METHOD OF PUTTING OUT OIL WELL FIRES
United States Patent 3782474
A method of putting out oilwell fires comprising the steps of providing carbon dioxide in liquid state at a well site and releasing the carbon dioxide to ambient atmosphere, allowing expansion to a gaseous state, to displace oxygen required for combustion and to dilute the combustible fuel for increasing the temperature required for combustion.
US Patent References:
Safety appliance for oil derricks
Wasson - January 1929 - 1697376
Method and apparatus for extinguishing fires
Ensminger et al. - September 1942 - 2295571
Safety appliance for oil derricks
Wasson - January 1929 - 1697376
Method and apparatus for extinguishing fires
Ensminger et al. - September 1942 - 2295571
Application Number:
05/195713
Publication Date:
01/01/1974
Filing Date:
11/04/1971
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
169/69, 169/61, 169/11, 169/46
International Classes:
A62C3/00; E21B35/00; A62C3/02
Field of Search:
169/1A,2R,4,11,16
Primary Examiner:
Wood Jr., Henson M.
Assistant Examiner:
Kashnikow, Andres
Attorney, Agent or Firm:
Howard, Moore Et Al E.
Parent Case Data:
CROSS REFERENCE TO RELATED PATENTS
This application is a continuation-in-part of my copending application Ser. No. 793,692 entitled "Device for Putting Out Oil Well Fires," filed Jan. 24, 1969 now U.S. Pat. No. 3,620,299, issued Nov. 16, 1971.
Claims:
Having described my invention I claim
1. A method of rendering fluid flowing from a well non-combustible comprising the steps of, providing a source of liquid carbon dioxide; and dispensing the liquid carbon dioxide into the well such that fluid issuing therefrom will have liquid carbon dioxide entrained therein to expand as fluid issues from the well to ambient atmosphere diluting the fluid and enveloping same in an atmosphere which will not support combustion.
2. The method of claim 1 wherein the liquid carbon dioxide is dispensed into the well at a rate substantially equal to the rate of flow of fluid from the well such that the mixture of fluid and carbon dioxide gas issuing from the well is at least 90 percent carbon dioxide by volume.
3. The method of claim 1 with the addition of the step of dispensing liquid carbon dioxide to ambient atmosphere adjacent the exterior of the well.
4. The method of claim 1 with the addition of the step of dispensing liquid carbon dioxide to ambient atmosphere adjacent the well at a rate of approximately 50 percent of the flow rate of fluid from the well.
5. The method of claim 1 with the addition of the steps of: sensing ultraviolet light; and dispensing the liquid carbon dioxide responsive to increase of ultraviolet light adjacent a well to a predetermined intensity.
6. The method of claim 1 with the addition of the steps of: sensing temperature adjacent the well, dispensing the liquid carbon dioxide responsive to an increase in temperature adjacent a well to a predetermined temperature.
7. The method of claim 1 with the addition of the steps of: sensing air pressure adjacent the well; and dispensing the liquid carbon dioxide responsive to an increase in air pressure adjacent a well to a predetermined pressure.
8. A method of extinguishing combustion of a stream of fluid issuing from a well comprising steps of, mixing liquid carbon dioxide with the fluid before the fluid issues from the well; and enveloping the stream of fluid in carbon dioxide as it issues from the well such that convection currents accompanying combustion will draw the carbon dioxide enveloping the stream of fluid to the point of combustion.
9. A method of preventing combustion of a stream of fluid issuing from an opening comprising the steps of; delivering liquid carbon dioxide; dispensing the liquid carbon dioxide to ambient atmosphere from a plurality of positions spaced about the opening; and directing the carbon dioxide toward the stream of fluid issuing from the opening, such that the carbon dioxide expands to a gaseous phase and the carbon dioxide gas is drawn into and around the stream of fluid.
10. The method of claim 6 wherein the liquid carbon dioxide is dispensed at a rate which is at least fifty percent of the volumetric flow rate of the fluid issuing from the opening.
11. The method of claim 6 wherein the liquid carbon dioxide is dispensed for a period of at least ten seconds.
12. The method of claim 11 wherein the liquid carbon dioxide is dispensed into the fluid at a volumetric flow rate substantially equal to the flow rate of fluid issuing from the opening.
13. A method of extinguishing a well fire comprising the steps of: refrigerating carbon dioxide to maintain same in a liquid phase; and dispensing liquid carbon dioxide into a stream of fluid flowing out of a well such that fluid issuing from the well has carbon dioxide gas entrained therein
14. A method of preventing oil well fires comprising the steps of, refrigerating a volume of a liquid carbon dioxide under pressure; dispensing liquid carbon dioxide into the well such that the liquid carbon dioxide will expand to a gaseous state and will be entrained in fluid issuing from the well; and releasing the liquid carbon dioxide to ambient atmosphere onto heated objects adjacent the well to cool the heated objects to a temperature below the temperature of combustion of fluid flowing from the well.
15. A method of preventing combustion of a stream of fluid issuing from an opening comprising the steps of: delivering liquid carbon dioxide; dispensing liquid carbon dioxide into the fluid before the fluid issues from the opening such that the carbon dioxide will expand to a gaseous state and will be entrained in the fluid issuing from the opening; dispensing the liquid carbon dioxide to ambient atmosphere from a plurality of positions spaced about the opening; and directing the carbon dioxide toward the stream of fluid issuing from the opening such that the carbon dioxide expands to a gaseous phase and the carbon dioxide gas is drawn into and around the stream of fluid.
16. A method of distinguishing a well fire comprising the steps of: providing a source of liquid carbon dioxide; dispensing liquid carbon dioxide into the well; and maintaining the volumetric flow rate of liquid carbon dioxide at least 50 percent of the volumetric flow rate of fuel flowing from the well for a period of at least 10 seconds.
17. A method of preventing combustion of fuel issuing from a well comprising the steps of: providing a source of liquid carbon dioxide; and dispensing the liquid carbon dioxide into the well adjacent choke manifolds such that the fuel is diluted.
1. A method of rendering fluid flowing from a well non-combustible comprising the steps of, providing a source of liquid carbon dioxide; and dispensing the liquid carbon dioxide into the well such that fluid issuing therefrom will have liquid carbon dioxide entrained therein to expand as fluid issues from the well to ambient atmosphere diluting the fluid and enveloping same in an atmosphere which will not support combustion.
