Patent Publication Number: US-9850753-B2

Title: Cable integrity monitor for electromagnetic telemetry systems

Description:
PRIORITY APPLICATION 
     This application is a continuation application of U.S. patent application Ser. No. 11/590,271, filed Oct. 31, 2006, which application is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     Various embodiments described herein relate to electromagnetic telemetry systems and methods including apparatus, systems, and methods for detecting faults in oil field electromagnetic telemetry systems. 
     BACKGROUND INFORMATION 
     During drilling and extraction operations of hydrocarbons, a variety of communication and transmission techniques have been attempted for data communications between the surface of the earth and the downhole tools. The data communications from the downhole tool to the surface may be used to provide information related to the evaluation of the formation, control of the drilling operations, etc. However, drilling, exploration, and extraction occur in remote and hostile conditions are hostile to electronic equipment and electronic communications. In some field communication schemes the signal will have significant power and if the communication channel is interrupted, then the power may cause arcing or other electromagnetic events that may be dangerous in view of the hydrocarbon extraction environment. This type of environment may be classified as a “hazardous” environment according to safety regulation authorities. See, e.g., The Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR) and Explosive Atmospheres Directive 99/92/EC (ATEX 137) which are enforced by the various government organizations, e.g., Petroleum Licensing Authorities, in Europe, or Underwriters Labs, National Electrical Code 500 and Canadian Services Association in North America. As a result there is a need to monitor the integrity of electronic communications between downhole and surface communication devices. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an apparatus according to various embodiments of the invention; 
         FIG. 2  is a schematic view according to various embodiments of the invention; 
         FIG. 3  is a more detailed view according to various embodiments of the invention; 
         FIG. 4  is a view of connections to a blowout preventer according to an embodiment of the invention; 
         FIG. 5  is a graph showing a fault zone according to an embodiment of the invention; 
         FIG. 6  is a flow chart illustrating a method according to various embodiments of the invention; and 
         FIG. 7  is a waveform captured according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a system  100  for the exploration, drilling, and extraction of hydrocarbons. An exploration/extraction rig structure  101  is in communication with electronics equipment  102  that in turn is in electrical communication with a grounding structure  104 . In an embodiment, the electrical equipment  102  is remotely positioned relative to the rig  101  and connected by a communication line  106 , such as a cable or wire. The communication line  106  may be a double core cable that has two separate signaling paths in a single construction. The communication line  106  may be a plurality of separate, parallel signaling paths in separate lines of cables. A further communication line  108 , such as a cable or wire, connects the electronics equipment  102  to the grounding structure  104 . Line  108  may also be a multiple core line or a plurality of single core lines. The grounding structure  104  may be a stake embedded in the earth  110 . The electronics equipment is positioned remote from the rig  101  to protect the electronics  102  from the harsh conditions of the rig site and protect the electronics  102  from damage while the rig is forming, drilling, or in other rig operations. Moreover, the electronics  102  can be mounted in a mobile platform and brought to a well site as needed. The electronics  102  may communicate with downhole devices and may be a logging facility for storage, processing, and analysis. Such a facility may be provided with electronic equipment  102  for various types of signal processing. Similar log data may be gathered and analyzed during drilling operations (e.g., during logging while drilling, measurement while drilling, seismic while drilling operations). That is, any data acquired downhole is sent to the surface via telemetry for use by the electronics  102 . The term “telemetry” is used in the hydrocarbon extraction art to define a method of transmitting information from the downhole to the surface. Telemetry can be achieved by many means, for example, “hardwire,” where the signal is passed along a conducting medium via electrical means and to which the downhole tool is in communication and/or attached. 
     Rig structure  101  includes rig support frame or derrick  115  located on a platform  116  at a surface of earth  110  of a well or subsurface formation  117 . Frame  115  provides support for downhole structures such as a drill string  119  and/or a logging device  150 . A drill string  119  may operate through surface level metal work such as a blowout preventer  120  to penetrate a rotary table  121  for drilling a borehole  122  through subsurface formations  124 . The drill string  119  may include a Kelly  126 , drill pipe  128 , and a bottom hole assembly  130 , perhaps located at the lower portion of the drill pipe  128 . The bottom hole assembly  130  may include drill collars  132 , a downhole tool  134 , and a drill bit  136 . 
