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METHOD FOR SUPPRESSING OIL WELL FIRES BACKGROUND OF THE INVENTION Oil wells contain and produce a liquid flow mixture

5 comprising varying amounts of highly flammable gaseous products, especially methane and derivative low flash point, low molecular weight gasses of extremely high vapor pressure, together with quantities of petroleum liquids of varying densities and weights having higher flash points but also having much higher heats of

10 combustion. Such a mixture, combining an entrapped low flash point gas within a high pressure stream of a higher flash point, higher burning rate liquid, is susceptible to easy ignition or re-ignition and also burns with excessive heat. For this reason, the suppression of oil well fires has been a particular problem

15 and has resulted in numerous alternate approaches.

One such series of approaches is the injection of a material into the oil well or into the oil well fire so as to quench the flames. The most common such method envisions the injection of water or a similar thermal blanketing fire

20 extinguishing liquid into the base of the flames or into the oil well drill string below the point of ignition.

Such liquid injection is intended to quench the fire by means of heat absorption, as by vaporization of the liquid. This is especially true in the case of water. Such heat absorption,

25 however, in practice has proven incapable of lowering the entire stream below the flash point of entrapped methane. In a typical oil well blowout, friction heating alone at the point of escape of the entrapped gas is sufficient to raise methane past its flash point, negating any beneficial effects of the subsequent

30 vaporization of the water. The excess heat produced by the methane is sufficient to ignite the oil stream, and water injection has generally been determined to be a failure unless such a sufficient quantity of water is entered at a high pressure that it actually interrupts the flow of the flammable liquids from the well.

For this reason it is found that a second alternate

injection envisions injecting a very high molecular weight liquid, such as a standard drilling mud, into the drill string so as to, in fact, quench to flow of the flammable liquids by overcoming the pressure head of the flammable liquids. This method is effective provided that the flow pressure of the flammable liquids is sufficiently low that it is possible to overcome it with the existing pumping apparatus. Since the fluid within a drill string is highly abrasive, and since the fire in an oil well fire is extremely destructive, is is generally found that the necessary equipments and pumps do not survive the initial explosion and fire or the subsequent wear from the out-of-control blowout, and thus there are common conditions found where there is insufficient pumping capacity to, in fact, back pump the drill string with mud. SUMMARY OF THE INVENTION

The essence of this invention is to provide a method of extinguishing an oil well fire by injecting, into the drill string, at the Blow Out Preventor (B.O.P.), and below the cutoff rams, a mixture of a high vapor pressure and a low vapor pressure halogeπated alkane so as to introduce a fire suppressing gas at a vapor pressure which is related to the vapor pressure of the more flammable low flash point gasses entrapped within an oil well spray, so as to effectively suppress the ignition of the low flash point materials, thus effectively quenching the primary source of ignition, re-ignition, and fire within an oil well blowout.

It is therefore the essence of the invention that a mixture of suitable vapor pressure Halons is injected into or beneath the B.O.P. of an oil well during a blowout or a fire condition. The Halons, being a selected vapor pressure mixture, selectively vaporize at the point of and in conjunction with the vaporization of the entrapped natural gas and other low flash point gasses within the overall spray of fluid from the drill string. The fire suppressing Halon is thus preferentially mixed with the low flash point natural gasses which provide the primary ignition source in an oil well fire and thereby provides

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maximal fire suppression effect during the point at which the natural gas would normally expected to be ignited. This includes two Critical points within the uncontrolled spray of liquid from an oil well: the first point is when the liquid passes the rams and chocks above the B.O.P. where the combined effects of friction and high pressure flow produces significant heating effect, generally raising the flow of the stream above the ignition point of methane. The second point is encountered during the free spray of the mixed gas and liquid petroleum on the heated residue of the oil well, which includes material that has been heated by previous fire to well above the ignition point of the vapors escaping from both the petroleum and the gas.

It is thus an object of this invention to provide a method of suppressing a fire in a standard oil well.

It is a further object of this invention to provide a method of suppressing re-ignition within an oil well fire once it has been initially quenched.

It is further an object of this invention to provide a fire suppression within an oil well which preferentially suppresses ignition and re-ignition of the more flammable components of the overall oil well fluid spray.

This and other objects of the invention can be ascertained from the detailed description of the preferred embodiment which follows

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional schematic of an oil well head showing an injection means and injection point, according to the method of the current invention. Figure 2 is a schematic of the auxiliary pumping network.

Figure 3 is a labeled schematic showing the interconnection of the preferred embodiment of the invention DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring to Figure 1 the method is shown as utilizing a bank 2 containing a liquified mixture of a high vapor pressure

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halogenated alkane and a low vapor pressure halogenated alkane. In a preferred embodiment of the invention, these are respectively Halon 1301 and Halon 1211.

Providing such a mixture of a high and a low vapor pressure halogenated alkane allows one to form a uniform agent mixture having all the desirable fire suppression properties of the halogenated alkanes, but simultaneously allowing one to establish an overall system vapor pressure at which the agent remains a liquid or vaporizes by varying the percentages of the Halon 1301 and the Halon 1211.

In the preferred embodiment of the invention, it has been found that a mixture of 35 percent Halon 1301, the high pressure component, and 65 percent Halon 1211 provides a mixture with a vapor pressure well adapted to the fire suppression method hereinafter outlined.

In as much as the Halon mixture is maintained at a high vapor pressure, it is stored and pumpe.d as a liquid, and thus may be readily pumped by standard high pressure liquid pumps 4 against the found pressure within the overall injection system 6 to be hereinafter described.

