Apparatus For Controllable In-situ Combustion

Abstract

A system of apparatus for controllable in-situ combustion in subterranean hydrocarbon bearing formations containing bitumens with simultaneous production and recovery of energy sources supplying the mechanical and thermal energy required for the in-situ combustion and operation of the facilities involved.

Parent Case Text

This is a division, of application Ser. No. 43,547, filed June 4, 1970, now U.S. Pat. No. 3,700,035.

Description

FIELD OF THE INVENTION

This invention relates to a system of apparatus for effecting in-situ combustion in subterranean hydrocarbon bearing formations especially formations containing bitumens whereby the in-situ combustion is controlled by using highly concentrated oxygen with residual nitrogen and a partial and/or temporary supply of superheated high-pressure steam, with simultaneous production of energy suitable for operating the necessary above ground facilities and auxiliary equipment.

DESCRIPTION OF THE PRIOR ART

In-situ combustion in subterranean hydrocarbon bearing formations use low hydrogen petroleum residues as fuel for the combustion front, and the heat developed from their combustion produces additional combustional gases such as carbon monoxide and hydrogen which together with the dissolved hydrocarbon gases and the combustion product, such as carbon dioxide, escape from the production wells in gaseous form. The heat from the combustion and the heat contained in the steam formed in the burn-out matrix behind the combustion front flows before the combustion front heating the hydrocarbon bearing reservoir and reducing the viscosity of the hydrocarbon therein and displacing the hydrocarbon toward the production wells.

The combustible gas mixtures and the carbon dioxide escaped enter into pressure-resistant fireboxes or pressure-resistant furnaces of a special steam boiler, are burnt with evolution of heat by means of highly concentrated oxygen with residual nitrogen or of air used in heavy excess, and produce forms of energy, such as steam or hot combustion gases under pressure, that may supply energies to the facilities installed above ground and may also partly be introduced into the deposit through injection boreholes.

The generation of combustion heat in the underground deposit and the additional production above ground of different forms of energy that are partly and temporarily supplied to the deposit from above ground create a more comprehensive effect upon the content of the deposit. The addition of high-pressure steam in quickly variable amounts leads to an even spreading of the combustion front, facilitates the start of the process in each injection borehole, and increases the yield from the deposit. The use of carbon dioxide recovered in minor quantities from the condensation plant improves safety in the injection boreholes and also has a favorable influence upon the yield. It is advantageous, therefore, to combine all conditioning agents above ground so that they can be produced, applied, and controlled with the operation of the surface plants. The activated combustion gas can easily be varied in its composition and adjusted to operating conditions at any given time. In the starting phase, it may temporarily consist almost exclusively of steam with little oxygen; in the actual burning phase, it may contain plenty of oxygen with small quantities of residual nitrogen and carbon dioxide. The formation of steam may be either reduced by throttling down the supply of fuel gas, or it may be increased to provide mechanical energy for covering other energy requirements in the production field.

It is, therefore, an object of the invention to use various process elements in the deposit and in the surface installations for making available all necessary operating agents at short notice and in a controllable manner. There are several possibilities of variation, thus allowing of several application techniques. Moreover, the plant and equipment involved can be readily transported owing to their light weight and small dimensions, thus facilitating adjustment to the conditions in oilfields being opened out.

SUMMARY

This invention relates to system of apparatus for controlling in-situ combustion using highly concentrated oxygen with residual nitrogen and a partial and/or temporary supply of superheated steam together with simultaneous production of energy for the operation of the necessary above ground facilities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagramatic cross-section of the firebox.

FIG. 2 is a diagramatic cross-section of high-pressure steam boiler.

FIG. 3 is a general illustration of the overall layout.

FIG. 4 is a diagramatic cross-section showing a double-walled steam boiler.

DESCRIPTION OF THE PREFERRED EMBODIMENT

When using high pressures of injection into the borehole, such as for steam coming from a closed system of tubes, it is envisaged that the pressure of the feed water flowing in the annular space of the double-walled firebox or steam boiler should be smaller or slightly higher that that prevailing in the combustion chamber, and only after leaving the annular space should the feed water be pumped up to the pressure required for injection into the borehole.

