Patent Publication Number: US-10768651-B1

Title: Shunt current regulator for downhole devices

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to devices used in hydrocarbon extraction. More particularly, the present disclosure relates to regulating current in an all-electric completion for downhole devices. 
     BACKGROUND 
     In drilling or operating wells for hydrocarbon extraction, understanding the structure and properties of the associated geological formation provides information to aid in drilling and operating the well more efficiently. The physical conditions inside the wellbore can be monitored to ensure proper operation of the well. A wellbore is a challenging environment, with temperatures that can approach 150 degrees C. (302 degrees F.), 175 degrees C. (347 degrees F.), or even 200 degrees C. (392 degrees F.), and pressures that can approach 25 kpsi (172 MPa, or about 1700 atmospheres), or even 30 kpsi (207 MPa, or about 2000 atmospheres). There is ongoing effort to develop systems and methods that can allow for more flexibility in making measurements and collecting data downhole, without significant loss of precision in systems and techniques to communicate efficiently downhole at a well site. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a well that includes a system for making measurements in a wellbore according to some aspects of the disclosure. 
         FIG. 2  is a block diagram of a downhole circuitry system according to some aspects of the disclosure. 
         FIG. 3  is a circuit schematic of a downhole circuitry system for stabilizing the current to downhole devices according to certain aspects of the disclosure. 
         FIG. 4  depicts a plot of the current levels within a downhole circuit of a downhole node according to some aspect of the disclosure. 
         FIG. 5A  depicts two diagrams of voltage and current measurements in two different circuits according to some aspect of the disclosure. 
         FIG. 5B  depicts communications from a downhole circuit to a surface computing device in two different circuits according to some aspect of the disclosure. 
         FIG. 5C  depicts communications from a surface computing device to a downhole circuit in two different circuits according to some aspect of the disclosure. 
         FIG. 6  is a flowchart of a process for regulating current drawn from a tubing encapsulated cable according to some aspects of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Certain aspects and features relate to a shunt current regulator for improving communication bitrate on a tubing encapsulated cable by maintaining approximately a constant current level and reducing noise in a downhole environment. Certain aspects and features provide an active noise canceller or current stabilizer to make a tubing encapsulated cable (cable) load on a downhole network system constant during operation of noisy downhole devices. Examples of noisy downhole devices include actuators and inductive couplers. For example, the operations of an inductive coupler may include antenna current chopping. Other devices may include high current with time variant current levels. Certain aspects and features of this disclosure stabilize the current consumption by actively, and in some examples dynamically, increasing current up to a level where all noise and current variations are cancelled. The result is a substantially steady (but, on average, higher) current consumption than the peak current consumption required by the downhole device. 
     As the downhole industry moves to reduce or eliminate hydraulic actuators in favor of electrically operated actuators, the industry needs a more complex downhole electric network system with many sensors and actuators on one electrical line or cable, e.g., a cable line. Increasing the proportion of electrical sensors introduces noise on the power and communication channel represented by the single cable line. Aspects and features provide for higher communication data rates and a more reliable and less noisy communication environment is provided. 
     Well systems face challenges with communication speed from instruments or actuators to surface control or computing systems. The communication speed can be slowed by noise caused by variations in the downhole load currents. Inductive couplers in particular are being used in downhole applications in more and more situations where wireless or contactless connections are needed. Inductive couplers connected to a cable tend to introduce noise onto the cable. This noise makes communication on the cable by equipment connected to the cable more difficult and can even prevents communication on the cable. This is particularly the case if the inductive coupler is driven by a square-wave signal. Sinusoidal driving signals for the inductive couplers would be kinder in terms of noise, but the driver transistors would then be operating more in the linear operating region, resulting in higher power dissipation and higher junction temperatures, leading to reduced reliability. Therefore, square-waves are often used. 
     Well systems also face challenges of controlling current variations when using inductive couplers for power transfer. When input power is supplied via a long cable, large capacitors are needed at the inductive coupler for stabilizing current while antennas are switching. If the antennas were purely resistive, the current drawn from the cable would be steady at all times, with just a small glitch when switching. However, the antennas are usually highly inductive, so that the current required from the cable will vary significantly over time. The variations in current can cause reverse currents that will influence the voltage stability of the cable and capacitors may be used to prevent reverse current. Capacitors are not very reliable over the long term in the downhole environment. Capacitors have the disadvantage of being unreliable at high temperatures. Depending on the design, the capacitors may also attenuate the communication signal when signaling on the same cable as the power is transferred. Accordingly, a circuit that reduces the current variation while eliminating the need for capacitors is advantageous. 
