Continuous pressure modulation scheme for fluid telemetry

Abstract

A telemetry system includes a telemetry unit (31) including a pulser (34), the pulser (34) configured to be operated to generate pressure pulses in a borehole fluid for transmission of a communication, and a processing unit (32) configured to control the pulser (34) according to a modulation scheme to generate a transmission signal (70a, 70b) in the borehole fluid. The modulation scheme is configured to generate a waveform (56) that includes a plurality of overlapping continuously differentiable functions (58, 60, 62, 64, 66), each function (58, 60, 62, 64, 66) corresponding to a symbol representing one or more bits of a bit sequence.

Description

CONTINUOUS PRESSURE MODULATION SCHEME FOR FLUID TELEMETRYCROSS REFERENCE TO RELATED APPLICATIONSThis application claims the benefit of an earlier filing date from U.S. Provisional Application Serial No. 63 / 550,885 filed February 7, 2024, the entire disclosure of which is incorporated herein by reference.BACKGROUND

[0001] In the resource recovery and fluid sequestration industries, various types of communication systems are employed for transmission of communications (e.g., data, commands, etc.) between downhole components, and / or between downhole components and a surface location.

[0002] For example, fluid telemetry systems, generally referred to as mud pulse systems, are used for transmission of information during subsurface operations (e.g., drilling, measurement, stimulation, etc.). Mud pulse systems transmit information via a series of modulated pulses applied to fluid in a borehole. Other examples of communication systems include wired pipe and wireline systems.SUMMARY100031 A telemetry system includes a telemetry unit including a pulser, the pulser configured to be operated to generate pressure pulses in a borehole fluid for transmission of a communication, and a processing unit configured to control the pulser according to a modulation scheme to generate a transmission signal in the borehole fluid. The modulation scheme is configured to generate a waveform that includes a plurality of overlapping continuously differentiable functions, each function corresponding to a symbol representing one or more bits of a bit sequence.

[0004] An embodiment of a method includes receiving a set of data at a telemetry unit, the telemetry unit including a pulser configured to be operated to generate pressure pulses in a fluid for transmission of a communication, and controlling the pulser according to a modulation scheme to generate a transmission signal in the fluid. The modulation scheme generates a waveform that includes a plurality of overlapping continuously differentiable functions, each function corresponding to a symbol representing one or more bits of a bit sequence. The method also includes detecting the transmission signal by a receiver.BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:

[0006] Figure 1 depicts an embodiment of a borehole system including a telemetry system;

[0007] Figure 2 depicts an example of waveforms and transmission signals generated by an embodiment of a telemetry system;

[0008] Figure 3 depicts an example of waveforms and transmission signals generated using a conventional modulation scheme;

[0009] Figure 4 depicts an example of waveforms and transmission signals generated using an existing modulation scheme; and

[0010] Figure 5 is a flow diagram depicting an embodiment of a method of communication.DETAILED DESCRIPTION

[0011] A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures.

[0012] Apparatuses and methods for transmitting and receiving communications using fluid telemetry are described herein. An embodiment of a telemetry system includes a pulser configured to be operated to generate a communication signal as a series of pressure pulses in a borehole fluid, and a processor configured to control the pulser according to a modulation scheme. Embodiments are not limited to downhole applications, and may be applicable to any system that utilizes fluid telemetry.

[0013] In an embodiment, a series of bits (i.e., a bit sequence, such as a series of discrete numbers each representing one of two possible statuses) is modulated by the processor according to the modulation scheme, such that the bit sequence is modulated according to a waveform that includes a plurality of overlapping non-rectangular and continuously differentiable functions (i.e., pulse shapes). A bit (i.e., a discrete number that represents one of two possible statuses) that is modulated by one of the pulse shapes corresponds to a desired data symbol (or simply symbol).

