US3314476A - Initiation of in situ combustion - Google Patents

Description

United States Patent 3,314,476 INITIATION OF IN SITU COMBUSTION Dallas R. Staples, Houston, and Joseph C. Allen, Bellaire, Tex., assignors to Texaco Inc., New York, N.Y., a corporation of Delaware N Drawing. Filed Dec. 26, 1963, Ser. No. 333,704 Claims. (Cl. 16632) This invention relates generally to the treatment of underground formations which produce petroleum. More particularly, this invention relates to the carrying out of an in situ combustion operation within a permeable underground formation. In accordance with one embodiment, the practice of this invention is directed to a method of initiating in situ combustion within a permeable underground formation, e.g., by initiating in situ combustion within a petroleum bearing underground formation by the use of spontaneous ignition agents.

Various techniques have been practiced for the secondary recovery of petroleum from underground formations, including thermal recovery methods, such as in situ combustion, which employ at least one injection well and at least one production well.

In a conventional in situ combustion operation, ignition of the oil in place in the formation may be effected by any one of several well known methods. One such method involves heating the petroleum bearing formation to a sufiieiently high ignition temperature as by means of a downhole electrical heater. A combustion-supporting gas, such as air or oxygen-enriched air, is then introduced into the formation by way of the well bore. A high temperature zone or combustion front with temperatures in the range 7002500 F., is created by the reaction between the thus-introduced oxygen and the combustible petroleum residues within the formation, such as combustible residues resulting from the distillation and/or thermal cracking of the petroleum orginally in place or introduced thereinto. As the operation proceeds, the combustion front moves outwardly from the well bore into the formation in the direction of flow of hot gaseous combustion products.

As a result of combustion of the in-place oil gaseous materials are generated which consist of the gaseous products of combustion and volatized components of the hydrocarbons present. These hot gases move outwardly into the formation and lose heat to the formation. Thus, as more oxygen-containing gas is supplied through the well bore, the high temperature combustion front moves outward from the well bore without further direct application of heat to the area immediately surrounding the well bore. The distance the combustion front moves outwardly, and accordingly, the volume of the petroleum producing formation swept by the combustion process, is dependent upon the relative magnitude of the rate of heat generation (due to the combustion of combustible residues) and the rate of heat loss to the surrounding formation. Although the exact mechanism of an in situ combustion is not known definitely, the following sequences of events is postulated and is presented herein for the purpose of enabling one skilled in the art to understand the practice of this invention.

As the combustion front approaches a given volume of the petroleum-containing formation, the temperature of this volume of formation increases. This results in a reduction in the viscosity of the formation liquids therein due to their temperature rise. These fluids then may be moved more readily under the influence of the hot gas stream continuously emanating from the combustion. As the temperature of this volume of formation continues to rise, distillation of the liquids therein begins. The products of the distillation condense in the cooler regions of the formations outward from the high temperature combus-tion front in the direction of gas flow. The distillation continues as the temperature rises until the heavier components remaining within the petroleum originally in place Within the formation or introduced thereinto prior to effecting in situ combustion begin to crack or otherwise thermally decompose, yielding hydrocarbon gases, coke and solid carbonaceous residues. As the temperature continues to rise, a point is reached at which the hot coke or hot combustible residues will begin to combine chemically with the oxygen with the resulting release of heat to the formation and the gas stream emanating therefrom. This heat is carried away by the outwardly moving gas stream and also to a limited extent is transferred to the adjacent regions of the formation by conduction. When the coke and combustible residues have been burned away, there remains a volume of substantially liquid-free formation which, unless otherwise treated, is cooled gradually by the oncoming relatively cool combustion-supporting gas or air entering the thus-treated given volume of the formation via the well bore.

One difficulty in carrying out an in situ combustion recovery operation involves the operation of initiating combustion in the formation. Various methods have been proposed heretofore for underground initiation of combustion. For example, electrical heating devices or gas fired bottom hole igniters or heaters suitable for lowering within the borehole opposite the formation wherein the combustion is to be initiated, have been suggested. Another method involves the introduction of phosphorus into the petroleum producing formation.

