Note: Descriptions are shown in the official language in which they were submitted.
1~37143
This invention relates to wells, and particularly to
apparatus for detecting and extinguishing fires in wells em-
ployed in the in si~u combustion of carbonaceous materials in
permeable subterranean formations to recover petroleum there-
from.
In situ combustion of a portion of the carbonaceous
material in a permeable subterranean reservoir to increase or
promote the production of petroleum therefrom is becoming a
more widely used oil recovery technique. In this technique of
production, air is injected through one or more wells penetrat-
ing the oil-bearing stratum to be stimulated, and combustion
initiated in the stratum. The resulting combustion zone is
caused to move through the stratum by either inverse or direct
air drive, whereby the heat of combustion of a proportion of
the carbonaceous materials in the stratum mobilizes and usually
upgrades a substantial proportion of the unburned material.
In the direct drive mode of conducting an in situ
combustion operation, air is injected into a petroleum-bearing
stratum through one or more injection wells in communication
therewith and the carbonaceous material ignited in the stratum
- adjacent to the injection wells. Air injection through the
ignition wells is continued to form a combustion zone that
progressively moves through the reservoir. The hot combustion
gases exiting the combustion zone mobilize petroleum in the
stratum and displace the mobilized petroleum toward one or
more production wells. In some applications inverse combustion
is employed. In this mode of operation, a combustion zone is
established around a well by injecting air through the well and
into the oil-bearing stratum;and, thereafter, air injection
through the well is discontinued and air fed through the
stratum to the combustion æone from one or more surrounding
wells. Also, in situ combustion is employed in the so-call~ed
1037~3
"huff and puff" combustion process. In this operation, air is
injected through a well and into the oil-bearing stratum, and
ignition established. Air injection is continued to form a
combustion zone. After this step has been conducted for a
period of time, air injection is discontinued and the injection
well returned to production. Several cycles of combustion and
production can be employed.
The in situ combustion processes all require that air
be injected through injection wells in communication with the
stratum to be stimulated. Experience has shown that combustion
can occur in the well or in the formation sufficiently close to
the well, to cause damage to the sub-surface well equipment,
such as the casing, liner and tubing. Moreover, high tempera-
tures can occur in the well during interruptions in the flow of
air through the tubing, such as occur on shut down of the air
compressors. High temperature problems can also be encountered
in wells producing from a combustion operation, either because
of burn through to the producing well, or because of the pro-
duction of high temperature fluids.
Apparatus has been proposed to extinguish well fires
and cool hot wells. This apparatus typically employs a tempera-
ture sensor in the well that detects the occurrence of a high
temperature, and a control mechanism at the surface that
initiates the flow of cooling water or steam into the well to
extinguish the fire or cool the well so as to prevent damage to
the well equipment. The ~se of both thermocouples and thermo-
meters as the temperature sensing element have been proposed.
However, both of these devices are subject to serious problems
that markedly decrease their effectiveness in detecting high
well temperatures. One major problem encountered is that the
oil-bearing interval open to the well may be several hundred to
several thousand feet thick. Since a thermocouple and some
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~0371~3
thermometers measure the temperature at one point location, a
large number of such devices are necessary to detect the exist-
ence of high temperatures in a long interval. While certain
thermometers, such as the resistance thermometers, can be
utilized to measure temperatures along a substantial distance,
such devices measure only the average temperature along the
length of the resistance element. Thus, a localized high
temperature of sufficient magnitude to damage the well can
occur, without raising the average temperature significantly.
While the foregoing problems have been described in
conjunction with an in situ combustion operatlon, similar prob-
lems are encountered any time that temperatures in a well can
exceed an allowable temperature. Hence, need exists for a
device to detect the occurrence of a high temperature at any
point along a substantial length of a well, and to initiate
corrective action to prevent damage to the well.
Accordingly, a principal object of this invention is
to provide a temperature sensing device capable of detecting
the occurrence of a high temperature at any point along a sub-
stantial length of the well.
Another object of the invention is to provide a
temperature sensing device capable of detecting the occurrence
of a high temperature at any point along a substantial length
of a well employed in an in situ combustion operation.
Still another object of the invention is to provide
a temperature sensing device capable of detecting the occurrenLe
of a high temperature at any point along a substantial length
of an air injection well employed in an in situ combustion
operation.
A further object of the invention is to provide a
device for detecting and extinguishing fires occurring in a
well.
1037143
A still further object of the invention is to provide a device
for protecting wells from excessive temperatures.
According to the present invention there is provided a device
for detecting the occurrence of a high temperature at any point within a
well penetrating a subterranean formation having at least one subsurface
interval potentially susceptible to high temperatures, which comprises in
combination: a well penetrating said subterranean formation and passing
into or through said subsurface interval potentially susceptible to high
temperaturej a small diameter tubing suspended in said well and extending
from the surface through that portion of said subsurface interval potentially
susceptible to high temperature that is traversed by the well; an elongated
temperature sensor capable of sensing the occurrence of a high temperature
at any point along its length, said temperature sensor being comprised of an
elongated metallic outer tube and a substantially coaxial center conductor,
the annulus between said outer tube and said center conductor being packed
with a eutectic material having a first electrical resistance at temperatures
below the eutectic temperature and a second different electrical resistance
at temperatures above the eutectic temperature; cable means for suspending
said temperature sensor in said small diameter tubing so as to extend a sub-
stantial distance through said interval potentially susceptible to high
temperaturej and detector means located at the surface and electrically
connected to said temperature sensor for detecting the occurrence of a high
temperature at any point along the length of said temperature sensor, said
detector means including a means for impressing a controlled a.c. voltage
between said center conductor and said outer tube of said temperature sensor,
means for measuring the flow of electrical current between said center con-
ductor and said outer tubej and means to generate a d.c. output signal having
a value indicative of the current flow between said center conductor and said
outer tube.
The manner of accomplishing the foregoing objects as well as further
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.~
1037143
ob~ects and advantages of the invention will be apparent from the following
description taken in con~unction with the accompanying drawings, wherein
like numerals refer to corresponding parts, and in which:
FIGURE 1 is a vertical cross-sectional view through a subterrsnean
earth formation schematically illustrating the apparatus of this invention
installed in an air injection well completed in a permeable petroleum
reservoir;
FIGURE 2 is an elevation view in cross section showing the connect-
or employed to connect the temperature sensing element to the supporting
cable;
; FIGURE 3 is a horizontal cross-sectional view of the temperature
sensing element taken along the line 3-3 of FIGURE 2;
FIGURE 4 is a block diagram schematically illustrating the
electrical circuitry employed in the monitoring and control unit, and
FIGURE 5 is a schematic circuit diagram illustrating the electrical
circuitry employed in the monitoring and control unit.
Referring now to FIGURE 1, an injection well 10 is completed in
a permeable subterranean reservoir comprised of permeable strata 12, 14 and
16, which can have the same or different permeabilities, interposed between
substantially impermeable strata 18. These strata are overlain by over-
burden 20 lying beneath surface 22. Well 10 is drilled through these strata
and provided with casing 24 cemented in place by outer cement sheath 26
around the periphery of the casing. Casing 24 is provided with a conventional
well head assembly 28 that
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1037143
forms a closure at the surface end of~the casing, and the cas-
ing and surrounding cement sheath are provided with perfora-
tions 30 that provide communication between the well and the
adjacent permeable strata. Tubing 32 extends from the surface
to a point adjacent the bottom of well 10. Air, from high
pressure source 34, which can be a compressor or other avail-
able source of high pressure air, is normally introduced into
well 10 through tubing 32 by means of conduit 36, valve 38 and
check valve 40. The air is introduced into well 10 at a pres-
sure sufficient to cause it to flow through perforations 30 andinto the permeable strata in communication therewith. Also 7 if
desired, air can be diverted directly into the well casing
through valve 42 and conduit 44 connected to casing port 46.
While FIGURE 1 depicts a conventional air injection well com-
pleted in a permeable strata, it is to be recognized that the
foregoing is used for illustrative purposes, and that various
modifications of well apparatus and air injection techniques
can be employed.
In accordance with the present invention, well 10 is
modified by providing a second relatively small diameter tubing
50 extending from the surface through the strata that will be
exposed to air. Tubing SO can be a conventional 1 1/2-inch
tubing string closed at the lower end and provided with packing
gland 52 at the surface end. It is preferred that tube 50 be
sealed to prevent the discharge of well fluids to the atmos-
phere in the event that the tubing develops a leak. Pressure
gauge 54 and bl~eder valve 56 are provided at the surface end
of tubing 50 to indicate the pressure in the tubing, which pro-
vides an indication that a leak has been developed. Tempera-
ture sensor 58 is suspended within tubing 50 by means ofarmored conductor cable 60 connected to the sensor by means of
connector 62, which will be hereinafter more fully described.
~0371~3
Cable 60 provides support for temperature sensor 58 while in
the well, provides means for lowering the sensor into position
and for withdrawing the sensor from tubing 50, and electrically
connects sensor 58 to control unit 64 located at the surface.
Control unit 64 detects the occurrence of a high
temperature at any place along the length of temperature sensor
58 and activates various control and warning devices in the
event of a high temperature. In the illustrated embodiment,
control unit 64 activates alarm horn 66, recorder 68 and opens
valve 70 to cause cooling water to flow from high pressure
water source 72 through conduit 74 to the well. Cooling water
can be introduced into the well through tubing 32 by means of
valve 76 and directly into the casing through valve 78 and
conduit 80 connected to casing port 82.
FIGURES 2 and 3 more specifically illustrate the con-
struction of a preferred embodiment of temperature sensor 58
and the means for supporting the temperature sensor within
tubing 50. Temperature sensor 58 is comprised of sensing
element 100 suspended within a thin outer protective tubing 102.
Both sensing element 100 and protective tubing 102 are supported
from connector 62, which in turn is attached to the lower end
of armored cable 60. Connector 62 provides both support for
temperature sensor 58 and electrically connects the sensor to
the electrical conductors in the cable.
Sensing element 100 is of the type that can detect
specific overheat conditions at any point along the entire
length of the sensing element without regard for rate of
temperature rise or average ambient temperature. One suitable
sensing element is marketed by Fenwal, Incorporated of Ashland,
Massachusetts and consists of a small diameter Inconel tube 108
and a coaxial nickel wire 104. A thermally sensitive, eutectic
insulating salt composition is packed into the annular space ~6
rQo~e ~ ~ r ~
1037143
between tube 108 and wire 104~ and hermetically sealed therein.
These elements are available in various lengths up to 15 feet,
and can be coupled together to provide a unit of any desired
length.
Under normal operating conditions, the salt packed
into annulus 106 of the sensor electrically insulates center
wire 104 from outer tubing 108. A small voltage is impressed on
thç sensor element, but the flow of electrical current between
the outer tubing and the central wire is restricted by the in-
sulating properties of the eutectic salt composition. However,
when an overheat condition occurs at any point along the entire
length of the element, the resistance of the eutectic salt com-
position drops sharply, allowing a higher current flow between
center conductor 104 and outer tubing 108 of the sensor. This
current flow is sensed by control unit 64 which produces an out-
put signal to actuate a visible or audible alarm. When the over-
heat condition is corrected, the resistance of the eutectic salt
compound returns to its original value, thereby decreasing the
currènt flow between the inner and outer conductors and return-
ing the unit to standby alert.
With this type of sensing element, the control point
is determined by the composition of the eutectic salt employed
in packing the annulus of the sensing element. Sensing elements
are available that function at specified temperatures between
about 255 F. and 900 F. The selection of a specific tempera-
ture settin~, or control point, will depend upon the well en-
vironment and the maximum temperature to be protected against.
For wells, such as air injection and producing wells, employed
in in situ combustion operations, it is preferred that the
control point of the detector be between about 250 and 400 F.
Sensors responsive to a selected temperature within this range
minimize false alarm conditions, yet rapidly detect localized
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overheating. lQ37~43
Connector 62 is comprised of an outer sleeve 110 pro-
vided with internal threads 112 at its upper end and a smaller
diameter bot+om opening so as to form inwardly protruding peri-
pheral shoulder 114. Externally threaded nut 116 threadably
engages the upper end of sleeve 10. Nut 116 is provided with
axial bore 118 for cable 60 to pass through and with a periph-
eral groove 120 to facilitate the grasping of the nut with a
fishing tool should it ever be necessary to fish the tempera-
ture detector from the well. Radial bores 120 are provided toreceive the lugs of a spanner wrench employed in assembling
and disassembling the device. External collar 122 is welded or
otherwise fixedly attached to the upper end of tubing 102 to
mate with shoulder 114, "0" ring 124 providing a fluid-tight
seal therebetween.
