GB2352376A

GB2352376A - Telemetry system in which data signals are modulated on power signals

Info

Publication number: GB2352376A
Application number: GB0010262A
Authority: GB
Inventors: David Sirda Shanks
Original assignee: WELL INTELLIGENCE TECHNOLOGIES
Current assignee: WELL INTELLIGENCE TECHNOLOGIES
Priority date: 1999-04-27
Filing date: 2000-04-27
Publication date: 2001-01-24
Anticipated expiration: 2020-04-27
Also published as: GB0010262D0; GB2352376B; GB9909621D0

Abstract

A telemetry system is capable of transmitting both power and data signals between a master unit 10 and at least one slave unit 50 (a,b) over a transmission system 12 which is part of a borehole, an oil well or a pipeline which may be a subsea installation. The transmission system comprises a tubing string or pipeline incorporating electrically isolating collars 200 a,b. A well casing or another pipeline may provide an earth/return path, the slave unit 50 being coupled between the tubing string and the well casing or between the two pipelines. The master unit 10 may use pulse width modulation of a power signal from driver 24 to send data to the slave unit 50. Power signals received by the slave unit are fed to regulators 56,58 to provide a local power supply for the slave unit. Data signals from the slave unit may be encoded by frequency shift keying at generator 64, synchronised with the pulses of the power signal, for transmission to the master unit. Data signals sent from the master unit may be detected by a timer circuit 70 and used to control valves, actuators or motors, while the data signals form the slave unit may represent the outputs of sensors. The data signals may be encrypted, e.g. using a Hamming code.

Description

1 2352376 I "Telemetry System" 2 3 The present invention relates to a

telemetry system, 4 particularly for use with an isolated pipeline or 5 tubing string. 6 7 Telemetry systems are typically used in the oil and 8 gas industry to transmit data from measuring devices, 9 sensors or the like located downhole to receivers 10 located at the surface. Conventional systems use 11 transmission mediums such as drilling fluid or mud in 12 which to transmit the signals between downhole and 13 surface locations. In addition, mono-conductor 14 instrument cables and single- or threephase power 15 cables are often used to transmit data communications 16 in addition to their primary function. 17 18 Such conventional systems typically require at least 19 two individual power sources: one at the surface to 20 drive the receiving circuitry, and at least one 2 1 downhole to drive the remote circuitry. This 2 duplication of power sources increases the cost of 3 the system and may make the system unreliable, as 4 more components are required. 5 6 Furthermore, the power source downhole has 7 limitations associated with it in that the power 8 output from the source is restricted due to the 9 remoteness of the source. For example, the downhole 10 power source may comprise batteries that have a 11 limited power output and also a limited lifetime 12 before they must be either replaced or recharged. 13 14 A typical production completion requires a mono 15 conductor cable to be installed during the completion 16 in order to recover signals or perform control of 17 downhole devices. The installation of this cable 18 creates cost and complexity in the completion design. 19 20 According to a first aspect of the present invention 21 there is provided a telemetry system, the system 22 comprising a master unit, and at least one slave unit 23 remote from the master unit, the master and slave 24 units communicating via a transmission system, 25 wherein the telemetry system is capable of 26 transmitting power and data transmissions between the 27 units, and wherein the transmission system includes 28 an at least partially isolated tubing string or 29 pipeline. 30 3 1 According to a second aspect of the present 2 invention, there is provided a method of transmitting 3 power and data from a master unit to at least one 4 slave unit remote from the master unit, the master and slave units communicating via a transmission 6 system, the transmission system including an at least 7 partially isolated pipeline or tubing string, the 8 method comprising the steps of 9 generating a power transmission at the master unit; 11 generating a data transmission and synchronising 12 the data transmission with the power 13 transmission at the master unit; 14 transmitting the power and data transmissions via the transmission system to the slave unit; 16 and 17 recovering the power and data transmissions at 18 the slave unit.

19 According to a third aspect of the present invention, 21 there is provided a method of transmitting data to a 22 master unit from at least one slave unit remote from 23 the master unit, the master and slave units 24 communicating via a transmission system, the transmission system including an at least partially 26 isolated tubing string or pipeline, the method 27 comprising the steps of 28 generating a power transmission at the master 29 unit and transmitting the power transmission to the slave unit; 4 1 recovering the power transmission at the slave 2 unit; 3 generating a data transmission at the slave unit 4 and synchronising the data transmission with the power transmission; 6 transmitting the data transmission via the 7 transmission system to the master unit; and 8 recovering the data transmission at the master 9 unit.

11 optionally, the method may include the further steps 12 of 13 dividing the data transmission into a series of 14 sub-windows; transmitting a specified data transmission from 16 the slave unit to the master unit; 17 receiving the specified data transmission at the 18 master unit; 19 determining which of the sub-windows reliably transmitted the specified data transmission.

21 22 The sub-windows that did not reliably transmit data 23 are typically filtered out or ignored for subsequent 24 transmissions. This technique may be used where the transmission system is particularly noisy or may be 26 subject to interference and increases the chances of 27 reliably retrieving data transmissions.

28 29 According to a fourth aspect of the present invention, there is provided a method of receiving 31 and converting power and data transmissions sent from 1 a master unit to at least one slave unit remote from 2 the master unit, the master and slave units 3 communicating via a transmission system, the 4 transmission system including an at least partially isolated pipeline or tubing string, the method 6 comprising the steps of 7 receiving a power transmission at the slave 8 unit; 9 dividing the power transmission into two channels; 11 rectifying and regulating the power transmission 12 in a first channel; and 13 recovering the data transmission in a second 14 channel.

16 According to a fifth aspect of the present invention, 17 there is provided a method of receiving data 18 transmitted by a master unit from at least one slave 19 unit remote from the master unit, the master and slave units communicating via a transmission system, 21 the transmission system including an at least 22 partially isolated pipeline or tubing string, the 23 method comprising the steps of 24 receiving the data transmission at the master unit; 26 filtering and conditioning the data 27 transmission; and 28 regenerating the transmitted data.

29 optionally, the method may include the further steps 31 of 6 1 dividing the data transmission into a series of 2 sub-windows; 3 transmitting a specified data transmission from 4 the slave unit to the master unit; receiving the specified data transmission at the 6 master unit; 7 determining which of the sub-windows reliably 8 transmitted the specified data transmission.

9 The sub-windows that did not reliably transmit data 11 are typically ignored for subsequent transmissions.

12 This technique may be used where the transmission 13 system is particularly noisy and increases the 14 chances of reliably retrieving data transmissions.

16 The pipeline or tubing string is typically 17 electrically isolated using at least one isolating 18 collar. The isolating collar typically comprises 19 first and second connectors, the first and second connectors being threadedly coupled together.

21 Preferably, an electrical isolating material is 22 injected between the first and second connectors to 23 isolate the connectors from one another. The 24 insulating material is typically epoxy or the like.

26 The isolating collar typically includes means for 27 conveying electrical signals from outwith the collar 28 to the second connector. Thus, any pipeline or 29 tubing string coupled to the second connector is typically capable of carrying electrical signals.

31 7 1 The pipeline or tubing string is typically coated 2 with an electrical isolating paint or the like to at 3 least partially isolate the pipeline or tubing 4 string. 5 6 The at least partially isolated pipeline or tubing 7 string typically comprises a surface pipeline or 8 tubing string. Alternatively, the at least partially 9 isolated pipeline or tubing string comprises a subsea 10 pipeline or tubing string, or a downhole pipeline or 11 tubing string. It will be appreciated that the at 12 least partially isolated pipeline or tubing string 13 may further comprise any combination of surface, 14 subsea or downhole pipelines or tubing strings. 15 16 The pipeline or tubing string typically includes a 17 first isolating collar at or near a source of fluid 18 flowing within the pipeline or tubing string. 19 optionally, the pipeline or tubing string includes a 20 second isolating collar at or near a sink for the 21 fluid in the pipeline or tubing string. The master 22 unit is typically electrically coupled to the 23 pipeline or tubing string via the first isolating 24 collar. At least one slave unit is coupled to the 25 pipeline or tubing string, preferably at one or more 26 locations between said first and second isolating 27 collars. 28 29 System components including the master and slave 30 units may be earthed by being connected to a local 31 earth.Alternatively, a system earth and/or 8 1 electrical return path may be provided by other 2 tubulars such as a second pipeline or tubing string 3 or by a downhole, surface or subsea casing or the 4 like surrounding the pipeline or tubing string. 5 6 The slave unit typically comprises a mandrel, a slave 7 module, and an electrical return path. The mandrel 8 typically facilitates attachment of the slave unit to 9 the pipeline or tubing string. The mandrel is 10 typically clamped, or otherwise coupled, to the 11 pipeline or tubing string. The mandrel typically 12 facilitates transmission of the electrical power and 13 data transmissions from the pipeline to the 14 electronics of the slave unit. 15 16 The slave module typically houses the electronics of 17 the slave unit. The electrical return path typically 18 comprises a spring contact for engaging an earth 19 point. The earth point may be a local earth, a 20 further tubular such as a second pipeline, a subsea 21 or surface casing or a casing of a downhole well. 22 23 The slave unit is typically coupled to the pipeline 24 using a mandrel, pipeline clamp or other conventional 25 means. The pipeline or tubing string typically 26 includes a wellhead. A first isolating collar is 27 typically located at or near the wellhead. The 28 master unit is typically electrically coupled to the 29 first isolating collar (and thus the isolated 30 pipeline or tubing string) via a wellhead penetrator. 31 Alternatively, the master unit may be electrically 9 coupled to the pipeline by directly attaching the output of the master unit to the pipeline using a pipeline clamp, or other conventional attachment 4 means, for example a tubing clamp provided with a cable coupling.

6 7 Pulse-width modulation is typically used to 8 facilitate data transmission from the master unit to 9 the slave unit. The power transmission is typically modulated with the data transmission using pulse 11 width modulation.

12 13 Frequency-shift keying (FSK) is typically used to 14 facilitate data transmission from the slave unit to the master unit. The FSK frequencies are typically 16 superimposed on a carrier frequency. The carrier 17 frequency is typically the same frequency as the 18 power transmission frequency. The data transmission 19 is typically synchronised to the "high" cycle of the power transmission. Alternatively, the data 21 transmission may be synchronised to the "low" cycle 22 of the power transmission, or optionally to both the 23 low and high cycles, or to any range of cycles to 24 circumvent the range of interference.

26 Where more than one slave unit is used, the data 27 transmission from the master unit to the slave unit 28 typically includes an address of the slave unit.