Still another method of the prior art, described in copcnding application Ser. No. 215,459 filed on Aug. 7, 1962, in the names of Valery N. Bednarski, Robert E. Kunetka and Joseph C. Allen, and now U.S. Patent No. 3,180,412, involves introducing into the petroleum-bearing formation to be ignited an ignition agent comprising an unsaturated aliphatic compound comprising only carbon, hydrogen and oxygen atoms and containing at least 16 carbon atoms per molecule, particularly a drying oil or semi-drying oil, and then passing into the same formation a gas comprising free oxygen to effect spontaneous .eombustion of the aliphatic compound with resulting ignition of the petroleum. An oxidation promoter, for example, an organic nitrogen base such as pyridine may be included in the ignition mixture to promote the spontaneous ignition reaction. Also, oxidation catalysts or dryers, such as cob-alt naphthenate have been included to promote spontaneous combustion. Powdered magnesium can also be used to increase the amount of heat released after spontaneous combustion has been initiated.

The above method has been satisfactory in many tests, but it has been found that it sometimes fails in injection wells wherein it is not possible to maintain high air pressures, such as more than psi, because of excessive permeability or fracturing in the pay formation adjacent the injection well.

It is an object of this invention to provide an improved method for initiating in situ combustion within a permeable petroleum-bearing formation.

A further object of the invention is to provide a thixotropic composition which, when placed in a permeable formation, will set up as a gel to yield conditions favorable to initiation of combustion in the formation.

In accordance with this invention, it has been discovered that the initiation of in situ combustion of the hydrocarbons contained in a petroleum bearing underground formation may be facilitated by introducing a combus- '2 a ously combustible material into the formation and then passing an oxygen-containing fluid therethrough, ignition may be enhanced and facilitated by introducing a combustible thixotropic substance into the formation prior to the introduction of the spontaneously combustible material.

It has further been found that a desirable thixotropic substance may be prepared by incorporating a saponifiable organic compound containing at least l6 carbon atoms per molecule and an alkali metal hydroxide with a petroleum derived material such as crude oil in such proportions that the mixture will set up as a gel when agitation is ceased.

Improved results can be obtained by preceding and following the injection of the thixotropic substance into the formation with the injection of crude oil or other combustible petroleum derived materials prior to the injection of the spontaneous ignition chemical.

Under some conditions spontaneous ignition can be obtained by the passage of air or oxygen-enriched air through a gelling substance prepared with an unsaturated saponifiable aliphatic compound, without the subsequent injection of a spontaneously combustible material into the petroleum bearing formation.

in practicing the method of this invention, the desired number of wellsis drilled into the formation, a minimum of two boreholes or wells usually being required, one of these being called an input or injection well, the other and output or production well. It is to be understood that there may be more than one well of each type if so desired. The input well provides access for ignition of the combustion reaction, and for injecting a combustion supporting gas or fluid into the formation. The output well, onthe other hand, serves primarily for collection of the oil being produced and the gaseous products of combustion, and also serves as a means for bringing such oil and combustion products to the surface.

It is a usual practice when an underground in situ combustion operation is contemplated to first establish a path or zone of permeability through the petroleum containing formation, extending from an injection well to a production well or wells. In order to establish such a permeable path, a gas, usually air although an inert gas such as nitrogen may be used if so desired, is pumped into the input well under sutficient pressure until it has been determined that a permeable path exists between the injection well and the output well or wells. If air pressure alone is not sufficient to achieve the desired degree of permeability, it is sometimes necessary to employ hydraulic fracturing at the input well to accomplish the desired result.

