Note: Descriptions are shown in the official language in which they were submitted.
3'73
This invention pertains to drilling of boreholes and
more particu]arly to means for controlling apparatus in the bore-
hole and to receiving information sensed by sensors in -the borehole.
The commercial importance of petroleum exploration and the
increasingly inhospitable geology which appears economically in-
teresting have led to many schemes for determining the direction
of a hole being drilled and the characteristics of the strata it
is traversing. Electrical apparatus in the hole must be supplied
with energy and controlled; and observations are preferably trans-
mitted to the surface without the necessity of raising the drill,
although many devices propose to record in a bore-hole recorder the
readings of instruments which will be available only too late to
avoid the mistakes they chronicle. The prior art teaches the use of
acoustic impulses through the drill string; conductors of different
number in the drill cable; carrier schemes of various sorts to relay
information out of the hole; the superposition of variously iden-
tifiable pulses on sinusoidal power voltages to transmit intelligence
in either direction; different schemes for multiplex or phantom
circuit transmission in either direction.
U.S. 3,93~,129 of Smither issued February 10, 1976, assigned
to the assignee of the present application, discloses the use of
a power line to transmit data from the hole to -the surface by changing
the phase relation of the voltage applied and current supplied at
the surface. This is done in the hole by switching a susceptance
in parallel with the normal down-hole loa~ to draw an out-of-phase
current large enough to be identified at the surface as representing
a binary pulse. In particular, it describes two different types of
phase detectors which may be used in the present invention.
U.S, 3,959,767 of Smither et al issued ~ay 25, 1976, assigned
to the assignee of the present application, teaches the use of phase
modulations to transmit binary-coded data back from the hole to the
surface, and further teaches the use of the sv,rface power supply -to
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control down-hole apparatus from the surface. This is done by sup-
pressing either a positive or a negative half-cycle of the power
voltage. This is detected in the down-hole apparatus.
No other art believed more nearly related to the present
invention is known to the applicants.
A combined power and signal carrier of nominal 1 kHz
frequency is generated by a voltage-controlled oscillator (VC0) and
amplified to a convenient power levle, for transmission via a single
conductor pair down a bore-hole to sensing equipment in the hole. The
VC0 may be frequency modulated with a deviation of about five percent
to convey pulse signals to the bore-hole equipment, which is provided
with FM demodulation means and digital means to receive various commands. -~
The mode of transmission of the commands is novel in that a command
message consists of a string of bits Or equal weight which will cause
a down-hole binary counter to reach a count at which its binary out-
put will excite appropriately the leads which would conventionally
represent values of 1, 2, 4, 8, etc. but in this invention represent
command #1, #2, #3, and #4, respectively. D-c supply for the bore-hole
equipment is provided by rectifying some of -the lkHz power. Data is
transmitted back to the surface by encoding it in binary digits and
connecting a susceptance, preferably capacitive, across the supply line
so that the power factor of the energy supplied grom the surface is
altered. This alteration is detected at the surface and is treated as
a pulse which is then decoded as a code bit. Neither mode of trans-
mission interferes with the other.
Fig 1 regresents by block diagram the embodiment of the
invention.
Fig 2 represents schematically the down-hole receiver,
clock detector, and FM demodulator.
Fig 3 represents schematically the means to convert the
demodulated FM signal to a digital signal.
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Fig 4 represnets schematically means to decode the
command.
Fig 5 represents schematically means to transmit data
to the surface.
Fig 1 represents in schematic block diagram form the -~
surface and downhole portions of the system as connected by a two-
conductor path. A voltage-controlled oscillator 10 with a nominal
or center frequency of 1 kHz drives a power amplifier 12 which feeds
its output to the primary of a transformer 14 whose secondary is
connected to the two-conductor path through the cable 16 running into
the well hole. A current transformer lg is connected with its primary
in series with the secondary of 14 and cable 16, and its secondary
connected to surface receiver 20. Surface receiver 20 is al$o con~
nected to receive a potential signal from VC0 10. Its function is
to determine the phase between the potential impressed on cable 16, and
the current through ;t; changes in this phase are produced down~hole
as a means of signalling to surface receiver 20, Detected signals are
transmitted from receiver 20 to digital computer 22 (which also receives
clock pulses from receiver 20~ for decoding of the binary~encoded
signal formed by the phase changes and any appropriate further processing
or storage.
