US3216499A

US3216499A - Fusible bottom-hole igniter

Info

Publication number: US3216499A
Application number: US291884A
Authority: US
Inventors: David R Parrish
Original assignee: Pan American Petroleum Corp
Current assignee: Pan American Petroleum Corp
Priority date: 1963-07-01
Filing date: 1963-07-01
Publication date: 1965-11-09
Anticipated expiration: 1982-11-09

Description

Nov. 9, 1965 D. R. PARRISH 3,216,499

FUSIBLE BOTTOM-HOLE IGNITER Filed July 1, 1963 DAVID R. PARRISH FIG. 1 L/ 94:

ATTORNE X United States Patent Ofl ice 3,216,499 Patented Nov. 9, 1965 3,216,499 FUSIBLE BOTTOM-HOLE IGNITER David R. Parrish, Tulsa, Okla, assignor to Pan American Petroleum Corporation, Tulsa, Okla., a corporation of Delaware Filed July 1, 1963, Ser. No. 291,884 9 Claims. (Cl. 166-38) The present invention relates to a device suitable for heating or igniting a hydrocarbon-containing formation penetrated by a well. More particularly, it is concerned with a novel heater or burner design which makes possible the use of the lowermost joint of the Well tubing string as the burner.

Briefly, this is accomplished by placing a fusible or combustible plug at or near the lower end of the first (lowermost) tubing joint. This plug contains a small passageway through which a pyrophoric materialwhich may be either a fluid or a solidcan pass. The tubing string is lowered into the well down to the level of the formation to be heated, a fire is initiated at this level preferably by contacting a pyrophoric material with air which may be circulated down the annulus. This, in turn, ignites a combustible air-fuel mixture provided in the well bore. The heat thus produced fuses or melts the plug.

Many methods have been employed in the prior art for applying heat to hydrocarbon-containing formations such as, for example, by electrical means, by injecting heattransfer agents such as steam, hot oil, etc., into the well, and by burning natural gas in the well bore. One of the principal difliculties has been that in the course of heating the formation to ignition temperature the casing or screen as well as any other equipment in the vicinity of the heated zone is damaged by the excessive temperatures generated. In fact, the temperatures produced have been so high that the burner itself was considered an expendable item. A further disadvantage of the previous bottomhole heaters of the type employing a fuel as the heat source has been that they require electricity to start the igniter. The application of such apparatus is limited to the shallower wells because it is very dilficult to provide enough electrical power to the bottom of a deeper well, i.e., in excess of about 5,000 feet, to ignite the burner. Also, these devices generally require at least one item to be lubricated through the well head and give rise to leaks which, in turn, cause difficulty in maintaining metered feed rates. It has also been found that the prior art igniters or heaters are often diflicult to remove from the well. It is sometimes necessary to resort to killing a well in order to remove the igniter. In some cases it has been found that the igniter during the course of its use had fused to the tubing, requiring the piece by piece removal of tubing, electrical cable and fuel line. Certain of these heater or igniter designs require a special seating nipple, causing partial obstruction of the tubing string. Electrical heaters employed for ignition and for paraflin deposition control are subject to a number of practical difliculties, including shorting out. In some instances such equipment has been lost in the well and is extremely diflicult to recover.

Accordingly, it is an object of my invention to avoid the above-mentioned difiiculties experienced with previous igniters or heaters by providing a device which is both dependable and simple in design. It is another object of my invention to provide an underground or bottomhole heater which can be placed in operation by using a pyrophoric material, the latter being brought into contact with a suitable air-fuel mixture in the vicinity of the hydrocarbon-containing formation to be heated. It is a further object of my invention to control the entry of substantial quantities of pyrophoric material into the well bore by placing a perforated, fusible plug into the lowermost length of the tubing string which terminates usually near the formation to be ignited or heated.