Ordinarily, once permeability has been established through the petroleum-containing formation, it is possible to initiate in situ combustion in accordance with one of the methods of the prior art. However, we have found that in many instances it is difficult to initiate combustion due to physical conditions within the formation which result in relatively low pressures in the zone where ignition is contemplated. These physical conditions may be excessive permeability-either natural or due to excessive hydraulic fracturing of the petroleum reservoir and so forth. We have found in general that in order to initiate combustion in the formation adjacent the input well that the pressure in this zone must be at least 150 p.s.i.g., and preferably above 200 p.s.i.g., when the combustion supporting gas is initially passed through the formation at the desired rate of gas flow. Accordingly, the method .of this invention is particularly useful when it is desired to carry out an in situ combustion operation for the recovery of petroleum from an underground formation wherein the pressure drop of the combustion supporting gas through the petroleum-bearing formation between the injection or input well and the production or output well is too low to maintain sufficient pressure at the input well to initiate combustion. The method may be employed advantageously with any of the ignition methods of the prior art, such as by means of down-hole heater, surface preheating of the injected combustion supporting fluid, and particularly by means of spontaneously combustible ignition materials.

It has been determined experimentally under well igni tion conditions that the pressure on a spontaneously combustible chemical, such as a fatty oil, placed in a well formation and exposed to an oxygen-containing gas, as in the initiation of in situ combustion by the method of copending application Ser. No. 215,459 referred to hereinbefore has a marked effect on the success with which spontaneously combustible material may be ignited by a combustion supporting gas. In general, moreover, when using the socalled chemical igniters, such as linseed oil fatty acids and similar materials, the induction time required for spontaneous ignition is reduced as the pressure is increased. It has been further ascertained that the shorter the induction time or in other words the shorter the length of time it is necessary to pass oxygen-containing gas through the combustible liquid before ignition takes place spontaneously, the higher are the temperatures reached upon spontaneous ignition for a combustible liquid of fixed B.t.u. content. It has also been demonstrated that the higher this ignition temperature, the better chance there is for successful ignition of the inplace crude. Through this relationship successful ignition of the crude is to a large degree dependent upon pressure maintained on the combustion liquid.

In wells in which ignition has been unsuccessful due to insufficient pressure in the input well, the principles of the present invention have been used successfully by forcing the thixotropio hydrocarbon gel into the injection well and then into the excessively permeable portion of the formation surrounding the borehole where its physical state changes from that of a pumpable liquid to a solid or semisolid gel, which results in sufficient blocking of the permeable path to enable attaining the required pressure at the input well. In a preferred embodiment, a Volume of petroleum derived from the formation by ordinary production practices, called lease crude, is first forced into the input well and the formations adjacent the input well. The lease crude is then followed by injection of the hydrocarbon gel of the present invention into the input well and the surrounding permeable formation. In the event chemical ignition is employed, the gel is then followed by injection of a chemical which ignites spontaneously when a combustion supporting gas such as air is passed therethrough. Preferably a volume of lease crude is injected.

into the formation between the hydrocarbon gel and the chemical igniter in the event any excess caustic in the gel may tend to act as a catalyst poison and interfere in any way with the spontaneous combustion properties of the chemical igniter.

Following the placement of the hydrocarbon gel and the chemical igniter in the petroleum containing formations adjacent the input well, a combustion-supporting oxygen-containing gas, such as air or oxygen-enriched air or substantially pure oxygen, is introduced into the formation via the input well. Air preheated to above F. and preferably above 200 F. is particularly suitable. If a downhole heater is used for initiating ignition, the procedure is the same except that the injection of the chemical igniter is omitted.

Reaction of the oxygen content of the combustion supporting gas with the chemical igniter causes ignition of the igniter by means of spontaneous combustion. The heat thus produced raises the temperature of the formation such that ignition of the petroleum content, including the thixotropic gel, occurs. Continued injection of combustion supporting gas into the input well results in the establishment of a combustion zone or reaction front which moves progressively away from the input well by the burning of combustible material contained in the pores of the formation.

