CIRCUITS AND METHODS FOR MONITORING CURRENT IN ELECTROMAGNETIC TELEMETRY SYSTEMS

Abstract

The present disclosure provides a current monitoring circuit for monitoring current in a electromagnetic telemetry system. The circuit includes a transmitter configured to generate an output current. One or more current monitors are positioned to detect current at or near the electrode stations or at positions along the one or more loops. Measured current data is transmitted back to the transmitter, which may be shut down if necessary. Methods for monitoring current in an electromagnetic telemetry system are also provided.

Claims

1. A current monitoring circuit for monitoring current flow in an electromagnetic telemetry system, comprising: a transmitter configured to generate an output current through one or more wires; and at least one current monitor for monitoring current in the one or more wire.

2. The current monitoring circuit of claim 1, further comprising at least one electrode station in electrical communication with the transmitter, wherein the at least one current monitor is positioned at or near the at least one electrode station.

3. The current monitoring circuit of claim 1, wherein the at least one current monitor comprises a radio for wirelessly transmitting data related to the monitored current to a receiver in communication with the transmitter.

4. The current monitoring circuit of claim 3, wherein the transmitter comprises circuitry, firmware and/or software for processing the data received from the at least one current monitor.

5. The current monitoring circuit of claim 4, wherein the transmitter is configured to detect an unwanted conduction path to ground in the system based on the data received from the one or more current monitors.

6. The current monitoring circuit of claim 5, further comprising a repeater for relaying the data from the current monitor to the receiver.

7. The current monitoring circuit of claim 1, further comprising fiber optic cable for transmitting data related to the monitored current from the at least one current monitor to a receiver in communication with the transmitter.

8. The current monitoring circuit of claim 1, wherein the at least one current monitor comprises a Hall device or a resistor.

9. The current monitoring circuit of claim 1, wherein the at least one current monitor comprises a signal conditioner.

10. The current monitoring circuit of claim 2, wherein the transmitter is connected to the at least one electrode station by insulated wire.

11. A method of measuring current flow in a electromagnetic telemetry system, comprising the following steps: providing a transmitter comprising a receiver and configured to generate an output current through one or more wires; providing at least one current monitor comprising a radio and configured to measure current at one or more positions along the one or more wires; and transmitting data related to the measured current from the one or more current monitors to the transmitter.

12. The method of claim 11, wherein the transmitter comprises circuitry, firmware and/or software configured to process the data received from the one or more current monitors.

13. The method of claim 12, wherein the processing comprises comparing the measure current to an expected value or an output value at the transmitter.

14. The method of claim 13, further comprising the step of shutting down the transmitter when the measured current is not equal to the expected or output value.

15. The method of claim 14, further comprising the step of detecting, by the transmitter, an unwanted conduction path to ground in the system based on the data received from the one or more current monitors.

16. The method of claim 15, wherein the electromagnetic telemetry system is a dipole-dipole system.

17. The method of claim 16, further comprising the step of providing one or more electrode stations, wherein the one or more current monitors are positioned at or near the one or more electrode stations.

18. The method of claim 12, wherein the wire is configured in one or more loops, and wherein the one or more current monitors are positioned along the one or more loops.

19. The method of claim 12, further comprising the step of providing a repeater, wherein the data is transmitted from the current monitor to the transmitter by relaying the data via the repeater.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

[0010] FIG. 1 shows an example of a typical electromagnetic telemetry system known in the prior art.

[0011] FIG. 2 shows examples of current flow disruptions in a telemetry system known in the prior art.

[0012] FIG. 3 shows a distributed RC network of a surface borehole telemetry system.

[0013] FIG. 4 shows a preferred embodiment of a borehole telemetry system according to the present disclosure.

[0014] FIGS. 5A and 5B shows two embodiments of a current monitor according to the present disclosure.