     In one aspect, control of an electrical current along a cable allows greater stability of the network. Maintaining the current within the cable approximately constant reduces a noise caused by current fluctuations on the cable. The current on the cable may be controlled by including a shunt current regulator couplable to the cable. The shunt current regulator reduces fluctuation of the current on the cable by counter-balancing the fluctuations of a downhole load. For example, if a downhole load decreases the current drawn from the cable, the shunt current regulator may increase its current drawn from the cable to maintain the overall current drawn at a stable level (e.g., total current may be the downhole loads added to the shunt current regulator and inherent electrical losses). Particularly in a system that implements power line communication (PLC), the use of a shunt current regulator can improve the communication throughput by maintaining a stable cable current. In some examples, the cable current can be maintained at approximately 100% stable when a shunt current regulator is implemented. 
     Certain aspects and features provide methods of current regulation. In some examples, the current regulation involves monitoring the current drawn from a cable disposed in a downhole system. In some aspects, a sensing element monitors the current drawn and generates a sense signal. In other aspects, a compensation signal is generated from the sense signal. The compensation signal may be used as input to control a transistor to regulate the current drawn from the cable. The transistor can dissipate power to stabilize the current drawn or provide compensation current to increase the current drawn. 
     In one example, a cable is disposed in a downhole environment that connects to a surface computing system and various downhole circuits. An apparatus connected to the cable can include a switch mode voltage regulator that may be connected to the cable and a downhole circuit. The downhole circuit may include a shunt current regulator and a current load in a parallel circuit. In some configurations, the current load includes both high-current loads and low-current loads. 
     Certain aspects and features of this disclosure provide for faster and more reliable communications downhole. Certain aspects and features can enhance reliability of and reduce the size of inductive couplers or other variable current devices (e.g., motors, actuators, etc.) by eliminating the need for high value capacitors and otherwise allow the use of less complex circuitry both uphole and downhole. Certain aspects and features reduce the need to shut down inductive couplers during communication, or to cease communication during active use of any downhole device that tends to create noise on the cable. 
     These illustrative examples are given to introduce the reader to the general subject matter discussed here and are not intended to limit the scope of the disclosed concepts. The following sections describe various additional features and examples with reference to the drawings in which like numerals indicate like elements, and directional descriptions are used to describe the illustrative aspects but, like the illustrative aspects, should not be used to limit the present disclosure. 
       FIG. 1  schematically illustrates an example well that includes a system for making measurements in a wellbore according to some aspects. System  100  illustrates multiple alternative aspects of a measurement system being used together, however, these aspects can be implemented independently. In system  100 , a cable  108  to the surface  106  provides electrical communication to a downhole sensor or actuator in a wellbore  102 . In one example, cable  108  may be a cable (e.g. a tubing encapsulated cable (TEC) or other cable types used downhole used to transmit power and/or signals) that connects to multiple loads downhole. The cable  108  may connect to a surface instrument  115  or a computing device  116 , or both. Either or both of the surface instrument or the computing device includes a processing device that is couplable to the cable  108  in the sense that the processing device can act on signals from or cause the generation of signals sent downhole. The cable  108  may connect to a downhole circuit  110 . Examples of downhole circuit  110  include and actuator, a sensor and the circuitry to couple the actuator or sensor to the cable  108 . The system may have multiple actuators or sensors included in or on a tool string  114 . As a more specific example, the circuit  110  can include an inductive coupler with antennas to transfer information from sensors behind a well casing or otherwise not directly connected to the cable  108 . 
