Treatment fluids containing a biodegradable chelating agent and methods for use thereof

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TREATMENT FLUIDS CONTAINING A BIODEGRADABLE CHELATING AGENT

AND METHODS FOR USE THEREOF

BACKGROUND

[0002] The present invention generally relates to treatment fluids containing biodegradable chelating agents, and, more particularly, to methods for treating at least a portion of a subterranean formation using treatment fluids containing a biodegradable chelating agent in conjunction with a hydrofluoric acid treatment.

[0003] Treatment fluids can be used in a variety of subterranean treatment operations. Such treatment operations can include, without limitation, drilling operations, stimulation operations, production operations, and sand control treatments. As used herein, the terms “treat,” “treatment” and “treating” refer to any subterranean operation that uses a fluid in conjunction with a desired function and/or for a desired purpose. Use of these terms does not imply any particular action by the treatment fluid. Illustrative treatment operations can include, for example, fracturing operations, gravel packing operations, acidizing treatments, scale dissolution and removal, consolidation treatments, and the like.

[0004] In acidizing treatments, for example, subterranean formations comprising acid-soluble components, such as those present in carbonate and sandstone formations, are contacted with a treatment fluid comprising an acid. After acidization is completed, the water and salts dissolved therein may be recovered by producing them to the surface, e.g., “flowing back” the well, leaving a desirable amount of voids or conductive pathways (e.g., wormholes in carbonates) within the formation, which enhance the formation’s permeability and may increase the rate at which hydrocarbons may subsequently be produced from the formation.

(0005] Acidizing a siliceous formation should be distinguished from acidizing a carbonate formation. Carbonate formations can be treated with a variety of acid systems, including hydrochloric, acetic and formic acids, often with similar success. The treatment of siliceous formations with these acids, however, may have little or no effect because they do not react appreciably with the silica and silicates that characterize siliceous formations. As used herein the term “siliceous” refers to the characteristic of having silica and/or silicate.

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Most sandstone formations are composed of over about 40% to about 98% sand quartz particles, i.e., silica (SiO₂) bonded together by various amounts of cementing material including carbonate (calcite or CaCCb), aluminosilicates, and silicates.

[0006] By far the most common method of treating sandstone formations involves introducing corrosive, very low pH acids comprising hydrofluoric acid into the well bore and allowing the acid to react with the surrounding formation. Hydrofluoric acid is very reactive with aluminosilicates and silicates. Hydrochloric acid may be used to maintain a low pH as hydrofluoric acid spends, retaining certain dissolved species in solution. The silicates include clays and feldspars. Hydrofluoric acidizing is often used to remove damage within the formation. Such treatments are generally not considered “stimulating” in the sense of creating or extending fractures in the formation as in a typical fracturing operation. As a result of a hydrofluoric acid treatment, it is desirable that the skin value in the formation be zero. It is not anticipated that it will be less than zero. Any damage left behind gives a positive skin value, which is not desirable.

[0007] Hydrofluoric acid can interact with the formation, fluids, or other fluids present therein to create precipitates, which leads to damage and a positive skin value. For instance, hydrofluoric acid tends to react very quickly with authigenic clays, such as smectite, kaolinite, illite and chlorite, especially at temperatures above 150°F (65.6°C), as a function of mineral surface area. Because of this quick reaction, acid may penetrate only a few inches into the formation before the hydrofluoric acid is spent. Simultaneously, precipitation of various aluminum and silicon complexes occur as a result of the reaction of the acid with the siliceous minerals. Damage to the formation may result from this precipitation. At certain temperatures and subterranean conditions dissolution of the sandstone matrix may occur so rapidly that uncontrolled precipitation can become an inevitable problem. The precipitation products plug pore spaces and reduce the porosity and permeability of the formation, thus impairing flow potential.

[00081 Because clays are normally a part of the cementitious material that holds the sandgrains of siliceous formations together, the dissolution of clay also weakens and deconsolidates the sandstone matrix in the vicinity of the well bore, thus causing damage to the formation. Any metal ion has the potential to create problems if not adequately managed. The damaging effects due to both the de-consolidation of the matrix and the precipitation of

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PCT/GB2012/000247 complexes which clog the pore spaces of the formation can eliminate or even revert the stimulation effect of the acid treatment.

[0009] Of particular concern is the formation of calcium fluoride, fluorosilicates, or other insoluble fluoro-compounds, which can negate the effectiveness of a hydrofluoric acid treatment and cause damage to the formation. This can lead to production delays while damage control operations are conducted. The fluorosilicates can be particularly problematic because they are the primary product of the dissolution of a clay and hydrofluoric acid. Fluorosilicates are difficult to remediate. Calcium fluoride can be a later concern in the process because the fluoride anion needs to be present, in its free ion form, and that does not happen until a higher pH is reached. Calcium fluoride can be remediated, in some instances. Remediation techniques include a commercially available treatment system from Halliburton Energy Services, Inc. known as “F-SOL™” acid system is used to dissolve calcium fluoride). Another source of concern is the production of fluoro-aluminates as a consequence of the reaction of fluorosilicates with clay minerals. These fluoro-aluminates are thought to be soluble as long as the pH is below 2 and the ratio of F/Al is maintained below 2.5. If precipitated, their dissolution requires strong HC1 (>5%).