     The drill bit  136  may operate to create a borehole  122  by penetrating the earth surface  110  and subsurface formations  124 . The downhole tool  134  may comprise any of a number of different types of tools  135  including MWD (measurement while drilling) tools, LWD (logging while drilling) tools, seismic while drilling, magnetic resonance image logging (MRIL), and others. During drilling operations, the drill string  119  may be rotated by rotary table  121 . In addition to, or alternatively, the bottom hole assembly  130  may also be rotated by a motor (e.g., a mud motor) that is located downhole. The drill collars  132  may be used to add weight to the drill bit  136 . The drill collars  132  also may stiffen the bottom hole assembly  130  to allow the bottom hole assembly  130  to transfer the added weight to the drill bit  136 , and in turn, assist the drill bit  136  in penetrating the surface  110  and subsurface formations  124 . 
     During drilling operations, a mud pump  142  may pump drilling fluid (sometimes known as “drilling mud”) from a mud pit  144  through a hose  146  into the drill pipe  128  and down to the drill bit  136 . The drilling fluid can flow out from the drill bit  136  and be returned to the surface  110  through an annular area  140  between the drill pipe  128  and the sides of the borehole  122 . The drilling fluid may then be returned to the mud pit  144 , where such fluid is filtered. In some embodiments, the drilling fluid can be used to cool the drill bit  136 , as well as to provide lubrication for the drill bit  136  during drilling operations. Additionally, the drilling fluid may be used to remove subsurface formation  124  cuttings created by operating the drill bit  136 . 
     In another embodiment, the rig structure  101  is positioned over a borehole  122 , which has been drilled or formed, to support a tool body  150  as part of a logging operation. Here it is assumed that the drilling string has been at least temporarily removed from the borehole  122  to allow logging tool body  150 , which includes an information gathering, downhole tool  134 , such as a probe or sonde, to be lowered by cable, wireline or logging cable  154  into the borehole  122 . Typically, the tool body  150  is lowered to the bottom of the region of interest and subsequently pulled upward at a substantially constant speed. During the upward trip, instrument tool  134  included in the tool body  150  may be used to perform measurements on the subsurface formations adjacent the borehole as the tools pass by. In an embodiment the tool body communicates with the surface electronics  102  via a communication line, such as casing pipe  160 , blowout preventer  120 , and line  106 . 
     It should also be understood that the apparatus and systems of various embodiments can be used in applications other than for drilling and logging operations, and thus, various embodiments are not to be so limited. The illustration of system  100  is intended to provide a general understanding of the structure of various embodiments, and they are not intended to serve as a complete description of all the elements and features of apparatus and systems that might make use of the structures described herein. 
     In operation the electronics  102  communicates via electromagnetic telemetry with downhole devices, such as those described in  FIG. 1  but embodiments of the present invention are not limited to only those specifically described, using power electronics to deliver a signal via line  106  to the metal work extending downhole. The metal work in an example include the drill string  119 . In a further example, the metal work includes the casing pipes  160  or other tubes extending below ground. The electronics may produce a carrier signal on which data is carried for example via modulation techniques. Examples of downhole telemetry are discussed in “Electric Drill Stem Telemetry” by J. Bhagwan and F. N. Trofimenkoff, IEEE Transactions on Geoscience and Remote Sensing, Vol. GE-20, No. 2, April 1982; “Propagation of electromagnetic Waves Along a Drillstring of Finite Conductivity” P. DeGauque and R. Grudzinski, SPE Drilling Engineering, June 1987; “Electromagnetic Basis of Drill-Rod Telemetry” by D. A. Hill and J. R. Wait, Electron. Letters Vol. 14, pages 532-533; and “Theory of Transmission of electromagnetic Waves Along a Drill Rod in Conducting Rock”, J. R. Wait and D. A. Hill, IEEE Transactions on Geoscience Electronics, Vol. GE-17, No. 2, April 1979. Each of these documents are hereby incorporated by reference for any purpose. The signal travels through the line  106  and metal work below ground where it is received by downhole tools  135 . The downhole tools  135  may also transmit data created during hydrocarbon exploration and extraction activities though the downhole metal work to the surface electronics  102 . In an example, the signal is a low frequency analog signal such that the signal can travel the length of the downhole metal work to reach a downhole tool. In an example, the signal is a sinusoidal signal having a frequency in a range of just over 0 Hz to about 250 kHz. However, such a low frequency signal would still require significant power from about 1 kilowatt and up. In an embodiment the power of the signal is about 2.0 kilowatts or higher. In an embodiment, the power is on a range up to 15. kilowatt. Moreover, the signal would be modulated using at least one of quantum phase shift key, pulse width modulation, amplitude modulation and pulse position modulation as a data encoding scheme. Other types of modulation may be used to enhance the bit rate of the communication. 
