WO2012088104A1

WO2012088104A1 - System and method for the reduction of ferric ion

Info

Publication number: WO2012088104A1
Application number: PCT/US2011/066141
Authority: WO
Inventors: Michael M. Brezinski
Original assignee: CESI Chemical Inc
Current assignee: Flotek Chemistry LLC
Priority date: 2010-12-20
Filing date: 2011-12-20
Publication date: 2012-06-28
Anticipated expiration: 2013-06-20

Abstract

A composition suitable for use in reducing ferric ion in an acidic environment includes an electron donor component and a catalyst, wherein the electron donor component includes a source of sulfite ions. The catalyst preferably includes a source of copper ions and a source of iodine or iodide ions. In another preferred embodiment, the present invention includes a well treatment fluid suitable for use in acidizing operations. The well treatment fluid preferably includes a strong acid, an electron donor component and a catalyst.

Description

FILED DECEMBER 20, 2011 PATENT

DOCKET NO.: P1945PC01

SYSTEM AND METHOD FOR THE REDUCTION OF FERRIC ION

Related Applications

[001] This application claims the benefit of United States Patent Application Serial No.

61/425,135, filed December 20, 2010, entitled "System and Method for the Reduction of Ferric Ion," the disclosure of which is hereby incorporated by references.

Field of the Invention

[002] This invention relates to the recovery of hydrocarbons from a subsurface formation. The invention further relates to the treatment of a hydrocarbon- bearing subterranean formation with an acidic composition to stimulate the recovery of hydrocarbons from the formation. The invention still further relates to the acid treatment of such a formation in the presence of ferric ions. The invention specifically relates to the treatment of a hydrocarbon-bearing subterranean formation with a mineral acid composition formulated to convert ferric ions in the acid to ferrous ions, and to resist the formation of sludge in crude oil present in the formation.

Background of the Invention

[003] Formation acidizing, or simply "acidizing," is a method known in the art for increasing the flow of fluid from a subterranean formation. According to accepted methods, the formation is contacted with an acidic composition to react with and dissolve materials contained therein for the purpose of increasing the permeability of the formation. The ability of fluid to flow from the formation is therefore enhanced because of the increase in formation permeability caused by the dissolution of the material.

[004] A common method of acidizing a subterranean formation includes the steps of conducting an acid composition to the formation through tubing disposed in a borehole penetrating the formation, forcing the acid composition into contact with the formation and permitting the acid to react with and dissolve certain materials contained in the formation to thereby enlarge pore spaces within the formation and thus increase the permeability of the formation. Acidizing calcareous formations, such as limestone formations, has been successfully conducted utilizing hydrochloric acid, certain organic acids, such as acetic acid, citric acid, formic acid, and mixtures thereof.

[005] The object of formation acidizing, which is to increase the permeability of the formation, can be frustrated if precipitates are produced in the treatment fluid. The precipitates, which can include compounds containing iron, nonferrous metals, free sulfur and metal sulfides, can fill and plug pore spaces in the formation with the consequent result that formation permeability is not increased and can be decreased.

[006] In the context of formation acidizing, ferric ion can be introduced into the acid as a result of reaction between ferric compounds, such as rust, mill scale and other iron-containing scale, from metal conduits and equipment associated with the well, and by reaction with iron-containing minerals, such as magnetite (Fe₃C"4), present in the formation. As the acid reacts and spends, the pH of the solution increases. Once the pH of the solution reaches a level of about 2.5 and greater, dissolved iron present in the solution in the ferric, Fe(III), oxidation state begins to precipitate in the form of ferric hydroxides, e.g., Fe(OH)₃ and Fe(0)(OH). The ferric hydroxide precipitate can plug the formation. Ferrous hydroxide is much more soluble and does not precipitate.

[007] Wells completed in formations that contain quantities of sulfide, and particularly hydrogen sulfide, are sometimes referred to as "sour wells." In these wells, the combination of sulfide ions and ferric ions create precipitation problems. In this regard, sulfide ions convert ferric ions to ferrous ions, and produce elemental sulfur by the following reaction:

2Fe³⁺ + S^2"→ S°J. + 2Fe²⁺

The elemental, or free, sulfur can precipitate and plug the formation.

