Data communications system

A three phase power system provided with a data communications system and associated method of data transmission for transmitting data over a three phase power system between a surface and a sub-surface location for an arrangement such as an oil field electrical submersible pump, the data communications system comprising a cabled connection from a surface system to a sub-surface system; a power module coupled to the cabled connection via a tuned circuit tuned to a first frequency, a data signal module coupled to the cabled connection via a tuned circuit tuned to a second frequency, independently of the coupled power module so as to minimize interference between the power signal module and data signal module during operation.

BACKGROUND OF THE INVENTION

The present invention relates to data transmission to and from down hole equipment and in particular, though not exclusively, to an improved data communication system and a method of data transmission through a three phase power system between the subsurface and a surface location.

“Down hole equipment” is understood to refer to any tool, equipment or instrument that is used in a wellbore.

Data needs to be transmitted between down-hole equipment and the surface for various reasons. For example, monitoring performance of motors/pumps; transmission of control signals for control of valves; measuring device orientation and position, and making physical measurements.

For motorised down hole equipment, such as an Electric Submersible Pump (ESP) motor system, data needs to be sent from below the equipment in a circuit that includes motor windings and the equipment's power cable which can be considered as a three phase power system. In such arrangements, as power cables are already present, there is the rationale that the cost of the solution of using these should be proportionately less than a solution where an appropriate length of communication cables is also supplied. It is also generally accepted that being able to maintain power on the down hole monitoring instrumentation when the main 3-phase power system is not powered up is needed, as this provides essential information in the event of pump shut downs or other major events in the well.

Thus these systems are challenging to design and operate to ensure data is successfully transmitted and an independent power supply is maintained at all times.

Due to the motor and power cable properties of a three phase power system, DC current based devices which are coupled to the power system using inductive couplings have been developed and are extensively used. Power is provided from a low current DC power supply at surface and data is transmitted to surface by modulating the current drawn from this supply.

Examples of digital and processor based devices are disclosed in U.S. Pat. No. 5,515,038; GB2283889 and U.S. Pat. No. 6,396,415. These systems utilise DC current injected onto the power signal and extracted through inductive Y-point couplings. These systems are all susceptible to failure when insulation on the power cable is lost or damaged, as any fault is in parallel with the independent power source, and the fault becomes another current modulation source thus causing signal integrity to be lost. These prior art systems are also typically either analogue in nature, thus introducing noise into the measurements or, where digital data is transmitted, it is at a very slow data rate.

AC based systems which make use of AC power and/or signal transmission have been developed to overcome these problems. However, these AC based systems introduce disadvantages of their own. A typical prior art AC based system is disclosed in U.S. Pat. No. 7,982,633 being a data communication system for use in downhole applications wherein electrical energy is supplied over a multiple-conductor power cable to an ESP motor assembly. A downhole unit is AC-coupled to the conductors of the power cable through the wye point of the ESP motor assembly. A surface unit is AC-coupled to the conductors of the power cable. Uplink communication of telemetry data occurs over an AC communication scheme supported by the downhole unit and the surface unit. Downlink communication of remote control command data occurs over a different AC communication scheme supported by the surface unit and the downhole unit. These AC communication schemes provide an independent supply of power to the downhole environment. All communication between the surface and downhole environment is accomplished through the power cable without the use of additional communication lines. Data communication is maintained in the event of a ground fault on the power cable.

This prior art AC based system has an interface circuit including an AC coupling capacitor between the wye point of the ESP motor and components of the down hole unit to provide for DC signal isolation. Likewise at the surface, an AC coupling capacitor is electrically coupled to a different one of each of the three conductors on the three-phase power cable for DC signal isolation. Disadvantageously, this arrangement means that the motor's power system is sensed using the same capacitors used to inject the AC power. This causes the signal amplitude to be reduced and thus, as the power supply system can cause distortion and attenuation of the transmitted and received data, the data becomes corrupted which results in data not being recoverable.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a method of data transmission for transmitting data over a three phase power system wherein the effect of the power system on the data signal integrity can be minimised.

According to a first aspect of the invention there is provided a data communications system for transmitting data over a three phase power system between a surface and a sub-surface location, said data communications system comprising a surface system module, a sub-surface system module, and a cable connection provided between the surface system module and the sub-surface system module wherein at least one of the surface system module and subsurface system module is provided with an AC power module and a data signal module such that the AC power module and the data signal module are coupled to the cabled connection independently of one another via tuned circuits which are tuned to different frequencies at at least one of the surface and sub-surface.

A data communications system having a sub-surface system with a power module and data signal module coupled independently of one another to the cabled connection means that the power coupling and the signal coupling can be optimised for the power signal and data signals applied so that the applied signals do not interfere with one another, or the host 3-phase power system. By providing an AC power supply and an AC data signal, the frequency of these inputs can be selected or tuned to ensure that interference between the inputs is minimised. The provision of a tuned circuit in the power module and in the data signal module also means that each independent coupling can be tuned to the exact frequency for the power and data signals respectively thus ensuring the two do not interfere with one another. In addition, the impedance of the power module and data signal module are relatively high at the data or carrier frequency of the system thus ensuring that signal and power attenuation and distortion is minimised.

In an embodiment, the tuned circuits are capacitive coupled. This is in contrast to inductive coupling which would restrict the bandwidth of any transmitted data or power frequencies, and would not inherently prevent the AC power interfering with the data signal and visa-versa. By using both capacitive and tuned couplings, for both the AC power and data signal to and from the sub-surface, the power and data frequencies can both be relatively high frequencies relative to the 3 phase host frequency but can also be made to be sufficiently different from each other that the coupling tuning prevents mutual interference and in particular the power frequency from interfering with the transmitted data.

In an embodiment, the power module and the data signal module are coupled to a common Y-point at the sub-surface location. This simplifies construction. In an embodiment, the power module and the data signal module are also coupled to a common point at the surface location. In this way parallel tuned coupling are provided at the common points.

The system may further comprise each of the surface system module and sub-surface system module being provided with a power module and a data signal module.

By providing each of the surface and sub-surface system modules with a power module and a data signal module the power coupling and signal coupling both at the surface and at the subsurface locations can be optimised for the power signal and the data signals applied so that the applied signals do not interfere with one another or the host three phase system.

In an embodiment, the system includes a motor at the sub-surface location. In an embodiment, the motor is an electrical submersible pump motor. In an embodiment, the common Y-point is at the motor. In this way standard industry fittings can be used.

In an embodiment, the system includes a down hole gauge at the subsurface location, wherein the three phase power supply is used to power the motor and the power and data signal modules are used for the down hole gauge. In this way, the frequency of the power module can be selected to be greater than the motor power frequency and also not at a harmonic of the motor power frequency. The frequency of the power module need not be too high because if you simply make the power module frequency very high so the filter separates the motor power frequency from the power module frequency you will end up with a power module frequency that is so high the losses in the cable and motor will be too great to actually allow power to be delivered to the down hole gauge. The only way to make this scheme work is to use a frequency selected so it is higher than the power frequency but not so high the power won't get to the gauge (or require excessive surface voltage, and power) and to overcome the still significant power from the motor using a tuned selective power coupling.

According to a second aspect of the invention there is provided a method of data transmission for transmitting data over a three phase power system between a surface and a sub-surface location, the method comprising providing a cabled connection between a surface system and a sub-surface system; providing at least one AC power module coupled to the cabled connection via a first tuned circuit being tuned to a first frequency; and providing at least one data signal module coupled to the cabled connection independently of the power module, via a second tuned circuit being tuned to a second frequency distinct from the first frequency.

The method may further comprise providing a power module and a data signal module at each of a surface system and the sub-surface system.

By providing a power module and data signal module coupled independently of one another to the cabled connection at one or both of the surface and sub-surface locations the power coupling and the signal coupling can be optimised for the power signal and data signals applied so that they do not interfere with one another. The power coupling and data signal coupling can also be designed to minimise the effect of the host three-phase power system on the independent power transmission and the data transmission. By providing an AC power supply and an AC data signal, the frequency of these inputs can be selected and tuned to ensure that interference between the inputs is minimised.

In an embodiment, the method further comprises providing an AC data signal to the data signal module. By providing an AC power supply and an AC data signal, the frequency of these inputs can be selected and tuned to ensure that interference between the inputs is minimised.

In an embodiment, the AC data signals are transmitted in the frequency range of 10 kHz to 300 kHz, and the AC power frequencies are transmitted in the frequency range of 500 Hz to 10 Khz.

In an embodiment, the method comprises capacitively coupling the AC power module to the cabled connection. In an embodiment, the method comprises capacitively coupling the data signal module to the cabled connection. In an embodiment, the method comprises coupling the AC power module and the data signal module through a common point on the cabled connection.

DETAILED DESCRIPTION

One category of down hole equipment is artificial lift systems, for use in wells where there is insufficient pressure in the reservoir to lift the well's fluid (e.g. oil, water or gas) to the surface. Types of artificial lift systems include hydraulic pumps, Rod pumps, Electric Submersible Pumps (ESPs), Jet Pumps, Progressing-Cavity pumps (PCPs) and gas lift.

Reference is initially made toFIG. 1of the drawings which illustrates a typical ESP completion in a wellbore. An ESP motor10is coupled through a seal12to a centrifugal pump14and used to lift the fluids through a tubing16to a surface18of the well20in a manner known to those skilled in the art. In order to monitor the operation, sensors or gauges22are located below the ESP10. Typically, the motor10is a three phase Y configuration. The motor is driven by a variable speed drive system24and is connected via a three phase power cable26. The system can be considered to comprise two distinct parts, a surface system, generally indicated by reference numeral28, and a down hole system, generally indicated by reference numeral30. These two parts28,30communicate using the ESP power cable26.

Surface equipment relating to the gauge system is shown inFIG. 1where there is a HV unit13connected directly to the 3 phase power supply to the down hole motor and there is a further LV or low voltage unit8which is safely isolated from the high voltage system. The LV system is primarily for data recovery and processing and data display etc. The HV unit is used to inject AC power and also make recovery of raw data from the 3-phase power system.

Referring now toFIG. 2of the drawings there is illustrated a functional block diagram of a data transmission system, generally indicated by reference numeral40, according to an embodiment of the present invention. In this arrangement data can be transmitted onto the three phase power cable26in either direction between the surface equipment28and subsurface or down hole equipment30.

At surface28the equipment is divided into a high voltage side32and a low voltage side34. The high voltage side32provides the power to the down hole system30. Tuned high-voltage AC coupling36ais used to connect to each of the phases in the power cable26. Thus a tripling of circuitry is used in the high-voltage equipment32. A microprocessor38controls the power distribution on to the three-phase cable26and is linked to a corresponding microprocessor40on the low voltage side34. Additionally the high-voltage side32uses tuned high-voltage AC coupling36c, in parallel to pick off the data signals on the three-phase cable26. These signals are then filtered42and de-modulated44by known methods. Data signals then pass via the microprocessor40for display46or transport to a data logger or SCADA system. Additionally, the process can work in reverse where microprocessor40provides data on to the power lines26via the tuned high-voltage AC coupling36on the high-voltage side32as is known in the art.

Down hole an ESP system48is provided as described herein with reference toFIG. 1. Like parts have the same reference numerals to aid clarity. Below the motor10is a standard Y-point connector50. At the Y-point connector50is arranged a down hole system52. The down hole system52provides monitoring in the form of measurement devices sensors or gauges54, hooked up via a microprocessor56. Power to drive the gauges54is provided via tuned HV AC coupling circuits36bto a power regulator58. Similarly, data from the measurement devices54is processed in the microprocessor56. Using a signal driver60and tuned HV AC coupling circuits36d, the data is transmitted on to the power line62for transmission to the Y-point50and onward transmission up the three-phase power cable26to the surface units28.

In the present invention, there are four tuned HV AC coupling circuits36a-d, three arranged at surface28and one sub-surface52. In the prior art only a single tuned HV AC coupling circuit is provided at the surface and sub-surface with each coupling to the power and data. An illustration of this prior art coupling arrangement is shown inFIG. 3.

InFIG. 3, a surface system84and a sub-surface system88with a cabled connection85therebetween to provide a three-phase power supply to a down hole location. An independent power supply80is provided at surface for down hole instrumentation along with a data signal recovery unit79. The power supply80and the data signal recovery unit79are both coupled to the cable85through the same coupling capacitor83. Likewise the sub-surface system88is coupled to the cable85through a single coupling circuit as a capacitor86. In this prior art system, sub surface power system89bleeds power from the signal driver87. In addition, the coupling86does not selectively couple the data, power or host 3-phase power frequency and so the power system can be subject to large variations in power from the host system. Furthermore, more load is placed upon the signal driver87by the power regulator89and the host system85, thus creating a requirement for much higher power levels in the transmitter. This requirement adds a larger power transmission requirement to the system than would otherwise be needed thus, further aggravating the problem. This same situation arises at surface84where the signal recovery circuit79is fed power directly from the independent power supply80and the host 3-phase power system85, and so data recovery is made more difficult. In addition, the amplitude of the recovered data signal sent from sub surface88is attenuated by the independent power supply80and the host 3-phase power system85which are both low impedance at the signal frequency.

