US3595316A - Aggregate process for petroleum production - Google Patents

Abstract

Water, hydrocarbons, and air are reacted together within a catalytic chamber to provide high temperatures, high-pressure products of reaction having increased percentage composition of hydrogen and carbon dioxide therein. A catalyst in the form of an alkali metal oxide or an alkaline earth metal oxide is carried to the reaction zone in the water stream, thereby providing the additional function of treating the water. The high temperature oxygen free gases are injected into a reservoir and contact the oil bearing formation thereof to increase the production of crude therefrom.

Description

Ft ami United States Patent 2,871,942 2/1959 Garrisonetal....-.. 166/260 2,973,812 3/1961 166/261X Walter A. Myrick, 111

MacSporran 10/1967 Lange..........

[21] Appl. No. [22] Filed May 19,1969 (45] Patented July 27, 1971 Primary Examiner- Stephen J. Novosad Attorney Marcus L. Bates {54] AGGREGATE PROCESS FOR PETROLEUM PRODUCTION 1 6D F 10 Ch m "mug igs' ABSTRACT: Water, hydrocarbons, and air are reacted [52] US. together within a Catalytic chamber to provide h igh tempera- 166/250, 166/64 tures, high-pressure products of reaction having increased 43/24 percentage composition of hydrogen and carbon dioxide 166/272, therein. A catalyst in the form of an alkali metal oxide or an alv 256, 302, v 57 kaline earth metal oxide is carried to the reaction zone in the water stream, thereby providing the additional function of treating the water. The high temperature oxygen free gases are s11rm.c|................. so

[56} References Cited UNITED STATES PATENTS 2/1956 Walter......................

injected into a reservoir and contact the oil bearing formation thereof to increase the production of crude therefrom.

PATENTED me? [an SHEET 1 OF 2 FIG. 2

m K Wm IR VI M R E m W BY MARCUS L. BATES PATENTED JUL27|97| 3,595,316

' sum 2 [1F 2 IN VIiN'I'OK WALTER A. MYRICK 111 m MARCUS L. BATES AGGREGATE PROCESS FOR PETROLEUM PRODUCTION BACKGROUND OF THE INVENTION The normal percentage recovery of liquid products from most petroleum reservoirs is between 30 percent and 40 percent, however, some distillate fields yield as high as 50 percent and some low gravity fields less than percent. Hence, the majority of reservoirs contain more than 60 percent of the original oil after they have been subjected to normal production methods. It is for this reason that secondary recovery operations are being vigorously pursued by the petroleum industry. Some forms of secondary recovery systems include the use of steam flood, water flood, fire flood, stripping or gas purge, inert gas, and dilution wash. Many low A.P.I. gravity oil fields exhibit low yields regardless of the methods of production employed and most field still contain at least 50 percent of the original liquid petroleum after application of secondary recovery methods thereto. The many theoretical advantages of the various secondary recovery processes have not been fully realized in most installations because of the high cost of the original installation as well as the many mechanical and process problems encountered.

It is therefore desirable to incorporate the more successful features of the older secondary recovery processes into a simple unified system while circumventing many of the imperfections and drawbacks inherent in the older methods, along with improved selection of temperature and pressure ranges so as to control the combustion process in a manner to provide a mixture of gases having chemical and physical properties which are highly desirable for adding displacement energy to the natural underground reservoirs, and in producing changes in the physical properties of the petroleum oils as well as the production formation to thereby facilitate increased recovery of the contained oils in a manner which has heretofore been unknown.

SUMMARY OF THE INVENTION This invention embraces a method of secondary recovery of petroleum oils from formations by the provision of a controlled combustion process which entails the production of mixed gases by the reaction ofa hydrocarbon, including natural gas, along with air, and water. The reaction occurs within a reactor at relatively high pressure and temperature and in the presence of an alkali metal oxide or an alkaline earth metal oxide catalyst to thereby provide combustion products having chemical and physical properties which are highly desirable for adding displacement energy to underground reservoirs as well as changing the physical properties of both the petroleum oils and the production formation in a manner which facilitates increased recovery of the contained oils. The catalyst also serves as a water treating chemical, and has advantages when carried downhole into the oil bearing formation.

It is therefore a primary object of the present invention to provide a new catalytic reaction process for producing products of combustion for use downhole in an oil well.