The aforesaid hydrocarbon gel is prepared at the surface by mixing crude oil or other petroleum derived liquid hydrocarbon with from 1.5 to 3.0 percent by weight of a saponifiable organic compound of a type to be described hereinafte-r and with sufficient caustic or alkali for neutralization of the acidic groups of the organic compound, ordinarily in the range of from 0.4 to 0.9 percent by weight. Mixing is not critical and may be carried out in conventional pump and tank type mixing units available to oil well drilling operators. If a catalyst or promoter is to be included in the gel composition, it ordinarily is added to the organic compound prior to mixing with the hydrocarbon. Although the proportions used will vary somewhat with the type of hydrocarbon or crude oil used, as well as with the particular organic compound employed, it has been found that a composition comprising about 2.0% of fatty acid and about 0.6% caustic soda by weight, the remainder being crude oil, yields a satisfactory thixotropic substance which is a gel under static conditions, but which becomes fluid when pumped or circulated. It is desirable that once the mixture has been compounded, it should not be allowed to stand in the mixing equipment prior to pumping it down the Well bore.

It further has been found that an unsaturated oxygenated aliphatic organic compound, such as an unsaturated long chain fatty acid, fat or fatty oil, and the glycerides and esters of unsaturated long chain fatty acids, including esters formed with unsaturated long chain fatty alcohols, are particularly suitable for use as the saponifiable organic compound in that the unsaturated linkages are subject to auto-oxidation under the conditions existing in the well bore when an oxygen-containing gas is passed into the permeable formation containing the hydrocarbon gel.

Exemplary unsaturated aliphatic organic compounds which are suitably employed in the practice of this invention include the following monocarboxylic acids, as well as their isomers and the glycerides and esters thereof, for example: monoethylenic types such as oleic, palmitoleic, phytenic and erucic; diethylenic types such as linoleic and dodecadienoic, triethylenic types such as linolenic; acetylenic types such as stearolic and eicosynoic; and hydroxy unsaturated types such as ricinoleic.

It has been found that the related saturated ali hatic organic compounds also are useful in carrying out the invention in that they are capable of producing hydrocarbon gels when mixed with oil and an alkali metal hydroxide. Examples of such saturated aliphatic organic compounds include the following monocarboxylic acids as well as their isomers and the corresponding alcohols and esters thereof: palmitic, margaric, stearic, arachidic and behenic. Hydroxy saturated acids include dihydroxystearic, dihydroxybehenic and tetrahydroxystearic or sativic acid.

Also encompassed by the invention are the natural processed fats and fatty oils containing one or more of the foregoing types of aliphatic organic compounds and more particularly the so-called drying oils and semi-drying oils. Suitable saponifiable nonhydrocarbon oils, vegetable and animal (mammal or fish), or mixtures thereof, which may be employed include corn oil, cottonseed oil, sesame seed oil, sunflower seed oil, soybean oil, poppyseed oil, perilla oil, tung oil, citicica oil, linseed oil, and fish oils, such as herring oil, sardine oil, menhaden oil, whale oil, seal oi'l, porpoise oil, dolphin oil, and the like. In general, any saponifiable nonhydrocarbon oil, animal or vegetable capable of producing thixotropic gel in accordance with the invention may be used. However, an unsaturated animal or vegetable oil is preferred. For the most part, these oils, such as linseed oil and the like, comprise triglycerides of unsaturated long chain fatty monocarboxylic acids.

It is also contemplated that gels formed by incorporating other types of emulsifying agents, such as aromatic sulfonates, also may be employed.

Desirably and in accordance with one embodiment of this invention, there is admixed with the hydrocarbon gel, preferably by mixing with the hydro-carbon oil, the saponifiable organic compound or the alkali metal hydroxide prior to gellation, and prior to introduction into the permeable formation undergoing treatment a suitable oxidation promoter. Organic nitrogen bases, such as pyridine, pyrrole, piperidine, aniline and dimethylaniline, are particularly useful as oxidation promoters to promote a spontaneous in situ combustion reaction in accordance with this invention.

In accordance with another embodiment of the invention, and particularly when the hydrocarbon gel comprises an unsaturated saponifiable organic compound, the gel also contains admixed therewith a minor amount of drying oil oxidation catalyst or dryer, such as cobalt naphthenate, cobalt tallate, cobalt octoate, and similar iron, manganese or lead dryers in order to catalyze oxida tion thereof.

