US3316962A

US3316962A - In situ combustion method for residualoil recovery from petroleum deposits

Info

Publication number: US3316962A
Application number: US540452A
Authority: US
Inventors: Lange Hans
Original assignee: Deutsche Erdoel AG
Current assignee: Wintershall Dea International AG
Priority date: 1965-04-13
Filing date: 1966-03-15
Publication date: 1967-05-02
Anticipated expiration: 1984-05-02
Also published as: NL6602327A; AT276273B; NL155912B; DE1242535B

Description

tion of preferred flowing United States Patent O D 12 Claims. (Cl. 166-11) The present invention relates to a method for recovering residual oil from petroleum deposits.

This application is a continuation-impart of application Ser. No. 440,852, filed Mar. 18, 1965, and applicant relies upon the disclosure and requests the filing date and all rights and priorities claimed therein.

The disclosure of application Ser. N-o. 215,493, filed Aug. 6, 1962, now U.S. Patent No. 3,276,518, and assigned to the assignee of ythe present invention is incorporated by reference into the disclosure of the present invention.

It is an object of the present invention to provide an improved method for the -recovery of residual oil remaining in partially exploited oil fields.

It is another object of the invention to provide an improved method of in situ combustion for the exploitation of bitumens from petroleum deposits.

Another object of the present invention is to provide a method of oil field exploitation comprising flooding the field with water in the direction of exploitation while conducting an in situ combustion in a direction perpendicular to the direction of exploitation.

Other objects of the invention are the pretreatment of oil fields prior to exploitation by the circulation of flood water containing salts and catalysts.

Still further objects of the invention are the use of compressed activated gases of combus-tion for the in situ combustion with controlled pressure variation of the combustion gases.

According to the pri-or art, when the production or recovery from a petroleum reservoir or deposit has become uneco-nomical, secondary recovery practices are initiated in order to recoverat least partiallythe still adhering proportions of hydrocarbons. The quantities involved amount on the average to 40 to 60% of the original content of the petroleum deposit.

Frequently employed prior art techniques for the secondary recovery effect an increase -of the pressure or of the temperature of the deposit or reservoir. For example, in the gas-drive methods, partially with light hydrocarbons, and when flooding with water from injection holes, the pressure of the deposit is displaced toward recovery holes. Such a prior art process is disclosed in British Patent No. 726,712. These steps are, however, only partially successful; preferred channels are generally formed and the oil of the deposit sections positioned between the drilled holes is hardly affected thereby.

For the purpose of increasing the tempera-ture of the deposit, hot water or vapor injections are carried out. In this prior art method, however, the danger of the formapat-hs directly to the recovery lholes is particularly great so that the media being introducedbeing used in part only to a very small extentare prematurely lifted or brought out again. For the purpose of increasing the deposit temperature an in situ combustion is also used. According to this method, the con-tent of the deposit is partially evaporated and partially rendered more readily flowable by means of a partial combustion. In the process of the direct linear flow path or passage from compression holes to adjacent recovery holes, a cylindrical burnt-out rock structure will `be formed in the deposit or reservoir in the course of the continuous supply of oxidation agents. From the compression holes to the recovery holes this rock structure will constantly increase and be lengthened, and eX- te-nd from the compression hole with a forwardly positioned gas-permeable tongue into the recovery hole. The axis of the combustion front extends from the compression hole to the recovery hole. In case the deposit is filled with liquid, this direction of the axis is predetermined by virtue of the fact that free-blowing thereof is required prior to beginning the in situ combustion, and the liquid will be rising to the upper edge of the deposit at the recovery hole. The oxidation tagents flow on this axis behind the combustion front in the burnt-out rock of the deposit. Ahead of the combustion front the `resultant inert combustion gases flow most rapidly, while at the casing of the burnt-out rock structure the oxidation agents will also flow in the direction of the axis, but more slowly due to the longer flowing path thereof. At the casing of the burnt-out rock structure the disturbing factor arises that resultant oxygen-poor combustion gases flowing laminarly in the rock of the deposit keep further oxidation agents almost entirely away from the surface of the casing, thus allowing oxidation agents to become effective at best only in a greater dilution so that at a large distance from the axis of flow coke particles are deposited, due to the existing heat, in this cylindrical casing and will no longer be burned because of the insufficient amount of oxygen. This behavior at the casing of the rock structure and the intensified flow in the vicinity of the axis result, for an oil field during exploitation at these surfaces, in a reduced action in both the horizontal and in .the vertical direction between the adjacent holes and the overlying rocks. The coke deposits render it diflicult to keep all of the flowing paths free and local increases of pressure may be produced in the deposit and often lead to undesirable flowing directions, thus guiding the combustion forcibly to other paths. These disturbing operational conditions have the result that vast parts of the reservoir or deposit remain unexploited.