29 This allows several slave units to receive commands from a single master unit.

31 1 The data transmissions preferably include data error 2 detection and/or correction. The data error 3 detection and/or correction typically comprise a 4 Hamming code, or other suitable technique. 5 optionally where no DC or secondary power source is 6 in the system the master and slave may optionally be 7 DC coupled. 8 9 The master unit and/or the slave unit are preferably 10 ac coupled to the transmission system using 11 capacitors. Most preferably, the system employs 12 separate and discrete capacitors for this purpose. 13 This is known as capacitive coupling and allows any 14 dc bias within the transmissions to be blocked, 15 whilst passing any ac signals. 16 17 The master unit typically comprises a processor to 18 control the operation of the master unit; a power 19 waveform generator; and signal recovery and 20 conditioning circuitry. 21 22 The processor typically applies pulse-width 23 modulation to the power transmission when data 24 transmission is required from the master unit to the 25 slave unit. When not transmitting data, the 26 processor typically defaults the power transmission 27 to a 50% duty cycle. 28 29 The power waveform generator typically comprises an 30 analogue driver, and a power drive electrically 31 coupled to the analogue driver. The processor 11 I typically applies the power transmission to the 2 analogue driver. The analogue driver typically 3 drives the power driver. The processor typically 4 controls the voltage amplitude of the power transmission.

6 7 The analogue driver typically includes an isolating 8 circuit that isolates the power driver from the 9 processor. Typically, the analogue driver further includes low voltage logic drivers to high voltage 11 driver stages, which in turn drive the power driver.

12 This prevents any damage being caused to the 13 processor.

14 The power driver typically comprises a field-effect

16 transistor (FET) based push-pull driver.

17 Alternatively, the power driver comprises a bi-polar 18 transistor based push-pull driver, or the like. The 19 power driver typically operates from a variable dc power supply. The master unit typically includes the 21 variable dc power supply.

22 23 The signal recovery and conditioning circuitry 24 typically allows data transmitted by the at least one slave unit to be extracted and recovered from the 26 transmission system. The signal recovery circuit 27 typically includes first and second data channels.

28 The first data channel typically includes a high 29 speed switch; a filtering system; an automatic gain control (AGC) stage; a comparator stage; and a first 31 counter.

1 2 The high-speed switch typically enables the data 3 transmission to be directed to the first and/or 4 second data channels when the power transmission is high. Alternatively, the high-speed switch directs 6 the data transmission to the first and/or second data 7 channels when the power transmission is low, or when 8 the power transmission is both high and low.

9 The filtering system typically removes any noise and 11 background signals from the recovered data.

12 Typically, the filtering system comprises a pair of 13 selective filters. The selective filters typically 14 comprise broad bandpass filters. Alternatively, the selective filters may comprise tuned filters. This 16 allows the filters to differentiate between the FSK 17 frequencies.

18 19 The AGC stage typically maintains the signal within a set voltage amplitude range.

21 22 The comparator stage typically compares the voltage 23 amplitudes of the FSK frequencies.

24 The slave unit typically comprises a processor to 26 control the operation of the slave unit; rectifying 27 and regulating circuitry in a first channel; recovery 28 and conditioning circuitry in a second channel; and 29 frequency generating and mixing means.

13 1 The rectifying and regulating circuitry typically 2 comprises a halfbridge rectifier to rectify the 3 received power transmission into a dc voltage; and at 4 least one voltage regulator to regulate the dc 5 voltage. 6 7 The recovery and conditioning circuitry typically 8 comprises an amplifier and filtering system; and a 9 timer circuit. The amplifier and filtering system 10 typically amplifies or attenuates the signal, and 11 filters the signal. This boosts the amplitude of the 12 signal and removes any background noise or other 13 interference. 14 15 The frequency mixing and generating means typically 16 comprises a frequency-shift keying (FSK) generator; 17 an FSK mixer; and a line driver. 18 19 The slave unit typically includes an analogue signal 20 conditioning circuit, and at least one analogue-to21 digital convertor. The analogue conditioning circuit 22 allows the slave unit to receive and process signals 23 from a plurality of sensors, such as pressure 24 sensors, temperature sensors or the like. 25 26 The slave unit is typically capable of controlling 27 loads. 28 29 Embodiments of the present invention shall now be 30 described, by way of example only, with reference to 31 the accompanying drawings, in which:-

14 1 Fig. 1 schematically illustrates an embodiment 2 of a telemetry system coupled to an isolated 3 pipeline; 4 Fig. 2 schematically illustrates an embodiment of a telemetry system similar to that of Fig. 1 6 with an additional slave unit; 7 Fig. 3 is a schematic block diagram of a 8 telemetry system in accordance with one 9 embodiment of the present invention; Fig. 4 is a cross-sectional elevation of a first 11 embodiment of an isolating collar for 12 electrically isolating a pipeline; 13 Fig. 5 is a cross-sectional elevation of a 14 second embodiment of an isolating collar for electrically isolating a pipeline, including an 16 electrical connector; 17 Fig. 6a shows an exemplary power waveform for 18 transmitting power from a master unit at the 19 surface to a slave unit downhole; Fig. 6b shows an exemplary signal transmit 21 waveform for transmitting data from a slave unit 22 to a master unit using frequency-shift keying 23 (FSK); 24 Fig. 7a shows the power waveform of Fig. 2a modulated using pulse-width modulation for 26 transmitting both power and data from a master 27 unit at the surface to a slave unit downhole; 28 Fig. 7b shows how data is encoded in the 29 modulated waveform of Fig. 3a; 1 Fig. 8a shows an exemplary power waveform 2 transmitted on the isolated pipeline to which 3 the telemetry system of Fig. I is attached; 4 Fig. 8b shows an exemplary power waveform for transmitting power from a master unit at the 6 surface to a slave unit downhole; 7 Fig. 8c shows an exemplary signal transmit 8 waveform. for transmitting data from a slave unit 9 to a master unit using frequency-shift keying (FSK); 11 Fig. 8d shows an enlarged portion of the 12 waveform of Fig. 8c; 13 Fig. 9 is a schematic illustration of an oilwell 14 that includes an isolated production tubing; Figs 10a and 10b illustrate two examples of a 16 wellhead penetrator; 17 Fig. 11 is a schematic illustration of a portion 18 of the oilwell of Fig. 9 showing connection of 19 an electrical signal to a pipeline or tubing string; 21 Fig. 12 is a cross-sectional elevation 22 illustrating an embodiment of a slave unit of 23 the telemetry system of Fig. 2 attached to an 24 isolated pipeline or tubing string; Figs 13a and 13b schematically illustrate a 26 subsea pipeline installation with dual and 27 single pipelines, respectively, with the 28 telemetry system of Fig. 2 attached thereto; 29 Fig. 14 is a cross-sectional elevation illustrating a method of attaching a slave unit 31 to a subsea pipeline; 16 1 Figs 15a and 15b schematically illustrate a 2 surface pipeline installation with dual and 3 single pipelines, respectively, with the 4 telemetry system of Fig. 2 attached thereto; Fig. 16 schematically illustrates a method of 6 attaching a slave unit to a surface pipeline; 7 and 8 Fig. 17 schematically illustrates an oilwell 9 that has a subsea or surface pipeline attached thereto.

11 12 Referring to the drawings, Fig. 1 shows an 13 illustrative embodiment of an exemplary embodiment of 14 a telemetry system coupled to an isolated pipeline or the like according to the present invention. As 16 shown more clearly in Fig. 3, the telemetry system 17 comprises a master unit 10 and a slave or node unit 18 50. The master and slave units 10, 50 communicate 19 with each other via a transmission system 12, i.e. a pipeline or well tubing string 100 (Fig. 1), that is 21 at least partially isolated from earth, e.g. by means 22 of at least one isolating collar 200 (Figs 4 and 5).

23 In the embodiment shown in Fig. 1, a first isolating 24 collar 200a is located at a first end of the pipeline 100. optionally, a second isolating collar 200b may 26 be positioned at a distal end of the pipeline 100 at 27 the end of a transmission zone, the transmission zone 28 being defined between the first and second isolating 29 collars 200a, 200b.

17 1 The master unit 10 typically includes a power supply 2 and controller unit that generates an electrical 3 power supply, and also transmits data to and receives 4 data from the remote slave unit 50. The slave unit 5 50 is powered by the master unit 10 as will be 6 described hereinafter, and can carry out control and 7 monitoring functions from where it is coupled to the 8 isolated pipeline 100. The master and slave units 9 10, 50 require the electrical circuit to be completed 10 by connection to an electrical ground or earth point, 11 as schematically shown in Fig. 1. 12 13 In this way, sensors, instrumentation systems or load 14 actuators coupled to the slave unit 50 can be 15 monitored and the load actuators can be controlled 16 from the master unit 10 using only the pipeline 100 17 for transmission of power and data transmissions. 18 Further the slave unit 50 can be coupled at any point 19 in the isolated portion of the pipeline 100 (i.e. the 20 transmission zone defined between isolating collars 21 200a, 200b). 22 23 As shown in Fig. 2, the system can support more than 24 one slave unit (i.e. slave units 50a, 50b) coupled to 25 the isolated portion of the pipeline 100. The system 26 can support multiple slave units 50a, 50b etc, with 27 each slave unit 50a, 50b etc, being coupled to the 28 pipeline 100 at any point in the isolated portion. 29 30 The system may be configured to transmit either 31 solely the power supply transmissions from the master 18 1 unit 10 to the slave unit 50, or to include data 2 transmissions in addition to transmitting power. The 3 data transmission is typically synchronised to the 4 power supply transmission and/or with a secondary and 5 larger power source running in parallel with the 6 power supply and data transmissions from the master 7 unit 10 to the slave units 50. This secondary power 8 source can either be used for pipeline heating and/or 9 powering large power actuators and motors attached to 10 the isolated portion of the pipeline 100. 11 12 The master unit 10 is typically located at the 13 surface, and the slave unit 50 is typically located 14 remote from the master unit 10, for example in a 15 borehole, oilwell, subsea installation or the like. 16 The location of the master unit 10 is dependent upon 17 the particular application, and the relative 18 positions of the master unit 10 and the slave unit(s) 19 50 described herein are by way of example only. 20 21 It should be noted that a number of slave units 50 22 may be coupled to the transmission system 12 (i.e. 23 the pipeline 100), and the operation of each slave 24 unit 50 controlled by the master unit 10 at the 25 surface. It should also be noted that the system may 26 use more than one master unit 10 if control of the 27 slave unit(s) 50 is required from more than one point 28 in the system. 29 30 The master and slave units 10, 50 are advantageously 31 coupled to the isolated pipeline 100 using capacitive 19 1 coupling. Discrete capacitors 14, 52 (Fig. 3) are 2 coupling or blocking capacitors that couple a signal 3 from a power source (discussed later) to the isolated 4 pipeline 100. Capacitors 14, 52 block any direct current (dc) bias that may be applied to the signal, 6 but do not affect any alternating current (ac) signal 7 that is simultaneously transmitted. When considering 8 dc, the capacitors 14, 52 act as open circuits as, at 9 zero frequency (dc), the reactance of a capacitor is infinite.

