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BACKGROUND 
       [0001]    This disclosure relates in general to data communications and, but not by way of limitation, to communication using a compliant medium. 
         [0002]    Electronic communication takes place wirelessly using radio frequencies, optically using light and with wires using electron flow. Often these communication mechanisms are not practical in certain applications. For example, wires are difficult to string along pipelines and down a bore hole. Equipment needs to communicate information despite limitations on available communications medium. 
         [0003]    There are systems for down hole communication using pressure in a hydraulic line. The pressure in the hydraulic line is modulated by the pump with data to communicate with sub-surface devices that have no other communication medium available. Over time, the pressure can be increased and decreased to send information. These systems only communicate away from the pump. 
         [0004]    Other systems use acoustic waves to communicate. An acoustic wave is produced and a gate may be inserted and removed to modulate the reflection of the acoustic wave. These systems require a generally direct path from the acoustic source back to the sensor registering the reflection. Heavily damped systems are not appropriate candidates for these systems. 
         [0005]    On occasion, drillstrings can become snagged somewhere down hole. To determine the location of the snag, tension is put on the drillstring. A point of the drillstring is marked. Tension is increased and the distance the mark moves is measured. The distance and the differential in tension can be used to determine how far down the drillstring the snag occurs. 
       SUMMARY 
       [0006]    In one embodiment, the present disclosure provides a communication system for communicating information with a compliant medium is disclosed. The communication device includes a constrained fluid, a valve, a modulator, a sensor and a demodulator. The constrained is fluid distributed along a length. The valve is configured to operatively engage a second point relative to the length. The modulator configured to actuate the valve according to information. The sensor configured to measure pressure at a first point relative to the length, where the first point is distant from the second point. The demodulator is coupled to the sensor to recover the information. 
         [0007]    In another embodiment, the present disclosure provides a communication system for communicating information with a compliant medium. In one step, a compliant medium has a first point and a second point, where the first point is distant from the second point. A compliance damper is configured to operatively engage the second point. A modulator is configured to actuate the compliance damper according to information. A sensor configured to measure compliance of the compliant medium at the first point. A demodulator is configured to operatively engage the first point to recover the information. 
         [0008]    In yet another embodiment, the present disclosure provides a communication system for communicating information with a compliant medium. In one step, a compliant medium includes a first point and a second point, where the first point is distant from the second point. A compliance damper is configured to operatively engage the second point. A modulator is configured to actuate the compliance damper according to information. A sensor configured to measure compliance of the compliant medium at the first point. The demodulator configured to operatively engage the first point to recover the information. 
         [0009]    Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating various embodiments, are intended for purposes of illustration only and are not intended to necessarily limit the scope of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The present disclosure is described in conjunction with the appended figures: 
           [0011]      FIGS. 1A through 1E  depict block diagrams of embodiments of a compliant communication system; 
           [0012]      FIG. 2  depicts a chart of an example of pressure measured at a point of a compliant medium; 
           [0013]      FIG. 3  depicts a chart of an example of a rate of pressure change over time; 
           [0014]      FIG. 4  depicts a chart of an example of an absolute value of the rate of pressure change over time; 
           [0015]      FIG. 5  illustrates a flowchart of an embodiment of a process for transmitting data using a compliant medium; and 
           [0016]      FIGS. 6 and 7  depict a block diagram of an embodiment a compliant communication system that uses a deployment wire as the compliant medium. 
       
    
    