     In view of these types of signals and, in particular, the signal power, a dangerous condition may occur if the communication channel, for example, cable  106 , or downhole metal such as drill string  119 , or casing pipe  160  is damaged, disconnected or disturbed. This may generate an electrical signal such as a spark that may ignite potentially explosive gases in addition to the risk of electrical shock or electrocution to attendant personnel. 
       FIG. 2  shows a schematic view of an embodiment of the present invention with the electronics  102  connected to the blowout preventor  120 , which is connected to the downhole metal work  201 . The electronics includes a host system  205  that controls a power source  207 , which are both in communication with a signal integrity monitor  210 . The host system  205  may include electronic circuitry used in high-speed computers, communication and signal processing circuitry, modems, processor modules, embedded processors, data switches, and application-specific modules, including multilayer, multi-chip modules. Such apparatus and systems may further be included as sub-components within a variety of electronic systems, such as displays, televisions, personal computers, workstations, vehicles, and conducting cables for a variety of electrical devices, among others. Power source  207  provides the power for the signal that is created by the host system  205  and is conducted to the hole site whereat the signal is communicated downhole to downhole tools. In an embodiment, the power source  207  is an analog power amplifier that outputs a signal in up to about 250 kHz with a root mean power of up to 2 kilowatts or higher. In an embodiment, the amplifier outputs a signal of about 1.8 kilowatts. In an embodiment, the power source is similar to an AC audio amplifier for audio listening equipment. In a further embodiment, the power source is a DC amplifier. 
     The cable signal integrity monitor  210  is connected through physical lines  106  to the host system  205 , power source  207 , and blowout preventor  120 . The lines  106  provide wired communication between these devices. Lines  106  may be housed in a single insulation, for example, coaxially. The lines  106  are adapted to provide a signal path for AC communication signals in the well site environment. The lines  106  are insulated and hardened to prevent damage thereto in this environment. However, the lines may still become damaged in this environment, for example, by workers using tools or other heavy equipment. The monitor  210  senses signals in the lines  106 . Based on the sensed signals, the monitor  210  either maintains the steady state, which allows electrical communication in the system, or will disconnect the power source from the communication system in an attempt to minimize stray electrical power in the event of a fault. It is also desirable to minimize false fault detection. Turning off the power will minimize the likelihood that the electrical power, which is needed for metal work communication with downhole equipment, will cause a hazardous situation such as electrical shock or ignition of gases. The cable integrity monitor  210  includes electrical signal detectors. In an embodiment, the monitor includes a resistance sensor to sense a change in resistance in the communication path. In an embodiment, the monitor  210  includes a voltage sensor to sense a change in voltage in the signals in the communication path. In an embodiment, the monitor  210  includes a current sensor to sense a change in current in the communication path. One example of a current sensor includes a current sense amplifier connected to the communication lines  106 . The current sense amplifier may include a comparator to compare the sensed signal to a reference signal that represents the signal produced by the host system  205 . In an embodiment, the current sense amplifier includes two internal comparators to produce a pulse-width output signal proportional to the current being sensed. In an embodiment, the current sensor includes a hall effect sensor that operated on a non-contact basis by measuring the change in the magnetic field produced by signals in the lines  106 . 
       FIG. 3  shows an embodiment of the monitor  210  with connections to the power source  207 , host system  205 , and blowout preventor  120 . In the illustrated embodiment, the communication connections  106  are shown as multiple wires, i.e., two wire connections. However, it will be recognized that a single wire may be used. Monitor  210  includes a safety manager circuit and safe mode driver  301  that is in direct connection with the host system  205 . Driver  301  may be implemented as a circuit. In an embodiment, the driver  301  is a software module operating in a processor/memory device. The driver  301  receives a modulated signal from the host system  205  and transmits the signal to the power amplifier  207  over connection  306 . Driver  301  further sends an on/off signal over connection  307  to the amplifier  207  to control the state of the amplifier  207 . Power amplifier  207  is in an on or off state depending on the signal from the driver  301 . The amplifier  307  outputs and amplified signal on connection  106  to inputs of a sensor circuit  310 . The sensor circuit determines the integrity of the signal path and further toggles the amplifier to off as well as feedbacks to the host system  205 . 