In accordance with still another embodiment of the invention, there is incorporated into the gel a suitable minor amount, in the range of 0.2510% by weight, of finely-divided, powdered magnesium or magnesium dust. Once spontaneous in situ combustion has been initiated, the powdered magnesium greatly increases the amount of heat released and the temperature generated during initiation of the in situ combustion process within the formation undergoing treatment.

The chemical igniter may be any of the several types disclosed in the prior art. However, it has been found that the materials disclosed in copending application Ser. No. 215,459 are particularly suitable for use in accordance with the present invention. Such igniters consist of materials characterized generally as an oxygenated aliphatic organic compound, such as an unsaturated long chain fatty acid or an unsaturated long chain fatty alcohol or fat or oil, and the glycerides of unsaturated long chain fatty acids, and more particularly unsaturated-aliphatic compounds comprising only carbon, hydrogen, andvoxy gen atoms and containing at least 16 carbon atoms per molecule. Particularly useful are the unsaturated nonhydrocarbon oils, particularly those oils, so-called drying oils or so-called semidrying oils having an iodine number greater than 100, especially greater than 130. Desirably, there may be admixed with the nonhydrocarbon oil a suitable oxidation promoter, of which the organic nitrogen bases such as pyridine, dimethylaniline and the like are particularly useful. Desirably also, the unsaturated nonhydrocarbon oil or unsaturated aliphatic compound may also contain admixed therewith an oxidation catalyst ordryer, such as cobalt naphthenate, cobalt tallate, cobalt octoate, and similar iron or lead driers. As still another ingredient a suitable amount of powdered magnesium or magnesium dust also may be incorporated to provide a source of intense heat upon ignition of the chemical igniter.

The following is an example of the process of this invention for initiating an in situ combustion as performed in an oil well in the Gulf Coast area of the United States.

Example Injection and production wells were drilled in preparation of an in sit-u combustion production program of an oil field in the southern portion of Texas in which primary production has been depleted. A line of injection wells were drilled across the width of the field and producing wells were drilled to strike on each side of the injection line.

In 65% of the injection wells in the field, ignition was accomplished without difficulty either by the injection of ignition chemicals in accordance with the method of copending application Ser. No. 215,459, or by means of an electrical heater for heating the face of the oil-bearing section in accordance with well known production practice. The ignition chemicals consisted of two drums of water-white distilled linseed oil fatty acids containing approximately one pound of cobalt naphthenate and one pound of dimethylaniline per hundred pounds of the fatty acids. The chemicals were introduced into the well bore and then forced into the formation by injection of nitrogen. Air injection was commenced at a relatively low rate of a few thousand cubic feet per hour at a maximum injection pressure in the neighborhood of 300 lbs. per square inch and was continued at the low rate for about 12 to 14 hours, after which time the rate was increased to the combustion injection rate of about 1 million cubic feet per day. Approximately one-half hour to 1 hour after the increase in air injection rate the temperature began to rise rapidly as a result of initiation of combustion.

It was found, however, that 35% of the injection wells could not be ignited by the procedure em loyed. Analysis of the conditions existing in the wells which did ignite and those which did not revealed that those wells which could not be ignited by the usual procedures had a com mon property in that the air pressure in the well bore during the ignition attempts could not be raised above 150 lbs. per square inch, whereas in the ignited wells the air pressure rose above 150 p.s.i.g.

The following is a description of the well completion procedure for one well in the field, a description of the unsuccessful attempt to ignite this well, and a description of the application of the present invention which resulted in successful ignition of the petroleum in the formation adjacent this well.

The well was prepared for ignition by drilling to a total of the hole with slotted casing being used opposite the pay depth of about 200 feet, or about 25 feet below the bottom of the pay zone. Casing was then run to the bottom zone. The casing was then cemented from the top of the pay zone to the surface. After this the Well was cleaned out to total depth. A string of tubing was run into the hole with the bottom of the tubing opposite the bottom of the pay zone.