The invention achieves these objects mainly by producing hot high-pressure steam in the combustion chamber, injecting water into a pressure flame from an open system of tubes, and by additionally producing high-pressure steam in a closed system of tubes. The two types of steam may be used both for injection into the deposit and for supplying surface installations. Moreover, a mixture of separated dry carbon dioxide and residual nitrogen may be introduced at combustion chamber pressure, or at increased pressure after passing through a compressor, into the deposit via special pipes in the injection boreholes.

Technically, these requirements are met by using means known per se, such as a firebox or a steam boiler provided with a high-pressure combustion chamber. Particularly suitable is a firebox or steam boiler surrounded by a double wall forming an annular space through which a cooling medium, such as the feed water for the firebox or steam boiler, is passed, the surface area of the interior wall being enlarged at the side of the flowing feed water so that the interior and exterior walls will always have the same temperature and thus the same expansion, enabling them to take up high pressure from within the combustion chamber.

According to the invention, when using highly concentrated oxygen at very high pressures up to and above 200 atmospheres, only a small volume of combustion gases will be present in the combustion chamber. Alternatively, at medium pressures ranging from 3 to 15 atmospheres, air will be used in heavy excess over the amount of air required to provide combustion of the fuel, and part of the air from the compressor for the combustion turbine before the steam boiler will be branched off for the oxygen plant. In both cases, however, flue gas is taken from the combustion chamber and steam is taken from the high-pressure steam section for two different purposes, the flue gas and the steam each simultaneously doing two different jobs above ground and in the deposit. The temperature of a flame is known to increase as the pressure of the gases in the combustion chamber and the oxygen content of the combustion air increase. The shorter the period of time during which a given quantity of oxygen is converted to combustion gas, and the smaller the combustion chamber volume in which this conversion takes place, the higher the flame temperature will be. The pressure flame used in the method of the invention meets all conditions that will increase the flame temperature at a high rate of combustion. Thus, it is a flame maintained in a small-volume combustion chamber. Its characteristic feature is an extremely high flame temperature with an extraordinarily strong radiation of heat, which cannot be cooled down sufficiently by a system of water and steam tubes even with normal circulation of the combustion gases. Almost invariably, film evaporation will occur in the water tubes, which will further deteriorate the cooling of the flame and will allow the temperatures to rise to an undesirable degree. To that case, the flow of feed water through the annular space between the two walls will scarcely lower the temperatures in these walls sufficiently to maintain adequate mechanical resistance values for the material of the walls.

To eliminate these disadvantages, water is injected into the flames so that a radiation-absorbing envelope of steam is formed around the flames which will effect an inertialess reduction of the flame temperature by evaporation of the water and will considerably diminish the effect of heat radiation on the walls of the combustion chamber. Heat distribution is further improved by providing in the combustion chamber and near the double wall of said combustion chamber a tube-mounted wall having circular openings to permit circulation of the cooled-down steam.

In such steam boilers or fireboxes having pressure-resistant features, it is also possible to withdraw from the combustion chamber, from a condensation plant, or from a closed system of tubes such combustion products as carbon dioxide with residual nitrogen and steam in the desired temperature range, or cold dry carbon dioxide with residual nitrogen, as diagrammatically shown in the attached drawings.

The simplest case is illustrated in FIG. 1, when the oxygen with a small amount of residual nitrogen is available at such a high pressure that it can be forced into the deposit at 20 against the pressure of the deposit, using an additional pressure of 50 to 75 atmospheres, a very small part stream of oxygen stream is introduced at its full pressure into a double-walled pressure-resistant firebox to be burnt with hydrocarbons to form carbon dioxide with residual nitrogen and steam. Since the combustion of hydrocarbons with highly concentrated oxygen leads to very high temperatures endangering the steel construction material of the firebox, water is injected at 15 and 16 through injection tubes 6 and 11 directly into the flame in combustion chamber 18. The injection water evaporates immediately thus reducing the temperature in the combustion chamber. To be able to resist the high pressures encountered, the firebox is surrounded with a double wall 1 and 2, enclosing an annular space 3. For cooling the two walls, the slightly preheated injection water is introduced into annular space 3 at 13. At 14, the water can be separated into two part streams and passed to the injection tubes via the inlet openings 15 and 16. Inlet 15 provides an upper injection water supply with injection openings 6 and inlet 16 provides a lower injection water supply with openings 11. The upper injection openings 6 form the steam envelope for protecting the combustion chamber, and with the lower injection openings 11 the outlet temperature of the combustion gases and vapors is adjusted to the necessary temperature for entry into the injection borehole 28. The tube-supporting wall 4 has openings fitted with steam injectors at 17 and further injectors 12 in the annular space 5 permitting circulation via outlet 10 of part streams from combustion chamber 18 to provide balanced temperature conditions.