[008] Attempts to control precipitation problems by maintaining the pH of the acid solution below a certain level, for example below 2.5, have not been successful. For example, when an acid, such as hydrochloric acid, is used to acidize a calcareous (e.g., limestone) formation, the acid typically spends to an extent such that the pH of the acid solution increases to a value of 4 or higher.

[009] The presence of acid soluble ferric ion in an acidizing composition can cause other problems as well. For example, the ferric ion can lead to increased corrosion, additive separation and emulsion formation. Ferric ion is difficult to reduce in mineral acid systems because reducing agents alone typically do not sufficiently reduce ferric ion. Many iron reducing agents are not effective at high acidity levels, e.g., greater than 5% hydrochloric acid, at which many of the above problems are caused or exacerbated.

[010] United States Patent No. 5,547,926, issued August 20, 1996 to Perthuis et al.

("Perthuis '926"), discloses the use of mercaptans in the presence of a copper- iodine catalyst system to reduce ferric ion to ferrous ion.

[011] United States Patent No. 6,060,435, issued May 9, 2000 to Beard et al. ("Beard '435"), discloses a solubilized and regenerating iron-reducing additive in which a cuprous-state reducing agent is used to reduce the ferric ions. Contrary to the mechanism disclosed by Perthuis '926, the Beard '435 patent states that the copper compound is the actual iron reducing agent, rather than a catalyst. While the Beard '435 patent discloses the use of certain sulfur-containing compounds, it states that these compounds are used to "regenerate" the copper-containing compound.

[012] United States Patent No. 6,706,668, issued March 16, 2004 to ("Brezinski '668"), discloses a ferric ion reducing system in which an electron donor supplies electrons to primary and secondary electron transfer agents, which in turn pass the donated electrons to the ferric ion in a reduction process. The Brezinski '668 patent discloses that the electron donor is selected from the group of thiols (e.g, mercaptans), hypophosphorous acid or a hypophosphourous acid precursor. The primary electron transfer agent is a source of rhenium ion and the secondary electron transfer agent is a source of iodide ion. [013] While generally effective, there are known problems associated with the use of organic materials, such as 2-mercaptoethanol, as the source of electrons for the reduction of ferric ion. Upon electron donation, the organic material tends to form disulfides. The formed disulfides, thus, consume two organic molecules while donating two electrons to reduce a stoichiometric amount of ferric ions. In addition to this inefficiency, the formed disulfides can produce undesirable problems for downstream processing, especially if the organic disulfides are oil soluble.

[014] Mercaptans and similar organic materials also tend to be very corrosive and are obnoxious smelling and toxic to humans. Certain mercaptans, such as 2- mercaptoethanol, decompose at relatively low temperatures, which significantly restrict the application of these mercaptans in many wellbore environments.

[015] For these and other shortcomings in the prior art, there is a continuing need for improved compositions and methods for controlling precipitation and sludge during acidizing operations.

Summary of the Invention

[016] In a preferred embodiment, the present invention includes a composition suitable for use in reducing ferric ion in an acidic environment having an electron donor component and a catalyst. The electron donor component of the present invention includes a source of sulfite ions. The catalyst preferably includes a source of copper ions and a source of iodine or iodide ions. In another preferred embodiment, the present invention includes a well treatment fluid suitable for use in acidizing operations. The well treatment fluid includes an acid, an electron donor component having a source of sulfite ions and a catalyst. Numerous other objects, features and advantages of the invention will be apparent to those skilled in the art upon reading the following description of preferred embodiments and accompanying examples.

Description of the Preferred Embodiments

[017] Preferred embodiments of the present invention generally include compositions that function as a reducing system for converting ferric ions to ferrous ions in the presence of an aqueous acid solution. The compositions generally include a catalyzed reduction additive that includes an electron donor component and a catalyst. The electron donor component is one or more materials which ionize in the presence of the aqueous acid and which are capable of donating at least two electrons per ion to the reducing system. As explained below, the catalyzed reduction additive is preferably mixed with water and acid to form a treatment composition.