2. The method of claim 1 wherein the liquid carbon dioxide is dispensed into the well at a rate substantially equal to the rate of flow of fluid from the well such that the mixture of fluid and carbon dioxide gas issuing from the well is at least 90 percent carbon dioxide by volume.
3. The method of claim 1 with the addition of the step of dispensing liquid carbon dioxide to ambient atmosphere adjacent the exterior of the well.
4. The method of claim 1 with the addition of the step of dispensing liquid carbon dioxide to ambient atmosphere adjacent the well at a rate of approximately 50 percent of the flow rate of fluid from the well.
5. The method of claim 1 with the addition of the steps of: sensing ultraviolet light; and dispensing the liquid carbon dioxide responsive to increase of ultraviolet light adjacent a well to a predetermined intensity.
6. The method of claim 1 with the addition of the steps of: sensing temperature adjacent the well, dispensing the liquid carbon dioxide responsive to an increase in temperature adjacent a well to a predetermined temperature.
7. The method of claim 1 with the addition of the steps of: sensing air pressure adjacent the well; and dispensing the liquid carbon dioxide responsive to an increase in air pressure adjacent a well to a predetermined pressure.
8. A method of extinguishing combustion of a stream of fluid issuing from a well comprising steps of, mixing liquid carbon dioxide with the fluid before the fluid issues from the well; and enveloping the stream of fluid in carbon dioxide as it issues from the well such that convection currents accompanying combustion will draw the carbon dioxide enveloping the stream of fluid to the point of combustion.
9. A method of preventing combustion of a stream of fluid issuing from an opening comprising the steps of; delivering liquid carbon dioxide; dispensing the liquid carbon dioxide to ambient atmosphere from a plurality of positions spaced about the opening; and directing the carbon dioxide toward the stream of fluid issuing from the opening, such that the carbon dioxide expands to a gaseous phase and the carbon dioxide gas is drawn into and around the stream of fluid.
10. The method of claim 6 wherein the liquid carbon dioxide is dispensed at a rate which is at least fifty percent of the volumetric flow rate of the fluid issuing from the opening.
11. The method of claim 6 wherein the liquid carbon dioxide is dispensed for a period of at least ten seconds.
12. The method of claim 11 wherein the liquid carbon dioxide is dispensed into the fluid at a volumetric flow rate substantially equal to the flow rate of fluid issuing from the opening.
13. A method of extinguishing a well fire comprising the steps of: refrigerating carbon dioxide to maintain same in a liquid phase; and dispensing liquid carbon dioxide into a stream of fluid flowing out of a well such that fluid issuing from the well has carbon dioxide gas entrained therein
14. A method of preventing oil well fires comprising the steps of, refrigerating a volume of a liquid carbon dioxide under pressure; dispensing liquid carbon dioxide into the well such that the liquid carbon dioxide will expand to a gaseous state and will be entrained in fluid issuing from the well; and releasing the liquid carbon dioxide to ambient atmosphere onto heated objects adjacent the well to cool the heated objects to a temperature below the temperature of combustion of fluid flowing from the well.
15. A method of preventing combustion of a stream of fluid issuing from an opening comprising the steps of: delivering liquid carbon dioxide; dispensing liquid carbon dioxide into the fluid before the fluid issues from the opening such that the carbon dioxide will expand to a gaseous state and will be entrained in the fluid issuing from the opening; dispensing the liquid carbon dioxide to ambient atmosphere from a plurality of positions spaced about the opening; and directing the carbon dioxide toward the stream of fluid issuing from the opening such that the carbon dioxide expands to a gaseous phase and the carbon dioxide gas is drawn into and around the stream of fluid.
16. A method of distinguishing a well fire comprising the steps of: providing a source of liquid carbon dioxide; dispensing liquid carbon dioxide into the well; and maintaining the volumetric flow rate of liquid carbon dioxide at least 50 percent of the volumetric flow rate of fuel flowing from the well for a period of at least 10 seconds.
17. A method of preventing combustion of fuel issuing from a well comprising the steps of: providing a source of liquid carbon dioxide; and dispensing the liquid carbon dioxide into the well adjacent choke manifolds such that the fuel is diluted.
Description:
U. S. Pat. No. 3,561,210 to Ben W. Wiseman, Jr., entitled "Method and Apparatus for Cooling Engine Exhaust Pipes" which issued Feb. 9, 1971 relates specifically to cooling exhaust pipes of engines to prevent ignition of combustible fluids while displacing oxygen adjacent the engines.
BACKGROUND OF THE INVENTION
The possibility of blowout or fire is an ever present danger to personnel and equipment on drilling rigs. Large sums of money are spent for equipment and in training personnel in an effort to prevent blowouts. However, a shortage of trained and experienced workmen, unexpected occurences and widely varying working conditions together with nonstandardized procedures and equipment results in blowouts accompanied by fire.
A well fire is very dangerous to personnel and is extremely costly because valuable equipment is usually damaged beyond repair and large quantities of oil and gas are wasted.
A well fire usually requires the services of highly skilled technicians for bringing the fire under control. These technicians are usually retained on a standby basis at great expense to the driller.
Heretofore noncombustible fluids have been used to fight well fires. However, attempts to provide sufficient quantities of such fluid at a well site had heretofore proved impractical.
In view of the extent of damages normally accompanying a blowout and fire, most drillers expend large amounts of money for insurance premiums to cover liabilities and to cover damage which will be incurred in case of a blowout. This expense is passed on to the consumer in increased prices of gasoline and other petroleum products.
Recent fires at offshore oil and gas wells have cost millions in wasted fuel, not to mention loss of life of workers and marine life, and damage to plant and animal life.
SUMMARY OF INVENTION
I have developed an improved method and apparatus including an extinguishing manifold which may be positioned around an oilwell opening connected to a source of extinguishing fluid, preferably liquid carbon dioxide, wherein the fluid may be dispensed through the manifold when a blowout, leakage or fire occurs at the well head. One gallon of liquid carbon dioxide, for example at 0° F and 300 psi., released to ambient atmosphere, for example at 60°F and 14.7 psi., yields 59.4 cubic feet of carbon dioxide gas. A valve in a line between the manifold and the source of extinguishing fluid may be opened by manipulating any one of a series of switches which are responsive to one or more pre-established occurrences. For example, the valve may be opened manually to prevent fire when leakage is detected or a blowout is suspected. The valve may be opened and closed automatically by a thermostat control, ultraviolet light sensor, or by air pressure sensitive means if leakage or blowout is not detected in time to prevent a fire.
