US3406755A - Forward in situ combustion method for reocvering hydrocarbons with production well cooling - Google Patents

Description

Il-A|R Oct. 22, 1968 L. G. SHARP 3,406,755

FORWARD IN SITU COMBUSTION METHOD FOR RECOVERING HYDROCARBO WITH PRODUCTION WELL COOLING iled May 31, 1967 PRODUCTION 34 WATER 24 v 4 FUEL INVENTOR LORLD 6. SHARP ATTORNEY United States Patent FORWARD IN SITU COMBUSTION METHOD FOR RECOVERING HYDROCARBONS WITH PRODUC- TION WELL COOLING Lorld G. Sharp, Irving, Tex., assignor to Mobil Oil Corporation, a corporation of New York Filed May 31, 1967, Ser. No. 642,561 5 Claims. (Cl. 166-41) ABSTRACT OF THE DISQLOSURE A method for the recovery of hydrocarbons, by forward in situ combustion, from a subterranean formation employing production well cooling. More articular- 1y, an in situ combustion front is moved by the injection of oxygen-containing gas into the formation through an injection well toward a spaced production well. The front displaces combustion-generated heated fluids, and formation fluid containing combustible hydrocarbons, into the production well. These fluids are produced from the production well and hydrocarbons recovered from them. Eventually, the combustion front moves sufliciently close to the production well to create temperatures therein at which combustion and thermal destruction of the desired hydrocarbons can occur. In accordance with this invention, water is passed from the well into the surrounding formation at an upper horizon, then downward about the production well to a lower horizon where the water is coproduced into the production well with fluids displaced before the combustion front. The combustion front approaches the production well between the mentioned upper and lower horizons. The flow of water maintains temperatures within the production well above about 160 F. and below the temperature wherein coking of the produced hydrocarbons occurs. In a preferred aspect, at least a part of the water produced into the production well is in the form of steam.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to the recovery of hydrocarbons from subterranean carbonaceous formations. More particularly, it relates to a method for the recovery of hydrocarbons from subterranean formations employing forward in situ combustion.

Description of the prior art The use of forward in situ combustion procedures for the recovery of hydrocarbons from a subterranean carbonaceous formation has been practiced in the oil industry. In these procedures, combustion is initiated in the carbonaceous material present within the formation, and then is maintained by a flow of an oxygen-containing gas between injection and production wells. The resulting combustion front is moved through the formation toward the production well. The combustion front may be described as a forward combustion front. Similarly, the procedure using this front for recovering hydrocarbons is generally known as forward in situ combustion. The combustion front displaces combustion-produced heated fluids, and formation fluid which includes combustible hydrocarbons, into the production well. The desired hydrocarbons are recovered from these fluids. The temperatures generated at the combustion front may be as high as 2500 F. Usually, fluid temperatures downstream of the front average about 1000 F. It will be apparent that, with the front close to the production well, these temperatures are sufficient to cause coking, and even combustion, of the produced hydrocarbons in the pro 3,406,755 Patented Oct. 22, 1968 duction well, and also thermal destruction of downhole well apparatus.

There have been several proposals for overcoming these difiiculties in the production well caused by the heated fluids generated by the combustion front, and the destructive temperatures which can be produced, by their flow, into the production well. For example, one method, of considerable usefulness, is described in US. Patent 3,259,185. Other procedures are described in Us. Patents 2,994,375, 3,013,609, 3,227,215, 3,228,471 and 3,240,270. Although the procedures described in these patents may be employed to prevent destructive temperatures generated by a closely adjacent combustion front, from occurring within the production well, they all use the production well as a heat exchanger.

More particularly, the procedures of these patents require that a cooling fluid is circulated through the production well to prevent occurrence of undesired temperature effects therein. It will be readily seen, in these procedures, that the production well serves as a heat exchanger. Should the flow of the cooling fluid suffer maladjustment in rate of flow, destructive temperatures can be quickly reached within the production well causing thermal destruction therein to well apparatus and produced hydrocarbons. Cooling of the production well by some means is necessary when hydrocarbons are produced from a formation by an adjacent in situ combustion front. The method of the present invention, in recovering hydrocarbons by forward in situ combustion, provides for cooling of the production well but without using the production well heat exchanger.