The apparatus of my invention will be further under stood by reference to the accompanying drawings, wherein FIGURE 1 is a vertical view, partly in section, of the apparatus installed in an oil well;

FIGURE 2 is a detailed view, primarily in section, of the burner portion of my invention showing the fusible plug employed therein.

Referring again to FIGURE 1, there is shown a well 2 penetrating an oil-bearing formation 4. Casing 6 is run approximately to the top of formation 4 and cemented to the surrounding formation along the area 8, leaving an open hole section 10 from that level substantially to the bottom of oil-bearing formation 4. Tubing string 12, fitted with

valves

13 and 15, extends down the well to top portion of formation 4. At the lower end of tubing 12 is a fusible plug 14, having a passageway 16 opening into the well. This passageway may vary in diameter, but ordinarily is generally from about A; to about A inch. The top of the plug is concave in order to direct flow of pyrophoric material through passageway 16 and out into the well bore area therebelow. Plug 14 may be of any of a number of materials, such as resin, rubber, high-melting-point wax, lead, Woods metal, Babbitt metal, etc.

Valved line 18 is connected to tubing string 12 and is used to carry fuel into the system. Casing 6 is fitted with valved line 20 used to supply air down the well annulus.

FIGURE 2 illustrates a preferred structure of the last, or lowermost, length of pipe in tubing string 12. This pipe 22 is connected to tubing string 12 by means of coupling 24. Outside pipe 22 is a layer of refractory cement lining 26 which serves to protect carbon steel pipe 22 from damage by oxygen corrosion at high temperatures. If desired, pipe 22 may be constructed out of refractory material such as, for example, high-temperature-resistant Ceramet material.

In operation, plug 14 is either inserted into or formed within the lower end of tubing string 12. The resulting section of pipe is then lowered into well 2 and is attached to a number of lengths of pipe making up string 12. When the section holding plug 14 is at the desired level, tubing string 12 is secured at the well head and air and a gaseous fuel such as natural gas, are introduced into the system via

lines

20 and 18, respectively. Tubing string 12 is initially purged of air by the use of an inert gas such as nitrogen or combustible gas inert with respect to the pyrophoric substance used. When tubing string 12 is purged of air, and the rates at which air and fuel are introduced have become stabilized, the pyrophoric material is inserted into tubing 12 by opening valve 13 and closing valve 15 while the flow of fuel into tubing string 12 via line 18 is temporarily discontinued. As soon a such material has been added, valve 13 is closed and valve 15 is opened. The pyrophoric material may be dropped into the tubing or lowered on a suitable line. In the meantime, air injection down the annulus is maintained so that any air-gas mixture below plug 14 is purged. In this manner air and combustible gas are driven into formation 4 so that only air remains below plug 14.

The pyrophoric material, if a liquid, may be added in a readily breakable container, preferably lowered on a line and then released several feet above the end of the tubing so that the ampoule or bottle breaks, allowing the contents to flow on out through passageway 16 in the plug at a controlled rate into the air atmosphere below. On contact with air, a flame is immediately produced and during the consumption of the pyrophoric material, plug 14 becomes hot. At this time, the gas supply in tubing 12 commences to flow into the space below, mixes with the air, and is ignited. Within a short time it begins to melt to an extent sufficient to permit the plug to drop from the tubing string. Successful ignition is generally indicated by an immediate drop in air rate and a rise in injection pressure.

In both starting this operation and maintaining it, I prefer an air-rich feed in the system. In the firstplace, it is a safeguard against the occurrence of an explosion during start-up and, secondly, the temperature required to heat the formation to stimulate the flow of oil from it, or to raise the formation to a satisfactory ignition temperature, is not very great, i.e., about 450 to 700 F. in the case of well stimulation, and about 600 to 1000 F. where ignition is desired.

The fuel portion of the feed mixture employed may be selected from a wide variety of substances such as, for example, light hydrocarbons, typically natural gas, propane, butane, and their unsaturated derivatives, as well as normally liquid fuels, such as kerosene, methanol, and the like, if used in vapor form.

The air and fuel feed rates, likewise, may vary widely, depending on whether it is desired to produce low or relatively high temperatures, the later being produced with feed mixtures richer in the fuel component or components. Generally, .air rates of from about 50,000 to about 1,000,000 s.c.f. per day. Corresponding fuel gas rates, where dry natural gas is employed may range from about 1,000 to about 20,000 s.c.f. per day. For other fuels, such as methanol vapors, propane, propylene, etc., the fuel-air mixture can be adjusted to produce the desired flame temperature. Air-rich mixtures produce lower temperatures, while the fuel-rich mixtures generate higher temperatures. Where ignition or heating of the formation is to occur in open hole, higher temperatures may be used, but if the well is cased, temperatures not generally exceeding 600 to 700 F. are usually desired.

Refractory cement 26 may be chosen from a wide range of materials, such as the high-alumina cements which generally contain from 35 to 40 percent A1 30 to 35 percent CaO, 10 to 15 percent Fe O and a combined percentage of silicon and magnesium oxides of from to percent. Any castable refractory material capable of withstanding temperatures of at least 2,500 to 3,000 F. is suitable. One particular refractory I have found useful for this purpose is Alfrax refractory cement manufactured by the Carborundum Company, Perth Amboy, New Jersey. This is a castable material which can be applied as a mud after mixing with water. The refractory sets within about 24 hours and generally firing before use is unnecessary.

Substantially any pyrophoric material, liquid or solid, is satisfactory for my purpose. Thus, I may employ alkyl boranes, such as triethylborane, pyrophoric metals, phosphorous, aluminum borohydride, aluminum alkyls, pentaborane, and the like. I may also use such solid materials as calcium phosphide which, on contact with water, generates the pyrophoric substance phosphine.

The term gas appearing in certain of the appended claims is to be construed as including liquid fuel in vapor form. Also the term metal used in the claims is to be interpreted to include a normally solid alloy or mixtures of metals having a melting point below about 625 F. The term fusible, as used in the present description and claims is intended to include combustible materials such as rubber, resins, etc. The value of a combustible material is that in the case the burning operation is momentarily interrupted owing to a fluctuation in pressure, etc, enough heat is supplied by this burning plug to reignite the air-fuel mixture flowing into the well via tubing 12.

I claim:

1. A method of supplying heat to an underground formation penetrated by a well comprising lowering a pyrophoric material into said well via a conduit in the presence of a gas inert with respect to said material, the flow of said material out of the lower end of said conduit being partially obstructed at said lower end with a fusible substance, injecting an oxygen-containing gas down said well via a second conduit to produce an atmosphere in the vicinity of said lower end composed primarily of an oxygen-containing gas, allowing said pyrophoric material to flow out said partially obstructed lower end to contact said atmosphere whereby said pyrophoric material is ignited to generate sufiicient heat to cause said fusible plug to at least partially melt or fuse at a temperature substantially lower than the fusion temperature of said conduit and drop into the space in said well below said lower end, immediately thereafter flowing a combustible gas out said lower end to mix with said atmosphere to produce a combustible mixture, and igniting the latter through the combustion of saidpyrophoric material. 7 g

2. The method of claim 1 in which the combustible gas employed is natural gas.

3. The method of claim 1 in which the combustible gas employed consists primarily of a normally gaseous hydrocarbon.

4. The method of claim 1 in which the fusible plug employed is made of rubber.

5. The method of claim 1 in which the fusible plug is a normally solid metal melting below about 625 F.

6. In a bottomhole oil well heater, the combination comprising a tubular member the exterior of which is refractory lined, means at one end of said member for attachment to a metal conduit, a fusible plug at the opposite end of said member, said plug being fusible at a temperature below about 625 R, which temperature is substantially below the melting point of said member, and an unrestricted passageway running through said plug coaxially with said member.