By injection of liquid carbon dioxide through a high pressure kill line into choke manifolds the oil and gas is diluted, increasing the temperature required to initiate combustion; the chemical composition of the oil and gas is modified since the carbon dioxide goes immediately into solution therewith; and excess carbon dioxide gas, when released to ambient atmosphere, displaces oxygen required for combustion.
The primary object of the invention is to provide a method which may be employed with conventional drilling or production equipment to prevent or put out oil well fires wherein liquid carbon dioxide is delivered to the fire and transformed to a gas to provide a sufficient quantity of carbon dioxide to effectively combat a fire or preclude combustion when liquid or gas is released to atmosphere.
A further object of the invention is to provide a method for preventing and putting out oil well fires which may be initiated manually or automatically by unskilled workmen.
A further object of the invention is to provide a method for preventing and putting out oil well fires which minimizes danger to personnel and equipment on the rig or adjacent a well.
A further object of the invention is to provide a method for preventing and putting out oil well fires wherein a plurality of means for dispensing extinguished fluid is employed whereby the malfunction of a single dispensing means will not result in failure of the apparatus.
A still further object of the invention is to provide a method for preventing and extinguishing oil well fires wherein liquid extinguishing fluid is injected into the well casing to be mixed with gas and oil as they are being blown from the well, the extinguishing fluid expanding to a gaseous state to dilute and cool the gas and oil.
A still further object of the invention is to provide a method for preventing oil well fires including cooling the exhaust pipes and exhaust manifolds of engines employed for driving the draw works, pumps and the like as soon as a blowout is detected to prevent ignition of combustible gases and oil which might contact the exhaust pipes.
Other and further objects of the invention will become apparent from the following detailed description and by reference to the accompanying drawings.
DESCRIPTION OF THE DRAWINGS
The enclosed drawings of the preferred embodiment of the invention are provided so that the invention may be better and more fully understood, in which:
FIG. I is a diagrammatic view of structure embodying the present invention mounted in relation to a conventional oil derrick;
FIG. II is a cross sectional view taken along lines II--II of FIG. I illustrating details of construction of an extinguishing manifold;
FIG. III is an enlarged diagrammatic view of a manually operated switch;
FIG. IV is a diagrammatic view of a fusible link;
FIG. V is a schematic diagram of a modified form of the invention; and
FIG. VI illustrates a third form of the invention.
Numeral references are employed to designate like parts throughout the various figures of the drawing.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to FIG. I of the drawing, oil derrick 1 has suitable dispensing means positioned about bore hole 2 for dispensing extinguishing fluid from container 4 to prevent or put out oil well fires.
Natural gas and fuel oil are combustible, but a large amount of oxygen is required before combustion can be accomplished. Carbon dioxide gas is very effective for extinguishing fires because it displaces oxygen, preventing combustion. However, heretofore the use of carbon dioxide gas was not feasible for extinguishing oil well fires because of the large quantities required to do so.
An uncontrolled fire of the type usually encountered at a well fire is extremely difficult to extinguish. There is usually an almost infinite amount of highly combustible fuel and the atmosphere supplies all of the oxygen necessary for combustion. Therefore, two methods of extinguishing a fire are available, controlling the combustion air or controlling the fluid mixture.
As is hereinafter more fully explained, liquid carbon dioxide released adjacent the base of a fire expands to a volume in excess of one hundred times the volume of the liquid and the gaseous carbon dioxide is drawn by convection currents to the flame. Thus, oxygen necessary for combustion is displaced from the fire.
If a sufficient volume of incombustible material is mixed with the oil or gas it will be rendered incombustible because the heating value of the fuel is reduced, increasing the temperature required to ignite the mixture and increasing the quantity of oxygen required to support combustion.
Assuming that fuel is flowing from a well at a rate of 33,000 cubic feet per minute and assuming that the fuel comprises hydrocarbon gas having a molecular composition, requiring 11.35 cubic feet of air per cubic foot of gas for combustion, combustion can be extinguished by displacing the air, or oxygen contained therein, from the fuel. It should be appreciated that the quantity of oxygen to sustain combustion or to permit ignition will vary depending upon the molecular composition of the fuel.
Calculations reveal that approximately seventy barrels of liquid carbon dioxide released at a uniform rate to ambient atmosphere adjacent the stream of the above indicated fuel will provide an atmosphere which will not support combustion for a period of approximately one minute.
Thus, the liquid carbon dioxide is released at a rate approximately 50 percent of the flow rate of fuel. Experimentation has shown that such a fire can be extinguished in less than ten seconds from the time a valve is opened to release the carbon dioxide.
Calculations further reveal that liquid carbon dioxide passing through a given restriction in ten seconds will deliver approximately the same volume of carbon dioxide gas as would be delivered if gaseous carbon dioxide were flowing through the same restriction for 18 minutes.
Seventy barrels of carbon dioxide can be stored at 0°F and 300 psi in a tank approximately 4 feet in diameter and 32 feet long.
Assuming the same conditions set out above, approximately 234 barrels of liquid carbon dioxide delivered into the well, for example, through a kill line, normally employed to fill a well with mud to stop the flow of oil and gas, and mixed with the gas before the gas issues from the well will render the gas incombustible regardless of the quantity of oxygen available for a period of about one minute. This volume of liquid carbon dioxide can be stored in a tank approximately six feet in diameter and 46 feet long and will yield about 740,000 cubic feet of carbon dioxide gas when mixed with fuel at 130°F. The mixture of fuel and carbon dioxide gas issuing from the well would be approximately 95.75 percent carbon dioxide by volume which is non-combustible.
While any suitable extinguishing fluid may be utilized, the following description will be limited to the use of liquid carbon dioxide which is released to form a large volume of carbon dioxide gas.
Container 4 and the contents thereof may be maintained at any desired temperature and pressure by suitable pressurization means such as a pump 4p and refrigeration means 4r comprising a refrigerant compressor, condenser, and evaporator having coils disposed in heat exchange relation with the inside of the container 4.
The critical temperature (the temperature just above which no pressure, no matter how great, can liquify gas) of carbon dioxide is 88°F. The critical pressure (the pressure which just suffices to liquify the gas at the critical temperature) of carbon dioxide is 1,073 pounds per square inch. As temperature is reduced, the pressure required to maintain the carbon dioxide in the liquid state is decreased.