Reference is now made toFIG. 4of the drawings which illustrates a sub-surface system, generally indicated by reference numeral90, wherein the high voltage supply cable62is coupled to a power module92within which is provided a first tuned circuit92a and which is also independently coupled to data signal module94within which is provided with second tuned circuit94a, according to an embodiment of the present invention. Power module92is then connected to power supply unit96from which is output a regulated power supply96a. Data signal module94is then connected to data source module98. It will be appreciated that first tuned circuit92aand second tuned circuit94amay be passive tuned circuits. In an embodiment the circuits92a,94aare capacitively tuned circuits.

In use, when the data communication channel is operational, that is to say data may be transmitted through cable62, an AC voltage is applied to said cable62and an AC data signal is created by data source module98. The first tuned circuit92ais tuned to a first frequency corresponding to the power signal frequency. At the same time, the second tuned circuit94ais tuned to a second frequency corresponding to the data signal frequency such that the first and second frequencies can be selected so as to minimise interference between the power signal and data signal meaning that transmission of data from data source98over high voltage system cable62can be achieved with minimal distortion of the transmitted and/or the received data being caused by the power module92.

The AC data signals are typically in the frequency range of 10 kHz to 300 kHz, and independent power frequencies would typically be in the frequency range of 500 Hz to 10 Khz and by having each of the power module and data signal module coupled to cable62independently of one another, the frequencies of each can be tuned to optimise the system performance. Such tuning of the first and second tuned circuits92a,94arespectively can be performed by selecting either passive or active circuits, with resonant frequencies matching the applied power or data frequencies. The tuned circuits will provide low impedance low loss couplings at the desired frequency and also provide high impedance (and low attenuation) at both the other of the two frequencies and also the host 3-phase power system operating frequency. This can result in a high quality of received data signal component at the surface location of the data communications system. This also reduces the losses in the independent power system to the host 3-phase power system and the data couplings. In addition, such an arrangement further results in the minimisation of interference between the data signal component and power signal components.

With reference toFIG. 5there is illustrated a surface and subsurface arrangement of the system40, according to an embodiment of the present invention. Simple tuned couplings158,159,165and169, in this case, include capacitors154,155,163,167respectively and inductors156,157,164and168respectively, in series with one another, with the impedance of the tuned couplings158,159,165and169given by Z=+jwL+1/jwC with resonance at f=1/(2n√(LC)).

By choosing matching couplings158(at the power injection point at surface) and165(in the sub surface where power is extracted), the power sub-surface166is primarily extracted from the power supply150at the frequency of the power supply150that was applied to the system40and not from the host 3-phase power system frequency. In addition, the sub-surface power166does not bleed power from the signal driver170in the sub-surface unit171.

Similarly, using matched couplings for data transmission units159and169this ensures that the data recovery circuit152at surface unit151does not receive the relatively high amplitude frequency signals from the host 3-phase power system and the independent power system150, but, in an embodiment, the signal from the matched signal source170and sub-surface coupling169.

Such a system40can be extremely effective where the three frequencies, namely the data, power and three phase system frequencies, are well separated, for instance where the three phase host system is running at 50-60 Hz the independent power system is running at 500 to 10 kHz and the data frequency is running at 10 kHz to 300 kHz.

The principle advantage of the present invention is that it provides a method of data transmission over a three phase power system where the interference between the power signal, data signal and host 3-phase power system is minimised.

A further advantage of the present invention is that it provides a method of data transmission over a three phase power system where the distortion of the transmitted and/or received data signal is minimised.

A yet further advantage of the present invention is that it provides a data communications system for communicating data over a three phase power system wherein the data signal and power signal couplings are completely independent from one another.

Various modifications may be made to the invention herein described without departing from the scope thereof. For example, the system could have two frequencies of transmission with multiple tuned couplings, one per frequency. The tuned coupling may have a processor controlled central frequency. The couplings could consist of both a passive tuned circuit and an active or digital tuned filter.