After an air injectivity test to determine that the well would accept air at the desired injection rate, the well was purged with two casing volumes of gaseous nitrogen injected at the well head assembly. Two drums, or 110 gallons, of ignition chemicals were then displaced into the well with nitrogen from a displacement vessel located at the surface. Additional nitrogen was injected to force the ignition chemicals into the formation and to purge the borehole, as well as to establish receptivity of the nitrogen to the formation at a decreasing pressure gradient. Injection of air for initiation of combustion was then started at an injection rate of 150,000 cubic feet per day for the first eight hours, after which the injection rate was raised to 210,000 cubic feet per day for another eight hours. After this, the rate was increased to 700,000 cubic feet per day for a two-hour period. No combustion of the ignition chemical was obtained and combustion of the in-place oil was not achieved.

The ignition chemicals employed in the foregoing ignition attempt consisted of water-white distilled linseed oil fatty acids containing one pound of cobalt naphthenate as an oxidation catalyst and one pound of dimethylaniline as an oxidation promoter per 100 pounds of fatty acids. This was approximately equivalent to onehalf gallon of each of these materials per 55 gallon drums of the fatty acids.

Following the unsuccessful attempts to obtain ignition in this and several other wells in the field, a study of the conditions in the wells which did not ignite and the other wells in which ignition was obtained by chemical ignition employing the same operating procedure revealed that following the injection of the ignition chemicals the well bore pressures during the injection of air were noticeably lower for the wells that did not ignite than for the wells in which ignition was achieved. It was found the well head pressures during this period were generally above 235 pounds per square inch in the wells in which ignition was achieved and below about 200 p.s.i. in the wells which failed to ignite.

In a further attempt to initiate combustion in the well of this example, the following procedure was employed. First, five barrels of lease crude, crude previously obtained by production from the field, were pumped into the well and forced into the pay zone by means of gaseous nitrogen. This was followed by the injection of fifteen barrels of gelled oil followed by injection of another five barrels of lease crude.

The gelled oil was prepared at the surface by mixing lease crude with 2.0 percent by weight of linseed oil fatty acids and 0.6 percent by weight of caustic soda in a continuous blender or proportioning device at ambient temperature. The output from the blender was connected directly to the surface injection pump in order that the crude-fatty-acid-caustic mixture not be allowed to stand quiescent as under static conditions this composition sets up into a gel. The composition of a suitable gelled oil may vary slightly depending on the crude or other oil used and upon the degree of gelling desired. However, the composition ordinarily will not vary greatly from that given above, namely 2.0% by weight fatty acids and 0.6% by weight caustic soda. It has been found that crudes containing in excess of about one percent water or those containing a high concentration of demulsifier, as from a desalting, deernulsifier, or dehydration operation, will not form a gel under static or quiescent conditions.

Following the second injection of lease crude, a short air injectivity test was made to ascertain the receptivity of the formation to air. The casing and tubing were then purged with gaseous nitrogen and the casing closed off at the surface. Three barrels of ignition chemicals of the same composition as previously used were injected into the tubing. These chemicals were comprised of water white distilled linseed oil fatty acids containing one pound of cobalt naphthenate and one pound of dimethylaniline per pounds of fatty acids. The ignition chemicals were forced into the formation by means of nitrogen injected down the tubing, following which air injection was started into the tubing at a rate of 180,000 cubic feet per day. As evidenced by both a pressure surge in the borehole and by an increase in borehole temperature in the vicinity of the pay zone, ignition was successfully achieved after an air injection period of about one hour. A pressure surge of 80 p.s.i. occurred upon ignition, which was considerably higher than the pressure surges noted in wells successfully ignited without the use of gelled oil. In those instances a pressure surge of from 20 to 30 p.s.i. was noted in several wells and in other instances the wells were ignited with only a slightly pressure surges of less than 10 p.s.i. In addition, in the example well using the gelled oil, a secondary pressure surge was noted after an additional 10-20 minutes of air injection, thereby indicating that another interval of the formation had ignited. Temperatures in the lower end of the tubing fluctuated wildly, going as high as 1100 F. The pressure after about two hours did not decline to the original pressure as had been the case in all of the previously ignited wells. Instead the pressure after about 5.4 hours was still p.s.i. or 20 p.s.i. higher than the initial pressure. This is another indication that the procedure of the present invention achieved more efficient ignition by igniting more of the pay section. This was in a well which previously did not respond to ignition by the method of the prior art.

