Modification of subsurface strata by in situ replacement reactions for sequestering mobilization of heavy metals, metalloids, radionuclides or other naturally occurring contaminants

Abstract

Methods for in situ formation of a replacement reaction crystalline coating, acting as an impermeable barrier along grain surfaces, pore throats or dissolution cavities of rocks containing a percentage of free reactive cations and/or carbonate-containing compounds. This replacement crystalline coating is comprised of fluoride compounds, such as fluorite (CaF2), fluorapatite (Ca5[F(PO4)3]) and sallaite (MgF2). The coating or lining is capable of sequestering mobilization and/or movement of radionuclides, metals, metalloids and other naturally occurring undesirables from the media, rock or strata, while allowing water, fluids and other compounds to pass through pre-existing or induced permeability. The sequestration is achieved by shielding the media, rock or strata grains and/or matrix from interacting with pore fluids, hence greatly reducing solubility, dissolution, geochemical leaching and/or other chemical reactions from proceeding. The crystalline coating will have minimal affect on existing natural or induced permeability of the carbonate-containing rock, formation or strata. The methods can be utilized in subsurface reservoirs and/or aquifers.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing of U.S. Provisional Patent Application Ser. No. 60/599,100, entitled In Situ Formation of Fluoride Compounds for Sequestering Heavy Metals, Metalloids, Radionuclides or other contaminants, filed on Aug. 5, 2004, and the specification thereof is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISC APPENDIX

Not Applicable

BACKGROUND OF THE INVENTION

The invention relates generally to the treatment of carbonate containing rock formations, reservoirs or aquifers with various concentrations of fluorine ions, via prepared solution, acid, or base in order to sequester undesirable movement and/or mobilization of heavy metals, metalloids and/or radionuclides initiated by injection and/or production of surface waters, meteoric waters, ground waters or other waste waters or fluids. Specifically, the invention relates to in-situ formation of fluoride compounds that acts as a coating or liner preventing mobilization of undesirable elements and/or compounds.

The formation of a coating or liner is designed in response to water resource wells where it is desirable to inject water underground for storage, and later recovery for use in supply or industrial uses. In this setting, mobilization of undesired heavy metals, metalloids and/or radionuclides during injection and/or production of waters contaminate those waters, adjacent reservoirs and/or aquifers. Several techniques have been developed to remove the undesirable contaminants, but most are not effective solutions technically or economically.

One current state of the art technique is to pre-treat the water being injected.

This involves the deoxygenation of the surface or meteoric waters being injected in order to reduce them to anoxic water prior to injection. The technique does not address the typical problem of the mixing of freshwaters and brackish or saline aquifer waters, which become undersaturated with respect to elements contained within the formation, rock or strata thus tending to dissolve carbonate-containing formation, rock or strata aquifer and/or reservoir; that in turn mobilizes undesired heavy metals, metalloids and/or radionuclides.

Another current state of the art technique is to treat the water after it is produced. The process involves strategically removing the undesired heavy metals, metalloids and/or radionuclides from the produced water. This typically requires a surface treatment facility that must be used for the duration of all well operations and functions, thereby inflating injection and/or production operational costs.

Another approach, specific to this invention, is to create a less soluble coating than the natural rock, strata or media that chemically binds or traps naturally occurring contaminants (i.e., sequesters mobilization), while allowing water and other fluid components to pass through the rock unaffected through its natural or induced permeability. Since, the replacement reaction coating or liner is less soluble from all injection and/or production waters, wastes or fluids, geochemical alteration, chemical leaching and/or dissolution of the carbonate-containing grains and/or matrix will not occur, thus alleviating the mobilization and migration of the undesired heavy metals, metalloids, radionuclides and/or naturally occurring contaminants.

