Patent Publication Number: US-2015077265-A1

Title: Telemetry on tubing

Description:
BACKGROUND 
     Tubing, such as coiled tubing, is a natural acoustic waveguide that can serve as a telemetry channel to establish bidirectional communication between surface operators and downhole sensors and tools in a subterranean well system. An acoustic telemetry system that operates on coiled tubing can include a single transmitter at the well system bottom hole assembly (BHA) and a receiver at the surface. For operations in extended and/or horizontal wells, however, the telemetry signal from the transmitter can be adversely attenuated. 
     Further, as coiled tubing is tripped into a well, it is commonly passed through a stripper packer to maintain well pressure. It may be difficult to use a conventional acoustic repeater to mitigate signal attenuation, because the combination of such a repeater and the coiled tubing may not fit through the stripper packer annulus while maintaining the well seal at the surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an example coiled tube system including multiple acoustic repeaters in accordance with some embodiments. 
         FIG. 2  illustrates a front view of an example acoustic repeater in accordance with some embodiments. 
         FIG. 3  illustrates a section view of an example acoustic repeater in accordance with some embodiments. 
         FIG. 4  illustrates a section view of an example modular acoustic repeater in accordance with some embodiments. 
         FIG. 5  is a schematic diagram of an example electrical system for an acoustic repeater for coiled tube telemetry in accordance with some embodiments. 
         FIG. 6  illustrates an example data frame structure for data transmitted by the acoustic repeater in accordance with some embodiments. 
         FIG. 7  is a flow diagram for data transmission by the acoustic repeater in accordance with some embodiments. 
         FIG. 8  is a flow diagram for data reception by the surface system in accordance with some embodiments. 
         FIG. 9  is a flow chart illustrating a training and synchronization method in accordance with some embodiments. 
         FIG. 10  illustrates a single hop relay mode for acoustic repeater communication in accordance with some embodiments. 
         FIG. 11  illustrates a multi-hop relay mode for acoustic repeater communication in accordance with some embodiments. 
         FIG. 12  is a flowchart illustrating a method for providing communication between acoustic repeaters and a surface system in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     To address some of the challenges described above, as well as others, systems, apparatus, and methods are described herein for using acoustic telemetry repeaters in a subterranean well system that employs coiled tubing. The acoustic repeaters may comprise a relatively thin, hinged annular housing, which can be coupled about the circumference of the coiled tubing before the stripper packer location along the tubing, as the tubing is tripped into a well. The annular housing of the acoustic repeater is configured to be concentric with the coiled tubing and symmetric about the longitudinal axis of the coiled tubing. Concentricity and symmetry combined with a relatively small radial thickness of the repeater housing enables the repeater to be attached to the coiled tubing before the tubing passes through the stripper packer into the well. Concentricity can also enable coupling of the repeater without creating discontinuities along the coiled tubing. When discontinuities are created, pressure may leak out, defeating the purpose of the stripper packer. 
       FIG. 1  illustrates a coiled tubing system (CTS)  10  including a reel  12 , coiled tubing (CT)  14 , a gooseneck  16 , an injector head  18 , and a stripper packer  20 . CTS  10  is configured to trip the CT  14  into and out of a wellbore  22  within a casing  24 . CTS  10  can be used for a number of interventions, and, in some cases, for production in subterranean wells. 
     In operation, injector head  18  draws CT  14  off of reel  12  and trips CT  14  into wellbore  22  through stripper packer  20 . Injector head  18  includes a mechanism that pushes CT  14  into and pulls CT  14  out of wellbore  22 . Injector head  18  operates in conjunction with gooseneck  16 , which acts as a curved guide beam that threads CT  14  into injector head  18 . 
     Below injector head  18  is stripper packer  20 . Stripper packer  20  can include rubber pack off members, which provide a seal around casing  24  to isolate the pressure within the well from the surface. Stripper packer  20  can be hydraulically opened and closed to contain wellbore pressure. By applying hydraulic pressure at stripper packer  20 , an operator at the surface of the well is able to compress rubber inserts and trip CT  14  into and out of wellbore  22  under pressure. 
     Although not shown in  FIG. 1 , CTS  10  can also include a blowout preventer (BOP) below stripper packer  20 . The BOP can provide the ability to cut CT  14  and seal wellbore  22  (shear-blind) to hold and seal around CT  14  (pipe-slip). 