[018] In preferred embodiments, the electron donor component is a source of sulfite ion.

Presently preferred sources of sulfite ion include salts of sulfite, bisulfite and metabisulfite. Preferred salts include sodium sulfite (Na₂S03), sodium bisulfite (NaHSOs), sodium metabisulfite (Na₂S₂0₅), ammonium sulfite (NH4SO3), ammonium bisulfite (NH₄HSO₃) and ammonium metabisulfite (NH₄S₂0₅). Sodium sulfite and sodium bisulfite each release 2 electrons upon oxidation to the (VI) oxidation state. Sodium metabisulfite releases 4 electrons as it oxidizes from a S(III)/S(V) pair to two S(VI). The use of an electron donor component that releases a plurality of electrons per ion of electron donor is a significant improvement over the prior art.

[019] The quantity of the electron donor component required to effect the reduction is dependent upon the molecular weight of the electron donor component employed. The number of electrons donated by the electron donor is quantitative, that is, the reaction is stoichiometric in nature. Accordingly, the quantity of electron donor agent component required is a function of its molecular weight, the number of electrons which it can donate and the quantity of ferric ion, Fe(III), to be reduced.

[020] For example, consider one liter of a fluid having a concentration of 5,000 ppm Fe(III) to be reduced. The fluid thus contains 0.089 moles Fe(III). Accordingly, a sufficient number electrons are required to be donated by a material to completely reduce 0.089 moles of Fe(III) to 0.089 moles of Fe(II). Based upon that quantity of iron to be reduced, the following quantities of prior art donor agents are required:

[021] Each of these prior art electron donor agents provides a single electron per mole of electron donor. In contrast, the use of a electron donor component capable of releasing multiple electrons during oxidation. For example, the following quantities of sodium sulfite and sodium metabisulfite are required to supply a sufficient quantity of electrons to reduce one liter of fluid having a concentration of 5,000 ppm Fe(III).

[022] Notice that sodium sulfite, an electron donor component of this invention, donates twice as many electrons as the compared materials. The increased availability of donated electrons per mole of sodium sulfite results in a substantial reduction in the quantity of material required to complete the required reduction. Furthermore, during oxidation, the oxidation state of the sulfur atom moves from a plus four (IV) to a plus six (VI) oxidation state, in which sulfur becomes stable. From a chemical standpoint, there is no known limit on the quantity of Fe(III) which can be reduced in accordance with the preferred embodiments.

[023] The catalyst is preferably one or more materials which, in the presence of the aqueous acid, release ions which are capable of transferring at least one electron from the reducing system to a ferric ion to convert the ferric ion to a ferrous ion. In a preferred embodiment, the catalyst includes a source of copper ions. Suitable materials include copper halide salts (cuprous or cupric), copper cuprous chloride, cupric chloride dihydrate, soluble copper containing complexes, such as copper disodium ethylene diamine tetraacetic acid (Na₂[Cu(EDTA)]), and copper ammonia [Cu(NH₃)₄]²⁺. Any form of copper that is soluble in acid, or which transports copper ions in solution will suffice, regardless of whether the form produces cuprous ion (+1) or cupric ion (+2). Both cuprous ion and cupric ion are capable of acting as the source of copper ions. The catalyst also preferably includes a source of iodide ions or iodine. Suitable materials include potassium iodide, sodium iodide and iodine.

[024] The quantity of the catalyst to be used is directly related to the rate of reduction of Fe(III) to Fe(II) desired, that is, the more catalyst employed the greater the rate of reduction. For example, if cupric chloride dihydrate, at a concentration of 2 lb/Mgal, and potassium iodide, at a concentration of 14 lb/Mgal, is present in 15% HC1, containing 2500 ppm Fe(III), then the reduction of Fe(III) to Fe(II) occurs virtually instantaneously. In this example, the concentration of electron donor, such as sodium sulfite, present in the acid solution is 2.8 lb/Mgal. If the aforementioned quantities are reduced by 50%, the reduction will take several minutes to complete.

