Multiple gap sub receiver-transmitter combinations for mitigating formation isolators

Abstract

A device includes a first transceiver, where first terminals of the first transceiver are coupled to a drill string at locations associated with a first electrically insulating gap included iii the drill string. The device includes a second transceiver, where second terminals of the second transceiver are coupled to the drill string at locations associated with a second electrically insulating gap included in the drill string. The device includes control circuitry configured to control switching circuitry coupled to the drill string. The switching circuitry is associated with at least one of the first electrically insulating gap and the second electrically insulating gap.

Description

65TEL-510231-WO-2_INT1027PCT MULTIPLE GAP SUB RECEIVER-TRANSMITTER COMBINATIONS FOR MITIGATING FORMATION ISOLATORS CROSS REFERENCE TO RELATED APPLICATIONS This application claims the benefit of an earlier filing date from U.S. Provisional Application Serial No.63 / 635,891, filed April 18, 2024, the entire disclosure of which is incorporated herein by reference. BACKGROUND

[0001] In the resource recovery and fluid sequestration industries, recovering hydrocarbons from subterranean zones may involve drilling wellbores.

[0002] Wellbores may be formed using surface-located drilling equipment which drives a drill string that eventually extends from the drilling equipment to the formation or subterranean zone of interest. In some cases, the drill string can extend thousands of feet or meters below the surface. The terminal end of the drill string may include a drill bit for drilling (or extending) the wellbore. Drilling fluid, in some cases in the form of a drilling “mud,” may be pumped through the drill string. The drilling fluid cools and lubricates the drill bit and also carries cuttings back to the surface. Drilling fluid may be used to control bottom hole pressure to inhibit hydrocarbon influx from the formation into the wellbore and potential blow out at surface.

[0003] Bottom hole assembly (BHA) refers to equipment at the terminal end of a drill string. In addition to a drill bit, a BHA may include elements such as, for example, an apparatus for steering the direction of the drilling (e.g., a steerable downhole mud motor or rotary steerable system), sensors for measuring properties of the surrounding geological formations (e.g., sensors for use in well logging), sensors for measuring downhole conditions as drilling progresses, one or more systems for telemetry of data to the surface, stabilizers, heavy weight drill collars, pulsers, and the like. The BHA may be advanced into the wellbore by a string of metallic tubulars (drill pipe).

[0004] Some drilling systems may include any of a wide range of mechanical / electronic systems in the BHA or at other downhole locations. Such mechanical / electronic systems may include active mechanical, electronic, and / or electromechanical systems capable of operating downhole. A downhole system may provide any of a wide range of functions including, without limitation, data acquisition, measuring properties of the surrounding geological formations (e.g., well logging), measuring downhole65TEL-510231-WO-2_INT1027PCT conditions as drilling progresses, controlling downhole equipment, monitoring status of downhole equipment, directional drilling applications, measuring while drilling (MWD) applications, logging while drilling (LWD) applications, measuring properties of downhole fluids, and the like. A downhole system may include or be connected to one or more systems for, for example, telemetry of data to the surface, collecting data by way of sensors (e.g., sensors for use in well logging) that may include one or more of vibration sensors, magnetometers, inclinometers, accelerometers, nuclear particle detectors, electromagnetic detectors, acoustic detectors, and others, acquiring images, measuring fluid flow, determining directions, emitting signals, detecting particles or fields, interfacing to other downhole equipment, sampling downhole fluids, and the like.

[0005] A downhole system may communicate a wide range of information to the surface by telemetry and / or receive a wide range of information from other systems which may be located at the surface and / or underground. Telemetry information can be invaluable for efficient drilling operations. For example, telemetry information may be used by a drill rig operator to make decisions about controlling and steering the drill bit to optimize the drilling speed and trajectory based on numerous factors, including legal boundaries, locations of existing wells, formation properties, hydrocarbon size and location, and the like. An operator may make intentional deviations from the planned path as applicable based on information gathered from downhole sensors and transmitted to the surface by telemetry during the drilling process. The ability to obtain and transmit reliable data from downhole locations allows for relatively more economical and more efficient drilling operations.

[0006] Some telemetry techniques include transmitting information by generating vibrations in fluid in the bore hole (e.g., acoustic telemetry or mud pulse (MP) telemetry) and transmitting information by way of electromagnetic signals that propagate at least in part through the earth (EM telemetry). Other telemetry techniques use hardwired drill pipe, fiber optic cable, or drill collar acoustic telemetry to carry data to the surface.

[0007] Advantages of EM telemetry, relative to MP telemetry, include generally faster data transmission rates, increased reliability due to no moving downhole parts, high resistance to lost circulating material (LCM) use, and suitability for air / underbalanced drilling. An EM telemetry system can transmit data without a continuous fluid column, which provides advantages for cases in which there is no drilling fluid flowing. This is advantageous when a drill crew is adding a new section of drill pipe, as the EM signal can transmit information (e.g., directional information) while the drill crew is adding the new pipe. Some disadvantages of EM telemetry include lower depth capability, incompatibility65TEL-510231-WO-2_INT1027PCT with some formations (for example, high salt formations and formations of high resistivity contrast), and some market resistance due to acceptance of older established methods. Also, as the EM transmission may be strongly attenuated over long distances through the earth formations, the amount of power involved in association with transmitting EM signals is relatively large in order for the EM signals to be detected at the surface. In some cases, the electrical power available to generate EM signals may be provided by batteries or another power source that has relatively limited capacity.

[0008] Improved systems for conveying data to and from downhole systems with, for example, higher data rates, reliable transmission at greater depths, or the like, are desired. SUMMARY

[0009] Embodiments of the present disclosure are directed to a downhole telemetry device disposed in a borehole through a subterranean formation, the downhole telemetry device including: a receiver, wherein first terminals of the receiver are coupled to a drill string at locations associated with a first electrically insulating gap included in the drill string; a transmitter, wherein second terminals of the transmitter are coupled to the drill string at locations associated with a second electrically insulating gap included in the drill string; and control circuitry configured to control a switching circuitry coupled to at least one of the first terminals or the second terminals, wherein the switching circuitry is associated with at least one of the first electrically insulating gap and the second electrically insulating gap.

[0010] Embodiments of the present disclosure are directed to a communication system disposed in a borehole through a subterranean formation and including: a set of downhole telemetry devices, wherein each downhole telemetry device of the set of downhole telemetry devices includes: a receiver, wherein first terminals of the receiver are coupled to a drill string at locations associated with a first electrically insulating gap included in the drill string; a transmitter, wherein second terminals of the transmitter are coupled to the drill string at locations associated with a second electrically insulating gap included in the drill string; and control circuitry configured to control a switching circuitry coupled to at least one of the first terminals or the second terminals, wherein the switching circuitry is associated with at least one of the first electrically insulating gap and the second electrically insulating gap.

[0011] Embodiments of the present disclosure are directed to a method for communicating within a borehole while drilling the borehole through a subterranean formation, the method including: controlling switching circuitry of a downhole telemetry device coupled to a drill string, wherein the switching circuitry is coupled to a first65TEL-510231-WO-2_INT1027PCT electrically insulating gap and a second electrically insulating gap of the drill string; and at least one of: receiving, at the downhole telemetry device, a first electromagnetic (EM) signal including data based on a configuration of the switching circuitry; or transmitting, by the downhole telemetry device, a second EM signal including the data based on the configuration of the switching circuitry.

[0012] Further aspects supported by the present disclosure and features of example embodiments are illustrated in the accompanying drawings and / or described in the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike.

[0014] FIG.1 is a diagram illustrating an example embodiment of a system in accordance with aspects of the present disclosure.

[0015] FIGS.2A, 2B, 2C, and 2D schematically illustrate a borehole string and an associated communication system in accordance with one or more embodiments of the present disclosure.

[0016] FIG.3 illustrates a block diagram of an example repeater node in accordance with one or more embodiments of the present disclosure.

[0017] FIG.4 illustrates a block diagram of an example repeater node in accordance with one or more embodiments of the present disclosure.

[0018] FIG.5 illustrates an example of a gap sub in accordance with one or more embodiments of the present disclosure.

[0019] FIGS.6A, 6B, and 6C illustrate block diagrams of a repeater node in accordance with one or more embodiments of the present disclosure.

[0020] FIG.7 illustrates an example of a repeater node configuration of a communication system in accordance with one or more embodiments of the present disclosure.

[0021] FIG.8 illustrates an example flowchart of a method in accordance with one or more embodiments of the present disclosure.65TEL-510231-WO-2_INT1027PCT DETAILED DESCRIPTION

[0022] 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.

[0023] According to one or more embodiments of the present disclosure, an EM transmission system network of repeater nodes is described that utilizes electrically insulating gaps (gap subs) in a drill string for improving EM transmission. In one or more embodiments, a repeater node detecting high resistivity associated with a formation can transmit a high frequency EM communication to an adjacent repeater node. In some aspects, using high frequency EM communication (e.g., of a lower propagation distance) supports inter-node communication between the repeater node and repeater nodes while preventing disruption to lower frequency EM transmissions of measurement-while-drilling (MWD) data by a MWD tool or other repeater nodes.

[0024] In one or more embodiments, a repeater node may provide (e.g., via high frequency EM communication described herein) various information or signaling to other repeater nodes indicating whether the repeater node is shorting a respective gap at a section of the drill string. In some cases, the information (e.g., signaling) may include a request for another repeater node to short a respective gap at another section of the drill string, and the other repeater node can in turn short out the respective gap. The targeted shorting of gaps at sections of the drill string may provide an effective dipole antenna effect that supports improved transmissions along the drill string. It is to be understood that within the context of the present disclosure, descriptions herein of antennas, antenna elements, and the like may refer to dipoles that are alternatingly polarized, rather than a real “antenna” such as a radiating antenna.

[0025] In some examples, communication between repeater nodes (e.g., of formation properties and / or signaling described herein), different from the lower frequency EM transmissions for MWD data, can be implemented using a data bus such as, for example, a CAN bus. In some aspects, implementing the intercommunication between repeater nodes using a data bus may provide advantages of increased isolation between the receiver and transmitter circuitry for maintaining a physical separation supportive of feedback control.

[0026] According to one or more embodiments of the present disclosure, the EM transmission system network may incorporate dual gap subs and / or triple gap subs. In an example, for a dual gap sub implemented in the drill string in association with a repeater65TEL-510231-WO-2_INT1027PCT node, a first gap is associated with the transmitter of the repeater node and a second gap is associated with the receiver of the repeater node.

[0027] In another example, for a triple gap sub implemented in the drill string in association with a repeater node, a third gap (between the first and second gaps) supports an interface between respective reference points of the receiver and the transmitter of the repeater node. Use of the triple gap sub configuration mitigates excessive feedback from saturating the receiver (e.g., input circuitry at the receiver), and the mitigation of excessive feedback allows for continuous transmission in the configuration of a repeater node chain.

[0028] The features described herein of controlled / selective shorting of gaps (of gap subs) included in the drill string provide advantages of improved lower frequency EM communication of MWD data (e.g., increased transmission efficiency associated with a target SNR, a target transmission rate, a reduction of transmission errors, and the like) and increased coupling of signals through the drilling fluid.

[0029] Example detailed descriptions are provided herein which support dual (or triple) gap subs in the drill string, per repeater node, in which switches at the gap subs and repeater nodes are controllable for selective shorting of one or more gaps (e.g., adaptively varying distances between gaps) and mitigating the effects of EM unfriendly formations. Example aspects of the repeater nodes, repeater node chains, and gap subs will further be described herein.

[0030] FIG.1 is a diagram illustrating an example embodiment of a system 100 for performing energy industry operations in accordance with aspects of the present disclosure. The system 100 supports an EM transmission repeater network for communications along a borehole string 140. The repeater network may include multiple gap sub receiver-transmitter combinations for mitigating formation isolators, example aspects of which are described herein.

[0031] The system 100 is configured to perform any suitable energy industry operation, such as, for example, a drilling operation, a stimulation operation, a measurement operation and / or a production operation. However, example aspects of communication techniques supported by the system 100 as described herein are not limited to energy industry operations and an associated downhole environment.