Another object of the present invention is the provision ofa method of increasing the H and CO content of products of combustion.

Still another object of the present invention is the provision of an improved method of secondary recovery of petroleum oils from oil bearing formations.

A further object of the present invention is the provision of a catalyst which is carried into a combustion reaction by means ofa water stream.

Another object is the provision of products of combustion which treat an oil reservoir in a new and different manner.

A further object of the present invention is the provision of a reactor for converting fuel, air, and water into products of combustion.

The above objects are attained in accordance with the present invention by the provision of a new process which is carried out essentially as set forth in the above abstract and summary.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow sheet n the form ofa schematical drawing or diagram which sets forth a generalization of the method of the present invention;

FIG. 2 is a cross-sectional detail of a hydrocarbon reactor which can be used in conjunction with the method taught in FIG. 1; and with additional flow control means and conduits being schematically represented therein;

FIG. 5 is a cross-sectional view taken along line 3-3 of FIG.

FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 2;

FIG. 5 is a cross-sectional view taken along lie 5-5 of FIG. 2; and

FIG. 6 is a cross-sectional view taken along line 6-6 of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In carrying out the method of the present invention, air, a hydrocarbon such as natural gas, and water, respectively, are flow conducted through conduits 10, 12, and 14, respectively, and into a hydrocarbon reactor. An alkali metal or an alkaline earth metal oxide, including potassium,,and magnesium, and specifically potassium sulfite and potassium carbonate, is transferred at 18 into a water treatment tank 16 prior to the treated water being flow conducted into the hydrocarbon reactor 20. The air, gas, and water react together within the combustion zone of the reactor and emerge as off-gases at 22 where they are subsequently flow conducted through a wellhead 24 and downhole as seen at 25 to the production zone.

The air, fuel, and water enter into chemical reaction in the presence of one or more of the before-mentioned catalyst at elevated temperatures and pressures, for example, 700 p.s.i.g. and 750 F. The catalyst serves the dual purpose of increasing the oxidation of the reactants to H and CO as well as reducing the corrosion and collection of scale which would otherwise occur throughout the system, as well as consuming and reacting with the dissolved oxygen which is present in the injection water, as will be described in greater detail later on.

Looking now to the details of FIG. 2, in conjunction with the remaining figures, the hydrocarbon reactor 20 is seen to have an external high-pressure shell 26 which terminates in an inner flange 27, with the flange being bolted to outer blind flange 28, and with central flange member 29 being sandwiched therebetween.

An igniter 30 has an ignition means 31 associated therewith and is operably disposed within the reactor where it is controllably extended into close proximity of the combustion area by means of adjustment handle 32. Housing 33 forms a support for the igniter control means.

Gas conduit 34 flow connects a regulated or controlled gas supply 12 with a gas nozzle 35. Burner 36 is spaced apart from and circumferentially encloses the gas nozzle therein, thereby leaving the illustrated annulus therebetween.

Air conduit 37 interconnects controlled air supply 10 with a toroidallike air passageway which serves as a preheater, as will be better appreciated when discussed in greater detail later on.

Reaction zone 38 is defined by the high temperature insulation 39 which is bonded to inner shell 40 with the inner shell being connected to the before-mentioned central flange 29. The inner shell together with the inside peripheral wall 42 of the outer shell cooperates together to form an annulus 41 therebetween. A series of nozzles, 43 and 44, are spaced apart from one another and flow communicate with annulus 41. Sleeve 45 is affixed to the lowermost portion of the inner shell of the reactor where it slidably receives reduced portion 47 of outlet tubing 46 in a telescoping manner to thereby provide an expansion joint.