Carbon dioxide is in the liquid state when maintained at 0°F under three hundred pounds per square inch pressure, limits which may be achieved in the field. Under normal operating conditions container 4 should be refrigerated and pressurized to assure that the carbon dioxide is maintained in the liquid phase which facilitates pumping at high velocity through conduits or allows the carbon dioxide to be simply released into the atmosphere.
One end of conduit 6 communicates with the inside of container 4 and the other end thereof is connected to shutoff valve 8.
Shut-off Valve 8 is of conventional construction having a passage extending therethrough which may be opened or closed as desired by manipulating suitable closure means therein.
Valve 8 is connected by conduit 10 to valve 12 which may be opened and closed by suitable actuating means such as a solenoid or motor 14 controlled by a suitable electrical circuit as will be hereinafter more fully explained.
Valve 12 is connected through line 16 to branch lines 18, 20, 22, 24 and 26 for controlling the flow of liquid carbon dioxide to suitable dispensing means which may be positioned in any desired location around the well opening.
In the particular embodiment illustrated in the drawings, lines 18, 20, and 22 are connected through a suitable coupling to conduit 16 and the other ends thereof are connected to manifolds 30, 32 and 34 respectively.
Manifold 30 is anchored to the ground underneath the floor 1a of oil derrick 1. Manifold 32 is anchored to the upper side of the derrick floor. Manifold 34 is positioned in the derrick 1 above the floor, preferably around the first girth 1c of the derrick.
Manifolds 30, 32 and 34 are of identical construction. A plan view of manifold 30, illustrated in FIG. II, consists of tubular members 35 having nozzles 36 disposed on the inner side thereof directed radially toward the well bore 2. Tubular members 35 of manifold 30 are connected through a suitable connector to line 18 which is in turn connected through a connector to conduit 16.
It should be readily apparent that carbon dioxide will be dispensed from nozzles 36 of manifolds 30, 32 and 34 when valve 12 is opened.
Valves 18a, 20a and 22a, disposed in lines 18, 20, and 22 respectively, will normally be in the open position. However, if it is desired that carbon dioxide not be dispensed from one or more of the manifolds, the valves may be manipulated as desired.
To stop the flow of oil or gas from a well drilling mud is pumped through a kill line to force the oil and gas back into the well. The kill line 2b communicates with the inside of intermediate casing 2c which extends into surface casing 2a. Blowout preventers 2d are mounted on the intermediate casing 2c to control flow and pressure.
One end of line 26 is connected to kill line 2b and the other end thereof is connected to the high pressure side of a gasoline driven pump 26a. The suction side of pump 26a is connected through line 26b, gate valve 26c and line 26d with conduit 10.
In case of blowout high velocity fluids will be flowing through casing 2c. When valve 26c is opened, carbon dioxide will be drawn through line 26 and mixed with the fluids in casing 2c as a result of the well known principles commonly referred to as venturi effect or may be forced thereinto by pump 26a depending upon pressures.
As hereinbefore noted it is contemplated that sufficient quantities of carbon dioxide being provided through conduit 26 for mixing with natural gas or oil to render same incombustible. It is contemplated that conduit 26 be connected to the kill line of the well through which fluid, such as drilling mud, may be pumped for controlling pressure in wells.
It should be appreciated that if the volume or capacity of container 4 is not sufficient to maintain safe conditions at the well head, a plurality of containers may be employed to direct carbon dioxide through valve 8 into line 26.
A blowout may not ignite if the gas and oil is not exposed to open flame, sparks or hot objects. The exhaust pipes on engines 38 which provide power to drawworks 40 reach very high temperatures and may ignite oil which blows from the well.
Line 24 is connected to pipes 42 which extend around a portion of exhaust pipe 39 of each engine 38 whereby opening valve 12 will cause carbon dioxide to be dispensed through conduit 16 and line 24 into pipes 42 around each exhaust pipe 39 to chill same instantaneously. If valve 12 is opened before a fire is started, cooling exhaust pipes 39 may prevent combustion.
An electrical circuit comprises blowout condition sensing and detecting means for automatically monitoring conditions adjacent the exterior of casing has heat sensing means 72 and 80; and is capable of being energized manually and is electrically connected to motor 14. In the particular embodiment illustrated in the drawing, direct current power supplies 46 and 48 are utilized for energizing circuits 56 and 54 because electricity is usually turned off as soon as a blowout is detected to prevent fire. A conventional trickle charger 50 may be employed to assure that batteries 46 and 48 are fully charged at all times.
An electromagnetically operated single pole relay 52 or other current responsive switching means is utilized to close an energizing circuit 54 when the sensing circuit 56 is broken manually or by sensing means 72, 78, 80 as will be hereinafter more fully explained.
The energizing circuit consists of a line 60 having one end thereof connected to the windings of motor 14 and the other end thereof connected to the negative terminal of battery 48 is connected through line 62 to contact 52a of relay 52. Contact 52b of relay 52 is connected through line 64 to the opposite side of the windings of motor 14 thereby completing a loop forming the energizing circuit 54.
Pole 52c of relay 52 is urged toward contact 52a as by spring 52d causing energizing circuit 54 to be completed.
A coil 52e of relay 52 is disposed in a sensing circuit 56.
One end of coil 52e is connected through line 70 to suitable heat sensing means such as thermostatically controlled switch 72. Switch 72 may be of any conventional design for example, a bimetallic strip positioned to open the contacts of the switch when the temperature reaches a predetermined value. Thermostatically controlled switch 72 may be positioned at any desired location for sensing excessive temperature at or near the opening of bore hole 2.
Thermostatically controlled switch 72 is connected in series with push button switch 74, best illustrated in FIG. III, through a line 73. Switch 74 is a conventional single pole single throw switch and consists of fixed contacts 74a and 74b which are normally connected by moveable pole 74c. When button 74e is pressed, pole 74c is moved away from the contact 74b to break the sensing circuit. Switch 74 may consist of any suitable switching medium.
Contact 74b of switch 74 is connected through line 76 to a suitable pressure actuated switch 78. The pressure actuated switch 78 is of conventional construction and is of the type normally employed to break a circuit when air pressure or sound at a predetermined level is detected. Switch 78 will be opened by sound waves or air pressure if an exceptionally loud noise, such as an explosion, is sensed. However, switch 78 will not be opened by noises normally accompanying drilling operations such dropping of tools and the like.
Switch 78 is connected in series through line 78a to ultraviolet light sensor 79 which is connected in series through line 79a with fusible link 80, best illustrated in FIG. IV of the drawing. The sensor 79 is preferably a Model C7037A available from Honeywell, Inc., Apparatus Controls Divsion, Minneapolis, Minnesota.