       FIG. 2  illustrates an example of a block diagram of a downhole circuit  110  connected to a cable  108 , e.g. TEC or other shielded cable used in permanent completions systems. In one or more embodiments, the cable  108  is connected to a switch mode voltage regulator  202  that regulates the node current IN to a periodically or permanently constant value. An example of a switch mode voltage regulator  202  is a switched mode power supply that varies the duty cycle to regulate the output voltage. As depicted in  FIG. 2 , the switch mode voltage regulator  202  provides node current IN that splits to provide shunt current IS to a shunt current regulator  204 , low-current load current I CL  to a low-current load  206 , and high-current load current I CH , a high-current load  208 . While  FIG. 2  depicts the shunt current regulator  204 , a low-current load  206 , and a high-current load  208  in a parallel configuration, other configurations are possible. Examples of the low-current load  206  are electronic devices associated with the node (e.g., sensors, controllers, etc.). Examples of the high-current load  208  are actuators or inductive coupler loads. The shunt current regulator  204  regulates the current I S  to keep I N  substantially constant and slightly greater than the maximum combination of I CL  and I CH . 
     Still referring to  FIG. 2 , this configuration provides significant improvements for systems with a remote power source or a low quality power distribution medium such as the downhole configuration illustrated by  FIG. 1 . Particularly in a system that implements power line communication (PLC) over the cable  108 , the use of a shunt current regulator improves the throughput and error rate of communication messages over the cable  108  by maintaining a stable current. In some examples, the current on the cable  108  is maintained approximately 100% stable with the use of the shunt current regulator. Accordingly, the communication messages over the cable  108  are not significantly impacted by downhole load current variation. 
       FIG. 3  depicts an example of a current stabilization circuit according to certain aspects of the disclosure. The shunt current regulator  304  maintains current on a cable  308  to be substantially stable during operation of a downhole device  309 . Cable  308  may be tubing encapsulated cable (TEC) or other cable types used downhole used to transmit power and/or signals. The current drawn from the cable  308  is approximately constant. In this example, the shunt current regulator  304  monitors the current drawn by monitoring the voltage over a sensing element (e.g., a sensing resistive element like R 16  or an active circuit) in the circuit  300 . In the shunt current regulator  304 , the voltage V 2  defines the level of current to be drawn by the current load  310 . In other configurations, voltage can be measured by a current mirror or Norton amplifier. The shunt current regulator  304  may include adaptive or automatic hardware. In other configurations, the shunt current regulator  304  may be dependent on a setting made via commands or software algorithms by a controller or computing system. 
     The shunt current regulator  304  may also facilitate sending and receiving communication messages via signals using PLC. For example, I 3  of the circuit  300  may be a digital signal representing data to be transmitted from the downhole node to the surface. In this particular example, the communication message may be represented by fifteen square pulses. As depicted in  FIG. 3 , the circuit  300  may use a transistor M 1  as a driver for the transmitter. In some examples, the transistor M 1  may also handle the compensation current needed to fill in the dips in load current (I TEC ). The resulting current on the cable  308  (I TEC ) is relatively smooth. The smoother current reduces complexity of signal decoding of communication messages. The reduction in complexity may be due to a lower error rate because the digital communication signals are not affected by the downhole load current variations. 
     Still referring to  FIG. 3 , the implementation of a shunt current regulator  304  allows for the removal of capacitors in the circuit  300  while maintaining the stability of the current on the cable  308 . Accordingly, the absence of capacitors improves signal quality by removing the capacitive effects that cause signal attenuation and noise. The shunt current regulator  304  also limits the effects of the current fluctuation of the downhole loads. Capacitors have the disadvantage of being unreliable at high temperatures. Depending on the design, the capacitors may also attenuate the communication signal when signaling on the same cable as the power is transferred. Accordingly, a circuit that reduces the current variation while eliminating the need for capacitors is advantageous. The potential reliability issues with capacitors are also eliminated. 
     In the example depicted in  FIG. 3 , amplifier U 1  may be a first amplifier that amplifies a sense signal as measured across the sensing element (depicted here as a sensing resistive element, R 16 ). Amplifier U 2  may be a second amplifier that generates a correction signal driving the transistor M 1  that maintains current in the cable  308 , I TEC , approximately constant as defined by the constant voltage V 2 . In one aspect, allowing simultaneous powering of multiple inductive couplers and other instruments on the network, polling commands can be transmitted to any instrument on the cable  308  or behind inductive couplers. In another aspect, broadcast messages or high-speed sequential polling can make the polling efficient. Multiple instruments may work in parallel since the network is stable. Each instrument on the network may generate data that can be stored temporarily in the node circuitry, including a shunt current regulator  304 , a noise canceller, or by the instrument itself. 
     In one aspect, the difference between the instantaneous current requirement and the set constant current level may be passed through the transistor (e.g., transistor M 1 ) working in its linear operating mode, meaning that power will be dissipated in the transistor. In the circuit  300  depicted in  FIG. 3 , I 1  represents the current through an inductive coupler coil driven by two half-bridges. Each half-bridge may drive the inductive coupler coil approximately 50% of the time and accordingly operate primarily in non-linear mode, either on or off, which reduces the power dissipation in the transistor. In this case, the transistor (M 1  in the circuit  300 ) may be in its linear mode of operation for relatively short periods of time right after switching from one half-bridge to the other. The transistor may still dissipate more power than a coil driving transistors. 
     In some examples, the power dissipated in the transistor (i.e., M 1 ) enters an excessive condition and the transistor is unable to handle the power dissipation due to temperature conditions or transistor current dimensioning. In this case, the shunt current regulator  304  may allow some current fluctuations on the cable  308 . During the current fluctuations on the cable  308 , high-speed communication may not be available. The noise level can still be reduced by aspects of the disclosure by removing the steepest edges of the current variation transitions. The reduction of noise by removing the steepest edges of the current variation transitions still achieves improvements in decoding communication messages even at electrical limits of the downhole devices. 
     Still referring to  FIG. 3 , in one or more embodiments, the data from each instrument can be read from the surface over the cable  308  at high-speed from multiple instruments as soon as data is generated. In spite of particular instruments performing at different rates and the latency of data rates over inductive couplers, collecting data from a network of multiple instruments may still be improved because the instruments on the network may work simultaneously. In some configurations, group polling to groups of instruments or fast polling without waiting for reply can be done to further improve data collection rates from the surface controller or computing device. 
     In some examples, the shunt current regulator  304  or noise canceller may be set in accordance with any of three operating modes when the current exceeds the set stable current level. In a first mode, the shunt current regulator  304  may increase the fixed current level to account for the change in required current. In a second mode, the shunt current regulator  304  may allow excessive current to be drawn from the cable  308  without adjusting the preset fixed current level. In a third mode, the shunt current regulator  304  may limit the current to the set level (causing a drop in supply voltage to an instrument). The shunt current regulator  304  can select any of these three modes responsive to commands from the surface. In some cases, the shunt current regulator  304  may include a protection feature that may automatically change operating mode based on transistor temperature or other physical properties. The shunt current regulator  304  may change the operating mode to protect the electronics from destruction or degradation. The shunt current regulator  304  may implement the protection feature in hardware or as firmware monitoring the health of critical components. 
       FIG. 3  illustrates other electronic components in some aspects of the circuit  300 . The cable  308  may have various resistive elements connected in series or parallel with capacitive elements, examples of these elements are resistors R 1 -R 14  and capacitors C 1 -C 6  as illustrated in  FIG. 3 . The cable  308  may also have inductive elements not shown in  FIG. 3 , however, it will be appreciated that cable  308  may represent a simplified equivalent circuit for many cable configurations (e.g., any type of cable). The shunt current regulator  304  may have various circuit components including resistors R 17 -R 22 , voltage sources V 2 -V 4 , and current source  13 . The current load  310  may include current sources I 1  and  12  and be coupled to resistors R 16  (i.e., a sensing element) and transistor M 1 . 
       FIG. 4  depicts a plot  400  of the current levels within a downhole circuit of a downhole node according to some aspect of the disclosure. In one example, the plot of the current levels depicted in  FIG. 4  may be measured in a downhole circuit, such as the downhole circuit depicted in  FIG. 2 . As illustrated by  FIG. 4 , a switch mode voltage regulator (i.e., switch mode regulator  202  in  FIG. 2 ) provides node current I N    406  (i.e., the hashed line) that is split by parallel circuit components. In one or more embodiments, the shunt current varies to maintain IN substantially constant and slightly greater than the maximum combination of I CL  and I CH , as illustrated by line  402 . The area below line  402  roughly represents the variable load current and the area above line  402  represents the varying shunt current. The low-current load current I CL  represented by line  404  may be provided to electronic components of the downhole circuit, such as measuring sensors and controllers. Accordingly, the current of the low-current load I CL  is substantially constant. The high-current load I CH  current may be an actuator and accordingly is characterized by a substantial variation in peak and valleys of the current waveform I CH . An example of the current I CH  peak may be activation of the actuator at a maximum current draw, while the valley of the current I CH  may indicate a deactivation of the actuator at a minimum current draw. 