Oxygen 8 and hydrocarbon 9 enter into the burner (not indicated) at 7 and leave the combustion chamber as combustion products together with steam from the injection water at 19, any entrained solids being kept back by small refractory bodies 31, which may consist of sintered iron or small ceramic bodies having large pores, to prevent obstructions in the deposit. Through sluices 29 and 30 the bodies 31 can be replaced without interrupting operations. A completely unchanged stream from outlet 19 is introduced into the interior corrosion-resistant tube 24 of the injection bore. After cooling, a smaller part stream of dry carbon dioxide with residual nitrogen passes into the annular space 27 of borehole 28 and temporarily, alternating with the oxygen, into the annular space 25 of the ascending tube 26. Similarly, the hydrocarbon 23, alternating with the combustion products and steam 21 and 22, passes into the interior tube 24.

FIG. 2 shows an additionally installed closed system of tubes 32 which is used as a high-pressure steam boiler. Since the interior wall 2 of the double wall is very closely covered with tubes, only small amounts of radiation and conduction heat can reach this wall, so that a special tube-supporting wall is not required. The water for the high-pressure steam boiler entering at 13 and the injection water pass through annular space 33 for cooling the double walls and enter the two systems of tubes at 33 and 35 at a controlled rate.

Combustion of the oxygen and hydrocarbons with cooling of the flame as well as the entry of the combustion products formed into the bore are effected in the same way as shown in FIG. 1. However, the amount of fuel and oxygen must be increased to such an extent, that the steam leaving at 39 can be used for operating steam turbine 36 and power generator 37, the waste steam being condensed in condenser 38. Opening 34 is used for introducing water for temperature regulation.

In FIG. 3 compressed air in the pressure range of 3 to 15 atmospheres is used as oxidation agent for combustion chamber 18, while highly concentrated oxygen with residual nitrogen is produced in an oxygen plant 57 on the oilfield and brought to the required pressure by means of high-pressure compressor 59 so that it can be introduced into the deposit in sufficient quantity through injection borehole 28.

The overall layout shown in FIG. 3 provides for a complete coordination of the methods of operating the in-situ combustion in the deposit with the supply of installations above ground. It will be desirable, however, to supplement the equipment shown in FIG. 3 by a firebox as shown in FIG. 1, so that in the event of breakdowns or when starting the in-situ combustion no major pause or delay can occur during which the fire in the deposit might be extinguished.

Two separate plants are installed for the energy production, accordingly the steam boiler with its pressure-resistant furnace is equipped for using compressed air, part of which serves for the production of oxygen. The second source of energy is based on steam; the steam has a pressure sufficient for injection into the borehole and is also used continuously or temporarily for driving a turbogenerator 36 whose energy output is used for operating installations above ground.

The inter-connected plate elements, air compressor 49 and combustion turbine 50, are combined with a steam boiler forming the combustion chamber. 85 percent .+-. 20 percent of the air is passed into annular space 44 between walls 2 and 43, where it is preheated. Then the air is passed through annular space 44 to point 7 and is mixed with the hydrocarbons 9 at the outlets to the burner (not indicated). The mixture is burnt in combustion chamber 18 using a heavy excess of air.

From line 47, a part quantity of 30 percent .+-. 15 percent of the compressed air is branched off to oxygen plant 57, supplementing the quantity of air from air compressor 56. Thus, there are two separate sources of air for the oxygen plant, each of which can provide about 50 percent of the total air required.