Fusible link 80 is of conventional construction and has a wire therein which will melt at a predetermined temperature level thereby opening the circuit.
The other side of fusible link 80 is connected through line 82 to the negative terminal of battery 46. The loop of the sensing circuit is completed by line 84 which connects the positive terminal of battery 46 with the coil 52e of relay 52.
When current is flowing through sensing circuit 56 coil 52e of relay 52 is energized and armature 52f causes pole 52c to disengage contact 52a holding energizing circuit 54 open.
From the foregoing, it should be readily apparent that motor 14 is inoperative as long as energizing circuit 54 is broken by current flowing in the sensing circuit 56 through coil 52e of relay 52. However, since thermostatically controlled switch 72, manually operated switch 74, sound detecting switch 78, ultraviolet sensor, and fusible link 80 are connected in series in the sensing circuit 56, opening any one of these switches will break the sensing circuit 56, causing pole 52c of relay 52 to move into engagement with contact 52a, thereby closing energizing circuit 54. When energizing circuit 54 is closed, motor 14 will open valve 12, causing carbon dioxide to flow from container 4 through line 16 to the various dispensing devices as hereinbefore described.
DESCRIPTION OF A SECOND EMBODIMENT
A modified arrangement of the electrical circuit 54' for energizing motor 14 is illustrated in FIG. V. The modified circuit includes thermostatically controlled switches 72' and 80', manually operated switch 74' and pressure responsive switch 78' connected in parallel, each being normally open. Closing any one of the switches 72', 74', 78' or 80' completes a circuit from battery 48' through the closed switch to motor 14 causing valve 12 to be opened.
It should be noted, that breaking a wire, as by an explosion, in the modified circuit shown in FIG. V opens the circuit de-energizing motor 14. In the first embodiment, FIG. I, the energizing circuit 54 may be located a safe distance from the well and breaking a line in the sensing circuit 56 will not de-energize the motor 14.
A bypass line 85 connects conduit 10 with conduit 16 routing carbon dioxide around valve 12. A manually controlled valve 86, which is normally closed, may be opened as an alternative means for releasing carbon dioxide gas. It should be readily apparent that a malfunction of the electrical system employed for opening valve 12 will not effect the operation of manually operated valve 86.
DESCRIPTION OF A THIRD EMBODIMENT
Oil well fires on off shore rigs creates a particularly hazardous condition because large numbers of workmen are concentrated in a small area on a platform above the surface of water. The primary consideration of workmen when it is discovered that a blow out is eminent is to clear the platform as quickly as possible. Workmen load into boats or "survival capsules" to escape the danger of the fire. Most survival capsules are fire resistant and completely enclosed to prevent suffocation of workmen.
The preferred embodiment of the present invention shown in FIGS. I-IV and the second embodiment shown in FIG. V are adaptable for use on an off shore rig as shown in FIG. VI of the drawing. Oil derrick 101 is mounted in conventional manner on a platform 101a which is secured to support legs 101b which extends downwardly from the said platform having lower ends anchored in the earth on the ocean floor.
Since space on the surface of platform 101a is limited and very expensive to construct, container 104 having extinguish-fluid therein is mounted on one of the legs 101b of the platform. Positioning container 104 on a support leg 101b below water line 101c allows installation of the invention hereinbefore described on the off shore rig without interfering with normal operating procedures because said container does not occupy any space upon the surface of drilling platform 101a. It should also be noted that container 104 may be submerged to a depth so as not to interfere with watercraft which are operated below platform 101a. The weight and buoyancy of container 104 may be substantially equalized if it is deemed expedient to do so. Any suitable attachment means may be employed for securing container 104 to support leg 101b, such as bands 104a, retainer ledges 104b and braces 104c.
Conduit 106 communicates with the inside of container 104 and the other end thereof is connected to shutoff valve 8. Manifolds 30, 32 and 34 are positioned adjacent casing 102a as hereinbefore described in the Description of the Preferred Embodiment of the Invention. However, manifold 30' may be secured to the lower surface of platform 101a.
From the foregoing detailed description of suitable embodiments of my invention, it should be readily apparent that very simple structure is employed for carrying out the objects of my invention. No training is necessary to use the device and it may be employed before before a blowout occurs to prevent a fire or after a fire has started to extinguish the fire. Carbon dioxide gas may be turned off by merely closing manually operated valve 8.
In addition to the advantages hereinbefore set out, it should be readily appreciated that the carbon dioxide gas dispensed from manifolds 30, 32 and 34 and venturi 27 will be blown by the wind in the same direction that the oil and gas is being blown. This will cause carbon dioxide gas to encompass and smother the flame even though the wind is blowing. It should also be readily apparent that the cold carbon dioxide gas will tend to cool metal objects on the derrick to prevent re-ignition of oil and gas coming in contact therewith. It should also be noted that the heat sensing means, thermostat control switch 72 and fusible link 80, are positioned at various locations in the derrick to assure that the sensing circuit 56 will be broken in case of fire.
Releasing the carbon dioxide gas at various levels below and above the opening of the well casing will assure that the carbon dioxide gas will be drawn into and encompass a fire and will mix with the oil as a result of convection currents and venturi effect. The carbon dioxide gas does not burn, nor does it support combustion, and being heavier than air, it forms a blanket around the well opening.
BACKGROUND OF THE INVENTION
The possibility of blowout or fire is an ever present danger to personnel and equipment on drilling rigs. Large sums of money are spent for equipment and in training personnel in an effort to prevent blowouts. However, a shortage of trained and experienced workmen, unexpected occurences and widely varying working conditions together with nonstandardized procedures and equipment results in blowouts accompanied by fire.
A well fire is very dangerous to personnel and is extremely costly because valuable equipment is usually damaged beyond repair and large quantities of oil and gas are wasted.
A well fire usually requires the services of highly skilled technicians for bringing the fire under control. These technicians are usually retained on a standby basis at great expense to the driller.
Heretofore noncombustible fluids have been used to fight well fires. However, attempts to provide sufficient quantities of such fluid at a well site had heretofore proved impractical.
In view of the extent of damages normally accompanying a blowout and fire, most drillers expend large amounts of money for insurance premiums to cover liabilities and to cover damage which will be incurred in case of a blowout. This expense is passed on to the consumer in increased prices of gasoline and other petroleum products.