According Ito the present invention, rows of recovery boreholes defining a recovery Zone, rows of treatment and leading boreholes defining a treatment zone, and rows of flooding boreholes are drilled in an oil eld for the recovery of residual oil therein. The direction of flow of the product to be recovered is controlled by the pressure gradient from the flooding boreholes to the recovery boreholes. The product being recovered is treated in the treatment zone by controlled in situ combustion in a direction perpendicular to the direction of flow.

-Other objects and advantages of the present invention will be apparent upon reference -to lthe accompanying drawings which schematically illustrate the manner in which the present process is carried out.

In the drawing a top plan view of a portion of an underground deposit of liquid bitumens is schematically illus-trated. A flooding zone, a treatment zone, and a recovery zone are illustrated with the respective flooding boreholes, treating and leading boreholes, and recovery boreholes therein. The sections of the drawing shown in Roman numerals illustrate the process steps of the invention conducted between the -treating boreholes and leading boreholes perpendicular to the direction of flow of the recovery.

A method has ibeen proposed to provide a more complete recovery of the contents of a petroleum deposit or reservoir by means of the in situ combustion -by opening an oil field with staggered rows of boreholes which serve as flooding boreholes in a structurally deep zone and as recovery boreholes in a structurally high zone. Arranged between these rows of boreholes are so-called treating boreholes an so-called leading boreholes in one treatment zone in which the content of the deposit is heated and loved in a circulation pattern by virtue of the fact tha-t it recovered from the leading boreholes above ground nd reintroduced, after heating, into the deposit through 1e treating boreholes. Heating is effected in that hot iodied and activated combustion gas is admixed above round to the liquid content of the deposit. The modied combustion gas which contains little nitrogen is prouced by burning predominantly gaseous deposit con- :nt with air enriched with oxygen from 8O to 95% in he pressure combustion chamber of a boiler. By admixng enriched oxygen containing, in addition to 80-95% txygen, also a residue of yfrom to 20% nitrogen, an .acti- 'ated combustion gas is recovered from the modified comustion gas. The treating -boreholes and the leading boreloles of one treatment zone are staggered and therefore tre arranged that the movement of the circulation takes )lace in a direction which differs from the flow lmovement `esulti'ng from the primary movement from the flooding )orehole to the recovery borehole. With the activated aombustion gas, an in situ combustion is initiated in the reatcd deposit and a reaction zone is created in the treatnent zone. As a result of the combustion of petroleum leposit -or reservoir -contents in the deposit or reservoir with the oxygen, modified combustion gas is produced which has the property of condensing and, respectively, 3f becoming dissolved -in the liquid deposit content with- Jut leaving a Igaseous phase.

It has now been found that for purposes of exploiting 1 deposit or reservoir by means of in situ combustion, other factors have to be taken into account if as complete as possible a recovery is to be achieved. The use of the linear flow 4between compression hole and the recovery hole not only involves the hazard of burning channels and thus a great loss because of untreated deposit portions, but the combustion procedure itself is an unstable process if the combustion gases iiow in the direction of the axis between the compression hole and the recovery hole. If the temperature is too high, a strong cracking Will occur in the content of the deposit and, .in turn, produce a high coke portion so that the burning progress or advance becomes smaller and thus the combustion ternperature is further increased. The further growing coke portion or constituent may, in places, become so high that obstacles :in the iiow movement will set in additionally also in the combustion front which may lead to local obstructions. In this in situ combustion process, the advance or progress of the combustion cannot be accelerated.

In order to be able to control this process and to stabilize the same, while simultaneously also avoiding the burning of channels, measures are thus required which render it possible to influence the reaction temperature `and the reaction direction in a regulating manner. The above-mentioned method for the in situ combustion in a separate reaction zone being positioned between a flooding borehole and a recovery borehole whose burning direction differs from the primary movement which results from a pressure gradient from the flooding borehole to the recovery borehole is suitable therefore if it is combined with a iiooding that is carried out in a specific manner.