Control signals are sent down-hole by frequency modulation
of the alternating potential applied to cable 16. In the present embodi-
ment, four different command signals are to be transmitted, completely
independently of each other to the extent that any of them may be
transmitted simultaneously. This is done by sending a burst of pulses
of equal weight whose total number is counted by a down-hole binary
counter of four stages. If down-hole command generator 24 is envisaged
as having four switches corresponding to the four commands, it is evident
that any conventional arrangement which causes switch #1 to contribute
one pulse, switch #2 two pulses, switch #3 four pulses, and switch #4
eight pulses, to the total in the burst will result in the down-hole
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counter which counts the total having its four binary output leads
excited correspondingly to the number of the switch which is turned
on--that is, if switch #4 is on and adds eight purses to the total,
the fourth output lead of the counter will be excited. In the present
instance these will be voltage pulses of the proper amplitude to
produce, when applied to VCO 10, the desires frequency deviation.
This may be of the order of five percent.
The down-hole apparatus is represented in block form;
since all these b]ocks are detailed in the remaining drawings, they
will merely be enumerated: power supply 26; transmitter 2g; data
acquisition system 30; clock detector 32; FM demodulator 34; and
down-hole command detector 36.
Referring to Fig 2, cable 16 is connected to a trans-
former whose center-tapped secondary is connected to down-hole power
supply 26, through diodes 40 and 42, whose outputs are connected
respectively to filter capacitors 44 and 46, to produce potentials of
+12 volts and -12 volts, respectively, with respect to ground for
supplying these potentials to the various electronic devices of the
down-hole installation. A conventional semiconductor squaring amp-
lifier 48 is connected to one side of the secondary of transformer 3g
to receive the nominal 1 kHz of the power system, which it squares
and transmits through amplifier 50 as clock 51. The output of 4g is
also fed to Miller integrator 52, whose output becomes a sawtooth
wave which is fed to a phase-locked loop 54 via a capacitor 56. Phase-
locked loop 54 contains a phase comparator 5g and a voltage-controlled
oscillator 60 which, in conventional fashion receives a control or
error voltage from phase comparator 5g to make its frequency follow
the frequency of the input to 54, which is effectively the frequency
of the output of VCO 10 on the surface. Since the error voltage is
a measure of the amount by which potentials within phase-locked loop
54 deviate from ground, and produces an output 64 which is the demod-
ulated FM signal at a fixed potential with respect to ground.
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Fig 3 represen-ts output 64 being fed to a ground clamp
d-c restoration circuit 66 and thence to a Schmidt trigger circuit 6g,
which squares it. This squared signal is transmitted to inverter 70,
which produces an output 72.
Binary counter 74 of Fig 4 receives clock 51 by which it
is stepped continuously. Its maximum registration is the maximum pos-
sible number of pulses in a command signal train from down-hole command
generator 24 of Fig 1. Binary counter 76 receives the data pulses 72
and counts only the actual number of such pulses. This mode of operation
has the advantage that synchronization of the counters with the actual
beginning of a command word is unnecessary. If there are six pulses
in the command word, and the first two arrive and are followed by a
long sequence of vacancies terminated by the final four pulses, the
toatal count is six even though the count was begun within the sequence
of six. This however, requires that two such counts be made in æuc-
cession, and compared with each other before the count can be accepted as
accurate, since a change in the command signal occurring during the count
could lead to error. This is in fact unobjectionable,since it is only
when a change in the command signal is made that this occurs. Once a
given set of commands has been entered into down-hole command generator
24, it is repeated continously until the command has been changed.
The detailed operation of the system is this: When binary
counter 74 reaches its maximum registration, it produced a signal at
terminal 7g which triggers toggle flop 80 and enables gate g2. Toggle
flop gO produces a pulse short compared with the clock period--about
500 nanoseconds long in the present embodimen-t. The trailing edge of
this strobes register g4 and causes it to store the then existing content
of counter 76. If data pulses 72 are arriving, gate g2 triggers a toggle
flop g6, which resets counters 74 and 76 to zero, beginning a new count.
When the next word period has passed, counter 74 again triggers toggle
flop ~0; toggle flop gO also triggers comparator gg, by the leading edge
of its output, so that comparator 8g compares the content of counter 76
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~nth that of register ~4. If the two are the same, the contentof counter
76 is loaded into output register 90, whose four outputs are the four
possible commands, which are sent to perform appropriate control functions
on the controllable apparatus whose nature is immaterial to the present
invention; it merely constitutes the apparatus to be controlled. The
trailing edge of the output of toggle flop ~0 resets co~mters 74 and 76
as above described. If comparator 84 finds a difference between the content
of counter 76 and register 84, nothing is fed to register 90, whi¢h
continues with its previous content. Register 84 receives the current
content of counter 76 slightly before counter 76 is reset, so that register
84 always has the previous content of counter q6 for the next comparison.
Fig 5 represents primarily the fown-hole transmitter 28.
Down-hole data acquisition system 36 is represented simply as a regtangle;
it is any conventional means to receive sensed data, convert it to digital
form, and serialize it, and so long as it provides digital data to be
transmitted is of no other consequence to the present invention. Its out-
put is received and amplified by operational amplifier 92, which drives
a Darlington type transistor circuit. The output of amplifier 92 via
a resistor 94 drives the base of a transistor 96 whose emitter is connected
to the base fo a transistor 98. The collectors of these two transistors
96 and 98 are tied together to one side Or a capacitor 100, and to the
cathode of a diode 102 whese anode is grounded. The other side of capa-
citor 100 is tied to one side of the secondary of transformer 38. A
binary zero in the data stream leaves the base of transistor 96 at zero,
which causes it and transistor 9g to be turned off. Capacitor 100 is
charged by the voltage from the secondary of transformer 38 to the peak
voltage of the alternating current, at which it is held by diode 102, so
that capacitor 100 does not have any effect. When a binary one drives
the base of transistor 96 positive, it also drives the base of transistor
9g positive, and they are both turned on. They thereby discharge capacitor
100 of its sotred charge. The transistors (when they are on) and the
diode in effect cause capacitor 100 to be tied between ground and the terminal
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of the secondary of transformer 3g. It is thus enabled to draw a
leading current from one-half of the transformer 3g secondary, and
produces a change in the overall power factor of the current drawn
from the surface power supply provided by power amplifier 12.
A brief word is in order concerning the magnitude of
the capacitor 100. It is required to draw a sufficiently large current
to produce a change in the phase of the total current sent down-hole
from amplifier 12 to be surely identifiable at the surface. If this
current includes apparatus having not only a substantial drain but
a possibly varying power factor of its own (such as a magnetic actuator,
or a motor whose power factor varies with load and speed), then capacitor
100 must draw such a large leading current that the phase change it
produces in the total current can surely be identified as due to that
cause, and not a casual variation caused by the operation of other equipment.
The detection of the indicated phase change is performed
by surface receiver 20 which is completely conventional in the art and
so not given in detail. Surface receiver 20 is connected to VCO 10 to
receive a voltage fixed in phase with respect to the voltage applied to
transformer 14 by power amplifier 12. From current transformer lg it
receives a signal fixed in phase with respect to the current flowing in
the conductors of cable 16. These two signals may be applied to a
product detector whose output amplitude will be a function of the phase of
the current in cable 16 conductors with respect to the potential applied
between them. The change in the product detector output may be detected,
and identified as a pulse transmitted by down-hole transmitter 2~. Each
such pulse is transmitted to digital computer 22, which also receives
clock pulses from VCO 10, via surface receiver 20. Digital computer 22
processes the data conveyed by the pulses in any desired manner. It is to
be noted that changes in the frequency of VCO 10 will not interfere with
these operations, since the clock pulses and the data pulses to digital
computer 22 will both change simultaneously.
Other methods of measuring phase are, of course, common in
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the art; for example, the zero crossings of the two signals may be
detected, and the time interval between these crossings may be measured
as a measure of the phase. However, it is not here required to measure
phases accurately, but simply to detect comparatively gross changes in
the phase; the simplest operative method for doing so will probably be
preferred.
The invention disclosed employs frequency modulation of
an applied voltage to send signals in one direction; and it employs
phase-shift modulation to send signals in the opposite direction by
means which are not hampered by the changes in frequency of the applied
voltage. This combination is economical in the number of conductors
required in cable 16, which has the practical advantage that these may
be used also as power conductors of considerable thickness, more rugged
and easily protected than would be a greater number of conductors. The
novel device of transmitting command signals down-hole by a succession
of pulses of equal weight facilitates the operation of the inveniton by
eliminating the requirement for careful synchroni~ation or timing in-
herent in conventional binary encoded transmission.
_g_