Recent fires at offshore oil and gas wells have cost millions in wasted fuel, not to mention loss of life of workers and marine life, and damage to plant and animal life.
SUMMARY OF INVENTION
I have developed an improved method and apparatus including an extinguishing manifold which may be positioned around an oilwell opening connected to a source of extinguishing fluid, preferably liquid carbon dioxide, wherein the fluid may be dispensed through the manifold when a blowout, leakage or fire occurs at the well head. One gallon of liquid carbon dioxide, for example at 0° F and 300 psi., released to ambient atmosphere, for example at 60°F and 14.7 psi., yields 59.4 cubic feet of carbon dioxide gas. A valve in a line between the manifold and the source of extinguishing fluid may be opened by manipulating any one of a series of switches which are responsive to one or more pre-established occurrences. For example, the valve may be opened manually to prevent fire when leakage is detected or a blowout is suspected. The valve may be opened and closed automatically by a thermostat control, ultraviolet light sensor, or by air pressure sensitive means if leakage or blowout is not detected in time to prevent a fire.
By injection of liquid carbon dioxide through a high pressure kill line into choke manifolds the oil and gas is diluted, increasing the temperature required to initiate combustion; the chemical composition of the oil and gas is modified since the carbon dioxide goes immediately into solution therewith; and excess carbon dioxide gas, when released to ambient atmosphere, displaces oxygen required for combustion.
The primary object of the invention is to provide a method which may be employed with conventional drilling or production equipment to prevent or put out oil well fires wherein liquid carbon dioxide is delivered to the fire and transformed to a gas to provide a sufficient quantity of carbon dioxide to effectively combat a fire or preclude combustion when liquid or gas is released to atmosphere.
A further object of the invention is to provide a method for preventing and putting out oil well fires which may be initiated manually or automatically by unskilled workmen.
A further object of the invention is to provide a method for preventing and putting out oil well fires which minimizes danger to personnel and equipment on the rig or adjacent a well.
A further object of the invention is to provide a method for preventing and putting out oil well fires wherein a plurality of means for dispensing extinguished fluid is employed whereby the malfunction of a single dispensing means will not result in failure of the apparatus.
A still further object of the invention is to provide a method for preventing and extinguishing oil well fires wherein liquid extinguishing fluid is injected into the well casing to be mixed with gas and oil as they are being blown from the well, the extinguishing fluid expanding to a gaseous state to dilute and cool the gas and oil.
A still further object of the invention is to provide a method for preventing oil well fires including cooling the exhaust pipes and exhaust manifolds of engines employed for driving the draw works, pumps and the like as soon as a blowout is detected to prevent ignition of combustible gases and oil which might contact the exhaust pipes.
Other and further objects of the invention will become apparent from the following detailed description and by reference to the accompanying drawings.
DESCRIPTION OF THE DRAWINGS
The enclosed drawings of the preferred embodiment of the invention are provided so that the invention may be better and more fully understood, in which:
FIG. I is a diagrammatic view of structure embodying the present invention mounted in relation to a conventional oil derrick;
FIG. II is a cross sectional view taken along lines II--II of FIG. I illustrating details of construction of an extinguishing manifold;
FIG. III is an enlarged diagrammatic view of a manually operated switch;
FIG. IV is a diagrammatic view of a fusible link;
FIG. V is a schematic diagram of a modified form of the invention; and
FIG. VI illustrates a third form of the invention.
Numeral references are employed to designate like parts throughout the various figures of the drawing.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to FIG. I of the drawing, oil derrick 1 has suitable dispensing means positioned about bore hole 2 for dispensing extinguishing fluid from container 4 to prevent or put out oil well fires.
Natural gas and fuel oil are combustible, but a large amount of oxygen is required before combustion can be accomplished. Carbon dioxide gas is very effective for extinguishing fires because it displaces oxygen, preventing combustion. However, heretofore the use of carbon dioxide gas was not feasible for extinguishing oil well fires because of the large quantities required to do so.
An uncontrolled fire of the type usually encountered at a well fire is extremely difficult to extinguish. There is usually an almost infinite amount of highly combustible fuel and the atmosphere supplies all of the oxygen necessary for combustion. Therefore, two methods of extinguishing a fire are available, controlling the combustion air or controlling the fluid mixture.
As is hereinafter more fully explained, liquid carbon dioxide released adjacent the base of a fire expands to a volume in excess of one hundred times the volume of the liquid and the gaseous carbon dioxide is drawn by convection currents to the flame. Thus, oxygen necessary for combustion is displaced from the fire.
If a sufficient volume of incombustible material is mixed with the oil or gas it will be rendered incombustible because the heating value of the fuel is reduced, increasing the temperature required to ignite the mixture and increasing the quantity of oxygen required to support combustion.
Assuming that fuel is flowing from a well at a rate of 33,000 cubic feet per minute and assuming that the fuel comprises hydrocarbon gas having a molecular composition, requiring 11.35 cubic feet of air per cubic foot of gas for combustion, combustion can be extinguished by displacing the air, or oxygen contained therein, from the fuel. It should be appreciated that the quantity of oxygen to sustain combustion or to permit ignition will vary depending upon the molecular composition of the fuel.
Calculations reveal that approximately seventy barrels of liquid carbon dioxide released at a uniform rate to ambient atmosphere adjacent the stream of the above indicated fuel will provide an atmosphere which will not support combustion for a period of approximately one minute.
Thus, the liquid carbon dioxide is released at a rate approximately 50 percent of the flow rate of fuel. Experimentation has shown that such a fire can be extinguished in less than ten seconds from the time a valve is opened to release the carbon dioxide.
Calculations further reveal that liquid carbon dioxide passing through a given restriction in ten seconds will deliver approximately the same volume of carbon dioxide gas as would be delivered if gaseous carbon dioxide were flowing through the same restriction for 18 minutes.
Seventy barrels of carbon dioxide can be stored at 0°F and 300 psi in a tank approximately 4 feet in diameter and 32 feet long.
Assuming the same conditions set out above, approximately 234 barrels of liquid carbon dioxide delivered into the well, for example, through a kill line, normally employed to fill a well with mud to stop the flow of oil and gas, and mixed with the gas before the gas issues from the well will render the gas incombustible regardless of the quantity of oxygen available for a period of about one minute. This volume of liquid carbon dioxide can be stored in a tank approximately six feet in diameter and 46 feet long and will yield about 740,000 cubic feet of carbon dioxide gas when mixed with fuel at 130°F. The mixture of fuel and carbon dioxide gas issuing from the well would be approximately 95.75 percent carbon dioxide by volume which is non-combustible.