7. Apparatus for heating an underground formation penetrated by a well having a string of tubing therein comprising a tubular member having a refractory lining on the exterior thereof and afiixed to the lower end of said tubing, a fusible plug melting below about 625 F. at the lowermost end of said member, which temperature is substantially below the melting point of said member, and an unrestricted passageway running through said plug coaxially with said member.

8. The apparatus of claim 7 in which the fusible plug employed is made of a metal melting below about 625 F.

9. The apparatus of claim 7 in which the fusible plug employed is made of rubber.

References Cited by the Examiner UNITED STATES PATENTS 1,657,751 1/28 Henderson 166--192 2,320,670 6/43 Scara-mucci 166-225 2,352,744 7/44 Stoddard 166-225 X 2,527,308 10/51 Brown 166--225 2,847,071 8/58 De Priester 16659 X 2,890,755 6/59 Eurenius et a1. 16659 2,941,596 6/60 Kaasa 16638 3,044,551 7/62 Pryor 16659 OTHER REFERENCES The Gallery Company, Callery Compounds To Lead You to New or Improved Products, Chemical and Engineering News, 33, 18, May 4, 1959, pp. 56-58.

BENJAMIN HERSH, Primary Examiner.

Claims

1. A METHOD OF SUPPLYING HEAT TO AN UNDERGROUND FORMATION PENETRATED BY A WELL COMPRISING LOERING A PYROPHORIC MATERIAL INTO SAID WELL VAI A CONDUIT IN THE PRESENCE OF A GS INERT WITH RESPECT TO SAID MATERIAL, THE FLOW OF SAID MATERIAL OUT OF THE LOWER END OF SAID CONDUIT BEING PARTIALLY OBSTRUCTED AT SAID LOWER END WITH A FUSIBLE SUBSTANCE, INJECTING AN OXYGEN-CONTAINING GAS DOWN SAID WELL VIA A SECOND CONDUIT TO PRODUCE AN ATMOSPHERE IN THE VICINITY OF SAID LOWER END COMPOSED PRIMARILY OF AN OXYGEN-CONTAINING GAS, ALLOWING SAID PYROPHORIC MATERIAL TO FLOW OUT SAID PARTIALLY OBSTRUCTED LOWER END TO CONTACT SAID ATMOSPHERE WHEREBY SAID PYROPHORIC MATERIAL IS IGNITED TO GENRATE SUFFICIENT HEAT TO CUASE SAID FUSIBLE PLUG TO AT LEAST PARTIALLY MELT OR FUSE AT A TEMPERATURE SUBSTANTIALLY LOWER THANT THE FUSION TEMPERATURE OF SAID CONDUIT AND DROP INTO THE SPACE IN SAID WELL BELOW SAID LOWER END, IMMEDIATELY THEREAFTER FLOWING A COMBUSTIBLE GAS OUT SAID LOWER END TO MIX WITH SAID ATMOSPHERE TO PRODUCE A COMBUSTIBLE MIXTURE, AND IGNITING THE LATTER THROUGH TEH COMBUSTION OF SAID PYROPHORIC MATERIAL.

6. IN A BOTTOM HOLE OIL WELL HEATER, TE COMBINATION COMPRISING A TUBULAR MEMBER THE EXTERIOR OF WHICH IS REFRACTORY LINED, MEANS AT ONE END OF SAID MEMBER FOR ATTACHEMENT TO A METAL CONDUIT, A FUSIBLE PLUG AT THE OPPOSITE END OF SAID MEMBER, SAID PLUG BEING FUSIBLE AT A TEMPERATURE BELOW ABOUT 625*F., WHICH TEMPERATURE IS SUBSTANTIALLY BELOW THE MELTING POINT OF SAID MEMBER, AND AN UNRESTRITED PASSAGEWAY RUNNING THROUGH SAID PLUG COAXIALLY WITH SAID MEMBER.