Although the invention has been described as employing a spontaneously combustible ignition chemical following the injection of the gelled oil, it is contemplated that ignition may be initiated by means of a down hole heater or one of the other ignition methods of the prior art. It is further contemplated that an unsaturated fatty acid may be employed as the saponifiable constituent of the gelled oil mixture with the gelled oil itself acting as an ignition chemical by spontaneous initiating combuston upon the injection of air, particularly when there are incorporated therein oxidation catalysts and promoters of the types described hereinbefore.

For the ignition of formations characterized by either highly permeable streaks or by fractures it is further contemplated that lease crude or heavy oil and caustic may be mixed with the unsaturated fatty oil ignition chemical containing an oxidation catalyst and/or promoter to achieve ignition by reducing the permeability of these larger passages through the formation being produced.

Obviously, many modifications and variations of the invention as hereinbefore set forth may be made Without departing from the spirit and scope thereof and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. In the method of initiating in situ combustion in a permeable petroleum bearing underground formation traversed by a borehole wherein combustion of the petroleum in the formation is initiated by placing a spontaneously combustible material in the formation and passing an oxygen-containing gas therethrough, the improvement comprising the introduction into said formation prior to the introduction of said spontaneously combustible material of a gelling composition comprising a spontaneous 1y oxidizable saponifiable constituent and having the property of being relatively fluid under dynamic conditions and of setting to a gel under static conditions.

2. In the method of claim 1, said gelling composition comprising a petroleum material, a spontaneously oxidizable saponifiable organic compound containing at least 16 carbon atoms per molecule and an alkali metal hydroxide.

3. In the method of claim 2, said spontaneously oxidizable saponifiable organic compound being an unsaturated long chain fatty acid.

4. In the method of claim 3, said unsaturated long chain fatty acid comprising fatty acids derived from linseed oil.

5. In the method of claim 2, said spontaneously oxidizable saponifiable organic compound being a glyceride of an unsaturated long chain fatty acid.

6. In the method of claim 2, said alkali metal hydroxide being sodium hydroxide.

7. In the method of claim 2, said spontaneously oxidizable saponifiable organic compound being present in an amount of approximately one and one 'half to three percent by weight of said gelling substance and said alkali metal hydroxide being present in an amount of approximately four-tenths to nine-tenths percent by weight of said gelling substance.

8. The method of initiating in situ combustion within a permeable petroleum bearing underground formation penetrated by at least an injection well comprising the forming of a zone of permeability in said underground formation by flowing air therethrough, purging said injection well by an inert gas, introducing into said formation a first amount of crude petroleum, introducing into said formation a combustible gelling composition having the property of being relatively fluid under dynamic conditions and of setting to a gel under static conditions, introducing into said formation a second amount of crude petroleum, introducing into said formation by displacement: with an inert gas an amount of a spontaneously combustible liquid mixture comprising an unsaturated aliphatic organic compound containing at least 16 carbon atoms per molecule together with an oxidation catalyst and an oxidation promoter, subsequently introducing through said injection Well into said formation a gaseous stream containing free oxygen for a period of time suflicient to increase the temperature of the treated formation by oxidation of said organic compound therein for ignition of the petroleum in said formation and flowing air through said formation for in situ combustion therein.

9. In the method of initiating in situ combustion in a permeable underground formation traversed by a borehole wherein combustion of the petroleum in the formation is initiated by placing a spontaneously combustible material in the formation and passing a combustion supporting gas therethrough, the improvement wherein said spontaneously combustible material is in the form of a thixotropic composition comprising crude petroleum, a spontaneously oxidizable saponifiable organic compound containing at least 16 carbon atoms per molecule and an alkali metal hydroxide.