SUMMARY OF THE INVENTION The present method is an improvement to a method for recovering hydrocarbons from a subterranean carbonaceous formation wherein combustion of combustible materials in the formation has been initiated. A flow of oxygen-containing gas through the formation between spaced-apart injection and production wells maintains combustion to produce a forward in situ combustion front which moves toward the production well. The front displaces combustion-produced heated fluids, and formation fluid containing combustible hydrocarbons, into the production well. Hydrocarbons are recovered from these fluids. More particularly, the present invention provides an improvement in this method, which comprises practicing the steps of:

(a) passing water from the production well into the surrounding formation at an upper horizon, then downward through the formation about the production well to a lower horizon, and then back into the production well from the surrounding formation at the lower horizon, the horizon at which the combustion front approaches the production well being intermediate the upper and lower horizons,

(b) controlling the rate of water flow so that the Water enters the production well in amounts sufficient to maintain therein a temperature between about 1-60 F. and the coking temperature of the hydrocarbons at a time when the combustion front is sufliciently close to the production well to cause increased temperatures in the production well, and

(c) producing the displaced formation fluid, heated fluids from the combustion front, and the mentioned water, from the lower horizon of the surrounding formation via the production well, and recovering hydrocarbons from the produced fluids.

In further improvement, the rate of water flow may be controlled to maintain the water entering the production well at least in part as steam. The rate of water flow may be arranged so that the temperatures, within the well, are maintained between the steam-water equilibrium temperature and the coking temperature of the hydrocarbons flowing through the production well. Other arrangements of steps may be taken as will be apparent from the following description of the present method.

DESCRIPTION OF THE DRAWING The drawing shows, in a vertical section taken through the earth, a subterranean carbonaceous formation in which forward in situ combustion is practiced according to the present invention for the recovery of hydrocarbons. Suitable apparatus is illustrated for carrying out the steps of the present method. Additionally, several results of practicing the steps of this method are illustrated graphically in the drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A description will be given, with reference to the drawing, of a formation and suitable apparatus for carrying out the steps of the present method. However, other formations, and arrangements of apparatus, may be employed in carrying out these steps. In illustration, there is shown a subterranean carbonaceous formation 11 which serves as a reservoir for formation fluid containing combustible hydrocarbons desired to be recovered. The formation 11 resides below the earths surface 12 covered by an overburden 13 and supported by strata 14. For present purposes, the overburden 13 and strata 14 can be considered without carbonaceous matter capable of supporting combustion. The formation 11 is of a suitable character wherein forward in situ combustion can be carried out for the recovering of hydrocarbons. The formation 11 may be, in example, the heavy oil-bearing sands of California in which forward in situ combustion has been used for recovering hydrocarbons.

The formation 11 is penetrated by spaced-apart injection and production wells 16 and 17, respectively. The wells 16 and 17 are of suitable construction for carrying out a procedure of forward in situ combustion for recovering hydrocarbons from the formation 11. For example, the well 16 has a casing 18 which extends from the earth's surface 12 down into the lower portions of the formation 11. Openings 19 in the lower portions of the casing 18 provide a fluid-entry to the surrounding formation 11. The bottom of the casing 18 is sealed by a casing shoe 21. A wellhead 22 encloses the top of the casing 18. A tubing 23 extends through the wellhead 22 downward to adjacent the lower extremity of the casing 18 and provides for conveying fluids between the earths surface 12 and the lower portion of the surrounding formation 11. An additional fluid connection to the well 16 is provided by port 24 to permit the flow of fluids between the earths surface 12 and the annulus formed between the tubing 23 and the casing 18.

The production well 17, for example, has a casing 26 which extends from the earths surface 12 down to the lower horizon of the formation 11. The bottom of the casing 26 is enclosed by a casing shoe 27. Openings 28 in the lower extremity of the casing 26 provide a fluid-entry to a lower horizon of the surrounding formation 11. A wellhead 29 encloses the top of the casing 26. A production tubing 31 extends from the earths surface downward to the lower extremity of the casing 26 and terminates adjacent the openings 28. Fluids produced into the production well 17 are recovered, via the tubing 31, and sent to a suitable hydrocarbon-recovery facility at the earths surface 12.