[0014] The functions (i.e., pulse shapes) are time-wise longer than the time duration between adjacent bits in the bit sequence, so that modulated adjacent bits overlap, and so that there is a continuous curve representing the modulated bit sequence (also known as baseband) that connects the various symbols independent of which bit they represent. Notably, the functions and / or the bits can be complex (i.e., comprising complex numbers) so that the modulated bit sequence (also known as base band) is a complex valued representation of a specific bit sequence. As such, a symbol may include a single bit or a plurality of bits, such as a sequence of bits. Pulse shapes may be selected or configured to generate continuous base bands independent of the bit sequence they are representing.LOO 15 J In an embodiment, a pulse shape is defined so that the pulse shape is longer than the distance (i.e., duration) between adjacent bits of the bit sequence. The modulated bit sequence (i.e., the base band) may be generated by merging or combining (e.g., adding) the overlapping portions of adjacent symbols to achieve the base band. Any suitable technique can be used to achieve the base band. An example of a technique for obtaining a base band is to use pulse shapes which start and end with zero. Another example is the use of a smoothening window function with suitable properties. In another example, an interpolation scheme is utilized to achieve continuous transitions between functions.

[0016] Each function is selected to correspond to a desired bit or symbol. Functions for each symbol in a transmission may be determined by selecting functions from a data structure (e.g., look up table) that stores templates for different symbols or bit sequences.

[0017] After modulating bits with pulse shapes to create the base band, the base band may then be modulated again by a carrier signal. Such carrier signals may comprise periodic functions (e.g., trigonometric functions, such as sinus functions or cosinus functions, and the like) with one or more selected carrier frequencies. Modulated base bands (also known as pass bands) are then transmitted by a transmitter (e.g., a mud pulse telemetry valve or a pulser) by creating a pressure signal in the drilling fluid (or other downhole fluid) that corresponds to the pass band. The pressure signal that corresponds to the pass band may then be received by a receiver that is in connection with a processor. The processor is configured to demodulate the pressure signal corresponding to the pass band to determine the bit sequence that was represented by the base band and the pass band.

[0018] Advantageously, the pressure signals that correspond to pass bands are continuous, in particular for systems that utilize fluid telemetry where valves including inertia masses have to be switched, which makes it difficult or even impossible to include steps into the pressure bands. Pulse shapes may be selected to generate continuous pass bands independent of the bit sequence they are representing and even independent of the carrier frequency of the carrier signal that is used to modulate the corresponding base band.

[0019] A transmission from the pulser may encompass a single symbol or multiple symbols. In an embodiment, the transmission is configured so that the waveform begins and ends with a zero amplitude.

[0020] Embodiments present a number of advantages. For example, the telemetry system described herein is capable of realizing significantly higher data rates as compared to existing systems, with comparable power consumption. Such higher data rates provide for increased data density for logging-while drilling (LWD) and measurement-while-drilling (MWD) applications, or the ability to maintain data density while increasing rate of penetration (ROP).

[0021] Other advantages include the ability to transmit arbitrarily complex symbol alphabets, as the telemetry system can transmit symbols with multiple bits. As compared to existing mud pulse telemetry systems, which are limited to one bit per symbol, the telemetry system described herein provides for greater spectral efficiency.

[0022] Additional advantages include flexible selection of carrier frequency and data rate (e.g., non-integer frequency to data rate ratios), which allows for enhanced flexibility and increased ability to optimize transmissions for various conditions. Further advantages include a reduction in errors in decoding, enhanced spectral containment to decrease vulnerability to interference, and others.

[0023] Figure 1 illustrates an embodiment of a downhole system 10 including a borehole string 12 disposed in a borehole 14 that penetrates a subterranean region. The subterranean region may include a formation 16. The downhole system 10 is configured to perform one or more downhole operations, such as drilling, measurement, data acquisition, and / or analysis system.