DETAILED DESCRIPTION

[0015] As is shown in FIG. 3, the current flowing out of the transmitter will not equal the current flowing into the ground at the electrode station. This is due to the distributed resistance of the wire (200-1 to 200-n and 201-1 to 201-n) and the distributed capacitance to ground along the wire (202-1 to 202-n and 203-1 to 203-n).

[0016] FIG. 4 shows a preferred embodiment of a current monitoring circuit according to the present disclosure. The circuit includes a transmitter 101 comprising a radio 106 for sending and receiving data. The data will typically be sent from and/or to current monitors 107. Radio 106 may be any system for transmitting and receiving information and/or data wirelessly between the transmitter and current monitors that are known in the art. Alternatively, transmitter 101 may be configured to receive current monitoring information or data from current monitors via a wired connection, such as fiber optic cable or a system of isolation amplifiers and wire. Transmitter 101 may further include a current monitor for monitoring output current or a reference current at the transmitter. Circuity, firmware and/or software may be included for processing and analyzing current data, including data received from current monitors 107 as well as current data obtained at the transmitter. For example, the circuity, firmware and/or software may be configured to compare a current measured by a current monitor at an electrode station 100 to a reference current that is output by the transmitter.

[0017] The circuit further includes electrode stations 100-1 and 100-2. While two electrodes stations are shown in the exemplary embodiment of FIG. 4, any number of electrode stations may be included in the circuit. Electrode stations 100-1-100-2 are in electrical communication with or otherwise connected to transmitter 101 via insulated transmitter wires 102-1-102-2, respectively. The number of wires included in the circuit may vary, but typically may correspond to the number of electrode stations in the circuit. The circuit further includes circuit monitors 105-1-105-2 in communication with electrode stations 100-1-100-2, respectively (as well as in communication with corresponding wires 102-1-102-2, respectively). The current monitors may be placed along the transmitter wires, typically at or near the electrode stations. The monitors may include a radio, as described below, for transmitting data or information regarding the current detected or measured by the current monitors back to transmitter 101. A radio may be any wireless system known in the art. Alternatively, a wired system or connection may be used for transmitting data to the transmitter. The current measured by the current monitors may then be compared to the output current of the transmitter or current switch. If the reported current at an electrode station is not equal to the output current of the transmitter adjusted for the distributed resistance and capacitance, the voltage may be removed, thereby rendering the electrodes and/or wiring safe.

[0018] FIGS. 5A and 5B shows two possible embodiments of a current monitor that can be used in accordance with the present disclosure. Referring to FIG. 5A, current monitors may be placed at any location in the circuit, but preferably are placed at or near electrode stations or at points distant from a transmitter in a loop or loops of a multiple loop system. In one embodiment, the current monitor 116-1 includes a Hall device 110 that detects and measures current at input current connections 115-1 and 115-2. A Hall device, also known as a Hall Effect sensor or Hall element, is well known in the art and operates based on the principles of the Hall Effect. It can detect direct and alternating currents and does not require direct contact with a wire or other element in which current is measured. Current monitor 116-1 may also comprise a signal conditioner 111, which may function to convert a detected current into transmittable information. The current monitor may further include circuitry, firmware and/or software for calculating a current, including an expected current. Current monitor 116-1 may further comprise a radio 112, which may transmit data or information about the detected current back to the transmitter, and an antenna 113.

[0019] In an alternative embodiment shown in FIG. 5B, a current monitor 116-2 may include a non-inductive resistor 114 for detecting and measuring current at current input connections 115-1 and 115-2. The use of a resistor 114 to detect and measure current can be accomplished according to several methods known in the art, including measuring the current based on the known resistance of the resistor and the voltage drop measured across the resistor. This embodiment of a current monitor may also include a signal conditioner 111 and a radio 112, which may transmit data or information about the detected current back to the transmitter, and antenna 113. Current monitors 116-1 and 116-2 may alternatively be configured to transmit and receive data or information through any other wireless or wired system or method known in the art.

