US3223165A - Method for heating or igniting well formations with pyrophoric materials - Google Patents

Description

K. L. HUJSAK Dec. 14, 1965 5 Sheets-Sheet 1 Filed pril a. 1965 Q4 M H\\ 2 2 .h.n K ubTK &\\\/ m T K mm h I I A m m IV/L lllcilIsY K 4 4 l I I. o m z w J a F 3 3 W 6 Aw m 3 w m 8 Q d l m Q 6 g 2 ATTORNEY.

K. L. HUJSAK Dec. 14, 1965 3,223,165 METHOD FOR HEATING OR IGNITING WELL FORMATIONS WITH PYROPHORIC MATERIALS 5 Sheets-Sheet 2 Filed April 8, 1963 INVENTOR.

KAROL L. HUJSAK BYw h i ATTORNEY.

K. L. HUJSAK 3,223,165 METHOD FOR HEATING OR IGNITING WELL FORMATIONS Dec. 14, 1965 WITH PYROPHORIC MATERIALS 3 Sheets-Sheet 3.

Filed April 8, 1963 INVENTOR BY M mw KAROL L. HUJSAK ATTORNEY.

METHOD FOR HEATING R IGNITING WELL FORMATIONS WITH PYROPHORIC MATERIALS Karol I... Hujsalr, Tulsa, ()kla, assignor to Pan American Petroleum Corporation, Tulsa, 0kla., a corporation of Delaware Filed Apr. 8, 1963, Ser. No. 271,262 Claims. ((Il. 166-38) The present invention relates to a method suitable for heating or effecting ignition of a hydrocarbon-containing formation penetrated by a well. More particularly, it is concerned with a novel method involving application of pyrophoric material to ignite a fuel-oxygen containing gas mixture the composition of which is controlled so as to regulate the resulting flame temperature. The expression flame temperature, as used herein, is intended to refer to the final adiabatic mixture temperature of the oxidation or combustion products and excess air.

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 heat transfer 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. The electric heaters employed for ignition and for paraffin deposition control have been subjected to a number of practical problems, including shorting out; in some instances, such equipment has been lost in the hole and is extremely diflicult to recover.

Accordingly, it is an object of my invention to provide a safe and eflicient method of igniting or heating a hydrocarbon-bearing zone at a temperature that will not damage the casing. It is another object of my invention to provide a method for readily igniting the heater in the event the flame is extinguished owing to fluctuations or surges in the fuel-air system. It is a further object of my invention to provide a method for stimulating the flow of oil from an underground deposit thereof by the use of heat without the formation of coke on the heat source, or elsewhere, in objectionable amounts.

Briefly, my invention comprises a method for using a wire line retrievable igniter or heater adapted to operate on gaseous or vaporized fuels. Such fuel is preferably passed down the tubing and air down the annulus. When all the air in the tubing has been displaced with fuel, a lubricator having a side opening is purged with an inert gas, such as nitrogen, and a pyrophoric material added to the cup portion of an igniter tube in the lubricator. The cup may contain crushed charcoal, or the equivalent, to prevent the pyrophoric materialif it is a liquid-from splashing and spilling over. The charcoal acts as a secondary ignition source if gas flow is temporarily interrupted due to pressure surges or other causes. Thereafter, the igniter is lowered to a level to feet from the bottom of the tubing. Gas flow is then stopped for a short time and air flow down the annulus is continued in order to purge the well bore below the bottom of the tubing free from a combustible fuel-air mixture. The igniter is then lowered further until it seats in the bottom of the tubing. At the same time, flow of fuel down the tubing is resumed. As soon as the pyrophoric material in the igniter is contacted with air, it ignites and, in turn, ignites the fuel. The igniter is then withdrawn from the burning zone and burning continues in the main burner structure provided at the bottom of the tubing. The burner can operate on a mixture of air and a light hydro- States Patent 3,223,165 Patented Dec. 14, 1965 carbon, preferably natural gas. The fuel and air are separately pumped to the burner through the tubing and easing, respectively. They mix at the end of the tubing inside a heat shield. A large excess of air, e.g., up to 500 percent of stoichiometric, is used to keep the adiabatic mixture temperature within the desired range. Satisfactory operation of my invention has been observed as low as 500 F. adiabatic mixture temperature; however, I generally prefer to operate within a temperature range of from about 900 to about 1,100 F.

The expression inert gas, as used herein, refers to any gas or vapor that does not react with the pyrophoric material used. Carbon dioxide, While normally considered an inert gas with respect to some pyrophoric substances, cannot be used for this purpose in my invention where triethylborane, for example, is employed because carbon dioxide readily reacts with it.

In the accompanying drawings,

FIGURE 1 is a vertical view, partly in section, of the apparatus employed in the method of my invention being installed in an oil well;

FIGURE 2 is a detailed sectional view of the heater used in my invention showing the igniter tube;

FIGURE 3 shows a cross-section of the apparatus and associated equipment used to prevent fluids from entering the tube when the latter is lowered into the well containing fluids and prior to placing the igniter tube in operating position;

FIGURE 4 is a sectional view of a modification of the igniter tube shown in FIGURE 2.

Referring now to FIGURE 1, a well 2 having protective casing 4 is equipped with a lubricator 6 affixed to a Wellhead 8. Igniter tube 10 is lowered on cable or wire line 12 into lubricator 6 while valve 14 is closed. The igniter tube comes to rest in the lubricator at a level such that the lower cup portion of the igniter is opposite T plug 16. A valved line 18 enters lubricator 6 a short distance above plug 16 and is used as a conduit through which inert purge gas is introduced into the lubricator. Tubing string 20 secured at the top by Wellhead 8 carries heat shield 22 held on the lower end of said string by means of threaded coupling 24. In addition to flow line 26, the well is equipped with valved fuel line 28 which flows into tubing 20, combustion air line 30 opening into the well annulus, and a second air line 32, off of line 39, fitted with valve 29 and check valve 31 and communicating directly with tubing 20.

In FIGURE 2, igniter 10, resting in seating nipple 34, comprises a barrel section 11 having a lower cup portion 36 suspended from barrel 11 by means of metal bars 38. A relatively fluid-tight seal above and below the seating position is provided by O-ring 40 fitted into the groove in shoulders 42 of the igniter barrel. Seating nipple 34 is held in position by means of spacer bars 44, the opposite ends of which are anchored to heat shield 22 having an inner refractory cement lining 46. The upper end of igniter 10 is engaged to a sinker bar 48 by means of threaded coupling 50. The upper portion of sinker bar 48 is threadedly engaged to cable clamp assembly 52 which, in turn, is connected to cable head 54. Also near the upper end of sinker bar 48 are gas ports 49 through which fuel flows when igniter 10 is seated in nipple 34. Resting inside igniter 10 is well 56 containing a thermocouple 58, e.g., a cbromel alumel thermocouple. This thermocouple has lead wires 64) and 62, the former of which is grounded to the sinker bar at 64 while the latter (62) runs on up through hollow cable 12 to a temperature recorder (not shown).

Referring to FIGURE 3, there is shown a plug 66 resting in the lower portion of nipple 34. The plug which may be composed of a laminated plastic or a soft metal, such as aluminum, is held by friction in nipple 34 through the use of O-ring 68 and is prevented from moving further into nipple 34 by means of shoulder 67. Plug 66 serves to prevent entry of fluids into the tubing when the burner assembly, i.e., heat shield 22 and seating nipple 34, is lowered into the well. The burner assembly, with the tubing plug installed, is attached to the lowermost joint of tubing 20 and should be landed so that the bottom of heat shield 22 is about 2 feet or so above the highest level of perforations 78 or open hole.

The burner assembly confines the flame and protects the casing from excessive temperatures. Assemblies constructed of Inconel, type 316 and type 304 stainless steel have been used with success. The diameter of heat shield 22 should be as large as practical for the size casing in the Well at the level the heater is to be used. Also, it is important that the openings between supports 44 be as large as possible to permit the flame temperature inside shield 22 to be maintained as low as possible.

FIGURE 4 is a modification or" the igniter shown in FIGURE 2 having a restricted extension 70 of barrel 11 resting in cup 71. Extension 70, which is welded to the bottom of cup 71, has perforations 72, permitting fuel to contact pyrophoric material 74 and force the latter into the well where it spontaneously ignites on contact with oxygen. The igniter design shown here is useful to prevent inactivation of the pyrophoric material as a result of hydrocarbon absorption. Such inactivation has been observed to occur where the pyrophoric substance is a liquid, such as triethylborane. There is a strong tendency for C and heavier hydrocarbons to absorb into the triethylborane or similar materials and, if the latter become diluted with hydrocarbons to the extent of about 80 percent, the resulting mixture does not spontaneously ignite in the presence of air. Under these circumstances, precaution should be taken to prevent such hydrocarbon absorption by placing in the annulus between extension 70 and cup 71 a temporary sealant 76 such as, for example, a heavy chassis grease, While the igniter is still in the lubricator. Absorption of hydrocarbons inside igniter by the pyrophoric material is prevented by placing a blanket of inert gas next to said material. This is done by pressuring up lubricator 6 with nitrogen or other suitable inert gas to tubing pressure after which it is closed and valve 14 opened. Ignition can then proceed in a normal manner. Under these conditions, the triethylborane, or other pyrophoric material, is in contact with an inert gas blanket which usually extends the full length of barrel 11. Generally, I prefer to pressure up lubricator 6 to a level approximately half that existing in tubing 20. This is for the reason that if the volume occupied by the inert gas is relatively large, there is a possibility that in forcing the triethylborane out of cup 71 with a gaseous fuel via tubing 20, the triethylborane will ignite and burn before it is able to contact the fuel. Once the heater reaches the level in the well where ignition is to occur, gas is pumped down tubing 20, ports 49, through barrel 11 and extension 70, forcing pyrophoric material 74 and sealant 76 out of the aforesaid annulus and into the well to ignite the combustible mixture therein.

In operation, heat shield 22 and seating nipple 34, which constitute the burner assembly, together with tubing plug 66, are lowered down the Well on tubing string 20 to a level approximately 2 feet above the top row of perforations 78 or open hole, whichever the case may be. After wellhead 8 has been assembled and the necessary surface installations completed, it is preferable to run a sinker bar on cable 12 through the lubricator to tubing plug 66 in order to locate the seating nipple accurately. With both tubing and casing open to air flow via lines 30 and 32, displacement of well fluids is begun. When the liquid level reaches top perforations 78, casing or annulus pressure drops. Check valve 31 prevents equalization of pressure via lines 30 and 32, resulting in a differential being created between tubing string 20 and the annulus. This pressure differential generally is great enough to force plug 66 out of the lower end of nipple 34 and into the well. When pressures equalize, a sinker bar should again be run through seating nipple 34 to confirm the removal of plug 66.

When plug 66 is removed, gas flow via line 28 is started down tubing 20. Valve 29 is closed and air flow is commenced down the annulus via line 30. From the gas injection rate and tubing capacity, the time to completely displace the air from the tubing can be determined. It is usually desirable to inject two tubing volumes of gas (noncombustion support gas) to insure complete purging of the air.

Igniter 10 should be installed in lubricator 6, after filling cup 36 with 4 to 8 mesh charcoal and then located at the level shown in FIGURE 1. Lubricator 6 is next purged free of air with cylinder nitrogen by pressuring to about 50 p.s.i.g. through line 18 and then depressuring. When the purging step is completed, plug 16 is removed and the igniter cup, containing ground charcoal, is filled to the top with triethylborane. This can be done conveniently through the use of a one-foot length of /8" copper tubing attached to a cylinder of triethylborane. After the igniter cup is full of triethylborane, T plug 16 is replaced and tightened in the lubricator T. The entire operation of filling cup 36 with triethylborane should be done quickly and with minimum opportunity to introduce air into lubricator 6. Tubing valve 14 below lubricator 6 should be opened as soon as the purging step is completed. Igniter tube 10 is then lowered to within about 20 or 25 feet of seating nipple 34. At this time, gas flow is stopped while air flow is continued via line 30 and the well annulus in order to purge the well below heat shield 22 free of the gas-air mixture. In this manner air and combustible gas are driven into formation 39 via perforations 78 so that only air remains below the burner assembly. Igniter tube 10 is then loW- ered to seating nipple 34 and gas flow is started down tubing 20 at the previously determined rate into igniter 10 via ports 49. Successful ignition is generally evidensed by an immediate drop in air rate and a rise in injection pressure. The rate of pressure rise may be high enough to stop the flow of gas but of the end of tubing 20, causing the flame to go out. The maximum tolerable rate of pressure rise should be calculated in advance and the actual rate of pressure rise held to not over about 6. that value by reducing air flow at a suitable bleed valve (not shown) upstream in air line 30. Using a Well depth of 1,000 feet, the well being equipped with 7 casing and 2" tubing, such calculation is made as follows:

Assume a gas injection rate of 400 s.c.f.h. and an air injection rate of 20,000 s.c.f.h., at 500 p.s.i.g. pressure. The tubing volume is 25.4 cu. ft. The maximum rate at which tubing pressure can be increased is:

The casing volume (annulus between casing and tubing) is 237 cu. ft. The maximum rate at which casing pressure can increase is:

In order to prevent stopping the gas flow out of the end of tubing 20 and pressuring the latter with air from the annulus, the rate of pressure increase at wellhead 8 should be kept below 3.85 p.s.i. per minute in this example. Preferably, the maximum rate of pressure increase would be held at about one-half this value by reducing the air injection rate by opening an air bleed valve upstream of the air meter (not shown). As soon as pressures stabilize, the air rate should be returned to normal slowly.

Thermocouple 58 should provide additional evidence of burner operation. Temperatures in the order of about 700 F. or higher are generally indicated. After about =3.85 p.s.i. per minute =20] p.s.i. per minute minutes with igniter tube 10 in seating nipple 34, the tube should be pulled off the seat and up the well about feet. This prevents sticking on the seat and insures the possibility of removal for reignition in case it is necessary as a result of a flow interruption. Igniter tube 10 may be lowered to seating nipple 34 periodically to test temperatures. If desired, the Inconel end of igniter tube 10 may be filed or polished to brightness before running to seating nipple 34. The polished area will be straw-colored or blue after short exposure to heat.

After the desired amount of heat has been injected, tubing string 20 should be purged free of natural gas. This operation is conveniently carried out by introducing about two 220 s.c.f. cylinders of nitrogen into the suction gas compressor, followed by opening the suction to air. The time required for the nitrogen to reach the burner should be computed. The burner can generally be observed to go out as the result of smooth action of the air rate and pressure pens on the air meter at approximately the calculated time.

Refractory cement 46 may be chosen from a wide range of materials such as the high alumina cements which generally contain from 35 to 40 percent A1 0 to percent CaO, 10 to 15 percent Fe O and a combined percentage of silicon and magnesium oxides of from 5 to 10 percent. Any castable refractory material capable of withstanding temperatures of at least about 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, in addition to alkyl boranes, typified by triethylborane, there may be mentioned pyrophoric metals, phosphorous, aluminum borohydride, aluminum alkyls, pentaborane, and the like.

The igniter and burner assembly of the design described herein have been used successfully over a wide range of conditions, i.e., pressures ranging from 250 to 900 p.s.i.g., depths up to about 3,300 feet, and heat output rates of 7 to 10 million B.t.u. per day, based on the natural gas consumed. The maximum amount of heat generated in any single application of this heater was 67 million B.t.u. in la seven-day period. Ordinarily, a heat generation rate in excess of about 10 million B.t.u. per day is not desirable because local overheating of the casing near the burner level can occur.

I claim:

1. A method for supplying heat to an underground formation penetrated by a well having a string of tubing therein and a lubricator affixed to the head of said well, the lower end of said tubing extending about to the level of said formation to be heated, comprising injecting a combustible gas down said tubing and an oxygen-containing gas down the space between said tubing and the wall of said well at respective injection rates sufiicient to produce a combustible mixture of said gases in said well, placing a confined mass of pyrophoric material in said lubricator in direct contact with an inert gas atmosphere, the presure of said inert gas being no greater than the pressure of the combustible gas in said tubing, thereafter lowering said mass in the presence of said inert gas from said lubricator into said tubing containing said combustible gas to a level corresponding to a major length of said tubing but less than the entire length thereof, next halting the flow of said combustible gas down said tubing and continuing the flow of said oxygen-containing gas down said space thereby forming a noncombustible oxygencontaining atmosphere in the vicinity of said formation, then lowering said mass through said tubing to an oxygen-containing atmosphere in said Well while resuming the flow of combustible gas down said tubing at an injection rate sufiicient to produce a combustible mixture of said gases in the vicinity of the lower end of said tubing whereby said mass and said mixture are substantially simultaneous-ly ignited, and continuing the separate introduction of said combustible and oxygen-containing gases in the manner described whereby the flow of said combustible gas from said tubing into said well is uninterrupted and combustion of said mixture is maintained.

2. The method of claim 1 in Which the combustible gas is natural gas and the pyrophoric material is triethylborane.

3. The method of claim 1 in which the combustible gas is natural gas and the oxygen-containing gas is air.

4. A method of supplying heat to an underground formation penetrated by a well, comprising injecting a combustible gas down a first confined path into said well and an oxygen-containing gas into said well down a second confined path at respective injection rates sufiicient to produce a combustible mixture in said well, lowering a pyrophoric material in an open container down said first path by means controlled from the ground surface in direct contact with the combustible gas inert with respect to said material to a level corresponding to a major length of said first path but less than the entire length thereof, discontinuing the flow of said combustible gas down said first path while continuing the flow of said oxygen-containing gas down said second path whereby said mixture below the lower end of said first path is purged from said well, said lower end being substantially at the level of said formation, then lowering said material on down said first path until said material contacts an oxygen-containing atmosphere in said well and resuming the flow of combustible gas down said first path at an injection rate sufficient to produce a combustible mixture in the vicinity of the lower ends of said paths whereby said material and the last-mentioned mixture are substantially spontaneously ignited, and continuing the formation of said mixture by the separate injection of said combustible and oxygen-containing gases in the manner described whereby the resulting combustion of said mixture is maintained.

5. The method of claim 4 in which the combustible gas is natural gas and the oxygen-containing gas is air 6. The method of claim 4 in which the pyrophoric material is triethylborane.

7. A method for supplying heat to an underground formation penetrated by a well, comprising lowering a pyrophoric material in an open container down said well by means controlled from the ground surface via a first conduit and in the presence of a combustible gas inert with respect to said material, said first conduit extending down to a level substantially opposite said formation, injecting an oxygen-containing gas down said well via a second conduit to a level substantially opposite said formation, thereby forming a noncombustible oxygen-containing atmosphere in the vicinity of said formation, thereafter lowering said container in said first conduit until said container is substantially opposite said formation whereby said material is brought into contact with said oxygencontaining atmosphere and ignited, immediately thereafter injecting said combustible gas down said first conduit while injecting said oxygen-containing gas down said second conduit at respective injection rates sufficient to produce a combustible mixture which is ignited by the burning pyrophoric material, and maintaining this combustion process by continuing to introduce said combustible and oxygen-containing gases into said well in the above-described manner.