[0010] Avoiding the formation of calcium fluoride, fluorosilicates, or other insoluble fluoro-compounds can be a primary design objective. Various means have been used with mixed success. Blends of organic acids and hydrofluoric acid have been used to slow the dissolution kinetics of sandstone formation solids. However, as organic acids have higher pKa values than do mineral acids, precipitation can become problematic as the treatment fluid pH rises. Pre-flush sequences with acids have been used to remove calcium salts from sandstone formations, before the main acidizing sequence is conducted to remove formation aluminosilicates. Generally, these flushes do not spend completely and typically return, upon flowback, with a persisting low pH. This can result in corrosion of downhole tubular goods (including coiled tubing) and surface equipment. Other multi-stage sandstone acidizing treatment operations have also been developed, particularly to remove calcium ions. Chelating agents can also be included in treatment fluids to sequester at least a portion of the formation cations that cause unwanted precipitation, however, there are certain operational problems that are encountered with use of many commonly used chelating agents. First, many commonly used chelating agents are not biodegradable or present other toxicity concerns that make their use in a subterranean formation problematic. Further, the salt form

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PCT/GB2012/000247 of some chelating agents can actually exacerbate precipitation problems in a hydrofluoric acidizing treatment rather than lessening the amount of precipitated solid.

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SUMMARY OF THE INVENTION

[0011] The present invention generally relates to treatment fluids containing biodegradable chelating agents, and, more particularly, to methods for treating at least a portion of a subterranean formation using treatment fluids containing a biodegradable chelating agent in conjunction with a hydrofluoric acid treatment.

[0012] According to one aspect of the present invention there is provided a method comprising: providing a treatment fluid that comprises: an aqueous base fluid; a hydrofluoric acid source selected from the group consisting of hydrofluoric acid, a hydrofluoric acid generating compound, and a combination thereof; and a biodegradable chelating agent comprising one of the following selected from the group consisting of: glutamic acid diacetic acid, a glutamic acid diacetic acid salt, a derivative thereof, and a combination thereof; and introducing the treatment fluid into at least a portion of a subterranean formation.

[0013] Preferably the method further comprises treating a proppant pack in the portion of the subterranean formation.

[0014] Preferably the method further comprises performing a stimulation operation in the portion of the subterranean formation.

[0015] Preferably the stimulation operation involves acidizing the formation or introducing another chelating agent to the subterranean formation.

[0016] Preferably the hydrofluoric acid generating compound is selected from the group consisting of fluoroboric acid, fluorosulfuric acid, hexafluorophosphoric acid, hexafluoroantimonic acid, difluorophosphoric acid, hexafluorosilicic acid, potassium hydrogen difluoride, sodium hydrogen difluoride, boron trifluoride acetic acid complex, boron trifluoride phosphoric acid complex, boron trifluoride dihydrate, polyvinylammonium fluoride, polyvinylpyridinium fluoride, pyridinium fluoride, imidazolium fluoride, ammonium fluoride, ammonium bifluoride, tetrafluoroborate salts, hexafluoroantimonate salts, hexafluorophosphate salts, bifluoride salts, and any combination thereof.

[0017] Preferably the subterranean formation comprises a sandstone formation.

[0018] Preferably the subterranean formation comprises a clay.

[0019] Preferably the biodegradable chelating agent comprises one of the following selected from the group consisting of: a sodium salt of glutamic acid diacetic acid, a rubidium salt of glutamic acid diacetic acid, a lithium salt of glutamic acid diacetic acid, a

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PCT/GB2012/000247 potassium salt of glutamic acid diacetic acid, a cesium salt of glutamic acid diacetic acid, an ammonium salt of glutamic acid diacetic acid.

[0020] Preferably the biodegradable chelating agent comprises one of the following selected from the group consisting of: a glutamic acid diacetic acid tetrasodium salt and a glutamic acid diacetic acid ammonium salt.

[0021] Preferably the step of introducing the treatment fluid into at least a portion of a subterranean formation is performed at a pressure at less than a fracturing pressure of the subterranean formation.

[0022] Preferably the step of introducing the treatment fluid into at least a portion of a subterranean formation is performed at a pressure equal to or greater than a fracturing pressure of the subterranean formation.

[0023] Preferably the glutamic acid is not a glutamic acid diacetic acid sodium salt.

[0024] According to a further aspect of the present invention there is provided a method comprising: providing a treatment fluid that comprises: an aqueous base fluid; a hydrofluoric acid source selected from the group consisting of hydrofluoric acid, a hydrofluoric acid generating compound, and a combination thereof; and a biodegradable chelating agent comprising one of the following selected from the group consisting of: glutamic acid diacetic acid, a glutamic acid diacetic acid salt, a derivative thereof, and a combination thereof; introducing the treatment fluid into at least a portion of a subterranean formation; and performing a fracturing treatment in the subterranean formation.

[0025] Preferably the hydrofluoric acid generating compound is selected from the group consisting of fluoroboric acid, fluorosulfuric acid, hexafluorophosphoric acid, hexafluoroantimonic acid, difluorophosphoric acid, hexafluorosilicic acid, potassium hydrogen difluoride, sodium hydrogen difluoride, boron trifluoride acetic acid complex, boron trifluoride phosphoric acid complex, boron trifluoride dihydrate, polyvinylammonium fluoride, polyvinylpyridinium fluoride, pyridinium fluoride, imidazolium fluoride, ammonium fluoride, ammonium bifluoride, tetrafluoroborate salts, hexafluoroantimonate salts, hexafluorophosphate salts, bifluoride salts, and any combination thereof.

[0026] Preferably the biodegradable chelating agent comprises an ammonium salt of glutamic acid diacetic acid.

[0027] Preferably the subterranean formation comprises a clay.

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[0028] Preferably the glutamic acid is not a glutamic acid diacetic acid sodium salt.

[0029] According to a further aspect of the present invention there is provided a method comprising: providing a treatment fluid that comprises: an aqueous base fluid; and a biodegradable chelating agent comprising one of the following selected from the group consisting of: a glutamic acid diacetic acid salt, a derivative thereof, and a combination thereof, wherein the glutamic acid is not a glutamic acid diacetic acid sodium salt; introducing the treatment fluid into at least a portion of a subterranean formation.