     Approximately constant current level represented by line  404  represents the current drawn by electronics associated with the downhole device. The shunt current regulator may set the constant current level I TEC  based on computing a long-term historic current requirement average, adjusting a moving average over a certain period of time, or adjusting according to a previous or future operating mode of the shunt current regulator. The constant current level, represented by line  406  in  FIG. 4  (e.g., ITEC in  FIG. 3 ) may be adjusted up or down at a configurable rate, for example, a rate that is set to minimize disturbance of the cable communication. 
       FIG. 5A  depicts two diagrams of voltage and current measurements in two different circuits according to some aspect of the disclosure. For purposes of explanation, the circuit  300  of  FIG. 3  provides circuit output data  502  and may be assumed to implement some aspect of the disclosure, while a circuit that does not implement a shunt current regulator as described herein in some aspects is represented by circuit output data  504 . In circuit output data  504 , the constant current level represented by line  404  (i.e., I TEC  current) has two components. In one example, I TE  is the combination of I 1  and  12  as referenced in circuit  300  of  FIG. 3  but without shunt current regulator  304 . For instance, I 1  may represent the current drawn by an inductive coupler unit and I 2  may represent an additional current for electronics supply or for communication signals carried over the inductive coupler as a signal modulated on the power in the inductive coupler. The combination (e.g., a sum) of the two components I 1  and I 2  results in I TE . In some cases, communications can be transmitted as one or more series of pulses. Comparing the communication from the node of the circuit that has circuit output data  502  with the communication from the node of the circuit that has circuit output data  504 , the example in  FIG. 5A  clearly depicts that the communication voltage waveform from the circuit corresponding to output data  502  evidences significantly more stability than the communication voltage waveform from circuit output data  504 . Accordingly, decoding the transmitted communication from the circuit that has circuit output data  502  is significantly less difficult than decoding the transmitted communication from the circuit that has circuit output data  504 . 
       FIG. 5B  depicts communications from a downhole circuit to a surface computing device in two different circuits according to some aspect of the disclosure. For example,  FIG. 5B  illustrates a communication  508  from a downhole circuit with a shunt current regulator to a surface computing device as compared with a communication  506  from a downhole circuit that does not implement the shunt current regulator to a surface computing device. In the particular example of  FIG. 5C , the communication is measured at the surface computing device. 
       FIG. 5C  depicts communications from a surface computing device to a downhole circuit in two different circuits according to some aspect of the disclosure. For example,  FIG. 5C  illustrates a communication  512  from a surface computing device to a downhole circuit with a shunt current regulator as compared with communication  510  from a surface computing device to a downhole circuit that does not implement the shunt current regulator. In the particular example of  FIG. 5C , the communication is measured at the downhole circuit. 
     Referring to  FIGS. 5A-5C , in downhole applications, implementation with minimal, sensitive components is crucial for reliability. Less noise on the communication channel may allow for increased bitrates and communication with relatively straightforward transmitter and receiver circuits. Inductive coupler communication is generally slow compared to other traffic on the cable line. Accordingly, if the inductive couplers in the system occupy a substantial quantity of time for powering or communication, or both, overall system performance may be reduced significantly. Some aspects of the disclosure enable communication at a higher bitrate. In addition, aspects of the disclosure enable communication with other instruments while waiting for data from one or many other active (e.g., creating current noise downhole) downhole instruments. Incorporating local data storage and high-speed readout on request when data is available will further improve the response time of the overall system. 
     In an example of communication timing improvements, the following non-limiting example is provided. In one example of a system, two downhole instruments each located in circuits behind four inductive couplers (i.e., a total of 8 inductive couplers) and an additional 15 instruments are connected directly to the cable line (i.e., 23 cable line connections total). 