     The sensor circuit  310  in the illustrated embodiment is a Wheatstone bridge. The bridge has a first input  311  connected to one of the lines  106  and a second input  312  connected to a second of the lines  106 . The bridge includes a circuit to determine a reference signal, which includes a first leg  316  in series with a second leg  317 . The bridge further includes a second circuit to determine a sense signal, which includes a third leg  318  and a fourth leg  319 . Each of legs  316 - 319  has a predetermined impedance. In an embodiment, each of the legs  316 - 319  have a known resistance. First leg  316  is between the first input  311  and a reference output  320 . Second leg  317  is between the reference output  320  and the second input  312 . Third leg  318  is between the first input and the sensed output  321 . Fourth leg  319  is between the sensed output  321  and the second input  312 . In one embodiment, the third leg includes an electrical line extending from the first input to a relay switch  330 . The relay  330  is a circuit breaker in an embodiment. The third leg  318  further includes an electrical line  331  extending from the relay. This electrical line  331  covers essentially the entirety of the distance from the electronics to the well site. In an embodiment, this distance is tens of meters. In an embodiment, this distance is up to about 100 meters. In an embodiment, the length is up to about 125 meters. In yet other embodiments, the length can be equal to or greater than 1,000 meters. That is the length of lines  106 ,  331  are up to or greater than 1 kilometer. The line  331  is connected to the blowout preventor  120 . In an embodiment, line  331  is clamped to an arm of the blowout preventor  120 . Adjacent the blowout preventor  120  and distal to the monitor  210 , leg  318  includes a known resistance, which is connected to a line  332  that returns to the relay  330  and connects to the sensed output  321 . In an embodiment, the lines  331 ,  332  are housed in a single insulator, dual core cable. In a further embodiment, the lines  331 ,  332  are in a braided cable. In an embodiment, the lines  331 ,  332  are separate lines. The reference signal at  320  and the sensed signal  321  are each fed to a comparator  340 . Comparator  340  is a ratiometric window comparator. The comparator  340  compares the reference signal to the sensed signal. If there is a certain deviation of the sensed signal from the reference signal, then comparator  340  outputs a signal to the driver  301 . Driver  301  then opens the normally closed relay  330  to disconnect the power amplifier  207  from the third leg  318 , and hence, the well site. The driver  310  further turns off amplifier  207 . Driver  310  signals host system  205  that the communication with the equipment at the well site is down. Additional data related to the shut down can be stored by the host system  205 . 
     It is recognized that the cable  106  is connected to a metal work such as a blowout preventor in the illustrated embodiment. However the invention is not so limited and may be connected to metal work at the surface known to those in the field of wells. The surface level metal work  120  may include one of a pump jack, a nodding donkey or a horsehead pump. In an embodiment, the cable  106  is connected to a conductive stake at the bore hole. In an embodiment, the cable  106  is connected to a pipeline service station. In an embodiment, the cable  106  extends from an offshore platform down to metal work at the borehole. 
       FIG. 4  shows an embodiment of the connection from the signal monitor  210  to the well site. The signal monitor  310  is electrically connected to the lines  331 ,  332 . Line  331  delivers the modulated power signal that contains the data to be transmitted downhole through the downhole metal work. Line  331  is connected to one side of the blowout preventor  120  by a clamp  402 . Line  332  is connected to another side of blowout preventor  120  by a clamp  403 . It will be understood that each of lines  331  and  332  could be connected to a single one of clamps  402 ,  403  in an embodiment. Signals arrive through powered line  331  and enter the blowout preventor  120 , which in turn transmits that electrical signal to the downhole metal work  201 . Return line  332  feeds the powered signal back through an impedance (e.g., a set sense resistance), to the monitor  210 . The set sense resistance is housed such that it is proximal to the well site and protected from the elements and accidental damage. 
       FIG. 5  shows a graphical representation of an acceptable waveform to provide cable or connection fault detection. The reference signal  401  is shown as a sinusoidal signal in which data is embedded. As the reference signal  401  travels a sinusoidal pattern, an upper threshold limit  402  and a lower threshold limit  403  is determined as a percentage of the reference signal. In an embodiment, the reference signal is a reference voltage. The sensed signal at output  321  is compared to the reference signal, which is at output  320 . If the sensed signal exceeds the upper threshold  402  or falls below the lower threshold  403 , then a fault is detected. The driver  301  trips the relay and turns off the power amplifier  207 . 