The combustion gases formed in combustion chamber 18, being products of the combustion of the hydrocarbons with compressed air, have a high temperature. These gases are exhausted from the combustion chamber 18 and are passed through combustion turbine 50 and thereafter passed into heat exchanger I and condenser I 52 wherein they are cooled by water provided from water treatment plant 55. The gases and condensed water are passed to condenser II, 53. The condensate from condenser II is passed through pipe 15 with openings 6, having been cooled to such an extent that no film evaporation can occur in pipes 32. The injection water, introduced through inlet 40 to pipe system 41 leading to the injection openings 42 into the combustion chamber is controlled so that the water entering the evaporator 45 at 46 is evaporated and the steam is drawn off through pipe 39, having the desired temperature both for the injection borehole 28 and for steam turbine 36 which may, for example, drive the power generator 37. The volume of steam formed by the injection water replaces the air from air compressor 49 branched off for oxygen plant 57, thus resulting in a total gas volume or additional steam volume for combustion turbine 50 driving power generator 51.

The waste steam from steam turbine 36 is partially condensed in heat exchanger II (point 38, combined with condenser III), and the residual steam in condenser III, point 38. The condensate is passed via pump 2 into heat exchanger I, point 52, which receives its heat from the waste gases of the combustion turbine 50. In heat exchanger I, point 52, combined with condenser I, the feed water from feed water treatment plant 55 introduced via pump 3 and the condensation water from point 38 introduced via pump 2 are heated, the water for the closed system of tubes 32 entering pipes 32 at 34 as a part stream. The steam from the injection water from combustion turbine 50 having an inlet temperature of about 450.degree. C. is cooled in heat exchanger I, point 52, condensed in condenser I, and mixed via pump 4 with part of the feed water 55 in condenser II, point 53. The heat from heat exchanger II and condenser III is further used at point 38 for heating the wet petroleum recovered from the deposit, thus separating oil and water. The separated water can be used in other boreholes for flooding purposes. Parts of the condensate obtained at 38 can be introduced without heating into annular space 3 between walls 1 and 2 at point 13 via pump 1.

The combustion gases from chamber 18 and steam generated by injecting water into the flame will enter the heat exchanger I (position 52) via line 48 and combustion turbine 50. The temperature of the gaseous mixture decreases from 950.degree. to 450.degree. C. while passing combustion turbine 50. Loss water from apparatus 55 for dehardening the feeding water also will enter the heat exchanger 52. The inside temperature of chamber 18 will be controlled furthermore by injecting feeding water at 34.

Inside the condenser II (position 53) especially near its upper warm end gaseous products, like nitrogen, oxygen, and carbon dioxide will escape from the condensate. A mixture from carbon dioxide and remaining nitrogen will be delivered at the bottom of condenser 53 and supplied to the injection borehole 28.

Owing to the cold water the carbon dioxide and residual nitrogen are also obtained cold containing very little steam, it may be considered in the borehole as dry carbon dioxide which is not corrosive even if it must be pressurized. With the same degree of cooling the oxygen may also become non-corrosive after compression.

Air from air compressors 49 and 56 is used for producing oxygen in plant 57, almost all of the nitrogen escaping at 58. In compressor 59 the oxygen is sufficiently pressurized for passing into the deposit via the injection borehole. Also in the case of combustion chamber 18 using compressed air as oxidation agent for the hydrocarbons from the deposit, the injection borehole 28 is supplied with the necessary agents as shown in FIG. 1.

The double-walled combustion chamber with its walls 1 and 2 also receives part of the feed water for reducing the temperature direct from condenser III, point 38, at a pressure below that of combustion chamber 18. The feed water enters the annular space 3 at 13, leaves it at 60, is brought to the pressure of the closed system of tubes 32 by means of pump 61, and passes into the closed system of tubes at 62.

In combustion chamber 18, the tube-supporting wall 4 is provided within pipe wall 43 so that in annular space 5 with injectors 12 and 17, a circulating effect can be achieved at 10 by means of the injection water introduced at 16 to create balanced temperature conditions.

This special double-walled steam boiler thus supplies the injection borehole 28 and turbines 36 and 50 so that a coherent system has been provided and a maximum of conditioning agents is available for controlling the in-situ combustion.

FIG. 4 is a diagrammatic drawing of a double-walled steam boiler having a multi-stage burner and pressure-resistant upper and lower cover plates. This design is suitable for higher pressures even at temperatures of 300.degree. C.

For transport from one oilfield to the other, the exterior wall can be removed so that the remaining low weight of the interior wall with its installations permits its transport as a unit. The lower rings 66 are suitably parted and fitted to the walls 1 and 2.