Looking again now to the details of FIGS. 2 through 5, it

stock because of its low cost and ease of handling, however, other hydrocarbon gases including propane, butane, as well as any suitable liquid hydrocarbon can be used to advantage in the present invention. The quantity of gas consumed by the will be noted that the center flange supports the inner shell reactor varies in accordance with the operating conditions, and also serves as a means ofcontrolling the flow of water and and assuming a lO/l air to fuel ratio with a flow rate of 100 catalyst into the reactor. Water inlet passageways 14' are flow mcf. of natural gas being consumed, l35 barrels of treated connected to the before-mentioned source of water 14, and water will be required. The water must be clarified and each of the passageways inwardly terminates in a circumpreferably contains less than l600 p.p.m.dissolved solids. The ferentially extending concavity or grooved passageway 50, sodium chloride content as well as the dissolved silica should with the lower wall surface of the concavity receiving a mulnot be excessively high. The injection pressure, that is, the tiplicity of apertures in the form of spaced apart drilled pressure within the reactor or at the wellhead is generally passageways each of which flow Communicate the Water detennined by the type and thickness of the reservoir formapp y with the annulus l 5 tion and is limited in accordance with the thickness of the 8 to demhs of the wmldal passageway, overburden. However, it is desired to maintain the temperaahd in Particular 2 in Conjunction With the air ture between 500750 F. with the pressure being controlled inlet 37 is seen to be connected to annulus 53 at a point adat 700 p.s.i.g. where permissible. The following examples of jacent to the illustrated baffle 52 which provides a circular flow rates are typical of most installations of the process:

Bbl. Natural water H2, CO1, Air flow, gas feed per mole mole Temp, Pressure, m.c.f. m.c. A/F ratio day percent percent F. p.s.i.g

flow path to the illustrated inlet located on the opposite side of As seen in the above examples which set forth two different the baffle so as to provide a continuous flow path for the air airflow rates, when the A/F ratio is maintained within the into chamber 54. Chamber 54 conducts the airflow through desired perimeters the hydrogen content and CO content inport 54' and into the annulus formed between burner 36 and crease as the A/F ratio decreases. The formation of H is ingas nozzle 35 to thereby enable air and gas to be admixed at creased while the formation of CO also increases but at a the free depending terminal end of the burner. The cylindrical relatively slower rate for the reason that the production of CO housing 60 is spaced apart from cylindrical housing so as to is largely avoi e due to the Water reaction. When the provide a dead air space therebetween. 4O hydrocarbon feed rate is increased to a value which exceeds Looking now to the flow control details as set forth in the the above desired perimeters, the hydrogen and CO content schematical portion of FIG. 2, there is disclosed the beforedecrease due to the formation of excessive carbon monoxide mentioned water and catalyst flow passageway 14, having flow and free carbon. When the A/F ratio is increased within the measuring orifice assembly 62 controllably connected to the desired Perimeters h hyd oge and 2 Content i recording ratio flow controller 63 which in turn is controllably ififi ih connected to and actuates a motor control valve 64, thereby An increase in the flow rate of injection water lowers the enabling the flow rates to be carefully maintained within a temperature of the off-gases and tends to more readily quench predetermined range of values. The ratio flow controller is the reaction, which increases the formation of H and connected to flow measuring orifice 66 and actuates the decreases the formation of CO. motor control valve 68 of the air supply. Pressure controller The optimum conditions for natural gas (1,000 B.t'.u./ft.") 74 resets ratio flow controller 63 so as to control the flow rate are set forth under column three of the above table. The acof water and air to thereby maintainapreset pressure. tual mass flow rate of effluent gases can be adjusted in ac- There is schematically shown arecording temperature concordance with the number of wells undergoing treatment. troller 70 which is pneumatically connected to the control Generally the gas consumption will be 46,000--l40,000 valve 72, and which actuates the valve in accordance with a scf./D for one reactor which is flow connected to several injecsignal received from temperature transmitter 76. Additionally, tion wells. g V H w the recording temperature controller records the P and The treatment chemicals which are added to the injection flow fate sensed at 74 and respectivelY water for corrosion control serve as a catalyst to increase the Pneumatically manua ly opera e Vent Valve 77 Provides 8 oxidation of the carbon monoxide to carbon dioxide and to Safety bypass for Venting the gases to the atmosphere Pheu" 6O enhance the formation of hydrogen. The catalyst is an alkali maticahy manually Operated flow valve 78 Provicles a metal oxide or an alkaline earth metal oxide,ora combination means for interrupting flow the Wellhead Check Valve 80 of the two, and preferably is added to the raw water as potassi- P' now of Products and gases from the weiiheadum carbonate and potassium sulfite, although magnesium car- Electri lly atituated Solenoid Valves 82, 83, 85, and 86 bonates and sulfites are also acceptable catalysts. The catalyst are actuated by switches (not shown) associated with recordi an gent whi h i selected from the following group of ing temperature controller 70, so as to enable emergency shutmaterials: potassium, lithium, rubidium, cesium, magnesium, down Of th system, n to vent the m n t0 the calcium, strontium, and barium, wherein the agent is in the mosphere. form of a bisulfate bicarbonate, sulfite, carbonate, or a nitrite, Relie valves 83 n 89 are automatically actuated at Any combination of these substances can be used, however, it elevated pressures which exceed the designed operating presi preferred to use a mixture comprised of potassium sure of the systembonate and potassium sulflte so as to realize the maximum advantage of the catalyst since this form of the catalyst offers OPERATION some form of treatment throughout the system.