11 12 Referring now to Fig. 3, the master unit 10 includes 13 a power input stage 16 that provides power for the 14 telemetry system, and may be either an ac or dc power source. The power input stage 16 is electrically 16 coupled to at least one (and preferably a plurality 17 of) dc voltage regulators 18. Voltage regulators 18 18 provide local power supplies (dc) for the circuitry 19 in the master unit 10. Generally, different components within the master and slave units 10, 50 21 operate using a plurality of different voltages, 22 depending upon the various specifications of these

23 components.

24 The master unit 10 includes a processor 20 that, 26 among other functions, controls the operation of the 27 telemetry system. One output of the processor 20 is 28 electrically coupled to an analogue driver stage 22, 29 the driver stage 22 being electrically coupled to a high voltage ac power driver 24.The output of the 1 power driver 24 is electrically coupled (via the 2 coupling capacitor 14) to the isolated pipeline 100. 3 4 The power driver 24 may be a field- effect transistor 5 (FET) or a bi-polar transistor based push-pull drive 6 stage, that typically operates using a variable but 7 relatively large dc voltage power supply. The dc 8 power supply is typically rated from 20 to 500 volts, 9 although voltages outwith this range may also be 10 used. The particular voltage used is dependent upon 11 the loading conditions and losses in the isolated 12 pipeline 100, and can be varied accordingly. 13 14 The power driver 24 is preferably electrically 15 isolated from the processor 20 to prevent damage to 16 the processor 20. Thus, the analogue driver stage 22 17 includes isolating circuits and low voltage logic 18 drivers to a high voltage drive stage, which in turn 19 drives the gates of the FET or bi-polar transistor 20 power driver 24. 21 22 The master unit 10 further includes a signal recovery 23 circuit 26 that retrieves data transmitted (via the 24 isolated pipeline 100 as will be described) by the 25 slave unit 50. The processor 20 controls operation 26 of the signal recovery circuit 26. The recovered 27 data from the signal recovery circuit 26 is processed 28 by a filtering system 28 that further extracts the 29 received information from any noise or other 30 background interference mixed with the recovered data 31 from the slave unit 50.

21 1 2 The output from the filtering system 28 is fed into a 3 signal conditioning unit that includes an automatic 4 gain control (AGC) stage 30, and a comparator stage 32. The output of the comparator stage 32 is fed 6 into a first counter 34. The first counter 34 is 7 electrically coupled to the processor 20, so that the 8 processor 20 can read the value in the first counter 9 34.

11 In certain embodiments of the present invention, the 12 raw signal from the slave unit 50 is additionally fed 13 into a second data channel that includes a signal 14 recovery circuit 36 to extract data from the power transmission on the isolated pipeline 100. The 16 output from the second signal recovery circuit 36 is 17 fed into a timer circuit 38 that performs pulse-width 18 measurements on the data extracted from the power 19 transmission. The output of the timer circuit 38 is fed into a second counter 40, the value in the 21 counter being read by the processor 20.

22 23 A remote station (not shown) typically controls 24 operation of the master unit 10, and is electrically coupled to the master unit 10 via a serial data link 26 46, such as an RS232/485 serial data port. The 27 remote station may be, for example, a personal 28 computer located remotely from the master unit 10.

29 The slave unit 50 includes a half-wave rectifier and 31 heat dissipation.unit 54. This unit 54 extracts 22 1 power transmitted via the isolated pipeline 100 to 2 the slave unit 50 as will be described. As with the 3 master unit 10, the slave unit 50 has a matched pair 4 of voltage regulators 56 and a plurality of low voltage dc regulators 58 to provide local power 6 supplies for the circuitry in the slave unit 50.

7 8 The slave unit 50 is provided with a processor 60 to 9 control the operation thereof. The processor 60 is electrically coupled to a line driver 62 that 11 transmits data onto the isolated pipeline 100.

12 13 In certain embodiments, the slave unit 50 transmits 14 data to the master unit 50 (via the isolated pipeline 100) using frequency-shift keying (FSK), as will be 16 described. A frequency generator 64 is used to 17 generate the two required frequencies F1, F2- The 18 frequencies F1, F2 are then mixed by a frequency mixer 19 66 to combine data from the processor 60 with carrier frequency Fc and the modulating frequencies F1,F2 21 22 The slave unit 50 further includes a signal recovery 23 circuit 68 to extract data from the isolated pipeline 24 100 generated by the master unit 10. A timer circuit 70 is used to perform pulse-width measurements on the 26 data extracted by the signal recovery circuit 68.

27 28 The slave unit 50 is provided with an analogue signal 29 conditioning circuit 74, and a plurality of analogue to-digital (A/D) convertors 76. The analogue 31 conditioning circuit 74 and the A/D convertors 76 23 1 allow a plurality of different types of 2 instrumentation and/or sensors (not shown) to be 3 coupled to the system. Thus, the slave unit 50 4 monitors these instruments and sensors and transmits data procured by them to the master unit 10 for 6 collection and analysis.

7 8 The slave unit 50 can accept a wide range of sensors, 9 and any electronic sensor that can be conditioned and measured using a processor can be used with the 11 system. Typical sensor inputs to the analogue signal 12 conditioning circuit 74 comprise either analogue 13 sensors with voltage outputs, or those with frequency 14 outputs. Typical examples of analogue sensors that may be used to collect information include pressure 16 sensors, temperature sensors, accelerometers and 17 fluid depth sensors (resistive or capacitive).

18 Typical examples of frequency or pulse output 19 sensors, include shaft speed indicators, high accuracy pressure and temperature sensors and flow 21 meters. These are exemplary only, and the range of 22 applications will be apparent to those skilled in the 23 art.

24 The analogue sensors coupled to the system can be 26 powered from the low-level regulators 58 in the slave 27 unit 50. The voltage or current outputs from the 28 sensors would be amplified or filtered in the 29 analogue signal conditioning circuit 74 if required, and the conditioned outputs fed into the multiplexed 24 1 A/D convertor 76, the outputs then being fed to the 2 processor 60 for transmission in digital format.

3 4 The data system architecture within the system typically operates using 16 or 24 bit data words for 6 transmission, and read values can be transmitted to 7 the master unit 10 as A/D counts in either 16 or 24 8 bit words, depending upon the required accuracy and 9 resolution of the measurements.

11 Where pulse or frequency signals are output from the 12 sensors, a reciprocal counter could be used to 13 measure the frequency locally in the analogue signal 14 conditioning unit 74. In this embodiment, the processor 60 typically forms part of the reciprocal 16 counter to minimise or reduce the electronics 17 required in the slave unit 50.

18 19 In addition to sensor measuring capabilities, the system could be utilised to control loads. As the 21 system in certain embodiments can facilitate two-way 22 communication, any electronic control that can be 23 implemented with the local processor 60 can be 24 implemented using the telemetry system. For example, the slave unit 50 may be used to control solenoids to 26 operate and control actuators, hydraulic valve 27 mechanisms, motors that open valves, or other similar 28 functions.

29 Operation of the telemetry system shall now be 31 described. The,processor 20 in the master unit 10 1 applies a power waveform to the driver 22 under 2 command from the remote station. The driver 22 3 drives the power driver 24 that applies a square-wave 4 power waveform (Fig. 6a), the power waveform being 5 transmitted to the isolated pipeline 100 through the 6 coupling capacitor 14. 7 8 Fig. 6a shows an exemplary power signal waveform that 9 is transmitted from the master unit 10 to the slave 10 unit 50 via the isolated pipeline 100. The frequency 11 of the waveform may be any suitable frequency; a 12 typical frequency range may be from 10 millihertz 13 (mHz) to 6 kilohertz (kHz) although frequencies 14 outwith this range may be used. Where there is even 15 a moderate bandwidth on the isolated pipeline 100, 16 the frequencies used to transmit power from the 17 master unit 10 to the slave unit 50 will be from 100 18 Hz to 100 kHz. 19 20 The amplitude of the waveform is variable and is 21 dependent upon the loading conditions and losses of 22 the isolated pipeline 100. The processor 20 using a 23 regulator (one of the plurality of regulators 18) 24 controls the voltage amplitude of the square-wave 25 power waveform (Fig. 6a). By controlling the 26 amplitude of the power waveform using a processor 20, 27 the amplitude may be adjusted either manually or 28 automatically to set and keep the amplitude constant 29 in varying operating conditions. 30 26 The slave unit 50 receives an attenuated power input from the isolated pipeline 100 through the coupling capacitor 52. Any background noise or other interference will be added to the power signal during transmission from the master unit 10 to the slave 6 unit 50, thus resulting in a degraded signal being 7 detected at the slave unit 50. The power is 8 rectified through the half-bridge rectifier 54 and is 9 then regulated in the regulating units 56, 58 to provide the local power supplies for the various 11 circuitry within the slave unit 50.

12 13 Fig. 6b illustrates how data may be transmitted from 14 the slave unit 50 to the master unit 10. Data is transmitted using frequency-shift keying (FSK) in a 16 continuous stream during data transmission. Two FSK 17 frequencies F1, F2 are superimposed on a carrier 18 frequency F, In the example shown in Fig. 6b, the 19 carrier frequency F, is the same frequency as the power waveform of Fig. 6a, and the data transmission 21 is synchronised to the "high" cycle of the power 22 waveform shown in Fig. 6a. It should be noted that 23 the data may be synchronised to the "low" cycle, or 24 to both the high and low cycles. This synchronisation allows the master unit 10 to 26 correctly detect the data transmission from the slave 27 unit 50.

28 29 The frequencies used to transmit data from the slave unit 50 are typically several hundred kilohertz 31 (kHz). For example, the transmit frequencies F1, F2 27 1 from the slave unit 50 to the master unit 10 may be 2 300 kHz for a logic one and 100 kHz for a logic zero. 3 Thus, if a logic one is to be transmitted, then the 4 higher of the two FSK frequencies (i.e. Fj) will be 5 transmitted for the duration of the high cycle of the 6 power waveform, and if a logic zero is to be 7 transmitted, the lower of the two FSK frequencies 8 (i.e. F2) is transmitted for the duration of the high 9 cycle of the power waveform. 10 11 The two FSK frequencies F1, F2 are preferably not 12 multiples of one another to minimise the occurrence 13 of false detections. The two frequencies F1, F2 are 14 typically also at least a factor of two different. 15 Although this increases the amount of bandwidth 16 required on the isolated pipeline 100, it allows for 17 the recovery of highly attenuated signals. Where 18 there is significant inductance on the isolated 19 pipeline 100, much lower frequencies may be used. 20 This reduces the speed of the system, but does not 21 affect the ability of the system to transmit and 22 receive data. Low carrier frequencies may be used 23 (in the order of a few hertz) with very high 24 frequency data carriers to increase data recovery in 25 noisy environments, such as that downhole. Where low 26 frequencies are required, the system may also be used 27 with fractions of a hertz for the carrier, and a 28 logic zero frequency of 100 Hz and a logic one 29 frequency of 350 Hz, for example. 30 28 1 Power across the slave unit 50 can be adjusted to 2 provide the power supplies necessary for the type of electronics being operated. For example, for any instrument systems being operated downhole, 15 volts 5 is normally required. Thus, the ac power across the 6 (downhole) slave unit 50 will be in the order of 30 7 volts to maintain the power supplies at a stable 8 level (due to losses etc). 9 10 The data recovery circuit 26 in the master unit 10 11 operates as follows. The low-level signal 12 transmitted by the slave unit 50 is sensed using a 13 sense resistor 42. The signal from the slave unit 50 14 develops a voltage across the sense resistor 42 as 15 the output of the push-pull power driver 24 is 16 effectively an ac ground. 17 18 The value of sense resistor 42 is typically twenty 19 times the resistive value of the isolated pipeline 20 100. For example, if the resistive value of the 21 isolated pipeline 100 is 10 ohms (Q) from a master 22 injection point 44 (Fig. 3) to the slave unit 50, 23 then the sense resistor 42 would have a value of 24 200Q. The value of this sense resistor 42 can be 25 chosen to match the particular isolated pipeline 100. 26 27 The raw signal from the sense resistor 42 is then 28 processed by the first data channel that includes the 29 first signal recovery circuit 26, and is fed through 30 an analogue high speed switch (not shown, but forms 31 part of the signal recovery circuit 26).The 29 1 processor 20 or a local zero-crossing detection 2 circuit or the like, enables data to be directed to 3 the first data channel only when the power waveform 4 is high, thus facilitating the synchronisation. The data channel then only receives and processes valid 6 segments of the recovered data. It should be noted 7 that the triggering mechanism for directing data into 8 the data channel may be configured to allow 9 transmission when the power waveform. is low, or both when it is high and low.