[025] As understood by those skilled in the art, laboratory screening procedures can be performed to determine the acid strength, amount of electron donor, and amount of electron transfer system required to achieve a desired reduction rate of ferric ion to ferrous ion.

[026] The catalyzed reduction additives of the preferred embodiments are preferably acid soluble in a strong mineral acid solution. The preferred aqueous acid solution contains in the range of from about 5% to about 35% hydrochloric acid by weight of the total solution. Hydrochloric acid at a concentration of about 15% by weight of the total weight of the solution is particularly preferred. The acid can alternatively include a mixture of both strong and weak organic and inorganic acids. Examples of preferred mixtures include a combination of hydrochloric acid when with one or more other inorganic acids, such as hydrofluoric acid, and organic acids, such as acetic acid, propionic acid, lactic acid, glycolic acid, citric acid and formic acid.

[027] The particular acid formulation as well as the exact concentration of acid(s) employed will vary depending on the type of acid(s) involved, the particular application (including formation characteristics and conditions) and other factors known to those skilled in the art.

[028] In a presently preferred embodiment, the treatment composition (catalyzed reduction additive and water before the addition of acid) includes 0-75% by weight electron donor, 0-90% by weight catalysts and about 10-70%) mixing water. In preferred embodiments, the electron donor is ammonium bisulfite and the catalysts include cupric chloride as the primary transfer agent and potassium iodide as the secondary transfer agent. In a particularly preferred embodiment, the treatment composition includes about 26.92% by weight ammonium bisulfite, about 23.08%) by weight cupric chloride and about 2.88% by weight potassium iodide, with the balance (47.12% by weight) water.

[029] Example 1

A composition useful for reducing ferric ion can be prepared in accordance with a preferred embodiment using the following formula. Each of the following components can be added to a mixing tank before the water, after the water, or after the acid. The quantities listed below are calculated for the complete reduction of 1000 gallons of 2400 ppm of ferric ion.

558 gallons water; 22.5 lbs sodium sulfite (electron donor component);

2 lbs cuprous chloride (primary electron transfer component);

5 lbs potassium iodide (secondary electron transfer component); and

442 gallons 20°Be HC1.

[030] The above fluid will reduce 1000 gallons of 2400 ppm ferric ion within a few seconds as determined by the de-colorization of the fluid. The quantities and proportions of the components set forth in this example are linearly scalable and easily adjusted to accommodate the demands for particular applications. The reducing system of this invention can be formulated in a simple mixing tank. No special mixing procedure or order of mixing is required.

[031] In an alternate embodiment, the present invention includes a well treatment fluid suitable for using in acidizing operations. The well treatment fluid preferably includes an acid, a source of sulfite ions, a source of copper ions and a source of iodine or iodide ions.

[032] The acid is preferably a strong mineral acid, such as hydrochloric (15% HC1) acid. The strong mineral acid may be a combination of hydrochloric acid and an organic acid selected from the group consisting of acetic acid, propionic acid, lactic acid, glycolic acid, citric acid and formic acid.

[033] The composition of this invention can also include various additives. In this regard, the reducing system of this invention, that is, the electron donor component and the electron transfer component, is soluble in all concentrations of mineral acid solutions, and, therefore, does not require any additional additives or components. However, additives commonly employed in well acidizing treatments can be used in the composition of this invention. In general, the ability of the reducing system to operate is not impaired by the presence of additives ordinarily employed in well acidizing methods known in the art. For example, one or more surface-active agents can be employed to improve dispersion of the various additives in the acid solution. Examples of surface-active agents that can be used are ethoxylated nonylphenols, fatty amines, ethoxylated fatty amines, quaternary fatty amines and ethoxylated quaternary fatty amines.

[034] Examples of other additives that can be included in the composition of this invention include corrosion inhibitors, pH control additives, fluid loss additives and non-emulsifying agents.

[035] Reduction of the ferric ion present in the acidizing composition helps prevent the formation of sludge in crude oil. The use of one or more surfactants in the inventive composition can further decrease sludge formation. For example, a useful surfactant for further decreasing sludge formation is dodecylbenzenesulfonic acid. Additional anti-sludge agents can be used as well. The specific surfactants and anti-sludge agents that should be used to combat sludge are dependent upon the specific crude oil and formation conditions and characteristics and other factors known to those skilled in the art.

[036] The present invention also includes a novel method for the treatment of an oil or gas formation in the presence of ferric ions. In a preferred embodiment, the catalyzed reduction additive is mixed with water and acid on the surface. In particularly preferred embodiments, the catalyzed reduction additive is provided in multiple containers to separate the electron donor and catalysts prior to mixing. The electron donor and catalysts are then mixed with water and acid to prepare the well treatment composition. Additional components, such as, for example, corrosion inhibitors, pH control additives, fluid loss additives and non- emulsifying agents, may be added to the well treatment composition. No special mixing equipment is required. Once mixed, the well treatment composition can be injected and circulated in the well by any technique known in the art.

[037] In a particularly preferred embodiment, a method for the treatment of an oil or gas formation in the presence of ferric ion includes the steps of providing a source of sulfite ions to a mixing tank, adding a first electron transfer catalyst to the mixing tank, adding water to the mixing tank, adding a mineral acid to the mixing tank; and injecting the contents of the mixing tank into the well, where the treatment composition will contact and reduce ferric ion. In an alternatively preferred embodiment, the method includes the additional step of adding a second electron transfer catalyst with the first electron transfer catalyst.

[038] In the presently preferred embodiments, the electron donor as noted above can be sulfite, bisulfite, or metabisulfite. Preferred salts include sodium sulfite, sodium bisulfite and sodium metabisulfite along with ammonium sulfite, ammonium bisulfite and ammonium metabisulfite. The catalyst is capable of transferring at least one electron from the reducing system to a ferric ion to convert the ferric ion to a ferrous ion. In the preferred embodiment, the catalyst (sometimes called the primary electron transfer component) includes a source of copper ions. Any form of copper that is soluble in acid, or which transports copper ions in solution will suffice, regardless of whether the form produces cuprous ion (+1) or cupric ion (+2).

[039] If used, the second electron transfer catalyst includes a source of iodide or iodine (sometimes called the secondary electron transfer component). Suitable materials include potassium iodine, sodium iodide, and iodine. The acid can be a strong mineral acid like 5% to 35% hydrochloric acid (HC1) with 15% HC1 acid being preferred. The acid can be a mixture of strong and weak organic acids and also inorganic acids. The organic acids can be acetic acid, propionic acid, lactic acid, glycolic acid, citric acid and formic acid while the inorganic acids can also include hydrofluoric (HF) acid.

[040] When the acid has spent and the pH increases to a value of about 2.5, the dissolved iron present in the solution in the ferric (III) oxidation state begins to precipitate in the form of ferric hydroxides (e.g., Fe(OH)2, Fe(0)(OH) , etc). The ferrous hydroxide precipitates can plug the formation and cause well damage. Ferrous hydride is much more soluble and typically does not cause a problem.

[041] The inventive acidizing compositions can be used in several ways. As a few illustrations, these include, but are not limited to, cleaning up disposal and injection wells and flow lines that have ferric corrosion products, both tubing and casing in sour wells, and acidizing sour wells with tubing from sweet wells. It can also be used as the spearhead for the leading volume of acid used for stimulation or fracturing treatments. For sour wells, the present invention prevents the formation of elemental sulfur. [042] As used herein the term "well" refers to a bore, a shaft, a hole or a wellbore which penetrates a subterranean formation and all piping and equipment associated therewith. The term "well" includes both injection and production wells. The expression "sour well" refers to a well which contains sulfides and produces oil and gas. Sulfides are also often produced from the well. The term "sulfides" includes free sulfide ions, sulfides combined with hydrogen in the form of hydrogen sulfide and sulfides combined with other elements, such as metals, in the form of other compounds. Examples of metal sulfides include ferrous sulfide, zinc sulfide and lead sulfide. The expression "sludge" refers to a solid material formed in crude oil which may, under certain conditions, precipitate from the crude oil. Formation of sludge, while the crude oil is in the formation, can render very difficult, if not impossible, the recovery of the oil from the formation. For purposes of this invention, crude oil subject to the formation of sludge is referred to as sludging crude.

[043] It is clear that the present invention is well adapted to carry out its objectives and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments of the invention have been described in varying detail for purposes of disclosure, it will be understood that numerous changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed within the spirit of the invention disclosed and claimed herein.

Claims

It is claimed:

1. A composition suitable for reducing ferric ion during acidizing operations, the composition comprising:

a source of sulfite ions;

a source of copper ions; and

a source of iodide ions.

2. The composition of claim 1, wherein the source of sulfite ions is selected from the group consisting of sodium metabisulfite, sodium sulfite and sodium bisulfite.

3. The composition of claim 2, wherein the source of copper ions is cupric chloride.

4. The composition of claim 3, wherein the source of iodide ions is potassium iodide.

5. A well treatment fluid suitable for using in acidizing operations, the well treatment fluid comprising:

an acid;

a source of sulfite ions; and

a source of copper ions.

6. The well treatment fluid of claim 5, wherein the acid is a strong mineral acid.

7. The well treatment fluid of claim 6, wherein the strong mineral acid is hydrochloric acid.

8. The well treatment fluid of claim 7, wherein the strong mineral acid is a combination of hydrochloric acid and an organic acid selected from the group consisting of acetic acid, propionic acid, lactic acid, glycolic acid, citric acid and formic acid.

9. The well treatment fluid of claim 8, wherein the source of sulfite ions is selected from the group consisting of salts of metabisulfite, sulfite and bisulfite.

10. The well treatment fluid of claim 9, wherein the source of sulfite ions is selected from the group consisting of sodium metabisulfite, sodium sulfite, sodium bisulfite, ammonium metabisulfite, ammonium sulfite and ammonium bisulfite.

11. The well treatment fluid of claim 9, wherein the source of copper ions is cupric chloride.

12. The well treatment fluid of claim 11, wherein the source of iodide ions is potassium iodide.

13. A method for acidizing a well, the method comprising the steps of:

adding a source of sulfite ions to a mixing tank;

adding a first electron transfer catalyst to the mixing tank;

adding water to the mixing tank;

adding a mineral acid to the mixing tank; and

injecting the contents of the mixing tank into the well.

14. The method of claim 13, further comprising the step of: adding a second electron transfer catalyst to the mixing tank.

15. The method of claim 14, wherein the step of adding a source of sulfite ions to a mixing tank comprises adding a source of sulfite ions selected from the group consisting of salts of metabisulfite, sulfite and bisulfite.

16. The method of claim 15, wherein the step of adding a source of sulfite ions to a mixing tank comprises adding a source of sulfite ions selected from the group consisting of ammonium metabisulfite, ammonium sulfite and ammonium bisulfite.

17. The method of claim 16, wherein the step of adding a source of sulfite ions to a mixing tank comprises adding ammonium bisulfite to the mixing tank.

18. The method of claim 14, wherein the step of adding a second electron transfer catalyst to the mixing tank comprises adding a source of iodide ions to the mixing tank.

19. The method of claim 18, wherein the step of adding a second electron transfer catalyst to the mixing tank comprises adding potassium iodide to the mixing tank.

20. The method of claim 13, wherein the step of adding a first electron transfer catalyst to the mixing tank comprises adding a source of copper ions to the mixing tank.

21. The method of claim 20, wherein the step of adding a first electron transfer catalyst to the mixing tank comprises adding cupric chloride to the mixing tank.