10. In the method of claim 9, said thixotropic composition comprising crude petroleum, a spontaneously oxidizable saponifiable organic compound containing at least 16 carbon atoms per molecule, an alkali metal hydroxide and a minor proportion of an organic nitrogen base.

11. In the method of claim 9, said thixotropic composition comprising crude petroleum, a spontaneously oxidizable saponifiable organic compound containing at least 16 carbon atoms per molecule, an alkali metal hydroxide and a minor proportion of a drying oil oxidation catalyst.

12. In the method of claim 9, said thixotropic composition comprising crude petroleum, a spontaneously oxidizable saponifiable organic compound containing at least 16 carbon atoms per molecule, an alkali metal hydroxide, a minor proportion of a drying oil oxidation catalyst and a minor proportion of powdered magnesium.

13. In the method of initiating in situ combustion in a permeable petroleum bearing underground formation traversed by a borehole wherein a combustion supporting gas is passed down the borehole and into the formation during the ignition procedure, the improvement comprising reducing the permeability of said formation prior to introducing said combustion supporting gas by introducing into said formation a combustible thixotropic materal which partially blocks the permeable passages and maintaining said reduced permeability until ignition has been effected.

14. The method of claim 13 wherein said combustion supporting gas is supplied to said formation during the initiation of combustion at a borehole pressure in excess of pounds per square inch.

15. In the method of initiating in situ combustion in a permeable petroleum bearing underground formation, traversed by a borehole the improvement comprising preparing a combustible thixotropic fluid mixture at the surface of the earth in the vicinity of said borehole, continuously mixing said prepared mixture until pumped down said borehole and into said formation, pumping said mixture down sad borehole and into said formation, stopping said pumping when said mixture is in place in said formation thereby allowing said mixture to set up as a gel with resulting partial plugging of said formation prior to and during initiation of combustion.

References Cited by the Examiner UNITED STATES PATENTS 2,863,510 12/1958 Tadema et al. 166-38 2,880,802 4/1959 Carpenter 16611 3,072,190 1/ 1963 Reichle 16639 3,180,412 4/1965 Bednarski et a1 166-11 3,198,249 8/1965 Willman 166-11 X 3,261,400 7/1966 Elfrink 16630 OTHER REFERENCES Rogers: Composition and Properties of Oil Well Drilling Fluids, 1st edition, Gulf Publishing Co., Houston, Texas, 1948, pp. 422 to 432 relied on.

JACOB L. NACKENOFF, Primary Examiner.

CHARLES E. OCONNELL, Examiner.

S. J. NOVOSAD, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,314,476 April 18, 1967 Dallas R. Staples et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 7, line 32, strike out "of the hole with slotted casing being used opposite the pay" and insert the same after "bottom" in line 34, same column 7 column 8, line 52, for "slightly" read slight column 10, line 51, for "sad" read said Signed and sealed this 7th day of November 1967.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

Claims (1)

1. IN THE METHOD OF INITIATING IN SITU COMBUSTION IN A PERMEABLE PETROLEUM BEARING UNDERGROUND FORMATION TRAVERSED BY A BOREHOLE WHEREIN COMBUSTION OF THE PETROLEUM IN THE FORMATION IS INITIATED BY PLACING A SPONTANEOUSLY COMBUSTIBLE MATERIAL IN THE FORMATION AND PASSING AN OXYGEN-CONTAINING GAS THERETHROUGH, THE IMPROVEMENT COMPRISING THE INTRODUCTION INTO SAID FORMATION PRIOR TO THE INTRODUCTION OF SAID SPONTANEOUSLY COMBUSTIBLE MATERIAL OF A GELLING COMPOSITION COMPRISING A SPONTANEOUSLY OXIDIZABLE SAPONIFIABLE CONSTITUENT AND HAVING THE PROPERTY OF BEING RELATIVELY FLUID UNDER DYNAMIC CONDITIONS AND OF SETTING TO A GEL UNDER STATIC CONDITIONS.