Thus, the exterior wall 1 and the interior wall 2 have inner and outer rings 66 at the top and bottom. The upper ring 82 has openings only for bolts 63.

The upper and lower cover plates 68 are welded to the inner rings 66 and 70.

By means of screw joints 63 and 64 the upper counter-ring 82 is pressed on the soft iron rings 65 and rings 66 to form a tight seal.

Additional seals are provided by rings 67 and 71.

The flange openings 69 are screwed to the upper and lower cover plate rims 68. The burner with its inner opening 74 and its outer opening 72 is welded or screwed to the upper flange opening.

The combustible gases enter at 9 and the oxidation agent at 44. The oxidation agent passes from 47 into the annular space 44 formed by walls 2 and 43. It passes between walls 72 and 73 and is mixed at ring burners 75 and 78 or, respectively, 79 and 81, at the conical outlet 80.

The burner having several ring burners 75 and 78 is able to produce a very long downward flame through the vertical openings 79 and 81. The feed water is introduced into annular space 3 at 13 and leaves it at 60.

The bottom of the boiler casing corresponds in design to the top part. The top and bottom of the boiler casing are practically symmetrical.

Claims

We claim:

1. A system including apparatus for recovering oil from a subterranean hydrocarbon-bearing formation by controllable insitu combustion whereby means are provided for regulating the injection of oxygen enriched gas, steam, and an exhaust gas containing carbon dioxide into said injection well comprising:

a. a combustion chamber for producing a gas-steam mixture having means for supplying thereto a fuel and an oxygen-containing gas, burner means for combustion of said fuel, a closed means for providing said combustion chamber with a first flow of water thereby generating steam in said closed means, a means for providing said combustion chamber with a second flow of water said means having nozzles directed into said combustion chamber, means for preheating said oxygen-containing gas, and means for exhausting said gas-steam mixture from said combustion chamber into a combustion turbine and thence into said injection well;

b. a first means for providing air to said system comprising a first source of compressed air in communication with an oxygen producing plant for producing a highly concentrated oxygen stream, a compressor and a means for providing injection of said oxygen concentrated stream into said injection well;

c. a second means for providing air to said system comprising an air compressor in communication with said combustion chamber, said air compressor being integral with a combustion turbine said combustion turbine being driven by said exhaust gases from said combustion chamber thereby generating power for said system of apparatus, and said first air means and said second air means being in communication with each other thereby to control the relative volumes of compressed air provided to said oxygen producing plant and said combustion chamber;

d. a means for providing water to said steam system comprising a water treatment plant a first heat exchanger in communication with said combustion turbine for passage of said exhaust gases from said combustion turbine, a portion of said water from said treatment plant being supplied to said combustion chamber whereby steam generation occurs in said combustion chamber and a second portion being supplied to said nozzles to supply steam in said combustion chamber said steam being generated in said combustion chamber being thereafter supplied into a steam turbine to provide power generation and thence means for providing said steam to said injection well;

e. means for providing said exhaust gas from said combustion chamber into said combustion turbine and to said first heat exchanger and thereafter providing means for injection of said exhaust gas into said injection well.

2. A combustion chamber according to claim 1 having an external wall, an interior wall and a tube supporting wall said tube supporting wall tightly fitting to the bottom of said combustion chamber thereby providing for the oxygen-containing air to be supplied to the burner of said combustion chamber separately from the circulation system of the steam and combustion gases.

3. A combustion chamber according to claim 1 wherein the tube supporting wall is provided with openings fitted with injectors to increase suction of water vapors and combustion gases from the combustion chamber.

4. A combustion chamber according to claim 1 wherein said combustion chamber is fitted with first and second tube systems, separately controlled, said first tube system being open and provided with injection nozzles directed into said combustion chamber and said second tube system being closed and separate from said combustion chamber for the production of high pressure steam, said first and second tube systems being provided with means for injecting water to control temperature.

5. A combustion chamber according to claim 1 wherein said combustion chamber has a burner with horizontally superimposed burner elements and a central jet directed downward.

6. A combustion chamber according to claim 1 wherein said combustion chamber is fitted with exchangeable filter bodies for absorbing solid or dust-like particles.