11 12 The sampled data is then fed through the filtering 13 system 28 that, in simple applications, typically 14 comprises a single broad bandpass filter. In noisy applications, it is preferable to use a pair of 16 selective filters designed for each transmit 17 frequency F1, F2 It may also be necessary in 18 exceptionally noisy environments to use tuned 19 filters.

21 The signal recovered from the filtering system 28 is 22 then fed through an automatic gain control (AGC) 23 stage 30. The AGC stage 30 maintains the amplitude 24 of the recovered signal within a set amplitude range.

The frequency response of the AGC stage 30 is 26 typically sufficient to allow the AGC amplifier to 27 correct for changes in amplitude over one cycle of 28 either the transmission medium power frequency or the 29 telemetry system power frequency, whichever is the higher frequency. The AGC stage 30 performs two 31 functions. It compensates for the difference in 1 amplitude from the high carrier to the low carrier 2 frequency received (i.e. the difference in amplitudes 3 between F, and F2)- In addition, there may also be 4 variations in the amplitude of the received signal over the time period of the high cycle of the power 6 waveform frequency (i.e. variations in amplitude of 7 the signal during a single bit transmission). The 8 AGC stage 30 must be able to react quickly enough to 9 compensate for these changes without becoming unstable. Thus, the frequency response of the AGC 11 stage 30 is related to the frequency of the power 12 waveform, and the bandwidth of the AGC stage 30 is 13 typically ten times greater than the power waveform 14 frequency (i.e. ten times greater than the baud is rate).

16 17 The recovered signal is then fed into the comparator 18 stage 32, the output of which is fed into the first 19 counter 34. The comparator stage 32 compares the signal level of each of the two FSK frequencies F1, 21 F2 to establish which is present. The output of the 22 comparator stage 32 is a signal that contains either 23 one of the two FSK frequencies F1, F2- The first 24 counter 34 then counts the number of pulses in the signal from the comparator stage 32, and the 26 processor 20 reads the value in the first counter 34 27 to determine which of the two FSK logic frequencies 28 F1, F2 are present (i.e. either the frequency 29 relating to a logic one or zero).

3 1 1 The slave unit 50 transmits in a continuous stream of 2 digital data (i. e. ones and zeros), with each high 3 cycle of the power waveform containing one of the two 4 FSK frequencies F1, F2 representing either a logic 5 one or zero. The process is thus continued for each 6 high cycle of the power waveform to determine whether 7 a one or a zero was transmitted in each high cycle. 8 Once the processor 20 has determined whether a one or 9 a zero was sent in each high cycle, the processor 20 10 may reconstruct the transmitted digital data from the 11 slave unit 50. 12 13 The slave unit 50 may also transmit bursts of 14 transmitted data in a poll response mode. In the 15 poll response mode, there are three states for 16 transmission from the slave unit 10 to the master 17 unit 50: a logic one, a logic zero and a "none" 18 state. Thus, when not requested to transmit data the 19 slave unit 50 ceases transmission. This poll 20 response mode is typically used where multiple slave 21 units 50 are operating on the same transmission 22 system. 23 24 Figs 7a and 7b illustrate a power and data 25 transmission waveform respectively, for the 26 transmission of data from the master unit 10 at the 27 surface to the slave unit 50. Data is transmitted 28 from the master unit 10 to the slave unit 50 using 29 pulse-width modulation. Use of this technique allows 30 the signal recovery circuitry in the slave unit 50 31 located downhole to be less complex than that in the 32 1 master unit 10, thus reducing the size, cost and 2 power consumption of the slave unit 50. 3 4 Fig. 7a illustrates the power waveform transmitted 5 when data is being transmitted from the master unit 6 10 to the slave unit 50. In order to transmit 7 digital data, the width of the pulses in the waveform 8 are modified to represent either a digital zero or 9 one. This technique is termed pulse-width 10 modulation. Fig. 7b illustrates the difference in 11 pulse-widths between a logic one and zero as an 12 example. There are typically three different pulse13 widths (frequencies) used, each relating to either a 14 logic one, a logic zero or an idle state. The idle 15 state is typically used to aid specific command 16 recovery in the slave units 50. For example, where 17 there is more than one slave unit 50 coupled to the 18 system, each unit 50 remains in the idle state and 19 polls the data transmissions from the master unit 10 20 until it receives a command intended for that 21 particular unit 50 identified by the command string. 22 23 When data is transmitted from the master unit 10 to 24 the slave unit 50 using pulse-width modulation, the 25 signal received at the slave unit 50 is fed through a 26 second ac coupling capacitor 72 into a signal 27 recovery circuit 70, that includes an amplifier and 28 filtering system. The signal is amplified or 29 attenuated, depending upon the application. 30 33 1 The relative frequency of the main transmission 2 system power, and the frequency of the telemetry 3 power carrier Fc determine the value of the coupling 4 capacitor 72. The value is chosen so that the 5 capacitive decoupling acts as a high pass filter to 6 remove substantially all of the transmission system 7 power waveform whilst recovering as much of the 8 telemetry system power waveform as possible. 9 10 The requirement to either attenuate or amplify the 11 signal after decoupling depends upon the attenuation 12 of the high pass filter described above. As the 13 signal is superimposed on the power waveform, it will 14 have a substantial peak-to-peak voltage at the slave 15 unit 50 connection. If this large voltage signal is 16 decoupled without any substantial losses, the 17 recovered signal fed to the first stage amplifiers in 18 the signal recovery circuit 68 will exceed the supply 19 rails and will thus require to be attenuated. 20 21 However, if the signal is decoupled with a 22 substantial amount of low frequency rejection (i.e. 23 through a high pass filter), then the signal fed to 24 the first stage amplifier will be relatively small 25 and will thus require to be amplified. The 26 requirement to amplify or attenuate the signal is 27 dependent upon the relative frequency of the power 28 waveform to the transmission medium frequency. 29 30 The recovered and filtered signal is then fed into a 31 processor-controlled timer circuit 70.The timer 34 1 circuit 70 may be replaced by a re-triggered 2 monostable. The timer circuit 70 allows pulse-width 3 measurements to be taken to determine whether a one 4 or a zero was sent. The processor 60 can then 5 reconstruct the data transmission from the master 6 unit 10 to the slave unit 50 by analysing and 7 recording each pulse-width in turn to determine the 8 sequence of ones and zeros in the data transmission. 9 10 Data sent by the master unit 10 to the slave unit 50, 11 or vice versa, is typically encrypted by use of a 12 Hamming Code, or other suitable data error detection 13 and correction encoding scheme. The data from the 14 master unit 10 may also include the address of the 15 slave unit 50 in the command string so that several 16 slave units 50 may receive different and individual 17 commands from a single master unit 10. 18 19 Where the isolated pipeline 100 is particularly noisy 20 or there is a large degree of background 21 interference, it is often not possible to determine 22 from the method described above whether a logic one 23 or zero was transmitted. To overcome this, the 24 recovered data is not measured as one of two 25 frequencies in windows delineated from the power 26 waveform, but each data detection window that is seen 27 by the processor 20 at the surface is sub-divided 28 into several sub-windows. Figs. 8a to 8d illustrate 29 this technique. 30

1 To operate correctly using this sub-dividing 2 technique, it is preferable to use a second data 3 channel within the master unit 10 that includes the 4 second signal recovery circuit 36, the timer circuit 5 38 and the second counter 40. 6 7 The telemetry system may be coupled to any isolated 8 pipeline 100 or a tubing string. For example, it may 9 be coupled to an existing pipeline that is used to 10 recover hydrocarbons from a borehole, subsea well or 11 the like. Fig. 8a shows a typical power waveform 12 that may be present on the isolated pipeline 100 and 13 may be, for example, a power waveform that is driving 14 a downhole motor. The second data channel in the 15 master unit 10 is used to determine the fundamental 16 operating frequency of the power waveform for the 17 downhole motor. The processor 20 within the master 18 unit 10 uses the second counter 40 to establish the 19 frequency at which the power waveform on the isolated 20 pipeline 100 is operating, using a similar technique 21 as described above to determine whether a zero or a 22 one was sent. The processor 20 then synchronises the 23 transmitted power for the slave unit 50 (waveform 24 shown in Fig. 8b) to the same frequency, or a 25 multiple thereof, as the power frequency of the 26 isolated pipeline 100. Thus, the power and data 27 transmissions are synchronised to the frequency of 28 the power on the isolated pipeline 100 over which 29 they are transmitted (i.e. they are synchronised with 30 the source of the noise which can cause a loss of 31 signal) thus reducing the effect of the noise.