While any suitable extinguishing fluid may be utilized, the following description will be limited to the use of liquid carbon dioxide which is released to form a large volume of carbon dioxide gas.
Container 4 and the contents thereof may be maintained at any desired temperature and pressure by suitable pressurization means such as a pump 4p and refrigeration means 4r comprising a refrigerant compressor, condenser, and evaporator having coils disposed in heat exchange relation with the inside of the container 4.
The critical temperature (the temperature just above which no pressure, no matter how great, can liquify gas) of carbon dioxide is 88°F. The critical pressure (the pressure which just suffices to liquify the gas at the critical temperature) of carbon dioxide is 1,073 pounds per square inch. As temperature is reduced, the pressure required to maintain the carbon dioxide in the liquid state is decreased.
Carbon dioxide is in the liquid state when maintained at 0°F under three hundred pounds per square inch pressure, limits which may be achieved in the field. Under normal operating conditions container 4 should be refrigerated and pressurized to assure that the carbon dioxide is maintained in the liquid phase which facilitates pumping at high velocity through conduits or allows the carbon dioxide to be simply released into the atmosphere.
One end of conduit 6 communicates with the inside of container 4 and the other end thereof is connected to shutoff valve 8.
Shut-off Valve 8 is of conventional construction having a passage extending therethrough which may be opened or closed as desired by manipulating suitable closure means therein.
Valve 8 is connected by conduit 10 to valve 12 which may be opened and closed by suitable actuating means such as a solenoid or motor 14 controlled by a suitable electrical circuit as will be hereinafter more fully explained.
Valve 12 is connected through line 16 to branch lines 18, 20, 22, 24 and 26 for controlling the flow of liquid carbon dioxide to suitable dispensing means which may be positioned in any desired location around the well opening.
In the particular embodiment illustrated in the drawings, lines 18, 20, and 22 are connected through a suitable coupling to conduit 16 and the other ends thereof are connected to manifolds 30, 32 and 34 respectively.
Manifold 30 is anchored to the ground underneath the floor 1a of oil derrick 1. Manifold 32 is anchored to the upper side of the derrick floor. Manifold 34 is positioned in the derrick 1 above the floor, preferably around the first girth 1c of the derrick.
Manifolds 30, 32 and 34 are of identical construction. A plan view of manifold 30, illustrated in FIG. II, consists of tubular members 35 having nozzles 36 disposed on the inner side thereof directed radially toward the well bore 2. Tubular members 35 of manifold 30 are connected through a suitable connector to line 18 which is in turn connected through a connector to conduit 16.
It should be readily apparent that carbon dioxide will be dispensed from nozzles 36 of manifolds 30, 32 and 34 when valve 12 is opened.
Valves 18a, 20a and 22a, disposed in lines 18, 20, and 22 respectively, will normally be in the open position. However, if it is desired that carbon dioxide not be dispensed from one or more of the manifolds, the valves may be manipulated as desired.
To stop the flow of oil or gas from a well drilling mud is pumped through a kill line to force the oil and gas back into the well. The kill line 2b communicates with the inside of intermediate casing 2c which extends into surface casing 2a. Blowout preventers 2d are mounted on the intermediate casing 2c to control flow and pressure.
One end of line 26 is connected to kill line 2b and the other end thereof is connected to the high pressure side of a gasoline driven pump 26a. The suction side of pump 26a is connected through line 26b, gate valve 26c and line 26d with conduit 10.
In case of blowout high velocity fluids will be flowing through casing 2c. When valve 26c is opened, carbon dioxide will be drawn through line 26 and mixed with the fluids in casing 2c as a result of the well known principles commonly referred to as venturi effect or may be forced thereinto by pump 26a depending upon pressures.
As hereinbefore noted it is contemplated that sufficient quantities of carbon dioxide being provided through conduit 26 for mixing with natural gas or oil to render same incombustible. It is contemplated that conduit 26 be connected to the kill line of the well through which fluid, such as drilling mud, may be pumped for controlling pressure in wells.
It should be appreciated that if the volume or capacity of container 4 is not sufficient to maintain safe conditions at the well head, a plurality of containers may be employed to direct carbon dioxide through valve 8 into line 26.
A blowout may not ignite if the gas and oil is not exposed to open flame, sparks or hot objects. The exhaust pipes on engines 38 which provide power to drawworks 40 reach very high temperatures and may ignite oil which blows from the well.
Line 24 is connected to pipes 42 which extend around a portion of exhaust pipe 39 of each engine 38 whereby opening valve 12 will cause carbon dioxide to be dispensed through conduit 16 and line 24 into pipes 42 around each exhaust pipe 39 to chill same instantaneously. If valve 12 is opened before a fire is started, cooling exhaust pipes 39 may prevent combustion.
An electrical circuit comprises blowout condition sensing and detecting means for automatically monitoring conditions adjacent the exterior of casing has heat sensing means 72 and 80; and is capable of being energized manually and is electrically connected to motor 14. In the particular embodiment illustrated in the drawing, direct current power supplies 46 and 48 are utilized for energizing circuits 56 and 54 because electricity is usually turned off as soon as a blowout is detected to prevent fire. A conventional trickle charger 50 may be employed to assure that batteries 46 and 48 are fully charged at all times.
An electromagnetically operated single pole relay 52 or other current responsive switching means is utilized to close an energizing circuit 54 when the sensing circuit 56 is broken manually or by sensing means 72, 78, 80 as will be hereinafter more fully explained.
The energizing circuit consists of a line 60 having one end thereof connected to the windings of motor 14 and the other end thereof connected to the negative terminal of battery 48 is connected through line 62 to contact 52a of relay 52. Contact 52b of relay 52 is connected through line 64 to the opposite side of the windings of motor 14 thereby completing a loop forming the energizing circuit 54.
Pole 52c of relay 52 is urged toward contact 52a as by spring 52d causing energizing circuit 54 to be completed.
A coil 52e of relay 52 is disposed in a sensing circuit 56.
One end of coil 52e is connected through line 70 to suitable heat sensing means such as thermostatically controlled switch 72. Switch 72 may be of any conventional design for example, a bimetallic strip positioned to open the contacts of the switch when the temperature reaches a predetermined value. Thermostatically controlled switch 72 may be positioned at any desired location for sensing excessive temperature at or near the opening of bore hole 2.