       FIG. 6  is a flow chart illustrating a method  600  of an embodiment of the present invention. A data signal is produced,  601 , which includes a carrier signal that is modulated to include data. The data signal typically does not have sufficient power to transmit through downhole metal work to subsurface tools. The data signal is then amplified,  603 , remote of the well site. The amplified signal is delivered to the downhole metal structures,  605 , such as drill strings or casing. A portion of the amplified signal is fed back to the location remote of the well site,  607 . The amplified data signal is sampled,  609 . The feed back signal is sampled,  611 . In an embodiment, the sample signals are analog and, hence, the sampling is performed at an analog circuit, such as a bridge circuit. In an embodiment, the sampled signals are digitally sampled. In a further embodiment, the sampling is performed at an analog circuit, such as bridge. The sampled signals are compared,  613 . This comparison is done in the digital domain when digitally sampled or using an analog comparator circuit if in an analog domain. If the sampled signals are within a range or threshold  615 , then the method continues, i.e., returns to step  601 . However, many of these steps can occur simultaneously. If the comparison shows that the feedback signal deviates from the reference amplified signal outside the threshold, then the power amplifier is disconnected from communication with the well site,  617 . The amplifier is also turned off based on the comparison,  619 . 
       FIG. 7  shows a data graph that illustrates the operation of the presently described structures, apparatus and methods. Waveform  701  shows an output waveform, which is a portion of sine wave that is applied at the well site. In an embodiment, the signal is a 30 volt peek to peek, 11.5 Hz signal. Waveform  702  represents the signal over the third leg of the bridge, sensing circuit. Waveform  703  represents the output from the comparator. Waveform  704  represents a fault latch signal in the driver. A brief description of the operation follows. At time t 0  a short circuit trip occurs, see waveform  702 . A short circuit fault may occur when the power line  331  and the sense line  332  are electrically connected together other than through the metal work  120 . This can occur when a cable that includes the power and sense lines  331 ,  332  is squashed together or otherwise damaged. The value at leg  318  goes to a low impedance value. In an example, the leg  318  goes to a low impedance at time t 1  as shown in  FIG. 7 . The bridge circuit  310  goes imbalanced, which causes the comparator to generate a fault signal. Returning to  FIG. 7 , at time t 1 , the fault is detected in the signal monitor  210 , see waveform  703 . The fault is latched in the monitor  210 , see waveform  704 . The driver  301  trips, i.e., opens the normally closed, relay  330 . The electrical power at the well site is no longer powered by the electronics based on the open relay. The power at the well site begins to decay at time t 1 . The time period between t 0  and t 1  is less than one millisecond. In an embodiment, the time period between the short and the sensing of the short is about 800 microseconds. The power at the well site decays rapidly to about 20% of its power at t 1  by time t 2 . The power in signal  701  begins to decay before the power amplifier is turned off. At time t 3 , the fault detector signal  703  returns to a no-fault state. However, the fault state is latched in waveform  704 , which will not allow the communication through relay  330  to reset without resetting the fault latch. The fault latch is reset after personnel inspect the communication system including all lines, wires, cables, and connections. As shown in this embodiment, the fault signal is a digital signal. 
     The present system  100  may further detect an open circuit fault, which will generate similar waveforms. An open circuit fault is where the Rsense portion of leg  318  is no longer connected to the bridge  310 . In an embodiment, the leg  318  is not electrically connected to the remainder of the bridge. The bridge  310  will become imbalanced and signal the comparator. The comparator will signal the driver  301  that a fault has occurred. More specifically, waveform  703  will show a fault. Waveform  704  will latch the fault. Waveform  701  will decay shortly after the fault is detected. 
     The present description refers to on shore structures examples. It will be recognized that the embodiments of the present invention are adaptable to monitor the integrity of offshore cables. 
     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. Information, including parameters, commands, operands, and other data, can be sent and received in the form of one or more carrier waves. 
     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 skill in the art upon reviewing the above description. 
     The Abstract of the Disclosure is provided to comply with 37 C.F.R. §1.72(b), requiring an abstract that will allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment.