US3400763A - Igniting a carbonaceous stratum for in situ combustion - Google Patents

Description

smcn m Sept. 10, 1968 F. A. KLEIN ET AL- IGNITING A CARBONACEQUS STRATUM FOR IN SZ 'IU IOMBUSTION Filed June 2:5, 1966 5 .1 6 uz om o l L w a x o I. 5 (1.21% 1 I 5 4 uzumomu: o a 1 4 636 a a J6 396 E03 w :o 9.6 wz a l 0 2 w H mac 2580 D 110 1 m 2550: I 15. .1 5 p k N o w w wwmm.m

DILUENT AP! GRAVITY PRODUCTION OR IGNITION-AND PRODUCTION WELL INJECTION WELL OIL STRATUM INVENTORS F. A. KLEIN M. R. DEAN PERMEABLE .LCERAMIC LINER 'mxr RE CDQESEL on.

UTOIGNITABLE FUEL (TUNG on.)

FIG.

9 v ATTORNEYS United States Patent "ice '3,400,763 lGNlTlNG A-- CARBONACEOUS STRATUM? FOR IN SlTU COMBUSTION" Frederick A. Klein and- Maurice R. Dean, llartlesullle, 0kla., assignors to v Phillips. Petroleum, Company,- a. corporation of Delaware Continuation-impart of application. Ser. No. 523,408, Jan. 27, 1966. This application June 23,. 1966, Sen.

6 Claims. (Cl. 16638) ABSTRACT'OF THE DISCLOSURE An annulus around a well. in an oil stratum is burned out to improve its permeabilityandsubsequent oil. production by installing. a permeable tubular ceramic liner downhole,"injecting a slug of autoignitable fuel, such as tung oil, thru the. liner into the oil. stratum, injecting a following slug of liquid-Qhydrocarbon miscible with said fuel tofree the liner of said fuel. driving the aforesaid slugs deeper into the stratum with injected inert gas. and thereafter injecting air thru the well into the stratum to contact, ignite, and burnout the injected fuel and iii-place carbonaceous material.

This application is a continuation-in-part of ourcopending application S.N. 523,408, filed Jan. 27-, 1966, which isa continuation-in-part of our copending application SN. 451,652,. filed Apr. 28, 1965 now. abandoned;-

This invention relates. to a process for igniting an oil.-

bearing subterranean stratum for propagating the resulting combustion zone thru. the stratum to produce oil therefrom, to an autoignitable fuel composition therefor, and to a method of opening upa stratum around. a well to increased flow. I

The production of oil from an, oil-bearing stratum by in situ combustion is an accepted process in the petroleum industry. In order to, propagate a combustion zone thru a stratum, it is necessary to. ignite the in-place oil in a selected area of the stratum prior to the actual driving step of the process. Common'techniques for igniting the oilin a stratum comprise burning a fuel pack such as. oilsoaked charcoal in a weli penetrating the stratum, heating thestratum around the ignition well with a gas-fired healer or an electric heater, heating the stratum with a thermitc starter, or with rocket fuels, etc. I

A more recent method is that disclosed in 11.5. Patent 2.683.510 (Dec. 9. 1958) wherein a fuel spontaneously ignitable in contact with a gaseous oxidant is burned in the ignition well by depositing the fuel therein and contacting same with the gaseous oxidant whereby the fuel ignites and raises the temperature of the crude oil in the stratum adjacent the well to ignition temperature. Continued injection of air into the ignited area moves the combustion zone thru the stratum toward a production well so as to produce oil therein.

In some in situ combustion operations, a. permeable ceramic liner isutilized in the ignition well which may thereafter become an injection well or a production well. Such a liner is disclosed and claimed in the copending application of G. B. Heckler and R. F. Meldau, S.N. l0,- .149, filed Nov. 29!, 1965.. When utilizing a permeable 33430363 Patented, Sept. 10, 1958 ceramic liner of this nature andan antpignitable fuel, the liner absorbs fuel which insome instances is polymerizable in place during. subsequent heating, resulting in plugging of the ceramic liner and obstruction of the flow of fluids into and/or out of the stratum.

In all of the foregoing ignition methods, for heat to flow into the stratum adjacent the ignition well. at a desirably high rate, it is necessary for the heat source to operate at a very high. temperature. In, some cases these.

high temperatures severely damage the formation around the ignition well. When the well casing extends thru the oil-bearing stratum, the casing can also be severely dam-- aged. These high temperatures canv even damage. other parts of the well. -co rnpletion apparatus.

This invention is concerned with an autoignitable fuel' composition for, use in a methodor process for igmtutg anoil bearing stratum around an ignition wellwithout overheating the wall of the wellbore and any downhole equipment within the oil-bearing stratum or in burning out solid to semi-solid carbonaceous deposits around a wellbore.

Accordingly, it is an object of the invention to provide an autoignitable fuel composition for igniting an oilbearing stratum around an ignition, well'which avoids overheating of the. wall of the wellbore. and equipment therein. Another object is to provide a method or process for igniting an oil-bearing stratum around a well therein to establish in situ combustion in the stratum, which prevents overheating and damage .to the wall ofthe wellbore and equipment therein. A further object is to. provide a method ofinitiating in situ combustion in an oil-bearing stratum for propagating the resulting combustion zone thru the stratum between wells therein to produce oil thru one of said wells. Another object is to prevent polymeriuition of certain'autoignitable fuels in a ceramic liner in an ignition well when using such fuels. Otherobjects of the invention will become apparent to one skilled in the art upon consideration of the accompanying disclosure.

A broad aspect of the process-of the invention comspontaneouslyignitable fuel and ignite same in an area of thestratum spaced from the wall of the-ignition well,

also. igniting the in-place crude oil. in this manner, the method or process develops a zone of elevated temperature within the oil-bearing stratum around the wellbore but spaced therefrom sutiiciently to provide an insulating annulus between the hot combustion zone and the wall of the wellbore. This technique avoids overheating downhole equipment and allows the well to be completed for best sand control where sand production is a problem, as in unconsolidated oil sandsLikewise,overheating 'of the sand in the combustion zone is avoided because of the relatively low ignition point of the spontaneously ignitable fuel and the ignition of the native crude oil at its kindling temperature. This technique also assures that after the ignition temperature has been achieved there ward the offset well(s) (reverse burning front). The other procedure comprises injecting air thru the well thru which the fuel was injected to establish a direct drive of the combustion zone. It is to be understood that the term air is illustrative of other O -contai'ning, combustionsupporting gases.

In one embodiment of the invention, injection of a slug -of the autoignitable fuel is followed by injection of a second slug of a hydrocarbon oil of substantially higher ignition point than the fuel to drive the autoignitable fuel into the stratum away from the wall of the ignition "well.

The liquid hydrocarbon thus injected should be miscible with the fuel so as to flush the fuel from a narrow annulus of the stratum adjacent the wellbore. In the event a ceramic liner is utilized in the ignition well, this feature of the invention is particularly advantageous in freeing the porous liner of autoignitable fuel, thereby decreasing the heating within the ignition borehole and preventing polymerization of the fuel in the liner (in the event the fuel is polymerizable).

v Hydrocarbon oils suitable for use as the second slug include liquid hydrocarbons ranging from gasoline to light crude oil and including diesel oil, kerosene, gas oi1, etc. The liquid hydrocarbon to be injected following the fuel slug should be miscible with the fuel and have an A.S.T.M. final boiling point less than 700 F. with a carbon residue less than 1.0 percent by weight. After injection of the slug of liquid hydrocarbon thru the ignition well into the surrounding stratum, it is preferable to inject a slug of nonoxidizing gas to drive the fuel and liquid hydrocarbon into the stratum away from the ignition well a short distance, such as one foot to several feet. However, this step may be omitted and oxidant, such as air or other O containing, combustion-supporting gas, may be injected directly behind the slug of hydrocarbon liquid which is not autoignitable. This assures ignition of the autoignitable fuel in an annulus spaced from the ignition well.

'After ignition of the autoignitable fuel, the injection of oxidant (air) is continued so as to move a combustion zone away from the wellbore toward one or more ofi'set wells to become production wells. It is also feasible to either reverse the How of air after ignition, or inject air thru the offset well( s) so as to move the resulting combustion front toward the offset well(s) countercurrently to the how of air thru the stratum.

Another embodiment of the invention comprises forming an intimate mixture of the autoignitable fuel, the higher ignition point hydrocarbon fuel and an oxidation catalyst and injecting the mixture into the area of the stratum to be ignited. Thereafter, the fuel composition is then contacted with injected (air) to ignite same,

The autoignitable fuel composition of the invention consists essentially of an intimate mixture of 1) an autoignitable fuel of the group tung oil, linseed oil (boiled or raw), red oil, castor oil, turpentine, tall oil, tall oil fatty acids, oleic acid, and linseed oil fatty acids and mixtures thereof in an amount in the range of 35 to 95 weight per cent of the composition, (2) a liquid oxidation catalyst or accelerator in a concentration in the range of 0.025 to 1.0 weight percent of the fuel of (l), and (3) a liquid hydrocarbon fuel having an ignition temperature substantially above the ignition temperature of the fuel of (1). said hydrocarbon fuel ranging from gasoline to heavy crude oil; The amount of the autoignitable fuel of 1) required increases with the lighter hydrocarbon fuels of (3), at least about 35 weight percent being sufficient with crude oils and at least 75 weight percent being required with gasoline.

Another embodiment of the invention comprises burning out an annulus of carbonaceous stratum around either an injection or a production well to increase the permeability thereof and open up same to permit faster injection and production rates. The autoignitable fuel or fuel composition is deposited in an annulus of about t to 5 feet or more in radius immediately surrounding the well and burning thereof is effected by contact with injected 0: and injection is continued to burn out the fuel and carbonaceous deposit, thereby greatly increasing the permeability of the annulus. The-termination of 0, injection then extinguishes the fire and injection of fluids there thru or the production of fluid hydrocarbons can be effected at faster rates. This aspect of the invention is excellent for well stimulation to increase production.

It has been demonstrated that 33 standard cubic feet of air per pound of tung oil in place in a sand. is required to burnthe tung oil. An Ottawa sand pack 26 inches long in a 2-inch combustion tube was saturated with tung oil. Air at 500 p.s.i. pressure was passed'thru the tube at a flux of 150 s.c.-f./hr.-ft. and the tung oil was ignited and consumed.

Another test was made to determine if tung oil, when admixed with reservoir oil, is subject to autoignition. This test was performed in an isothermal 2-inch.Pyrex combustion tube using an Ottawa sand pack containing 9 weight percent of a mixture of percent catalyzed tung oil and 25 percent Morichal Group I crude oil (cobalt naphthenate catalyst). Air was injected into the tube at an air flux of 50 s.c.f./hr.--ft. and the temperature reached 400 F. in 2.3 hours, the initial temperature being 140 F., simulating reservoir conditions. The pressure was 500 p.s.i. This test demonstrates the feasibility ofutilizing a mixture of autoignitable fuel and crude oil as a fuel in the instant process. It also demonstrates that an autoignitable fuel, when admixed with in-place crude oil, will stiii onction in the manner required.

In operation of the process, the injected slug of spontaneously ignitable fuel is driven into the stratum so that the leading edge thereof is at least one foot, preferably several feet, and up to 50 feet from the wall of the wellbore before contacting with the gaseous oxidant. In one embodiment of the invention, a non-oxidizing gas is injected thru the ignition well subsequent to the injection of the readily oxidizable fuel so as to drive the fuel into the stratum remote from the wellbore and render the stratum gas permeable. Any non-oxidizing gas such as oil field gas (natural gas), light gaseous hydrocarbons, combustion gas, nitrogen, etc., may be used for this purpose but oil field gas is preferred because of its ready availability and low cost.

In igniting an oil-bearing stratum containing a crude oil of high kindling or ignition point such as one of about 375' or 400 F.,' it is preferred to injectin admixture with the spontaneously combustible fuel a second'fuei having a kindling or ignition point substantially lower-than the ignition point of the native'crude oil but substantially higher than theignition point of the spontaneously combustible fuel. The less readily oxidizable fuel is incorporated in the injected slug in a concentration in the range of about 1 to 50 volume percent, the readily oxidizable fuel being in the range of 99 to 50 volume percent ofthe injected slug. The second fuel of higher ignition temperature comprises any liquid hydrocarbon material having an ignition temperature under ambient conditions in the range of about 275-350 F. Such fuels as kerosene, distillate, cycle oil, and some crude oils have ignition points" the oil in place. it also helps'to adjust theigniti'on temperature of all-of'the combustible material in' the'slugthru' mixing.

The spontaneously ignitable' component of-the' iniected Gil slug is seiected'from any ofthe well known-*materiais which ignite spontaneously under oxidative conditions at the temperature prevailingin the-stratum which 5510 treated. Such materials inc'lude'unsaturated compounds like turpentine, linseed oil, tall-oil, tung'oil, red-oil; etc.

Generally, the oxidizableliquids disclosed in"U.S." Patent 2,863,510. excepting-the aminecompounds, are; operablein the process. Hypergolic-fuelsgenerally'are-withirfithe".

scope of the invention."

Suitable gaseous oxidants-include air,-'oxygen,-oxygen-" enriched air, ozone, gaseous-nitrogen oxides, and m'ixtures of thesegases. when'utilizing airwithout--th'e 0,-

enrichment and without an oxidation-catalyst; the'=ptes'-= sure required for spontaneous ignition-is usually=atleast edge of the fuel slug. The'O -containi'ng gas must'have an oxygen partial pressureof at least 6 lbs. whether atmospheric air or 'oxygen-enriched'air is utilized.

It has been found 'that-incorporationbf an oxidation" catalyst in minor concentration'in'the injected fuel slug facilitates spontaneous ignitiori' ofthe fuel and: makes-it feasible to ignite the'fuel slug' withordinary' air at atmospheric pressure. It is preferred to utilize the catalyst in liquid form so as to avoidpluggin'g the-stratum: A' preferred catalyst is cob'altnaphthenate, which is readily soluble in such fuels as thosenamed'abovm. Other catalysts include oilsoluble salts and other compounds-of the metals listed as oxidationcatalyst's in -Berk'hianet' aL,

Catalysis, Reinhold Publishing Corp..- 330 W: 42nd St'., NewYork'; N.Y'., 1940; pages'797-809:

While theignition-step can be effected in: the: stratum in the presence'of connate 'water; it is preferred tol'air 'dry the stratum prior to the injection ofthe fuePsIug' When any substantialamount of connate"- water is'presentJ-In 'the presence of small concentrations of con'nat'e' water the heating produced bythe spontaneous ignition of' the fuel slug increases the temperaturein-the'contacting zone'until the boiling: point of w'ater' is'-' reached under arn'biem'comditions and the water this heatingzone is-vaporizecl until the ignition zone'is'relatively dry. Theri'the-tempera' ture produced by the spontaneous" heating of the fuel' in contact with oxygenrises until the ignition point is reached and igniti'oii' is'actually' initiated so as to produce a burning zone. Drying-our of the stratum intermediate. the ignition and surrounding injection wellsis readily accomplished by driving air or other drying: gas thru' the stratum between the wells. Following the step of dry- "mg-out with an oxidizing gas, such as air, an'inertgas'is injected to displace the'air fromthe section of stratum into which the autoignitable fuel is to be injected;

v The following examples demonstrate the invention but are not to be construed as unnecessarily limitingsamer Example I Runs were made with several spontaneously ignita'ble fuels under'controlled' conditionsin a 2" diameter Pyrex tube containinga 2-" long section of sand and liquid fuel in a sand to fuel ratio' of 9:1; In all cases, the contained" pack was preheated to'150 F. while flushing with nitrogen. In runs' 1-13, inclusive, oxygen was passed intonthe tube at a rate of s-.c.f./h'r.-ft. at atmospheric pressure.

In runs 14' and air was passed into the tube at a rate of s.c.f./hr.-ft. at atmospheric pressure. The rise in.

temperature within the" tube was balanced by extemalh.

f t 'u TA BLE Spontaneous- Ruu i ()xidlznhlo material 1 1 ignition tcmp.. F.

l.'... lurthnilml linseed oil; 150 I 2. 75% i. ll. linseed oil. Murinlml (in. ii crude.- 200 3 1. ll. linseed oil. Mnriehul-tlp ll enido; 265 4 ill-hydrated castor oil 1X5 5 Tununil 155 6 lat acids. 150

Tull nil fatty acids; 8. Rr-d oil (olnic acid)- 204 0.. Crude tnlioil 200 I 10 ruditall'nll l',,. catalyst l 174 ll llt-tlolH-ifl caialysl L... IN) I 12 Tall oil fatty twi l+1% catalyst 1.50 13 Tall oil fatty aeirl+0.5,7. catalyst l H l"; B: linseed oiH- catalyst- 150 15'. Tall oil fatty ucltl+cntyalst 3 15) Catalyst: solution was lead naphthenate-+oobalthaphtheuate (9:1). 1 Catalyst solution was cobalt. naphthenate (0.! wt. prcceut. cobalt).

Example ll- Similar tests to'those'of' Example I were run with Morichai GroupIiand- Morichalffiroup II crude oil in the sand: The crude oil was admixed with cobalt naph-' thenate-sin' a concentration of 0.1 percent cobalt. The

sandtemperature was raised to 150 F. and 0 at a flow rate of'5' s. :.f.'/hr.-ft; was passed into the'packed sand in'the/ combustion tube. and therewas no autoignition of spontaneouslyignitable' fuel with concentration. of catalyst varying from 0.025 to 0.1 weight-percent and autoignition' was readily achieved at a starting-temperature of 150 F. v Igniting: the' spontaneouslycombustible fuel disclosed herein with'air as an' oxidant isaided by increasing the pressuresubstantially above-atmospheric pressure. Using O enriched. aircontaining: at least" 40% O, enhancesautoignition.

Example 111' In anotherrun using pure'O instead of air, the pack in'the'combustion-tubeof=Example I hada water saturationof" 16% of the-=pore-volume and: an autoignitable oil 1 saturation-=of 50% ofthe" pore .volume, using tall oil fatty acid and cobalt'inaphthenate in a. concentration of 0.1 weight PCX'CBHFCO'JZJE. In this run'. the temperature rose slowly until thewater inthe sand was evaporated and then much-more rapidly asignition= took place. The ignition wasterminatedat 440 F. while the temperature was risin'g=att.6 F.:per minute. i

Example In testing" the mechanics" of the spontaneous ignition procedure, an 18-inch long; Fla-inch diameter stainless steel tube was used. it .waspacked with 9.2-inch section of Ottawasand mixed with autoignitable oil (pius cobalt naphthenate) sandwiched between two sections of Ottawa sandcontaining Group '11 Morichal'oil. Counterflow comb'ustiorr was initiated in the autoignitable section by subiecti'ng it to the flowof oxygen at aflux of 10 s.c.f./hr.-

ing 0.1 weight percent cobalt as cobalt naphthenate as catalyst. This oil mix. was present at a concentration of 17-10 BPAF and the flanking sections contained 1350 BPAF of Morichal Group-II oil.

The total pack was heated to 150 F. (the reservoir temperature of the Group II Morichal sands), while it was fiushed'with nitrogen. The loss of the spontaneously generated heat when oxygen wasiniected was prevented by maintaining the temperature of the outside of the tube substantially equal to that of the interior with an electric heatenA period of 6.5 hours was required tobring the temperature of the sand to 800 F..by spontaneous heating. During this time, the combustion front movedfrom 7 I the middle section containing the autoignitable oil mix into the upstream section containing Group II oil.

The above test with Morichal oil clearly demonstrates that in-place crude oil is readily ignitable by the process of the invention and that a combustion zone can be moved thru an oil sand countercurrently to the flow of oxygencontaining, combustion-supporting gas.

Example V ofN- and air was then substituted for N, at a pressure of 500 p.s.i.g. There was immediate sustained reaction at a 140 F. and the temperature of the pack rose from 140 to 201 F. in 130 minutes. Thereafter, the rate of temperature rise increased substantially, rising to 398 F. in 30 minutes. The run was terminated when the pack reached 398 F. at which time the temperature was increasing at the rate of 4 F. per minute.

A more complete understanding of the invention may be had by reference to the schematic drawing of which FIGURE'l is an elevation in partialcross section thru an oil stratum penetrated by an ignition well and an offset well and FIGURE 2 is a graph showing the relationship between API gravity of the hydrocarbon fuel and the minimum autoignitable oil required.

Referring to FIGURE 1 of the drawing, an oil stratum 10 is penetrated by an ignition well 12 and an offset well 14. Well 12 is provided with a perforate injection tubing 16 and a permeable surrounding ceramic liner 18, tubing 16 being imperforate above the liner 18 and the liner l8 terminating substantially at the upper level of the oil stratum. Well- 14 is provided with a tubing string 20 extending thru the wellhead. I

In the stage of the process illustrated'in the drawing, a slug of autoignitable fuel, such as tung oil 22, has been injected thru tubing 16, liner l8, and into the stratum. A second slug of liquid hydrocarbon such as diesel oil 24 has been injected in the same manner behind the slug of 1 fuel, forming a mixture 26 of the fuel and diesel oil adjacent' the interface of the slugs. At the stage of operation illustrated, the next step in the process comprises either injecting an oxidant such as air or a non-oxidizing gas such as nitrogen, combustion gas, etc., followed by oxi dant injection.

It is also feasible to inject a non-oxidizing, nondeleterious gas thru well 12 to drive the fuel and liquid hydrocarbon deeper into the stratum and then inject air or other oxidant continuously thru tubing string 20 of well 14 so as to initiate ignition at the leading edge of fuel slug 22 and cause the resulting combustion zone to move thru the stratum toward well 14 with production passing thru well 12 and out tubing string 16, which passes thru the wellhead. Such gases include CO flue gas,

, N etc.

' reservoirs of substantial depth temperatures are at this level and upwards so that autoignition of such a fuel is readily effected by injecting air, particularly at the pres-- sures required for such injection.

To illustrate with FIGURE 2, Moric'nal Group II crude oil has an API gravity of 8 and requires at least 35 wt.

percent tung oil mixed therewith and with catalyst to provide an autoignitable fuel composition at the minimum temperature of about 150 F. Naphtha requires a minimum of wt. percent and gasoline, a minimum of wt. percent..0f course, higher concentrations of tung oil up to wt. percent of the composition are operable and provide suflicient added fuel to be effective in igniting the native oil or carbonaceous material. Increasing the air injection pressure lowers the ignition point of the fuel composition in the presence of catalyst.

When combining a high viscosity crude or tar with tung oil, it improves the handling characteristics of the composition to incorporate therein at least 5 and up to 15 wt. percent of a low viscosity hydrocarbon fuel having a considerably higher API gravity. Thus, when using a crude of 8 API gravity admixed with tung oil, the viscosity of the composition is so high that it is desirable to blend therewith a hydrocarbon fuel ranging from a heavy gas oil to gasoline to lower the viscosity of the composition. The required concentration of tung oil increases as the gravity rises. Other autoignitable fuels behave simiing in situ combustion process wherein air is fed thru an offset injection well and forced to the combustion zone to propagate same thru the stratum to the injection well(s). Any suitable well pattern may be utilized in this operation. It is also feasible to ignite the stratum by the method of the invention in a section of the stratum spaced from the ignition well by injecting the oxidant thru an offset well and subsequently terminating injection thru the offset well and injecting air thru the ignition well so as to propagate the combustion zone to the original injection well by direct drive.

Certain modifications of-the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

We claim: j

1. A process for igniting and burning carbonaceous material in a restricted section of oil stratum adjacent but spaced from an ignition well therein in which a perme-. able ceramic tubular liner is positioned in said well downhole within said stratum, which comprises the steps of:.

(l) injecting into said stratum thru said ignition well a slug of an autoignitable fuel (when contacted with O in an amount sufficient to impregnate a substantial but limited section of the surrounding stra tum;

(2) injecting a liquid hydrocarbon miscible with the fuel of step (1) through said well and thru said ceramic liner to remove substantiallyall of said fuel from said liner, prevent formation of plugging material in said liner when oxidant of step (3) is injected therethru, and move said fuel out of a narrow section contiguous to said well; 7

(3) subsequent to step (2) injecting a gaseous oxidant providing sufficient 0, concentration to cause autoignition of the fuel of step (1) into said stratum thru said well and said liner into contact with said fuel so as to effect ignition thereof in said restricted scction; and i v (4) continuing the injection of oxidant of step (3) so 2. The process of claim 1 wherein said fuel includes an oxidation catalyst and said gaseous oxidant consists essentially of air.

3. The process of claim 2 wherein said liquid hydrocarbon in step (2) consists principally of diesel oil. I

4. The process of claim vl wherein the oil in said stratum has an ignition point of at least 375 F. and a liquid hydrocarbon material having an ignition point in the range of 275m 350 F. is incorporated in the fuel of step (1) in a concentration in the range of l to 50 volume percent of the resulting fuel.

5. The process of claim 1 wherein a substantial slug of an inert gas is injected into said stratum thru said 9 well and said liner intermediate steps (2) and (3) to displace fuel of step (1) and liquid hydrocarbon of step (2) radially into said stratum away from said well.

6. The process of claim 1 wherein the autoignitable fuel of step. (1) is selected from the group consisting of tung oil, linseed oil, tall oil, red oil, castor oil, .oleic acii linseed oil fatty acids, tall oil fatty acids, turpentine, and

References Cited UNITED STATES PATENTS Tadema et al 166 -38 Parker '16611 XR Wyllie 166-25 Cline et al. 166-418 Bednarski et al. 166-38 XR Prats 15611 3 10 STEPHEN J. NOVOSAD, Primary Examiner.

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