CA1205376A - Apparatus for, and a method of, signalling within a borehole while drilling - Google Patents
Apparatus for, and a method of, signalling within a borehole while drillingInfo
- Publication number
- CA1205376A CA1205376A CA000376546A CA376546A CA1205376A CA 1205376 A CA1205376 A CA 1205376A CA 000376546 A CA000376546 A CA 000376546A CA 376546 A CA376546 A CA 376546A CA 1205376 A CA1205376 A CA 1205376A
- Authority
- CA
- Canada
- Prior art keywords
- signal
- transformer
- drill string
- transmitting
- winding
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 238000005553 drilling Methods 0.000 title claims abstract description 14
- 238000000034 method Methods 0.000 title claims abstract description 11
- 230000011664 signaling Effects 0.000 title claims abstract description 10
- 238000005259 measurement Methods 0.000 claims abstract description 13
- 230000015572 biosynthetic process Effects 0.000 claims abstract description 9
- 238000005755 formation reaction Methods 0.000 claims abstract description 9
- 239000012212 insulator Substances 0.000 claims abstract description 5
- 238000004804 winding Methods 0.000 claims description 28
- 239000000615 nonconductor Substances 0.000 claims description 2
- 230000008569 process Effects 0.000 claims description 2
- 238000010276 construction Methods 0.000 abstract description 2
- 239000011162 core material Substances 0.000 description 18
- 230000005540 biological transmission Effects 0.000 description 3
- 230000008878 coupling Effects 0.000 description 2
- 238000010168 coupling process Methods 0.000 description 2
- 238000005859 coupling reaction Methods 0.000 description 2
- 230000004907 flux Effects 0.000 description 2
- 241000033695 Sige Species 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- XWHPIFXRKKHEKR-UHFFFAOYSA-N iron silicon Chemical compound [Si].[Fe] XWHPIFXRKKHEKR-UHFFFAOYSA-N 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- VOVZXURTCKPRDQ-CQSZACIVSA-N n-[4-[chloro(difluoro)methoxy]phenyl]-6-[(3r)-3-hydroxypyrrolidin-1-yl]-5-(1h-pyrazol-5-yl)pyridine-3-carboxamide Chemical compound C1[C@H](O)CCN1C1=NC=C(C(=O)NC=2C=CC(OC(F)(F)Cl)=CC=2)C=C1C1=CC=NN1 VOVZXURTCKPRDQ-CQSZACIVSA-N 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 239000000523 sample Substances 0.000 description 1
Classifications
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B17/00—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
- E21B17/02—Couplings; joints
- E21B17/028—Electrical or electro-magnetic connections
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B17/00—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
- E21B17/02—Couplings; joints
- E21B17/028—Electrical or electro-magnetic connections
- E21B17/0285—Electrical or electro-magnetic connections characterised by electrically insulating elements
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B47/00—Survey of boreholes or wells
- E21B47/12—Means for transmitting measuring-signals or control signals from the well to the surface, or from the surface to the well, e.g. for logging while drilling
- E21B47/13—Means for transmitting measuring-signals or control signals from the well to the surface, or from the surface to the well, e.g. for logging while drilling by electromagnetic energy, e.g. radio frequency
Landscapes
- Engineering & Computer Science (AREA)
- Mining & Mineral Resources (AREA)
- Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Physics & Mathematics (AREA)
- Geochemistry & Mineralogy (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Environmental & Geological Engineering (AREA)
- Fluid Mechanics (AREA)
- Mechanical Engineering (AREA)
- Remote Sensing (AREA)
- Geophysics (AREA)
- Electromagnetism (AREA)
- Geophysics And Detection Of Objects (AREA)
- Arrangements For Transmission Of Measured Signals (AREA)
- Earth Drilling (AREA)
- Drilling And Exploitation, And Mining Machines And Methods (AREA)
- Farming Of Fish And Shellfish (AREA)
Abstract
"Apparatus for, and a Method of, Signalling within a Borehole while Drilling"
ABSTRACT OF THE DISCLOSURE
A telemetry sub for a drill string comprises upper and lower portions electrically insulated from one another by an insulator. The sub incorporates a transformer having its secondary connected between the upper portion and the lower portion. In operation a measurement data signal in the form of pulses is supplied to the primary of the transformer by suitable electronic circuitry and a pulsating current signal is thereby induced in the secondary. This pulsating signal is passed along the drill string towards the surface, a return path for the signal being provided by the earth formations through which the borehole is drilled. The signal is passed to a receiving station on the surface either directly or by way of one or more repeater subs of the same general construction as the aforementioned sub. Such a system is capable of transmitting signals at a high rate and with an acceptable signal-to-noise ratio. Furthermore the subs are relatively inexpensive to produce so that a large number of repeater subs may be distributed along the drill string if desired.