The production well 17 has a segregated fluid entry to an upper horizon of the surrounding formation 11. More particularly, a packer 32 is placed in the casing 26 below the upper horizon and divides the production well 17 into two discrete fluid-handling areas. The lower area serves for the collection of produced fluids into the production well from the lower horizon of the formation 11. The upper area serves for the passing water, at the upper horizon, from the production well 17 into the surrounding formation. For this purpose, openings 33 are provided in the casing 26 above the packer 32. A fluid connection to the production well 17 is provided a port 34 into the casing 26 so that water can be passed from the earths surface 12 through the openings 33 into the upper horizon of the surrounding formation 11.

The production well 17 carries structures for monitoring the temperature of the produced fluids as they flow through the production well 17. Such temperature-monitoring function can be provided by any suitable apparatus. For example, the production well 17 has a thermocouple Well 36 which extends through the wellhead 29 downward to adjacent the lower extremity of the casing 26. A thermocouple assembly 36a, within the thermocouple well 36 provides for the measurement of temperature at various positions within the production well 17. The output from the thermocouple assembly 36a is applied to a temperature-indicating device 37. Preferably, the temperature-indicating device 37, of suitable design, permits automation of flow control functions.

Forward in situ combustion for recovering hydrocarbons from the formation 11 may now be undertaken. For this purpose, combustible material in the formation 11 adjacent the injection Well 16 is ignited. Also, an oxygen-containing gas is passed through the injection well 16, via the openings 19, to traverse the formation 11 and then to be produced, via openings 28, into the production well 17. The oxygen-containing gas will usually be air. However, any other fluid substance, which contains sufficient oxidant for carrying out in situ combustion, may be used. In many instances, the flow of air through the formation 11 will cause ignition of the carbonaceous materials therein by auto-oxidation. However, the combustible matter may be heated to ignition by a source of heat applied through the injection well 16. For example, an electrical heater may be energized in the well 16 adjacent the openings 19. The continued injection of air after the combustible material in the formation 11 has been ignited creates a combustion front 38 which moves through the formation 11 toward the production well 17. The combustion front 38 is illustrated in the drawing as having moved closely adjacent the production well 17. The combustion front 38, in its traverse of the formation 11, produces a burned-out or swept area 39 from which formation fluid has been displaced. The heated fluids generated by the combustion front 38, and the formation fluid which contains the combustible hydrocarbons desired to be recovered, are displaced to and produced through the openings 28 into the production well 17. These fluids are removed from the production well 17 through the tubing 31. The heated fluids produced into the production well 17 from the combustion front 38 can cause temperatures to increase rapidly in the production well 17. Obviously, after a period of time, increased temperatures occur within the production well 17 suflicient that the produced hydrocarbons are subject to coking and even to being completely thermally destroyed. Cooling must be provided for these produced heated fluids to avoid this undesired result.

At the time when the temperatures increase undesirably in the production well 17, the following steps of the present invention are practiced. Water is introduced through the port 34 under suflicient pressure to flow downwardly through the well 17 and then to be forced, via the openings 33 in the casing 26, into the surrounding formation 11 at the upper horizon. More particularly, the water is injected at a sufficient rate to form an annular body of water about the production well 17. With the injection of water, fluid is produced from the lower horizon of the surrounding formation 11 through the openings 28 into the production well 17. This produced fluid is removed to the earths surface 12 through the tubing 31. This fluid is produced through the openings 28 from the surrounding formation 11 at the lower horizon until the injected water from the openings 33 has flowed coaxially downwardly about the production well 17. Stated in another manner, this fluid is produced through the openings 28 until the annular body of water about the production well 17 has expanded coaxially downward to extend in the surrounding formation 11 between the upper and lower horizons. As a result,'there is formed a body of water 41 surrounding the production well 17. The body of water 41 is interposed between the production well 17 and the advancing combustion front 38 at a horizon intermediate the mentioned upper and lower horizons.