     Example CTS  10  also includes multiple acoustic repeaters  26 ,  27  communicatively coupling a downhole transmitter (not shown) and a surface receiver  28 . The bottommost acoustic repeater  27  may serve as the downhole transmitter. As described in more detail below, acoustic repeaters  26  include a thin hinged annular housing, which can be coupled about the circumference of CT  14  before passing through stripper packer  20  as CT  14  is tripped into wellbore  22 . The annular housing of acoustic repeaters  26  is configured to be concentric with CT  14  and symmetric about the longitudinal axis of the tubing, however embodiments are not limited thereto. Concentricity and symmetry combined with a relatively small radial thickness of the housing can enable acoustic repeaters  26  coupled to CT  14  to pass through stripper packer  20 . The ability to trip acoustic repeaters  26  into wellbore  22  through stripper packer  20  enables multiple repeaters to be deployed downhole to mitigate signal attenuation in extended and/or horizontal subterranean wells. 
       FIG. 2  depicts a front view of an example acoustic repeater  26  in accordance with some embodiments. Acoustic repeater  26  includes an annular housing  28 . Annular housing  28  engages an outer surface of CT  14  using, for example, hinges  30 . While some example acoustic repeaters  26  may have a relatively smooth outer surface (e.g., spherical or ovoid as depicted in  FIG. 2 ) that can be useful in some embodiments to provide less leakage as the repeater  26 ,  27  passes through the strip packet  20  and into the well, other acoustic repeaters  26 ,  27  can have other shapes, such as hexagonal or rectangular shapes. 
       FIG. 3  depicts a section view of acoustic repeater  26  in accordance with some embodiments. Annular housing  28  encloses acoustic transmitter  32 . Acoustic transmitter  32  can also serve as an acoustic telemetry signal detector (e.g., a receiver). Acoustic transmitter  32  can include a piezoelectric actuator  56  ( FIG. 5 ). The piezoelectric actuator  56  may be flexible to enable the piezoelectric actuator  56  to be mounted in annular housing  28  that is concentrically mounted about CT  14 . The flexible piezoelectric actuator  56  can include a micro-fiber composite (MFC) piezoelectric actuator. Some references for MFC piezoelectric actuators quote stress generation capabilities of +/−4000 psi at temperatures up to 180 degrees Celsius. Acoustic transmitter  32  can include a plurality of flexible piezoelectric actuators (not shown in the figures) arranged in a stack to actuate together. In this manner, the actuators can generate acoustic signals with higher power than the actuators could individually generate for transmission on CT  14 . 
     Acoustic repeater  26  includes electrical circuitry  34 . Electrical circuitry  34  may include some of the elements described in more detail below with respect to  FIG. 5  (e.g., elements  44 - 50  and  54 ). Annular housing  28  may enclose electrical circuitry  34 , or electrical circuitry  34  may be enclosed in another separate annular housing as described below with respect to  FIG. 4 . Electrical circuitry  34  and acoustic transmitter  32  may be exposed to at least some ambient pressure to permit a thinner annular housing  28  design. A thinner annular housing  28  design may enable further reduction in the profile of acoustic repeater  26 , as it appears against the outer surface of the coiled tubing. A thinner annular housing  28  may provide capability for insertion of additional electrical circuitry  34  into annular housing  28 . 
     Acoustic repeater  26  can include a flexible battery element  36 . Flexible battery element  36  can include a plurality of flexible battery portions, which may be housed in separate annular housing (not shown in  FIG. 3 ). Some references for flexible battery elements quote a thickness of about 0.5 millimeters. Flexible battery portions may be combined in series or parallel to achieve greater power capacity in acoustic repeater  26 . In some embodiments, a flexible battery such as the FLEXION (Model SF 4823-25EC) lithium polymer battery made by Solicore corporation (Lakeland, Fla., United States of America) can be used as the flexible battery element  36 . 
     Annular housing  28  can have an inner diameter about equal to an outer diameter of CT  14  to prevent, for example, leakage or loss of pressure between acoustic repeater  26  and CT  14 . Some references for CT quote outer diameters of about 1.2 inches to about 2.5 inches. Annular housing  28  may have an outer diameter larger than an inner diameter of stripper packer  20 . For example, annular housing  28  may have an outer diameter larger than an inner diameter of rubber inserts of stripper packer  20 , described above with respect to  FIG. 1 , yet small enough that the annual housing  28  does not apply excessive stress to the rubber inserts or other elements of stripper packer  20 . Some references for the stripper packer  20  quote through-bore sizes of about 2.5 inches to about 5 inches. 