ABSTRACT OF THE DISCLOSURE
A telemetry sub for a drill string comprises upper and lower portions electrically insulated from one another by an insulator. The sub incorporates a transformer having its secondary connected between the upper portion and the lower portion. In operation a measurement data signal in the form of pulses is supplied to the primary of the transformer by suitable electronic circuitry and a pulsating current signal is thereby induced in the secondary. This pulsating signal is passed along the drill string towards the surface, a return path for the signal being provided by the earth formations through which the borehole is drilled. The signal is passed to a receiving station on the surface either directly or by way of one or more repeater subs of the same general construction as the aforementioned sub. Such a system is capable of transmitting signals at a high rate and with an acceptable signal-to-noise ratio. Furthermore the subs are relatively inexpensive to produce so that a large number of repeater subs may be distributed along the drill string if desired.
Description
` glL;lZ~5~'76 r "Apparatus forL_and a Metbod_of, Sige~ n~ within a Borehole ~ i G
This invention relates to apparatus for, and a method of, signalling within a borehole while drilling. I
The invention also concerns a telemetry sub for a drill -string.
S Various measurements-while-drilling (MWD) systems have been proposed for taking measurements within a borehole while drilling is in progress and for transmitting the measurement data to the surface.
Since time is not lost in stopping the drill and inserting a measurement probe into the borehole in such systems 9 MWD systems lead to a substàntial saving in drilling time and hence to a considerable reduction in the overall cost of the drilling operation. Those systems which have so far been sugges-ted are of four basic types, namely mud pressure pulse systems, electromagnetic systems, hard-wire systems and acoustic systems. A wide variety of electromagnetic (EM) systems have been proposed, all of which rely on the transmission of electromagnetic data signals through the earth and~or ~ ;
drill string. However, none of the EM systems so far proposed has been shown to give a reasonable signal-to-noise ratio for the signals detected at the surface 9 and accordingly the data transmission rate is severely limited.
An EM system is proposed in U.S. Specification No. 2,354,887 (D. Silverman et al) in which the measurement data signals are supplied in the form of pulses to a toroidal coil surrounding the drill string in the vicinity of the drill bit. A varying magnetic field is associated with the pulsating current in the coil and this field induces signals in the form of pulsating currents in the drill string. The return circuits for the currents which flow in -the drill string as a result o~ this action are through the earth itself.
Tne transmitted signals are detected at the surface by means of a receiving station connected between the drill string and a grounded electrode at a distance from the drill string. However, due to attenuation of the signals in the earth and the core losses in the coil, the signal-to-noise ratio of the detected signals is poor, and the system is therefore unsatisfactory in practice.
It is an object of the invention to provide signalling apparatus constituting an EM system which is t inexpensive and is capable of transmitting signals at a high ra-te and with an acceptable signal-to-noise ratio.
According to the invention the signalling apparatus incorporates transformer having one windin~ ¦
:~5376 electrically connected between a first portion of the drill string for drilling the borehole and a second portion of the drill string which is electrically insulated from the fIrst portion, and signal transmitting and/or receiving means electrically connected to the other winding of the transformer, the first portion providing a current path for signals travelling between the transformer and a signal receiving and/or transmitting station at a remote location along the drill string, and a return path being provided between the transformer .- and the signal receiving and/or transmitting station by way of the second portion and the earth formations through which the borehole is being drilled.
Preferably said one winding is the secondary winding of the transformer and said other winding is the primary winding of the transformer and transmitting means are electrically connected to the primary winding for transmitting signals to a remote receiving station.
With this system the size of the transformer and the number of turns of the primary and secondary windings of the transformer may be chosen so as to reduce.
core loss. Moreover the tr~nsformer, which is advantageously a toroidal transformer, may be made very small so that i.t is inexpensive to produce and may be accommodated within a small chamber in the wall bf the drill string. Since the core loss is small, the power requirement of the signal transmitting and/or receiving means is small, of the order of 1W, for example, and may _ 4 _ be supplied by a battery.
In a preferred embodiment of the invention, the first and second portlons are the upper and lower portions respectively of a special telemetry sub, the portions being separated by an electrical insulator, and the transformer is disposed within a chamber in the wall of the sub together with signal transmitting means comprising a battery and signal processing means.