Cylindrical insert 126 is fitted within sleeve 110
and is provided with a smaller diameter section 128 adapted to
fit into the upper end of tubing 102. Insert 128 is adapted
to fit into the upper end of tubing 102. Insert 126 is provided
with a longitudinal bore 130 having a necked-down, or small-
diameter section 132 intermediate its length. Both ends of
insert 126 are provided with internal threads, and the insert
is provided with peripheral groove 134 fitted with "O" ring 136
to provide a fluid-tight seal between the insert and the inner
wall of sleeve 110.
Cable 60 is a two conductor electrical cable having a
central core of two electrical conductors 140 and 142 protected
by spirally wound armor wires 144. Threaded bushing 146 having
a cylindrical lower section 148 is screwed into insert 126.
Bushing 146 is provided with a longitudinal bore to receive
cable 60. Cable 60 passes through the longitudinal bores of
nut 116 and bushing 146, and armor wires 144 are crimped up
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1037i43
around the cylindrical lower section 148 of bushing 146. These
wires are clamped between bushing 146 and the necked-down sec-
tion 132 of insert 126 so as to maintain connector 62 securely,
but removably, attached to cable 60. Conductor 142 serves as
a ground wire and is also clamped between bushing 146 and necked-
down section 132. Alternatively, a single wire cable can be
employed and the outer armor wires used for grounding. Conduc-
tor 140 passes downwardly through bore 130 of insert 126 and is
connected to cable connector 150 which is threadably attached
to the lower end of insert 126. Sensing element 100 is thread-
ably attached to cable connector 150 by means of sensing eleme~
connector 152. Cable connector 150 electrically connects con-
ductor 140 to central conductor 104 of the sensing element, and
connects outer tubing 108 to ground.
The electrical circuitry of control unit 64 is illus-
trated in FIGURES 4 and 5. The unit is battery powered and in-
cludes a battery charger to convert 115 volt a.c. to 12 volt
d.c. The 12 ~olt d.c. is converted to approximately 8 volt a.c.
and amplified for power input to the detector circuitry, which
includes an isolating transformer having an output of about 24
volts a.c., a wheatstone bridge and a full wave rectifier to
convert the a.c. output to a d.c. signal. The d.c. output
signal is amplified and employed to actuate alarm horn 66 and
cooling water valve 70, and this output is recorded on record-
ing microampmeter 68 and indicated on microampmeter 316.
Referring particularly to FIGURE 5, a 115 volt a.c.
supply 200 is connected by means of conductor's 202 and 204
through fuse 206 and a.c. power switch 208 to the primary of
transformer 210 which reduces the 115 volt a.c. to 24 volt a.c.
Neutral power conductor 204 is connected to ground by conductor
212. The secondary of transformer 210 is connected by means
of conductor 212 and 214 across full wave bridge rectifier 216
~037~43
which consists of four bridge-connected diodes. Capacitor 222
and fi~st stage series regulator 224 are parallel connected
across the output of rectifier 216 by means of conductor 218
and negative d.c. supply conductor 220. The output of the first
stage rectifier is connected in series through second stage
rectifier 226 to battery 228. First stage series recitifier
224 includes Zener diodes 230 and 232 and resistor 234 series
connected between positive and negative d.c. conductors 218 and
220 by means of conductors 236 and 238, and NPN transistors 240
and 242. The base of transistor 240 is connected to conductor
; 238, the collector to conductor 218, and the emitter is connect-
ed by conductor 244 to the base of transistor 242. The collec-
tor of transistor 242 is connected to conductor 218 and the
emitter is connected by conductors 246 and 248 through parallel
connected resistors 250 and 252 to the collectors of NPN tran-
sistors 254 and 256, and through resistor 258 and conductor 260
to the base of transistor 254 and through series connected
, diode 262 and Zener diode 264 to negative d.c. supply conductor! 220. The emitter of transistor 254 is connected to the base of
transistor 256 by conductor 266. The emitter of transistor 256
is connected to positive d.c. supply conductor 268, which is
connected through fuse 270 and d.c. power switch 272 to the posi-
tive terminal of battery 228, and d.c~ power supply conductor
220 is connected to the negative terminal of battery 228.