REFERENCES CITED

U.S. Patent Documents

4,869,621	September 1989	McLaren et. al.	405/263.
6,592,294	July 2003	Moore	405/129.
6,416,252	July 2002	Moore	405/129.
Reference more

OTHER REFERENCES

• Ames, L. L., 1961, The Metasomatic Replacement of Limestones by Alkaline, Fluoride-Bearing Solutions: Economic Geology, v. 56, p. 730-739.
• Ames, L. L., 1961, Volume Relationships During Replacement Reactions: Economic Geology, v. 56, p. 1438-1445.
• Ames, L. L., 1963, Kinetics of A Replacement Reaction, Economic Geology, v. 58, p. 1229-1236.
• Baer, N. S. and Lewin, S. Z., 1970, The Replacement of Calcite by Fluorite: A Kinetic Study: The American Mineralogist, v. 55, p. 466-476.
• Garrels, R. M. and Christ, C. L., Solutions, Minerals and Equilibrium, Harper and Row, New York, N.Y.
• Glover, E. B., and Sippel, R. F., 1962, Experimental pseudomorphs: Replacement of calcite by fluorite: American Mineralogist, v. 47 (9-10), p. 1156-1165.
• Nicholson, R. V., Gillham, R. W., and Reardon, E. J., 1990, Pyrite oxidation in carbonate-buffered solution: 2. Rate control by oxide coating: Geochemica et Cosmochimica Acta, v. 54, p. 395-402.
• Pyne, David G., 2003, Water Quality in Aquifer Storage Recovery (ASR) Wells: Presented at American Water Works Association (Florida Section) Annual Meeting, Orlando, Fla.
• Reardon, Eric J. and Wang, Yanxin, 2000, A Limestone Reactor for Fluoride Removal from Wastewaters: Environmental Science Technology, v. 34, p. 3247-3253.
• Smith, R. M. and Martell, A. E., 1976, Critical Stability Constants, Plenum Press, New York, N.Y.

SUMMARY OF THE INVENTION

The invention relates to methods of in-situ formation of fluoride compounds in subsurface strata containing naturally formed carbonates or man-made carbonates. The desired outcome is similar to what McLaren (1989) envisioned; however, we are using a fluorine solution to modify the existing carbonate rock or strata. One major difference is this process, the invention is not intended to create a hydraulically sealed system, and only creates a coating or lining on the exposed surface of the rock and/or strata grains, constituents or compounds via a replacement reaction of fluorine compounds.

A preparation of fluorine ions in a solution, acid or base, is prepared and injected through a well bore, either open or cased, or other opening into the carbonate-containing rock reservoir and/or aquifer or similar antropogenic structure. The carbonate-containing rock or strata reservoir or aquifer is comprised of limestone, dolostone and/or calcite and/or dolomite cemented siliciclastic constituents or a combination of any said constituents. The carbonate-containing reservoir or aquifer reacts with the fluorine ions in solution forming a coating or lining of less soluble fluoride salts on the calcium carbonate and/or dolomitic grains and/or cementing matrix essentially immobilizing any attached heavy metals, metalloids, radionuclides and/or naturally occurring contaminants contained within or attached to the lattice structure of the carbonate-containing reservoir or aquifer. The free fluorine reacts with the carbonate reagent to form a replacement reaction of a fluoride compound, such as fluorite (CaF₂), fluorapatite (Ca₅[F(PO₄)₃]) and sallaite (MgF₂). Under the proper chemical conditions, fluoride compounds will replace the outer section of the carbonate grains or matrix by replacement reaction. Encasing the elements with fluoride precipitates will sequester naturally occurring contaminants such as heavy metals, metalloids and radionuclides, including (but not limited to) arsenic, iron, strontium and uranium, or used to prevent commingling of layers or fluids.

The treatment outlined is optimized to the application. The optimization may include energizing the treatment fluid such as nitrification or pressurized pumping in conjunction with carbon dioxide or nitrogen gas. This general treatment could be pumped or injected above or below the minimum in-situ pressure of the rock requiring treatment. The optimization also includes the delayed release of the fluorine ion by various methods, including chemical and mechanical means.

BRIEF DESCRIPTION OF THE DRAWINGS

No drawings are contained within this application.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to in-situ methods of forming an impermeable lining or coating comprising fluorine compounds by injecting a prepared solution, acid, or base, into subsurface strata, rock and/or formations or other similar conditions that make an impermeable coating or lining favorable. The conditions for the reaction to occur require free ions and/or carbonate-containing media that will allow the replacement reaction to go to completion.

A number of studies over the past several decades have mentioned the nearly insoluble fluoride precipitates may occur naturally when the fluorine ion is released into carbonate substrates (Aimes, 1961, 1961, 1963; Baer, 1970; Glover, 1962). In the upstream petroleum exploration and production industry, this reaction is avoided, if at all possible, due to its nearly insoluble nature, and its ability to limit hydrocarbon production from a subsurface hydrocarbon reservoir. Typically, large volumes of a variable concentration HCl (hydrochloric) acid solution would be pumped or injected through a well bore into said hydrocarbon reservoir to dissolve the carbonate-containing rock formation or strata prior to injection of a variable concentration HF (hydrofluoric) acid or other fluorine ion containing solution is subsequently pumped or injected for the dissolution of silicate-rich minerals or rocks. The reaction preferably avoided in this type of application is the introduction of a fluorine ion solution with carbonate-containing rock or strata. The said chemical reaction is favorable in certain situations due to its nearly insoluble nature and coating or lining abilities in carbonate-containing subsurface environments such as rock, formations, strata and/or other porous media.

The nature of the replacement reaction between carbonate rock and a fluorine ion causes many or all of the outermost carbonate molecules to be replaced with fluorine compounds. For example, the reaction of calcium carbonate (calcite) with a fluorine ion solution yields carbon dioxide, water, and fluorite (CaF₂). The exposed calcite of this chemical reaction will not be fully replaced with fluorite; however, the calcite will be completely or for the most part entirely coated or lined with the more insoluble fluorite. The treated calcite sample in the example is essentially non-reactive to many chemicals that are aggressive to calcite. Placement of said example in hydrochloric acid (being very aggressive to calcite) invokes no or severely limited chemical reaction with fluorite coating from the replacement reaction. This example does not show the limits of such a chemical system, but clarifies the concept of the replacement reaction system in this invention.

The use of a replacement reaction is beneficial to modify the interaction between injected waters or fluids and the subsurface rock formation, strata or media of a reservoir and/or aquifer. The invention is especially useful in conditions where waters or fluids are intended to be stored below ground in a natural reservoir and/or aquifer for a specified period of time and subsequently recovered for use in supply, agriculture and/or industrial times of need. The coating or lining detailed in this invention minimizes and/or sequesters mobilization or movement of metals, metalloids, radioculides and/or naturally occurring contaminants caused by the injectate waters or fluids chemical affinity for reaction, dissolution and/or leaching of said constituents and/or compounds within the rock, strata, formation and/or media.

This technique is valuable for specified zones within a subsurface formation, rock, strata and/or media that require the storage of contaminated fluids by limiting the reactions between the natural subsurface environment and the contaminated fluids. In a situation where fluorine-enriched waters are undesirable, they can be injected via one well into a carbonate-containing stratum, rock, formation and/or medium and recovered or produced from an another well placed or drilled within the same or an adjacent subsurface strata, rock formation and/or reservoir or aquifer resulting in a substantially lower water or fluid fluorine concentration.

The generation of a coating or lining is useful in any environment where the homeostasis of a system is altered by injection, storage and/or recovery from the same and/or adjacent system. The system can include natural carbonate rock, man-made carbonate environments, or other subsurface environments below the surface of the earth.

Claims

1. A method for sequestering mobilization or movement of naturally occurring contaminants in carbonate-containing rock, formations and/or strata:

Artificially inducing fluorine compound growth to create a lining or coating on the surface of a rock extending laterally over a pre-selected area;

A fluorine enriched solution, acid, or base reacts with free ions of carbonate-containing media to chemically replace said media with a fluoride compound;

The creation of fluorine compounds allows the substitution of free ions to be bound in its crystal structure, or contained in voids within its structure;

The fluoride compound acts as a coating or lining to prevent contaminated zones from commingling with zones of interest;

The coating or lining generated will use, but not limited to using, components in the naturally occurring rock as a reactant;

Allows nitric acid to be injected in certain cases to dissolve minerals or compounds that do not react with the replacement fluoride compound;

Allows injection of fluids into treated zones while protecting stratum from direct contact and unwanted reactions with injected fluids.

2. The method of claim 1, wherein the active replacement reaction allows for substitution within the compound to bind and/or sequester undesirable elements.

3. The method of claim 1, wherein the replacement reaction acts as an impermeable liner on the surface of pore throats, dissolution cavities, or rock surface to minimize native rock chemical reactions, dissolution and/or leaching.

4. The method of claim 1, wherein the replacement reaction uses fluorine as a catalyst to form replacement compounds with a phosphate of or a magnesium component.

5. The method of claim 1, wherein the reaction to form a fluoride compound has occurred, leaves a coating that will be non-reactive to nitric acid in some cases, allowing nitric acid to dissolve any non-fluoride compounds or minerals exposed that are soluble to said acid.

6. The method of claim 1, wherein the creation of the desired compounds entails the injection of treatment fluids below the surface of the earth.

7. The method of claim 1, wherein the pH of the solution is in need of buffering, or other pH controls; other acids, fluids, or bases can be employed.

8. The method of claim 6, wherein the treatment requires, said treatment would be injected or pumped with an energized fluid.

9. The method of claim 8, wherein the term ‘energized’ refers to the use of nitrogen, carbon dioxide, or other addition that creates a volume change of treatment fluid after the pump head.

10. The method of claim 6, wherein the desired reaction requires a temperature different from the native subsurface environment, methods can be employed to modify the temperature of the treatment environment.

11. The method of claim 10, wherein the temperature of the subsurface environment must be modified, the use of steam injection, pumping of heated fluids, or other methods designed to achieve a temperature change in the treatment environment.

12. The method of claim 5, wherein many compounds are soluble in nitric acid, many fluoride compounds are not.

13. The method of claim 1, delaying the release of fluorine, for reasons such as delayed replacement reaction.

14. The method of claim 13, wherein a solution, acid, or base has the ability to delay the release of the fluorine ion for replacement reaction treatment, such as due to chemical reactions that have fluorine being released as a product of other reactions.

15. The method of claim 6, wherein a fluorine solution, acid, or base is injected in an effort to open pathways through the rock, strata or formation or through the matrix of a rock, strata, formation or media.

16. The method of claim 15, wherein a fluorine solution, acid, or base can be pumped at pressures below the minimum in-situ pressure of the rock, formation or strata, through natural or induced permeability (matrix rates); or at pressures exceeding the minimum in-situ pressures of a rock (fracturing) with a goal of precipitating a fluoride compound.

17. A method of cleaning and/or filtering industrial injected waters or fluids that entails injection in one well, and recovering in an adjacent well.

18. The method of claim 17, wherein fluoride enriched waters or fluids are injected below the surface into a confined or unconfined aquifer and recovered in an adjacent well.

19. A method of protecting a confined zone in a subsurface rock, formation and/or strata from deleterious effects of injection of wastewaters or waste fluids.

20. The method of claim 19, wherein an subsurface zone of rock, formation and/or strata is targeted for use as waste disposal, a treatment is performed before, during or after the injection of waste waters or fluids to protect the disposal zone of rock formation and/or strata from chemical reaction, dissolution or other undesired effects from waste waters or fluids.