       FIG. 4  is a section view of acoustic repeater  26  arranged in a modular design in accordance with some embodiments. Acoustic repeater  26  can be separated into acoustic transmitter module  38 , electrical module  40 , battery modules  42  and  44 , or any combination of modules thereof. Acoustic repeater  26  may be arranged in a modular design to gain flexibility in acoustic repeater  26  configuration and for ease of maintenance. For example, operators can add or remove additional battery modules  42 ,  44  to adjust to changing energy requirements or change or add electrical modules  40  to adjust to changing requirements or replace non-functioning modules of acoustic repeater  26 . The modular design as shown in  FIG. 4  may also allow for a further reduced profile of the overall acoustic repeater  26 , with respect to the distance the repeater  26  rises above the outer surface of the coiled tubing. 
       FIG. 5  is a schematic diagram of an electrical system for acoustic repeater  26  in accordance with some embodiments. Acoustic repeaters  26  in accordance with this disclosure can be constructed with a number of electronic components. The components described with respect to  FIG. 5  can include application-specific integrated circuits (ASICs) or field programmable gated arrays (FPGAs) designed for acoustic telemetry applications. Any of the components shown in  FIG. 5  may be housed separately or together in the annular housing  28  ( FIG. 2-3 ) or in one or more modules such as modules  38 ,  40 ,  42 ,  44  ( FIG. 4 ) of the acoustic repeater  26 . While some components are shown in  FIG. 5 , acoustic repeater  26  may include other components not shown in  FIG. 5  or acoustic repeater  26  may include a subset of the components shown in  FIG. 5 . Different acoustic repeaters  26  of system  10  may have different subsets of the components shown in  FIG. 5 . 
     In some embodiments, acoustic repeater  26  includes a floating point digital signal processing (DSP) board  45 . DSP board  45  is configured to receive digital data from, for example, transducer interface board  46 , gamma board  48 , accelerometer  50  or other data sources over communication links, for example an RS232 communication link or other data and control lines. Transducer interface board  46  can receive and digitize data from casing collar locator assembly  52 , pressure transducers  54  or other sources within or external to the acoustic repeater  26  assembly. 
     Accelerometer  50  can be a single-axis accelerometer or a multi-axis accelerometer. For example, accelerometer  50  can be multi-axis to provide increased precision or sensitivity with respect to off-axis movement. Using accelerometer  50 , acoustic repeater  26  can also detect pressure pulses in the fluid within, for example, CT  14  or elsewhere. In this way, acoustic repeater  26  can detect and relay mud pulse telemetry signals to surface system  28  ( FIG. 1 ). 
     DSP board  45  compresses and packages the digital data and transmits the data over a communication link to acoustic driver board  54 . Acoustic driver board  54  can be used to drive piezoelectric stack  56  of acoustic transmitter  32 , which generates acoustic signals that are transmitted through CT  14  ( FIG. 1-4 ). As described above with respect to  FIG. 3-4 , acoustic repeater  26  can include low profile batteries  36 . Acoustic repeater  26  can also include power supply boards  60  and  62 . 
     Piezoelectric stack  56 , another piezoelectric stack (not shown in  FIG. 5 ) or accelerometer  50  can also serve as a receiver for acoustic repeater  26 . In some embodiments, acoustic repeater  26  may include processor  58  that can be programmed to implement different modulation schemes or trained to allow acoustic receiver  26  to receive and transmit on different frequencies as described below with respect to  FIG. 7 . In some embodiments, acoustic transmitter  32  can additionally or alternatively be programmed to implement different modulation schemes or trained to allow acoustic receiver  26  to receive and transmit on different frequencies. 
       FIG. 6  illustrates a generic data frame structure for a data frame  64  transmitted by acoustic repeater  26  in accordance with some embodiments. Data frame  64  can include preamble  66 . Preamble  66  can include a pattern of data to allow acoustic repeaters  26 , surface system  28  or other devices to detect new incoming data frames  64 . Data frame  64  can include a data frame delimiter  68  to denote the end of preamble  66 . Data frame  64  can include a header  70 . Header  70  can have identification information for data frame  64  such as type identifiers, sources of the data, etc. Data frame  64  can include a data payload  72 , which can include sensor data or other data being transmitted by acoustic repeater  26 . Data frame  64  can include a cyclic redundancy check (CRC)  74  for detection of corrupted data within data frame  64 . Data frame  64  can include all of fields  66 ,  68 ,  70 ,  72 , and  74 , or a subset of these fields, or other fields (not shown in  FIG. 6 ). 
