Communications: electrical – Wellbore telemetering or control – Using a specific transmission medium
Reexamination Certificate
2000-07-14
2002-10-22
Horabik, Michael (Department: 2635)
Communications: electrical
Wellbore telemetering or control
Using a specific transmission medium
C367S082000, C175S040000
Reexamination Certificate
active
06469635
ABSTRACT:
The present invention relates to the transmission of data in the context of pipeline systems, for example, surface, sub-sea or downhole pipelines.
U.S. Pat. No. 5,130,706 discloses an apparatus for transmitting data from a downhole location in a borehole to the surface. A downhole power source is used to apply a signal to an earth-drillstring system at the downhole location. Data is transmitted from the downhole location along the drillstring and is received at the surface.
Systems in which the power requirement for the transmission of data is met from the data transmission location have disadvantages. A large amount of power can be required for transmitting data over the distances typically associated with pipeline systems. Local power supplies, for example batteries, have disadvantages. These disadvantages are more pronounced at inaccessible locations and in particular at downhole locations. The batteries may be ‘one-shot’ batteries or rechargeable batteries. These have limited life and replacing or recharging can be slow, expensive and wasteful of energy. Further the temperature in the downhole environment can be high and this can reduce life further, cause high self discharge and can cause electrolyte boiling problems.
U.S. Pat. No. 4,322,728 discloses the idea of using a surface based power source to extract data from a downhole location. A current pulse is sent along a wireline to a downhole transducer assembly where the resistance of each transducer is indicative of a quantity to be measured. The resistance level can be detected at the wellhead by monitoring the voltage produced by the current pulse and hence the quantity of interest can be determined. However, the system of U.S. Pat. No. 4,322,728 makes use of a wireline along which the current pulse travels. The use of separate wirelines has disadvantages in terms of expense and susceptibility to damage both during and after installation.
It is an object of the present invention to provide a data transmission system which alleviates at least some of the problems of the prior art.
According to a first aspect of the present invention there is provided a data transmission system for use with a pipeline system having at least one electrically conductive pipe arranged for carrying a fluid comprising,
reference signal generating means for applying a reference signal to a signal circuit,
effective impedance varying means for varying the effective impedance of the signal circuit in dependence on data to be transmitted, and
monitoring means for monitoring changes in the reference signal caused by varying the effective impedance of the signal circuit to thereby extract data, wherein the reference signal generating means is arranged for applying a signal to a pipe in the pipeline system whereby, in use, the signal circuit comprises said pipe.
According to a second aspect of the present invention there is provided a method of data transmission for use with a pipeline system having at least one electrically conductive pipe arranged for carrying a fluid comprising the steps of,
generating and applying a reference signal to a signal circuit,
varying the effective impedance of the signal circuit in dependence on data to be transmitted, and
monitoring changes in the reference signal caused by varying the effective impedance of the signal circuit to thereby extract data, including the steps of using a pipe in the pipeline system as part of the signal circuit and applying the reference signal to said pipe.
This arrangement has the advantage that the high power supply requirement for data transmission can be removed from the location from which data is to be transmitted whilst a separate cable or wireline is not required.
The reference signal generating means and the varying means may be disposed at distinct locations. Typically the power requirements of the reference signal generating means will be high whereas the power requirements of the varying means will be relatively low and so can be more easily met from a battery. The monitoring means and varying means are typically disposed at distinct locations.
The data transmission system may comprise the signal circuit. The signal circuit can comprise a signal channel along which data is transmitted and a return conduction path. The signal channel can comprise the conductive pipe to which the reference signal generating means is connected. The signal circuit can comprise a return conduction path via earth.
In use, one terminal of the reference signal generating means can be connected to the conductive pipe and the other to earth via an earth connection point. Preferably the reference signal generating means comprises a constant current source. This has the advantage that the monitoring means can be decoupled from any imperfections in the earth connection point used to complete the signal circuit.
The monitoring means may be arranged to monitor changes in the potential difference, due to the reference signal, between a terminal of the current source and earth. The monitoring means may be connected across the terminals of the current source. In this case the earth connection used for monitoring changes in potential difference is the same as that used to complete the signal circuit through earth. This has disadvantages because the earth connection point will not be true earth and its potential difference relative to earth will vary as the effective impedance of the signal circuit is varied.
Preferably a separate reference earthing point is provided and the monitoring means is arranged to monitor the potential difference between an output of the current source and the reference earthing point. This has advantages because the signal detected by the monitoring means is not then effected by the changing potential at the earth connection point and consequently noise is reduced. The reference earthing point can be a remote earth.
The monitoring means may comprise a voltage measuring means. One terminal of the voltage measuring means may be connected to the terminal of the current source connected to the conductive pipe and the other terminal of the voltage measuring means may be connected to the reference earthing point.
The current source can be arranged to generate a constant dc current signal.
The signal channel may comprise an isolation joint which electrically isolates adjacent sections of the signal circuit from one another. The isolation joint may be provided in the conductive pipe to electrically isolate one section of the pipe from an adjacent section.
The transmission means may be arranged for use in a well having downhole structure. The pipe to which the reference signal generating means is connected in use can comprise the downhole structure. The advantages of the system are particularly useful in downhole situations because the large power requirement for transmitting data from downhole to the surface can be met from the surface. This is done by locating the reference signal generating at the wellhead and the impedance varying means downhole.
Preferably the downhole structure is treated as a single conducting channel. The downhole structure can comprise a production string and a casing. Preferably the production string and the casing are electrically connected to form the single conducting channel.
It has been found that a system which uses the production string as a signal line and the casing as the return is unsatisfactory in circumstances where the space between the production string and the casing is filled with a high density brine solution for pressure equalisation purposes. The brine solution has a relatively high electrical conductivity. This means that a system relying on the production string and casing to form a circuit is susceptible to extremely high losses due to the conduction path directly from the production string to the casing through the brine solution. Using the downhole structure as a single conducting channel avoids the problems which arise due to the conduction path between the production string and casing which exists when the intervening space is filled with a
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Flight Refuelling Ltd.
Horabik Michael
Wong Albert K.
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