The catalysts are added to the feed water, as for example,

In operation, natural gas is preferred as the reactor feed potassium bisulfite, and as potassium carbonate for pH control. Potassium sulfite and potassium bicarbonate can also be used where deemed desirable. Where removal of dissolved oxygen from the feed water is required, the catalyst can be introduced as potassium nitrite as well as the sulfite as an oxygen scavenger.

As a more specific example of catalyst introduction into the feed water, and assuming the metal potassium to be available for use, sufficient sulfite or nitrite is added to remove the free oxygen from the feed water. Potassium bicarbonate and potassium carbonate is then added in order to balance the pH. The total weight percent of potassium must provide sufficient potassium ions to promote the desired reaction within the combustion chamber. This requirement will vary between and 100 ppm. potassium ions in the feed water, with 30 ppm. being considered optimum.

Assuming that the feed water has been chemically treated by the catalysts, and flowing through conduit 14, its rate of flow will be maintained constant by the ratio flow controller as the water enters passageway 14'. The water flows through the grooved passageway, through the apertures 51, and through the annulus 41 where it enters the reactor at 43, 44, and through the slip joint between sleeve 54 and 47, thus maintaining the shell 40 within its structural limitations so far as regards the temperature and pressure existing within combustion chamber 38. As the water, along with the catalyst, enters the combustion chamber, it is a least partially in the form of steam and accordingly the potassium carbonate, for example, will now be converted to potassium oxide, which is the required form of the catalyst in order to promote or influence the combustion reaction to be driven in a direction which enhances the formation of CO and H and minimizes the presence ofO and CO.

Motor valve 68 controls the rate of flow of air as it enters inlet 37, flows about the path formed by annulus 53, through the illustrated port adjacent the baffle, into the chamber 54, where it continues to flow about the igniter and burner and then enters the port 54' and flows into the burner annulus where the air then mixes with the natural gas or other suitable hydrocarbon from nozzle 35. The igniter 31, when it is not in use, is maintained in the retracted position clear of the area of intense heat within the combustion chamber.

Generally, the system is controlled as follows: the temperature transmitter 76 forms the primary control means for controlling the combustion process. The transmitter provides a signal which is sensed by the recording temperature controller 7, which is pneumatically connected to the control valve 72 in order to actuate the valve in accordance with the signal. This enables the temperature at 70 to be selected, whereupon the temperature will thereafter be maintained within a predetermined limit.

The pressure controller 74 resets the ratio flow controller 63 in accordance with the pressure sensed at 74, and maintains the flow ratio of water and air within a predetermined range of values. The pressure controller is connected back to the recording temperature controller for recording purposes, as well as enabling actuation of the before-mentioned pressure limit switches. Also associated with the recording temperature controller are temperature limit switches connected to sense the temperature at transmitter 76. The pressure and temperature limit switches are connected to valves 82 through 86 to provide automatic shutdown in the event the temperature or pressure of the system should diverge from a predetermined range or limit ofvalues.

As the water, hydrocarbons, and air are burned or reacted together within the reaction chamber of the reactor, a multitude of complex reactions occur, the details of which are unnecessary for a clear understanding of the invention, but which may be summarized as follows:

C,,H H O O, N, H O CO H N C0 trace of NO and N0 The'catalyst, together with the reactants exit at outlet tubing 22 along with a significant quantity of potassium sulflte, which becomes available as an oxygen scavenging agent as the gases flow through the remainder of the equipment.