       FIG. 7  is a flow diagram for data transmission by acoustic repeater  26  in accordance with some embodiments. Functional elements can be performed within acoustic repeater  26  by, for example, DSP board  44 , acoustic driver board  54 , processor  58 , or acoustic transmitter  32 . 
     Data to be transmitted 76 may be received at acoustic transmitter  32 , or as digital data received from the acoustic driver board  54  and encoded as acoustic data in an encoder  78 . Circuitry, for example the circuitry of processor  58  or acoustic transmitter  32 , can perform modulation  80 , preamble generation  82 , and header generation  84  to assemble  86  a data packet  64  ( FIG. 6 ). Acoustic transmitter  32  transmits the data packet  64 . For example, piezoelectric stack  56  of the acoustic transmitter  32  can launch an acoustic signal into CT  14 , which then acts as an acoustic transmission medium. 
     Modulation  80  can be performed according to various modulation schemes, including at least one of pulse position modulation (PPM), on-off keying (OOK), frequency shift keying (FSK), amplitude modulation (AM), and phase shift keying (PSK). 
     Modulation  80  can also be performed using orthogonal frequency division multiplexing (OFDM), which is a method currently used in some broadband communication applications for encoding digital data on multiple carrier frequencies. With OFDM, a large number of closely-spaced orthogonal sub-carrier signals are used to carry the data on parallel channels. Each sub-carrier is modulated with a modulation scheme such as, for example, FSK, at a low symbol rate. 
     In some embodiments, OFDM may be used because the movement of CT  14  can generate loud noises or other interference. OFDM can reduce the impact of the noise at the surface, where signals may be processed, thus improving reliability of some embodiments. OFDM can reduce the impact of noise at least because OFDM&#39;s low symbol rate can permit the use of a guard interval between symbols (e.g., a representation of bits of data), thus reducing or eliminating interference between symbols and, in turn, leading to a signal-to-noise ratio improvement. 
       FIG. 8  is a flow diagram for data reception by surface system  28  in accordance with some embodiments. In functional blocks  88 ,  90 ,  92 ,  94 , and  96 , surface system  28  can detect various portions of a data frame  64  ( FIG. 6 ). In functional block  94 , surface system  28  can perform a demodulation of the data signal that was modulated by acoustic repeater  26 . Surface system  28  can perform error checking in functional block  96 . Surface system  28  can then, in functional block  98 , receive or prepare to receive a next data frame  64 . 
       FIG. 9  is a flow chart illustrating a training and synchronization method  900  in accordance with some embodiments. The training and synchronization method  900  can be performed when acoustic repeaters  26 ,  27  are downhole. The training and synchronization method  900  can be performed when the surface system  28  detects that downhole conditions have change, when additional acoustic repeaters  26  are coupled to CT  14 , or for other reasons. Training and synchronization may be executed by processor  58  or acoustic transmitter  32  of an acoustic repeater  26 . The training and synchronization method  900  can include functionalities  901  performed by surface system  28  and other functionalities  903  performed by acoustic repeaters  26 ,  27 . 
     Surface system  28  can scan  902  a set of predetermined frequency channels. Acoustic repeater  26  can transmit  904  on the predetermined frequency channels. Surface system  28  can listen on the predetermined frequency channels for these transmissions of acoustic repeater  26  to identify  906  frequency channels that have at least a threshold signal-to-noise ratio (SNR). Acoustic repeater  26  can wait  908  for a certain time duration after each transmission, and then turn on  910  a listen mode to listen for a channel identifier. If a channel identifier is received  912  from the surface system  28 , acoustic repeater  26  can send an acknowledgement  914  and repeater identifier on the frequency channel identified. 
     If surface system  28  receives  916  a response, including an acknowledgement and an acoustic repeater identifier, to the surface system  28 &#39;s transmission of the channel identifier, the acoustic repeater  26  can begin  918  transmissions on the determined frequency channel, and surface system  28  can receive  920  data from acoustic repeater  26  on the frequency channel. Otherwise, the synchronization process may begin anew, or other channel identifiers can be transmitted to the acoustic repeater  26 . 
     Instead of or in addition to the process described above with respect to  FIG. 9 , acoustic repeaters can be pre-programmed to transmit on a given frequency channel. The frequency channel can be adapted at a later time using the process described above with respect to  FIG. 9 . 