[0020] In an exemplary embodiment, the present disclosure provides a method for monitoring current in an electromagnetic telemetry system. A transmitter or switch is provided for generating an output current and voltage. The transmitter may be connected to one or more electrode stations via insulated wire, which carries the output current and voltage from the transmitter. One or more current monitors may be provided at or near the electrode stations in the dipole-dipole system. Additional current monitors may also be positioned at points between the electrode stations and the transmitter.

[0021] The current monitors are used to monitor and measure current at points away from the transmitter. Preferably, the current monitors measure current at or near the one or more electrode stations in a telemetry system. Current monitors may include a Hall device, resistor, current transformer, or any other known sensor for measuring current, as well as a signal conditioner (including circuitry, firmware, software, etc.) for converting detected current into transmittable information. Current monitors also may include a system for transmitting information related to the measured current back to the transmitter in real-time. Such a system may be wireless, such as a radio with an antenna. Alternatively, such a system may be wired, such as a fiber optic cable or a system of isolation amplifiers and wire. Any wireless or wired system known in the art may be used for data transmission between the current monitors and transmitter.

[0022] The transmitter also includes a system for receiving information from the current monitors. The receiver may be configured to receive the data wirelessly. For example, the receiver may be a radio with an antenna. Alternatively, the receiver may be configured to receive the data through a wired connection, such as a fiber optic cable or a system of isolation amplifiers and wire.

[0023] The transmitter may also include circuity, firmware and/or software for processing and/or analyzing the current data received from the current monitors. For example, the transmitter may be configured to compare the received current data to an expected current, which may be calculated, or to an output current at the transmitter, which may be obtained from a separate current monitor located at the transmitter. The transmitter may further be configured to shut down or otherwise decrease or eliminate the output current and voltage in response to the processing and analysis of the received data. For example, if the received data from a current monitor reflects a current that is not equal to the expected output current, the transmitter may completely or partially shut down. That is, all output current and voltage from the transmitter may be eliminated, or alternatively only output current or voltage to the current monitor reporting the disparate current reading may be eliminated, for example. In this manner, the safety of the electromagnetic telemetry system is enhanced. A current monitor that measures a current that is not equal or not substantially equal to the output current at the transmitter may be indicative of an unwanted conduction path to ground, including poor wire insulation and splices, wet ground, high resistance electrodes, broken wires, open loops, a person touching or otherwise interacting with the wire, and/or an animal touching, chewing on, or otherwise interacting with the wire. Such unwanted conductions paths may be dangerous because of the risk of electric shock, and accordingly, shutting down the transmitter may serve to eliminate some or all of the danger.

[0024] In addition or alternatively to shutting down the transmitter in response to data received from a current monitor, the transmitter may be configured to send an alert or notification. The alert or notification may be sent via any wired or wireless system known in the art to alert relevant personnel that there may potentially be a problem (e.g., an unwanted conduction path to ground) with the electromagnetic telemetry system. Such a notification system is not only beneficial for addressing and reducing the dangerous conditions noted above, but also for repairing the system and ensuring that the electromagnetic telemetry system is functioning properly (e.g., collecting accurate data).

[0025] In one embodiment, expected current may be determined using the following algorithm.

The current, I(x) along a horizontal wire h meters above the surface of a lossy half space can be calculated using