The heated fluids from the combustion front 38 must pass into the injected water, forming the body of water 41, then be coproduced through the openings 28 into' the production well 17, and subsequently removed through the tubing 31. The injected water 'cools these heated fluids on their mixing in the formation 11 The degree of such cooling effect depends upon the magnitude of flow of injected water passed through the formation 11 from the openings 33. It will be noted that, during this cooling function, a lower part of the body of water 41'may be converted into steam. The steam, in the body 'of water 41, is designated by the numeral 41'.

The injected water passed from the openings 33 downward along the well 17 toward the openings 28 is: controlled in rate of flow so that the water which enters the production well 17, via the openings 28, is sufficient in amounts to maintain therein a temperature between about 160 F. and the coking temperature of the hydrocarbons being produced. For this purpose, the temperature-sensing mechanism in the thermocouple well 36 and the temperature-indicating device 37 are employed to monitor the temperatures within the production'well 17. Preferably, the temperature-indicating device 37 is employed by automation to control the rate of flow of water into the port 34 for injection'through the openings 33 into the surrounding formation 11. Such arrangements are conventional and will not be included in the present description.

In some instances, it is of advantage that the water, flowing into the openings 28, be at least in part steam. Steam flowing in the lower portion of the production well 17 assists in maintaining well apparatus clear of carbon residues carried therein by the heated fluids which are generated by the combustion front 38. Additionally, the steam provides an inert atmosphere within the production well 17 so that explosive mixtures, and possible explosion thereof, cannot occur.

Preferably, the temperature maintained within the production well 17 is between the steam-equilibrium temperature under downhole conditions in the production well 17, and the coking temperature of the desired hydrocarbons being produced thereinto. This insures a flow'of steam in the production well 17 at all times.

The advantages of providing, by the aforedescribed steps, a flow of water through the formation 11 to produce the body of water 41 surrounding the production well 17 will be apparent from the drawing. All heated fluids generated by the combustion front 38 must commingle with water in the body of water 41 before they can enter into the openings 28 and be produced from the production well 17. Thus, the portion of the formation 11 which surrounds the production well 17 serves as a heat exchanger. Therefore, an inadvertent temporary change of condition controlling cooling of these heated fluids in this particular formation area merely converts more or less of the water, in the body of water 41, into steam. Additionally, any extreme temperatures which result from a reduction in cooling, downstream of the adjacent combustion front 38, arise in a portion of the formation 11 which contains Water. Thus, the only damage that can be expected to occur would be that to the formation 11 at such high-temperature area and not the production well 17. Thus, the operability of the production well 17 is preserved, and the produced hydrocarbons which flow through the tubing 31 are conserved against thermal injury or destruction.

The'combustion front 38 has a tendency to move vertically upwardly in its movement toward the production well 17. The downward flow of water about the production well 17 causes the combustion front 38 to move toward the lower horizon of the formation 11. Obviously, this increases the vertical sweep efliciency of the combustion front 381 and improves hydrocarbon recovery.

As mentioned, the displaced formation fluid which contains the combustible hydrocarbons is coproduced with the other described fluids from the lower horizon of the formation 11 through the openings 28 into the production well 17. Thence, these fluids are removed to the earths surface 12 through the tubing 31. Thereafter, hydrocarbons are recovered from these produced fluids by any suitable means, many forms of which are known to those skilled in the art.

From the foregoing, it will be apparent that there has been provided a method employing in situ combustion for recovering hydrocarbons from a subterranean formation including improvements in steps for cooling a production well which is subject to being heated to elevated temperatures. Various changes and adaptations may be made to the present method by a person skilled in the art without departing from the spirit of this invention. It is intended that the foregoing description be considered as illustrative of the present invention whose scope is defined by the appended claims.