[0030] Preferably the method further comprises: treating a proppant pack in the portion of the subterranean formation.

[0031] Preferably the method further comprises a step of remediating precipitation damage present on a surface in the subterranean formation.

[0032} Preferably the glutamic acid diacetic acid salt comprises a salt of glutamic acid diacetic acid chosen from the group consisting of: a potassium salt of glutamic acid diacetic acid; a tetrapotassium salt of glutamic acid diacetic acid; an ammonium salt of glutamic acid diacetic acid; a tetraammonium salt of glutamic acid diacetic acid; and any combination thereof.

[0033] Preferably .the treatment fluid further comprises a hydrofluoric acid source selected from the group consisting of hydrofluoric acid, a hydrofluoric acid generating compound and a combination thereof.

[0034] Preferably the hydrofluoric acid generating compound is selected from the group consisting of fluoroboric acid, fluorosulfuric acid, hexafluorophosphoric acid, hexafluoroantimonic acid, difluorophosphoric acid, hexafluorosilicic acid, potassium hydrogen difluoride, sodium hydrogen difluoride, boron trifluoride acetic acid complex, boron trifluoride phosphoric acid complex, boron trifluoride dihydrate, polyvinylammonium fluoride, polyvinylpyridinium fluoride, pyridinium fluoride, imidazolium fluoride, ammonium fluoride, ammonium bifluoride, tetrafluoroborate salts, hexafluoroantimonate salts, hexafluorophosphate salts, bifluoride salts, and any combination thereof.

[0035] Preferably the treatment fluid lacks a second acid.

[0036] The biodegradable chelating agent may comprise a glutamic acid diacetic acid.

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[0037] The features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of the preferred embodiments that follows.

[0037a] In accordance with one aspect of the present invention, there is provided a method comprising: providing a treatment fluid that comprises: an aqueous base fluid, a hydrofluoric acid source selected from the group consisting of hydrofluoric acid, a hydrofluoric acid generating compound, and a combination thereof, a biodegradable chelating agent comprising one of the following selected from the group consisting of a rubidium salt of glutamic acid diacetic acid, a potassium salt of glutamic acid diacetic acid, a cesium salt of glutamic acid diacetic acid, glutamic acid diacetic acid, an ammonium salt of glutamic acid diacetic acid, a sodium salt of glutamic acid diacetic acid, a lithium salt of glutamic acid diacetic acid, a glutamic acid diacetic acid tetrasodium salt, and a combination thereof, at least one of an additional salt in the amount of from about 0.1% to about 75% by weight of the treatment fluid, wherein the salt is selected from the group consisting of: an aromatic sulfonate, an aromatic carboxylate, a hydroxynapthalene carboxylate, a salicylate, a phthalate, a chlorobenzoic acid, a phthalic acid, a 5-hydroxy-l-naphthoic acid, a 6-hydroxy-l-naphthoic acid, a 7-hydroxy-lnaphthoic acid, a l-hydroxy-2-naphthoic acid, a 3-hydroxy-2-naphthoic acid, a 5hydroxy-2-naphthoic acid, a 7-hydroxy-2-naphthoic acid, a l,3-dihydroxy-2-naphthoic acid, a 3,4-dichlorobenzoate, a trimethylammonium hydrochloride, a tétraméthylammonium chloride, a water-soluble potassium salt, a water-soluble sodium salt, a water-soluble ammonium salt, calcium chloride, calcium bromide, magnesium chloride, a zinc halide salt, and any combination thereof, a viscoelastic surfactant in the amount of from about 0.5% to about 10% by volume of the treatment fluid, and a cosurfactant in the amount of from about 0.05% to about 5% by volume of the treatment fluid, wherein the cosurfactant is selected from the group consisting of a tallow alkyl sulfonate, a coconut alkyl glyceryl ether sulfonate, a sulfated condensation product of a Cg-Cio tallow alcohol with about 1 to about 14 moles of ethylene oxide, and any combination thereof; and introducing the treatment fluid into at least a portion of a subterranean formation.

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8a

[0037b] In accordance with another aspect of the present invention, there is provided a method comprising: providing a treatment fluid that comprises: an aqueous base fluid, a hydrofluoric acid source selected from the group consisting of hydrofluoric acid, a hydrofluoric acid generating compound, and a combination thereof, a biodegradable chelating agent comprising one of the following selected from the group consisting of: glutamic acid diacetic acid, a glutamic acid diacetic acid salt, a derivative thereof, and a combination thereof, at least one of an additional salt in the amount of from about 0.1% to about 75% by weight of the treatment fluid, wherein the salt is selected from the group consisting of: an aromatic sulfonate, an aromatic carboxylate, a hydroxynapthalene carboxylate, a salicylate, a phthalate, a chlorobenzoic acid, a phthalic acid, a 5-hydroxy-l-naphthoic acid, a 6-hydroxy-l-naphthoic acid, a 7-hydroxy-lnaphthoic acid, a l-hydroxy-2-naphthoic acid, a 3-hydroxy-2-naphthoic acid, a 5hydroxy-2-naphthoic acid, a 7-hydroxy-2-naphthoic acid, a l,3-dihydroxy-2-naphthoic acid, a 3,4-dichlorobenzoate, a trimethylammonium hydrochloride, a tétraméthylammonium chloride, a water-soluble potassium salt, a water-soluble sodium salt, a water-soluble ammonium salt, calcium chloride, calcium bromide, magnesium chloride, a zinc halide salt, and any combination thereof, a viscoelastic surfactant in the amount of from about 0.5% to about 10% by volume of the treatment fluid, and a cosurfactant in the amount of from about 0.05% to about 5% by volume of the treatment fluid, wherein the cosurfactant is selected from the group consisting of a tallow alkyl sulfonate, a coconut alkyl glyceryl ether sulfonate, a sulfated condensation product of a Cio-Cig tallow alcohol with about 1 to about 14 moles of ethylene oxide, and any combination thereof; and introducing the treatment fluid into at least a portion of a subterranean formation wherein the subterranean formation includes 10% or greater carbonates; and thereafter, performing a fracturing treatment in the subterranean formation.