Since the degree of attenuation of the transmitted signals is dependent on the distance over which the signals are transmitted and the electrical conductivity of the ear-th formations through which the borehole is being drilled, it may be advantageous to provide one or more repeater subs between the sub containing the measuring instrument and the surface.
Each repeater sub may contain identical signal transmitting, signal receiving and amplifying means, with the signal transmitting means being the same as that contained in the sub containing the measuring instrument. Since the subs are relativelv inexpensive to produce, a large number of repeater subs may be provided as necessary along the drill string.
The invention also provides a method of signalling within a borehole while drilling, utilising a drill string having first and second portions electrically insulated from one another, which method comprises passing signals between signal transmitting and/or receiving means and a signal receiving and/or transmitting station spaced apart along the drill string by way of a transformer having one winding electrically _-~L~05;3~76 connected between the first and second portions and the other winding electrically connected to the signal transmitting and/or receiving means, the first portion providing a current p~th for signals travelling between the transformer and the signal receiving and/or transmitting station, and a return path being provided between the transformer and the signal receiving and/or transmitting station by way of the second portion and the earth formations through which the borehole is being drilled.
The invention further provides a telemetry sub for a drill string, comprising first and second portions electrically insulated from one another, a transformer having one winding electrically co~nected between the first and second portions, and signal transmitting and/or receiving means electrically connected to the other winding of the transformer, the first portion providing a current path for signals travelling between the transformer and a signal receiving and/or transmitting station at a remote location along the drill string when the telemetry sub is disposed in a drill string, and a return path bei~g provided during drilling between the transformer and the signal receiving and/or transmitting station by way of the second portion and the earth formations through which a borehole is being drilled.
In order that the invention may be more fully understood, reference will now be made, by way of example9 to the accompanying drawing, in which:
Figure 1 is a diagram of part of a drill string incorporating a telemetry sub in accordance with the invention; and Figure 2 is a longitudinal section through a telemetry sub in accordance with the invention.
Referring to Figure 1, which is intended only to illustrate the principle of the invention and not to ; show the detailed construction of the telemetry sub, the 10 telemetry sub 1 is shown disposed between two drill string sections 2 and 3 within a borehole 10. The sub 1 is coupled to the section 2 by means of a male screwthreaded coupling 4 on the sub 1, and to the section 3 by means of a female screwthreaded coupling 5 on the sub 1. The section 2 is coupled to a rotary table (not shown) at the surface by way of.other sections and the section 3 is coupled to a drill bit (not shown) optionally by way of other sections.
The sub 1 comprises an upper portion 6 electrically connected to the section 2 and a lower portion 7 electrically connected to the section 3. The upper and lower portions 6 and 7 are electrically insulated from one another by an insulator 8. Within the side wall of the sub is a chamber 9 containing electronic circuitry 11 and a toroidal output transformer 12 ha~ing its secondary connected between the upper portion 6 and the lower portion 7. In operation ~ measurement data signal.
in the form of pulses is supplied to the primary of the 5~7~
transformer 12 by -the electronic circuitry 11, the measurement data being, for example, the data outputted by an instrument for measusuring the orientation of a bor~ho].e such as that described in U.K. Patent Specification No. 1,5099293. A pulsating current signal is thereby induced in the secondary of the transformer 12, and this signal is passed to the surface by way of the section 2 and the further sections of drill string between the section 2 and the surface.
A return path for the signal is provided through the earth formations through which the borehole 10 is drilled.
The telemetry sub shown in Figure 1 may be either a transmit-only sub for transmitting measurement data supplied to it by an adjacent measuring instrument or a repeater sub which receives a signal supplied to it along the drill string, processes this signal and transmits the processed signal. In the former case the electronic circuitry 11 will comprise a battery and a signal processing circuit for modulating the current supplied by the battery in accordance with the measurement data~
A repeater sub is shown in longitudinal section in Figure 2. Like parts are given the same reference numerals in this figure as in Figure 1. It will be noted that the annular insulator 8 extends between the chamber 9 and the inside wall of the sub in the vicinity of the chamber 9, and that the insulator is generally S-shaped in section so as to strengthen the joint between the upper and lower portions 6 and 7. The chamber 9 is closed off from the outside by a cover 13 which is sealed at its edges by means of a seal 14, and is electrically insulated in such a manner that it does not provide a current path between the upper l;
and lower portions 6 and 7. The chamber contains, in addition to the output transformer 12, an input transformer 15, an input amplifier 16, a signal processing circuit 18, and an output amplifier 17. The input and output transformers 15 and 12 could be replaced by a single transformer whose function is both to receive and transmit signals.