8. The method of claim 7 in which said pyrophoric material is mixed with ground charcoal.

9. The method of claim 7 in which, in addition to the pyrophoric material, a secondary ignition source is employed.

It). A method for supplying heat to an underground formation, penetrated by a perforated cased well having a liquid standing therein above said perforations, said perforations being opposite said formation, the steps comprising placing a temporary plug at one end of a tubing string, lowering the plugged end of said string into said well to a level substantially opposite said perforations, injecting a gas into said string and down the annulus between said string and said casing at substantially the same pressure, maintaining said pressure in said string and continuing the injection of said gas down said annulus to force the level of said liquid down to said perforations and below the lowermost end of said string, whereby the pressure in said annulus becomes less than that in said string to force said plug from said string by means of the resulting pressure differential and thereafter, while maintaining said pressure differential, injecting a combustible gas down said string and an oxygen-containing gas down said annulus at respective rates sutficient to form a combustible mixture at the lowermost end of said string, lowering a pyrophroic material in an open container down said well by means controlled from the ground surface via said string and in the presence of la combustible gas inert with respect to said material, temporarily halting the lowering of said material while it is in said string and then injecting an oxygen-containing gas down said well via said annulus, thereby purging said combustible mixture from the vicinity of said lowermost end leaving an oxygen-containing atmosphere, resuming lowering said container in said string until said container emerges from the end thereof, whereby said material is brought into contact with said oxygen-containing atmosphere land ignited, immediately thereafter injecting said combustible gas down said string while injecting said oxygen-containing gas down said annulus at respective injection rates sufficient to produce a combustible mixture which is ignited by the burning pyrophoric material, and maintaining this combustion process by continuing to introduce said combustible and oxygen-containing gases into said well in the above-described manner to form said mixture substantially opposite said formation.

References Cited by the Examiner UNITED STATES PATENTS 1,973,935 9/1934 Thorson 158110 2,055,366 9/1936 Shrader 158110 2,762,436 9/1956 Brown l6646 2,793,698 5/1957 Ta'usch l6646 2,847,071 8/1958 De Priester 166-39 2,863,510 12/1958 Taderna et a1. l6638 2,941,596 6/1960 Kaasa 166-38 3,147,804 9/1964 Wyllie 166ll 3,159,216 12/1964 Reed et a1. 166-11 CHARLES E. OCONNELL, Primary Examiner.

BENJAMIN HERSH, Examiner.

Claims (1)

1. 7. A METHOD FRO SUPPLYING HEAT TO AN UNDERGROUND FORMATION PENETRATRED BY A WELL, COMPRISING LOWERING A PYROPHORIC MATERIAL IN AN OPEN CONTAINER DOWN SAID WELL BY MEANS CONTROLLED FROM THE GROUND SURFACE VIA A FIRST CONDUIT AND IN THE PRESENCE OF A COMBUSTIBLE GAS INERT WITH RESPECT TO SAID MATERIAL, SAID FIRST CONDUIT EXTENDING DOWN TO A LEVEL SUBSTANTIALLY OPPOSITE SAID FORMATIN, INJECTING AN OXYGEN-CONTAINING GAS DOWN SAID WELL VIA A SECOND CONDUIT TO A LEVEL SUBSTANTIALLY OPPOSITE SAID FORMATION, THEREBY FORMING A NONCOMBUSTIBLE OXYGEN-CONTAINING ATMOSPHERE IN THE VICINITY OF SAID FORMATION, THEREAFTER LOWERING SAID CONTAINER IN SAID FIRST CONDUIT UNTIL SAID CONTAINER IS SUBSTANTIALLY OPPOSITE SAID FORMATION WHEREBY SAID ATERIAL IS BROUGHT INTO CONTACT WITH SAID OXYGENCONTAINING ATMOSPHERE AND IGNITED, IMMEDIATELY THEREAFTER INJECTING SAID COMBUSTIBLE GAS DOWN SAID FIRST CONDUIT WHILE INJECTING SAID OXYGEN-CONTAINING GAS DOWN SAID SECOND CONDUIT AT RESPECTIVE INJECTION RATES SUFFICIENT

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