[00001]$\begin{array}{cc}I\left(x\right)=I_o.Math.e^{-{\mathrm{ik}}_L.Math..Math.x.Math.}+I_{+}.Math.e^{-{\mathrm{ik}}_L.Math.x}+I_{-}.Math.e^{{\mathrm{ik}}_L.Math.x}& \left(1.1\right)\\ \mathrm{where}& \\ k_L=k_0.Math.\left\{1-\frac{1}{\ln \left(\frac{2.Math.h}{a}\right)}\left[\ln \left(k_1.Math.h\right)+0.07721+i\left(\frac{\pi }{2}-\frac{4}{3}.Math.k_1.Math.h-\frac{2}{45}.Math.{\left(2.Math.k_1.Math.h\right)}^3\right)\right]\right\}& \left(1.2\right)\\ k_1=\sqrt{\mathrm{\omega \mu }-i.Math..Math.\sigma }=\mathrm{subsurface}.Math..Math.\mathrm{propagation}.Math..Math.\mathrm{constant}.Math..Math.\left(1.Math.\text{/}.Math.m\right)& \left(1.3\right)\\ I_{+}=\frac{-{\Gamma }_1\left[e^{-2.Math.{\mathrm{ik}}_L.Math.L_1}-{\Gamma }_2.Math.e^{-2.Math.{\mathrm{ik}}_L\left(L_1+L_2\right)}\right]}{1-{\Gamma }_1.Math.{\Gamma }_2.Math.e^{-2.Math.{\mathrm{ik}}_L\left(L_1+L_2\right)}}.Math.I_o& \left(1.4\right)\\ I_{-}=\frac{-{\Gamma }_2\left[e^{-2.Math.{\mathrm{ik}}_L.Math.L_2}-{\Gamma }_1.Math.e^{-2.Math.{\mathrm{ik}}_L\left(L_1+L_2\right)}\right]}{1-{\Gamma }_1.Math.{\Gamma }_2.Math.e^{-2.Math.{\mathrm{ik}}_L\left(L_1+L_2\right)}}.Math.I_o& \left(1.5\right)\\ I_o=I_{\mathrm{Tx}}.Math.\frac{1-{\Gamma }_1.Math.{\Gamma }_2.Math.e^{-2.Math.{\mathrm{ik}}_L\left(L_1+L_2\right)}}{\left(1-{\Gamma }_1.Math.e^{-2.Math.{\mathrm{ik}}_L.Math.L_1}\right).Math.\left(1-{\Gamma }_2.Math.e^{-2.Math.{\mathrm{ik}}_L}\right)}& \left(1.6\right)\\ {\Gamma }_1=\frac{Z_{L.Math..Math.1}-Z_c}{Z_{L.Math..Math.1}+Z_c}& \left(1.7\right)\\ {\Gamma }_2=\frac{Z_{L.Math..Math.2}-Z_c}{Z_{L.Math..Math.2}+Z_c}& \\ {\Gamma }_c=60.Math.\frac{k_L}{k_1}.Math.\ln \left(\frac{2.Math.h}{a}\right)& \\ \begin{array}{c}\omega =\mathrm{radial}.Math..Math..Math.\mathrm{frequency}.Math..Math.\left(\mathrm{radians}.Math.\text{/}.Math.\sec \right),.Math.\\ \mu =\mathrm{subsurface}.Math..Math.\mathrm{permeability}.Math..Math.\left(H.Math.\text{/}.Math.m\right),.Math.\\ \sigma =\mathrm{subsurface}.Math..Math.\mathrm{conductivity}.Math..Math.\left(S.Math.\text{/}.Math.m\right),.Math.\\ a=\mathrm{wire}.Math..Math..Math.\mathrm{radius}.Math..Math.\left(m\right),.Math.\\ h=\mathrm{wire}.Math..Math..Math.\mathrm{height}.Math..Math.\mathrm{above}.Math..Math.\mathrm{ground}.Math..Math.\left(m\right).Math.\end{array}& \end{array}$

(See also Chen, Luo & Zhang, 2008, An analytic formula of the current distribution for the VLF horizontal wire antenna above a lossy half-space, Progress in EM Research Letters, v1, p 149-158).

[0026] It should be emphasized that the above-described embodiments of the present disclosure, particularly, any “preferred” embodiments, are merely possible examples of implementations, merely set forth for a clear understanding of the principles of the disclosure. Many other variations and modifications may be made to the above-described embodiments of the disclosure without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of the present disclosure and protected by the following claims.