[0024] In an embodiment, the downhole system 10 includes devices or systems for in- situ measurement of characteristics of the formation, the borehole 14 and / or the borehole string 12. For example, the system 10 includes a measurement tool 18 having a tool body 20, such as a mandrel, pipe segment or other elongated structure. The body 20 may be part of a rotating component, such as a logging-while drilling (LWD) or drilling sub connected to a drilling assembly 22. The body 20 has a fluid conduit or inner bore (not shown) for allowing flow of drilling mud, formation fluids and other fluids.

[0025] The measurement tool 18 may be configured to perform electromagnetic measurements, such as resistivity and / or nuclear magnetic resonance (NMR) measurements. For example, the measurement tool 18 includes a static magnetic field source 24 thatmagnetizes formation materials and a transceiver assembly 26 (e.g., one or more antennas that transmits RF energy or pulsed energy and detect measurement signals.

[0026] The borehole string 12 and the measurement tool 18 may be configured to perform other measurements. Examples include pressure, temperature, direction, and deviation of the well bore. Other examples include density, porosity, induction, selfpotential, and pressure gradients.

[0027] The tool 18 and / or other downhole components are equipped with transmission components to communicate with one or more surface devices or systems. The transmission components may be used to communicate with a surface processing unit 28. The surface processing unit 28 may receive and transmit communications via a wired or wireless communication channel connected to surface equipment 30 (e.g., a drilling rig).

[0028] In an embodiment, the borehole string 12 includes components for communication by mud pulse telemetry, which utilizes pressure pulses in downhole fluid. The downhole fluid may be a drilling fluid (drilling mud) or combination of drilling fluid and fluids from the formation, such as gases, water and oil. It is noted that the term “mud pulse telemetry” is not intended to limit embodiments described herein to any particular type or composition of fluid.

[0029] For example, the borehole string 12 includes a mud pulse telemetry system that includes a telemetry unit 31, which includes a pulser 34. The telemetry unit 31 includes or is connected to a downhole processing unit 32 including a processor configured to control a pulser 34. The pulser 34 is controlled to generate pulses in borehole fluid that are transmitted to the surface and detected by a suitable receiver (not shown). The pulses are modulated according to a waveform generated as described herein. Pressure pulses may be modulated using the waveform using any suitable modulation (e.g., phase or amplitude modulation. The processing unit 32 may perform other functions, such as detection of received mud pulse telemetry signals, control of downhole tools, data processing, analysis and others.

[0030] The surface processing unit 28, the downhole processing unit 32, the tool 18, and / or other components of the system 10 include devices as necessary to provide for control of downhole components, and / or storing and / or processing data collected from the tool 18 and other components of the system 10. Exemplary devices include, without limitation, at least one processor, storage, memory, input devices, output devices, and the like.

[0031] The telemetry system is configured to communicate based on generating and / or receiving fluid pulses that are modulated using a modulation scheme that representsdata symbols as a linear combination of consecutive overlapping non-rectangular functions (e.g., sine functions). Such telemetry systems are disclosed, for example by US Patent Publication No. 20210003230A1, the contents of which are incorporated herein in its entirety. Adjacent functions overlap temporally, such that portions of adjacent functions occur within the same time range or time window.

[0032] In an embodiment, the functions overlap in a continuous manner (e.g., via interpolation or other technique(s)), so that there is a gradual or continuous transition between adjacent functions. Each function corresponds to a respective data symbol. As noted above, a symbol refers to a series of one or more bits.

[0033] The telemetry system generates a waveform for modulation that corresponds to a transmission of a symbol or symbols. The waveform includes a function specific to each transmitted symbol. For example, a symbol alphabet, including a waveform template for each available symbol, is pre-determined and stored for use in generating a waveform for transmission. As there is no discontinuity between adjacent functions, the waveform is used to modulate consecutive data symbols without any abrupt changes between symbols.

[0034] In an embodiment, each transmission is controlled so that the transmission begins and ends with a zero amplitude. For example, if the transmission includes a single symbol, the beginning and end of the symbol is a zero value. If the transmission includes multiple symbols, the beginning of the first symbol is zero, and the end of the last symbol in the transmission is zero.

[0035] In an embodiment, the waveform / signal is modulated using continuous pressure modulation (CPM), or other modulation scheme that results in a waveform having a continuous phase (e.g., Continuous-phase frequency- shift keying (CPFSK)). In a continuous phase waveform, the carrier phase is modulated by gradually changing the phase over a symbol durations, so that there is no discontinuity or abrupt change in phase between symbols.

[0036] Embodiments are not so limited and can be applied to any of various modulation schemes. Examples include frequency modulation schemes, phase modulation schemes such as phase shift keying (PSK), and amplitude modulation such as amplitude shift keying (ASK) and quadrature amplitude modulation (QAM). The modulation scheme, in an embodiment, is able to transmit signals having multiple bits per symbol. Examples include 4- PSK, 4-QAM, 256-QAM modulation.

[0037] In an embodiment, the modulation scheme is a single carrier continuous pressure modulation that results in a continuous linear combination of functions. Thismodulation scheme is referred to as linear continuous pressure modulation (LCPM). LCPM uses arbitrarily selected non-rectangular filter functions for signal shaping.

[0038] An example of the LCPM modulation scheme is represented by the following equations, which describe a waveform or signal having an amplitude SLCPM as a function of time t:

[0039] In the above, fcis the carrier signal frequency, Tsis a symbol duration (inverse of symbol rate fs), and n is a symbol index. dnis the complex valued representation of one or more bits (symbol) in the bit sequence of length M. g is a function defining a pulse shape having a length L, where the length L is related to a number of individual bits per symbol duration Ts. An index I represents a summation index. An index n represents a counting index of bits in the bit sequence. The pulse shape combines a filter function for each symbol to be transmitted. Note that both the symbol mapping for dnand the pulse shape g can be selected arbitrarily according to the needs of a given application. R and I are the real part and the imaginary part of a complex number. It is noted that the pulse shape may encompass a single filter function or a plurality of filter functions (where each filter function is an individual pulse shape).

[0040] In an embodiment, the waveform begins and ends with a zero amplitude. For example, the pulse shape g is selected so that the pulse shape g has an amplitude of zero at the start and at the end of the waveform.

[0041] LCPM modulation as described herein does not require a constant energy per symbol, and has an adjustable bandwidth. In addition, the modulation scheme has high adaptivity due to, for example, the flexibility in carrier selection, as well as the flexibility in pulse shape and symbol mapping selection.

[0042] Figure 2 shows examples of transmission signals generated according to waveforms derived using the LCPM modulation scheme. The waveforms are shown as graphs of normalized signal amplitude 5 (vertical axis) as a function of time t. An exemplary bit sequence is modulated to generate a series of data symbols 58, 60, 62, 64, 66. In the following, vertical lines cl, c2, c3, c4, c5 within the graphs indicate the center position of each distinct one-bit data symbol.

[0043] Figure 2 shows an example of a communication performed using LCPM modulation for transmission of a signal having five one-bit symbols. In this example, a distinct filter function was selected for each symbol.

[0044] Figure 2 includes a graph 50 of normalized amplitude S_as a function of time t (in milliseconds) that includes a curve 52 representing an example of a filter function used in LCPM modulation. The filter function (curve 50) in this example, defines a pulse shape for a single bit in the bit sequence.

[0045] A graph 54 shows a base band signal as a curve 56. Curves 58, 60, 62, 64 and 66 represent individual data symbols generated by modulating filter functions (pulse shapes) on each bit in the bit sequence (represented by vertical lines cl - c5). Curves 58, 60, 62, 64 and 66 are calculated by modulating one or more bits with the curve 52. While curves 58, 60, 62, 64 and 66 are shown as real numbers, embodiments where these curves comprise complex values are also possible. Each curve 58, 60, 62, 64 and 66 is defined by a respective filter function, where each respective filter function has an amplitude selected to represent a given bit or one-bit symbol. The center position of each one-bit symbol is shown by vertical lines cl, c2, c3, c4 and c5. As shown, the functions overlap because the pulse shape 52 is longer in time than the distance of adjacent bits in the bit sequence. In other words, L is larger than one. In the example of Figures 2 - 4, L is 3 but other numbers for L are possible as well. Curves 58, 60, 62, 64 and 66 are used to calculate the continuous curve 56 (for example, by summation of individual curves 58, 60, 62, 64 and 66 to produce the base band signal.

[0046] The base band signal may be used to modulate a carrier to produce a pass band signal. Figure 2 shows pass bands resulting from modulation of different carrier frequencies. A first pass band signal is shown in a graph 68a as a transmission signal curve 70a after modulation for transmission using a 5 Hz carrier frequency. A graph 68b includes a transmission signal curve 70b representing the pass band signal after modulation of a 10 Hz carrier. Notably, the pulse shape 52, the curve 56 representing the base band, as well as transmission signal curves 70a, 70b, are continuously differentiable.

[0047] Figures 3 and 4 show signals for the same symbol sequence, generated according to existing modulation schemes. Figure 3 shows aspects of modulation using conventional binary phase shift keying (referred to as “conventional BPSK”), which uses rectangular pulses (i.e., continuous but not differentiable as shown in graph 72 of amplitude 5 as a function of time t in milliseconds) as a normalized rectangular curve 74). The base band signal generated for this particular symbol sequence using conventional BPSK is then alsocontinuous but not differentiable as shown in a graph 76 as a curve 78. The pass band signal for a 5 Hz carrier frequency is shown in a graph 80a as a curve 82a, and the pass band signal for a 10 Hz carrier frequency is shown in a graph 80b as a curve 82b. Curves 82a and 82b show that pass band signal then may comprise discontinuities. The graphs 76, 80a and 80b are graphs of amplitude .S' as a function of time t in seconds.

[0048] Figure 4 shows aspects of modulation using a modified version of BPSK (referred to as “modified BPSK”). Modified BPSK avoids phase jumps or discontinuities inherent to conventional BPSK, by introducing transition signals as bit values to be transmitted. A graph 84 (amplitude .S' as a function of time t in milliseconds) includes a curve 86 representing a pulse shape used in modified BPSK. Curve 86 is continuous but not differentiable as it contains singularities. A graph 88a includes a curve 90a representing the corresponding pass band signal for a 5 Hz carrier frequency, and a graph 88b includes a curve 90b representing the corresponding pass band signal for a 10 Hz carrier frequency. The graphs 84, 88a and 88b are graphs of amplitude S' as a function of time / in seconds. The base band signal (not shown) is significantly more complex than the base band signals of conventional BPSK and LCPM.

[0049] As shown, conventional BPSK modulation results in abrupt (discontinuous) transitions between at least some symbols. The modified BPSK modulation provides for continuous transitions between symbols, but is limited to one bit per symbol. LCPM modulation, in comparison, provides for both continuous transitions and allows for multiple bits per symbol. In addition, LCPM modulation does not require a constant envelope. LCPM modulation is also more flexible and adaptive than the BPSK and modified BPSK, at least due to flexibility in carrier frequencies, pulse shape and symbol mapping.

[0050] Figure 5 illustrates a method 100 of communication using fluid telemetry. The method 100 includes one or more of stages represented by blocks 101-105, at least portions of which may be performed by a processor (e.g., a processor in the telemetry unit 31). In one embodiment, the method 100 includes the execution of all of stages represented by blocks 101-105 in the order described. However, certain stages may be omitted, stages may be added, or the order of the stages changed.

[0051] Aspects of the method 100 are discussed in conjunction with the system 10 of Figure 1. However, the method is not so limited, and can be performed in conjunction with other systems that utilize fluid telemetry.

[0052] At block 101, a data structure, such as a lookup table, is generated or acquired. The data structure relates specific symbols with respective filter functions. The filterfunctions may be selected randomly or using any desired criteria. For examples, filter functions selected to represent symbols may be selected to reduce or minimize reflections or other disturbances in a transmission channel.

[0053] At block 102, a borehole string such as the drill string 12 is deployed into a borehole, and a subterranean operation is performed. In an embodiment, the operation is a drilling and / or measurement operation, such as a LWD operation. During the operation, various measurements may be performed by using suitable tools in a bottomhole assembly or otherwise located at the string.

[0054] At block 103, a processor such as the downhole processing unit 32 receives data, such as measurement data and / or communications, and encodes the measurement data as a set of symbols (i.e., one or more symbols). Each symbol may have one or more bits. A non-rectangular filter function is selected for each symbol (e.g., by consulting stored symbol templates in the lookup table).

[0055] At block 104, the processor generates a waveform that includes a linear combination of each selected filter function. The functions are configured to overlap using, for example, an interpolation scheme.

[0056] At block 105, the processor controls a pulser or other device to generate a telemetry signal in borehole fluid according to the generated waveform. For example, a carrier signal is modulated, and the pulser 34 is controlled according to the modulated carrier signal to transmit modulated pressure signals through fluid in the borehole annulus, which travel to the surface and are detected by a suitable receiver or detector (e.g., a pressure sensor).

[0057] In some cases, the telemetry signal is transmitted after transmission of a preceding signal. If the preceding signal is not a signal having overlapping functions as described herein (i.e., is not overlapping), the processor may transmit a zero symbol that immediately precedes transmission of the waveform, the symbol represented by a zero value.

[0058] Various actions can be performed based on the transmitted signal. For example, measurement data is extracted by decoding detected pressure signals, and the extracted data is processed as desired and used to estimate a property or properties of the borehole and / or a subterranean region. The property or properties may be presented to a user or operator, and / or used for planning and / or adjusting operational parameters such as rotational rate, rate of penetration and others. For example, the surface processing unit 28 (or other processor, device or system) receives and decodes a transmission signal, and adjusts or otherwise controls parameters of an operation, such as flow rate, pump pressure, rotationalrate and / or rate of penetration. The surface processing unit 28 may also transmit a response or other communication to the telemetry unit 31.

[0059] Set forth below are some embodiments of the foregoing disclosure:

[0060] Embodiment 1: A telemetry system characterized by: a telemetry unit (31) including a pulser (34), the pulser (34) configured to be operated to generate pressure pulses in a borehole fluid for transmission of a communication; and a processing unit (32) configured to control the pulser (34) according to a modulation scheme to generate a transmission signal (70a, 70b) in the borehole fluid, the modulation scheme configured to generate a waveform (56) that includes a plurality of overlapping continuously differentiable functions (58, 60, 62, 64, 66), each function (58, 60, 62, 64, 66) corresponding to a symbol representing one or more bits of a bit sequence.

[0061] Embodiment 2: The telemetry system of any prior embodiment, wherein each function (58, 60, 62, 64, 66) function (58, 60, 62, 64, 66) overlaps one or more adjacent functions (58, 60, 62, 64, 66).

[0062] Embodiment 3: The telemetry system of any prior embodiment, wherein each function (58, 60, 62, 64, 66) has a length or duration that is greater than a time between two adjacent bits in the bit sequence.

[0063] Embodiment 4: The telemetry system of any prior embodiment, wherein the waveform (56) has a continuous phase.

[0064] Embodiment 5: The telemetry system of any prior embodiment, wherein the waveform (56) is continuously differentiable.

[0065] Embodiment 6: The telemetry system of any prior embodiment, wherein the processing unit (32) is configured to generate the waveform (56) based on a data structure storing a set of templates, each template relating a given function (58, 60, 62, 64, 66) to a respective symbol.

[0066] Embodiment 7 : The telemetry system of any prior embodiment, wherein the transmission signal (70a, 70b) is continuously differentiable.

[0067] Embodiment 8: The telemetry system of any prior embodiment, wherein the waveform (56) is modulated with a carrier signal with a selected carrier frequency to create the transmission signal (70a, 70b).

[0068] Embodiment 9: The telemetry system of any prior embodiment, further comprising a receiver unit (28) configured to receive the transmission signal (70a, 70b) and to extract the bit sequence out of the transmission signal (70a, 70b).

[0069] Embodiment 10: A method (100) characterized by: receiving a set of data at a telemetry unit (31), the telemetry unit (31) including a pulser (34) configured to be operated to generate pressure pulses in a fluid for transmission of a communication; controlling the pulser (34) according to a modulation scheme to generate a transmission signal (70a, 70b) in the fluid, the modulation scheme generating a waveform (56) that includes a plurality of overlapping continuously differentiable functions (58, 60, 62, 64, 66), each function (58, 60, 62, 64, 66) corresponding to a symbol representing one or more bits of a bit sequence; and detecting the transmission signal (70a, 70b) by a receiver (28).

[0070] Embodiment 11: The method (100) of any prior embodiment, wherein each function overlaps one or more adjacent functions (58, 60, 62, 64, 66).

[0071] Embodiment 12: The method (100) of any prior embodiment, wherein each function (58, 60, 62, 64, 66) has a length or duration that is greater than a time between two adjacent bits in the bit sequence.

[0072] Embodiment 13: The method (100) of any prior embodiment, wherein the waveform (56) is generated by combining overlapping portions of adjacent functions (58, 60, 62, 64, 66) so that there is a continuous transition between the adjacent functions (58, 60, 62, 64, 66).

[0073] Embodiment 14: The method (100) of any prior embodiment, wherein the waveform (56) is continuously differentiable.

[0074] Embodiment 15: The method (100) of any prior embodiment, wherein the waveform (56) begins and ends with an amplitude of zero.

[0075] Embodiment 16: The method (100) of any prior embodiment, wherein the processing unit (32) is configured to generate the waveform (56) based on a data structure storing a set of templates, each template relating a given function (58, 60, 62, 64, 66) to a respective symbol.

[0076] Embodiment 17: The method (100) of any prior embodiment, wherein the transmission signal (70a, 70b) is continuously differentiable.

[0077] Embodiment 18: The method (100) of any prior embodiment, wherein the waveform (56) is modulated with a carrier signal with a selected carrier frequency to create the transmission signal (70a, 70b).

[0078] Embodiment 19: The method (100) of any prior embodiment, further comprising extracting the bit sequence out of the transmission signal (70a, 70b) by the receiver (28).

[0079] Embodiment 20: The method (100) of any prior embodiment, wherein the telemetry unit (31) is disposed in a borehole (14), and the pulser (34) is operated to generate the transmission signal (70a, 70b) in a borehole fluid.

[0080] The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Further, it should be noted that the terms “first,” “second,” and the like herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The terms “about”, “substantially” and “generally” are intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application. For example, “about” and / or “substantially” and / or “generally” can include a range of ± 8% of a given value.

[0081] The teachings of the present disclosure may be used in a variety of well operations. These operations may involve using one or more treatment agents to treat a formation, the fluids resident in a formation, a borehole, and / or equipment in the borehole, such as production tubing. The treatment agents may be in the form of liquids, gases, solids, semi-solids, and mixtures thereof. Illustrative treatment agents include, but are not limited to, fracturing fluids, acids, steam, water, brine, anti-corrosion agents, cement, permeability modifiers, drilling muds, emulsifiers, demulsifiers, tracers, flow improvers etc. Illustrative well operations include, but are not limited to, hydraulic fracturing, stimulation, tracer injection, cleaning, acidizing, steam injection, water flooding, cementing, etc.

[0082] While the invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited.

Claims

CLAIMSWhat is claimed is:

1. A telemetry system characterized by: a telemetry unit (31) including a pulser (34), the pulser (34) configured to be operated to generate pressure pulses in a borehole fluid for transmission of a communication; and a processing unit (32) configured to control the pulser (34) according to a modulation scheme to generate a transmission signal (70a, 70b) in the borehole fluid, the modulation scheme configured to generate a waveform (56) that includes a plurality of overlapping continuously differentiable functions (58, 60, 62, 64, 66), each function (58, 60, 62, 64, 66) corresponding to a symbol representing one or more bits of a bit sequence.

2. The telemetry system of claim 1, wherein each function (58, 60, 62, 64, 66) function (58, 60, 62, 64, 66) overlaps one or more adjacent functions (58, 60, 62, 64, 66).

3. The telemetry system of claim 1 or 2, wherein each function (58, 60, 62, 64, 66) has a length or duration that is greater than a time between two adjacent bits in the bit sequence.

4. The telemetry system of any of claims 1-3, wherein the waveform (56) has a continuous phase.

5. The telemetry system of any of claims 1-4, wherein the waveform (56) is continuously differentiable.

6. The telemetry system of any of claims 1-5, wherein the processing unit (32) is configured to generate the waveform (56) based on a data structure storing a set of templates, each template relating a given function (58, 60, 62, 64, 66) to a respective symbol.

7. The telemetry system of any of claims 1-6, wherein the transmission signal (70a, 70b) is continuously differentiable.

8. The telemetry system of any of claims 1-7, wherein the waveform (56) is modulated with a carrier signal with a selected carrier frequency to create the transmission signal (70a, 70b).

9. The telemetry system of any of claims 1-8, further comprising a receiver unit (28) configured to receive the transmission signal (70a, 70b) and to extract the bit sequence out of the transmission signal (70a, 70b). .

10. A method (100) characterized by: receiving a set of data at a telemetry unit (31), the telemetry unit (31) including a pulser (34) configured to be operated to generate pressure pulses in a fluid for transmission of a communication;controlling the pulser (34) according to a modulation scheme to generate a transmission signal (70a, 70b) in the fluid, the modulation scheme generating a waveform (56) that includes a plurality of overlapping continuously differentiable functions (58, 60, 62, 64, 66), each function (58, 60, 62, 64, 66) corresponding to a symbol representing one or more bits of a bit sequence; and detecting the transmission signal (70a, 70b) by a receiver (28).

11. The method ( 100) of claim 10, wherein each function overlaps one or more adjacent functions (58, 60, 62, 64, 66).

12. The method (100) of claim 10 or 11, wherein each function (58, 60, 62, 64, 66) has a length or duration that is greater than a time between two adjacent bits in the bit sequence.

13. The method (100) of any of claims 10-12, wherein the waveform (56) is generated by combining overlapping portions of adjacent functions (58, 60, 62, 64, 66) so that there is a continuous transition between the adjacent functions (58, 60, 62, 64, 66).

14. The method (TOO) of any of claims 10-13, wherein the waveform (56) is continuously differentiable.

15. The method (100) of any of claims 10-14, wherein the waveform (56) begins and ends with an amplitude of zero.

16. The method (100) of any of claims 10-15, wherein the processing unit (32) is configured to generate the waveform (56) based on a data structure storing a set of templates, each template relating a given function (58, 60, 62, 64, 66) to a respective symbol.

17. The method (100) of any of claims 10-16, wherein the transmission signal (70a, 70b) is continuously differentiable.

18. The method (TOO) of any of claims 10-17, wherein the waveform (56) is modulated with a carrier signal with a selected carrier frequency to create the transmission signal (70a, 70b).

19. The method (100) of any of claims 10-18, further comprising extracting the bit sequence out of the transmission signal (70a, 70b) by the receiver (28).

20. The method ( 100) of any of claims 10-19, wherein the telemetry unit (31) is disposed in a borehole (14), and the pulser (34) is operated to generate the transmission signal (70a, 70b) in a borehole fluid.

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