The catalyst, in addition to removing free oxygen from the feed water, enhances the combustion of CO to CO by causing the dissociated oxygen from the water molecule to combine with the CO molecule, which in turn leaves the dissociated hydrogen from the water molecule free to recombine with itself, thereby increasing the molecular hydrogen content of the effluent gases to a value between the limits of l percent to 6 percent, depending upon the flow rates of the air, gas, and water. The water of combustion together with the excess feed water remains in the gaseous phase, and is referred to herein as superheated steam.

The superheated steam is available to increase the temperature of the formation downhole in the well to thereby reduce the viscosity and specific gravity of the petroleum contained within the reservoir which in turn reduces the oils resistance to flow. The increased temperature coupled with the carbon 1 dioxide which is adsorbed in the condensate enables the water to preferentially wet or to be adsorbed on the surface of the sand or production formation, thereby displacing oil therefrom. ln paraffinic oil the increased temperature increases the solubility of the paraffin in the formation oils thus reducing the tendency of the paraffin to plug the well bores. The Co also dissolves in the oil to reduce its viscosity as well as its specific gravity, while some of the CO combines with water to form carbonic acid which reacts with lime, dolomites, and other calcareous formations to produce water soluble salts, thereby increasing the porosity of the formation. The carbonated water droplets are more easily pushed through the formation by the nitrogen and accordingly tends to wash the oil from the formation. The carbonic acid lowers the ph of the formation fluids thereby lowering the surface tension of the oil which enables the oil to be washed or displaced from the surface of the sand.

The nitrogen increases the reservoir pressure and drives the condensed steam through the formation so as to produce a washing action. The small amount of nitrogen oxides which are produced in the reactor is converted to nitrous and nitric acids in the production formation and reacts with calcareous formations to produce soluble salts. The acids also produce free hydrogen ions which are available to displace alkaline earth elements from the lattice structure of the clays, thus effectively increasing the porosity of the formation.

The potassium oxide is converted back to potassium carbonate due to the presence of CO downhole, which enables reaction with various alkaline earths to occur; calcareous deposits for example, to give a potassium-magnesium carbonate, which is soluble in water, thus enabling the calcareous rock deposits to be solubilized, to thereby effectively increase the porosity of the formation.

Hydrogen produced by the reactor serves in a mannersimilar to nitrogen but more importantly it produces a reducing atmosphere which tends to reduce corrosion of the metal equipment. Dissolved hydrogen tends to reduce oil viscosity and specific gravity. The hydrogen is readily dispersed through the formation because of its small molecular size.

As will now be evident to those skilled in the art, the water injection within the reactor is utilized to produce superheated steam which is the primary carrier of heat into the formation; to react with carbon monoxide and hydrocarbons to produce hydrogen and CO which improves the overall efficiency of the operation by producing a larger volume of gas per unit of fuel consumed; to control the reaction temperature as well as to cool the reactor and the reaction products; and as the solution medium for carrying the catalyst into the reactor where the catalyst can promote production of hydrogen and CO from hydrocarbons and CO.

The increased pressure in the formation caused by the injection gases tends to reduce the flashing of the light ends from the petroleum which would otherwise be caused by the increased temperature within the formation. The light ends (C C C and C are maintained in solution and contribute to reduction of viscosity and specific gravity The wells are placed on 3- to lO-day cycles, depending upon the formation depth and characteristics. At the end ofeach injection period, upon initial production. dissolved salts will be returned to the wellhead where they can be accumulated for subsequent disposal.

It is necessary to insulate the upper portion of the production tubing to prevent damage to the well head, cement, and casing.

The cost of operation and installation is low, the apparatus lends itself to automatic control, and many wells heretofore considered depleted by secondary recovery methods can actually be revitalized by the instant invention, and hence in many cases the present invention constitutes a tertiary recovery system rather than a secondary recovery system.

lclaim:

1. An improved method of recovering hydrocarbons from a well bore which is connected to a subterranean natural reservoir by treating the reservoir according to the following steps:

1. treating water with an agent selected from the group consisting of potassium, lithium, rubidium, cesium, magnesium, calcium, strontium, and barium, wherein the agent is in the form of either a bisulfite, bicarbonate, sulfite, carbonate, or a nitrite;

2. reacting the treated water of step (1) by combusting the water with a hydrocarbon in the presence of air to produce a gaseous product comprised of superheated steam, the agent, and flue gases;

. maintaining the product obtained in step (2) at a temperature which avoids condensation of the superheated steam within the injection tubing of the well bore;

4. flowing the product into the subterranean reservoir.

2. The method of claim 1 wherein the gaseous products are maintained above 500 F. and p.s.i. at the reactor outlet.

3 The method of claim 1 wherein the agent is comprised of a mixture of potassium carbonate and potassium sulfite.

4. The method of claim 1 wherein the agent is comprised of potassium nitrite, and the air/fuel ratio is maintained between the limits of 8/1 and l2/l.

5. The method of claim I wherein the agent is comprised of potassium bicarbonate, and the air/fuel ratio is between the limits of8/l and 12/1.

6. The method of claim 1 wherein the agent is magnesium and is in the form of a nitrite or a carbonate.

7. The method of claim 1 wherein the agent is magnesium nitrite and the air/fuel is 8/1 to l2/l. 4

8. An improved method of recovering hydrocarbons from a well bore which is connected to a subterranean natural reservoir by treating the reservoir according to the following steps:

1. treating water with an agent selected from the group consisting of potassium and magnesium wherein the agent is in the form of a carbonate, sulfite, or nitrite;

2. reacting the treated water of step (i) by combusting the water i with a hydrocarbon in the presence of air to produce a gaseous product comprised of superheated steam, the agent, and flue gases;

. flowing the product obtained in step (2) into the subterranean reservoir by using an injection tubing within a well bore connected to the reservoir;

4. maintaining the product obtained in step (2) at a temperature which avoids condensation of the superheated steam within the injection tubing of the well bore.

9. The method of claim 8 wherein the agent is comprised of a mixture of potassium carbonate and potassium sulfite.

10. The method of claim 8 wherein the agent is magnesium and is in the form of a nitrite or a carbonate.

Claims (16)

1. An improved method of recovering hydrocarbons from a well bore which is connected to a subterranean natural reservoir by treating the reservoir according to the following steps: 1. treating water with an agent selected from the group consisting of potassium, lithium, rubidium, cesium, magnesium, calcium, strontium, and barium, wherein the agent is in the form of either a bisulfite, bicarbonate, sulfite, carbonate, or a nitrite; 2. reacting the treated water of step (1) by combusting the water with a hydrocarbon in the presence of air to produce a gaseous product comprised of superheated steam, the agent, and flue gases; 3. maintaining the product obtained in step (2) at a temperature which avoids condensation of the superheated steam within the injection tubing of the well bore; 4. flowing the product into the subterranean reservoir.

2. reacting the treated water of step (1) by combusting the water with a hydrocarbon in the presence of air to produce a gaseous product comprised of superheated steam, the agent, and flue gases;

2. The method of claim 1 wherein the gaseous products are maintained above 500* F. and 170 p.s.i. at the reactor outlet.

2. reacting the treated water of step (1) by combusting the water with a hydrocarbon in the presence of air to produce a gaseous product comprised of superheated steam, the agent, and flue gases;

3. flowing the product obtained in step (2) into the subterranean reservoir by using an injection tubing within a well bore connected to the reservoir;

3. The method of claim 1 wherein the agent is comprised of a mixture of potassium carbonate and potassium sulfite.

3. maintaining the product obtained in step (2) at a temperature which avoids condensation of the superheated steam within the injection tubing of the well bore;

4. flowing the product into the subterranean reservoir.

4. The method of claim 1 wherein the agent is comprised of potassium nitrite, and the air/fuel ratio is maintained between the limits of 8/1 and 12/1.

4. maintaining the product obtained in step (2) at a temperature which avoids condensation of the superheated steam within the injection tubing of the well bore.

5. The method of claim 1 wherein the agent is comprised of potassium bicarbonate, and the air/fuel ratio is between the limits of 8/1 and 12/1.

6. The method of claim 1 wherein the agent is magnesium and is in the form of a nitrite or a carbonate.

7. The method of claim 1 wherein the agent is magnesium nitrite and the air/fuel is 8/1 to 12/1.

8. An improved method of recovering hydrocarbons from a well bore which is connected to a subterranean natural reservoir by treating the reservoir according to the following steps:

9. The method of claim 8 wherein the agent is comprised of a mixture of potassium carbonate and potassium sulfite.

10. The method of claim 8 wherein the agent is magnesium and is in the form of a nitrite or a carbonate.

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