       [0017]    In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label. 
       DETAILED DESCRIPTION 
       [0018]    The ensuing description provides preferred exemplary embodiment(s) only, and is not intended to limit the scope, applicability or configuration of the disclosure. Rather, the ensuing description of the preferred exemplary embodiment(s) will provide those skilled in the art with an enabling description for implementing a preferred exemplary embodiment. It being understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope as set forth in the appended claims. 
         [0019]    In one embodiment, a compliant communication system has sensors that are distributed along a compliant medium (e.g., a tank, a pipe, a hydraulic line, or a wire). Sparse data is transmitted at low power levels for applications such as telemetry. Above-ground equipment continuously applies a displacement to one part of the compliant medium to provide a bias (e.g., pumping or extracting fluid for the hydraulics, or pulling or releasing tension for the wire), and measures the rate of change of force (e.g., pressure or tension) as flow rate or displacement. Pinching (e.g., valves or grippers) along the compliant medium can actively isolate or connect the section of line below the sensor from the section above. The rate of change of force is inversely proportional to the compliance of the system above the pinching mechanism. By modulating the isolation and reconnection of the line above and below the sensor, data may be communicated from a sub-surface to a surface receiver by continuously measuring the observed compliance at the surface. In one embodiment, modulation of the bias communicates information to the sub-surface devices coupled to the compliant medium. 
         [0020]    Data from downhole production gauges and sensors may be desired over the lifetime of a well, but only using a very low data rate to communicate information. Hourly, daily or even weekly data may be all that is required to monitor the performance of a well, for example. In some embodiments, there may be a limited amount of stored energy available downhole, without such limits above ground. When fluid is added to (or withdrawn from) the hydraulic line the pressure will rise (respectively fall). For a uniform line, the rate of rise (respectively fall) is inversely proportional to the length of line, so signals can be transmitted by varying the length of the line using valves. 
         [0021]    The power required for to transmit data can be very low, especially if valve operations only take place when the hydraulic line pressure is at one preset value as is the case in one embodiment. The compliant system can be used to communicate with a device at the end of a hydraulic line by deploying a hydraulic reservoir beyond the device—effectively lengthening the line. 
         [0022]    The data rate can be variable between embodiments or for one embodiment. Viscous effects of the compliant media define a characteristic time for the system. In one embodiment, the time taken to transmit one bit is a multiple of the characteristic time. Multiple transmitters may use the same compliant medium by use of time division, different data rates, etc. 
         [0023]    Referring first to  FIG. 1A , a block diagram of an embodiment of a compliant communication system  100 - 1  is shown. A compliant medium  124  or hydraulic line in this embodiment is connected to a reservoir  104  of hydraulic fluid. In one embodiment, the reservoir  104  might be at the surface of an oil well, the line  124  being used to operate a flow-valve deep underground. The reservoir  104  would therefore also be underground. A pump  108  can pump at a measured rate both into and out of the hydraulic line  124 . There is a pressure sensor  112 , measuring the pressure inside the hydraulic line  124 . 
         [0024]    Below surface there are one or more data devices  128  from which data is to be sent with a sub-surface transmitter  122 . Each of sub-surface transmitter  122  is connected to a mechanism for intermittently blocking the hydraulic line  124 , for example, a valve  116 . The sub-surface transmitter  122  sends information from the data device  128  to the surface receiver. By opening and closing the valve  116 , the sub-surface transmitter modulates the pressure on the hydraulic line  124 . The pressure is read by the pressure sensor  112  and fed to the surface receiver  134  for decoding back into the information. 
         [0025]    The pump  108  pumps hydraulic fluid in and out of the line  124 . By biasing the fluid in the line  124 , the constrained fluid is enhanced as a complaint medium. In one embodiment, the pump  108  would normally cycle between pumping a fixed volume in and then out again. The pumping is periodic. The data that the sub-surface transmitter sends is encoded into bits. A 2-level, 4-level, 8-level, etc. modulation scheme could be used. For example, in a 2-level modulation scheme zero or closed is used for one level and one or open is used for the other. For more than two modulation levels, the valve could be partially opened or closed. Positive or negative logic could be used along with an optional error correction scheme. More complicated modulation schemes such as NRZ (non-return zero) could be used in other embodiments. 