36 2 Fig. 8b shows an exemplary power waveform for 3 transmission of power and/or data from the master 4 unit 10 to the slave unit 50. The waveform shown in 5 Fig. 8b is similar to that shown in Fig. 6a and may 6 operate over the same frequency range (i.e. in the 7 order of a few mHz to several kHz). 8 9 Fig. 9c illustrates the data transmission from the 10 slave unit 10 downhole to the master unit 50 at the 11 surface. The waveform is similar to that shown in 12 Fig. 6b wherein the data transmission is superimposed 13 upon and synchronised to the high cycle of the power 14 waveform. Although the example shows data being 15 superimposed on and synchronised to the high cycle, 16 it should be noted that data could also be 17 superimposed on and synchronised to the low cycle or 18 both. 19 20 Frequency-shift keying (FSK) is used to transmit data 21 from the slave unit 50 to the master unit 10. In the 22 example shown in Fig. 8c, F, that represents a logic 23 one is 200 kHz and F2 that represents a logic zero is 24 90 kHz. As with the previous example, the two FSK 25 frequencies F1, F2are preferably not multiples of one 26 another to minimise the occurrence of false 27 detections. The two frequencies F1, F2 are typically 28 also at least a factor of two different. Although 29 this increases the amount of bandwidth required on 30 the isolated pipeline 100, the system allows for the 31 recovery of highly attenuated signals.Where there 37 1 is significant inductance on the isolated pipeline 2 100, much lower frequencies may be used. This 3 reduces the speed of the system, but does not affect 4 the ability of the system to transmit and receive data. Low carrier frequencies may be used (in the 6 order of a few hertz) with very high frequency data 7 carriers to increase data recovery in noisy 8 environments, such as those downhole. Where low 9 frequencies are required, the system may also be used with fractions of a hertz for the carrier, and a 11 logic zero frequency of 100 Hz and a logic one 12 frequency of 350 Hz, for example.

13 14 The frequency used to transmit data to and from the slave unit 50 is typically several hundred kilohertz 16 (kHz) For example, the transmit frequencies F1, F2 17 from the slave unit 50 to the master 10 may be 200 18 kHz for a one and 90 kHz for a zero. Thus, if a 19 logic one is to be transmitted, then the higher of 20 the two FSK frequencies F, (i.e. 200 kHz) will be 21 transmitted for the duration of the high cycle of the 22 power waveform, and if a logic zero is to be 23 transmitted, the lower of the two FSK frequencies F2 24 (i.e. 90 kHz) is transmitted for the duration of the 25 high cycle of the power waveform. 26 27 However, where the isolated pipeline 100 is 28 particularly noisy, for example where the 29 transmission system 12 is also used to drive a 30 downhole motor, it may not be possible to determine 31 whether a logic one or zero was sent from the basic 38 1 counter discrimination technique. A further 2 technique is used to aid in discriminating between a 3 logic one and zero that sub-divides each of the data 4 windows in the data transmission waveform into a 5 series of sub-windows. An example of a sub-window is 6 shown in Fig. 8d, which is an enlarged view of one of 7 the data windows from the waveform in Fig. 8c. The 8 data window is sub-divided into a number of sub9 windows, such as ten shown in Fig. 8d. Each of the 10 ten sub-windows is then studied and measurements 11 taken to determine which of the two FSK frequencies 12 (i. e. F, or F2) is present within that sub-window. 13 14 Every high period (the receive window) of the slave 15 unit power waveform (Fig. 8c) is segmented in the 16 processor code into smaller time slots (typically ten 17 per receive window). When the system is first 18 initiated, or on command from the master unit 10, the 19 slave unit 50 transmits a specified pattern of ones 20 and zeros to calibrate the transmission data windows. 21 The master unit 10 receives and processes this 22 pattern and determines from the pattern received the 23 reliability of the recovered data. The reliability 24 of the recovered data indicates which of the sub25 windows in the received window has reliably 26 transmitted a one or a zero. The sub-windows in 27 which a one or a zero cannot be reliably recovered 28 are mapped as being "not usable" in the memory of the 29 processor 20 and are thus not used for data recovery. 30 In this way, the reliability of the system is 31 increased, as the test transmission allows the system 39 1 to assess which sub-windows are being affected by 2 noise and other interference, these sub-windows then 3 being ignored for future transmissions. This 4 technique allows for enhanced reliability and also 5 the ability to allow the system to be calibrated to 6 particular environments. 7 8 Thus, this technique provides a method of data 9 transmission and recovery that uses sub-divided and 10 synchronised data recovery windows to enhance the 11 noise immunity of the system, and also the use of a 12 calibrating pattern to allow the master unit 10 to 13 determine the reliable portions of the recovered data 14 transmitted by the slave unit 10. 15 16 Referring to Fig. 4, isolating collar 200 is used to 17 provide electrical isolation whilst maintaining 18 pressure sealing in the pipeline 100. Isolating 19 collar 200 is described in US Patent Nos 4,861,074 20 and 4,716,960 assigned to Production Technologies 21 Inc, the entire disclosure of these patents being 22 incorporated herein by reference thereto. The 23 function of isolating collar 200 is conventionally to 24 electrically isolate at least a portion of the 25 pipeline, wherein electrical power is applied to the 26 pipeline or tubing string to facilitate heating of 27 the pipeline or tubing string. Heating of the 28 pipeline or tubing string is to prevent the formation 29 of solids, particularly for use with pipelines or 30 tubing strings containing paraffin. 31

1 Isolating collar 200 is provided with threads 204 at 2 an upper end of an inner connector 202. Threads 204 3 facilitate connection of the isolating collar 200 to 4 a tubing string or the like thereabove. Inner 5 connector 202 is substantially tubular and is 6 typically of a steel construction with material to 7 suit the pipeline or tubing string to which it is 8 attached. 9 10 Inner connector 202 is provided with a continuous 11 screw thread 206 on an exterior surface for 12 engagement with an inner insulating seal sleeve 208. 13 Inner sleeve 208 is provided with a thread 210 that 14 allows it to be threadedly coupled to the thread 206 of the inner connector 202, and a thread 212 provided 16 on the interior of an outer connector 214. Inner 17 connector 202 is typically provided with sealing 18 means, such as O-rings 218, at a lower end thereof to 19 seal against sleeve 208. 20 21 Outer connector 214 is typically formed of 22 electrically conducting material such as steel, and 23 is concentrically attached to the inner connector 202 24 to be supported thereby. Outer connector 214 is 25 provided with an internal thread 216 at a distal end 26 thereof to facilitate connection of the isolating 27 collar 200 into a pipeline or tubing string attached 28 therebelow. The distal end of outer connector 214 is 29 also provided with sealing means, for example 0-rings 30 220, on the inner bore thereof for sealing with the 31 sleeve 208.

1 2 An insulating material 222 is typically injected into 3 an annulus between the inner and outer connectors 4 202, 214 via a port 226. The insulating material 222 provides for electrical insulation between the inner 6 and outer connectors 202, 214, and can additionally 7 provide mechanical strength to support the weight of 8 the string below the collar 200. The insulating 9 material may be, for example, an epoxy such as aromatic amine.

11 12 The insulating material 222 typically includes sleeve 13 208 that is typically formed of a plastic material.

14 Sleeve 208 bridges the space between the lower end of the inner connector 202 and the seal means 220 and 16 prevents electrical contact between the inner and 17 outer connectors 202, 214 through water being 18 contained within the fluids flowing through the 19 collar 200.

21 Sleeve 208 and the first and second seals 218, 220 22 insulate between the inner and outer connectors 202, 23 214 and additionally prevent fluids from reaching the 24 insulating material 222 from the interior of the isolating collar 200. The insulating material 222 is 26 preferably protected from contact with well fluids 27 that may cause a short circuit within the isolating 28 collar 200.

29 In certain embodiments of the isolating collar 200, a 31 nonsolid, noncompressible material is injected into 42 1 cavities in the lower end of the isolating collar 2 200. This material is confined under pressure so 3 that sleeve 208 is supported against internal 4 pressure. Thus, as pressure within the bore of the 5 isolating collar 200 increases, the pressure on the 6 nonsolid material increases and no substantial 7 pressure differential is created. The material is 8 preferably silicone. Before the nonsolid material is 9 injected, the area that it fills istypically 10 evacuated. 11 12 Isolating collar 200 is based on an oilfield thread 13 for coupling but can be adapted to other pipe 14 coupling threads and indeed flange couplings without 15 compromising or altering the core design of the 16 collar. Thus, those skilled in the art will 17 appreciate that isolating collar 200 can be coupled 18 to the pipeline or tubing string in any conventional 19 manner, depending upon the particular application 20 and/or the structure of the pipeline or tubing 21 string. 22 23 Isolating collar 200 includes a ring 228 that allows 24 external electrical power and transmissions to be 25 coupled to the outer connector 214. Ring 228 is 26 provided with internal threads 230 that engage 27 external threads 232 on an upper end of the outer 28 connector 214. A blind conduit 234 is provided on 29 the ring 228 to allow for connection of electrical 30 signals using any conventional means. Thus, 31 electrical signals, such as power and/or

43 1 communications, may be transmitted via the outer 2 connector 214 to any receiver that is electrically 3 coupled to the pipeline or tubing string suspended 4 below the isolating collar 200. 5 6 Fig. 5 shows an alternative embodiment of an 7 isolating collar 300. Collar 300 is substantially 8 the same as collar 200. Isolating collar 300 is 9 described in US Patent Nos 4,861,074 and 4,716,960 10 assigned to Production Technologies Inc, the entire 11 disclosure of these patents being incorporated herein 12 by reference thereto. 13

14 Isolating collar 300 includes an upper connector 302 15 and a lower connector 304. The upper and lower 16 connectors 302, 304 are threadedly coupled using 17 threads 306 on the upper connector 302 and threads 18 308 on the lower connector 304. It should be noted 19 that the upper and lower connectors 302, 304 may be 20 coupled in any conventional manner. 21 22 The cavity between the threads 306, 308 is preferably 23 filled with an insulating material 310 as in the 24 previous embodiment, the material 310 typically being 25 epoxy. The insulating material 310 typically 26 provides for electrical insulation between the two 27 connectors 302, 304, andthe interlocking threads 28 306, 308 give mechanical support to allow a tubing 29 string to be suspended from the lower connector 304. 30 44 1 The lower connector 304 is provided with a threaded 2 bore 312 for receiving an electrical conduit 314. 3 4 The upper and lower connectors 302, 304 are provided 5 with a central bore 302b, 304b respectively, to allow 6 the passage of fluids through the collar 300, and 7 also threads 302t, 304t respectively, to allow the 8 collar 300 to be coupled into a tubing string or 9 pipeline. 10 11 The upper connector 302 is provided with a 12 counterbore 316 that receives the electrical conduit 13 314. The counterbore 316 is typically filled with 14 epoxy insulating material when the electrical conduit 15 314 is in place. 16 17 Electrical conduit 314 typically comprises a metal 18 rod having a lower threaded end 3141 for threadedly 19 engaging threaded bore 312 in the lower connector 304 20 to facilitate electrical connection. The conduit 314 21 has an enlarged diameter portion 314e to reduce the 22 electrical resistance of the conduit 314 in the area 23 of the enlarged portion 314e, so that the insulating 24 material in this area is not overheated when high 25 power signals are transmitted. 26 27 The electrical conduit 314 is provided with an 28 electrical connector 318 at its upper end, the 29 connector 318 being attached by any suitable means, 30 such as a screw thread. The connector 318 is 31 provided with a blind internal bore 320 to which 1 electrical connection may be made, for example by 2 soldering. The connector 318 is typically 3 electrically insulated by using a rubber boot, for 4 example, positioned over the connector 318. 5 6 Thus, both isolating collars 200, 300 facilitate 7 electrical isolation of the pipeline above the 8 collars 200, 300 but allow transmission of electrical 9 signals on the pipeline suspended below the collars 10 200, 300. 11 12 In addition to the use of the isolating collar 200, 13 300 the pipeline system 100 (Fig. 1) is preferably 14 isolated form electrical ground between the collars 15 200a, 200b to maintain the isolation. This requires 16 the pipeline to have a degree of insulation or be 17 spaced off any grounded objects, by insulating mounts 18 or protectors, as will be described hereinafter. 19 20 It will be appreciated that the pipeline 100 is 21 required to be isolated to some extent from ground. 22 23 Referring now to Fig. 9, there is shown an oilwell, 24 generally designated 400, with tubular casing 412 and 25 a pipe based production tubing. The oilwell 26 generally includes a well head 402 that may be of any 27 conventional type, that has a tubing string suspended 28 therebelow. The tubing string typically comprises a 29 plurality of tubulars 404 that are coupled together 30 in a known manner (such as by threaded couplings). A 31 numberof isolatng collars 200a, 200b, 200c are 46 1 coupled into the tubular string at specified 2 locations, to electrically isolate the tubular 3 string. The isolating collars 200 may comprise the 4 isolating collars 300. 5 6 The master unit 10 can be either directly or 7 capacitively coupled to the single wire connection to 8 the downhole system, via the isolating collar 200a. 9 Power and data transmissions to and from the master 10 unit 10 are driven between the single live contact 11 through a wellhead penetrator 406 provided in the 12 wellhead 402. The wellhead penetrator 406 would be 13 the type of penetrator used for electrical 14 submersible pump (ESP) installations or permanent 15 gauge installations. Fig. 10 shows a typical 16 penetrator 406, although any proprietary well head 17 penetration device with suitable pressure and 18 electrical rating may be used. 19 20 Referring now to Figs iOa and 10b, the function of a 21 wellhead penetrator 406 is to allow electrical cables 22 to be fed through an oil field wellhead 402. The 23 wellhead 402 forms a pressure cap on the well and so 24 any electrical penetration has to maintain the 25 pressure seal of the wellhead 402. 26 27 Fig 10a illustrates an API flange unit, and Fig. 10b 28 illustrates an NPT mounted unit, but both units 29 perform the same function and are substantially the 30 same. The penetrators 406 include a primary pressure 31 seal 450 that typically comprises a metal-to-metal

47 1 seal. Seal 450 couples the body of the penetrator 2 406 to the wellhead (schematically shown in Figs 10a 3 and 10b as 452) itself. A seal 454 seals against a 4 cable running through the wellhead 452 itself, seal 5 454 typically being a metal-to-metal seal. 6 7 A glass-to-metal electrical penetrator allows 8 electrical inner conductors to pass through a 9 pressure-tight barrier 456. 10 11 The penetrator 406 includes a connector 458 to 12 facilitate coupling of an external cable onto the 13 wellhead penetrator 406. Connector 458 may comprise 14 a gland or any other type of cable exit. 16 The penetrator 406 may be mounted to the wellhead 452 17 using any conventional means, such as bolts 460 (Fig. 18 10a) or a screw thread 462 (Fig. 10b). The wellhead 19 protector 406 typically includes a pressure-tight 20 steel body 464 that houses and generally mounts the 21 major components of the penetrator 406. 22 23 The single wire from the base of the penetrator 406 24 is fed on to the isolating tubing collar 200a mounted 25 below the wellhead 402 and a tubing hanger 408 (Fig. 26 9). Electrical contact between the single wire of 27 the wellhead penetrator 406 and the isolated portion 28 of the tubing below the isolating collar 200a can be 29 achieved by using either of the isolated collars 200, 30 300 described herein, or otherwise. 31 48 1 Alternatively, the single wire of the wellhead 2 penetrator 406 can be coupled directly to any part of 3 the isolated tubing string using a simple tubing 4 based connection as shown in Fig. 11. Fig. 11 5 schematically illustrates the wellhead penetrator 406 6 and two methods of coupling the wire from the 7 penetrator 406 to the isolated portion of tubing. 8 The first method is described above, wherein the 9 isolating collar 200a is used to transmit electrical 10 signals from the wellhead penetrator 406 to the 11 isolated portion of the tubing string. 12 13 Alternatively, the wire from the wellhead penetrator 14 406 may be coupled to the isolated pipeline using a 15 cable coupling (not shown) that is coupled to a 16 tubing clamp 410. 17 18 Referring again to Fig. 9, the tubing string is 19 prevented from touching casing 412 of the oilwell 400 20 by insulated protectors 414. The insulated 21 protectors 414 can be mounted at either couplings 416 22 between successive tubulars 404 or at a mid point 418 23 in the length of a tubular 404. The insulated 24 protectors 414 are typically of a rubber or plastic 25 construction and are commonly used in the oil and gas 26 industry. They are generally two types of protectors 27 414, either protecting across the tubing joint (cross 28 coupling protectors) such as at coupling 416 or 29 clamping at any point in the pipe (mid joint 30 protectors) such as at mid point 418. 31 49 1 The slave units 50 are typically mounted to the 2 production tubing 404. In this example, two slave 3 units 50a, 50b are shown. Fig. 9a shows an enlarged 4 view of a section of the tubing of Fig. 9 5 illustrating how the slave units 50a, 50b are coupled 6 to the tubing string. Slave units 50a have a carrier 7 or mandrel 420 that attaches the slave unit 50a to 8 the tubing 404, a slave module 422 that contains the 9 electronic- circuitry described above, and an io electrical return path that typically comprises the 11 casing 424 of the slave unit 50a. Casing 424 12 typically comprises a spring contact. 13 14 The slave unit 50a is further illustrated in Fig. 12. 15 The slave unit 50a is electrically connected to the 16 tubing 404 by clamping the electronic module 422 17 containing the circuitry onto the tubing based 18 mandrel 420. Mandrel 420 may be machined from solid 19 steel, fabricated or a combination of solid machining 20 and bolted clamps. The general structure of the 21 mandrel 420 is of steel to suit the rest of the 22 tubing string. The electronics of the slave unit 50a 23 are isolated from a protective pressure housing 426, 24 housing 426 being conventionally grounded, but being 25 live in this particular embodiment. The electronic 26 module 422 mounted to the mandrel 420 has insulated 27 end pieces 428 that the spring contact 424 is mounted 28 to. This electrically isolates the spring loaded 29 contacts 424 from both the mandrel 420 and the body 30 of the electronic module 422. The slave unit 31 pressure housing 426 typically supports the spring 1 contact 424 and also maintains pressure integrity 2 during wiping action of the spring contact 424. 3 4 Thus, the electronics in the electronics module 422 5 is coupled between the live pipe or tubing 404 and 6 the ground potential casing 412 (not shown in Fig. 7 12), thus drawing power from the live tubing 404. 8 9 The simplest return path connection is a spring-loaded wiper arm 424 (Fig. 12), that pushes 11 against the casing 412 of the well 400. The 12 electrical return contact can be a hydraulically 13 operated latching arm (not shown) or alternatively, 14 may comprise the grips of a hydraulically set packer 15 (not shown). 16 17 Thus, the slave units 50 are electrically coupled to 18 the master unit 10 using only the production tubing 19 404 and can monitor sensors and control actuators 20 (not shown) as described above. 21 22 Furthermore, the telemetry system can be used in a 23 multi-lateral well (several branches downhole from a 24 single borehole) and slave units 50 can be installed 25 in each of the multiple branches (not shown). Thus, 26 the system may operate with multiple slave units 50 27 in various branches of the well, with all of the 28 slave units 50 acting in parallel on the same system, 29 and with no requirement for any splicing or joint in 30 the system other than a union on the tubing system 31 404 that is inherent for the well to function.

51 1 2 Referring again to Fig. 9, the system is shown as 3 having multiple slaves 50a, 50b, 50c coupled to the 4 production tubing 404 at any convenient locations.

The slave units 50a, 50b, 50c may be positioned to 6 allow for the control, operation and interrogation of 7 a plurality of different instruments, sensors or load 8 actuators as required.

9 Where a slave unit 50 requires to be mounted below a 11 packer or valve 430 (which cannot be isolated 12 electrically from the casing 404) an isolating tubing 13 collar 200b will be mounted above the packer or valve 14 430, and a further isolating collar 200c mounted below the packer or valve 430. A cable 432 is used 16 to circumvent the packer or valve 430 (or any other 17 obstructing object) using a standard isolated packer 18 penetrator 434.

19 The slave units 50a, 50b, 50c in this embodiment may 21 be used for reservoir monitoring using pressure 22 and/or temperature sensors, flow meters, and fluid 23 temperature probes. These slave units 50a, 50b, 50c 24 may also be used to operate and control gas lift valves, fluid production intake valves and fluid 26 circulating valves. The slave units 50a, 50b, 50c 27 may also be used to control a packer with a flow 28 through valve controlled from the master unit 10.