The mixture is injected through control valves 8 into the "Kill Line" valving system 10 in an existing oil well, and thence may be injected under control immediately beneath the B.O.P.14. This injection point which is in the form of a injection orifice 16, is essentially perpendicular to the directional flow of the liquids within the drill string, and provides a venturi effect during high flow rates within the drill string such as would be encountered during a blow out. The venturi effect aids in the establishment of a pressure injection differential and also in the dispersal of the fire suppression agent into the flow stream beneath the B.O.P. 14.

Referring to Figure 2, the method is shown to include an auxiliary section reservoir 18 of Halon 1301 and Halon 1211, a standard high-pressure triplex pump 4, and a suitable valve system 8 capable of isolation of said pump 4 from the aforementioned system 6 shown in Figure 1.

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In the event of the failure of a diverter system 10 to provide substantial assurance against the development of an excessive back pressure in the drill string and the drill string annulus, the triplex pump 4 may be utilized in order to overcome back pressure and allow injection of the extinguishing mixture. It is found that at this point in the stream of flow during a blowout that the liquid within the B.O.P. 14 comprises a non-homogeneous mixture of entrapped gas, varying weights of petroleum products in liquid form, and various abrasive components such as sand, drilling mud residue and the like. During a blowout condition, as would be encountered in an oil well fire or where there was risk of an oil well fire, it will be found that this fluid is moving at a very high speed.

Immediately above the point of injection the fluid passes, at this high speed, through the B.O.P. 14 or blowout preventor. The blowout preventor as known in the art is intended to prevent this flow of fluid and therefore may be assumed to have failed in some mariner when ^' the danger of oil well fire exists. Likewise there is provided either as a component to B.O.P. 14 or as a separate component at least one pair of cutoff jaws (not shown) which are power jaws designed to close, by crushing, the casing and the drill string in an oil well so as to cut off fluid flow. Again, it is to be assumed that this mechanism has in some form failed, else there would be no danger of an oil well fire and no need for the method of the current invention.

In operation therefore, when an accident has occurred to the oilwell, including the B.O.P. 14 or the cutoff jaws, it is found that the oil well fluid is being spewed from drill string into the air at an extremely high rate of speed. The frictional effects of the passage of this fluid through the apparatus of the B.O.P. 14 and into the free air are such as to heat at least the entrapped natural gas and some of the lower molecular weight petroleum products past their flash point, thus initiating ignition. Once ignition occurs the heat of the initial burning of the gasses then vaporizes and ignites the heavier petroleum

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products within the stream, producing an extremely hot fire, rapidly raising the surviving metallic components of the external drill rig to well above the ignition temperature of any of the petroleum components within the spray. The instant invention is activated upon the occurance of a blowout, preferably prior to ignition, but if that is not possible, subsequent to the initial ignition. The fire suppression agent of the instant invention is injected, as a liquid, through the venturi effect and intermingles with the liquid flow within and beneath the B.O.P. 14, dispersing itself throughout the liquid.

By control of the proportion of the high and low vapor pressure Halons within the particular mixture proposed by the instant method, the fire suppression mixture is provided at a vapor pressure slightly greater than the most dangerous low flash point gases within the stream. Thus the mechanics of flow of the stream within the oil well preferentially segregates the fire suppression agent within the oil well spray. For the same reason, as the fluid within the drill string is ejected into the open atmosphere, the fire suppression agent will vaporize slightly before and co-jointly with the natural gas, methane or other highly flammable products. Since the halogenated alkanes provide fire suppression by a chemical blanking technique which 'interferes with the process of combustion, rather than by the requirement that they thermally cool the entire stream of fluid and the surrounding material below any of the flash points concerned, they will be found to be successful in suppressing combustion of the petroleum vapor products and the natural gas vapor products even at elevated temperatures. Thus it is found that the given method, by selectively extinguishing the vaporized products of the petroleum stream, suppresses the fire by interfering with the primary mechanism of ignition and re-ignition within an oil well fire. Further, it is found that the method of the instant invention is capable of suppressing fires under elevated temperature conditions, including suppressing fires and suppressing re-ignition in the presence of

a preceding flame, and the resulting elevated temperature of the surviving oil well structure.

Whereas the preferred embodiment of the invention as described above has been the injection of a liquid mixture formed of Halon 1301 and Halon 1211 through a specific described existing valving system into a position into, or immediately beneath, the B.O.P. of an existing oil well, it can be seen that the actual invention extends to those equivalent mixtures of halogenated alkanes having the particular overall vapor pressure properties described, injected at a first point of mechanical mixing prior to the ejection of the fluid spray from within the oil well drill string.

Thus the invention extends to those equivalents as are embodied in the claims. Figure 3 shows a complete embodiment including the invention, having the alternate legend where:

1' are the Halon Supply Tanks, one ton each 2' are Halon Discharge Manifold Isolation Valves 3' are remotely activated Solenoid Valves 4' is a remotely activated Solenoid Valve controlling a Pump By-Pass Line

5' are Booster Pump Isolation Valves 6' is a Booster Pump, optionally electric motor or Diesel driven 7' are check valves

8' is a Spool Connection for addressing annular blowout 9 ¹ is a Derrick nozzle arrangement, primarily for Drill Pipe Blowout

10' is a discharge Isolation Valve for Optional Fire protection for other rig areas, in cooperation with 11', a remotely activated Soleniod Valve.