What is claimed is:

1. In a method for recovering hydrocarbons from a subterranean carbonaceous formation wherein combustion of combustible material in the formation has been initiated and is maintained by injection of oxygen-containing gas into the formation through an injection well whereby there results an in situ combustion front which moves towards a spaced production well, and movement of this front displaces heated fluids produced by the front and formation fluid containing combustible hydrocarbons into the production well, and then hydrocarbons are recovered from these fluids, the'improvement which comprises the steps of;

(a) passing water from the production well into the surrounding formation at an upper horizon, then downward through the formation about the production well to a lower horizon, and then back into the production well from the surrounding formation at the lower horizon, the horizon at which the combustion front approaches the production well being intermediate the upper and lower horizons,

(b) controlling the rate of water flow so that the water enters the production well in amounts sufficient to maintain therein a temperature between about F. and the coking temperature of the hydrocarbons at a time when-the combustion front is sufliciently close to the production well to cause increased tem peratures in the production well, and

(c) producing the displaced formation fluid, heated fluids from the combustion front, and the water, from the lower horizon of the surrounding formation via the production well, and recovering hydrocarbons from the produced fluids.

2. The method of claim 1 wherein the rate of water flow is controlled to maintain the water entering said production well at least in part as steam.

3. The method of claim 1 wherein the rate of water flow is controlled to maintain the water entering the production well at a rate sufficient to maintain therein, at downhole conditions, a temperature between the steamwater equilibrium temperature and the coking tempera ture of the hydrocarbons flowing through the production well.

4. In a method for recovering hydrocarbons from a subterranean carbonaceous formation wherein combustion of combustible material in the formation has been initiated and is maintained by injection of oxygen-containing gas into the formation through an injection well whereby there results an in situ combustion front which moves towards a spaced production well, and movement of this front displaces heated fluids produced by the front and formation fluid containing combustible hydrocarbons into the production well, and then hydrocarbons are recovered from these fluids, the improvement which comprises the steps of;

(a) injecting water, at an upper horizon, from the production well into the surrounding formation to form an annular body of water about the well,

(b) producing fluid including injected water at a lower horizon, via the production well, from the surrounding formation until the body of injected water has expanded coaxially downward about the production well to extend between the upper and lower horizons, said upper and lower horizons residing above and below the horizon at which the combustion front approaches the production well,

(c) injecting the water from the production well into the surrounding formation at the upper horizon at a suflicient rate that the injected water produced from the lower horizon of the formation into the production well is adequate in amount to maintain the temperature within the production well between a temperature where the water is at least in part steam and the temperature where the desired hydrocarbons are subject to coking at a time when the combustion front is sufliciently close to the production well that the heated fluids from the front can cause thermal destruction of hydrocarbons therein when no injected water is present, and

(d) producing the displaced formation fluid, heated fluids from the combustion front, and injected water, from the surrounding formation at the lower horizon via the production well, and recovering hydrocarbons from said produced fluids.

5. In a method for recovering hydrocarbons from a subterranean carbonaceous formation wherein combustion of combustible material in the formation has been initiated and is maintained by injection of oxygen-containing gas into the formation through an injection well whereby there results an in situ combustion front which moves towards a spaced production well, and movement o STEPHEN of this front displaces heated fluids produced by the front and formation fluid containing combustible hydrocarbons into the production well, and then hydrocarbons are recovered from these fluids, the improvement which comprises the steps of;

(a) injecting water into the formation surrounding the production well at a first horizon,

(b) producing said injected water from the surrounding formation at a second horizon, via the production well, until the injected water flows coaxially downward about the production well to extend between the first and second horizons, said first and second horizons residing above and below the horizon at which the combustion front initially approaches the production well,

(c) controlling the flow of water injected into the formation to an amount such that the injected water produced into the production well maintains the temperature within the production well between about 160 F. and the temperature at which substantial thermal destruction of the desired hydrocarbons occurs at a time when the combustion front is suflicently close to the production well that the heated fluids from the front can produce thermal destruction of hydrocarbons therein, and

(d) producing the displaced formation fluid, heated fluids from said combustion front, and said injected water, into said production well from the surrounding formation at said second horizon and recovering hydrocarbons from said produced fluids.

References Cited UNITED STATES PATENTS J. NOVOSAD, Primary Examiner.

Images