     For explanatory purposes, the response times in the system may be a one-second response time from each instrument directly connected to the cable line and two seconds from each instrument located in circuits behind inductive couplers. Using these examples of values, the communication time for the instruments can generally be computed as four seconds for the two instruments multiplied by the number of inductive couplers yielding a total of 16 seconds. The additional 15 instruments would add 15 seconds (i.e., one second each) to the total response time. Accordingly, the total response time in this example is 31 seconds. Implementing some aspects of the disclosure and including local storage capabilities, the total response time can be reduced to four seconds. 
     The additional 15 instruments on the cable line can be polled simultaneously in a group that may include the additional 15 instruments. The simultaneous polling of the additional instruments can take place while waiting for the instruments behind the inductive couplers to get ready. In this example, at a time when the slowest instrument behind the inductive coupler is ready to communicate (e.g., after about 4 seconds), all the other instruments have already been polled and data has been read at relatively high-speed on the cable. The communication improvement is approximately eight-fold by receiving the instrument data from 23 instruments in four seconds compared with a typical speed of receiving the instrument data from 23 instruments in 31 seconds. 
       FIG. 6  is a flowchart of a process for regulating current drawn from a tubing encapsulated cable according to some aspects of the disclosure. Process  600  as illustrated in  FIG. 6  provides a method of controlling a transistor to regulate current drawn from the cable. At block  602 , the system provides a current to a cable. At block  604 , the downhole circuit (e.g., downhole circuit  110 ) draws a current from the cable. At block  606 , the current drawn from the cable is monitored by a sensing element. For instance, a sensing element (e.g., R 16  of  FIG. 3 ) monitors the voltage and determines the current level on the cable. At block  608 , the sensing element generates a sense signal. For instance, a sense signal may be generated by measuring the voltage across the sensing element (i.e., R 16 ). In some cases, the sense signal may be amplified by amplifier U 1 . At block  610 , a compensation signal is generated from the sense signal to control current according to the selected one of the operating modes. For instance, a compensation signal may be generated by transistor M 1  of  FIG. 3 . In one example, the transistor M 1  may provide compensation current to fill a dip in load current to maintain the current level in the cable stable. At block  612 , a transistor is controlled to regulate the current drawn from the cable according to the set operating mode as described with regards to  FIGS. 1-5 . 
     Terminology used herein is for describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” or “comprising,” when used in this specification, specify the presence of stated features, steps, operations, elements, or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, or groups thereof. Additionally, comparative, quantitative terms such as “above,” “beneath,” “less,” and “greater” are intended to encompass the concept of equality, thus, “less” can mean not only “less” in the strictest mathematical sense, but also, “less than or equal to.” Use of terms such as “first” and “second” when describing components is for convenience of description only, and does not imply a location, order of operation, or order of assembly. 
     The order of the process blocks presented in the examples above can be varied, for example, blocks can be re-ordered, combined, or broken into sub-blocks. Certain blocks or processes can be performed in parallel. The use of “configured to” herein is meant as open and inclusive language that does not foreclose devices configured to perform additional tasks or steps. Additionally, the use of “based on” is meant to be open and inclusive, in that a process, step, calculation, or other action “based on” one or more recited conditions or values may, in practice, be based on additional conditions or values beyond those recited. Elements that are described as “connected,” “connectable,” or with similar terms can be connected directly or through intervening elements. 
     In some aspects, a system for regulating current is provided according to one or more of the following examples: 
     As used below, any reference to a series of examples is to be understood as a reference to each of those examples disjunctively (e.g., “Examples 1-4” is to be understood as “Examples 1, 2, 3, or 4”). 
     Example 1 is an apparatus comprising: a voltage regulator couplable to a cable extending downhole from a surface through a wellbore; and a shunt current regulator communicatively coupled to the voltage regulator, the shunt current regulator including a sensing element to monitor a current drawn from the cable downhole, wherein the shunt current regulator is couplable to a current load. 
     Example 2 is the apparatus of examples 1, wherein the current load comprises a high-current load connected to the switch mode voltage regulator. 
     Example 3 is the apparatus of example 1, wherein the current load comprises a high-current load and a low-current load coupled in parallel. 
     Example 4 is the apparatus of examples 1-3, further comprising a computing device to receive a communication from the current load via the cable. 
     Example 5 is the apparatus of examples 1-3, wherein the sensing element comprises a current sensing resistive element to produce a voltage monitored by the shunt current regulator. 
     Example 6 is the apparatus of examples 1-3, further comprising a transistor communicatively coupled to the sensing element, wherein a sense signal from the sensing element is configurable to provide a compensation signal that is applied to the transistor to control the transistor to regulate the current drawn from the tubing encapsulated cable downhole. 
     Example 7 is the apparatus of example 6, further comprising: a first amplifier connected to the sensing element to amplify the sense signal, wherein the sense signal comprises a voltage across the sensing element; and a second amplifier connected to the transistor to amplify a correction signal to produce the compensation signal. 
     Example 8 is a method of current regulation, the method comprising: monitoring, by a sensing element, a current drawn from a tubing encapsulated cable disposed downhole extending downhole from a surface through a wellbore; generating a sense signal from the sensing element; generating a compensation signal from the sense signal; and controlling a transistor to regulate the current drawn from the tubing encapsulated cable, wherein the controlling comprises: dissipating power in the transistor to stabilize the current drawn; and providing compensation current to increase the current drawn. 
     Example 9 is the method of current regulation of example 8, wherein the sensing element comprises a current sensing resistive element connected between the tubing encapsulated cable and a shunt current regulator. 
     Example 10 is the method of current regulation of example 8, further comprising setting a substantially constant current level, the setting comprising at least one of: a first mode that increases the substantially constant current level to meet a current draw demand; a second mode that allows an excessive current to be drawn from the tubing encapsulated cable preserving the substantially constant current level; or a third mode that limits the current to the substantially constant current level. 
     Example 11 is the method of current regulation of example 10, further comprising transitioning between modes automatically based on a temperature of the transistor or other physical properties of the transistor. 
     Example 12 is a system comprising: a processing device couplable to a tubing encapsulated cable extending downhole from a surface through a wellbore, wherein the processing device is operable to: decode communication from a downhole node; and send communication to the downhole node; the downhole node comprising: a switch mode voltage regulator couplable to the tubing encapsulated cable; a shunt current regulator couplable to the switch mode voltage regulator, the shunt current regulator including a sensing element to monitor a current drawn from the tubing encapsulated cable downhole; and a current load. 
     13. The system of example(s) 12, wherein the current load comprises a high-current load and a low-current load connected in parallel. 
     Example 14 is the system of example 12, wherein the downhole node further comprises a current sensing active circuit connected between the tubing encapsulated cable and the shunt current regulator. 
     Example 15 is the system of example 12, wherein the sensing element comprises a current sensing active circuit, wherein the current sensing active circuit produces a voltage monitored by the shunt current regulator. 
     Example 16 is the system of example 12, comprising a transistor communicatively coupled to the sensing element, wherein a sense signal from the sensing element provides a compensation signal that is applied to the transistor to control the transistor to regulate the current drawn from the tubing encapsulated cable. 
     Example 17 is the system of examples 12-16, further comprising: a first amplifier connected to the sensing element to amplify the sense signal, wherein the sense signal comprises a voltage across the sensing element; and a second amplifier connected to the transistor to amplify a correction signal to produce the compensation signal. 
     Example 18 is the system of examples 12-16, further comprising an inductive coupler connected to the downhole node. 
     Example 19 is the system of examples 12-16, wherein at least one of the communication from the downhole node or the communication to the downhole node comprises power line communication over the tubing encapsulated cable. 
     Example 20 is the system of examples 12-16, wherein the shunt current regulator sets the current drawn from the tubing encapsulated cable in accordance with at least one of: a first mode that increases a substantially constant current level to meet a current draw demand; a second mode that allows an excessive current to be drawn from the tubing encapsulated cable preserving the substantially constant current level; or a third mode that limits the current to the substantially constant current level. 
     The foregoing description of the examples, including illustrated examples, has been presented only for the purpose of illustration and description and is not intended to be exhaustive or to limit the subject matter to the precise forms disclosed. Numerous modifications, combinations, adaptations, uses, and installations thereof can be apparent to those skilled in the art without departing from the scope of this disclosure. The illustrative examples described above are given to introduce the reader to the general subject matter discussed here and are not intended to limit the scope of the disclosed concepts.