[0037c] In accordance with yet another aspect of the present invention, there is provided a method comprising: providing a treatment fluid that comprises: an aqueous base fluid, a biodegradable chelating agent comprising a potassium salt of glutamic acid diacetic acid, at least one of an additional salt in the amount of from about 0.1% to about 75% by weight of the treatment fluid, wherein the salt is selected from the group consisting of: an aromatic sulfonate, an aromatic carboxylate, a hydroxynapthalene

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8b carboxylate, a salicylate, a phthalate, a chlorobenzoic acid, a phthalic acid, a 5-hydroxy-lnaphthoic acid, a 6-hydroxy-l-naphthoic acid, a 7-hydroxy-l-naphthoic acid, a 1hydroxy-2-naphthoic acid, a 3-hydroxy-2-naphthoic acid, a 5-hydroxy-2-naphthoic acid, a 7-hydroxy-2-naphthoic acid, a l,3-dihydroxy-2-naphthoic acid, a 3,4-dichlorobenzoate, a trimethylammonium hydrochloride, a tétraméthylammonium chloride, a water-soluble potassium salt, a water-soluble sodium salt, a water-soluble ammonium sait, calcium chloride, calcium bromide, magnesium chloride, a zinc halide salt, and any combination thereof, a viscoelastic surfactant in the amount of from about 0.5% to about 10% by volume of the treatment fluid, and a cosurfactant in the amount of from about 0.05% to about 5% by volume of the treatment fluid, wherein the cosurfactant is selected from the group consisting of a tallow alkyl sulfonate, a coconut alkyl glyceryl ether sulfonate, a sulfated condensation product of a Cio-C_]8 tallow alcohol with about 1 to about 14 moles of ethylene oxide, and any combination thereof; and introducing the treatment fluid into at least a portion of a subterranean formation.

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BRIEF DESCRIPTION OF THE DRAWINGS

[0038J The following figure is included to illustrate certain aspects of the present invention, and should not be viewed as an exclusive embodiment. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those skilled in the art and having the benefit of this disclosure.

[0039] Figure 1 shows a fractional pore volume effluent analysis

DETAILED DESCRIPTION

[0040] The present invention generally relates to treatment fluids containing biodegradable chelating agents, and, more particularly, to methods for treating a least a portion of a subterranean formation using treatment fluids containing a biodegradable chelating agent in conjunction with a hydrofluoric acid treatment

[0041] There are many advantages of the present invention, only a few of which are discussed or alluded to herein. The compositions and methods of the present invention involve biodegradable chelating agent compositions that can be used in conjunction with hydrofluoric acid treatments in subterranean formations that avoid many of the disadvantages associated with other chelants discussed above. Because of this chelation effect, this biodegradable chelating agent composition (when used in conjunction with a hydrofluoric acid treatment), is able to aid in the prevention or remediation of precipitates. Additionally, the biodegradable chelating agent of the present invention can be used in an ammonium salt form. This can avoid the additional precipitation problems that other chelating agents present in the context of this invention. Furthermore, the biodegradable chelating agents compositions and methods of the present invention may be used in prevention embodiments to prevent the formation of precipitates with hydrofluoric acid as discussed above as well as remediation embodiments to remove damage in a well bore or subterranean formation. These features beneficially allow treatment fluids containing glutamic acid diacetic acid (“GLDA”) to perform single stage treatment operations including, for example, acidizing treatments (e.g., matrix acidizing) and proppant pack treatments, particularly in subterranean formations that have carbonates present especially those with >10% carbonates.

[0042] The treatment fluids of the present invention comprise an aqueous base fluid, hydrofluoric acid, and a biodegradable chelating agent composition of the present invention that GLDA, a GLDA salt, or a GLDA derivative. Optionally, salts, other pH

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PCT/GB2012/000247 additives corrosion inhibitors, surface active agents, anti-sludging agents, mutual solvents, scale inhibitors, viscosifiers, gases, diverting/fluid loss agents, and the like may be included in the treatment fluids of the present invention. These acidic treatment fluids may be used in subterranean formations to prevent or remediate precipitation damage caused by the interaction of the hydrofluoric acid and ions present in the formation.

[0043] Generally, the carrier fluid of the present invention may comprise any aqueous or non-aqueous fluid. In particular embodiments, the carrier fluid may comprise freshwater, saltwater (e.g., water containing one or more salts dissolved therein), brine (e.g., saturated saltwater), seawater, glycol, combinations thereof, or derivatives thereof. In other embodiments, the carrier fluid may comprise a liquid chelating agent or scale control agent by itself. Generally, the carrier fluid may be from any source, provided that it does not contain components that might adversely affect the stability and/or performance of the treatment fluids of the present invention.

[0044] The biodegradable chelating agent compositions of the present invention comprise a biodegradable chelants: GLDA, a GLDA salt, or a GLDA derivative. Examples of suitable derivatives of glutamic acid diacetic acid include esters, and alkylated derivatives. Examples of suitable salts of GLDA include sodium salts of GLDA, rubidium salts of GLDA, lithium salts of GLDA, potassium salts of GLDA, cesium salts of GLDA, ammonium salts of GLDA. Specific examples of suitable GLDA salts include a glutamic acid diacetic acid tetrasodium salt and a glutamic acid diacetic acid ammonium salt. GLDA is manufactured from a readily biodegradable, renewable, and human-consumable raw material, monosodium glutamate. In addition, GLDA is readily soluble in high concentrations over a wide pH range. In this regard GLDA is thought of as superior to many other chelating agents. GLDA chelates metal ions such as, but not limited to, calcium, iron, aluminum, and magnesium over a wide pH range and is highly soluble in aqueous treatment fluids.