[0032] The system 100 includes a borehole 135 in a subsurface formation 130. A borehole string 140 (also referred to herein as a drill string) is disposed in the borehole 135 that penetrates the formation 130. The borehole 135 may be an open hole, a cased hole or a partially cased hole. In one embodiment, the borehole string 140 is a stimulation or injection65TEL-510231-WO-2_INT1027PCT string that includes a tubular, such as a coiled tubing, pipe (e.g., multiple pipe segments) or wired pipe, that extends from a wellhead at a surface location (e.g., at a drill site or offshore stimulation vessel).

[0033] As described herein, a “string” refers to any structure or carrier suitable for lowering a tool or other component through a borehole or connecting a drill bit to the surface, and is not limited to the structure and configuration described herein. The term "carrier" as used herein means any device, device component, combination of devices, media and / or member that may be used to convey, house, support or otherwise facilitate the use of another device, device component, combination of devices, media and / or member. Example non- limiting carriers include casing pipes, wirelines, wireline sondes, slickline sondes, drop shots, downhole subs, BHAs and drill strings.

[0034] In one embodiment, the system 100 is configured as a hydraulic stimulation system. As described herein, “hydraulic stimulation” includes any injection of a fluid into a formation. A fluid may be any flowable substance such as a liquid or a gas, and / or a flowable solid such as sand. In this embodiment, the borehole string 140 includes a stimulation assembly that includes one or more tools 150 or components to facilitate stimulation of the formation 130. Non-limiting examples of the tools 150 included in the borehole string 140 include a fracturing assembly (e.g., a fracture or “frac” sleeve device), a perforation assembly (e.g., shaped charges, torches, projectiles and other devices for perforating the borehole wall and / or casing), and isolation or packer subs.

[0035] One or more of the tools 150 may include suitable electronics or processors configured to communicate with a surface processing unit (e.g., a computing device 105) and / or control the respective tool 150 or assembly. One or more tools 150 may be included, for example, in a bottom hole assembly (BHA) 151.

[0036] The system 100 includes surface equipment 110 for performing various energy industry operations. For example, the surface equipment 110 is configured for injection of fluids into the borehole 135 in order to, e.g., fracture the formation 130. In one or more embodiments, the surface equipment 110 includes an injection device such as a high pressure pump 115 in fluid communication with a fluid tank 120, mixing unit or other fluid source or combination of fluid sources. The pump 115 injects fluid into the borehole string 140 or the borehole 135 to introduce fluid into the formation 130, for example, to stimulate and / or fracture the formation 130. The pump 115 may be located downhole or at a surface location.

[0037] One or more flow rate and / or pressure sensors 125 may be disposed in fluid communication with the pump 115 and the borehole string 140 for measurement of fluid65TEL-510231-WO-2_INT1027PCT characteristics. The sensors 125 may be positioned at any suitable location, such as proximate to (e.g., at the discharge output) or within the pump 115, at or near the wellhead, or at any other location along the borehole string 140 or the borehole 135. The sensors described herein are exemplary, as various types of sensors may be used to measure various parameters.

[0038] A computing device 105 (e.g., computing device 105-a) may be disposed in operable communication with components such as sensors 125 located above the surface, the pump 115, and / or downhole components. For example, the computing device 105 may be in operable communication with sensors (e.g., pressure sensors, temperature sensors, vibration sensors, gas sensors, and the like) located below the surface and / or in the borehole string 140. In some examples, the computing device 105 may be in operable communication with a tool 150 (or multiple tools).

[0039] The system 100 supports communication between the computing device 105 and other devices of the system 100 via wired communication protocols, wireless communication protocols (e.g., electromagnetic (EM) signals, WiFi, Bluetooth™, ZigBee™, Ubiquiti™, 3G, 4G, 5G, LTE, and the like), and / or combinations including one or more of the foregoing.

[0040] The system 100 supports telemetry techniques capable of transmitting data from components located downhole to the surface and / or surface equipment 110. Non- limiting examples of the telemetry techniques include acoustic telemetry or mud pulse (MP) telemetry supportive of transmitting information by generating vibrations in fluid in the borehole 135, electromagnetic (EM) telemetry supportive of transmitting information by way of signals that propagate at least in part through the earth (e.g., through formations 130). Other non-limiting examples of telemetry techniques supported by aspects of the present disclosure include the use of hardwired drill pipe, fibre optic cable, or drill collar acoustic telemetry to carry data to the surface and / or surface equipment 110.

[0041] The system 100 may include one or more repeater nodes 170 supportive of communicating data along the borehole string 140 (e.g., up or down the borehole string 140). In one or more embodiments, the repeater nodes 170 may be implemented in the borehole 135 or a communication borehole (not illustrated) separate from the borehole 135. In some examples, the one or more repeater nodes 170 may provide functionality as wireless access nodes for repeating or relaying data from a tool 150 to the surface (e.g., to a computing device 105).

[0042] In one or more embodiments, the system 100 may include a chain of repeater nodes 170 spaced apart along the borehole string 140, and the chain of repeater nodes 17065TEL-510231-WO-2_INT1027PCT may support repeating of data in a unidirectional (e.g., downhole to surface or surface to downhole) or bidirectional manner. For example, a repeater node 170 (or chain of repeater nodes 170) may support the communication of data between a computing device 105 and a tool 150, and the like.

[0043] The system 100 may include one or more electrically insulating gap subs 155 (also referred to herein as insulating joints or connectors) supportive of improving EM transmission in the downhole and uphole directions. For example, the borehole string 140 may be divided into multiple (e.g., two, three, or more) conductive sections by including one or more gap subs 155 in the borehole string 140. In some cases (not illustrated), a gap sub 155 may be placed at the top of BHA 151 such that metallic drill pipe in the borehole string 140 above the BHA 151 serves as an antenna element and metallic sections in the BHA serve as another antenna element. Example aspects of the gap subs 155 are described with reference to FIGS.5 through 7.

[0044] Accordingly, for example, the communication protocols and telemetry techniques supported by the system 100 enable communication between computing devices 105 (e.g., computing device 105-a, computing device 105-b, and the like) and downhole components.

[0045] The computing device 105 is configured to receive, store and / or transmit data generated from components (e.g., pump 115, fluid tank 120, sensors 125, and the like) included in the surface equipment 110 and / or downhole components (e.g., a tool 150, downhole sensors, BHA 151, and the like). The computing device 105 includes processing components configured to analyze received data (e.g., data received from the pump 115, fluid tank 120, sensors 125, a tool 150, and the like). The computing device 105 includes processing components configured to provide data (and / or control signals to other components of the system 100. The computing device 105 includes any number of suitable components, such as processors, memory, communication devices and power sources.

[0046] In accordance with one or more embodiments of the present disclosure, a data telemetry system is provided that supports the communication of data 165 along a borehole string 140 in either direction (e.g., upwards towards the surface, downwards towards the tool 150) by providing a chain of repeater nodes 170 spaced apart along the borehole string 140. The data 165 may be generated or provided by components (e.g., a computing device 105, surface equipment 110, a tool 150, BHA 151, or a repeater node 170) of the system 100. In some examples, the data 165 may include MWD data provided by the BHA 151 and / or tool 150. In some other examples, the data 165 may include commands (e.g., signaling) associated65TEL-510231-WO-2_INT1027PCT with controlling the tool 150 and / or the BHA 151. In some other examples, the data 165 may include measurements of formation properties as described herein.

[0047] In accordance with one or more embodiments of the present disclosure, each repeater node 170 may be electrically coupled to a respective gap sub 155. The data telemetry system supports features for shorting out gaps at one or more gap subs 155 (and effectively bypassing respective repeater nodes 170) via controllable switches in order to mitigate or bypass formations that prohibit effective EM transmission, example aspects of which will be described herein. In some examples, the data 165 may include commands (e.g., signaling) associated with controlling a repeater node 170 (e.g., controlling the switches of the repeater node 170).

[0048] FIG.2A illustrates schematically a borehole string 140 including a communication system 171 supportive of communicating data 165 to and from surface equipment 110 (and / or a computing device 105) by way of one or more repeater nodes 170 that are spaced apart along borehole string 140. The communication system 171 supports unidirectional (e.g., downhole to surface, or surface to downhole) and bidirectional data communication.

[0049] The communication system 171 supports the communication of signals carrying the data 165. In some examples, the data 165 may be generated by tool 150 and / or the repeater nodes 170, and the communication system 171 supports the transmission of the data 165 to surface equipment 110 (and / or computing device 105). The communication system 171 supports the transmission of other data (e.g., control signals) from the surface equipment 110 and / or computing device 105 to the tool 150 via the repeater nodes 170.

[0050] The signals may be EM telemetry signals generated using modulation techniques capable of encoding the data 165. Non-limiting examples of the modulation techniques include phase shift keying, quadrature phase shift keying (QPSK), binary phase shift keying (BPSK), amplitude phase shift keying (APSK), frequency-shift keying (FSK), quadrature amplitude modulation (QAM), 8 amplitude shift keying (8ASK), and the like. Aspects of the present disclosure are not limited thereto, and the communication system 171 may support communication techniques including any combination of changes in phase, amplitude, timing of pulses, and frequency suitable for communicating the data 165. Example aspects of frequencies used by the repeater nodes 170 in association with communicating the data 165 are later described herein.

[0051] A PSK (phase-shift keying) encoding scheme may use a number of cycles (at a current frequency) to transmit each symbol. The number of cycles used to transmit each65TEL-510231-WO-2_INT1027PCT symbol may be varied. For example, in low-noise environments, the communication system 171 is capable of successfully transmitting (e.g., meet target transmission criteria) EM telemetry symbols using two cycles per symbol. In higher noise environments, the communication system 171 may be configured to use three cycles (or more) to transmit each symbol. In some implementations, the communication system 171 may select the number of cycles to be used to encode a symbol based on a measured signal-to-noise ratio (SNR).

[0052] The communication system 171 may include a series of repeater nodes 170 (EM telemetry repeaters) spaced apart along and capable of carrying data along borehole string 140, and the communication system 171 supports various modes of communication. For example, the communication system 171 supports an ‘echo’ mode in which each repeater node 170 receives and records a block of data (e.g., data 165), for example from one or more other repeater nodes 170.

[0053] After receiving the block of data, the repeater node 170 may retransmit the block of data. In some cases, the echo mode may introduce latency, since a repeater node 170 transmitting according to the echo mode transmits after having received a block of data, and data blocks are transmitted at spaced apart times to allow time for a repeater node 170 to retransmit the data of a given block of data before starting to receive data for the next data block. In a ‘continuous’ mode, each repeater node 170 may receive and transmit data simultaneously.

[0054] Modes of operation supported by the communication system 171 and the repeater nodes 170 can differ in the degree to which received signals are processed.

[0055] In some modes, a repeater node 170 may operate by decoding received signals to extract the data encoded in the received signals and optionally performing error correction using error correction information (e.g., parity or cyclic redundancy check (CRC) information) encoded in the received signals. The repeater node 170 may then reencode and retransmit the received signals (including the extracted data). In some cases, reencoding and retransmission may introduce some latency, and a repeater node 170 may include circuits for decoding and encoding received data. In such example modes, the transmitted signal may differ from the received signal in various ways including, for example, frequency, data encoding scheme, and / or data content. Such differentiation between the received and transmitted signals may beneficially reduce feedback from the transmitted signal to the received signal and / or may be applied to adapt transmitted signals for improved reception in view of formation properties between a repeater node 170 and another repeater node 170 (e.g., a subsequent repeater node 170 included among the communication system 171). In65TEL-510231-WO-2_INT1027PCT some aspects, a repeater node 170 may include processing circuitry configured to detect whether data extracted from a received signal has been corrupted, and the repeater node 170 may transmit or refrain from transmitting the corrupted data.

[0056] In some modes of operation supported by the communication system 171, a repeater node 170 may refrain from decoding a signal and / or received data, and the repeater node 170 may instead characterize and retransmit the received data signal. For example, a repeater node 170 may detect a waveform (e.g., a cycle of a sine wave) in a received EM telemetry signal and recreate the waveform including features of the waveform (e.g., phase shifts) that encode data. In some embodiments, the repeater node 170 may recreate the waveform based on a priori knowledge of the nature of signals. In some cases, each repeater node 170 may be informed of the communication modality (or be capable of informing other repeater nodes 170 of the communication modality) through one or more signaling techniques.

[0057] In an example, the communication system 171 may be configured such that EM telemetry signals being transmitted by repeater nodes 170 are sine waves of a given frequency or frequencies. A repeater node 170 may be configured to search for such sine waves in received signals. Such example communication modes can have the advantage of reduced latency. In such modes, for example, a repeater node 170 may recreate the waveform (e.g., sine waves) such that the recreated waveform is substantially the same as (or different in part from) the waveform detected in the received signal. For example, the waveform of a signal transmitted by a repeater node 170 may be configured to differ from the waveform of a signal received by the repeater node 170 with respect to frequency, number of cycles per bit, and / or other suitable parameters supportive of the techniques described herein.

[0058] According to one or more embodiments of the present disclosure, a repeater node 170 may be configured to operate in a single mode described herein. In one or more additional and / or alternative embodiments, the repeater node 170 may be switchable or reconfigurable to operate in two or more different modes described herein. In some embodiments, repeater nodes 170 of the communication system 171 are configured for unidirectional communication (e.g., transmitting data in an uphole direction or transmitting data in a downhole direction) or for bidirectional operation. The communication system 171 may be implemented using repeater nodes 170 of any suitable mode or configuration described herein.

[0059] Referring to the example of FIG.2A, six transmission frequencies are used. Three transmission frequencies F1D, F2Dand F3Dare used for data transmission in the65TEL-510231-WO-2_INT1027PCT downhole direction and three transmission frequencies F1U, F2Uand F3Uare used for data transmission in the uphole direction. In an example, the repeater nodes 170 may cycle among the transmission frequencies moving along borehole string 140 such that, for example, each repeater node 170 may respectively transmit according to a subsequent transmission frequency. The receiver 305 (cf. FIG.3) of each repeater node 170 is configured to receive signals according to a downhole transmission frequency used by an adjacent repeater node 170 located in a direction uphole of the repeater node 170. The receiver 305 of each repeater node 170 is configured to receive signals according to an uphole transmission frequency used by an adjacent repeater node 170 located in a direction downhole of the repeater node 170.

[0060] Other embodiments supported by aspects of the present disclosure include using different quantities of transmission frequencies. For example, FIG.2B illustrates an example in which four transmission frequencies are used. Two transmission frequencies F1D, F2Dare used for data transmission in the downhole direction and two transmission frequencies F1U, F2U are used for data transmission in the uphole direction.

[0061] FIG.2C illustrates an example implementation in which four transmission frequencies F1, F2, F3 and F4 are used for both data transmission in the downhole direction and data transmission in the uphole direction. Accordingly, for example, FIGS.2A through 2C illustrate examples of a variable frequency mode supported by the communication system 171, example aspects of which are later described herein.

[0062] FIG.2D illustrates an example implementation of a continuous mode supported by the communication system 171. In an example of the continuous mode, a continuous frequency F1 is used for data transmission in the uphole direction and a continuous frequency F2 is used for data transmission in the downhole direction. Example aspects of the continuous mode are later described herein.

[0063] In some embodiments, the communication system 171 supports reconfiguration of the frequencies at which repeater nodes 170 receive and / or transmit signals while the repeater nodes 170 are downhole. Each repeater node 170 (or a subset of the repeater nodes 170) may monitor (in real-time) factors such as, for example, properties of the earth formation surrounding the repeater node 170, power constraints, signal levels, or the like. Based on the factors, each repeater node 170 may dynamically configure the frequencies at which the repeater node 170 receives and / or transmits signals. In some embodiments, based on the factors, each repeater node 170 may dynamically configure the power level at which the repeater node 170 transmits signals. In some embodiments, based on the factors,65TEL-510231-WO-2_INT1027PCT each repeater node 170 may dynamically open or close one or more switches (e.g., switches 412 later described with reference to FIGS.6A through 6C).

[0064] For example, in response to a repeater node 170 detecting a high resistivity of an earth formation, the repeater node 170 may adjust (e.g., reduce) the transmission frequency to reduce signal attenuation by the earth formation of a signal transmitted by the repeater node 170. Additionally, or alternatively, the repeater node 170 may adjust (e.g., increase to a higher frequency band) the transmission frequency so as not to disrupt the signal transmission by an adjacent repeater node 170. Additionally, or alternatively, the repeater node 170 may adjust the receiving frequency at which the repeater node 170 receives signals so as to improve reception of signals at the repeater node 170.

[0065] In some embodiments, the repeater node 170 may activate a switch (e.g., a switch 412 later described with reference to FIGS.6A through 6C) in association with shorting a gap corresponding to a transceiver (within the context of this disclosure, a “transceiver” is to be understood as a component that includes a receiver, a transmitter, or both - i.e., a “transceiver” is to be understood as a component that includes a transmitter, a receiver, or both, or a component that can act as a receiver, a transmitter, or - simultaneously or subsequently - as a transmitter and a receiver) of the repeater node 170, such that the repeater node 170 is bypassed in association with retransmitting a signal along borehole string 140.

[0066] Additionally, or alternatively, the repeater node 170 may provide data indicating the high resistivity of the earth formation to one or more other repeater nodes 170 (e.g., by broadcasting the data, directly transmitting the data, or the like). Based on the data, the other repeater node(s) 170 may dynamically configure the frequencies at which the other repeater node(s) 170 receives and / or transmits signals (e.g., operating frequencies and / or sampling frequencies). In some embodiments, based on the data, the other repeater node(s) 170 may activate a switch (e.g., switch 412 of FIGS.6A through 6C) in association with shorting a gap corresponding to a first transceiver (e.g., a transmitter) or a second transceiver (e.g., a receiver) of the other repeater node 170.

[0067] In some embodiments, the repeater nodes 170 may exchange collected real- time data with other repeater nodes 170. Example aspects of the exchange of collected real- time data are later described herein.

[0068] FIG.3 illustrates a block diagram 300 of a repeater node 170 in accordance with one or more embodiments of the present disclosure.65TEL-510231-WO-2_INT1027PCT

[0069] As shown in FIG.3, repeater node 170 includes an EM telemetry receiver 305, an EM telemetry transmitter 315, and electronic circuitry 310 (also referred to herein as electronics). In one or more embodiments, (not illustrated), receiver 305 and transmitter 315 may be housed in separate housings. In another example, the repeater node 170 may be implemented without the housings. The receiver 305, electronic circuitry 310, and transmitter 315 may be electrically coupled via one or more busses (e.g., data bus 490 later described herein) included in the repeater node 170.

[0070] The electronic circuitry 310 may receive data from the receiver 305 and control the transmitter 315 to retransmit the received data. In some aspects, the repeater node 170 may retransmit the received data, with or without modifying the data. Electronic circuitry 310 is configured to receive from and / or provide data to receiver 305 and transmitter 315, control receiver 305 and transmitter 315, and control one or more switches (e.g., switches 412 of FIG.6A through 6C and FIG.7) as described herein.

[0071] In one or more embodiments, the receiver 305 may be a standalone receiver circuit, and transmitter 315 may be a standalone transmitter circuit. In one or more additional and / or alternative embodiments, receiver 305 and transmitter 315 may be integrated in a single transceiver. In one or more additional and / or alternative embodiments, receiver 305 may be implemented in a first transceiver (e.g., transceiver 405 of FIG.4), and transmitter 315 may be implemented in a second transceiver (e.g., transceiver 415 of FIG.4).

[0072] Non-limiting examples of modifying the received data as supported by a repeater node 170 are described herein. The repeater node 170 supports modifying received data in accordance with one or more of the examples described herein. In one or more embodiments, the repeater node 170 may modify the received data by correcting one or more errors in the received data using, for example, error correction codes included in the data. In one or more additional and / or alternative embodiments, the repeater node 170 may add, to the received data, data identifying the repeater node 170, data from sensor(s) integrated with or connected to repeater node 170, and / or temporal information (e.g., a time stamp) associated with the received data.

[0073] In one or more additional and / or alternative embodiments, the repeater node 170 may reduce the size of the received data, for example, by applying data compression operations and / or reducing a resolution of the received data. In one or more additional and / or alternative embodiments, the repeater node 170 may modify a data format of the received data. In one or more additional and / or alternative embodiments, the repeater node 170 may65TEL-510231-WO-2_INT1027PCT reorder data included in a received signal prior to retransmitting the data in a subsequent signal, for example, to prioritize certain data over other data.

[0074] In accordance with one or more embodiments of the present disclosure, the communication system 171 supports a continuous mode in which repeater nodes 170 are configured to simultaneously transmit and receive signals carrying data (e.g., such that respective temporal periods associated with transmitting the signals at least partially overlap). In one or more embodiments, the continuous mode may be facilitated by using separate respective antenna elements (e.g., separate electrically-insulating gaps 144 (e.g., later illustrated at FIG.6A through 6C and FIG.7) in the borehole string 140) for transmitting and receiving. In one or more additional and / or alternative embodiments, the communication system 171 may facilitate the continuous mode through one or more anti-feedback schemes as discussed herein.

[0075] In some example embodiments described herein, a repeater node 170 may receive and retransmit a signal in real-time. In some embodiments, the repeater node 170 may refrain from decoding the signal and / or refrain from extracting data from the signal. In some embodiments, the repeater node 170 may modify (e.g., clean up) a received signal before retransmitting the signal. For example, for cases in which the received signal is of a particular form (e.g., a sine wave of a known frequency with phase shifts that encode data) known by the repeater node 170, the repeater node 170 may recreate (from the received signal) a signal that has the known form of the received signal. In an example, the repeater node 170 may recreate a received signal by fitting a sinusoid of the known frequency to the received signal and locating phase changes in the received signal.

[0076] The communication system 171 may support implementations in which the transmission and receiving frequencies at a repeater node 170 are the same or different. The transmission and receiving frequencies may be selected based on one or more criteria.

[0077] In an example, for a signal to be transmitted by one repeater node 170 and received at another repeater node 170, the repeater node 170 may transmit the signal according to a frequency which mitigates the amount of signal attenuation of the transmitted signal (e.g., due to distance and / or formations between the repeater nodes 170), such that the transmitted signal may be successfully received at the other repeater node 170.

[0078] For example, EM signals tend to be attenuated as they propagate through earth formations. In general, the attenuation increases with frequency and / or depth of operation. The repeater node 170 may transmit the signal according to a target power level and a target transmission frequency (e.g., a low enough frequency) such that the signal to noise ratio65TEL-510231-WO-2_INT1027PCT (SNR) of the signal, as received at a subsequent repeater node 170 along the borehole string 140, is equal to or greater than a target SNR. In another example, for a signal to be transmitted by one repeater node 170 and received at another repeater node 170 in a repeater node chain, one or more of the repeater nodes 170 may selectively short one or more respective gaps 144 in association with achieving an effective dipole antenna effect for transmitting the signal along the drill string and / or bypassing a repeater node 170, example aspects of which are later described herein.

[0079] In one or more embodiments, the repeater node 170 transmitting a signal may configure the transmission frequency based in part on one or more factors including, but not limited thereto, the distance between repeater nodes 170, the nature (e.g., properties) of the earth formations through which borehole string 140 passes, the efficiency of the coupling of signals from transmitters 315 (of the repeater node 170 and / or other repeater nodes 170) into the borehole string 140 and earthen formations, the available transmission power of the transmitters 315 (of the repeater node 170 and / or other repeater nodes 170), the sensitivity of receivers 305 (of the repeater node 170 and / or other repeater nodes 170), and any electrical noise present. In another example, one or more repeater nodes 170 included in the repeater node may selectively short one or more respective gaps 144 based on the one or more factors.

[0080] In some EM telemetry applications where a downhole EM transmitter transmits directly to the surface from a location in a wellbore, transmission frequencies are typically set to 20 Hz or lower because of the strong attenuation at higher frequencies. In some embodiments of the present invention, repeater nodes 170 are spaced closely enough together to allow the practical use of frequencies higher than 20 Hz. For example, repeater nodes 170 are spaced apart by distances of 30 m to 600 m in some embodiments. In such cases, frequencies of up to 100 Hz or higher, such as at least a few hundred Hz or even 1 kHz or higher, such as a few kHz may be practical. In one or more embodiments, the selective shorting of gaps 144 in the borehole string 140 may effectively increase or decrease distances between active repeater nodes 170 (e.g., non-bypassed repeater nodes 170).

[0081] According to one or more embodiments of the present disclosure, additional factors may be considered where different transmission and receive frequencies are used. In an example, the communication system 171 may be selected or configured so that the transmission and receiving frequencies for a repeater node 170 are non-interfering. For example, the communication system 171 may support selecting (e.g., by a repeater node 170) the transmission and receive frequencies to differ such that a repeater node 170 may filter the transmission frequency out of a received signal (of a given receive frequency), while65TEL-510231-WO-2_INT1027PCT avoiding implementations in which the receive frequency is close to a harmonic frequency of the transmission frequency (or vice versa).

[0082] Additionally, or alternatively, the communication system 171 may support configuring and utilizing transmission frequencies and / or receive frequencies based on the direction (e.g., downhole, uphole) in which data is being transmitted. Additionally, or alternatively, the communication system 171 may support utilizing and configuring transmission frequencies and / or receive frequencies based on the depths at which repeater nodes 170 are operating. Additionally, or alternatively, the communication system 171 may support utilizing and configuring transmission frequencies and / or receive frequencies, selectively shorting one or more respective gaps 144, and the like as described herein based on formation properties measured by the repeater nodes 170.

[0083] In some cases, attenuation of EM telemetry signals can be advantageous, as the attenuation may reduce the likelihood of interference between repeater nodes 170 using the same transmission frequencies, for example, for cases in which the repeater node 170 are spaced apart by a distance supportive of reducing the interference. Accordingly, for example, the communication system 171 supports reusing the same transmission frequency (or frequencies) for parts of the borehole string 140 in which the distance between repeater nodes 170 (e.g., between two repeater nodes 170) is such that the potential for interference is mitigated due to attenuation of the signals transmitted by the repeater nodes 170.

[0084] As described herein, the techniques described herein support controlling positive feedback at a repeater node 170. For example, since the receiver 305 of a repeater node 170 is located relatively close to the transmitter 315 of the same repeater node 170, the amplitude (at the receiver 305) of the signal transmitted by transmitter 315 is typically several orders of magnitude greater than the amplitude of signals received at the receiver 305 from other repeater nodes 170.

[0085] In an example, at the receiver 305 of a repeater node 170, the amplitude of an EM signal transmitted from the transmitter 315 of the repeater node 170 may be at least thousands of times larger than the amplitudes of signals received at the receiver 305 from adjacent repeater nodes 170. For example, for a repeater node 170, the transmitter 315 may generate and transmit signals having an amplitude of 1 volt or higher, while the amplitudes of signals received at the receiver 305 from other repeater nodes 170 may be in the millivolts or microvolts. In some embodiments, for a repeater node 170, the transmitter 315 may generate and transmit signals having an amplitude between 10 volts and 50 volts. It is to be understood that the amplitudes described herein are examples, and the transmitter 315 may be configured65TEL-510231-WO-2_INT1027PCT for generating and transmitting signals of a suitable amplitude supportive of transmission efficiency described herein.

[0086] According to one or more embodiments of the present disclosure, the systems and techniques described herein address the problems associated with the output of the transmitter 315 feeding back to the input of the receiver 305 by providing and controlling one or more switches (e.g., one or more switches 412 later described with reference to FIGS.6A through 6C and FIG.7) capable of disconnecting the input of the receiver 305 and / or the output of the transmitter 315 according to one or more criteria. As later described herein, the systems and techniques described herein further support implementations using the switches such that the reception and transmission of signals at a repeater node 170 is not simultaneous and / or partially overlaps.

[0087] According to one or more embodiments of the present disclosure, techniques are described for mitigating the problems described herein in which a receiver 305 of a repeater node 170 is impacted by positive feedback due to signals being transmitted by the transmitter 315 of the same repeater node 170. The techniques may include connecting the receiver 305 across a gap in borehole string 140 and connecting the transmitter 315 across a different gap in borehole string 140. The gaps may, for example, each be provided by a gap sub 500 later described with reference to FIG.5. In some embodiments, two or more gaps may be provided by the same gap sub.

[0088] FIG.4 illustrates a block diagram 400 of a repeater node 470 configured for bidirectional communication of data in accordance with one or more embodiments of the present disclosure. The repeater node 470 includes aspects of a repeater node 170 described herein, and repeated descriptions of like elements and like features (e.g., operational modes) are omitted for brevity.

[0089] With reference to FIG.4, repeater node 470 includes EM transceivers 405 and 415 electrically coupled to electronic circuitry 410 (also referred to herein as electronics). Transceivers 405 and 415 each may be capable of receiving and / or transmitting EM telemetry data. Electronic circuitry 410 is configured to receive received data from transceivers 405 and 415 and to control transceivers 405 and 415 and one or more switches (e.g., switches 412 later described herein) to retransmit the received data. The received data may be retransmitted with or without modification in accordance with the example techniques described herein.

[0090] FIG.5 illustrates an example of a gap sub 500 in accordance with one or more embodiments of the present disclosure.65TEL-510231-WO-2_INT1027PCT

[0091] With reference to FIG.5, the communication system 171 may support EM telemetry through using parts of the borehole string 140 as an antenna. For example, the borehole string 140 may be divided into multiple (e.g., two, three, or more) conductive sections by including an insulating joint or connector (a gap sub 500) in the borehole string 140. The gap sub 500 may be placed at the top of a bottom hole assembly such that metallic drill pipe in the borehole string 140 above the BHA serves as one antenna element and metallic sections in the BHA serve as another antenna element.

[0092] The communication system 171 supports transmission of EM telemetry signals by applying electrical signals between two antenna elements. In some cases, the EM telemetry signals include low frequency AC signals (e.g., about 1 Hz to 50 Hz) applied in a manner that codes information for transmission to the surface. Those skilled in the art will appreciate that even for these low frequencies where the magnetic part is almost insignificant, the term “EM telemetry” is used as a technical term known in the art that includes all frequencies down to very low frequencies and even DC measurements (i.e., signals with an operating frequency of 0 Hz). In some examples, the communication system 171 may utilize lower frequency signals (e.g., about 1 Hz to 50 Hz and / or other suitable frequencies for preventing or mitigating signal attenuation), as lower frequency signals are less susceptible to attenuation compared to relatively higher frequency signals. The electromagnetic signals may be detected at the surface, for example by measuring electrical potential differences between the borehole string 140 or a metal casing that extends into the ground and one or more ground rods. In some other examples, the communication system 171 may use relatively higher frequency signals (e.g., frequencies between 50 Hz and 100 Hz or even 1 kHz) based on the spacing between repeater nodes 170.

[0093] Gap sub 500 includes a tubular section 510 having a bore 520 configured with fittings that support coupling the tubular section 510 in line into borehole string 140. For example, the gap sub 500 includes tool joints 530-a and 530-b. Tool joint 530-a includes a threaded box end, and tool joint 530-b includes a threaded pin end. The threads of tool joints 530-a and 530-b may, for example, include threads which satisfy American Petroleum Institute (API) standard specifications.

[0094] Gap sub 500 includes a gap 144-b spaced longitudinally apart from a gap 144- a. Each of gaps 144-a and 144-b provide electrical insulation between electrically-conductive parts 142 of section 510 on either side of the gaps 144. In the example illustrated at FIG.5, gap 144-b electrically insulates electrically-conductive part 142-c (which includes tool joint 530-a) from electrically conductive part 142-b1, and gap 144-a electrically insulates65TEL-510231-WO-2_INT1027PCT electrically-conductive part 142-b2 from electrically-conductive part 142-a (which includes tool joint 530-b). Accordingly, for example, the gaps 144 described herein further support isolating repeater nodes 170 from each other.

[0095] In an example, output terminals 360-a and 360-b of a transmitter 315 of a repeater node 170 described herein may be connected across one of gaps 144-b and 144-a, and input terminals 320-a and 320-b of a receiver 305 of the repeater node 170 may be connected across the other one of gaps 144-b and 144-a.

[0096] Some embodiments may provide three (or more) electrically-insulating gaps 144 in association with a repeater node 170. In some aspects, providing at least one additional gap 144 (e.g., gap 144-c as illustrated at FIGS.6B, 6C, and 7) between gaps used by a receiver 305 and a transmitter 315 in a repeater node 170 may support the further reduction of feedback by permitting the transmitter 315 and receiver 305 to use different references.

[0097] FIG.6A illustrates an example 600 of a repeater node 170-a in accordance with example aspects of the present disclosure. The repeater node 170-a includes aspects of a repeater node 170 (e.g., repeater node 170-a, repeater node 470) described herein, and repeated descriptions of like elements are omitted for brevity. It is to be understood that transceiver 405, electronic circuitry 410, and transceiver 415 of repeater node 170-a illustrated in FIG.6A may be implemented as receiver 305, electronic circuitry 310, and transmitter 315 as described with reference to FIG.3.

[0098] With reference to repeater node 170-a, terminals 420-a and 420-b of transceiver 405 are connected across a gap 144-a and terminals 460-a and 460-b of transceiver 415 are connected across a gap 144-b that is spaced apart from gap 144-a. In an example in which data transmissions are primarily in the downhole-to-uphole direction, gap 144-a may be downhole from gap 144-b. It is to be understood that terminals 420-a and 420-b of transceiver 405 (and similarly, terminals 460-a and 460-b of transceiver 415) may be referred as an input terminal or output terminal based on whether the transceiver 405 acts as a receiver or a transmitter.

[0099] Each of gaps 144-a and 144-b provides electrical insulation between adjacent electrically conductive parts 142 of borehole string 140 (also referred to herein as electrically conductive sections of borehole string 140). In the example of FIG.6A, gap 144-a electrically insulates parts 142-a and 142-b of borehole string 140 from one another while maintaining the mechanical integrity of borehole string 140, and gap 144-b electrically insulates parts 142-b and 142-c of borehole string 140 from one another while maintaining the mechanical integrity of borehole string 140.65TEL-510231-WO-2_INT1027PCT

[0100] In some aspects, as illustrated at FIG.6A, the systems and techniques described herein support implementing one or more switches 412 (e.g., switch 412-a, switch 412-c), and by opening or closing the switches 412, the communication system 171 may adjust the length of drill pipe (e.g., the effective length of an electrically conductive part 142) that is electrically connected to either side of a gap 144. For example, by implementing switches 412 at one or more gaps 144, the systems and techniques described herein may controllably increase or decrease the length of drill pipe that is electrically connected to either side of a gap 144.

[0101] In an example, the effective length of drill pipe connected to a transceiver 415 connected across a gap 144-b may be increased by providing an electrical switch 412 (e.g., switch 412-a) that can selectively electrically connect the conductive sections (e.g., conductive part 142-a, conductive part 142-b) of borehole string 140 on either side of an adjacent gap 144-a. In another example, the effective length of drill pipe connected to a transceiver 405 connected across a gap 144-a may be increased by providing an electrical switch 412 (e.g., switch 412-c) that can selectively electrically connect the conductive sections (e.g., conductive part 142-c, conductive part 142-b) of borehole string 140 on either side of an adjacent gap 144-b.

[0102] In some examples, increasing the length of drill pipe that is electrically connected to either side of a gap 144 may provide increased efficiency associated with transmitting EM signals (e.g., due to reduced transmission power at a transceiver 415, an associated reduction in feedback experienced at a transceiver 405, and resultant effects). In some other examples, where separate gaps 144 (e.g., 144-b and 144-a) are used for transmission and reception of EM telemetry signals, practical considerations (e.g., due to spacing, target performance criteria, or the like) may involve maintaining the length of conducting drill pipe between gaps 144-b and 144-a to be relatively short, and some gap subs 500 and repeater node 170 configurations may be implemented with a further gap 144-c (illustrated at FIG.6B) or without gap 144-c (as illustrated in FIG.6A).

[0103] In the example of FIG.6A, repeater node 170-a includes a switch 412- a connected across gap 144-a and switch 412-c connected across gap 144-b, and switches 412-a and 412-c are controllable by electronic circuitry 410 (e.g., by controller 414).

[0104] In an example of transmitting data by the repeater node 170-a of FIG. 6A, repeater node 170-a may transmit data via transceiver 415, while maintaining switch 412-c in an OFF state (an open state) and maintaining switch 412-a at the transceiver 405 in an ON state (a closed state), effectively bypassing the transceiver 405. The repeater node65TEL-510231-WO-2_INT1027PCT 170-a may then receive data from another repeater node 170 via transceiver 405, while maintaining switch 412-a in an OFF state (an open state) and maintaining switch 412-c at the transceiver 415 in an ON state (a closed state), effectively bypassing the transceiver 415. The repeater node 170-a may again set switch 412-a to the ON state (closed state) to improve transmission efficiency, retransmit the data (while maintaining switch 412-a in the closed state), and subsequently return switch 412-a to the OFF state (open state) (and, in some embodiments, return switch 412-c to the ON state (closed state) such that transceiver 405 can monitor for the next data to be received and retransmitted.

[0105] The example switching techniques described with reference to FIG.6A eliminates feedback from transceiver 415 to the corresponding transceiver 405 by causing transmissions and receptions of data at the repeater node 170-a to occur at different times. Use of a switch 412 (e.g., switch 412-a, switch 412-c) as described herein may support increased distances between repeater nodes 170 along a borehole string 140, while maintaining transmission efficiency (e.g., achieving a target transmission power and / or a target transmission frequency (for example, a low enough frequency) supportive of a target SNR, a target transmission rate, or the like).

[0106] Repeater node 170-a may include or be coupled to data bus 490. The data bus 490 supports the reduction of unwanted pickup at transceiver 405 of signals transmitted by transceiver 415. In some embodiments, the data bus 490 may carry (from the transceiver 405) data to be transmitted to transceiver 415.

[0107] Data bus 490 may include any suitable data bus such as, for example, a controller area network (CAN) BUS. In an example embodiment, data bus 490 may be a differential CANBUS. In the examples illustrated at FIGS.6A – 6C, electronic circuitry (not illustrated) including interfaces for data bus 490 are integrated with transceiver 405 and transceiver 415. Where a data bus 490 is provided, data bus 490 may carry data which has been extracted from a received signal. The transceiver 415 may reencode the data and transmit a signal comprising the data.

[0108] In another example, the data may be a digitized version of the received signal. For example, electronic circuitry 410 associated with transceiver 405 may include an analog to digital converter that samples the received signal at a sampling frequency. Electronic circuitry 410 associated with transceiver 415 may then control transceiver 415 to transmit a replica of the received signal. The replica may, for example, be an amplified version of the received signal. In an example, the transceiver 415 (and / or electronic circuitry 410) may generate the replica of the received signal by processing the received signal. In one65TEL-510231-WO-2_INT1027PCT or more embodiments, processing of the received signal may include phase shifting and / or cleaning up of the received signal.

[0109] Data bus 490 may be a wired or wireless communication bus. For example, data bus 490 may include a wireless interface which may include wireless interfaces such as, for example, WiFi, Bluetooth™, ZigBee™, Ubiquiti™, 3G, 4G, 5G, LTE, or the like.

[0110] In another example embodiment, data bus 490 may be replaced with an analog connection which carries the received signal in analog form. For example, data bus 490 may support communication of analog signals between transceiver 405, electronic circuitry 410, and transceiver 415. In one or more embodiments, data bus 490 may support transmission and reception of digital and / or analog signals.

[0111] The communication system 171 supports multiple gaps 144 for use by a repeater node 170, and the gaps 144 may be implemented by a single drill string component or gap sub 500 in some embodiments, example aspects of which are later described herein.

[0112] FIG.6B illustrates an example 601 of a repeater node 170-b further including an electrically insulating gap 144-c. When gap 144-c is present, transceiver 405 has terminals 420-a and 420-b connected at different respective sides of gap 144-a, transceiver 415 has terminals 460-a and 460-b connected at different respective sides of gap 144-b, and gap 144-c is provided in borehole string 140 between gaps 144-a and 144-b. Gap 144-c electrically isolates terminals 420-a and 420-b of transceiver 405 from terminals 460-a and 460-b of transceiver 415.

[0113] Gap 144-c, illustrated in the examples of FIG.6B, FIG.6C, and FIG. 7, may support increased feedback reduction as described herein. Gap 144-c allows an interface between the reference point (e.g., conductive part 142-b2) of the transceiver 405 and the reference point (e.g., conductive part 142-b1) of the transceiver 415. In FIG.6B, an electrical switch 412-b is provided that is coupled to borehole string 140 at terminal 440-a and terminal 440-b.

[0114] In some embodiments, as illustrated at FIG.6B, the effective length of drill pipe connected to a transceiver 415 connected across gap 144-b may be increased by providing electrical switch 412-b that can selectively electrically connect conductive sections (e.g., conductive part 142-b1 and conductive part 142-b2 separated by gap 144-c) of borehole string 140, and further, by providing electrical switch 412-a that can further selectively electrically connect conductive sections (e.g., conductive part 142-b2, conductive part 142-a) of borehole string 140.65TEL-510231-WO-2_INT1027PCT

[0115] Similarly, for example, the effective length of drill pipe connected to a transceiver 405 connected across gap 144-a may be increased by controlling electrical switch 412-b to electrically connect conductive sections (e.g., conductive part 142-b1, conductive part 142-b2) of borehole string 140, and further, by controlling electrical switch 412-c to electrically connect conductive sections (e.g., conductive part 142-b1, conductive part 142-c) of borehole string 140.

[0116] Fig.6C illustrates an example 602 of a repeater node 170-c in accordance with example aspects of the present disclosure. The repeater node 170-c includes aspects of a repeater node 170 (e.g., repeater node 170-a, repeater node 170-b, repeater node 470) described herein, and repeated descriptions of like elements are omitted for brevity.

[0117] Referring to FIG.6C, the repeater node 170-c may include filters 411-a and 411-b respectively connected across gaps 144-a and 144-b. Filter 411-a has a pass band corresponding to the transmission frequency of transceiver 415 or to the frequency (such as an operating frequency or a carrier frequency) of a signal received by transceiver 415, and filter 411-b has a pass band corresponding to the transmission frequency of transceiver 405 or to the frequency of a signal received by transceiver 405.

[0118] Filter 411-a may reduce amplitudes of signals with selected frequencies (e.g., signals transmitted by transceiver 415 of the same or a different gap sub 155) as received at transceiver 405 and / or amplitudes of electrical noise present in signals received by transceiver 405, thereby enabling the transmission of signals from transceiver 415 at higher power / higher amplitude and improving the distance over which signals transmitted by transceiver 415 can be detected. Similarly, for example, filter 411-b may reduce amplitudes of signals (e.g., signals transmitted by transceiver 405) as received at transceiver 415 and / or amplitudes of electrical noise present in signals received by transceiver 415, thereby enabling the transmission of signals from transceiver 405 at higher power / higher amplitude and improving the distance over which signals transmitted by transceiver 405 can be detected by other repeater nodes 170.

[0119] In one or more embodiments, the filters 411 may be bandpass filters implemented in hardware or firmware / software. In an example in which gap 144-a is downhole from gap 144-b, uplink data may be received at transceiver 405, processed and sent by electronics 410 to transceiver 415 and retransmitted by transceiver 415, and downlink data may be simultaneously received at transceiver 415, processed and sent by electronics 410 to transceiver 405 and retransmitted by transceiver 405.65TEL-510231-WO-2_INT1027PCT

[0120] With reference to FIGS.6A through 6C, in some embodiments, gaps 144-a and 144-b used by a repeater node 170 (e.g., repeater node 170-a, repeater node 170-b) are spaced apart along borehole string 140 from one another by a distance up to about 10 meters. In some example embodiments, gaps 144-a and 144-b may be spaced apart along borehole string 140 from one another by a distance of up to 30 meters. In some embodiments associated with a gap sub 155 (e.g., gap sub 155-a) having dual gaps 144, the distance between gaps 144-a and 144-b may be selected and / or modified to achieve a target amount of positive feedback at transceiver 405 and / or transceiver 415. In some embodiments associated with a gap sub 155 (e.g., gap sub 155-b) having three gaps 144, the distance between gaps 144-a, 144-b, and 144-c may be selected and / or modified to achieve a target amount of positive feedback at transceiver 405 and / or transceiver 415.

[0121] Optionally, the frequency band of a wireless interface and / or the distance between gaps 144-a, 144-b, and / or 144-c of one or more repeater nodes 170 in a repeater node chain may be adaptively altered to sustain reliable communication (e.g., based on data rate, signal integrity, SNR, and the like) between transceivers 405 and 415 of the same repeater node 170 or different repeater nodes 170, example aspects of which are later described with reference to FIG.7.

[0122] According to one or more embodiments of the present disclosure, as described with reference to FIGS.6A through 6C, a repeater node 170 (e.g., repeater nodes 170-a, 170-b, 170-c) may include a first transceiver 405, where terminals 420 of the first transceiver 405 are coupled to a borehole string 140 at locations associated with a first electrically insulating gap 144-a included in the borehole string 140. The repeater node 170 may include a second transceiver 415, where second terminals 460 of the second transceiver 415 are coupled to the borehole string 140 at locations associated with a second electrically insulating gap 144-b included in the borehole string 140. The repeater node 170 may include control circuitry (e.g., controller 414) configured to control switching circuitry (e.g., switches 412 and associated circuitry in electronics 410 to control and power switches 412) coupled to the borehole string 140, where the switching circuitry is associated with at least one of the first electrically insulating gap 144-a and the second electrically insulating gap 144-b.

[0123] In some aspects, the first transceiver 405 is receptive of a first EM signal including data (e.g., MWD data), where the first EM signal comprises a first frequency (e.g., a first operating frequency or a first carrier frequency). In some aspects, the second transceiver 415 is configured to transmit a second EM signal including the data based on the first EM signal, where the second EM signal is of a second frequency (e.g., a second65TEL-510231-WO-2_INT1027PCT operating frequency or a second carrier frequency, for example, a frequency higher than the first frequency). In some examples, the first transceiver 405 and the second transceiver 415 are configured to transmit or receive a third EM signal including second data associated with the control of the switching circuitry, where the third EM signal is of a third frequency (e.g., a third operating frequency or a third carrier frequency) different from at least one of the first frequency and the second frequency.

[0124] The repeater node 170 may include a data bus 490 coupled to the first transceiver 405 and the second transceiver 415, where the first transceiver 405 and the second transceiver 415 and electronics 410 are configured to transmit or receive data, e.g., received data to be re-transmitted or data associated with the control of the switching circuitry, via the data bus 490.

[0125] In some aspects, the data bus 490 is coupled to the control circuitry and the switching circuitry, where the control circuitry is configured to provide one or more data signals to the switching circuitry via the data bus 490 in association with controlling the switching circuitry.

[0126] In some aspects, the control circuitry is configured to control the switching circuitry based on a target effective gap length associated with the borehole string 140.

[0127] The repeater node 170 may include sensing circuitry (not illustrated) configured to determine one or more properties of a formation, where the control circuitry is configured to control the switching circuitry based on the one or more properties.

[0128] In some aspects, the switching circuitry includes a first switch 412-a associated with the first electrically insulating gap 144-a, where the first switch 412-a is configured to couple the terminals 420 of the first transceiver 405 based on one or more signals provided by the control circuitry. In some aspects, the switching circuitry includes a second switch 412-b associated with the second electrically insulating gap 144-b, where the second switch 412-b is configured to couple the second terminals 460 of the second transceiver 415 based on the one or more signals provided by the control circuitry.

[0129] In some aspects (e.g., with reference to repeater node 170-b of FIG. 6B), the switching circuitry includes a switch 412-b associated with a third electrically insulating gap 144-c included in the borehole string 140. In an example, the switch 412-b is configured to couple a first portion (e.g., conductive part 142-b1) of the borehole string 140 associated with the third electrically insulating gap 144-c and a second portion (e.g.,65TEL-510231-WO-2_INT1027PCT conductive part 142-b2) of the borehole string 140 associated with the third electrically insulating gap 144-c based on one or more signals provided by the control circuitry.

[0130] In an example, the third electrically insulating gap 144-c is between the first electrically insulating gap 144-a and the second electrically insulating gap 144-b in a direction parallel to the borehole string 140.

[0131] In some aspects, the repeater node 170 is configured to transmit, via the first transceiver 405 or the second transceiver 415, one or more signals including an indication of a state of the switching circuitry. In some aspects, a frequency associated with the one or more signals is different from at least one of: a first frequency of a first EM signal received at the first transceiver 405; and a second frequency of a second EM signal transmitted by the second transceiver 415.

[0132] In some aspects, the repeater node 170 is configured to receive, via the first transceiver 405 or the second transceiver 415, one or more signals including an indication of a target state of the switching circuitry. In an example, a frequency associated with the one or more signals is different from at least one of: a first frequency of a first EM signal received at the first transceiver 405; and a second frequency of a second EM signal transmitted by the second transceiver 415.

[0133] Fig.7 illustrates an example 700 of a repeater node configuration of a communication system 171 in accordance with one or more embodiments of the present disclosure.

[0134] In the example of FIG.7, the repeater node configuration includes repeater nodes 170-b1 through 170-b3. Repeater nodes 170-b1 through 170-b3 include aspects of a repeater node 170 (e.g., repeater node 170-a through 170-c, repeater node 470, etc.) described herein, and gap subs 155-c through 155-e include aspects of a gap sub 155 (e.g., gap sub 155-a, gap sub 155-b, gap sub 500) described herein, and repeated descriptions of like elements are omitted for brevity.

[0135] In the example of FIG.7, each repeater node 170 is illustrated as having three switches 412 respectively corresponding to three electrically insulating gaps 144. However, aspects of the present disclosure are not limited thereto, and each repeater node 170 may include any suitable quantity (e.g., two, three, more than three) of switches 412 corresponding to a respective quantity (e.g., two, three, more than three) of electrically insulating gaps 144. In an example implementation different from FIG.7, (not illustrated), gap sub 155-c may omit electrically insulating gap 144-c, and repeater node 170-b1 may omit switch 412-c.65TEL-510231-WO-2_INT1027PCT

[0136] According to one or more embodiments of the present disclosure, as described with reference to FIG.7, the communication system 171 includes a set of repeater nodes 170 (e.g., repeater node 170-a through repeater node 170-c). Each repeater node 170 (e.g., repeater node 170-b1) of the set of repeater nodes 170 includes a first transceiver 405, where terminals 420 of the first transceiver 405 are coupled to a borehole string 140 at locations associated with a first electrically insulating gap 144 (e.g., gap 144-a) included in the borehole string 140. Each repeater node 170 includes a second transceiver 415, where second terminals 460 of the second transceiver 415 are coupled to the borehole string 140 at locations associated with a second electrically insulating gap 144 (e.g., gap 144-b) included in the borehole string 140. Each repeater node 170 includes control circuitry (e.g., controller 414-a) configured to control switching circuitry (e.g., switch 412-a, switch 412-b, or the like) coupled to the borehole string 140, where the switching circuitry is associated with at least one of the first electrically insulating gap 144 and the second electrically insulating gap 144.

[0137] In some aspects, control of respective switching circuitry of the set of repeater nodes 170 is associated with bypassing transmission of signals by at least one repeater node 170 of the set of repeater nodes 170. For example, with reference to repeater node 170-b2, closing switch 412-d of repeater node 170-b2 may effectively bypass the ability of repeater node 170-b2 to receive signals, and further, retransmit any signals transmitted by other repeater nodes 170 should switch 412-d remain closed for a temporal period greater than a threshold amount. Advantageously, all switches 412 of one particular repeater node 170 may be closed if the repeater node (such as 170-b2) is bypassed. Closing all switches 412-d through 412-f of repeater node 170-b2 has the effect that gap sub 155-d has no electrical effect and the other gap subs (such as gap subs155-c and 155-e) may be operated as if gap sub 155-d was not installed in borehole string 140.

[0138] In some aspects, control of respective switching circuitry of the set of repeater nodes 170 is associated with configuring an effective antenna length associated with at least one second repeater node 170 of the set of repeater nodes 170. For example, with reference to repeater node 170-b1 and repeater node 170-b2, closing switch 412-a at repeater node 170-b1 (alone, or in combination with further closing switch 412-b or further closing switch 412-b and switch 412-c) may increase an effective antenna length associated with the transceiver 405-b of repeater node 170-b2. In another example, with reference to repeater node 170-b2 and repeater node 170-b3, closing switch 412-g at repeater node 170-b3 (alone, or in combination with further closing switch 412-h or further closing switch 412-h and65TEL-510231-WO-2_INT1027PCT switch 412-i) may increase an effective antenna length associated with the transceiver 415-b of repeater node 170-b2.

[0139] In some aspects, the first transceiver 405 is receptive of a first EM signal including data (e.g., MWD data), where the first EM signal is of a first frequency. In some aspects, the second transceiver 415 is configured to transmit a second EM signal including the data based on the first EM signal, where the second EM signal is of a second frequency (e.g., a frequency higher than the first frequency).

[0140] In some aspects, the first transceiver 405 and the second transceiver 415 are configured to transmit or receive a third EM signal including second data associated with the control of the switching circuitry, where the third EM signal is of a third frequency different from at least one of the first frequency and the second frequency.

[0141] In some examples, the third EM signal may include real-time data including formation properties described herein. In some other examples, the real-time data may include an indication of whether a repeater node 170 has updated its own transmission frequency and / or transmission power, activated a switch 412 associated with shorting a gap 144 respective to the repeater node 170, or the like. In some examples, the real-time data may include a request for another repeater node 170 to update the transmission frequency and / or transmission power of the other repeater node 170, a request for the other repeater node 170 to activate a switch 412 associated with shorting a gap 144 respective to the other repeater node 170, or the like.

[0142] In some embodiments, the repeater nodes 170 may exchange the real- time data (e.g., formation properties, current transmission frequency and / or transmission power, requested transmission frequency and / or transmission power, current switch states, request for a switch state, and the like) via wireless communication as described herein. Each repeater node 170 may be coupled to a respective communication bus (e.g., communication bus 490-1, communication bus 490-2, communication bus 490-3, or the like) which supports communication among components of the repeater node 170.

[0143] In one or more embodiments, the control circuitry is configured to control the switching circuitry (e.g., one or more of switch 412-a through switch 412-c) of the repeater node 170, second switching circuitry (e.g., one or more of switch 412-d through switch 412-i) of at least one other repeater node 170 of the set of repeater nodes 170, or both based on a target effective gap length associated with the borehole string 140. For example, setting a switch 412 to an open state may increase the effective gap length of the borehole string 140. In another example, setting a switch 412 to a closed state may increase the65TEL-510231-WO-2_INT1027PCT effective distance between gaps 144, thereby increasing the effective antenna length at a transceiver 405 or a transceiver 415 of a repeater node 170, which may provide improved transmission and / or reception of signals among repeater nodes 170.

[0144] In one or more embodiments, at least one repeater node 170 of the set of repeater nodes 170 includes sensing circuitry (not illustrated) configured to determine one or more properties of a formation. In some aspects, at each device, the control circuitry is configured to control the switching circuitry based on the one or more properties.

[0145] In one or more embodiments, for a given repeater node 170 (e.g., repeater node 170-b1), the switching circuitry includes at least one of: a first switch 412 (e.g., switch 412-a) associated with the first electrically insulating gap 144 (e.g., gap 144-a), where the first switch 412 is configured to couple the terminals of the first transceiver 405 based on one or more signals provided by the control circuitry; a second switch 412 (e.g., switch 412- b) associated with the second electrically insulating gap 144 (e.g., gap 144-b), where the second switch 412 is configured to couple the second terminals of the second transceiver 415 based on the one or more signals provided by the control circuitry; and a third switch (e.g., switch 412-c) associated with a third electrically insulating gap (e.g., gap 144-c) included in the borehole string 140, where the third switch 412 is configured to couple a first portion of the borehole string 140 associated with the third electrically insulating gap 144-c and a second portion of the borehole string 140 associated with the third electrically insulating gap 144-c based on one or more signals provided by the control circuitry.

[0146] According to one or more embodiments of the present disclosure, the repeater nodes 170 further support adaptively varying distances between gaps 144 through one or more switches 412. In an example implementation, the systems and techniques described herein may include preconfiguring the communication system 171 such that the spacing between repeater nodes 170 is set up for worst-case scenarios. For example, the respective distances between repeater nodes 170 may be fixed in accordance with worst-case scenarios (e.g., worst-case attenuation due to worst-case or predicted formation properties).

[0147] In an example, the amplitude of a signal received at a repeater node 170-b2 (and transmitted by repeater node 170-b1) may be relatively high due to formation properties which permit the propagation of the signal with relatively minimal attenuation of the transmitted signal. In this example case, a switch 412-d at the transceiver 405-b of the repeater node 170-b2 and a switch 412-f at the transceiver 415-b of the repeater node 170-b2 may be utilized (e.g., switched ON or to the closed state) to bypass the repeater node 170-b2 completely and save power for the bypassed repeater node 170-b2. For example, the repeater65TEL-510231-WO-2_INT1027PCT node 170-b2 may remain in an idle mode. Once the EM friendly formation is passed (e.g., the location of the repeater node 170-b1 and / or the location of the repeater node 170-b2 with respect to the surface changes during a drilling operation), the repeater node 170-b2 may resume a standard operational mode (e.g., in which the switch 412-d and switch 412-f are switched OFF or to the open state).

[0148] According to one or more embodiments of the present disclosure, the communication system 171 may support other suitable feedback mitigation strategies which may be implemented additional and / or alternative to the switch-based feedback mitigation strategies described herein. Non-limiting examples of other feedback mitigation strategies which may be implemented at a repeater node 170 include: adaptive subtraction by a subtraction circuit included in a repeater node 170, e.g., as part of controller 414, in which the subtraction effectively reduces or eliminates feedback (at the transceiver 405) due to a signal transmitted by transceiver 415; high frequency modulation of an output signal to be transmitted by the transceiver 415 (e.g., through clock gating to yield a chopped signal, in which the clock frequency is higher than the frequency of the signal received at the transceiver 405); and phase shifting and pulse shaping of an output signal to be transmitted by a transceiver 415.

[0149] The systems and techniques described herein support an EM repeater or EM transmission system network capable of utilizing gap subs 155 for EM transmission. The systems and techniques may use multiple gap subs 155 with various receive and transmit circuitry arrangements. The techniques described herein provide provisions and methods for shorting out appropriate gaps 144 (e.g., using switches 412) in order to mitigate formations prohibitive of effective EM transmission. Additionally, or alternatively, the systems and techniques described herein provide functionality of the communication system 171 (e.g., at one or more repeater nodes 170) for measuring local formation resistivity and intercommunication between adjacent repeater nodes 170.

[0150] The intercommunication supports the ability for each repeater node 170 to warn (e.g., via signaling described herein) other repeater nodes 170 of impending EM unfriendly zones, for example, due to properties of formations included in the zones. In some aspects, each repeater node 170 may be capable of providing (e.g., via signaling described herein) other repeater nodes 170 of expected times and durations to perform gap sub shorting out mitigation behavior (e.g., for countering EM friendly zones).

[0151] As described herein, the techniques described herein support implementations using multiple gap subs 155 (e.g., at FIG.7) in which repeater nodes 17065TEL-510231-WO-2_INT1027PCT may communicate with each other to facilitate EM unfriendly formation mitigation through functionality for shorting out formation isolation gap subs 155. In some aspects, the techniques described herein provide advantages for modifying effective gap sub node length using the gap shorting function of adjacent repeater nodes 170 in the repeater node network of the communication system 171. In some other aspects, using multiple gaps 144 supports a simultaneous EM transmission scheme (e.g., as in a multi-node booster network) to not saturate a receiver (e.g., receiver 305, transceiver 405) with the signal level of an EM signal transmitted by a corresponding transmitter (e.g., transmitter 315, transceiver 415).

[0152] In accordance with one or more embodiments of the present disclosure, when a repeater node 170 (a multi-gap node) is traveling through a formation, the repeater node 170 may measure resistivity of the formation (e.g., constantly, semi-constantly, or based on other trigger criteria). Resistivity may also be measured (continuously logged while drilling) by a tool in the BHA 151 (e.g., by a tool 150, such as a LWD tool). In some aspects, the logged data may be used to configure transceivers of the EM tool, for example by opening or closing one or more of switches 412 or setting parameters for filters 411.

[0153] In an example, the detection of resistivity above a threshold value (e.g., a high resistivity) can signal the repeater node 170 to first send out a higher frequency EM communication to an adjacent repeater node 170. Accordingly, for example, the use of the higher frequency allows the inter-node communication to not disrupt lower frequency EM transmissions (e.g., of MWD data) since the higher frequency EM communication is out of band with the lower frequency EM transmissions and has a lower propagation distance. In an example, the repeater node 170 may then short out its respective transmission gap 144 (e.g., by closing one or more of switches 412) to avoid signal attenuation of the main EM telemetry from the MWD tool (e.g., tool 150) or repeater node EM communications. For example, for a repeater node 170 transmitting via a transceiver 415, the repeater node 170 may short out a gap 144 respective to the transceiver 415 by closing a corresponding switch 412.

[0154] The systems and techniques described herein for utilizing gap subs 155 for EM transmission provide advantages of obtaining a more reliable EM signal (increased reliability), particularly in deeper wells than historically possible and / or wells with EM unfriendly zones. An example advantage is that, for a case in which a transmitter or receiver associated with a gap sub 155 is no longer functional, the gap sub 155 can be shorted and operation can still be pursued (in some cases, with a reduced telemetry rate). The systems and techniques described herein support communication among repeater nodes 170 of a repeater node network that mitigates issues with poor and intermittent EM telemetry critical for65TEL-510231-WO-2_INT1027PCT drilling operations. Other example advantages provided by the techniques described herein include a reduction or prevention of EM signal loss while drilling through EM unfriendly zones. Other example advantages include increased EM communication throughput with less intermittency. The techniques described herein support power savings, as the techniques may achieve the described advantages (e.g., increased signal reliability, reduction or prevention of EM signal loss, increased EM communication throughput with less intermittency, and the like) without increasing the EM transmission power of the main MWD tool (e.g., tool 150 at BHA 151), which is different from other approaches.

[0155] The systems and techniques described herein provide solutions for cases in which, for some non-limiting implementations, the transmitter and the receiver of a repeater node are both connected across the same gap of a borehole string 140. For example, problems associated with positive feedback can be especially severe when the transmitter is transmitting at high voltage via the gap and the receiver (receiving channel) becomes saturated when attempting to receive via the same gap. The systems and techniques described herein provide a solution through the use of a double gap collar (e.g., a gap sub 155-a of FIG. 6A) in which a lowermost gap 144 (e.g., gap 144-a) is the receiver gap and the uppermost gap 144 (e.g., gap 144-b) is the transmitter gap. The receiver electronics (e.g., of transceiver 405) are able to use the isolated lowermost gap 144 to receive low voltage signals, and the transmitter electronics (e.g., of transceiver 415) are able to use the isolated uppermost gap 144 for transmission. The separation supports the prevention of saturation of signals at the receiver electronics.

[0156] The systems and techniques described herein support improved EM signal transmission through the controlled increase in length of the drill pipe connected to either side of a given gap sub 155. For example, in some repeater systems, the section of a dual gap that is used as an uphole receive and transmission reference may be relatively small even when compared to the BHA 151. The repeater scheme supported by the systems and techniques described herein includes first sensing the transmission from the below BHA 151 or a below oriented repeater node 170. For example, a repeater node 170 (disposed above the BHA 151) may sense a transmission from the BHA 151, or a repeater node 170 may sense a transmission from a below oriented repeater node 170.

[0157] In some aspects, a transmission scheme of the various repeater nodes 170 may include times when data is only transmitted (transmit periods), times when no data is transmitted and data is only received (receive periods), and times data is neither transmitted or received (delay times). Between transmit times and receive times, for example, during65TEL-510231-WO-2_INT1027PCT delay times, one or more of switches 412 may be operated to switch from an ON state to an OFF state or vice versa to prepare for the next step in the transmission scheme. For example, referring to repeater node 170-b2 and gap sub 155-d of FIG.7, the repeater node 170-b2 during a receive period may set switch 412-d to OFF status, set switch 412-f (associated with gap 144-f) to ON status, and optionally set switch 412-e (associated with gap 144-e) to ON status. The repeater node 170-b2 may then receive, via the gap sub 155-b, transmissions from gap sub 155-c (and optionally gap sub 155-e). The repeater node 170-b2 waits until transmissions are completely finished to set the switch 412-d (associated with gap 144-d) to ON, set the switch 412-f (associated with gap 144-f) to OFF, and optionally set the switch 412-e (associated with gap 144-e) to OFF. The repeater node 170-b2 may then transmits the data during transmission period. After that, the repeater node 170-b2 may then switch back to the configuration for receiving, and the cycle restarts. The repeater section could then short out an intermediate gap 144 (e.g., third electrically insulating gap 144-c of FIG.5 and FIG. 6B) used as the reference for the receive signal in the dual gap arrangement to the pipe section connected to the BHA 151 or below oriented repeater node 170 to significantly increase the dipole antenna length for uphole transmission to the surface or the next repeater node 170 located in the uphole direction.

[0158] The controlled increase in length of the drill pipe through the selective shorting of an intermediate gap 144 supports improved signal transmission (e.g., improved signal quality, increased data rate, increased signal integrity, increased SNR, reduced attenuation, and the like) and receipt of the signal at the surface (e.g., by surface equipment 110, computing device 105, or the like) or the next repeater node 170 in the repeater chain. The improved signal transmission and receipt of the signal supports a reduction in the overall quantity of repeater nodes 170, a reduction of overall cost, and a reduction in complexity associated with constructing a repeater system.

[0159] The systems and techniques described herein address complications experienced due to some approaches for transmitting EM signals through one or more repeater nodes. The systems and techniques described herein for further implementing a communication channel between the receiver and transmitter circuitry at a repeater node 170 in a triple gap sub design via data bus 490. As described in some examples herein, the communication channels may include using a differential CAN bus for communications within the repeater subsections, which supports isolation between the receiver and transmitter circuitry at a repeater node 170 in order to maintain physical separation for feedback control.65TEL-510231-WO-2_INT1027PCT

[0160] The techniques described herein for using a repeater node 170 with a triple gap (e.g., gap sub 155 having three gaps 144) in combination with a mechanical design coupled with a communications bus described herein supports continuous transmission in a repeater setup while providing increased robustness and reliability.

[0161] The systems and techniques described herein address complications of saturation experienced due to some approaches for transmitting EM signals to a repeater node in a continuous signal chain fashion. For example, in some approaches, depending on the combination of the repeater signal transmission amplitude and the repeater receiver input amplification sensitivity, the receiver input can become saturated, leading to the effect known as feedback. The feedback leads to a runaway condition of the transmitter saturating the receiver, overriding the output with an unusable signal.

[0162] Using a triple gap sub (e.g., gap sub 155-b including three gaps 144) described herein, the third gap (e.g., third electrically insulating gap 144-c) allows an interface between the receiver circuitry reference point and the transmitter circuitry reference point. The systems and techniques described herein support tuning the transmitter and receiver reference points in length. Tuning the reference points in length may result in an increased distance between the transmitter (e.g., transmitter 315, transceiver 415) and receiver (e.g., receiver 305, transceiver 405), creating an effective impedance between the two points in order to help mitigate excessive feedback from saturating the receiver input circuitry and catastrophic superposition of the input signal. The systems and techniques described herein provide advantages which allow continuous transmission in a repeater setup capable of circumventing feedback from saturating the repeater receiver input circuitry.

[0163] FIG.8 illustrates an example flowchart of a method 800 in accordance with one or more embodiments of the present disclosure. The method 800 is an example computer-implemented method that may be implemented by the example aspects of a system 100, a communication system 171, a repeater node 170, and / or a computing device 105 as described herein.

[0164] At 805, the method 800 includes controlling switching circuitry of a device (i.e., system 100, a communication system 171, a repeater node 170, and / or a computing device 105) coupled to a drill string based on one or more criteria, where the switching circuitry is coupled to a first electrically insulating gap and a second electrically insulating gap of the drill string.

[0165] In one or more embodiments, the one or more criteria includes at least one of: one or more properties of a formation; an effective antenna length associated with65TEL-510231-WO-2_INT1027PCT receiving the first EM signal or transmitting the second EM signal; and a target effective gap length of the drill string.

[0166] In one or more embodiments, the method 800 includes transmitting or receiving a data signal including second data associated with controlling the switching circuitry, a frequency of transmitted / received signals, one or more filter parameters (e.g. parameters for filter 411), or data from one or more other tools 150 (such as mud or formation resistivity or mud or formation conductivity from an LWD tool). Non-limiting examples of transmitting or receiving such a data signal are respectfully described with reference to 810 and 815 .

[0167] At 810, the method 800 includes receiving, at the device, a first electromagnetic (EM) signal including data based on a configuration of the switching circuitry, a frequency of transmitted / received signals, one or more filter parameters (e.g. parameters for filter 411), or data from one or more other tools 150 (such as mud or formation resistivity or mud or formation conductivity from an LWD tool), where the first EM signal is of a first frequency. In an example, the method 800 may include receiving the first EM signal before controlling the switching circuitry.

[0168] In some embodiments, controlling the switching circuitry at 805 may further includesetting parameters (e.g., setting filter parameters, selecting frequency, or the like), based on the data included in the first EM signal.

[0169] At 815, the method 800 includes transmitting, by the device, a second EM signal including the data based on the configuration of the switching circuitry, a frequency of transmitted / received signals, one or more filter parameters (e.g. parameters for filter 411), or data from one or more other tools 150 (such as mud or formation resistivity or mud or formation conductivity from an LWD tool), where the second EM signal is of a second frequency. In an example, the method 800 may include transmitting the second EM signal before or after controlling the switching circuitry.

[0170] In some aspects, the method 800 may restart after performing the operations described with reference to 815. For example, the process of the method 800 may restart at performing the operations described with reference to 805.

[0171] In the descriptions of the flowcharts herein, the operations may be performed in a different order than the order shown, or the operations may be performed in different orders or at different times. Certain operations may also be left out of the flowcharts, one or more operations may be repeated, or other operations may be added to the flowcharts.65TEL-510231-WO-2_INT1027PCT

[0172] In the descriptions of the flowcharts herein, the operations may be performed in a different order than the order shown, or the operations may be performed in different orders or at different times. Certain operations may also be left out of the flowcharts, one or more operations may be repeated, or other operations may be added to the flowcharts.

[0173] Set forth below are some embodiments of the foregoing disclosure:

[0174] Embodiment 1. A downhole telemetry device disposed in a borehole through a subterranean formation, the downhole telemetry device comprising: a receiver, wherein first terminals of the receiver are coupled to a drill string at locations associated with a first electrically insulating gap included in the drill string; a transmitter, wherein second terminals of the transmitter are coupled to the drill string at locations associated with a second electrically insulating gap included in the drill string; and control circuitry configured to control a switching circuitry coupled to at least one of the first terminals or the second terminals, wherein the switching circuitry is associated with at least one of the first electrically insulating gap and the second electrically insulating gap.

[0175] Embodiment 2. The downhole telemetry device of embodiment 1, wherein the switching circuitry comprises: a first switch, wherein the first switch is configured to couple the first terminals; and a second switch, wherein the second switch is configured to couple the second terminals.

[0176] Embodiment 3. The downhole telemetry device of any of embodiments 1 and 2, wherein: the receiver is receptive of a first electromagnetic (EM) signal comprising first data, wherein the first EM signal is of a first frequency; the transmitter is configured to transmit a second EM signal comprising second data based at least in part on the first EM signal, wherein the second EM signal is of a second frequency .

[0177] Embodiment 4. The downhole telemetry device of any one of embodiments 1 to 3, wherein at least one of the transmitter or the receiver is included in a transceiver.

[0178] Embodiment 5. The downhole telemetry device of any one of embodiments 1 to 4, further comprising: a data bus coupled to the control circuitry and the switching circuitry, wherein the control circuitry is configured to communicate with at least one of the transmitter, the receiver, or the switching circuitry via the data bus, and wherein the data bus supports isolation between the receiver and transmitter.65TEL-510231-WO-2_INT1027PCT

[0179] Embodiment 6. The downhole telemetry device of any one of embodiments 1 to 5, wherein the control circuitry is further configured to control at least one of: a first filter parameter of the receiver; or a second filter parameter of the transmitter.

[0180] Embodiment 7. The downhole telemetry device of any one of embodiments 1 to 6, wherein the control circuitry is configured to control the switching circuitry based on data about one or more formation properties, and wherein the data about the one or more formation properties are sensed by a sensing circuitry in the downhole telemetry device or are received by the receiver .

[0181] Embodiment 8. The downhole telemetry device of any one of embodiments 2 to 7, wherein the switching circuitry comprises: a third switch associated with a third electrically insulating gap included in the drill string, wherein the third switch is configured to couple a first portion of the drill string associated with the third electrically insulating gap and a second portion of the drill string associated with the third electrically insulating gap.

[0182] Embodiment 9. The downhole telemetry device of any one of embodiments 1 to 6, wherein the control circuitry is configured to control the at least one of the first parameter filter or the second filter parameter based on data about one or more formation properties, and wherein the data about the one or more formation properties are sensed by a sensing circuitry in the downhole telemetry device or are received by the receiver.

[0183] Embodiment 10. The downhole telemetry device of any one of embodiments 1 to 9, wherein: the downhole telemetry device is configured to transmit, via the transmitter, one or more signals comprising an indication of a state of the switching circuitry .

[0184] Embodiment 11. The downhole telemetry device of any one of embodiments 1 to 10, wherein: the downhole telemetry device is configured to receive, via the receiver, one or more signals comprising an indication of a target state of the switching circuitry .

[0185] Embodiment 12. A communication system disposed in a borehole through a subterranean formation and comprising: a set of downhole telemetry devices, wherein each downhole telemetry device of the set of downhole telemetry devices comprises: a receiver, wherein first terminals of the receiver are coupled to a drill string at locations associated with a first electrically insulating gap included in the drill string; a transmitter, wherein second terminals of the transmitter are coupled to the drill string at locations65TEL-510231-WO-2_INT1027PCT associated with a second electrically insulating gap included in the drill string; and control circuitry configured to control a switching circuitry coupled to at least one of the first terminals or the second terminals, wherein the switching circuitry is associated with at least one of the first electrically insulating gap and the second electrically insulating gap.

[0186] Embodiment 13. The communication system of embodiment 12, wherein control of respective switching circuitry of the set of downhole telemetry devices is associated with bypassing transmission of signals by at least one downhole telemetry device of the set of downhole telemetry devices.

[0187] Embodiment 14. The communication system of any one of embodiments 12 and 13, wherein each downhole telemetry device of the set of downhole telemetry devices is configured to transmit data to and receive data from two other downhole telemetry devices of the set of downhole telemetry devices.

[0188] Embodiment 15. A method comprising: controlling switching circuitry of a device coupled to a drill string based on one or more criteria, wherein the switching circuitry is coupled to a first electrically insulating gap and a second electrically insulating gap of the drill string; and at least one of: receiving, at the device, a first electromagnetic (EM) signal comprising data based on a configuration of the switching circuitry, wherein the first EM signal is of a first frequency; and transmitting, by the device, a second EM signal comprising the data based on the configuration of the switching circuitry, wherein the second EM signal is of a second frequency.

[0189] Embodiment 16. The method as in any prior embodiment, wherein the one or more criteria comprises at least one of: one or more properties of a formation; an effective antenna length associated with receiving the first EM signal or transmitting the second EM signal; and a target effective gap length of the drill string.

[0190] Embodiment 17. The method as in any prior embodiment, further including: transmitting or receiving a data signal including second data associated with controlling the switching circuitry, a frequency of transmitted / received signals, one or more filter parameters, or data from one or more other tools.

[0191] 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” are65TEL-510231-WO-2_INT1027PCT 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.

[0192] The teachings of the present disclosure may be used in a variety of well operations. Illustrative well operations include, but are not limited to, hydraulic fracturing, stimulation, tracer injection, cleaning, acidizing, steam injection, water flooding, cementing, etc.

[0193] Unless the context clearly requires otherwise, throughout the description and the claims, the terms “comprise,” “comprising,” and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to.” The terms “connected”, “coupled”, or any variant thereof, means any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements can be physical, logical, or a combination thereof. The terms “herein,” “above,” “below,” and words of similar import, when used to describe this specification shall refer to this specification as a whole and not to any particular portions of this specification. The term “or,” in reference to a list of two or more items, covers all of the following interpretations of the term: any of the items in the list, all of the items in the list, and any combination of the items in the list. The singular forms “a,” “an,” and “the” also include the meaning of any appropriate plural forms.

[0194] Terms that indicate directions such as “vertical”, “transverse”, “horizontal”, “upward”, “downward”, “forward”, “backward”, “inward”, “outward”, “vertical”, “transverse”, “left”, “right”, “front”, “back”,” “top”, “bottom”, “below”, “above”, “under”, and the like, used in this description and any accompanying claims (where present) depend on the specific orientation of the apparatus described and illustrated. The subject matter described herein may assume various alternative orientations. Accordingly, these directional terms are not strictly defined and should not be interpreted narrowly.

[0195] In some embodiments, the invention may be implemented in software. For greater clarity, “software” includes any instructions executed on a processor, and may include (but is not limited to) firmware, resident software, microcode, and the like. Both processing hardware and software may be centralized or distributed (or a combination thereof), in whole or in part, as known to those skilled in the art. For example, software and other modules may be accessible via local memory, via a network, via a browser or other application in a distributed computing context, or via other means suitable for the purposes described above.65TEL-510231-WO-2_INT1027PCT

[0196] Where a component (e.g., a circuit, module, assembly, device, drill string component, drill rig system, etc.) is referred to herein, unless otherwise indicated, reference to that component (including a reference to a “means”) should be interpreted as including as equivalents of that component or any component which performs the function of the described component (i.e., that is functionally equivalent), including components which are not structurally equivalent to the disclosed structure which performs the function in the illustrated exemplary embodiments of the invention.

[0197] Specific non-limiting examples of systems, methods and apparatus have been described herein for purposes of illustration. The technology provided herein can be applied to systems other than the example systems described above. Many alterations, modifications, additions, omissions and permutations are possible within the practice of this invention. This invention includes variations on described embodiments that would be apparent to the skilled addressee, including variations obtained by: replacing features, elements and / or acts with equivalent features, elements and / or acts; mixing and matching of features, elements and / or acts from different embodiments; combining features, elements and / or acts from embodiments as described herein with features, elements and / or acts of other technology; and / or omitting combining features, elements and / or acts from described embodiments.

[0198] It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions, omissions and sub-combinations as may reasonably be inferred. The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.

[0199] 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, they65TEL-510231-WO-2_INT1027PCT 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

65TEL-510231-WO-2_INT1027PCT CLAIMS What is claimed is:

1. A downhole telemetry device disposed in a borehole through a subterranean formation, the downhole telemetry device characterized by: a receiver, wherein first terminals of the receiver are coupled to a drill string at locations associated with a first electrically insulating gap included in the drill string; a transmitter, wherein second terminals of the transmitter are coupled to the drill string at locations associated with a second electrically insulating gap included in the drill string; and control circuitry configured to control a switching circuitry coupled to at least one of the first terminals or the second terminals, wherein the switching circuitry is associated with at least one of the first electrically insulating gap and the second electrically insulating gap.

2. The downhole telemetry device of claim 1, wherein the switching circuitry comprises: a first switch, wherein the first switch is configured to couple the first terminals; and a second switch, wherein the second switch is configured to couple the second terminals.

3. The downhole telemetry device of any of claims 1 and 2, wherein: the receiver is receptive of a first electromagnetic (EM) signal comprising first data, wherein the first EM signal is of a first frequency; the transmitter is configured to transmit a second EM signal comprising second data based at least in part on the first EM signal, wherein the second EM signal is of a second frequency.

4. The downhole telemetry device of any one of claims 1 to 3, wherein at least one of the transmitter or the receiver is included in a transceiver.

5. The downhole telemetry device of any one of claims 1 to 4, further comprising: a data bus coupled to the control circuitry and the switching circuitry, wherein the control circuitry is configured to communicate with at least one of the transmitter, the receiver, or the switching circuitry via the data bus, and wherein the data bus supports isolation between the receiver and transmitter.

6. The downhole telemetry device of any one of claims 1 to 5, wherein the control circuitry is further configured to control at least one of:65TEL-510231-WO-2_INT1027PCT a first filter parameter of the receiver; or a second filter parameter of the transmitter.

7. The downhole telemetry device of any one of claims 1 to 6, wherein the control circuitry is configured to control the switching circuitry based on data about one or more formation properties, and wherein the data about the one or more formation properties are sensed by a sensing circuitry in the downhole telemetry device or are received by the receiver.

2. The downhole telemetry device of any one of claims 2 to 7, wherein the switching circuitry comprises: a third switch associated with a third electrically insulating gap included in the drill string, wherein the third switch is configured to couple a first portion of the drill string associated with the third electrically insulating gap and a second portion of the drill string associated with the third electrically insulating gap.

3. The downhole telemetry device of any one of claims 1 to 6, wherein the control circuitry is configured to control the at least one of the first parameter filter or the second filter parameter based on data about one or more formation properties, and wherein the data about the one or more formation properties are sensed by a sensing circuitry in the downhole telemetry device or are received by the receiver.

4. The downhole telemetry device of any one of claims 1 to 9, wherein: the downhole telemetry device is configured to transmit, via the transmitter, one or more signals comprising an indication of a state of the switching circuitry.

5. The downhole telemetry device of any one of claims 1 to 10, wherein: the downhole telemetry device is configured to receive, via the receiver, one or more signals comprising an indication of a target state of the switching circuitry.

6. A communication system disposed in a borehole through a subterranean formation and characterized by: a set of downhole telemetry devices, wherein each downhole telemetry device of the set of downhole telemetry devices characterized by: a receiver, wherein first terminals of the receiver are coupled to a drill string at locations associated with a first electrically insulating gap included in the drill string; a transmitter, wherein second terminals of the transmitter are coupled to the drill string at locations associated with a second electrically insulating gap included in the drill string; and65TEL-510231-WO-2_INT1027PCT control circuitry configured to control a switching circuitry coupled to at least one of the first terminals or the second terminals, wherein the switching circuitry is associated with at least one of the first electrically insulating gap and the second electrically insulating gap.

7. The communication system of claim 6, wherein control of respective switching circuitry of the set of downhole telemetry devices is associated with bypassing transmission of signals by at least one downhole telemetry device of the set of downhole telemetry devices.

8. The communication system of any one of claims 12 and 13, wherein each downhole telemetry device of the set of downhole telemetry devices is configured to transmit data to and receive data from two other downhole telemetry devices of the set of downhole telemetry devices.

9. A method for communicating within a borehole while drilling the borehole through a subterranean formation, the method characterized by: controlling switching circuitry of a downhole telemetry device coupled to a drill string, wherein the switching circuitry is coupled to a first electrically insulating gap and a second electrically insulating gap of the drill string; and at least one of: receiving, at the downhole telemetry device, a first electromagnetic (EM) signal characterized by data based on a configuration of the switching circuitry; or transmitting, by the downhole telemetry device, a second EM signal characterized by the data based on the configuration of the switching circuitry.

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