The in situ combustion according to the method of the present application in combination with a flooding is automatically stabilized in lthe following manner. Deposit proportions or portions which are present predominantly in solid form as coke are burned in the reaction zone during the in :situ combustion. This solid fuel is formed during cracking in the residue from a flash evaporation by means of hot gases and vapors from the react-ion zone and is a process which corresponds to a process for the treatment of petroleum which has been called delayed coking. If the temperature in the reaction zone is very high in the presence of many solid coke proportions or constituents, the deposit rock is heated to a high temperature. The flood water owing in directly behind the traveling reaction or combustion front will form at this rock large amounts of highly heated vapor. The heated vapor effects in sections lying ahead of the combustion front, an intensified iiash evaporation of the liquid petroleum so that only small quantities of solid coke portions are left over and after subsequent combustion less high temperatures arise. With these lower temperatures, the rock is heated to not quite as high a temperature. Less vapor is produced at this lower temperature rock which, accordingly, will effect a lower Hash evaporation so that from the ash evaporation large amounts of heavy liquid hydrocarbons will again remain behind. As a result, in the delayed coking a larger amount lof lcoke will lbe deposited as solid fuel in the =re action zone. The gaseous and vaporous cracking products are mixed with the modified combustion gas and the resultant water vapor, so that the procedure and events described hereinabove are repeated. The in situ combustion in the react-ion zone is carried out with activated combustion gas consisting of carbon dioxide, water vapor and larger amounts of enriched oxygen. Mixed therewith is the additional vapor, formed at the hot rock, in the reaction zone and increases the endothermic water vapor reduction which additionally keep the temperature peaks low. The reaction temperature will thus folilow a course in an undulatory manner about a mean Value as a result of which fact the combustion process becomes stabilized since it cannot increase beyond control nor cause itself to be spent.

According to the present invention iiood water is introduced under pressure through flooding boreholes behind the reaction zone and guided in the direction of the primary movement from the iiood zone to the recovery zone. Additional amounts of vapor resulting from contact with the hot burntout rock `are compressed by a pressure gradient corresponding to the primary movement through the reaction zone at an tangle to the axis perpendicular thereto. Limited amounts of an a-ctivated combustion gas having increased oxygen content for the purpose of attaining high combustion temperature are introduced in the combustion zone -with a liow perpendicular to the primary movement and therewith a delayed coking is carried out with the residues still being present in the reaction zone. Thereupon a strong flash evaporation `of the hydrocarbons is effected with the resultant hot modified combustion gas together with the equally strongly heated water vapors ahead of the reaction zone so that only small amounts of residue will remain for -a subsequent Adelayed coking during the advance movement of the reaction zone. All the vapors and gases from the flash evaporation condense in colder sections of the petroleum deposit positioned before the reaction zone or are possibly `recovered through recovery holes positioned at the reaction zone.

Accordingly, it is important that the flood zone follow the moving reaction zone which is displaced, due to the pressure gradient of the primary movement, parallel to the axis of the combustion direction. Corresponding to the advance of the flooding water, additional amounts of water vapor are formed at the hot burnt-out rock, which has been left behind by the moving reaction zone, and will tiow into the reaction zone positioned thereahead. The pressure gradient -in the primary movement and the `direction of flow of the resultant water vapor force also miiuence the activated combustion gas having been introduced into this direction of flow. The oxidation agent is thus forced to always flow into the deposited coke from the delayed coking so that marginal problems or burntout rock structures cannot be formed or be produced. The water vapor with the formation of water gas acts in this care in a temperature-regulating or controlling manner; the major portion is converted into over-heated vapor which latter, after iiowing through the reaction zone being disposed at right angles to the direction of its iiow, will bring about a iiash evaporation of the deposit or reservoir content ahead of the reaction zone. The regulation or control of the portions to be burned in the reaction zone as well as the regulation of the reaction temperature renders it possible to use an activated combustion gas having an increased content of enriched oxygen (the quantity thereof may be increased up to a portion of 40% in the combustion gas). lIf such a reactive gas were used for the in situ combustion without the combination with water vapor, the consequences referred to and enumerated hereinabove would be inevitable.

During the condensation of the water vapor in the colder parts of the deposit or revervoir, considerable amounts of electrolyte-free water are produced, which may cause swelling of the clay-containing or argillaceous constituents of the reservoir rock, particularly in deposits having a low content of salt-bearing adhering water. The permeability is thus impaired to a more or less considerable degree and the path of the combustion gases and of the combustion front is unfavorably influenced.

It has, therefore, been proposed that, prior to initiating the in situ combustion, ilood water being charged with salt and/or catalysts be circulated between the treating boreholes and the leading boreholes. With this ilood water, a salt enrichment in the treatment zone is achieved so that swelling by condensate water of the subsequent in situ combustion is prevented. This accentuation or increase of the salinity is particularly important if the combustion is carried out with enriched oxygen since at that time an intensive combustion at high temperature takes place so that aside from the reaction water also a great amount of evaporated adhering water will reach forwardly positioned colder sections.

The catalysts which are deposited possibly at the same time as the salt may become effective once the reaction zone has penetrated into the respective section or compartment of the deposit or reservoir. They may serve for influencing the cracking, coking or combustion of the deposit content and, respectively, support the same.

In order to render the production of or recovery from a petroleum deposit or reservoir independent of the respective conditions prevailing therein and in order to make the recovery as complete as possible, the process is carried out as follows, with particular reference given to the drawing of the invention.

The starting point or basis is the process or method .known in the art of opening a field by flood boreholes and recovery boreholes between which treating boreholes and leading boreholes are disposed. An in situ combustion is initiated from the treating borehole to the leading borehole and a reaction zone is thus created having a movement of flow differing from the primary movement from the flooding borehole to the recovery borehole. As is shown in the drawing, the iield to be recovered is subdivided into individual sections extending at right angles to the primary movement and being delimited by rows of boreholes or wells in the direction of the primary movement. In the same direction, the field to be recovered is subdivided into flood zone, a treatment zone, and a recovery zone. Disposed in the treatment zone are two boreholes which delimit the section laterally, namely as treating boreholes BB and as leading boreholes LB. Content from the deposit is recovered from the leading boreholes LB aboveground and there subjected to a treatment, as indicated at A in section I. This treatment consists of a heating operation by admixing hot combustion gases which are completely soluble in the deposit content and, respectively, are condensable therein without leaving a gaseous phase. These gases defined as modified combustion gas, consist of carbon dioxide, water vapor and some nitrogen and may be recovered by burning hydrocarbons with an oxidation agent, predominantly air, containing only a little nitrogen. The treatment may, moreover, consist also in a separation of the deposit or reservoir content being removed from the leading borehole into liquid and gaseous portions, at which time the 4liquid constituents are separated as recovered product and the gaseous portions serve for producing the modified combustion gas. The treated and, respectively, converted product is introduced once again under pressure into the deposit through the treating borehole BB. Due to the fact that the medium is compressed into the treating borehole and that the discharge or removal is effected through the leading borehole, a forced flow is produced under the influence of the pressure gradient between these two boreholes in the deposit or reservoir. After the circulation with the forced flow and heating of the deposit section has been carried out for some time, an enriched oxygen containing aside from to 90% of oxygen additionally also from 5 to 15% of nitrogen is admixed to the medium aboveground, as shown at B in section III of the drawing, and an activated combustion gas is thus formed. With the latter, an in situ combustion is initiated in the deposit and a reaction or combustion front is produced whose axis is at right angles to the primary movement resulting from the pressure gradient ahead of the flooding zone to the recovery zone. Accordingly, the reaction Zone in which the in situ combustion is carried out is laterally delimited by the leading borehole and the treating borehole.

In order to include and entrain further parts of the deposit or reservoir section being delimited by the two boreholes into the range of action of the reaction Zone, a pressure gradient is produced in the direction of the primary movement to thus effect a parallel displacement of the reaction zone in the direction toward the recovery zone. The traveling speed or speed of 'movement thereof depends upon the oxygen content of the activated cornlbustion gas supplying the combustion in the reaction zone and upon the amount of fuel being formed in the reaction zone and is controlled by the amount of oxygen. The progress or advance of the combustion is always slower than the speed of flow of the gases and vapors. The pressure gradient is built up Iby compressing the flood water into the flooding boreholes and by recovering deposit content from the recovery boreholes. The flood water line follows the reaction zone and ilows into the burnt-out hot rock. While water vapors are formed, the recovery of the heat being stored there taires place and the vapor acts in a regulating manner on the combustion process in the manner described hereinabove. The: reaction zone is thereby displaced in a direction toward the recovery zone, as illustrated in sections V and VII of the drawing.

In the stage illustrated at sections V and VII, activated combustion gas may be introduced both into the treating borehole and into the leading borehole of the deposit in order to supply the traveling or moving reaction front with this mediu-m. When the reaction zone has traveled, for example, half the distance to the next row of boreholes, a large heat source will have been produced in many instances ahead of and behind the reaction zone which is sufficient to assure that the second half to the next row of wells is now de-oiled by flooding only so that for this operational section additional oxygen is no longer required since the ilood water will drive the heat being introduced ahead of it. If, however, in unfavorable deposits or reservoirs with the content thereof the traveling reaction front comes into the area or region of the next row of boreholes in the direction toward the recovery zone, these boreholes will assume the function of the leading and, respectively, treating boreholes and the boreholes left behind will then serve as flooding boreholes. The flood water being introduced therethrough is converted into vapor on the still hot rock of the burnt-out deposit section and this vapor will fulfill the abovedescribed important functions in the course of the process.

Furthermorenin the case of highly viscous deposit content or in the case of a low permeability of the reservoir rock, flood water being charged with oxygen is compressed into the flooding borehole and the supply of ac-` tivated combustion gas to the reaction zone is discontinued when approximately half of the -distance between two parallel rows of boreholes has been burnt out by the reaction zone traveling therebetween. The oxygen con- :nt of the flood water is so chosen that it willsuice to iaintain a weak combustion since the latter will take lace only in the preheated deposit or reservoir rock. `he process or method modification may be carried out ieriodically, possibly until the next row of boreholes has leen reached. This stage of the method is illustrated in ection IX of the drawing.

The process steps illustrated in sections I, III, V, VII ind IX of the drawing have been shown in separately aositioned sections side-by-side only for reasons of greater zlarity. They take place, of course, successively in each `ection.

It has been found to be expedient not to take all of he sections being positioned side-by-side into treatment 1nd production at the same time, but to separate simul- ,aneously treated sections by inter-posed sections. The Jegi'nning of the treatment in these intermediate sections nay .be effected at different time periods, for example, if ln the first sections no treatment above ground is required and the oxygen requirement is reduced. It may, however, also be started only after the first sections have been redered empty by recovery. In this particular mode of carrying out the method, the requirement with respect to devices, such as pumps, compressors, boilers and oxygen plants, may be kept smaller than is the case if simultaneously the entire deposit field is opened up. Since the combination of the in situ combustion with water fiooding a deposit or reservoir can be exploited more rapidly and more completely than in the practices and techniques of the prior art, the economical success is also considerable. On the average, only half of the deposit surface needs to be treated with oxygen.

As has been pointed out, it is of importance for the purpose of recovering the deposit or reservoir content as completely as possible to influence and to guide apart from the forced flow in the reaction zone also the directions of flooding in the ooding range. This may be achieved, for example, in that individual ooding boreholes or treating or leading boreholes which have become flooding boreholes are supplied temporarily with different and varying amounts of ood water, or that specific lboreholes are temporarily closed off completely. It is also possible to move flood water in a circuit between neighboring boreholes. With all of these modifications, intersecting and traversing flows, ow directional and pressure changes or reversals are attained, the formation of preferred channels and small narrow channels is rendered impossible and, in this manner, the entire content of a reservoir or deposit is put into motion and lifted out.

In order to be able to carry out the recovery of an extensive deposit field with greater distances of the boreholes of, for example, 30() meters, it has `been found to be advantageous to modify the method described herein in the following manner. Activated combustion gas is compressed into a atreatment zone delimited by a treating borehole and a leading borehole, and specifically into one of the two boreholes in a periodically changing sequence, and the other borehole is then closed. The movement of flow of the water vapor flowing vertically through the combustion zone is maintained at that time. The two movements of flow act upon one another in the form of displacement bodies which are inuenced by the pressure gradient (from the compressed borehole to the closed-off borehole) and by the viscosity gradient (from the comhusion gas to the water vapor having considerably lower viscosity). A conical displacement of the range of action of the activated combustion gas takes place thereby, with a broad base of the cone in the region of the high pressure of the combustion gas around the compressed borehole and with the apex in the range of the lower pressure where the borehole is closed. The

predominance of the activated combustion gas at the base results in an intensified cracking, the reduction thereof at the apex of the cone results in an intensified flash evaporation of the deposit content. Due to the periodic change of the compressed borehole, and, respectively, of the closed borehole, the cone-shaped range of action is, in each case, reversed. The result thereof is the desired ,guiding or control of the reaction process-even in case of a larger distance between the lboreholes--and a favorable utilization of the vapor produced in the deposit or reservoir.

There exists the danger, however, that after a prolonged period of time of operation -only few combustible residues will remain in the vicinity of the compressed borehole. In order to prevent and counteract this, a further process step is proposed which consists in lthat, during the reversal of the direction of ow, liquid or gaseous hydrocarbons, possibly together with modified combustion gas, are introduced into the heretofore closed borehole for a short time. The hydrocrabons may be led or branched off from the products of the recovery boreholes or from other boreholes which are in a different period or phase of the process at that particular time. They serve for renewing and, respectively, complementing the supply of combustible media in the zone or area of the borehole. Thereafter oxygen is supplied by compressing activated combustion gas into the borehole and the combustion front is thereby further kept in motion, or possibly, also newly ignited.

If a deposit or reservoir contains a borehole-permeable reservoir rock, or if the deposit content is thinly liquid and easily movable, it may be advantageous to carry rout the two process steps of the in situ combustion and of the flooding separately and successively, rather than simultaneously. A combustion zone is initially built up in the treatment zone of a deposit or reservoir and guided in a forced flow by introducing oxidation agents between the Itreating borehole and the leading borehole. After stopping the forced flow between the two boreholes, a ooding of the treatment zone is subsequently initiated and carried out at an angle differing from the direction of the forced fiow of the combustion and which is enhanced by taking up the recovery in the direction of the primary movement. The heat which is produced in the combustion zone is sufficient to Iflood out the deposit con-tent to the next row of boreholes.

When a deposit or reservoir field reaches the end stages of the recovery thereof, compressed air together with flood water is compressed into the fiooding boreholes. The field is thus charged with a supply of pneumatic energy which is sufficient to keep up the recovery over a period of time which may be considerable, under certain circumstances, and without additionally requiring the use of the conventional devices and means which are thus free to be employed in a different place at an earlier period of time.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of .the remainder of the specification and claims in any way whatsoever. 60

Example In a 15 meter thick deposit located l250meters underground an in situ combustion and flooding was performed in accordance with this process. This stratum is under a pressure of atm. at 60 C. It has a porous volume of 26% by volume, filled with mineral oil, natural gas and natural water. In a section of this stratum a burning front is formed between a leading borehole and a treating borehole and extending transversely to the primary pressure gradient from the flooding borings to the recovery borings. The burning front is maintained by the introduction of 35.6 Nm.3 (cubic meters `at normal conditions of pressure and temperature) oxygen mixed with steam and carbon dioxide per m.3 of the rock that is contained in the burning front. This amount of oxygen burns 17.15 kg. carbon and hydrocarbons per m of the deposit, thereby liberating 146,000 kcal. T-he latent heat of the hot mixture of steam and CO2 contains a total of 151,400 kcal. of heat energy per m.3 of the deposit. In the burning front a temperature of, e.g. 480 C. reached. In the completely burnt-out rock which remains behind the burning front during its advance in the direction of the pressu-re gradient, there is contained at this temperature 195,000 kcal. of heat energy per m of the deposit. This amount of heat energy was produced in part by the heat of combustion per m.3 of deposit, and also in part by the steam and gases of combustion which were heated by the previously burnt-out rock.

The process is contained as follows:

The flooding water advance into the rock which has been burned empty and is there vaporized and forms per m.3 of the deposit 166 kg. steam under the pressure in the stratum. The steam then forces its way through the burning front where it is further superheated. From the hot rock 133,000 kcal. per m.3 of heat energy are thus recovered, w-hile in the burnt-out rock at 200 C., 62,000 kcal. per m.3 remain behind. The heat loss therefore amounts to 40.8%. However, by a further utilization of this residual heat for subsequent warming of more of the flooding water in a region of lower temperature, another 20,000 kcal. are recovered so that the loss of heat in the rock is further diminished by about or down to 27.5% with only 42,000 kcal. remaining in the stratum. Further heat losses occur as the result of convection. In a deposit 15 m. thick, the loss by convection from the two base surfaces with a total area of 2 m2 is 49,300 kcal. In relation to the introduced or generated heat, this represents a heat loss of 32.8%. The total loss of heat per m of the burnt-out rock during this process is therefore 60.3% of the heat introduced or generated.

The excess of heat energy remaining in the stratum is therefore l51,4009l,300=60,100 kcal. per m of the deposit. This retained heat in conjunction with the pressure drop ahead of the burning front converts some of the flooding water into steam which in turn heats the stratum contents that are encountered by the steam. This considerable excess of heat energy is sufllcient to vaporize the hydrocarbons which fill half the distance between two rows of borings as viewed in the primary direction. It is, therefore, not necessary to keep a burning front, in operation over the entire distance between rows of borings, it being sufficient to do the burning in only the first half of that distance to obtain the hydrocarbons of that entire section up to the next row of borings by partial vaporzation, without any further expenditure of energy. The energy addition from the burnt-out rock is supported and increased by the hot gases of combustion which were produced in the burning front but which without forming a gaseous phase became dissolved 4in the liquid stratum contents and heated up the latter. 'If the heat energy of a burning front which is advanced over only half the distance between two rows of borings is sufficient to obtain the hydrocarbons between such rows, then the total amount of oxygen needed per m.3 of the deposit will be diminished to Nm. This amount includes a slightly higher oxygen requirement for the building up of a burning zone between the treatment borings and the leading borings. This amount will change by i10% if the specific gravity of the mineral oil is above or below the assumed value of 0.91 kg./l. and the pore volume of the rock in the stratum remains within the above-mentioned limits.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to Various usages and conditions. Consequently, such changes and modifications are properly, equitably, and intended to be, within the full range of equivalence of the following claims.

What is claimed is:

1. A method for the recovery of residual oil from underground petroleum deposits by flooding and in situ combustion comprising the following steps:

(a) locating in a petroleum deposit at least one row of flooding boreholes connecting a structurally deep zone of said deposit, at least one row of recovery boreholes connecting a structurally high zone of said deposit, and at least one row of tre-ating boreholes and leading boreholes, said treating and leading boreholes pdsitioned between said flooding and recovering boreholes and connecting an intermediate zone of said deposit;

(b) introducing under pressure into `said treating boreholes a limited amount of activated combustion g-as having an increased oxygen content for achieving moderate combustion temperatures and igniting said activated combustion gas in said deposit between said treating boreholes and said leading boreholes whereby there is produced in the reaction zone a burning zone in which in situ combustion is performed in the stratum contents which have been extensively changed by the hot vapors and gases;

(c) introducing flood water into said flooding boreholes under pressure whereby a primary direction of flow of the stratum contents is established in said deposit between said flooding boreholes and said recovery boreholes whereby the axis of the re-action front between the treating boreholes and the leading boreholes is shifted in parallelism in the direction toward the recovery boreholes, further conducting the flood water first through the burnt-out rock while being heated and then through the reaction Zone while being further heated and vaporized, and conducting the resulting vapors through the burning front, burning and gasifying in the burning front, by said activated gases of combustion with increased oxygen content, of the stratum contents which have been strongly altered by contact with said vapors, whereby from the -activated oxygen-containing gases of combustion a modified gas of combustion is formed, further conducting the steam which during pass-age into the reaction zone has become further heated so that at greater distances from the burning zone it will cause further flash vaporzation of the stratum contents in the primary ilow direction and so that the hot gases and vapors of the modified gases of combustion from the burning front will produce a delayed coking in the stratum contents which have already been ashed, so that forthe trailing burning front there will remain only a strongly altered stratum contents; and

(d) condensation and dissolving in the colder portions of the stratum of the modified combustion gases and vapors which are caused by the pressure gradient in the primary flow direction to flow toward the recovery boreholes while warming that portion of the stratum.

2. The method of claim 1, in which salt-containing flood water is introduced into said treating boreholes and circulated between the latter and said lead-ing boreholes between steps (c) and (d) of claim 1.

3. The method of claim 1, in which, after step (c), a pressure gradient is established between the flooding boreholes and the recovery boreholes and the migration Velocity of the burning zone is controlled by varying the amount of oxygen that is introduced into the combustion gas, so that during the combined flash vaporzation and delayed coking of the stratum contents, by diminishing the amount of oxygen, larger portions of the stratum contents will remain behind as combustible materials which retard the rate of burning, and conversely by increasing the amount of oxygen smaller portions of the stratum contents will remain behind -as combustible materials which strongly incre-ase the rate of burning.

`4. The method of claim 1, in which several rows of said treating and leading boreholes which are simulta- :ously tre-ated as in claim 1 step (c) are separated from 1e another by intermediate rows of tre-ating and leading Jreholes which at the beginning are only under the inlence of the pressure gradient and whose treatment under aim 1 step (c) does not begin until after the burning )nes which are formed by the first-mentioned rows of eating and leading boreholes are driven back about half ie distance to the nearest row of boreholes.

5. The method of claim 4, wherein at least a second )w of treating and leading boreholes is located perpenicular to said primary direction of recovery of the deposit ontents, the introduction of combustion gases into the rst row'of treating and leading boreholes being disconnued when said reaction zone is advanced approximately alf way between the first and second row of treating and :ading boreholes and flood water containing dissolved xygen under pressure is introduced into said first row of reating and leading boreholes whereby the following iiood later is heated by said hot burnt-out rock, oil residues in he burnt-out rock are burned by the dissolved oxygen and he oil-water contact line is advanced to said second row lf tre-ating land leading boreholes while the temperature evel is maintained.

6. The method of claim 1, wherein certain of the fioodng boreholes are temporarily closed while varying tmounts of flood Water are moved into circulation through tdjacent flooding boreholes.

7. The method of claim 6, wherein treating and leadng boreholes which are no longer used as such, are now 1sed as flooding boreholes in the same manner as the floodng boreholes of claim 6.

`8. A method for the recovery of residual oil from inderground petroleum deposits by flooding and in situ :ombustion comprising the following steps:

(a) locating in a petroleum deposit at least one row of flooding boreholes connecting a structurally deep zone of said deposit, at lea-st one row of recovery boreholes connecting a structurally high zone of said deposit, and at least one row of treating boreholes and leading boreholes, said treating and leading boreholes positioned between said ilooding and recovery boreholes and connecting an intermediate zone of the deposit;

(b) introducing under pressure into said treating boreholes a limited amount of activated combustion gas having an increased oxygen content for achieving moderate combustion temperatures and igniting said activated combustion gas in said deposit between said treating boreholes and said leading boreholes whereby there is produced in the reaction zone a burning zone in which in situ combustion is performed in the stratum contents which have been extensively changed by the hot vapors and gases;

(c) introducing ood water into said flooding boreholes under pressure whereby a primary direction of flow of the stratum contents is established in said deposit between said flooding boreholes and said recovery boreholes whereby the -axis of the reaction front between the treating boreholes and the leading boreholes is shifted in parallelism in the direction toward the recovery boreholes, further conducting the ood water first through the burnt-out rock while being heated and then through the reaction zone while being further heated and vaporized, and conducting the resulting vapors through the burning front, burning and gasifying in the burning front, by said acti- 12 vated gases of combustion with increased oxygen content, of the stratum contents which have been strongly altered by contact with said vapors, whereby from the activated oxygen-containing gases of combustion a modified gas of combustion is formed, further conducting the steam which during passage into the reaction zone has become further heated so that at greater distances from the burning zone it will cause further flash vaporization of the stratum contents in the primary flow direction and so that the hot gases and vapors of the modified gases of combustion from the burning front will product a delayed coking in the stratum contents which have already been flashed, so that for the trailing burning front there will remain only a strongly altered stratum contents; and (d) delivering from the leading boreholes or from the recovery boreholes of light gaseous hydrocarbons and other combustible gases during an advanced stage of the process.

9. The method of claim 1, in which the combustion gas of step (b) is forced alternately into said treatment boreholes or into said leading boreholes while the other one of these boreholes is closed, whereby a conical displacement of the region of activity of the activated combustion gas is effected by the pressure gradient that exists between the treating boreholes and the leading boreholes, which results in an intensied activity of the conical displacement where the activated combustion gas enters the stratum, while at the same time the steam which is pro-l duced by contact of the flooding water with the burnt-out stone, mixed with activated combustion gas by the conical displacement in the direction of the closed borehole, is crowded out to such an extent that it will cause flash vaporization of the stratum contents, and where on the side toward the open borehole the activated gas of combustion which occurs there will cause a delayed coking in the greatly changed stratum contents immediately ahead.

10. The method of claim 9, wherein the borehole not in use in opened, and prior to compressing said activated combustion gas, hydrocarbons with modified combustion gas are temporarily introduced into the treatment zone.

11. The method of claim 1, wherein only one re-action zone is initially built up, the reaction zone is then discontinued, and a flooding from flooding boreholes is initiated at angles varying with respect to the axis of said reaction zone previously built up, thereby transmitting the heat energy stored in the reaction zone in a direction toward the next row of borings.

12. The method of claim 1 wherein compressed air and flood water are introduced into said ooding boreholes near the end of the production period of the petroleum deposits.

References Cited by the Examiner UNITED STATES PATENTS 2,734,578 2/1956 Walter 166-11 2,839,141 6/1958 Walter l66l1 2,841,375 7/1958 Salomonsson 166--11 X 2,969,226 1/1961 Huntington 166-11 X 3,150,715 9/1964 Dietz 166--11 X 3,153,448 10/1964 Dew et al. 166-11 X 3,196,945 7/1965 Craig et al. 166--11 CHARLES E. OCONNELL, Primary Examiner.

STEPHEN J. NOVOSAD, Examiner,

Claims

1. A METHOD FOR THE RECOVERY OF RESIDUAL OIL FROM UNDERGROUND PETROLEUM DEPOSITS BY FLOODING AND IN INSTU COMBUSTION COMPRISING THE FOLLOWING STEPS: (A) LOCATING IN A PETROLEUM DEPOSIT AT LEAST ONE ROW OF FLOODING BOREHOLES CONNECTING A STRUCTURALLY DEEP ZONE OF SAID DEPOSIT, AT LEAST ONE ROW OF RECOVERY BOREHOLES CONNECTING A STRUCTURALLY HIGH ZONE OF SAID DEPOSIT, AND AT LEAST ONE ROW OF TREATING BOREHOLES AND LEADING BOREHOLES, SAID TREATING AND LEADING BOREHOLES POSITIONED BETWEEN SAID FLOODING AND RECOVERING BOREHOLES AND CONNECTING AN INTERMEDIATE ZONE OF SAID DEPOSIT; (B) INTRODUCTING UNDER PRESSURE INTO SAID TREATING BOREHOLES A LIMITED AMOUNT OF ACTIVATED COMBUSTION GAS HAVING AN INCREASED OXYGEN CONTENT FOR ACHIEVING MODERATE COMBUSTION TEMPERATURES AND IGNITING SAID ACTIVATED COMBUSTION GAS IN SAID DEPOSIT BETWEEN SAID TREATING BOREHOLES AND SAID LEADING BORE HOLES WHEREBY THERE IS PRODUCED IN THE REACTION ZONE A BURNING ZONE IN WHICH IN SITU COMBUSTION IS PERFORMED IN THE STRATUM CONTENTS WHICH HAVE BEEN EXTENSIVELY CHANGED BY THE HOT VAPORS AND GASES; (C) INTRODUCING FLOOD WATER INTO SAID DEPOSIT UNDER PRESSURE WHEREBY A PRIMARY DIRECTION OF FLOW OF THE STRATUM CONTENTS IS ESTABLISHED IN SAID DEPOSIT BETWEEN SAID FLOODING BOREHOLES AND SAID RECOVERY BOREHOLES WHEREBY THE AXIS OF THE REACTION FRONT BETWEEN THE TREATING BOREHOLES AND THE LEADING BOREHOLES IS SHIFTED IN PARALLELISM IN THE DIRECTION TOWARD