The repea-ter is arranged to receive and transmit signals in a multiplexed manner. Thus, in a first period of, for example, one second, an input signal transmitted by a transmit-only sub or by another repeater sub further down the drill string is detected by the input transformer 15 whose primary is coupled between the lower sections of the drill string and the earth return, and is amplified by the input amplifier 16. In a second period of, for example, 100 milliseconds, the signal is digitally processed by the circuit 18 so as to remove errors, and, in a third period of, for example, one second, the processed signal is amplified by the output amplifier 17 and transmitted by the output transformer 12 either to a receiver at the surface or to another repeater further up the drill string.
~2~1537~
Since the telem~ry subs are relatively inexpensive to produce and the bandwidth, and hence the data transmission rate capability, of a signal drops off as a function of the distance over which it is transmitted, repeater subs may be provided with a spacing as low as 1000 feet along the drill string if necessary. This then enables signals to be transmitted at a data rate of about 100 bits per second with a power input of about 1W per sub and a bandwidth of about ~00 Hz.
If, in the system proposed in U.S. Specification No. 2,354,887, the drill string and conductive return through the earth are considered as a single turn secondary winding of a toroidal transformer having the toroidal coil surrounding the dril~ string as its primary, the core losses in the system disclosed in that specification and the system illustrated in the accompanying drawing may be ~ompared.
If the area of cross-section of the toroidal core is AC and the maximum saturation flux density for the core material is BSAT~ then clearly max ~ BSAT-AC ........................................ (i) If the impedance of the secondary is ZS then the power injected into the secondary can be written as Ps = Vs2 / 2ZS ............. ,..... ,................... (ii) The maximum value of the emf induced in the secondary can be written as VS = Ns~ max.~ .............................. (iii) 9.2~053b7~
where NS is the number of turns on the secondary, max is~the maximum value of the magnetic flux through the toroidal core cross-section~ and ~ = 2.~ .f where f is the frequency of the primary drive.
From equations (i), (ii) and (iii) it follows that A ~ ................. (iv) NS.2-~ f BSAT
Typical values for Silicon Iron toroidal transformer core material may be taken as:-BmaX = 1.2 Tesla Core Loss at 200 Hz = 5.5 watts.kg 1 Core Density = 7 gm.cm 3 From previous calculations at 200 Hz, theimpedance ZS of the drill pipe and earth can be taken as 0.17 ohm.
Thus, for a toroid of average diameter 14 cm surrounding the drill string having a single turn secondary winding, these typical values indicate a minimum value for the cross-sectional area of the core of 3.9 cm2 and a resulting minimum core volume of 156 cm3, and the minimum mass of the core is calculated at 1.1 kg when the case~for PS = 1 watt is considered. Thus~ in order to deliver 1 watt to the secondary circuit at 200 Hz, the ~2~D537~i !
resulting core loss is about 6 watts. Furthermore such a core will be expensive to manufacture.
By contrast, if the toroidal transformer of the system illustrate~ in the drawing has 100 turns on its secondary, the minimum value for the cross-sectional area of the core is about 4 ~m and the core may therefore be extremely small so that the core loss is negligible.
This invention relates to apparatus for, and a method of, signalling within a borehole while drilling. I
The invention also concerns a telemetry sub for a drill -string.
S Various measurements-while-drilling (MWD) systems have been proposed for taking measurements within a borehole while drilling is in progress and for transmitting the measurement data to the surface.
Since time is not lost in stopping the drill and inserting a measurement probe into the borehole in such systems 9 MWD systems lead to a substàntial saving in drilling time and hence to a considerable reduction in the overall cost of the drilling operation. Those systems which have so far been sugges-ted are of four basic types, namely mud pressure pulse systems, electromagnetic systems, hard-wire systems and acoustic systems. A wide variety of electromagnetic (EM) systems have been proposed, all of which rely on the transmission of electromagnetic data signals through the earth and~or ~ ;
drill string. However, none of the EM systems so far proposed has been shown to give a reasonable signal-to-noise ratio for the signals detected at the surface 9 and accordingly the data transmission rate is severely limited.