Thermostatically controlled switch 72 is connected in series with push button switch 74, best illustrated in FIG. III, through a line 73. Switch 74 is a conventional single pole single throw switch and consists of fixed contacts 74a and 74b which are normally connected by moveable pole 74c. When button 74e is pressed, pole 74c is moved away from the contact 74b to break the sensing circuit. Switch 74 may consist of any suitable switching medium.
Contact 74b of switch 74 is connected through line 76 to a suitable pressure actuated switch 78. The pressure actuated switch 78 is of conventional construction and is of the type normally employed to break a circuit when air pressure or sound at a predetermined level is detected. Switch 78 will be opened by sound waves or air pressure if an exceptionally loud noise, such as an explosion, is sensed. However, switch 78 will not be opened by noises normally accompanying drilling operations such dropping of tools and the like.
Switch 78 is connected in series through line 78a to ultraviolet light sensor 79 which is connected in series through line 79a with fusible link 80, best illustrated in FIG. IV of the drawing. The sensor 79 is preferably a Model C7037A available from Honeywell, Inc., Apparatus Controls Divsion, Minneapolis, Minnesota.
Fusible link 80 is of conventional construction and has a wire therein which will melt at a predetermined temperature level thereby opening the circuit.
The other side of fusible link 80 is connected through line 82 to the negative terminal of battery 46. The loop of the sensing circuit is completed by line 84 which connects the positive terminal of battery 46 with the coil 52e of relay 52.
When current is flowing through sensing circuit 56 coil 52e of relay 52 is energized and armature 52f causes pole 52c to disengage contact 52a holding energizing circuit 54 open.
From the foregoing, it should be readily apparent that motor 14 is inoperative as long as energizing circuit 54 is broken by current flowing in the sensing circuit 56 through coil 52e of relay 52. However, since thermostatically controlled switch 72, manually operated switch 74, sound detecting switch 78, ultraviolet sensor, and fusible link 80 are connected in series in the sensing circuit 56, opening any one of these switches will break the sensing circuit 56, causing pole 52c of relay 52 to move into engagement with contact 52a, thereby closing energizing circuit 54. When energizing circuit 54 is closed, motor 14 will open valve 12, causing carbon dioxide to flow from container 4 through line 16 to the various dispensing devices as hereinbefore described.
DESCRIPTION OF A SECOND EMBODIMENT
A modified arrangement of the electrical circuit 54' for energizing motor 14 is illustrated in FIG. V. The modified circuit includes thermostatically controlled switches 72' and 80', manually operated switch 74' and pressure responsive switch 78' connected in parallel, each being normally open. Closing any one of the switches 72', 74', 78' or 80' completes a circuit from battery 48' through the closed switch to motor 14 causing valve 12 to be opened.
It should be noted, that breaking a wire, as by an explosion, in the modified circuit shown in FIG. V opens the circuit de-energizing motor 14. In the first embodiment, FIG. I, the energizing circuit 54 may be located a safe distance from the well and breaking a line in the sensing circuit 56 will not de-energize the motor 14.
A bypass line 85 connects conduit 10 with conduit 16 routing carbon dioxide around valve 12. A manually controlled valve 86, which is normally closed, may be opened as an alternative means for releasing carbon dioxide gas. It should be readily apparent that a malfunction of the electrical system employed for opening valve 12 will not effect the operation of manually operated valve 86.
DESCRIPTION OF A THIRD EMBODIMENT
Oil well fires on off shore rigs creates a particularly hazardous condition because large numbers of workmen are concentrated in a small area on a platform above the surface of water. The primary consideration of workmen when it is discovered that a blow out is eminent is to clear the platform as quickly as possible. Workmen load into boats or "survival capsules" to escape the danger of the fire. Most survival capsules are fire resistant and completely enclosed to prevent suffocation of workmen.
The preferred embodiment of the present invention shown in FIGS. I-IV and the second embodiment shown in FIG. V are adaptable for use on an off shore rig as shown in FIG. VI of the drawing. Oil derrick 101 is mounted in conventional manner on a platform 101a which is secured to support legs 101b which extends downwardly from the said platform having lower ends anchored in the earth on the ocean floor.
Since space on the surface of platform 101a is limited and very expensive to construct, container 104 having extinguish-fluid therein is mounted on one of the legs 101b of the platform. Positioning container 104 on a support leg 101b below water line 101c allows installation of the invention hereinbefore described on the off shore rig without interfering with normal operating procedures because said container does not occupy any space upon the surface of drilling platform 101a. It should also be noted that container 104 may be submerged to a depth so as not to interfere with watercraft which are operated below platform 101a. The weight and buoyancy of container 104 may be substantially equalized if it is deemed expedient to do so. Any suitable attachment means may be employed for securing container 104 to support leg 101b, such as bands 104a, retainer ledges 104b and braces 104c.
Conduit 106 communicates with the inside of container 104 and the other end thereof is connected to shutoff valve 8. Manifolds 30, 32 and 34 are positioned adjacent casing 102a as hereinbefore described in the Description of the Preferred Embodiment of the Invention. However, manifold 30' may be secured to the lower surface of platform 101a.
From the foregoing detailed description of suitable embodiments of my invention, it should be readily apparent that very simple structure is employed for carrying out the objects of my invention. No training is necessary to use the device and it may be employed before before a blowout occurs to prevent a fire or after a fire has started to extinguish the fire. Carbon dioxide gas may be turned off by merely closing manually operated valve 8.
In addition to the advantages hereinbefore set out, it should be readily appreciated that the carbon dioxide gas dispensed from manifolds 30, 32 and 34 and venturi 27 will be blown by the wind in the same direction that the oil and gas is being blown. This will cause carbon dioxide gas to encompass and smother the flame even though the wind is blowing. It should also be readily apparent that the cold carbon dioxide gas will tend to cool metal objects on the derrick to prevent re-ignition of oil and gas coming in contact therewith. It should also be noted that the heat sensing means, thermostat control switch 72 and fusible link 80, are positioned at various locations in the derrick to assure that the sensing circuit 56 will be broken in case of fire.
Releasing the carbon dioxide gas at various levels below and above the opening of the well casing will assure that the carbon dioxide gas will be drawn into and encompass a fire and will mix with the oil as a result of convection currents and venturi effect. The carbon dioxide gas does not burn, nor does it support combustion, and being heavier than air, it forms a blanket around the well opening.