         [0026]    With reference to  FIG. 1B , a block diagram of another embodiment of a compliant communication system  100 - 2  is shown. This embodiment has three different data devices  128 , each with its own sub-surface transmitter  122  to modulate a different valve  116 . At any given moment only one of the sub-surface transmitters  122  is modulating the compliant medium or line  124 . For example, the first and third valves  116 - 1 ,  116 - 3  could be open, while the second valve  116 - 2  opens and closes to encode information onto the compliant medium  124 . 
         [0027]    Various schemes could be used to allow all the data devices  128  to use the compliant medium  124  for data transfer. For example, time-division could be used in one embodiment. The downhole equipment  122 ,  128  may either have a way to measure the line pressure to avoid transmissions from others or may be able to synchronize to the pump period. In the present embodiment, each data device tracks time and only transmits in a particular time slot. Another embodiment avoids time synchronization and randomly transmits information in the hope of avoiding overlap enough of the time to send an adequate amount of data for a given application. 
         [0028]    Referring next to  FIG. 1C , a block diagram of yet another embodiment of a compliant communication system  100 - 3  is shown. This embodiment allows bi-directional communication. The pump  108  modulates the volume inserted or removed from the line  124 . Each sub-surface transceiver  120  has a pressure sensor  112  to detect these changes in pressure. After decoding, that information is passed to the data device  128 . The surface transceiver  132  can send information on the compliant medium  124  to set up time slots, poll the data devices  128 , configure the data device and/or sub-surface transceiver, etc. 
         [0029]    In order to transmit information from a data device  128 , the valve  116  is opened and shut under the control of the sub-surface transceiver  120 . In one embodiment, the opening and closing is synchronized with the pump  108 . The pressure sensor  112  coupled to the sub-surface transceiver  120  allows actuating the valve  116  when there is generally the same volume of fluid in the line  124 . 
         [0030]    This embodiment includes a second reservoir  104 - 2  at the end of the line  124  proximate to the last sub-surface transceiver  120 . For a data device  128 - 2  at the end of the line  124 , the second reservoir  104 - 2  is used to enhance the difference in compliance between the valve  116 - 2  opening and closing. 
         [0031]    With reference to  FIG. 1D , a block diagram of still another embodiment of a compliant communication system  100 - 4  is shown. This embodiment has three different data devices  128  where each has a pressure sensor  112  to enable bi-directional communication and/or time slot determination. The terminal data device  128  in this embodiment is not close to the end of the line  124  such that a second reservoir may not used as the terminal end of the line  124  provides a reservoir for the fluid. 
         [0032]    This embodiment allows peer communication between the sub-surface transceivers  120 . Each data device  128  could be addressed such that singlecast or multicast messaging could be done. A surface transceiver  132  could be used in other embodiments and still allow peer communication between the sub-surface transceivers  120 . 
         [0033]    Referring next to  FIG. 1E , a block diagram of another embodiment of a compliant communication system  100 - 5  is shown. This embodiment includes a second reservoir  104 - 2  at the terminal end of the line  124  to enhance compliance of the line for a valve  116  close to the terminal end of the line  124 . 
         [0034]    With reference to  FIG. 2 , a chart of an example  200  of pressure measured at a point of a compliant medium is shown. This figure shows the pressure measured at the sensor  112  over approximately one hundred minutes of operation. The pump cycle lasts for about twelve minutes in this example. If there were no fluid viscosity, the pressure would either rise or fall linearly with time, giving a triangular saw-tooth pattern. The viscous pressure, which is proportional to flow rate, results in an asymmetric shape to the teeth in the curve. The valve  116  is closed initially, then opening after two cycles, next shutting again after two cycles, opening again for the sixth cycle, and closing for the final two cycles. In a two-level modulation scheme this would be transmitting the binary digits 11001011. 
         [0035]    Referring next to  FIG. 3 , a chart of an example  300  of a rate of pressure change over time is shown. In this example, there is a transient at each change in flow rate, but this is short compared to the bit length. The transient is longer when the valve is open (and hence the hydraulic line is longer). The characteristic time, T, of the system is given by the following formula: 
         [0000]    
       
         
           
             T 
             = 
             
               
                 
                   ( 
                   
                     L 
                     r 
                   
                   ) 
                 
                 2 
               
                
               
                 η 
                 κ 
               
             
           
         
       
     
         [0000]    Where L is the length of the line, r is the radius, η is the viscosity, and κ is the bulk modulus of the hydraulic fluid possibly corrected for the compliance of the line wall. Typically, the characteristic time is from 10 s of seconds to minutes. 
         [0036]    With reference to  FIG. 4 , a chart of an example  400  of an absolute value of the rate of pressure change over time is shown. This figure shows the same data as  FIG. 3 , now normalized by the direction of flow, and with the time divided into bit times. The level changes can clearly be seen. If the bits are transmitted over at least one cycle (as shown), then instead of level being measured by rate of pressure change, it can be measured by using peak (or trough) pressures. Bits can be transmitted over less than one cycle, or asynchronously with the flow cycles, but has greater transients each time a valve opens or shuts, as the pressure may not be the same on each side of the valve. Some embodiments may filter the signal in the figure to remove the spikes. 
         [0037]    Referring next to  FIG. 5 , a flowchart of an embodiment of a process  500  for transmitting data using a compliant medium  124  is shown. The depicted portion of the process begins in step  504  where the tube or line has fluid pumped into it. This pumping happens continuously to bias the compliant medium  124 . The data device  128  is gathering information in block  508 . In block  512 , a determination is made as to whether a time slot is available for sending information. 
         [0038]    When a time slot is available, information is modulated in step  516 . By actuating the valve  116  according to the data being sent in step  520  the complaint medium is given the information. The receiver  134  is coupled to a pressure sensor  112  that measures the pressure in step  512 . With the pressure curve, the data is demodulated according to  FIGS. 2-4  in step  528  to recover the data. 
         [0039]    Referring next to  FIGS. 6 and 7 , another embodiment of a compliant communication system  700  is shown that uses a deployment wire  604  as the compliant medium. In this embodiment, a downhole tool  616  is installed in a borehole and connected to the surface by the deployment wire  604 . The compliance of the system  700  is modified by the downhole tool  616 . 
         [0040]    The deployment wire  604  is attached to the downhole tool  616 . A gripping arrangement is used to pinch the deployment wire  604 , for instance hydraulic grippers  612  are used in this embodiment. The compliant medium or deployment wire  604  is biased with a spring  608  in this embodiment. When the grippers  612  are closed, the compliance of the wire  604  is defined by the compliance of the length of wire above the grippers  612 . When the grippers  612  are opened, the additional compliance of the spring  608  is in series with the wire compliance, thus when the same force is applied to the deployment wire  604 , a larger displacement is seen. The data device  128  uses a sub-surface transmitter  122  to modulate the grippers  612  to communicate information to the surface. 
         [0041]    The downhole tool  616  is firmly attached to the borehole walls  708  by a mechanism such as a wireline-deployed packer  704 . The deployment wire  604  joins the tool  616  to a surface winch and reel (not shown), via a pulley wheel  712  and a carrier mechanism  716  for pulling and releasing the deployment wire  604 , within which the force-displacement characteristics of the wire deployment system can be measured and demodulated back into information by the surface receiver  134 . The range of displacement of the carrier mechanism  716  is chosen so that the spring  608  will not be extended beyond the grippers  612 . 
         [0042]    The carrier mechanism  716  rhythmically or periodically pulls and releases the deployment wire  604 , and measures the force versus displacement, i.e., the system compliance. In order to transmit data from the downhole tool  616  to surface, the grippers  612  are engaged and dis-engaged by the sub-surface transmitter  122  in order to modulate the compliance according to information produced by the data device  128 . Other embodiments could have multiple downhole tools that use the same deployment wire to send information to the surface. Although this embodiment only sends information in one direction, other embodiments could use the carrier mechanism to send information to the downhole tool, allowing bidirectional communication. 
         [0043]    A number of variations and modifications of the disclosed embodiments can also be used. For example, some of the above embodiments describe an application where there are portions of the system above ground and other portions below ground. In other embodiments, all the components could be above or below ground or underwater. Some of the above embodiments discuss the complaint medium being a hydraulic line, but other embodiments could be a tank of fluid, a pipeline, or a wire. 
         [0044]    Specific details are given in the above description to provide a thorough understanding of the embodiments. However, it is understood that the embodiments may be practiced without these specific details. For example, circuits may be shown in block diagrams in order not to obscure the embodiments in unnecessary detail. In other instances, well-known circuits, processes, algorithms, structures, and techniques may be shown without unnecessary detail in order to avoid obscuring the embodiments. 
         [0045]    Implementation of the techniques, blocks, steps and means described above may be done in various ways. For example, these techniques, blocks, steps and means may be implemented in hardware, software, or a combination thereof. For a hardware implementation, the processing units may be implemented within one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described above, and/or a combination thereof. 
         [0046]    Also, it is noted that the embodiments may be described as a process which is depicted as a flowchart, a flow diagram, a data flow diagram, a structure diagram, or a block diagram. Although a flowchart may describe the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be re-arranged. A process is terminated when its operations are completed, but could have additional steps not included in the figure. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, etc. When a process corresponds to a function, its termination corresponds to a return of the function to the calling function or the main function. 
         [0047]    While the principles of the disclosure have been described above in connection with specific apparatuses and methods, it is to be clearly understood that this description is made only by way of example and not as limitation on the scope of the disclosure.

Summary:
A communication system for communicating information with a compliant medium is disclosed, the communication device includes a constrained fluid, a valve, a modulator, a sensor and a demodulator. The constrained is fluid distributed along a length. The valve is configured to operatively engage a second point relative to the length. The modulator configured to actuate the valve according to information. The sensor configured to measure pressure at a first point relative to the length, where the first point is distant from the second point. The demodulator is coupled to the sensor to recover the information.