       FIG. 10  illustrates an example single hop relay mode for acoustic repeater  26  communication in accordance with some embodiments. In the illustrative example, two frequency channels f 1  and f 2  are in use. At least one acoustic repeater  26  receives data on frequency channel f 1  and retransmits on frequency channel f 2 . Adjacent acoustic repeaters  26  transmit on different frequency channels f 1 , f 2  to avoid signal contamination between the channels. Frequency channels f 1  and f 2  may have been programmed into acoustic repeaters  26  when the acoustic repeaters  26  were coupled to CT  14 , or at a later time during a synchronization process as described above with respect to  FIG. 9 . 
       FIG. 11  illustrates a multi-hop relay mode for acoustic repeater communication in accordance with some embodiments. In the multi-hop relay mode, adjacent acoustic repeaters  26  still transmit on different frequencies f 1 , f 2 . Each acoustic repeater  26  receives and retransmits on a same frequency f 1  or f 2 . Accordingly, when data is transmitted on, for example, frequency f 1 , that data is not received by a next adjacent acoustic repeater  26  but instead by a subsequent acoustic repeater  26 . 
       FIG. 12  is a flowchart illustrating an example method  1200  for providing communication between acoustic repeaters and a surface system in accordance with some embodiments. Some elements of method  1200  can be implemented by a surface receiver system  28  ( FIG. 1 ). 
     Example method  1200  starts at block  1210  with programming a first acoustic repeater  26  to transmit information at a first operating frequency. In some embodiments, the programming of block  1210  proceeds similarly to the training and synchronization method described above with respect to  FIG. 9 . In some embodiments, first acoustic repeater  26  is preprogrammed to transmit at a first operating frequency and later trained to transmit at different operating frequencies as described above with respect to  FIG. 9 . First acoustic repeater  26  can also be programmed to use a modulation scheme for modulating signals containing the sensor information. The modulation scheme can include OFDM, as described above with respect to  FIG. 7 . 
     Example method  1200  continues at block  1220  with coupling the first acoustic repeater  26  circumferentially around a CT  14  portion, an inner diameter of the first acoustic repeater  26  being about equal to an outer diameter of the CT  14  portion. 
     Example method  1200  continues at block  1230  with programming a second acoustic repeater  26  to receive information transmitted by the first acoustic repeater  26 . 
     Example method  1200  continues at block  1240  with receiving sensor information transmitted at the first operating frequency by the first acoustic repeater and relayed by the second acoustic repeater. The second acoustic repeater is coupled to the coiled tubing portion uphole from the first acoustic repeater. The second acoustic repeater can relay the information on a second operating frequency different from the first operating frequency. 
     Any number of additional acoustic repeaters  26  can be coupled to CT  14 . The number can be selected based on or in response to a determination that a wellbore condition has changed. If additional acoustic repeaters  26  are added, a synchronization process as described above can be performed. This process can include at least transmitting synchronization instructions to the first acoustic repeater, subsequent to the coupling or uncoupling, to instruct the first acoustic repeater to transmit test information using another frequency different from the first frequency. 
     Example method  1200  can include receiving mud pulse telemetry signals from first acoustic repeater  26  based on a measurement by an accelerometer  50  ( FIG. 5 ) of first acoustic repeater  26 . 
     It should be noted that the methods described herein do not have to be executed in the order described, or in any particular order. Moreover, various activities described with respect to the methods identified herein can be executed in iterative, serial, or parallel fashion. 
     In summary, using the apparatus, systems, and methods disclosed herein can provide surface systems with downhole sensor data that uses the coiled tubing itself as an acoustic communication channel between a series of acoustic repeaters. As a result, real-time downhole conditions can be monitored during CT-delivered services or processes, such as fracturing processes, in extended or horizontal wells. At the same time, a surface system can send commands, through the repeaters, to instruct downhole tools to carry out desired operations. The low-profile of the repeaters makes it possible to trip them into a well, through a conventional stripper packer, without loss of pressure or other problems, and without the need to modify existing surface equipment. 
     The accompanying drawings that form a part hereof, show by way of illustration, and not of limitation, specific embodiments in which the subject matter may be practiced. The embodiments illustrated are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed herein. Other embodiments may be utilized and derived therefrom, such that structural and logical substitutions and changes may be made without departing from the scope of this disclosure. This Detailed Description, therefore, is not to be taken in a limiting sense, and the scope of various embodiments is defined only by the appended claims, along with the full range of equivalents to which such claims are entitled. 
     Such embodiments of the inventive subject matter may be referred to herein, individually and/or collectively, by the term “invention” merely for convenience and without intending to voluntarily limit the scope of this application to any single invention or inventive concept if more than one is in fact disclosed. Thus, although specific embodiments have been illustrated and described herein, it should be appreciated that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of ordinary skill in the art upon reviewing the above description.