29 The telemetry system has the capability to apply substantial electrical power to downhole actuators 31 (not shown) due to the low resistance of the pipe 404 52 1 in the tubing string. Thus, the telemetry system can 2 be implemented to drive and control large motors, 3 actuators and the like. 4 5 In some downhole applications, fluid in the space 6 between the casing 412 and the outside surface of the 7 production tubing 404 is conductive. In this case, 8 the tubing 404 in addition to being spaced from the 9 casing 412 by the insulating protectors 424, would 10 also be coated with an insulating paint or the like 11 to increase the amount of electrical isolation 12 between the tubing 404 and casing 412. 13 14 The telemetry system can tolerate a certain degree of 15 leakage current from the tubing 404 to the casing 412 16 so that complete coating and full isolation is not a 17 primary requirement. The leakage tolerance is 18 achieved by using telemetry signal levels that have 19 sufficient margin to tolerate this leakage current. 20 21 Referring now to Figs 13a and 13b, Fig. 13a shows a 22 subsea pipeline system 500, that includes a dual 23 pipeline 502, 504, and Fig. 13b illustrates a subsea 24 pipeline system 550 that includes a single pipeline 25 552. In Figs 13a and 13b, the pipelines 502, 504, 26 552 are typically under water (either fresh or sea 27 water) and the pipelines 502, 504, 552 are used as 28 the power and communications transmission medium for 29 the telemetry system. 30 53 1 The master unit 10 of the telemetry system includes a 2 power supply and master control unit, and is 3 typically located above the water level and before 4 the point where the pipeline 502, 504, 552 enters the 5 water. The pipelines 502, 504, 552 generally do not 6 have any other power source present on the pipelines 7 502, 504, 552 in such applications, and thus it is 8 not necessary to capacitively couple the master unit 9 10 to the pipeline 502, 504, 552. Thus, direct 10 coupling of the ac power from the master unit 10 to 11 the pipelines 502, 504, 552 may be used. However, it 12 will be appreciated that capacitive coupling will be 13 required where the pipelines 502, 504, 552 are used 14 to carry any other power source. 15 16 A single or two wire connection is made from the 17 master unit 10 to a connection point 504 at or near 18 the isolating collar 200a. At the connection point 19 504, the live power wire from the master unit 10 is 20 coupled to an isolated portion 502i of the pipeline 21 502, by making connection to the metallic body of the 22 isolated portion 502i of the pipeline 502. The 23 electrical contact can be made by clamping to the 24 pipeline 502, or using a modified portion of pipe 25 with an electrical connector or coupling fitted 26 thereto, or in any other suitable manner. An 27 isolating tubing collar 200a in the pipeline 502 28 electrically isolates the pipeline 502 from a source 29 506 of the transported fluid, and supports the weight 30 or tension in the pipeline 502. A second isolating 31 collar 200b is positioned at or near a delivery end 54 1 502d of the pipeline 502. The isolating collars 2 200a, 200b can be either of an oil field thread type, 3 or may be coupled to the pipeline 502 at the 4 termination of the dual pipe couplings, where the 5 couplings may be modified to suit the pipeline 6 material and coupling method, but the internal 7 structure of the collars 200a, 200b is as described 8 above. It should be noted that either of the 9 isolating collars 200, 300 may be used. 10 11 In this way, a transmission zone 502z is defined 12 between the isolating collars 200a, 200b. The master 13 unit 10 is electrically coupled to the transmission 14 zone 502z using the isolating collar 200a, for 15 example, as described above. Slave units 50a, 50b 16 can then be electrically coupled at any point within 17 the transmission zone 502z so that any power and/or 18 data transmissions from the master unit 10 (or data 19 transmissions from the slave units 50a, 50b to the 20 master unit 10) can be retrieved. 21 22 The isolated portion 502i of the pipeline 502 is 23 insulated partially from the water by both coating of. 24 the pipeline 502 and insulating protectors 510. The 25 coating can be selected from any of a number of 26 available techniques. The insulating coatings 27 typically provide a substantial fluid resistance, and 28 complete water sealing is preferable but not 29 essential. Similarly, at pipe joints under water in 30 the pipeline 502, the joints should be covered with 31 plastic or rubber insulating covers to provide

1 protection against physical damage, any electrical 2 shorting and also water ingress into the joints. 3 Injection of insulating grease or sealant into the 4 joint covers is again preferable but not necessary. 5 6 At any point in the transmission zone 502z, slave 7 units 50a, 50b can be attached to provide monitoring 8 of sensors or control of actuators as described 9 above. Any number of slave units 50 may be coupled 10 into the system as required. 11 12 Referring to Fig. 14, the slave units 50a, 50b are 13 typically mounted so that the units 50a, 50b make 14 electrical contact with the live metal of the 15 transmission zone 502z. If the body of the 16 protective pressure housing 426 (Fig. 14) is attached 17 to the metal of the pipe 502, 504, SS2 then it will 18 be live and will require an isolated ground contact 19 that is connected to the local ground 554 (Fig. 13b) 20 or second pipeline 504 (Fig. 13a) that are used as 21 ground returns. The ground contact is typically made 22 by attaching a fly lead 436 to one of the insulated 23 end pieces 428, and thus end pieces 428 are typically 24 grounded. The protective pressure housing 426 25 typically protects the electronics from the water 26 pressure, and additionally isolates the ground 27 contact from the live pipe 502, 504, 552. 28 29 The slave units 50 require a ground or earth to 30 complete the electrical circuit. This can be 31 achieved using local grounding 554 such as the 56 1 seabed, a lake bed or the like, schematically 2 illustrated in Fig. 13b. Alternatively, this may 3 also be achieved by using another pipeline 504 4 running next to the "live" one as the ground return, 5 schematically illustrated in Fig. 13a. 6 7 The slave unit 50 located underwater can have several 8 functions including strain gauge measurement on 9 pipeline stress, lifting forces from riser buoyancy 10 elements, fluid temperature measurement, flow rate 11 measurement in co-mingled lines, or the like.

12 Further uses could be to provide control of a subsea 13 installed wellheads using the underwater pipeline as 14 the only power and communications medium. The 15 functionality of the slave unit 50 could include the 16 control of wellhead actuators, measurement of choke 17 positions and measurement of local pressure and 18 temperatures. 19 20 A further use of this system would include coupling 21 an underwater acoustic modem to the slave unit 50 to 22 allow interrogation of long pipeline sensor systems 23 from floating rigs, FPSO and ships while working on 24 the pipe line 502, 504, 552 or associated systems. 25 26 Referring now to Figs 15a and 15b, there is shown a 27 dual and single pipeline system 600, 650 28 respectively, that are typically located on the 29 surface. The master unit 10 includes a power supply 30 and master control unit and is typically located near 31 the source 610 of the pipeline 602, 604, 650, or 57 1 coupled to the pipeline 602, 604, 652 using a 2 suitable cable. An isolating tubing collar 200a is 3 coupled into the pipeline 602, 652 to isolate the 4 pipe 602, 652 from the source 606 of the transported 5 fluid, and support the pipeline 602, 652. In 6 addition, there is a second isolating collar 200b 7 positioned at the delivery end 602d, 652d of the 8 pipeline 602, 652. Either isolating collar 200 or 9 collar 300 may be used. 10 11 The live or power line from the master unit 10 is 12 coupled to an isolated section 602i, 652i of the 13 pipeline 602, 652 using a clamp or connector to 14 attach to the steel of the pipeline 602, 652, similar 15 to the embodiments shown in Figs 13a and 13b. The 16 isolated section 602i, 652i of the pipeline 602, 652 17 is insulated partially from the weather and/or the 18 surrounding surface by both coating of the pipeline 19 602, 652 and insulating protectors 610. The coating 20 and insulating joint protectors 610 typically provide 21 a substantially water-tight cover. It is not a 22 requirement that the coating and protectors 610 are 23 completely water-tight. 24 25 In this way, a transmission zone 602z is defined 26 between the isolating collars 200a, 200b. The master 27 unit 10 is electrically coupled to the transmission 28 zone 602z using the isolating collar 200a, for 29 example, as described above. Slave units 50a, 50b 30 can then be electrically coupled at any point within 31 the transmission zone 602z so that any power and/or 58 1 data transmissions from the master unit 10 (or data 2 transmissions from the slave units 50a, 50b to the 3 master unit 10) can be retrieved 4 5 Where the pipeline 602, 652 is on the surface, the 6 pipeline 602, 652 is supported along its length by 7 insulating supports (not shown) to prevent it from 8 grounding to earth. These supports are typically 9 fabricated from standard supports with isolating 10 rings to space the mounting from the pipeline 602, 11 652. 12 13 As before, a slave unit 50 can be coupled to the 14 transmission zone 602z, 652z at any point along its 15 length, and multiple slave units 50 may be used. 16 Slave units 50a, 50b can be coupled to the 17 transmission zone 602z, 652z to provide monitoring of 18 sensors or control of actuators, as described above. 19 20 Referring now to Fig. 16, the slave units 50a, 50b 21 would typically be mounted on a grounded structure 22 (not shown) around the pipeline 602, 652 and a single 23 wire 620 run to a clamp 622 or connector connecting 24 the slave unit 50a, 50b live connect to the metal of 25 the pipeline 602, 652. 26 27 The slave units 50 require a ground or earth to 28 complete the electrical circuit. This can be 29 achieved by either using local grounding 624 like the 30 earth (schematically illustrated in Figs 15b and 16), 31 or may also be achieved by using another pipeline 604 59 1 running next to the "live" one as the ground return 2 (as illustrated in Figs 15a and 16). 3 4 The slave unit 50 can perform a plurality of 5 functions in relation to a surface pipeline 602, 652, 6 such as fluid flow measurement, valve control, pipe 7 corrosion or strain measurement, fluid composition 8 measurement, pressure, temperature, vibration and 9 also pipe inclination for subsidence monitoring. 10 Shut down valves could also be driven from a slave 11 unit 50 as well as control of pumps and drain or 12 bleed valves to control fluid pumping or control 13 equipment remotely using the pipeline 602, 652 as the 14 control link. 15 16 This particular embodiment is useful for controlling 17 remote pumping stations where the station is far 18 removed from electrical power and/or telephone lines. 19 The telemetry system can provide both power to the 20 pumps, and also the ability to measure and control 21 the pumping operation. 22 23 Fig. 17 illustrates a surface pipeline comprising 24 first and second isolated pipelines 702, 704 (similar 25 to the system shown in Figs 13a, 13b), and an 26 isolated subsea or downhole tubing 706 (similar to 27 the system shown in Fig. 9). An oilwell 708 which 28 has a wellhead 712 on the surface has the isolated 29 pipelines 702, 704 coupled thereto from the surface, 30 and on the same system has the isolated downhole 31 production tubing 706 suspended therebelow.

2 The pipeline 702 from the surface is isolated with an 3 isolating tubing collar 200a at the surface, and a 4 second isolating collar 200b is provided at or near the wellhead 712, creating a transmission zone 6 therebetween. An electrical link 714 couples the 7 power and data transmissions from the isolated supply 8 from the surface pipeline 702 to a wellhead 9 penetrator 716 and this in turn couples the power and data transmissions to the isolated downhole tubing 11 706. The downhole tubing 706 typically has at least 12 one slave unit 50 coupled thereto (Fig. 17 shows two 13 slave units 50a, 50b) that are connected back to 14 electrical ground through the downhole casing 718.

As before, slave units 50c and 50d can be coupled 16 anywhere in the isolated transmission zone of the 17 surface pipeline 702, or the downhole tubing 706.

18 The slave units 50c, 50d may use the second pipeline 19 704 as a ground return, or may be grounded locally, 20 depending upon the application and/or the location of 21 the slave units 50c, 50d. 22 23 A further extension of this system would be to use a 24 single subsea pipeline (not shown) to couple several 25 downhole wells together on the same system. This 26 would also apply where the oilwell had multi-lateral 27 bore holes and each arm of the multi-lateral system 28 was both isolated and connected to the same power 29 source. The system would have the ability to supply 30 substantial levels of power to drive the electronics 61 1 and controls at each of the wells that are coupled to 2 the slave units 50. 3 4 Thus, there is provided a telemetry system that in 5 certain embodiments allows for both power and data 6 transmissions across an isolated tubing string or 7 pipeline. The system in certain embodiments uses 8 frequency-shift keying (FSK) and pulse-width 9 modulation to allow for the transmission of data 10 across the pipeline or tubing string. 11 12 The system in certain embodiments is flexible in that 13 it allows for a number of slave units to be located 14 remotely from one or more master units, the master 15 units being used to control the operation of the 16 slave units. The slave and master units are 17 typically coupled to a single transmission medium, 18 such as the isolated pipeline or tubing string. The 19 system in certain embodiments can also support the 20 use of more than one master unit to control the slave 21 units from more than one point within the system. 22 23 There is also provided a method of transmitting 24 pulse-width modulated power over an isolated pipeline 25 or tubing string and recovering this as both power 26 and data. There is also provided a method of 27 transmitting frequency-shifted data that is 28 synchronised to a received power waveform. 29 62 1 Modifications and improvements may be made to the 2 foregoing, without departing from the scope of th 3 present invention.

63

Claims

1 CLAIMS 2 1. A telemetry system comprising a master unit, and 3 at least

one slave unit remote from the master unit, 4 the master and slave units communicating via a 5 transmission system, wherein the telemetry system is 6 capable of transmitting power and data transmissions 7 between the units, and wherein the transmission 8 system includes an at least partially isolated tubing 9 string or pipeline. 10 11

2. A telemetry system according to claim 1, wherein 12 the pipeline or tubing string is electrically 13 isolated using at least one isolating collar. 14 15

3. A telemetry system according to claim 2, wherein 16 the isolating collar comprises first and second 17 connectors, the first and second connectors being 18 threadedly coupled together. 19 20

4. A telemetry system according to claim 3, wherein 21 an electrical isolating material is injected between 22 the first and second connectors to isolate the 23 connectors from one another. 24 25

5. A telemetry system according to claim 3 or claim 26 4, wherein the isolating collar includes means for 27 conveying electrical signals from outwith the collar 28 to the second connector. 29 30

6. A telemetry system according to any preceding 31 claim, wherein the pipeline or tubing string is

64 1 coated with an electrically isolating coating to at 2 least partially isolate the pipeline or tubing 3 string.

4

7. A telemetry system according to any preceding 6 claim, wherein the at least partially isolated 7 pipeline or tubing string comprises a surface 8 pipeline or tubing string.

9

8. A telemetry system according to any one of 11 claims I to 7, wherein the at least partially 12 isolated pipeline or tubing string comprises a subsea 13 pipeline or tubing string, or a downhole pipeline or 14 tubing string.

16

9. A telemetry system according to any preceding 17 claim, wherein the at least partially isolated 18 pipeline or tubing string comprises any combination 19 of surface, subsea or downhole pipelines or tubing strings.

21 22

10. A telemetry system according to any preceding 23 claim, wherein the pipeline or tubing string includes 24 a first isolating collar at or near a source of fluid flowing within the pipeline or tubing string.

26 27

11. A telemetry system according to claim 10, 28 wherein the pipeline or tubing string includes a 29 second isolating collar at or near a sink for the fluid in the pipeline or tubing string.

31 1

12. A telemetry system according to claim 10 or 2 claim 11, wherein the master unit is electrically 3 coupled to the pipeline or tubing string via the 4 first isolating collar. 5 6

13. A telemetry system according to any preceding 7 claim, wherein at least one slave unit is coupled to 8 the pipeline or tubing string. 9 10

14. A telemetry system according to any preceding 11 claim, wherein the slave unit comprises a mandrel, a 12 slave module, and an electrical return path. 13 14

15. A telemetry system according to claim 14, 15 wherein the mandrel facilitates attachment of the 16 slave unit to the pipeline or tubing string. 17 18

16. A telemetry system according to claim 14 or claim 19 15, wherein the mandrel facilitates transmission of 20 the electrical power and data transmissions from the 21 pipeline or tubing string to the electronics of the 22 slave unit. 23 24

17. A telemetry system according to any one of 25 claims 14 to 16, wherein the slave module houses the 26 electronics of the slave unit. 27 28

18. A telemetry system according to any one of 29 claims 14 to 17, wherein the electrical return path 30 comprises a spring contact for engaging an earth 31 point.

66 1 2

19. A telemetry system according to claim 18, 3 wherein the earth point is a local earth, a further 4 tubular such as a second pipeline, a subsea or surface casing, or a casing of a downhole well.

6 7

20. A telemetry system according to any preceding 8 claim, wherein pulse-width modulation is used to 9 facilitate data transmission from the master unit to the slave unit.

11 12

21. A telemetry system according to claim 20, 13 wherein the power transmission is modulated with the 14 data transmission using pulse-width modulation.

is 16

22. A telemetry system according to any preceding 17 claim, wherein frequency-shift keying (FSK) is used 18 to facilitate data transmission from the slave unit 19 to the master unit.

21

23. A telemetry system according to claim 22, 22 wherein the FSK frequencies are superimposed on a 23 carrier frequency.

24

24. A telemetry system according to claim 23, 26 wherein the carrier frequency is the same frequency 27 as the power transmission frequency.

28 29

25. A telemetry system according to any one of claims 22 to 24, wherein the data transmission is 67 1 synchronised to the "high" cycle of the power 2 transmission.

3 4

26. A telemetry system according to any one of claims 22 to 25, wherein the data transmission is 6 synchronised to the "low" cycle of the power 7 transmission.

8 9

27. A telemetry system according to any one of claims 22 to 26, wherein the data transmission is 11 synchronised to both the high and the low cycles of 12 the power transmission.

13 14

28. A telemetry system according to any preceding claim, wherein more than one slave unit is used.

16 17

29. A telemetry system according to claim 28, 18 wherein the data transmission from the master unit to 19 the slave unit includes an address of the slave unit.

21

30. A telemetry system according to claim 29, 22 wherein the data transmissions include data error 23 detection and/or correction.

24

31. A telemetry system according to claim 30, 26 wherein the data error detection and/or correction 27 comprises a Hamming code.

28 29

32. A telemetry system according to any preceding claim, wherein the master unit comprises a processor 31 to control the operation of the master unit; a power 68 1 waveform generator; and signal recovery and 2 conditioning circuitry. 3 4

33. A telemetry system according to claim 32, 5 wherein the processor applies pulse-width modulation 6 to the power transmission when data transmission is 7 required from the master unit to the slave unit. 8 9

34. A telemetry system according to claim 32 or 10 claim 33, wherein when not transmitting data, the 11 processor defaults the power transmission to a 50% 12 duty cycle. 13 14

35. A telemetry system according to any one of 15 claims 32 to 34, wherein the signal recovery and 16 conditioning circuitry allows data transmitted by the 17 at least one slave unit to be extracted and recovered 18 from the transmission system. 19 20

36. A telemetry system according to any preceding 21 claim, wherein the slave unit comprises a processor 22 to control the operation of the slave unit; 23 rectifying and regulating circuitry in a first 24 channel; recovery and conditioning circuitry in a 25 second channel; and frequency generating and mixing 26 means. 27 28

37. A telemetry system according to claim 36, 29 wherein the frequency mixing and generating means 30 typically comprises a frequency-shift keying (FSK) 31 generator; an FSK mixer; and a line driver.

69 2

38. A method of transmitting power and data from a 3 master unit to at least one slave unit remote from 4 the master unit, the master and slave units communicating via a transmission system, the 6 transmission system including an at least partially 7 isolated pipeline or tubing string, the method 8 comprising the steps of 9 generating a power transmission at the master unit; 11 generating a data transmission and synchronising 12 the data transmission with the power 13 transmission at the master unit; 14 transmitting the power and data transmissions via the transmission system to the slave unit; 16 and 17 recovering the power and data transmissions at 18 the slave unit.

19

39. A method of transmitting data to a master unit 21 from at least one slave unit remote from the master 22 unit, the master and slave units communicating via a 23 transmission system, the transmission system 24 including an at least partially isolated tubing string or pipeline, the method comprising the steps 26 of 27 generating a power transmission at the master 28 unit and transmitting the power transmission to 29 the slave unit; recovering the power transmission at the slave 31 unit; 1 generating a data transmission at the slave unit 2 and synchronising the data transmission with the 3 power transmission; 4 transmitting the data transmission via the transmission system to the master unit; and 6 recovering the data transmission at the master 7 unit.

8 9

40. A method according to either claim 38 or claim 39, wherein the method includes the further steps of 11 dividing the data transmission into a series of 12 sub-windows; 13 transmitting a specified data transmission from 14 the slave unit to the master unit; receiving the specified data transmission at the 16 master unit; 17 determining which of the sub-windows reliably 18 transmitted the specified data transmission.

19

41. A method according to claim 40, wherein the sub 21 windows that did not reliably transmit data are 22 filtered out or ignored for subsequent transmissions.

23 24

42. A method of receiving and converting power and data transmissions sent from a master unit to at 26 least one slave unit remote from the master unit, the 27 master and slave units communicating via a 28 transmission system, the transmission system 29 including an at least partially isolated pipeline or tubing string, the method comprising the steps of 71 1 receiving a power transmission at the slave 2 unit; 3 dividing the power transmission into two 4 channels; rectifying and regulating the power transmission 6 in a first channel; and 7 recovering the data transmission in a second 8 channel.

9

43. A method of receiving data transmitted by a 11 master unit from at least one slave unit remote from 12 the master unit, the master and slave units 13 communicating via a transmission system, the 14 transmission system including an at least partially isolated pipeline or tubing string, the method 16 comprising the steps of 17 receiving the data transmission at the master 18 unit; 19 filtering and conditioning the data transmission; and 21 regenerating the transmitted data.

22 23

44. A method according to either claim 42 or claim 24 43, wherein the method includes the further steps of dividing the data transmission into a series of 26 sub-windows; 27 transmitting a specified data transmission from 28 the slave unit to the master unit; 29 receiving the specified data transmission at the master unit; 72 1 determining which of the sub-windows reliably 2 transmitted the specified data transmission. 3 4

45. A method according to claim 44, wherein the sub5 windows that did not reliably transmit data are 6 ignored or filtered out for subsequent transmissions. 7 8

46. A method according to any one of claims 38 to 9 45, wherein pulse-width modulation is used to 10 facilitate data transmission from the master unit to 11 the slave unit or vice versa. 12 13

47. A method according to claim 46, wherein the 14 power transmission is modulated with the data 15 transmission using pulse-width modulation. 16 17

48. A method according to any one of claims 38 to 18 47, wherein frequency-shift keying (FSK) is used to 19 facilitate data transmission from the slave unit to 20 the master unit or vice versa. 21 22

49. A method according to claim 48, wherein the FSK 23 frequencies are superimposed on a carrier frequency. 24 25

50. A method according to claim 49, wherein the 26 carrier frequency is the same frequency as the power 27 transmission frequency. 28 29

51. A method according to any one of claims 38 to 30 50, wherein the data transmission is synchronised to 31 the "high" cycle of the power transmission.

73 1 2

52. A method according to any one of claims 38 to 3 51, wherein the data transmission is synchronised to 4 the "low" cycle of the power transmission.

6

53. A method according to any one of claims 38 to 7 52, wherein the data transmission is synchronised to 8 both the low and high cycles of the power 9 transmission.

11

54. A method according to any one of claims 38 to 12 53, wherein the data transmissions include data error 13 detection and/or correction.

14

55. A method according to claim 54, wherein the data 16 error detection and/or correction comprises a Hamming 17 code, or other suitable technique.

18