the field of oil and gas exploration and extraction, pressure
sensors are customarily used at the surface for reading data provided by
acoustic transducers at the downhole. The data travels through the drilling mud
along the wellbore. There are many modulation schemes that can be used to
encode the data. Some of the modulation schemes using pulses include Pulse
Position Modulation (PPM), Differential Pulse Position Modulation (DPPM), and
Pulse Width Modulation (PWM). In these and other modulation schemes data
packets are divided into symbols. Each symbol is divided to fixed intervals
called 'chips'. Each symbol includes at least one period of "l's that makes a
pulse. In PPM, the data is encoded by the position of the pulse in the symbol.
I n DPPM, data is encoded in the distance from the previous pulse. In PWM the
information is encoded in the width of the pulse. In the above, position,
distance, and width are measured as integer numbers of 'chips.' The amount of
information transmitted increases with the symbol length. But the time it takes
for transmitting the signal also increases with symbol length, leaving the
transmission rate unchanged, if not reduced, with increased symbol length.
Attempts to increase transmission rates have focused on improving acoustic
transducer hardware, such as for example reducing a recovery time of acoustic
emitters and detectors. However, this approach is expensive and provides slow
progress with marginal improvements. Other approaches attempt to reduce the
chip-width and increase the symbol rate. However, these methods are limited
by the available Signal to Noise Ratio (SNR). When the chip rate increases,
pulses become narrower and this reduces the SNR of the data transmission,
increasing the Bit Error Rate (BER).
BRIEF DESCRIPTION OF THE DRAWINGS
[0002] The following figures are included to illustrate certain aspects of
the present disclosure, and should not be viewed as exclusive embodiments.
The subject matter disclosed is capable of considerable modifications,
alterations, combinations, and equivalents in form and function, without
departing from the scope of this disclosure.
[0003] FIG. 1 illustrates a drilling system using a pressure sensor
configured to transmit data for digital signal processing in mud pulse telemetry,
according to some embodiments.
[0004] FIG. 2 illustrates a pulse position modulation waveform (PPM)
scheme in a digital signal processing method, according to some embodiments.
[0005] FIG. 3 illustrates a plurality of waveforms including pulse
position modulation (PPM) scheme and pulse width modulation (PWM) scheme in
a Gray mapping configuration for digital signal processing in mud pulse
telemetry, according to some embodiments.
[0006] FIG. 4 illustrates a computer system configured for digital signal
processing in mud pulse telemetry, according to some embodiments.
[0007] FIG. 5 illustrates a flow chart including steps in a method for
digital signal processing in mud pulse telemetry, according to some
embodiments.
[0008] FIG. 6 illustrates a flow chart including steps in a method for
digital signal processing in mud pulse telemetry, according to some
embodiments.
DETAILED DESCRIPTION
[0009] The present disclosure relates to methods and devices for
telemetry schemes used in oil and gas exploration and extraction and, more
particularly, to methods and devices for digital signal processing in mud pulse
telemetry. Accordingly, embodiments disclosed herein provide modulation
schemes with a symbol mapping that increases the data rate for mud pulse
telemetry, also decreasing the bit error rate (BER) at the receiver.
[0010] I n mud pulse telemetry, one popular type of Ό h/ Of Keying
based (OOK) modulation scheme is pulse position modulation (PPM). In PPM
schemes, a data symbol has a fixed duration, and the pulse location within the
symbol period indicates the symbol value. Other techniques applicable in
embodiments consistent with the present disclosure include, without limitation,
pulse width modulation (PWM) schemes. I n PWM schemes, a data symbol is
associated with a time duration of a sequence of pulses, therefore the data
transmission includes a variable number of consecutive pulses in each data
packet. Typically, a Bit Error Rate (BER) and the data rate of signals transmitted
in mud pulse telemetry are affected by physical constraints in the acoustic
transducers that create and read the signals. Embodiments disclosed herein
increase the bit rate by using a combination of PPM and PWM while keeping the
chip rate unchanged.
[0011] For example, acoustic transducers typically have a response
time determined by a charging/de-charging time of a capacitor in the circuit that
creates the acoustic pulses. This delay creates a minimum time interval
between two consecutive pulses. Furthermore, each acoustic pulse itself has a
minimum time duration also related to the time response of the acoustic
transducer and the bandwidth of the acoustic channel formed by the mud flow.
Another factor that enters into consideration is a limited total number of pulses
through the lifetime of an acoustic transducer and its limited response time.
Thus, signaling schemes as disclosed herein make optimal use of the limited
number of pulses generated by the acoustic transducer. These constraints are
exacerbated in current drilling configurations, where the acoustic transducer
may be as far as 5000 feet (ft), 10000 ft, 20000 ft, or even 30000 ft below the
surface, in any drilling configuration. Accordingly, embodiments as disclosed
herein are configured to work at each of the above different depths, without a
substantial change in performance.
[0012] In the present disclosure, systems and methods for digital signal
processing for mud pulse telemetry are provided. A method consistent with
embodiments herein may include identifying a symbol in a pulse sequence,
identifying a pulse width for a pulse in the symbol and identifying a pulse start
for the pulse in the symbol. The method may further include determining a
symbol value based on the pulse width and the pulse start, reading a message
using the symbol value for each symbol in a string of symbols, and modifying a
drilling configuration according to the message. In yet other embodiments, a
method includes mapping a symbol in a pulse sequence by using a pulse width
and a pulse start in the symbol, reading a message using a symbol value for
each symbol in a string of symbols, and modifying a drilling configuration
according to the message.
[0013] A device according to some embodiments includes a memory
circuit storing commands and a processor circuit configured to execute the
commands. When the processor circuit executes the commands, it causes the
device to identify a symbol in a pulse sequence, associate the symbol with a
symbol value using a one-to-one correspondence between the symbol value and
a symbol characteristic, and read a message using the symbol value for each
symbol in a string of symbols. Furthermore, the device may be configured to
modify a drilling configuration according to the message.
[0014] A method according to some embodiments includes determining
a drilling condition and forming a message based on the drilling condition. The
method further includes forming a string of symbol values comprising the
message. The method may also include identifying a pulse width and a pulse
start for the pulse, based on a symbol value, providing a first pulse at a selected
chip location, and providing subsequent pulses to form the pulse width. In some
embodiments, the method includes forming a quiet period at the end of the
pulse width for each symbol.
[0015] FIG. 1 illustrates a drilling system 100 using a pressure sensor
101 configured to suppress pulse reflections in a pulse modulation telemetry
configuration, according to some embodiments. Drill system 100 may be a
logging while drilling (LWD) system, as is well known in the oil and gas industry.
A pump 105 maintains mud flow 125 down a wellbore 120 dug by a drill tool
130. A drill string 133 couples drill tool 130 with equipment on the surface, such
as pump 105 and pressure sensor 101. The tools are supported by drilling rig
150. A controller 110 is coupled to pressure sensor 101, to pump 105, and to
acoustic transducer 102 via wellbore 120. Controller 110 may include a
computer system configured to receive data from and transmit commands to
pressure sensor 101, to acoustic transducer 102, and to pump 105.
[0016] Mounted near drill tool 130, an acoustic transducer 102 is
configured to transmit to and receive messages from the surface with
information related to the drill process. Messages created by acoustic
transducer 102 may be digitally encoded sequences of acoustic pulses
transmitted through mud flow 125 and read by pressure sensor 101.
Accordingly, a plurality of digital signal modulation techniques may be used to
transmit messages between acoustic transducer 102 and pressure sensor 101,
such as PPM and PWM. As a response to the messages transmitted between
pressure sensor 101 and acoustic transducer 102, controller 110 may adjust a
drilling configuration in drilling system 100. For example, a drilling speed may
be increased, reduced, or stopped by controller 110, based on messages
received from acoustic transducer 102. Moreover, in some embodiments
controller 110 may cause drill tool 130 to steer in a different direction. For
example, in some embodiments drill tool 130 may be steered from a vertical
drilling configuration (as shown in FIG. 1) to a horizontal or almost horizontal
drilling configuration. I n some embodiments, adjusting the drilling configuration
may include adjusting mud flow 125. For example, mud flow 125 may be
increased or reduced, or the pressure exerted by pump 105 may be increased or
reduced. Moreover, in some embodiments adjusting the drilling configuration
may include adding chemicals and other additives to mud flow 125, or removing
additives from mud flow 125.
[0017] FIG. 2 illustrates a pulse position modulation (PPM) waveform
200 in a digital signal processing method, according to some embodiments. PPM
waveform 200 corresponds to a symbol in a digital signal processing scheme.
The symbol spans a period of time Tsy m oi 201 which is divided into an integer
number of sub-periods, or 'chips,' each spanning a time TC i 202. The
parameters used to describe PPM waveform 200 are K, TpU Se 211, and T 212.
The parameter K indicates the number of bits in one symbol. Parameter TpU Se
211 is the pulse width. Parameter T 212 is a "quiet period" before start of a
new symbol. Tq 212 allows for the recovery of the physical mechanism of the
transducer producing and detecting the pulses before a new symbol is started.
In embodiments used for mud pulse telemetry, T 212 indicates a period of time
where a mud pulser valve in pressure sensor 101 or acoustic transducer 102 is
in the rest position (cf. FIG. 1). I n some embodiments, T 212 equals the
recharging time for a battery or a capacitor in pressure sensor 101 or acoustic
transducer 102, before another pulser open (for negative pulser) or close ( for
positive pulser) action is made. A value Tstart 210 indicates the time within Tsymboi
201 at which the pulse starts. Hereinafter, time values such as Tsym oi 201, TpU Se
211, Tq 212, and Tstart 210 will be given in integer values representing a number
of periods TC iP 202 in each time interval, as the unit of time.
[0018] FIG. 2 shows a PPM waveform 200 with Tsymb0 i 201 is equal to
10, K is equal to three (3), TpU Se 211 is equal to two (2), and T 212 is equal to
one (1). The pulse in PPM waveform 200 is positive, although negative pulses
may also be used without departing from the scope of the present disclosure.
The positive pulse occurs at beginning of the 7th chip, thus Tst art 210 is equal to
seven (7). A binary sequence 0000000110 describes PPM waveform 200. The
last three bits in the binary sequence, "110" represent the pulse shape in PPM
waveform 200. Accordingly, the number of values for Tst art 210 in FIG. 2 is eight
(8). That is, a symbol in PPM waveform 200 may take any of eight values,
which in binary code corresponds to a three bit number string (K=3).
[0019] Table 1 illustrates an exemplary embodiment where Tsym oi 201
is equal to seven (7), TpU Se 211 is equal to three (3), and T 212 is equal to one
(1). Using a PPM modulation as in FIG. 1, Table 1 lists the binary sequence
representation for the original PPM modulation waveforms and the corresponding
symbol values. Accordingly, the corresponding binary bit string has K equal to 2
(two).
TABLE 1
[0020] To improve throughput, some embodiments encode more bits
within the same Tsym oi 201 by varying TpU Se 211, thus combining a PPM and a
PWM scheme. To simplify the transmission protocol and to accommodate for
physical sensor limitations in terms of response speed and sensitivity, some
embodiments have a minimum value for TpU Se 211. Likewise, some
embodiments include a single, continuous sequence of pulses per symbol and a
minimum value T 212 of 1 (one), for all symbols. Accordingly, in some
embodiments TpU Se 211 may take values from a minimum value up to Tsym oi-Tq .
This scheme provides a wider selection of waveforms within Tsymb0i 201. Each
waveform within the new scheme can be assigned a unique symbol value.
Accordingly, the combination of PWM with PPM produces a more robust and
powerful signal encoding scheme.
[0021] FIG. 3 illustrates a plurality of waveforms 300a-h, including
PPM and PWM in schemes in a Gray mapping configuration for digital signal
processing in mud pulse telemetry, according to some embodiments. Each one
of waveforms 300a-h has a different combination of values for Tstart 210 and
TpU|Se 211 (cf. FIG. 2). I n particular, each one of waveforms 300a-h has a value
Tpulse > 3, and a value T > 1. Waveforms 300a-h are selected according to a
'Gray' coding scheme in addition to a combination of PPM and PWM schemes. I n
a 'Gray' coding scheme, waveforms within Tsym oi 201 differing by only 1 chip are
assigned symbol values that only differ by 1 binary bit. By using Gray coding,
when the most likely error happens {i.e., one chip error), the symbol error only
corresponds to a 1 bit error.
[0022] Accordingly, each one of waveforms 300a-h differs from its
immediate neighbor by one chip. For example, waveform 300c differs from
waveform 300b in the last chip of the pulse: 0' for waveform 300c, and 1' for
waveform 300b. Likewise, waveform 300c differs from waveform 300d in the
first chip of the pulse: for waveform 300c, and 0' for waveform 300b. A Gray
code scheme reduces the magnitude of the message error, or computational
error because of the higher likelihood of single bit mistakes in any data
transmission scheme. For example, acoustic reflections and drill tool noise could
distort the received pulse shape in drilling system 100 (cf. FIG. 1). Acoustic
reflections may erroneously increase Tpulse 211 by one chip. It is less likely
that acoustic reflections increase Tpulse by more than one chip. Therefore,
waveform 300c could be mistaken for waveform 300b, or waveform 300d could
be mistaken for waveform 300c. The resulting symbol error has minimal impact
in the message, as the two mistaken symbols have consecutive value in either
case (cf. Table 2). This helps reducing the raw bit error rate and facilitates use
of a forward error correction module to correct the remaining errors.
[0023] The combined PPM and PWM scheme shown in FIG. 3 uses eight
(8) out of ten (10) possible waveforms. Two waveforms are sacrificed in order
to satisfy a one-to-one Gray mapping from a waveform to a symbol value.
Namely, a waveform havingTstart = 0, TpU Se =3, and T =4 is not included in FIG.
3, nor in Table 2. Also, a waveform havingTstart = 3, TpU Se =3, and T = 1 is not
included in FIG. 3, nor in Table 2. Accordingly, FIG. 3 illustrates that
embodiments using a Tsym oi 201 of seven chips can encode symbols
corresponding to a bit string of K=3 in a robust configuration. Table 2 lists the
Gray coded, combined PPM and PWM waveforms and associated symbol values.
The data rate has increased 50% since for the same symbol period, the
embodiment disclosed in Table 2 represents 3 bits (8 symbol values) instead of
2 bits (4 symbol values, cf. Table 2). In addition, the Gray mapping helps to
keep bit error rate low.
TABLE 2
[0024] Note that in Table 2, due to Gray mapping, symbol 0 (waveform
300a in FIG. 3) and symbol 7 (waveform 300h in FIG. 3) differ by one chip only.
One of ordinary skill recognizes that other mappings that achieve the same goal
are possible.
[0025] Generally speaking, for a PPM scheme with arbitrarily chosen K,
TpU|Se and T value, those skilled in the art could apply the above principle to
come up with a symbol to waveform mapping table that minimizes raw bit error
rate.
[0026] FIG. 4 illustrates a computer system 400 configured for digital
signal processing in mud pulse telemetry, according to some embodiments.
According to one aspect of the present disclosure, computer system 400 may be
included in a controller for a drilling system (e.g., controller 110 in drilling
system 100, cf. FIG. 1). Computer system 400 includes a processor circuit 402
coupled to a bus 408. Bus 408 may also couple other circuits in computer
device 400, such as a memory circuit 404, a data storage 406, an input/output
(I/O) module 410, a communications module 412, and peripheral devices 414
and 416. In certain aspects, computer system 400 can be implemented using
hardware or a combination of software and hardware, either in a dedicated
server, or integrated into another entity, or distributed across multiple entities.
[0027] Computer system 400 includes a bus 408 or other
communication mechanism for communicating information, and a processor
circuit 402 coupled with bus 408 for processing information. By way of example,
computer system 400 can be implemented with one or more processor circuits
402. Processor circuit 402 can be a general-purpose microprocessor, a
microcontrol ler, a Digital Signal Processor (DSP), an Appl ication Specific
Integrated Circu it (ASIC), a Field Programmable Gate Array (FPGA), a
Programmable Logic Device (PLD), a control ler, a state machine, gated logic,
discrete hardware components, or any other suitable entity that can perform
calcu lations or other manipu lations of information .
[0028] Computer system 400 incl udes, in addition to hardware, code
that creates an execution environment for the computer program in question,
e.g. , code that constitutes processor firmware, a protocol stack, a database
management system, an operating system, or a combination of one or more of
them stored in an included memory circuit 404, such as a Random Access
Memory (RAM), a flash memory, a Read Only Memory (ROM), a Prog rammable
Read-Only Memory (PROM), an Erasable PROM (EPROM), reg isters, a hard disk,
a removable disk, a CD-ROM, a DVD, or any other suitable storage device,
cou pled to bus 408 for storing information and instructions to be executed by
processor circu it 402. Processor circu it 402 and memory circu it 404 can be
supplemented by, or incorporated in, special purpose logic circuitry.
[0029] The instructions may be stored in memory circuit 404 and
implemented in one or more computer program products, i . e. , one or more
modu les of computer program instructions encoded on a computer readable
mediu m for execution by, or to control the operation of, the computer system
400, and according to any method wel l known to those of skill in the art,
including, but not limited to, computer languages such as data-oriented
la nguages (e.g. , SQL, dBase), system languages (e.g. , C, Objective-C, C+ + ,
Assembly), architectu ral lang uages (e.g. , Java, .NET), and application languages
(e.g. , PHP, Ruby, Perl, Python) . Instructions may also be implemented in
computer la nguages such as array languages, aspect-oriented languages,
assembly languages, authoring languages, command line interface languages,
compiled la nguages, concu rrent languages, curly-bracket languages, dataflow
languages, data-structu red languages, declarative lang uages, esoteric
la nguages, extension languages, fou rth-generation lang uages, functional
la nguages, interactive mode languages, interpreted languages, iterative
languages, list-based languages, little languages, logic-based languages,
machine languages, macro languages, metaprog ramming languages,
multiparadigm languages, numerical analysis, non-Engl ish-based languages,
object-oriented class-based languages, object-oriented prototype-based
languages, off-side rule languages, procedu ral languages, reflective languages,
rule-based languages, scripting languages, stack-based languages, synchronous
languages, syntax handl ing languages, visual languages, wirth languages,
embedda ble languages, and xml-based languages. Memory circu it 404 may also
be used for storing tempora ry variable or other intermediate information during
execution of instructions to be executed by processor circuit 402.
[0030] A computer program as discussed herein does not necessarily
correspond to a file in a file system . A program can be stored in a portion of a
file that holds other programs or data (e.g. , one or more scripts stored in a
marku p language document), in a sing le file dedicated to the program in
question, or in multiple coordinated files (e.g. , files that store one or more
modules, subprograms, or portions of code) . A computer program can be
deployed to be executed on one computer or on multiple computers that are
located at one site or distributed across multiple sites and interconnected by a
communication network. The processes and logic flows described in this
specification can be performed by one or more programmable processors
executing one or more computer programs to perform functions by operating on
input data and generating output.
[0031] Computer system 400 further incl udes a data storage device 406
such as a magnetic disk or optical disk, cou pled to bus 408 for storing
information and instructions. Computer system 400 is coupled via input/output
module 410 to various devices. The input/output module 410 are any
input/output module. Example input/output modules 410 incl ude data ports
such as USB ports. The input/output module 410 is configured to connect to a
communications module 412. Example communications modules 412 incl ude
networking interface cards, such as Ethernet cards and modems. I n certain
aspects, the input/output module 410 is configu red to connect to a plu rality of
devices, such as an input device 414 and/or an output device 416. Example
input devices 414 include a keyboard and a pointing device, e.g. , a mouse or a
trackbal l, by which a user can provide input to the computer system 400. Other
kinds of input devices 414 are used to provide for interaction with a user as well,
such as a tactile input device, visual input device, aud io input device, or braincomputer
interface device. For example, feedback provided to the user can be
any form of sensory feedback, e.g. , visual feedback, auditory feedback, or tactile
feedback; and input from the user can be received in any form, including
acoustic, speech, tactile, or brain wave input. Example output devices 416
include display devices, such as a LED (light emitting diode), CRT (cathode ray
tube), or LCD (liquid crystal display) screen, for displaying information to the
user.
[0032] Computer system 400 may be configured to perform steps in a
method consistent with any of the methods disclosed herein in response to
processor circuit 402 executing one or more sequences of one or more
instructions contained in memory circuit 404. Such instructions may be read
into memory circuit 404 from another machine-readable medium, such as data
storage device 406. Execution of the sequences of instructions contained in
main memory circuit 404 causes processor circuit 402 to perform the process
steps described herein. One or more processors in a multi-processing
arrangement may also be employed to execute the sequences of instructions
contained in memory circuit 404. I n alternative aspects, hard-wired circuitry
may be used in place of or in combination with software instructions to
implement various aspects of the present disclosure. Thus, aspects of the
present disclosure are not limited to any specific combination of hardware
circuitry and software.
[0033] FIG. 5 illustrates a flow chart including steps in a method 500
for digital signal processing in mud pulse telemetry, according to some
embodiments. Some embodiments may include steps in method 500 in the
context of adjusting a drilling configuration in a drilling system including a
drilling rig supporting a drill string coupled to a drill tool forming an underground
wellbore (e.g., drilling system 100, drilling rig 150, drill string 133, drill tool 130,
and wellbore 120, cf. FIG. 1). In the drilling system, an acoustic transducer
near the drill tool may transmit messages between a controller in the surface
and the drill tool (e.g., acoustic transducer 102 and controller 110, cf. FIG. 1).
The messages may be transmitted through a mud flow and received at the
surface by a pressure sensor, the mud flow being pressurized by a pump at the
surface (e.g., mud flow 125, pressure sensor 101, and pump 105, cf. FIG. 1).
The messages in method 500 may include a string of symbols having values
according to signal processing methods such as Gray code mapping.
Specifically, some embodiments of method 500 use PPM and PWM schemes with
Gray code mapping. More generally, methods consistent with method 500 may
incorporate any digital signal processing protocol used in the telecommunication
industry.
[0034] The symbols in method 500 may include a waveform having a
selected length spanning a period of time Tsym oi divided into an integer number
of sub-periods, or 'chips,' each spanning a time Tchip (e.g., Tsymb0i 201 and Tchip
202, cf. FIG. 2). Other parameters used to describe waveforms defining
symbols in method 500 include a number, K, of bits used by the symbol, a pulse
time T pUSe, and a quiet period T , after each pulse (e.g., TpU Se 211, and T 212,
cf. FIG. 2).
[0035] Steps in methods consistent with method 500 may be at least
partially performed by a computer system having a processor circuit executing
commands stored in a memory circuit (e.g., computer system 400, processor
circuit 402, and memory circuit 404, cf. FIG. 4). Methods consistent with
method 500 may include at least one but not all of the steps in FIG. 5,
performed in any order. More generally, methods consistent with the present
disclosure may include at least some of the steps in FIG. 5 performed
overlapping in time. For example, some embodiments may include at least two
steps in FIG. 5 performed simultaneously, or almost simultaneously, in time.
[0036] Step 502 includes identifying a symbol in a pulse sequence. I n
some embodiments, step 502 includes identifying a pulse followed by a quiet
period. Moreover, in some embodiments step 502 includes finding within a pulse
sequence a number of chips forming a symbol, the pulse sequence having a pre
selected configuration. I n some embodiments, step 502 includes detecting a
pulse sequence using the acoustic transducer, the pulse sequence traveling
along the mudflow in the wellbore. Step 504 includes identifying a pulse width
from a pulse in the symbol. Accordingly, step 504 may include counting a
number of consecutive pulses within the period of time Tsym oi. Step 506 includes
identifying the pulse start (Tstart) within the symbol. I n some embodiments, step
506 may include identifying a pulse width (TpU Se ) for the pulse in the symbol.
Step 508 includes determining a symbol value based on the pulse width and the
symbol start. I n some embodiments, step 508 includes mapping the symbol
value to the pulse width and the pulse start using a Gray code.
[0037] Step 510 includes reading a message contained in a string of
symbols. I n some embodiments, the message may include information
regarding the drilling configuration in the drilling system. For example, in some
embodiments the information may include a Gas-Oil-Ratio (GOR) of an oil
sample in the bottom of the borehole. I n some embodiments, the information
may include a characteristic of the mud in the mud flow, or a characteristic of
the mud flow itself. Step 512 includes modifying a drilling configuration
according to the message. In some embodiments, step 512 may include
steering the drill tool in the drilling system. For example, step 512 may include
steering the drill tool from a vertical drilling configuration to a horizontal drilling
configuration. Step 512 may also include adjusting a mud flow parameter, such
as pump pressure.
[0038] FIG. 6 illustrates a flow chart including steps in a method 600
for filtering pump interference in mud pulse telemetry, according to some
embodiments. Method 600 may be performed in the context of a drilling system
including a drilling rig supporting a drill string coupled to a drill tool forming an
underground wellbore (e.g., drilling system 100, drilling rig 150, drill string 133,
drill tool 130, and wellbore 120, cf. FIG. 1). I n the drilling system, an acoustic
transducer near the drill tool may transmit messages between a controller in the
surface and the drill tool (e.g., acoustic transducer 102 and controller 110, cf.
FIG. 1). The messages may be transmitted through a mud flow and received at
the surface by a pressure sensor, the mud flow being pressurized by a pump at
the surface (e.g., mud flow 125, pressure sensor 101, and pump 105, cf. FIG.
[0039] The messages may be transmitted through a mud flow and
received at the downhole by an acoustic transducer, the mud flow being
pressurized by a pump at the surface (e.g., mud flow 125, acoustic transducer
102, and pump 105, cf. FIG. 1). The messages in method 600 may include a
string of symbols having values according to signal processing methods such as
Gray code mapping. Specifically, some embodiments of method 600 use PPM
and PWM schemes with Gray code mapping. More generally, methods consistent
with method 600 may incorporate any digital signal processing protocol used in
the telecommunication industry.
[0040] The symbols in method 600 may include a waveform having a
selected length spanning a period of time Tsym oi divided into an integer number
of sub-periods, or 'chips,' each spanning a time TC (e.g., Tsym oi 201 and TC
202, cf. FIG. 2). Other parameters used to describe waveforms defining
symbols in method 500 include a number, K, of bits used by the symbol, a pulse
time TpU|Se, and a quiet period T , after each pulse (e.g., TpU|Se 211, and T 212,
cf. FIG. 2).
[0041] Steps in methods consistent with method 600 may be at least
partially performed by a computer system having a processor circuit executing
commands stored in a memory circuit (e.g., computer system 400, processor
circuit 402, and memory circuit 404, cf. FIG. 4). Methods consistent with
method 600 may include at least one but not all of the steps in FIG. 6,
performed in any order. More generally, methods consistent with the present
disclosure may include at least some of the steps in FIG. 6 performed
overlapping in time. For example, some embodiments may include at least two
steps in FIG. 6 performed simultaneously, or almost simultaneously, in time.
[0042] Step 602 includes determining a drilling condition and a
message based on the drilling condition. For example, the message may include
changing the drilling condition based on at least one measurement parameter
obtained by determining the drilling condition. In some embodiments, step 602
may include determining the drilling condition includes a vertical drilling
configuration, and determining a message to steer the drilling configuration to a
horizontal or almost horizontal configuration.
[0043] Step 604 includes forming a string of symbol values containing
the message. I n some embodiments, step 604 may include selecting the
number, k, of bits in a binary code for each of the symbols in the message.
[0044] Step 606 includes identifying a pulse width and a pulse start
based on the symbol value. In some embodiments, step 604 may include using
a Gray code mapping to establish a one-to-one correlation between a symbol
waveform and a symbol value. Step 608 includes providing a first pulse at a
selected chip location. Accordingly step 608 may include selecting the Tstart
value for the pulse, according to a combined PPM and PWM scheme. Step 610
includes providing subsequent pulses to form a desired pulse width.
Accordingly, step 610 may include selecting the TpU Se value in the combined PPM
and PWM scheme. Step 612 includes forming the quiet period, T , at the end of
the pulse width. Step 612 may include forming a T lasting for at least one chip
after the last pulse in a waveform forming the symbol.
[0045] I t is recognized that the various embodiments herein directed to
computer control and artificial neural networks, including various blocks,
modules, elements, components, methods, and algorithms, can be implemented
using computer hardware, software, combinations thereof, and the like. To
illustrate this interchangeability of hardware and software, various illustrative
blocks, modules, elements, components, methods and algorithms have been
described generally in terms of their functionality. Whether such functionality is
implemented as hardware or software will depend upon the particular application
and any imposed design constraints. For at least this reason, it is to be
recognized that one of ordinary skill in the art can implement the described
functionality in a variety of ways for a particular application. Further, various
components and blocks can be arranged in a different order or partitioned
differently, for example, without departing from the scope of the embodiments
expressly described.
[0046] Computer hardware used to implement the various illustrative
blocks, modules, elements, components, methods, and algorithms described
herein can include a processor configured to execute one or more sequences of
instructions, programming stances, or code stored on a non-transitory,
computer-readable medium. The processor can be, for example, a general
purpose microprocessor, a microcontroller, a digital signal processor, an
application specific integrated circuit, a field programmable gate array, a
programmable logic device, a controller, a state machine, a gated logic, discrete
hardware components, an artificial neural network, or any like suitable entity
that can perform calculations or other manipulations of data. I n some
embodiments, computer hardware can further include elements such as, for
example, a memory (e.g., random access memory (RAM), flash memory, read
only memory (ROM), programmable read only memory (PROM), erasable read
only memory (EPROM)), registers, hard disks, removable disks, CD-ROMs,
DVDs, or any other like suitable storage device or medium.
[0047] Executable sequences described herein can be implemented with
one or more sequences of code contained in a memory. In some embodiments,
such code can be read into the memory from another machine-readable
medium. Execution of the sequences of instructions contained in the memory
can cause a processor to perform the process steps described herein. One or
more processors in a multi-processing arrangement can also be employed to
execute instruction sequences in the memory. I n addition, hard-wired circuitry
can be used in place of or in combination with software instructions to
implement various embodiments described herein. Thus, the present
embodiments are not limited to any specific combination of hardware and/or
software.
[0048] As used herein, a machine-readable medium will refer to any
medium that directly or indirectly provides instructions to a processor for
execution. A machine-readable medium can take on many forms including, for
example, non-volatile media, volatile media, and transmission media. Non
volatile media can include, for example, optical and magnetic disks. Volatile
media can include, for example, dynamic memory. Transmission media can
include, for example, coaxial cables, wire, fiber optics, and wires that form a
bus. Common forms of machine-readable media can include, for example,
floppy disks, flexible disks, hard disks, magnetic tapes, other like magnetic
media, CD-ROMs, DVDs, other like optical media, punch cards, paper tapes and
like physical media with patterned holes, RAM, ROM, PROM, EPROM, and flash
EPROM.
[0049] Embodiments disclosed herein include:
[0050] A. A method, including mapping a symbol in a pulse sequence
by using a pulse width and a pulse start in the symbol, reading a message using
a symbol value for each symbol in a string of symbols, and modifying a drilling
configuration according to the message.
[0051] B. A device, including a memory circuit storing commands, a
processor circuit configured to execute the commands and cause the device to:
identify a symbol in a pulse sequence, associate the symbol with a symbol value
using a one-to-one correspondence between the symbol value and a symbol
characteristic, read a message using the symbol value for each symbol in a
string of symbols, and modify a drilling configuration according to the
message.
[0052] C. A method, including determining a drilling condition and
forming a message based on the drilling condition, forming a string of symbol
values including the message, identifying a pulse width and a pulse start for the
pulse, based on a symbol value, providing a first pulse at a selected chip
location, providing subsequent pulses to form the pulse width, and forming a
quiet period at the end of the pulse width.
[0053] Each of embodiments A, B, and C may have one or more of the
following additional elements in any combination. Element 1, wherein mapping
the symbol includes mapping consecutive Gray code symbols to two pulse
sequences differing by one chip from each other, wherein each symbol includes
a pre-determined number of chips. Element 2: wherein mapping the symbol in
a pulse seq uence incl udes identifying a waveform having a selected number of
chips, and identifying a pulse and a quiet period within the waveform . Element
3: wherein mapping the symbol in a pulse sequence incl udes identifying a mud
pressu re signal in an acoustic transducer. Element 4 : wherein modifying a
drill ing config uration according to the message incl udes modifying a mud pump
operation . Element 5: wherein modifying a drill ing config uration according to
the message incl udes steering a dril l tool from a vertical drill ing configuration to
a horizontal drill ing configuration.
[0054] Element 6: wherein the processor further executes comma nds to
cause the device to receive an acoustic sig nal from an acoustic transducer.
Element 7: wherein the symbol characteristic incl udes one of a pulse width and
a pulse start. Element 8: wherein the one-to-one correspondence includes a
Gray code mapping . Element 9: wherein identifying a symbol in a pulse
sequence incl udes identifying a plural ity of chips disposed in a pre-selected
pattern. Element 10 : wherein the dril ling configu ration incl udes at least one of
a vertical configuration or a horizontal configuration .
[0055] Element 11: wherein providing a first pulse at a selected chip
location includes providing a pressu re signal to an acoustic transducer in a
wel lbore of a dril ling system . Element 12: wherein provid ing subsequent pulses
to form the pulse width includes providing more than a minimu m val ue of pulses
for the pulse width. Element 13: wherein forming a quiet period at the end of
the pulse width incl udes forming a quiet period of one chip or more after the
pulse. Element 14 : further including selecting the chip location and the desired
pulse width accord ing to at least one of a pulse-position-modulation (PPM) and a
pulse-width-modulation (PWM) scheme. Element 15 : wherein identifying a
pulse width and a pulse start for the pulse includes selecting a pulse value from
a number of values in a binary code having a selected number of bits. Element
16 : wherein identifying the pulse width and the pulse start based on the symbol
value includes correlating the symbol val ue with the pulse width and the pulse
start using a Gray code mapping . Element 17 : wherein forming a message
based on the drill ing condition includes steering a drill tool from a vertical
configu ration to a horizontal configuration.
[0056] The exemplary embodiments described herein are well adapted
to attain the ends and advantages mentioned as well as those that are inherent
therein. The particular embodiments disclosed above are illustrative only, as the
exemplary embodiments described herein may be modified and practiced in
different but equivalent manners apparent to those skilled in the art having the
benefit of the teachings herein. Furthermore, no limitations are intended to the
details of construction or design herein shown, other than as described in the
claims below. It is therefore evident that the particular illustrative embodiments
disclosed above may be altered, combined, or modified and all such variations
are considered within the scope and spirit of the present disclosure. The
disclosure illustratively disclosed herein suitably may be practiced in the absence
of any element that is not specifically disclosed herein and/or any optional
element disclosed herein. While compositions and methods are described in
terms of "comprising," "containing," or "including" various components or steps,
the compositions and methods can also "consist essentially of" or "consist of" the
various components and steps. All numbers and ranges disclosed above may
vary by some amount. Whenever a numerical range with a lower limit and an
upper limit is disclosed, any number and any included range falling within the
range is specifically disclosed. In particular, every range of values (of the form,
"from about a to about b," or, equivalently, "from approximately a to b," or,
equivalently, "from approximately a-b") disclosed herein is to be understood to
set forth every number and range encompassed within the broader range of
values. Also, the terms in the claims have their plain, ordinary meaning unless
otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite
articles "a" or "an," as used in the claims, are defined herein to mean one or
more than one of the element that it introduces. If there is any conflict in the
usages of a word or term in this specification and one or more patent or other
documents that may be incorporated herein by reference, the definitions that are
consistent with this specification should be adopted.
[0057] As used herein, the phrase "at least one of" preceding a series of
items, with the terms "and" or "or" to separate any of the items, modifies the list
as a whole, rather than each member of the list {i.e., each item). The phrase
"at least one of" does not require selection of at least one item; rather, the
phrase allows a meaning that includes at least one of any one of the items,
and/or at least one of any combination of the items, and/or at least one of each
of the items. By way of example, the phrases "at least one of A, B, and C" or "at
least one of A, B, or C" each refer to only A, only B, or only C; any combination
of A, B, and C; and/or at least one of each of A, B, and C.

CLAIMS
What is claimed is :
1. A method, comprising :
mapping a symbol in a pulse sequence by using a pulse width and a pulse
start in the symbol ;
reading a message using a symbol value for each symbol in a string of
symbols; and
modifying a drill ing configuration according to the message.
2. The method of claim 1, wherein mapping the symbol comprises mapping
consecutive Gray code symbols to two pulse sequences differing by one chip
from each other, wherein each symbol comprises a pre-determined number of
chips.
3. The method of claim 1, wherein mapping the symbol in a pulse sequence
comprises identifying a waveform having a selected number of chips, and
identifying a pulse and a quiet period within the waveform .
4. The method of claim 1, wherein mapping the symbol in a pulse sequence
comprises identifying a mud pressure signal in an acoustic transducer.
5. The method of claim 1, wherein modifying a dril ling configuration
according to the message comprises modifying a mud pump operation.
6. The method of claim 1, wherein modifying a dril ling configuration
according to the message comprises steering a drill tool from a vertical drill ing
configu ration to a horizontal drill ing configuration .
7. A device, comprising :
a memory circuit storing commands;
a processor circu it configu red to execute the commands and cause the
device to:
identify a symbol in a pulse sequence;
associate the symbol with a symbol value using a one-to-one
correspondence between the symbol val ue and a symbol characteristic;
read a message using the symbol value for each symbol in a
string of symbols; and
modify a dril ling configu ration according to the message.
8. The device of claim 7, wherein the processor further executes commands
to cause the device to receive an acoustic signa l from an acoustic transducer.
9. The device of claim 7, wherein the symbol characteristic comprises one of
a pulse width and a pulse start.
10. The device of cla im 7, wherein the one-to-one correspondence comprises
a Gray code mapping .
11. The device of claim 7, wherein identifying a symbol in a pulse sequence
comprises identifying a plu rality of chips disposed in a pre-selected pattern .
12. The device of claim 7, wherein the dril ling configu ration comprises at least
one of a vertical configuration or a horizontal configu ration.
13. A method, comprising :
determining a dril ling condition and forming a message based on the
dril ling condition ;
forming a string of symbol val ues comprising the message;
identifying a pulse width and a pulse start for the pulse, based on a
symbol val ue;
providing a first pulse at a selected chip location;
providing subsequent pulses to form the pulse width ; and
forming a quiet period at the end of the pulse width.
14. The method of claim 13, wherein providing a first pulse at a selected chip
location comprises providing a pressu re sig nal to an acoustic transd ucer in a
wel lbore of a drill ing system .
15. The method of claim 13, wherein providing subsequent pulses to form the
pulse width comprises providing more than a minimum value of pulses for the
pulse width.
16. The method of claim 13, wherein forming a quiet period at the end of the
pulse width comprises forming a quiet period of one chip or more after the pulse.
17. The method of claim 13, further comprising selecting the chip location and
the desired pulse width according to at least one of a pulse-position-modulation
(PPM) and a pulse-width-modulation (PWM) scheme.
18. The method of claim 13, wherein identifying a pulse width and a pulse
start for the pulse comprises selecting a pulse value from a number of values in
a binary code having a selected number of bits.
19. The method of claim 13, wherein identifying the pulse width and the pulse
start based on the symbol value comprises correlating the symbol value with the
pulse width and the pulse start using a Gray code mapping.
20. The method of claim 13, wherein forming a message based on the drilling
condition comprises steering a drill tool from a vertical configuration to a
horizontal configuration.