[0045] GLDA, at the present time, is available in a sodium salt form. Other salts may be available noncommercially, or in smaller quantities, or may be made through an ionexchange discussed below. The preferred form for use in conjunction with the methods described herein is not the monovalent metal salt form, but rather an ammonium salt of the GLDA. A suitable commercial source of GLDA is a 47 wt. % aqueous solution from AkzoNobel Corp, available under the tradename “DISSOLVINE®.”

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[0046] For use in some embodiments wherein a sodium salt of the GLDA is available, it may be desirable to exchange the sodium cations for other cations such as, for example, potassium or ammonium cations. An ammonium salt is the preferred salt in the context of the present invention concerning clays and sandstones. In the case of carbonates in some embodiments potassium is preferred. Exchange of these cations is contemplated to take place under conditions known to one of ordinary skill in the art. Methods for exchanging the sodium cations for potassium or preferably ammonium cations are contemplated to include, without limitation, ion exchange chromatography and selective precipitation techniques. Other means for exchanging the sodium cations can be envisioned by one having ordinary skill in the art. As discussed further below, it is contemplated that exchange of at least a portion of the sodium cations can produce better solubility properties and beneficially improve other operational characteristics that can further facilitate the use of GLDA as a biodegradable chelating agent in the treatment fluids of the present invention.

[0047] Lesser concentrations of the free acid can be produced under acidic conditions by diluting the acid in an appropriate volume of water. The amount to include will depend on the specific minerals and their quantity present in the subterranean formation and the purpose of use and the desired pH of the biodegradable chelants composition. Exemplary ranges are discussed below. In some embodiments, the pH window for clays is about 1 to about 6. In other embodiments, the pH window for clays is about 1.6 to about 4.5. In other embodiments, the pH window for clays is about 1.5 to about 1.8, and in other embodiments about 1.6. When trying to remove carbonate or carbonate scale, the pH of the fluid may be about 5 to about 10. A preferred pH range for carbonate formations may be 6 to about 9. The pH will be dependent on what purpose the biodegradable chelating agent will serve downhole. A person having ordinary skill in the art with the benefit of this disclosure will be able to select the appropriate pH for a given application.

[0048] In some embodiments, the ratio of the biodegradable chelant to water is about 1% to about 50% by weight based on known or existing concentration. In some embodiments, the ratio of the biodegradable chelant to water is about 1 % to about 20% by weight based on known or existing concentration. In some embodiments, this may be about 3% to about 6%.

[0049] In some embodiments, the hydrofluoric acid in a treatment fluid of the present invention may be produced from any suitable hydrofluoric acid generating

CA 02829451 2015-07-16 component. Examples of suitable hydrofluoric acid generating components include, but are not limited to, fluoroboric acid, fluorosulfuric acid, hexafluorophosphoric acid, hexafluoroantimonic acid, difluorophosphoric acid, hexafluorosilicic acid, potassium hydrogen difluoride, sodium hydrogen difluoride, boron trifluoride acetic acid complex, boron trifluoride phosphoric acid complex, boron trifluoride dihydrate, polyvinylammonium fluoride, polyvinylpyridinium fluoride, pyridinium fluoride, imidazolium fluoride, ammonium fluoride, ammonium bifluoride, tetrafluoroborate salts, hexafluoroantimonate salts, hexafluorophosphate salts, bifluoride salts, and any combination thereof.

[0050] The treatment fluids of the present invention may also include a viscoelastic surfactant. Generally, any suitable surfactant that is capable of imparting viscoelastic properties to an aqueous fluid may be used in accordance with the teachings of the present invention. These surfactants may be cationic, anionic, nonionic, zwitterionic or amphoteric in nature, and comprise any number of different compounds, including methyl ester sulfonates (such as those described in U.S. Patent Nos. 7,299,874, 7,159,659, and 7,303,019, and U.S. Patent Publication Nos. 20060183646, betaines, modified betaines, sulfosuccinates, taurates, amine oxides, ethoxylated fatty amines, quaternary ammonium compounds, derivatives thereof, and combinations thereof. When present in the treatment fluids of the present invention, the surfactant is generally present in an amount sufficient to provide the desired viscosity (e.g., sufficient viscosity to divert flow, reduce fluid loss, suspend particulates, etc.) through the formation of viscosifying micelles. In particular embodiments, the surfactant generally comprises from about 0.5% to about 10%, by volume, of the treatment fluid. In particular embodiments, the surfactant comprises from about 1% to about 5%, by volume, of the treatment fluid.

[0051] When including a surfactant, the treatment fluids of the present invention may also comprise one or more cosurfactants to, among other things, facilitate the formation of and/or stabilize a foam, facilitate the formation of micelles (eg., viscosifying micelles), increase salt tolerability, and/or stabilize the treatment fluid. The cosurfactant may comprise any surfactant suitable for use in subterranean environments that does not adversely affect the treatment fluid. Examples of cosurfactants suitable for use in the present invention include, but are not limited to, linear Cio-Cu alkyl benzene sulfonates, branched Cio-Cu alkyl benzene sulfonates, tallow alkyl sulfonates, coconut alkyl glyceryl ether sulfonates, sulfated condensation products of mixed Cio-C|g tallow alcohols with about 1 to about 14 moles of

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PCT/GB2012/000247 ethylene oxide, and mixtures of higher fatty acids containing about 10 to about 18 carbon atoms. In particular embodiments, the cosurfactant may be present in an amount in the range of from about 0.05% to about 5% by volume of the treatment fluid. In particular embodiments, the cosurfactant may be present in an amount in the range of from about 0.25% to about 0.5% by volume of the treatment fluid. The type and amount of cosurfactant suitable for a particular application of the present invention may depend upon a variety of factors, such as the type of surfactant present in the treatment fluid, the composition of the treatment fluid, the temperature of the treatment fluid, and the like. A person of ordinary skill, with the benefit of this disclosure, will recognize when to include a cosurfactant in a particular application of the present invention, as well as the appropriate type and amount of cosurfactant to include.

[0052] The treatment fluids of the present invention may optionally comprise one or more salts to modify the rheological properties (e.g., viscosity) of the treatment fluids. These salts may be organic or inorganic. Examples of suitable organic salts include, but are not limited to, aromatic sulfonates and carboxylates (such as p-toluene sulfonate and napthalene sulfonate), hydroxynapthalene carboxylates, salicylate, phthalate, chlorobenzoic acid, phthalic acid, 5-hydroxy-1-naphthoic acid, 6-hydroxy-l-naphthoic acid, 7-hydroxy-lnaphthoic acid, 1-hydroxy-2-naphthoic acid, 3-hydroxy-2-naphthoic acid, 5-hydroxy-2naphthoic acid, 7-hydroxy-2 -naphthoic acid, l,3-dihydroxy-2-naphthoic acid, 3,4dichlorobenzoate, trimethylammonium hydrochloride and tétraméthylammonium chloride. Examples of suitable inorganic salts include water-soluble potassium, sodium, and ammonium salts (such as potassium chloride and ammonium chloride), calcium chloride, calcium bromide, magnesium chloride, and zinc halide salts. Any combination of the salts listed above also may be included in the treatment fluids of the present invention. Where included, the one or more salts may be present in an amount in the range of about 0.1% to about 75% by weight of the treatment fluid. In particular embodiments, the one or more salts may be present in an amount in the range of about 0.1% to about 10% by weight of the treatment fluid. A person of ordinary skill, with the benefit of this disclosure, will recognize when to include a salt in a particular application of the present invention, as well as the appropriate type and amount of salt to include.

[0053] The treatment fluids of the present invention may also include one or more well-known additives, such as gel stabilizers, fluid loss control additives, particulates, acids,

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PCT/GB2012/000247 corrosion inhibitors, catalysts, clay stabilizers, biocides, friction reducers, additional surfactants, solubilizers, pH adjusting agents, bridging agents, dispersants, flocculants, foamers, gases, defoamers, H2S scavengers, CO2 scavengers, oxygen scavengers, scale inhibitors, lubricants, viscosifiers, weighting agents, and the like. Those of ordinary skill in the art, with the benefit of this disclosure, will be able to determine the appropriate type and amount of such additives for a particular application. For example, in some embodiments, it may be desired to foam a treatment fluid of the present invention using a gas, such as air, nitrogen, or carbon dioxide.

[0054] In some embodiments, methods described herein comprise providing a treatment fluid that comprises an aqueous base fluid, hydrofluoric acid, and a biodegradable chelating agent comprising glutamic acid diacetic acid, a salt, or a derivative thereof, and introducing the treatment fluid into at least a portion of a subterranean formation. The treatment fluid may remove potentially damaging precipitates from the formation.

[0055] In some embodiments, treatment fluids comprising an aqueous base fluid and a biodegradable chelating agent comprising glutamic acid diacetic acid, a salt, or a derivative thereof are described herein.

[0056] In some embodiments, methods described herein comprise providing a treatment fluid that comprises an aqueous base fluid and a biodegradable chelating agent comprising glutamic acid diacetic acid, a salt, or a derivative thereof, and introducing the treatment fluid into at least a portion of a subterranean formation.

[0057] In some embodiments of the methods of the present invention, an acidic treatment fluid of the present invention that comprises an aqueous base fluid, hydrofluoric acid, and a biodegradable chelating agent composition that comprises glutamic acid diacetic acid, a glutamic acid diacetic acid salt, or a glutamic acid diacetic acid derivative can be used in prevention methods to prevent the formation of precipitates, for example, those produced in conjunction with a hydrofluoric acid treatment in a sandstone formation. These embodiments are most appropriate for formations that comprise clays that include ions that can be problematic in terms of precipitate formation.

[0058] In some embodiments, the chelating fluids of the present invention may be used as a pre-treatment to a fracturing treatment, especially in subterranean formations that contain different layers of sedimentary rock. In such embodiments, a treatment fluid of the present invention comprising an aqueous base fluid, hydrofluoric acid, and a biodegradable

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WO 2012/127183

PCT/GB2012/000247 chelating agent composition of the present invention that comprises glutamic acid diacetic acid, a glutamic acid diacetic acid salt, or a glutamic acid diacetic acid derivative is placed in a subterranean formation via a well bore before a fracturing treatment. The subsequent fracturing treatment can be a traditional fracturing treatment or an additional acidizing treatment directed at treating the particulate pack introduced during the fracturing operation. In such embodiments, the use of the treatment fluid of the present invention may be considered a prevention mechanism to prevent the formation of potentially problematic precipitates.

[0059] In some embodiments, a treatment fluid of the present invention comprising an aqueous base fluid, hydrofluoric acid, and a biodegradable chelating agent composition of the present invention that comprises glutamic acid diacetic acid, a glutamic acid diacetic acid salt, or a glutamic acid diacetic acid derivative may be used to clean the well bore area before bringing the well into final production. Using such a fluid can remove damage, blockages, debris, and natural clays in the formation. In at least some embodiments, this method may be considered a remediation method of the present invention.

[0060] In some embodiments, the chelating fluids of the present invention may be useful in formations that comprise siliceous materials, for example, naturally occurring sandstone, propping material, etc. A siliceous material can be naturally present in the formation, e.g., the sandstone, or deliberately introduced, e.g., quartz proppant. Due to the geochemical processes operative in the formation, such as high temperature, high pressure, abrupt changes to the geochemical balance after the introduction of treating fluids of different ionic strength, the siliceous material can undergo rapid changes that lead to reduction of permeability or hydraulic conductivity. When the treatment is carried out in the matrix of the sandstone, the effect is believed to remove aluminosilicates from the conductive pathways. In a particulate pack, a propped fracture, the effects are compounded because, under certain scenarios, geochemical scaling can occur. Another reason is due to fines migration, which is the displacement of particles from the rock matrix into the pack and their subsequent deposition. Furthermore, the presence of aluminum in a sandstone and in those ceramic proppants made of alumina exacerbate the problem due their intrinsic reactivity in low pH media or under abrupt changes to the chemical potential of a fluid leading to dissolution of the material. This signifies that varying amounts of silicon and/or aluminum are placed into

CA 02829451 2015-07-16 solution, can migrate and reprecipitate or crystallize and form new minerals that obstruct the flow of fluids.

[0061] In some embodiments where clays are not present in the formation, then the treatment fluid may not include hydrofluoric acid. Glutamic acid diacetic acid, a glutamic acid diacetic acid salt, or a glutamic acid diacetic acid derivative may be sufficient to perform the desired preventive action. In some embodiments where clays are present in the formation, it may be desirable to remediate precipitate damage present in the well bore or in the formation that may be blocking pore throats within the formation. Such methods may be appropriate any time where production has declined due to the presence of particulates or fines that obstruct pore throats in the near well bore area.

[0062] In some embodiments, methods described herein comprise providing a treatment fluid that comprises an aqueous base fluid, a hydrofluoric acid source selected from the group consisting of hydrofluoric acid and a hydrofluoric acid generating compound, and a biodegradable chelating agent comprising glutamic acid diacetic acid, a glutamic acid diacetic acid salt, or a glutamic acid diacetic acid derivative, and introducing the treatment fluid into at least a portion of a subterranean formation.

[0063] In some embodiments, an additional acid, such as hydrochloric acid, may be included in the treatment fluid with the hydrofluoric acid, for example, to keep the pH of the fluid at a low level, or any other acid whose pKa brings the pH to the desirable level.

[0064] In some embodiments, it may be desirable to include a salt or a salt substitute in the treatment fluid. This is surprising, given that traditional wisdom indicates that adding a salt can exacerbate the precipitation problems. A preferred example of a suitable salt is ammonium chloride. It is believed that this is a problem specific to the use of an HF fluid, any fluid that contains HF. The salts that cause precipitation are sodium and potassium. Adding an ammonium salt will not exacerbate the problem.

J0065] In some embodiments, the treatment fluids of the present invention may be used to treat a proppant pack, particularly where the proppant pack’s hydraulic conductivity has been impaced.

10066] To facilitate a better understanding of the present invention, the following examples of preferred embodiments are given.

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PCT/GB2012/000247

EXAMPLES

[0067] Experiment 1

[0068] A solution of DISSOLVINE® (GLNA40S) available from AkzoNobel was used in the preparation of treating fluid. A solution containing 3.5%wt of GLNA40S was prepared by dissolving 363.5 g of concentrated form into a base fluid. The base fluid consisted of 2% NaCl containing 20 g/L of tannic acid. After fully mixing all components, the pH of the final volume of solution (4 L) was adjusted to pH 1.6 with 35% HC1. The solution was filtered through a 0.40 micron membrane. It is stable for the duration of the testing period (days). A 2” x 12” long Hassler sleeve was employed to conduct a core flood acid test at 320°F (160°C). The sleeve was packed with a homogenized mixture of quartz (Oklahoma #1 sand) 94%wt, K-feldspar 2%wt, and the aluminosilicate chlorite 4%wt; the pore volume of the packed column corresponded to 110 mL.

[0069] The column was treated with the following fluid sequence:

[0070] 4 PV, 2% NaCl (pH 6),

[0071] 2 PV, 3.5% GLNA40S(pH 1.6) with Tannic acid,

[0072] 3 PV, 5% Ammonium acetate (pH 4.5), and

[0073] 3 PV, 2% NaCl (pH 6).

[0074] The results of the core flood indicate that during the 2 PV of DISSOLVINE® (GLNA40S) exposure, indicated on Figure 1 by the arrow spanning samples 4-12, the amount of A13+, as detected by ICP-OES, increase gradually until the chelating agent injection was stopped. Once the sand/chlorite pack was no longer exposed to the chelating fluid the aluminum released into solution ceased. The flow rate was 2 mL/min throughout the first 1.5 PV and then increased to 5 mL/min during the last 0.5 PV. The effluent collected at intervals of 0.5 and 1 PV was analyzed for Al³⁺ and Si⁴⁺ by ICP, no quantitative precipitates were observed in the effluent which was stable for days at room temperature after collection. The respective effluent samples collected for ICP analysis were not acidified with any additional acid, rather they were analyzed in their respective pH at collection time. The amount of Silicon remains nearly constant.

[0075] Experiment 2

[0076] The following description corresponds to visual observations, and titrations conducted. All tests, including the core flood (describe above in Experiment 1), made use of a fluid consisting of DISSOLVINE® GLDA (GL-NA40S) and tannic acid.