The oscillator includes resistor 280, variable resis-
tor 282 and capacitor 284 connected in series by conductors
286 and 288 between positive d.c. supply conductor 268 and
negative d.c. supply conductor 220. Conductor 288 is also
connected to the base of NPN transistor 290 and to oscillator
292. One leg of oscillator 292 is connected to positive d.c.
supply conductor 268 through resistor 294 and the other leg is
connected through resistor 296 to negative d.c. supply conductor
--10--
lU37~43
220 and to test jack 302. Negative d.c. supply conductor 220
is connected to test jac]c 300 and positive d.c. supply conductor
268 is connected to test jack 304. The collector of transistor
290 is connected to positive d.c. supply conductor 268 and the
emitter is connected through resistor 306 and parallel connected
capacitor 308 and resistor 310 to the base of transistor 312.
The emitter of transistor 312 is connected by conductor 314 to
one side of microampmeter 316 and the collector is connected by
conductor 318 through resistor 320 to positive d.c. supply con-
ductor 268 and to the base of NPN transistor 322. The collector
of transistor 322 is connected to positive d.c. supply conductor
268 and the emitter is connected through the primary of trans-
former 324 and series connected resistor 326 to negative d.c.
supply conductor 220. The secondary of transformer 324 is con-
nected by conductors 326 and 328 across Wheatstone bridge 330,
which includes bridge connected resistors 332, 334 and 336, and
parallel connected capacitor 337 and variable resistor 338.
Sensing element 100, not shown, is connected in parallel with
resistor 332.Variable resistor 338 is connected in the bridge
circuit in parallel w~th capacitor 337 to provide means for
balancing the bridge circuit. Full wave bridge rectifier 340
is connected by conductors 342 and 344 across Wheats ~ e bridge
330 to convert the a.c. output of bridge 340 to a d.c. signal.
One junction of bridge rectifier 340 is connected to negative
d.c. supply conductor 220 and the opposite junction is connected
by conductor 346 to the base of NPN transistor 348, through
resistor 352 to negative d.c. supply conductor 220, and through
capacitor 354 to terminal 4 of recorder 68. The collector of
transistor 348 is connected to positive d.c. supply conductor
268 and the emitter is connected through resistor 356 to the
base of NPN transistor 358 and through resistor 360 to the other
side of microampmeter 316. The collector of transistor 358 is
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1~37~43
connected by conductor 362 to the number 4 terminal of integrated
circuit 364 and through resistor 366 to positive d.c. supply
conductor 268.
Sensitivity adjustment is provided by variable resis-
tor 368 connected between positive d.c. supply conductor 268 and
negative d.c. supply conductor 220, the variable leg of resistor
370 being connected to -the number 5 terminal of integrated cir-
cuit 364. Positive d.c. supply conductor 268 is connected to
the number 11 terminal of integrated circuit 364 and negative
d.c. supply conductor 220 is connected to the number 7 terminal.
The number 10 terminal of integrated circuit 364 is connected
through resistor 372 to the base of NPN transistor 374. The
collector of transistor 374 is connected through the coil of
relay 376 to positive d.c. supply conductor 268 and the emitter
is connected to negative d.c. supply conductor 220. Relay con-
tact 378 actuates alarm horn 66 through conductors 380, 382, and
384; and relay contact 386 operates cooling water valve 70
through conductors 388 and 390. Switch 392 is provided in posi-
tive d.c. supply conductor 268 to valve 70. The output signal
from relay contact 386 is also supplied to meter 68 through
resistor 394 by means of conductor 396.
In operation, the 12 volt power supply is converted to
8 volt a.c. and passed through transformer 324 to isolate any
d.c. power from the bridge circuit. Wheatstone bridge circuit
330 is balanced to provide an output signal that is amplified
and converted to a d.c. signal. The circuit is adjusted to pro-
vide a normal d.c. output of about 20 milliamps. An alarm condi-
tion causes an output of about 70 milliamps. A normal output of
less than 20 milliamps is indicative of a mechanical or electri-
cal defect in the sensor or the sensing circuit, or imbalance of
the bridge circuit.
A testing circuit consisting of resistor 400, push
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1037~43
button 402, and timer 404 is connected across resistor 332 and
sensing element 100, not shown, by means of conductors 406 and
408. On manually actuating test button 402, or at periodic
intervals initiated by timer 404, an alarm condition is simu-
lated. This alarm condition is detected by the sensor circuitry,
and alarm horn 66 and cooling water valve 70 actuated and the
alarm condition recorded by recorder 68.
Various embodiments and modifications of this inven-
tion have been described in the foregoing description and
examples, and further modifications will be apparent to those
skilled in the art. Such modifications are included within the
scope of this invention as defined by the following claims.
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