An EM system is proposed in U.S. Specification No. 2,354,887 (D. Silverman et al) in which the measurement data signals are supplied in the form of pulses to a toroidal coil surrounding the drill string in the vicinity of the drill bit. A varying magnetic field is associated with the pulsating current in the coil and this field induces signals in the form of pulsating currents in the drill string. The return circuits for the currents which flow in -the drill string as a result o~ this action are through the earth itself.
Tne transmitted signals are detected at the surface by means of a receiving station connected between the drill string and a grounded electrode at a distance from the drill string. However, due to attenuation of the signals in the earth and the core losses in the coil, the signal-to-noise ratio of the detected signals is poor, and the system is therefore unsatisfactory in practice.
It is an object of the invention to provide signalling apparatus constituting an EM system which is t inexpensive and is capable of transmitting signals at a high ra-te and with an acceptable signal-to-noise ratio.
According to the invention the signalling apparatus incorporates transformer having one windin~ ¦
:~5376 electrically connected between a first portion of the drill string for drilling the borehole and a second portion of the drill string which is electrically insulated from the fIrst portion, and signal transmitting and/or receiving means electrically connected to the other winding of the transformer, the first portion providing a current path for signals travelling between the transformer and a signal receiving and/or transmitting station at a remote location along the drill string, and a return path being provided between the transformer .- and the signal receiving and/or transmitting station by way of the second portion and the earth formations through which the borehole is being drilled.
Preferably said one winding is the secondary winding of the transformer and said other winding is the primary winding of the transformer and transmitting means are electrically connected to the primary winding for transmitting signals to a remote receiving station.
With this system the size of the transformer and the number of turns of the primary and secondary windings of the transformer may be chosen so as to reduce.
core loss. Moreover the tr~nsformer, which is advantageously a toroidal transformer, may be made very small so that i.t is inexpensive to produce and may be accommodated within a small chamber in the wall bf the drill string. Since the core loss is small, the power requirement of the signal transmitting and/or receiving means is small, of the order of 1W, for example, and may _ 4 _ be supplied by a battery.
In a preferred embodiment of the invention, the first and second portlons are the upper and lower portions respectively of a special telemetry sub, the portions being separated by an electrical insulator, and the transformer is disposed within a chamber in the wall of the sub together with signal transmitting means comprising a battery and signal processing means.
Since the degree of attenuation of the transmitted signals is dependent on the distance over which the signals are transmitted and the electrical conductivity of the ear-th formations through which the borehole is being drilled, it may be advantageous to provide one or more repeater subs between the sub containing the measuring instrument and the surface.
Each repeater sub may contain identical signal transmitting, signal receiving and amplifying means, with the signal transmitting means being the same as that contained in the sub containing the measuring instrument. Since the subs are relativelv inexpensive to produce, a large number of repeater subs may be provided as necessary along the drill string.
The invention also provides a method of signalling within a borehole while drilling, utilising a drill string having first and second portions electrically insulated from one another, which method comprises passing signals between signal transmitting and/or receiving means and a signal receiving and/or transmitting station spaced apart along the drill string by way of a transformer having one winding electrically _-~L~05;3~76 connected between the first and second portions and the other winding electrically connected to the signal transmitting and/or receiving means, the first portion providing a current p~th for signals travelling between the transformer and the signal receiving and/or transmitting station, and a return path being provided between the transformer and the signal receiving and/or transmitting station by way of the second portion and the earth formations through which the borehole is being drilled.
The invention further provides a telemetry sub for a drill string, comprising first and second portions electrically insulated from one another, a transformer having one winding electrically co~nected between the first and second portions, and signal transmitting and/or receiving means electrically connected to the other winding of the transformer, the first portion providing a current path for signals travelling between the transformer and a signal receiving and/or transmitting station at a remote location along the drill string when the telemetry sub is disposed in a drill string, and a return path bei~g provided during drilling between the transformer and the signal receiving and/or transmitting station by way of the second portion and the earth formations through which a borehole is being drilled.
In order that the invention may be more fully understood, reference will now be made, by way of example9 to the accompanying drawing, in which:
Figure 1 is a diagram of part of a drill string incorporating a telemetry sub in accordance with the invention; and Figure 2 is a longitudinal section through a telemetry sub in accordance with the invention.
Referring to Figure 1, which is intended only to illustrate the principle of the invention and not to ; show the detailed construction of the telemetry sub, the 10 telemetry sub 1 is shown disposed between two drill string sections 2 and 3 within a borehole 10. The sub 1 is coupled to the section 2 by means of a male screwthreaded coupling 4 on the sub 1, and to the section 3 by means of a female screwthreaded coupling 5 on the sub 1. The section 2 is coupled to a rotary table (not shown) at the surface by way of.other sections and the section 3 is coupled to a drill bit (not shown) optionally by way of other sections.
The sub 1 comprises an upper portion 6 electrically connected to the section 2 and a lower portion 7 electrically connected to the section 3. The upper and lower portions 6 and 7 are electrically insulated from one another by an insulator 8. Within the side wall of the sub is a chamber 9 containing electronic circuitry 11 and a toroidal output transformer 12 ha~ing its secondary connected between the upper portion 6 and the lower portion 7. In operation ~ measurement data signal.
in the form of pulses is supplied to the primary of the 5~7~
transformer 12 by -the electronic circuitry 11, the measurement data being, for example, the data outputted by an instrument for measusuring the orientation of a bor~ho].e such as that described in U.K. Patent Specification No. 1,5099293. A pulsating current signal is thereby induced in the secondary of the transformer 12, and this signal is passed to the surface by way of the section 2 and the further sections of drill string between the section 2 and the surface.
A return path for the signal is provided through the earth formations through which the borehole 10 is drilled.
The telemetry sub shown in Figure 1 may be either a transmit-only sub for transmitting measurement data supplied to it by an adjacent measuring instrument or a repeater sub which receives a signal supplied to it along the drill string, processes this signal and transmits the processed signal. In the former case the electronic circuitry 11 will comprise a battery and a signal processing circuit for modulating the current supplied by the battery in accordance with the measurement data~
A repeater sub is shown in longitudinal section in Figure 2. Like parts are given the same reference numerals in this figure as in Figure 1. It will be noted that the annular insulator 8 extends between the chamber 9 and the inside wall of the sub in the vicinity of the chamber 9, and that the insulator is generally S-shaped in section so as to strengthen the joint between the upper and lower portions 6 and 7. The chamber 9 is closed off from the outside by a cover 13 which is sealed at its edges by means of a seal 14, and is electrically insulated in such a manner that it does not provide a current path between the upper l;
and lower portions 6 and 7. The chamber contains, in addition to the output transformer 12, an input transformer 15, an input amplifier 16, a signal processing circuit 18, and an output amplifier 17. The input and output transformers 15 and 12 could be replaced by a single transformer whose function is both to receive and transmit signals.
The repea-ter is arranged to receive and transmit signals in a multiplexed manner. Thus, in a first period of, for example, one second, an input signal transmitted by a transmit-only sub or by another repeater sub further down the drill string is detected by the input transformer 15 whose primary is coupled between the lower sections of the drill string and the earth return, and is amplified by the input amplifier 16. In a second period of, for example, 100 milliseconds, the signal is digitally processed by the circuit 18 so as to remove errors, and, in a third period of, for example, one second, the processed signal is amplified by the output amplifier 17 and transmitted by the output transformer 12 either to a receiver at the surface or to another repeater further up the drill string.
~2~1537~
Since the telem~ry subs are relatively inexpensive to produce and the bandwidth, and hence the data transmission rate capability, of a signal drops off as a function of the distance over which it is transmitted, repeater subs may be provided with a spacing as low as 1000 feet along the drill string if necessary. This then enables signals to be transmitted at a data rate of about 100 bits per second with a power input of about 1W per sub and a bandwidth of about ~00 Hz.
If, in the system proposed in U.S. Specification No. 2,354,887, the drill string and conductive return through the earth are considered as a single turn secondary winding of a toroidal transformer having the toroidal coil surrounding the dril~ string as its primary, the core losses in the system disclosed in that specification and the system illustrated in the accompanying drawing may be ~ompared.
If the area of cross-section of the toroidal core is AC and the maximum saturation flux density for the core material is BSAT~ then clearly max ~ BSAT-AC ........................................ (i) If the impedance of the secondary is ZS then the power injected into the secondary can be written as Ps = Vs2 / 2ZS ............. ,..... ,................... (ii) The maximum value of the emf induced in the secondary can be written as VS = Ns~ max.~ .............................. (iii) 9.2~053b7~
where NS is the number of turns on the secondary, max is~the maximum value of the magnetic flux through the toroidal core cross-section~ and ~ = 2.~ .f where f is the frequency of the primary drive.
From equations (i), (ii) and (iii) it follows that A ~ ................. (iv) NS.2-~ f BSAT
Typical values for Silicon Iron toroidal transformer core material may be taken as:-BmaX = 1.2 Tesla Core Loss at 200 Hz = 5.5 watts.kg 1 Core Density = 7 gm.cm 3 From previous calculations at 200 Hz, theimpedance ZS of the drill pipe and earth can be taken as 0.17 ohm.