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[0077] The solubility of Al³⁺ in concentrations of 200 to 3000 ppm of was independently tested at room temperature. 100 mL of a stock solution, 1.45 M pH 1.45, was placed in a stirred beaker and the pH, gradually raised with strong base (1 M NaOH or 2 M NH4OH in order to minimize volume changes due to dilution). Precipitation of aluminum hydroxide ensues shortly after reaching pH 2.5 and nearly fully precipitates quantitatively at pH 3 in the absence of any chelating agent. When GLDA was employed in concentrations of 3,5 or 12 %wt precipitation was effectively suppressed as the pH increased from the starting pH of 1.45 to 4. After reaching pH 4 relatively minor amount of flocculated particles were evident but no precipitate formed for days. The solution employed of GLDA in this case contained tannic acid, for different application (the same application filed for silica and tannic acid) but the effect of the latter had no effect on the chelation of A13+, rather, the effective complexation of A13+ in the presence of another reagent was proven to be effective in the same pH range.

[0078] Experiment 3

[0079] A glass vial containing 5 g of mineral (clay or quartz) was mixed with 15 or 20 mL of treating fluid. The treating fluid was composed of GLDA 15% and 3 %wt NH4HF2 with sufficient HC1 to adjust the pH to the indicated value in the Table 1. The reaction mixtures were heated in a heated cylinder to 95°C for 0.5, 1, 2, 3, 4 hours and automatically shaken (at 200 rpm). The reaction fluid was collected via a syringe and filtrated through a 0.45 micron membrane filter prior to ICP-AES analysis, the pH of the solution was not adjusted via any means. The elemental analysis for each mineral is provided in Table 1.

[0080] It is noteworthy to point out that the point of these experiments was not to optimize the fluid composition, but rather show the effectiveness of the GLDA, monosodium, even in the presence of an hydrofluoric acid generating compound like ammonium bifluoride. While there are sodium pentafluorosilicates and hexafluorosilicates, known damaging precipitates resulting from the reaction of HS1F5- (primary reaction) as identified by powder XRD of the solid mixture after completely drying in an oven at 100 °C for 2-4 h, the amount of dissolved silicon in these fluids is substantial. The reaction of illite with the fluid shows that the clay was attacked by the fluid as the spent fluid contained all the elements present in the virgin structure. The reaction of chlorite proved to be more effective as demonstrated by the larger concentration of A1 and Si, as well as all others having ions. Kaolinite on the other hand showed diminished dissolution, as expected, for this clay mineral under the experiment

CA 02829451 2015-07-16 conditions. Bentonite also showed diminished reactivity, this could be due to actual precipitation for the dissolved silica or pentafluorosilicates. Sand did not significantly react.

Table 1

<td></td><td> Sample</td><td> Al mg/L IPPJPl</td><td> Si iDDnfl</td><td> fiH</td><td> Vol. (mL)</td>

<td> Illite</td><td> 1</td><td> 816</td><td> 304</td><td> 1.3</td><td> 20</td>

<td></td><td> 2</td><td> 768</td><td> 309</td><td> 1.3</td><td> 20</td>

<td></td><td> 3</td><td> 2,041</td><td> 364</td><td> 1.3</td><td> 20</td>

<td></td><td> 4</td><td> 531</td><td> 258</td><td> 1.3</td><td> 20</td>

<td></td><td> 5</td><td> 522</td><td> 281</td><td> 1.3</td><td> 20</td>

<td> Chlorite</td><td> 6</td><td> 1,789</td><td> 754</td><td> 1.3</td><td> 20</td>

<td></td><td> 7</td><td> 1,654</td><td> 752</td><td> 1.3</td><td> 20</td>

<td></td><td> 8</td><td> 1,702</td><td> 748</td><td> 1.3</td><td> 20</td>

<td></td><td> 9</td><td> 1,400</td><td> 933</td><td> 1.3</td><td> 20</td>

<td></td><td> 10</td><td> 1,375</td><td> 898</td><td> 1.3</td><td> 20</td>

<td> Kaolinitc</td><td> 11</td><td> 750</td><td> 220</td><td> 1.3</td><td> 20</td>

<td></td><td> 12</td><td> 1,167</td><td> 220</td><td> 1.3</td><td> 20</td>

<td></td><td> 13</td><td> 684</td><td> 197</td><td> 1.3</td><td> 20</td>

<td></td><td> 14</td><td> 684</td><td> 201</td><td> 1.3</td><td> 20</td>

<td> Bentonite</td><td> 15</td><td> 138</td><td> 273</td><td> 3</td><td> 15</td>

<td></td><td> 16</td><td> 275</td><td> 198</td><td> 3</td><td> 15</td>

<td></td><td> 17</td><td> 177</td><td> 257</td><td> 3</td><td> 15</td>

<td></td><td> 18</td><td> 132</td><td> 277</td><td> 3</td><td> 15</td>

<td> Sand</td><td> 23</td><td> X</td><td> 405</td><td> 1.3</td><td> 20</td>

<td></td><td> 24</td><td> X</td><td> 103</td><td> 1.3</td><td> 20</td>

<td></td><td> 25</td><td> X</td><td> 112</td><td> 1.3</td><td> 20</td>

<td></td><td> 26</td><td> X</td><td> 50</td><td> 1.3</td><td> 20</td>

[0081] Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different manners apparent to those skilled in the art having the benefit ofthe teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown. It is therefore evident that the particular illustrative embodiments disclosed above may be altered, combined, or modified and all such variations are considered within the scope described herein. While compositions and methods are described in terms of comprising, containing, or including various components or steps, the compositions and methods can also consist

CA 02829451 2015-07-16 essentially of or consist of the various components and steps. All numbers and ranges disclosed above may vary by some amount. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, from about a to about b, or, equivalently, from approximately a to b, or, equivalently, from approximately a-b) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles a or an, as used in the claims, are defined herein to mean one or more than one of the element that it introduces. The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.