Thus, for a toroid of average diameter 14 cm surrounding the drill string having a single turn secondary winding, these typical values indicate a minimum value for the cross-sectional area of the core of 3.9 cm2 and a resulting minimum core volume of 156 cm3, and the minimum mass of the core is calculated at 1.1 kg when the case~for PS = 1 watt is considered. Thus~ in order to deliver 1 watt to the secondary circuit at 200 Hz, the ~2~D537~i !
resulting core loss is about 6 watts. Furthermore such a core will be expensive to manufacture.
By contrast, if the toroidal transformer of the system illustrate~ in the drawing has 100 turns on its secondary, the minimum value for the cross-sectional area of the core is about 4 ~m and the core may therefore be extremely small so that the core loss is negligible.
Claims (16)
1. Apparatus for signaling within a borehole while drilling with a drill string, incorporating a transformer having one winding electrically connected between a first portion of the drill string for drilling the borehole and a second portion of the drill string which is electrically insulated from the first portion, and signal transmitting and/or receiving means electrically connected to the other winding of the transformer, the first portion providing a current path for signals travelling between the transformer and a signal receiving and/or transmitting station at a remote location along the drill string, and a return-path being provided between the transformer and the signal receiving and/or transmitting station by way of the second portion and the earth formations through which the borehole is being drilled.
2. Apparatus according to claim 19 wherein said one winding is the secondary winding of the transformer and said other winding is the primary winding of the transformer, and signal transmitting means is electrically connected to the primary winding for transmitting signals to a remote receiving station.
3. Apparatus according to claim 2, wherein the signal transmitting means includes signal processing means for modulating a carrier signal in accordance with the measurement data received from a measuring instrument.
4. Apparatus according to claim 1, incorporating a plurality of signalling units distributed along the drill string, each comprising a transformer having one winding electrically connected between respective first and second portions of the drill string and signal transmitting and/or receiving means electrically connected to the other winding, one of said units being a transmit-only unit for transmitting measurement data supplied to it by a measuring instrument and the or each other unit being a repeater unit for receiving a signal supplied to it along the drill string, processing the signal and transmitting the processed signal.
5. Apparatus according to claim 1, wherein the transformer is a toroidal transformer.
6. Apparatus according to claim 1, wherein the transformer and the transmitting and/or receiving means are accommodated within a chamber in the wall of the drill string.
7. Apparatus according to claim 1, wherein the signal transmitting and/or receiving means is adapted to be supplied by a battery.
8. Apparatus according to claim 1, wherein the first and second portions are the upper and lower portions respectively of a special telemetry sub, the portions being separated by an electrical insulator.
9. A telemetry sub for a drill string, comprising first and second portions electrically insulated from one another, a transformer having one winding electrically connected between the first and second portions, and signal transmitting and/or receiving means electrically connected to the other winding of the transformer, the first portion providing a current path for signals travelling between the transformer and a signal receiving and/or transmitting station at a remote location along the drill string when the telemetry sub is disposed in a drill string, and a return path being provided during drilling between the transformer and the signal receiving and/or transmitting station by way of the second portion and the earth formations through which a borehole is being drilled.
10. A telemetry sub according to claim 9, being a transmit-only sub for transmitting measurement data supplied to it by a measuring instrument.
11. A telemetry sub according to claim 9, being a repeater sub for receiving a signal supplied to it along the drill string, processing the signal and transmitting the processed signal.
12. A telemetry sub according to claim 9, wherein the transformer and the transmitting and/or receiving means are accommodated within a chamber in the wall of the sub.
13. A telemetry sub according to claim 12, wherein the chamber is closed off from the outside by a cover.
14. A telemetry sub according to claim 9, wherein the first and second portions are insulated from one another by an annular insulator which is generally S-shaped in radial section.
15. A method of signalling within a borehole while drilling, utilising a drill string having first and second portions electrically insulated from one another, which method comprises passing signals between signal transmitting and/or receiving means and a signal receiving and/or transmitting station spaced apart along the drill string by way of a transformer having one winding electrically connected between the first and second portions and the other winding electrically connected to the signal transmitting and/or receiving means, the first portion providing a current path for signals travelling between the transformer and the signal receiving and/or transmitting station, and a return path being provided between the transformer and the signal receiving and/or transmitting station by way of the second portion and the earth formations through which the borehole is being drilled.
16. A method according to claim 15, which method comprises successively passing signals between a plurality of signalling units, each comprising a transformer having one winding electrically connected between respective first and second portions of the drill string and signal transmitting and/or receiving means electrically connected to the other winding, the first of said units being a transmit-only unit which transmits measurement data supplied to it by a measuring instrument and the or each other unit being a repeater unit which receives a signal supplied to it from a previous unit, processes the signal and transmits the processed signal.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8016759A GB2076039B (en) | 1980-05-21 | 1980-05-21 | Apparatus for and method of signalling within a borehole while drilling |
| GB8016759 | 1980-05-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1205376A true CA1205376A (en) | 1986-06-03 |
Family
ID=10513559
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000376546A Expired CA1205376A (en) | 1980-05-21 | 1981-04-29 | Apparatus for, and a method of, signalling within a borehole while drilling |
Country Status (5)
| Country | Link |
|---|---|
| CA (1) | CA1205376A (en) |
| FR (1) | FR2483006A1 (en) |
| GB (1) | GB2076039B (en) |
| NL (1) | NL8102401A (en) |
| NO (1) | NO159615C (en) |
Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4578675A (en) * | 1982-09-30 | 1986-03-25 | Macleod Laboratories, Inc. | Apparatus and method for logging wells while drilling |
| DE3402386A1 (en) * | 1984-01-25 | 1985-08-01 | Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt | INDUCTIVE ENERGY AND DATA TRANSFER |
| US4839644A (en) * | 1987-06-10 | 1989-06-13 | Schlumberger Technology Corp. | System and method for communicating signals in a cased borehole having tubing |
| US5172112A (en) * | 1991-11-15 | 1992-12-15 | Abb Vetco Gray Inc. | Subsea well pressure monitor |
| GB2338253B (en) | 1998-06-12 | 2000-08-16 | Schlumberger Ltd | Power and signal transmission using insulated conduit for permanent downhole installations |
| US8695727B2 (en) | 2011-02-25 | 2014-04-15 | Merlin Technology, Inc. | Drill string adapter and method for inground signal coupling |
| US9000940B2 (en) | 2012-08-23 | 2015-04-07 | Merlin Technology, Inc. | Drill string inground isolator in an MWD system and associated method |
| CN103731191A (en) * | 2012-10-11 | 2014-04-16 | 中国石油化工股份有限公司 | Signal transmission repeater of electromagnetic measurement-while-drilling system |
| WO2014084889A1 (en) * | 2012-11-29 | 2014-06-05 | Chevron U.S.A. Inc. | Transmitting power within a wellbore |
| US8857522B2 (en) | 2012-11-29 | 2014-10-14 | Chevron U.S.A., Inc. | Electrically-powered surface-controlled subsurface safety valves |
| US9422802B2 (en) * | 2013-03-14 | 2016-08-23 | Merlin Technology, Inc. | Advanced drill string inground isolator housing in an MWD system and associated method |
| US9267334B2 (en) | 2014-05-22 | 2016-02-23 | Chevron U.S.A. Inc. | Isolator sub |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2379800A (en) * | 1941-09-11 | 1945-07-03 | Texas Co | Signal transmission system |
| US2400170A (en) * | 1942-08-29 | 1946-05-14 | Stanolind Oil & Gas Co | Time cycle telemetering |
| US2354887A (en) * | 1942-10-29 | 1944-08-01 | Stanolind Oil & Gas Co | Well signaling system |
| CA953785A (en) * | 1971-03-09 | 1974-08-27 | Rudolf J. Rammner | Apparatus for transmitting data from a hole drilled in the earth |
-
1980
- 1980-05-21 GB GB8016759A patent/GB2076039B/en not_active Expired
-
1981
- 1981-04-28 NO NO811446A patent/NO159615C/en unknown
- 1981-04-29 CA CA000376546A patent/CA1205376A/en not_active Expired
- 1981-05-06 FR FR8108985A patent/FR2483006A1/en active Granted
- 1981-05-15 NL NL8102401A patent/NL8102401A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| NL8102401A (en) | 1981-12-16 |
| NO159615C (en) | 1989-01-18 |
| FR2483006A1 (en) | 1981-11-27 |
| NO811446L (en) | 1981-11-23 |
| NO159615B (en) | 1988-10-10 |
| GB2076039A (en) | 1981-11-25 |
| FR2483006B1 (en) | 1985-04-12 |
| GB2076039B (en) | 1983-12-14 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |