METHODS FOR REMOVING SCALE AND SOLUBILIZING SULFATE AND AQUEOUS COMPOSITION

Abstract

Methods for removing scale and solubilizing sulfate and aqueous composition. The present invention discloses a novel aqueous composition for use in removing mixed sulfate scale from a surface contaminated therewith, said composition comprising: a chelating agent and a counter-ion component selected from the group consisting of: Li5DTPA; Na5DTPA; K5DTPA; CS5DTPA; Na4EDTA; K4EDTA; TEAH4DTPA; and TBAH5DTPA; a dissolution enhancer; optionally, a compound, such as sodium gluconate or the like, and a carboxyl-containing fructan, such as carboxymethyl inulin. Methods for using such compositions are also disclosed.

Description

METHODS FOR REMOVING SCALE AND SOLUBILIZING SULFATE AND AQUEOUS COMPOSITION FIELD OF THE INVENTION

[001] The present invention is directed to a composition and method for use in oilfields and industrial operations, more specifically to compositions used in the removal of mixed sulfate scale. BACKGROUND OF THE INVENTION

[002] Scaling or the formation of mineral sulfate deposits can occur on the surfaces of metal, rock, or other materials. Scaling is caused by a precipitation process as a result of thermodynamic and hydrodynamic factors or changes in pressure, velocity rates, and temperature and the subsequent change in the composition of a solution (usually water).

[003] Typical homogeneous fouling consists of, for example, calcium carbonate, calcium sulfate, barium sulfate, strontium sulfate, iron sulfide, iron oxides or iron carbonate. Sulfate fouling, and in particular common barium sulfate fouling, is a major challenge for industry and, in particular, for the oilfield industry.

[004] In some cases, scale deposits restrict or even shut down the production pipeline if the flow dynamics of the produced water composition are disrupted by changes in pressure and / or temperature. In many cases, this is due to well components such as downhole blockers, safety valves, or flow controls. In addition to the problems of scale formation in produced brine water due to mineral content, other source water used in well repair or completion operations can also be potential sources of scale minerals, including water flooding operations or operations Petition 870210119280, dated 12 / 21 / 2021, pages 120 / 165 2 / 39 geothermal.

[005] Sulfate scale precipitation can occur at any point in a production, injection, or abandonment-discharge well and associated equipment cycle, and can also be caused by mismatches between injected water and formation water, in addition to the temperature and pressure dynamics changes mentioned above, as well as wellbore additives or flow equilibrium disturbances. Scale in surface equipment (e.g., heat exchangers, piping, valves, flow control devices) is also a catalyst for sulfate scale. In oil and gas operations, seawater or brine is frequently injected into reservoirs for pressure maintenance, and as these have a high sulfate ion content and formation water or drilling fluids often have a high content of barium, calcium, and / or strontium ions donated from the formation, these waters often cause sulfate mineral precipitation.Sulfate fouling on surface equipment, such as heat exchangers and associated piping, is a major problem for the industry as well, as it typically needs to be managed by mechanical means, such as disassembling the equipment in question, manually cleaning the fouling, and reassembling, which is very time-consuming and expensive. Having a chemical solution that can treat these sulfate foulings with minimal agitation and at lower temperatures would be very advantageous for the industry. As the multiple challenges of sulfate fouling composition occur offshore-onshore, they are typically very difficult to manage efficiently as a whole. Having a sulfate solvent that solubilizes all typical sulfate foulings found individually or as a composition is advantageous for the industry versus having to deploy a specific chemical for each type of fouling or manage fouling problems with mechanical means. Petition 870210119280, dated 12 / 21 / 2021, pp. 121 / 165 3 / 39

[006] The most obvious way to avoid scale formation during production is to prevent the creation of supersaturation of the brine being handled and to manage the fluid flow path to minimize pressure and rate differentials, and also to add scale inhibitors, which are minimally effective and expensive. Sometimes it may also be possible by altering reservoir operating conditions, for example, ensuring that the well pressure is sufficient to prevent gas release and injecting water that is compatible with the formation water. However, economics generally dictates that the use of inhibitors or the treatment of any precipitated scale is preferable to manage costs.

[007] Controlling fouling through the use of inhibitors, as well as understanding and mitigating fouling tendencies, is important for production and injection wells, but so is having an economical solution or means of treating any fouling that occurs, even after best practices have been implemented during the production cycle.

[008] Designing scale treatment programs requires extensive knowledge of scale / chemistry theory and a broad base of practical operational experience to be successful. Occasionally, applications arise where the ideal selection of chemicals and fluids may be beyond the scope of a well site engineer's experience or theoretical knowledge. Rules of thumb and general formulas may not be adequate, and selection procedures based on broader experience and deeper knowledge may be necessary. Deposit analysis and solvent screening are ideally necessary when considering a potential scale dissolution application; the scale causing the problems will have to be analyzed.

[009] The most common sulfate incrustations are barium, calcium and strontium. Petition 870210119280, dated 12 / 21 / 2021, pp. 122 / 165 4 / 39 These alkaline earth metal salts have many similar properties and frequently precipitate together, forming problematic sulfate scale. The deposition of this scale is a serious problem for oil and gas producers globally, causing fouling in wellbore and related surface processing equipment. This fouling not only restricts the flow of hydrocarbons from the formation, resulting in production loss, but once the formation or injection water is saturated with sulfates, continued deposition causes fouling and potentially failures of critical equipment such as drills, casing, tubing, valves, and surface equipment, all with the potential to reduce oil production rates and result in substantial revenue loss. There is a need in the industry for an effective solution to this existing challenge.Sulfate scale, such as radium sulfate, barium sulfate, calcium sulfate, etc. – sometimes referred to as NORM scale due to their solubility characteristics – typically 0.0023 g / l in water – is more difficult to handle than carbonate scale. Sulfate scale is not soluble in traditional acid scale removal solvents. Radium sulfate, while not the most common sulfate scale, presents a challenge in its removal as it is often embedded within barium sulfate scale and is also radioactive, thus posing a risk of exposure and causing very expensive cleaning or disposal costs for downhole tubing and equipment, etc., when removed from the well for replacement, general service, or abandonment.Having a chemical product that can be used to wash these components while still in the well and effectively clean / remove the NORM materials, leaving them at the bottom of the well, allows the operator to significantly reduce handling / disposal costs related to wells containing NORM, which is very advantageous. Petition 870210119280, dated 12 / 21 / 2021, pp. 123 / 165 5 / 39

[010] Once this water / acid insoluble scale has formed, it is extremely difficult to remove it with the chemical options available on the market.

[011] The solubility of barium sulfate is reported to be approximately 0.0002448 g / 100 ml (20°C) and 0.000285 g / 100 ml (30°C). Existing methods for removing sulfate scale include mechanical removal and / or low-performance scale solvents currently on the market, but both have limitations and disadvantages. Mechanical removal involves the use of milling, scraping, or high-pressure jetting tools and / or dismantling of major production equipment, causing substantial downtime of production and processing equipment. These methods have limited efficiency as the scale is extremely difficult to remove, often forming in areas beyond the reach of mechanical equipment, as many installations have welded joints and limited access. High-pressure jetting typically only removes the surface of the scale.

[012] Sulfate scale removers have been developed to overcome the low solubility of these types of scale. Sulfate scale removers work by chelating / cleaning the dissolved sulfate present in the water, allowing more to be dissolved. To aid the reaction rate / increase the speed and efficiency of dissolution, these products are typically implemented at elevated temperatures of 50°C to 90°C. As a result, dissolving sulfate scale will take much longer than, for example, dissolving carbonate scale using acid. Typical scale removers, such as ethylenediaminetetraacetic acid (EDTA), and variations of this molecule (such as DTPA) are used by industry to dissolve sulfate scale with some success and by sequestering barium, calcium, and strontium ions. However, this Petition 870210119280, dated 12 / 21 / 2021, pp. 124 / 165 The 6 / 39 process requires a higher temperature (generally above 75°C), is time-consuming, and has limited dissolving capacity.

[013] The following includes some patent disclosures of sulfate scale removers. U.S. Patent No. 4,980,077 A teaches that alkaline earth metal scale, especially barium sulfate scale deposits, can be removed from oilfield pipes and other tubular products with a scale removal composition comprising an aqueous alkaline solution with a pH of about 8 to about 14, a polyaminopolycarboxylic acid, preferably EDTA or DTPA, and a catalyst or synergist comprising oxalate anion. It is stated that when the scale removal solution is contacted with a surface containing a scale deposit, substantially more scale is dissolved at a faster rate than previously possible.

[014] WO 1993024199 A1 teaches the use of low-frequency sonic energy in the sonic frequency range to enhance the dissolution of alkaline earth metal scale using a scale removal solvent comprising an aqueous alkaline solution having a pH of about 8 to about 14 and containing EDTA or DTPA and a catalyst or synergist, preferably an oxalate anion. It is stated that when the scale removal solvent is brought into contact with a surface containing a scale deposit while simultaneously transmitting low-frequency sonic energy through the solvent, substantially more scale is dissolved at a faster rate than previously possible.

[015] U.S. Patent No. 4,030,548A teaches that a barium sulfate or solid encrustation can be economically dissolved by flowing a stream of relatively dilute aqueous solution of salt chelating agent. Petition 870210119280, dated 12 / 21 / 2021, pages 125 / 165 7 / 39 aminopolyacetic acid in contact with and along the surfaces of the scale while correlating the composition and flow rate of the solution so that each portion of the solution contains an amount of chelating agent effective to dissolve barium sulfate and the portions upstream of the scale are contacted by portions of the solution that are unsaturated with respect to the barium chelating complex.

[016] U.S. Patent No. 6,613,899 B1 teaches carboxyl-containing fructans, such as carboxymethyl inulin, used to prevent the deposition of scale composed of, for example, calcium, barium, and strontium salts of sulfuric acid and carbonic acid in oil extraction. In the oil extraction method, 0.5 to 200 ppm of a carboxyl-containing fructan containing 0.3 to 3 carboxyl groups per monosaccharide unit is incorporated into the process water, process equipment, or oil-containing formation.

[017] U.S. Patent No. 3,625,761A teaches a method for removing an alkaline earth metal sulfate scale deposit in an aqueous system comprising contacting said scale deposit with a treatment composition heated to a temperature in the range of about 86 to about 194°F (30 to 90°C) consisting essentially of an aqueous alkaline solution containing about 4 to about 8 percent by weight of disodium hydrogenethylenediaminetetraacetate dihydrate and having a pH in the range of about 10 to 13 for a period sufficient to dissolve at least part of said scale, acidifying said solution to lower the pH thereof to a pH in the range of 7 to 8 with an acid selected from the group consisting of sulfuric acid, hydrochloric acid, oxalic acid, a mixture of sulfuric acid and oxalic acid, and a mixture of acid hydrochloric and oxalic acid, to precipitate any alkaline earth metal ions present.

[018] U.S. Patent No. 5,084,105A teaches that metal inlays Petition 870210119280, dated 12 / 21 / 2021, pp. 126 / 165 8 / 39 Alkaline earth deposits, especially barium sulfate scale deposits, can be removed from oilfield pipes and other tubular products with a scale removal composition comprising an aqueous alkaline solution having a pH of about 8 to about 14, preferably about 11 to 13, of a polyaminopolycarboxylic acid, preferably EDTA or DTPA, and a catalyst or synergist comprising a monocarboxylic acid, preferably a substituted acetic acid, such as mercaptoacetic acid, hydroxyacetic acid, or aminoacetic acid, or an aromatic acid, such as salicylic acid. The description states that when the scale removal solution is contacted with a surface containing a scale deposit, substantially more scale is dissolved at a faster rate than would be possible without the synergist.

[019] U.S. Patent No. 7,470,330 B2 teaches a method for removing metal scale from surfaces that includes contacting the surfaces with a first aqueous solution of a chelating agent, allowing the chelating agent to dissolve the metal scale, acidifying the solution to form a precipitant of the chelating agent and a precipitant of the metal from the metal scale, isolating the precipitant of the chelating agent and the precipitant of the metal from the first solution, selectively dissolving the precipitated chelating agent in a second aqueous solution, and removing the precipitated metal from the second solution is disclosed. This is understood to be a multi-step process that would cause longer production downtimes and is not determined to be actually applicable in the field.

[020] Despite the existing state of the art, there are very few commercial compositions available for removing barium sulfate scale; the situation becomes even more complex since most of the Petition 870210119280, dated 12 / 21 / 2021, pp. 127 / 165 9 / 39 Barium sulfate fouling occurs in wells, pipelines, and other equipment associated with oil production and / or oil exploration in offshore or highly regulated jurisdictions, such as the North Sea. Therefore, removing oil-contaminated barium sulfate fouling presents an even more challenging task for oilfield operators. It is highly advantageous for the industry to have a chemical option that meets these stringent environmental and HSE parameters.

[021] Thus, there is still a profound need for compositions and methods capable of removing very difficult-to-remove mixed sulfate scale present in oilfield equipment. SUMMARY OF THE INVENTION

[022] According to one aspect of the present invention, a method for removing mixed sulfate scale is provided, said method comprising: - to provide a liquid composition comprising: or a chelating agent selected from the group consisting of: L5DTPA; Na5DTPA; K5DTPA; Cs5DTPA; Na4EDTA; K4EDTA; TEAH4DTPA; and TBAH5DTPA; or optionally, a scale removal enhancer; a fructan containing a carboxyl group, such as carboxymethyl inulin; and a compound selected from the group consisting of: sodium gluconate; gluconic acid; glucono-delta-lactone; sodium gluconate; calcium gluconate; potassium gluconate; - exposing a surface contaminated with the aforementioned mixed sulfate incrustation to the liquid composition; - Allow sufficient exposure time to remove the aforementioned mixed sulfate encrustation from the contaminated surface. Petition 870210119280, dated 12 / 21 / 2021, pp. 128 / 165 10 / 39

[023] Preferably, the scale removal enhancer is selected from the group consisting of: potassium carbonate; potassium formate; cesium formate; cesium carbonate; and combinations thereof.

[024] Preferably, the carboxyl-containing fructan is a derivative of inulin or another fructan containing 0.3 to 3 carboxyl groups per anhydrofructose unit. Preferably, the inulin derivative or other fructan containing 0.3 to 3 carboxyl groups per anhydrofructose unit contains at least 0.8 carboxyl groups per anhydrofructose unit. More preferably, the carboxyl-containing fructan is carboxymethyl inulin (CMI).

[025] According to one aspect of the present invention, an aqueous composition is provided for use in removing mixed sulfate scale from a surface contaminated therewith, said composition comprising: - a chelating agent and a counter-ion component selected from the group consisting of: LisDTPA; NasDTPA; K5DTPA; CssDTPA; Na4EDTA; K4EDTA; TEAH4DTPA; and TBAH5DTPA; - optionally, a scale removal enhancer; - fructan containing a carboxyl group, such as carboxymethyl inulin; and - a compound selected from the group consisting of: sodium gluconate; gluconic acid; glucono-delta-lactone; sodium gluconate; calcium gluconate; potassium gluconate; and combinations thereof.

[026] Preferably, the scale removal enhancer is selected from the group consisting of: potassium carbonate; potassium formate; cesium formate; cesium carbonate and combinations thereof. Preferably, the scale removal enhancer is present in the composition in an amount ranging from 5 to 20% by weight of the composition. More preferably, the scale removal enhancer is present in the composition in an amount ranging from Petition 870210119280, dated 12 / 21 / 2021, pp. 129 / 165 11 / 39 from 10 to 15% by weight of the composition. Even more preferably, the scale removal enhancer is present in the composition in an amount of approximately 10% by weight of the composition. More preferably, the scale removal enhancer is selected from the group consisting of: K5DTPA; Cs5DTPA; Na4EDTA; and K4EDTA.

[027] According to a preferred embodiment of the present invention, the chelating agent and the counter-ion are present in the composition in an amount ranging from 5 to 40% by weight of the composition. More preferably, the chelating agent and the counter-ion are present in the composition in an amount ranging from 10 to 30% by weight of the composition. Even more preferably, the chelating agent and the counter-ion are present in the composition in an amount ranging from 10 to 20% by weight of the composition.

[028] According to a preferred embodiment of the present invention, the pH of the composition ranges from 10 to 11.

[029] According to a preferred embodiment of the present invention, carboxymethyl inulin is present in the composition in an amount ranging from 0.5 to 15% by weight of the composition.

[030] According to a preferred embodiment of the present invention, sodium gluconate is present in the composition in an amount ranging from 1% to 20% by weight of the composition.

[031] According to one aspect of the present invention, a method is provided for removing anhydrous calcium sulfate scale present on a contaminated surface, said method comprising: - to provide a liquid composition comprising: a chelating agent selected from the group consisting of: Li5DTPA; Na5DTPA; K5DTPA; Cs5DTPA; Na4EDTA; K4EDTA; TEAH4DTPA; and Petition 870210119280, dated 12 / 21 / 2021, pages 130 / 165 12 / 39 TBAHsDTPA; or optionally, a scale removal enhancer; carboxymethyl inulin; and a compound selected from the group consisting of: sodium gluconate; gluconic acid; glucono-delta-lactone; sodium gluconate; calcium gluconate; potassium gluconate; - expose the aforementioned surface contaminated with said mixed sulfate incrustation to the liquid composition; - Allow sufficient exposure time to remove the aforementioned anhydrous calcium sulfate encrustation from the contaminated surface.

[032] Preferably, the composition comprises: a chelating agent selected from the group consisting of: LisDTPA; NasDTPA; K5DTPA; CssDTPA; Na4EDTA; K4EDTA; TEAH4DTPA; and TBAH5DTPA; optionally, a scale removal enhancer; carboxymethyl inulin; and sodium gluconate. Preferably, the scale removal enhancer is selected from the group consisting of: potassium carbonate; potassium formate; cesium formate; cesium carbonate and combinations thereof.

[033] According to one aspect of the present invention, a method is provided for solubilizing barium sulfate into particles smaller than 1 micron in size, said method comprising: - To provide a surface contaminated with a fouling containing barium sulfate; - to provide a liquid composition comprising: or a chelating agent selected from the group consisting of: Li5DTPA; Na5DTPA; K5DTPA; Cs5DTPA; Na4EDTA; K4EDTA; TEAH4DTPA; and TBAH5DTPA; or optionally, a scale removal enhancer; Petition 870210119280, dated 12 / 21 / 2021, pp. 131 / 165 13 / 39 or a carboxyl-containing fructan, such as carboxymethyl inulin; and - expose the aforementioned surface contaminated with said barium sulfate encrustation to the liquid composition; - Allow sufficient exposure time to remove barium sulfate scale particles from the contaminated surface; wherein the aforementioned barium sulfate particles have complexed with carboxymethyl inulin and have a particle size smaller than 1 micron; - allowing the pH of the solution to drop from a pH ranging from 10 to 11 to a pH ranging from 7 to 8, thus causing a reprecipitation of the solubilized barium sulfate to a particle size smaller than 1 micron.

[034] Preferably, the scale removal enhancer is selected from the group consisting of: potassium carbonate; potassium formate; CS2COOH; CS2CO3 and combinations thereof. Preferably, the carboxyl-containing fructan is a derivative of inulin or another fructan containing 0.3 to 3 carboxyl groups per anhydrofructose unit. According to a preferred embodiment of the present invention, the inulin derivative or other fructan containing 0.3 to 3 carboxyl groups per anhydrofructose unit contains at least 0.8 carboxyl groups per anhydrofructose unit. More preferably, the carboxyl-containing fructan is carboxymethyl inulin (CMI).

[035] According to a first aspect of the present invention, an aqueous composition is provided for use in removing mixed sulfate scale from a surface contaminated therewith, said composition comprising: - a chelating agent and a counter-ion component selected from the group consisting of: L15DTPA; NasDTPA; K5DTPA; CssDTPA; N34EDTA; K4EDTA; TEAH4DTPA; and TBAH5DTPA; Petition 870210119280, dated 12 / 21 / 2021, pp. 132 / 165 14 / 39 - a scale removal enhancer; - sodium gluconate or similar; and - carboxymethyl inulin.

[036] According to another aspect of the present invention, a method for removing mixed sulfate scale is provided, said method comprising the steps of: - to provide a liquid composition comprising: a chelating agent selected from the group consisting of: LisDTPA; NasDTPA; KsDTPA; CssDTPA; Na4EDTA; K4EDTA; TEAH4DTPA; and TBAHsDTPA; a scale removal enhancer; Sodium gluconate or similar substances; and carboxymethyl inulin; - exposing a surface contaminated with mixed sulfate encrustation to the liquid composition; Allow sufficient exposure time to remove the mixed sulfate fouling from the contaminated surface.

[037] According to another aspect of the present invention, an aqueous composition is provided for use in removing mixed sulfate scale from a surface contaminated therewith, said composition comprising: - a chelating agent and a counter-ion component selected from the group consisting of: LisDTPA; NasDTPA; K5DTPA; CssDTPA; Na4EDTA; K4EDTA; TEAH4DTPA; and TBAHsDTPA; - a scale removal enhancer; - sodium gluconate or similar; and - carboxymethyl inulin.

[038] Preferably, the scale removal enhancer is Petition 870210119280, dated 12 / 21 / 2021, pages 133 / 165 15 / 39 selected from the group consisting of: potassium carbonate; potassium formate; cesium formate; cesium carbonate and combinations thereof. Preferably, the scale removal enhancer is present in the composition in an amount ranging from 5 to 20% by weight of the composition. More preferably, from 10 to 15% by weight of the composition. Also preferably, the scale removal enhancer is present in the composition in an amount of approximately 10% by weight of the composition.

[039] Preferably, the chelating agent and the counter-ion are present in the composition in an amount ranging from 5 to 40% by weight of the composition. More preferably, from 10 to 30% by weight of the composition. Also preferably, the chelating agent and the counter-ion are present in the composition in an amount ranging from 10 to 20% by weight of the composition.

[040] Preferably, the pH of the composition ranges from 10 to 11.5. More preferably, the composition has a pH ranging from 10 to 11. BRIEF DESCRIPTION OF THE FIGURE

[041] The invention can be more fully understood by considering the following description of various embodiments of the invention in connection with the accompanying figures, in which: Figure 1 is a graphical representation of the dissolution performance of a composition according to a preferred embodiment of the present invention compared with various other commercially available sulfate scale solvents over a 24-hour period at 60°C. DETAILED DESCRIPTION OF PREFERRED OPTIONS

[042] By adding potassium carbonate to K5DTPA, the same solubility numbers can be obtained at a lower pH. Instead of 13.5, a pH Petition 870210119280, dated 12 / 21 / 2021, pp. 134 / 165 16 / 39 of 11 was sufficient to obtain comparable solubility numbers. This represents a considerable difference compared to typical products available on the market. This allows an operator to conduct scale removal operations at a lower pH and therefore increases safety for personnel handling the remover or anyone in the surrounding area, as well as environmental risks and cleanup costs in the event of an uncontrolled release.

[043] According to a preferred embodiment of the present invention, the mixed sulfate scale removal composition provides greatly improved scale dissolution rates. This, in turn, reduces well downtime where scale is being removed and the associated costs. It also reduces the cost of this treatment by limiting treatment time and allowing production to resume.

[044] As shown below, the compositions tested for removing uncontaminated barium sulfate scale allow for its removal at a much lower pH than has been practiced until now. In fact, such a composition can effectively remove barium scale under conditions where the pH is 11, instead of other scale removal compositions that require conditions where the pH is 13 or higher. Consequently, a preferred composition according to the present invention can remove, at pH = 10, up to 30 kg / m3 of uncontaminated BaSO4 scale. When using the term uncontaminated BaSO4 scale, it should be understood by those skilled in the art that what is meant is that the barium sulfate scale is not contaminated by a petroleum product or a petroleum-based product.

[045] According to a preferred embodiment of the present invention, a composition for removing mixed sulfate scale allows the removal Petition 870210119280, dated 12 / 21 / 2021, pages 135 / 165 17 / 39 of the same with a superior dissolving capacity. This, in turn, allows for a reduction in the volume of scale remover needed. This also lowers transportation costs and many other related items resulting from the use of smaller volumes of scale remover.

[046] According to a preferred embodiment of the present invention, the additional sulfate scale solvent comprises sodium gluconate or the like. Compounds with a gluconate component or moiety are considered to belong to the latter category, but do not comprise the entire category, as other sugars are also considered to be within this description. Preferably, compounds with a gluconate component or moiety include, but are not limited to: gluconic acid (CAS# 526-95-4); glucono-delta-lactone (CAS# 90-80-2); sodium gluconate (CAS# 527-07-1); calcium gluconate (CAS# 299-28-51 1801624-5); potassium gluconate (CAS# 299-27-4). Potassium gluconate is preferred.

[047] According to a preferred embodiment of the present invention, carboxyl-containing fructans are understood to be a derivative of inulin or another fructan containing 0.3 to 3 carboxyl groups per anhydrofructose unit. In particular, the derivative contains at least 0.8 carboxyl groups per anhydrofructose unit. Preferably, the carboxyl groups may be present in the form of carboxyalkyl groups, such as carboxymethyl, carboxyethyl, dicarboxymethyl, or carboxyethoxycarbonyl groups. According to a preferred embodiment of the present invention, mixed carboxyfructans may also be used. Preferably, the number of carboxymethyl groups is greater than the number of other carboxyl groups. The most preferred of the carboxyl-containing fructans is carboxymethyl inulin (CMI). Carboxymethyl inulin (CMI) with a degree of substitution of 0.15 to 2.5 is disclosed Petition 870210119280, dated 12 / 21 / 2021, pages 136 / 165 18 / 39 in WO 95 / 15984. Mixed carboxyl derivatives, inulin may have been first carboxymethylated and then oxidized or vice versa. According to a preferred embodiment of the present invention, the carboxyl-containing fructan has an average chain length (= degree of polymerization, DP) ranging from 3 to 1000, but preferably, the average chain length ranges from 6 to 60 monosaccharide units. Absolute solubility of barium sulfate scale.

[048] The inventors previously noted that chelating agents, such as EDTA (ethylenediaminetetraacetic acid) or DTPA (diethylenetriaminepentaacetic acid), and the ability to dissolve uncontaminated barium sulfate depend substantially on the size and ionic strength of the counterion.

[049] In Tables 1 and 2 (absolute solubility test) the absolute (or maximum) solubility of uncontaminated substances increases with the size of the lithium counterion for cesium. TEAH (tetraethylammonium hydroxide) and TBAH (tetrabutylammonium hydroxide) as organic bases (counterions) are showing the same trend. The information indicates that the size of the TBAH cation (including the hydrate layer) is comparable to potassium.

[050] The solubility numbers for both were considered very similar. In order to adequately compare kg / solubility quantitatively, the BaSO4:chelating agent ratio was calculated in g / mol and the Ba2+:chelating agent ratio was calculated in mol / mol. The mol:mol ratio indicates the number of chelating agent molecules needed to dissolve one Ba2+ ion (complex). The highest ratio found was almost 0.5, meaning that on average there should be 2 DTPA molecules to dissolve 1 Ba2+ ion, but it could be much less.

[051] The tests performed indicated that, in addition to the nature of Petition 870210119280, dated 12 / 21 / 2021, pp. 137 / 165 19 / 39 counter-ion, an excess of the counter-ion also improves solubility. K5DTPA was tested in conjunction with KCl, K2CO3 and KOOCH (potassium formate). It appears that the counter-ion also plays a large role as K2CO3 (with the larger anion) was much more effective than KCl (with a small anion). Table 1 - Absolute solubility of uncontaminated barium sulfate scale (when using a 40% solution of the scale removal composition) PH 40 wt% soluble BaSO4 (kg / m3) BaSO4 (g / mol) Ba2+ (mol / mol) Li5DTPA 2 Na5DTPA 13.01 17 20.24 0.088 K5DTPA 13.25 46 62.16 0.266 K5DTPA + 10 wt% K2CO3 13.21 38 51.35 0.22 Cs5DTPA 13.4 52 72.2 0.309 Na4EDTA 13.11 9 7.89 0.034 K4EDTA 13.32 31 32.98 0.141 TEAH4DTPA 13.1 14 43.75 0.187 TBAH5DTPA 13.33 18 64.28 0.275 Table 2 - Absolute solubility of uncontaminated barium sulfate scale (when using a 20% solution of the scale removal composition) at 60°C Petition 870210119280, dated 12 / 21 / 2021, pages 138 / 165 20 / 39 PH 20 wt% soluble BaSÜ4 (kg / m3) BaSCh (g / mol) Ba2+ (mol / mol) K5DTPA 13.19 27 72.97 0.313 K5DTPA + 5 wt% K2CO3 13.32 41 110.81 0.475 K5DTPA + 5 wt% K2CO3 11.25 40 108.11 0.463 K5DTPA + 5 wt% K2CO3 10 33 89.19 0.3821 Cs5DTPA + 5 wt% CsCO3 35 Cs5DTPA + 10 wt% CSCO3 35 Cs5DTPA + 10 wt% HCOOCs 30 TEAH4DTPA + 10% by weight of K2CO3 21 TBAH5DTPA + 10% by weight of K2CO3 25

[052] Furthermore, the composition of K5DTPA (at 40%) was determined to dissolve 30 kg / m3 of FeS for a total g / mol of 40.54.

[053] Preferably, the dissolution of uncontaminated barium sulfate in an amount above 20 kg / m3. More preferably, the dissolution of barium sulfate above 30 kg / m3 is desired. Barium Scale Dissolution Rate Petition 870210119280, dated 12 / 21 / 2021, pp. 139 / 165 21 / 39

[054] A second set of tests was carried out to study the dissolution rate of uncontaminated barium sulfate scale. In order to determine the rate, a relatively small amount of BaSÜ4 (0.25 g - this equates to 10 kg / m3) was used and the time was measured until the solution became clear. Large differences were observed. The best results involved the combination of KsDTPA with K2CO3. This combination provided a dissolution time almost 4 times faster than K5DTPA alone.

[055] The dissolution rate of the compositions according to the preferred embodiment of the present invention was tested and studied. Table 3 summarizes the test findings. The experiment involved dissolving 0.25 g of BaSÜ4 in a volume of 50 ml of fluid at 60 °C under gentle stirring with a magnetic stir bar. Table 3 - Dissolution rate of uncontaminated barium sulfate scale Fluid Time PH KsDTPA (40%) lh44 min 13.26 KsDTPA (40%) + 10% TBAH lh38 min 13.4 KsDTPA (40%) + 20% TBAH lh21 min 13.43 KsDTPA (40%) + 30% TBAH lh20 min 13.49 KsDTPA (40%) + 10 wt% KCI lh24 min 13.27 KsDTPA (40%) + 10% K2CO3 30 min 13.22 KsDTPA (20%) + 5% K2CO3 22-23 min 10.5 to 11

[056] This test indicates that both the extent of barium scale dissolution and the rate at which it is dissolved represent marked improvements compared to known compositions.

[057] Preferably, the scale removal enhancer is Petition 870210119280, dated 12 / 21 / 2021, pages 140 / 165 22 / 39 selected from the group consisting of: K2CO3; KOOCH; CsCOa; CsCOOH and combinations thereof. Preferably, the scale removal enhancer is K2CO3. Also preferably, the scale removal enhancer is present in an amount ranging from 5 to 30% by weight of the scale removal composition. More preferably from 10 to 20% by weight and even more preferably, the scale removal enhancer would be present in an amount of approximately 10% by weight. Impact of Temperature

[058] The dissolution rate of a barium scale dissolving composition was tested and studied under different temperature conditions in uncontaminated barium sulfate scale. Table 4 summarizes the test findings. The experiment involved dissolving 0.25 g of BaSO4 in a volume of 50 ml of fluid at various temperatures under gentle stirring with a magnetic stir bar. The tested composition comprised a 20 wt% K5DTPA and 5 wt% K2CO3 solution. Table 4 - Impact of Temperature on Barium Sulfate Dissolution Temperature in °C (°F) Time (minutes) 25 (77) 225 40 (104) 50 60 (140) 22 80 (176) 3.5 90 (194) 1.5 Laboratory test for dissolving scale.

[059] The sample selected for the solubility test sources from an oilfield tubular containing sulfate scale crystals originally used for demonstration purposes. Scale crystals of Petition 870210119280, dated 12 / 21 / 2021, pages 141 / 165 23 / 39 uncontaminated barium sulfate samples were removed from the tubular sample for use in the solubility test. 200 cc (200 mL) of composition (20% by weight K5DTPA and 5% by weight K2CO3) was used. A weighted portion of the oilfield sulfate fouling sample was submerged in 200 cc (200 mL) of each descaling composition. A small magnetic stirrer was added to create a minimal vortex, creating a small fluid movement without rigorously agitating the fluid. The fluid was heated to 70° Celsius. Results

[060] 25.165 grams of uncontaminated oilfield sulfate scale were weighed and added to the fluid. The stirrer and heater were turned on. After 1 hour, a slight discoloration of the fluid was observed. After 4 hours at the temperature, when no continuous visual reduction of scale was observed, the fluid was filtered and the filter rinsed with water, dried, and weighed back. The maximum scale solubility was achieved and subsequently calculated.

[061] The composition of the base barium scale dissolver (used in subsequent tests and referred to as BSD base) comprises a 20% by weight solution of K5DTPA and 5% by weight of K2CO3. The BSD base was able to dissolve 52.97 grams per liter of scale at 70°C. The test was also performed with a commercially available product (Barsol NS™), an alkali / EDTA-based product, and an EDTA-based product. The Barsol NS™ product was able to dissolve 24.19 grams per liter, while EDTA alone dissolved only about 6 grams per liter. Under identical conditions, the BSD base demonstrated more than twice the performance of Barsol NS™.

[062] According to a preferred embodiment of the present invention, a one-step process is provided for removing mixed sulfate scale within a well, said process comprising: Petition 870210119280, dated 12 / 21 / 2021, pp. 142 / 165 24 / 39 - to provide a liquid composition comprising: or a chelating agent selected from the group consisting of: LÍ5DTPA; Na5DTPA; K5DTPA; K5DTPA; Cs5DTPA; Na4EDTA; K4EDTA; TEAH4DTPA; and TBAH5DTPA; or a fructan containing a carboxyl group or a salt thereof, such as carboxymethyl inulin; and a compound selected from the group consisting of: sodium gluconate; gluconic acid; glucono-delta-lactone; sodium gluconate; calcium gluconate; potassium gluconate; - exposing a surface contaminated with mixed sulfate encrustation to the liquid composition; - Allow sufficient exposure time to remove some or all of the mixed sulfate scale from the contaminated surface. A person skilled in the art will understand that what is meant by one step is that there is a single treatment step in the process (or method) for removing mixed sulfate scale.

[063] When the surface contaminated with mixed sulfate fouling is deep underground or in a hard-to-reach pipe or tubing, the exposure consists of circulating the liquid composition through the pipes or tubing until it has been established that the fouling has been removed beyond a predetermined desired point. Therefore, in some cases, it is quite possible that not all of the fouling present will be removed, but the amount removed is sufficient to restart operations and provide the desired productivity and / or circulation through the affected piping / tubing. The liquid composition may also be heated in order to improve fouling removal and the speed at which removal is effected.

[064] According to another preferred embodiment of the present invention, the mixed sulfate scale treatment method in which the fluid is Petition 870210119280, dated 12 / 21 / 2021, pages 143 / 165 25 / 39 "stained," that is, placed in a pipe / tank / tubing / equipment in an immersion operation. This may, in some cases, be slightly less efficient than circulating or agitating the fluid due to the reaction nature of the fluid surface, but it is used in some cases to remove sufficient fouling to operate tools, pull out stuck pipes or blocked flow control equipment, etc., for example.

[065] Sulfate scale that is commonly found inside wells includes calcium sulfate, strontium sulfate, and barium sulfate. Until now, it was believed that an effective barium sulfate scale solvent was the missing link to removing very stubborn scale. It has been surprisingly discovered that depending on the type of calcium sulfate present in the mixed sulfate scale, the scale can be more or less easy to remove. The most common form of calcium sulfate is the dihydrate. Upon exposure to pressure and temperature, the dihydrate converts to hemihydrate and finally to the anhydrous form. Anhydrous calcium sulfate presents substantially more difficult scale removal than its dihydrate counterpart.

[066] Tests were conducted to evaluate the advantage of a composition according to a preferred embodiment compared to a typical sulfate fouling mixture found during petroleum industry operations. As calcium sulfate is by far the most common fouling component, these tests are believed to be quite representative of the actual mixture. The solubility of the fouling mixture was evaluated in relation to the BSD base composition and two preferred embodiments of the present invention. The results are listed in Table 5 below. Table 5 - Solubility of mixed sulfate scale comprising Petition 870210119280, dated 12 / 21 / 2021, pages 144 / 165 26 / 39 calcium sulfate, strontium sulfate and barium sulfate at 60°C Sodium Gluconate Solution (% by weight) 25 to 30 UP (vol%) Scale weight of scale (g) weight of filter (g) weight of filter and product (g) Total Solubility kg / m3 100% BSD base 5 1 80% CaSO4 2H2O SrSO4 at 1% BaSO4 at 19% 10.0003 0.2764 3.1851 70.916 100% BSD base 10 1 80% CaSO4 2H2O SrSO4 at 1% BaSO4 at 19% 10.0006 0.2872 3.1888 70.990 100% BSD base \ \ 80% CaSO4 2H2O SrSO4 at 1% BaSO4 at 19% 10.0017 0.2904 3.6249 66.672 80% BSD base, 20% H2O 10 1 80% CaSO4 2H2O SrSO4 at 1% BaSO4 at 19% 10.0048 0.2829 3.9884 62.993

[067] NB: 100% BSD base refers to an undiluted solution of the composition as set forth above. A diluted BSD base solution is referred to as the residual stock concentration amount after dilution. 25-30 UP refers to a commercial composition of sodium carboxymethyl inulin with a NaCMI content of 30-32% by weight.

[068] Tests were carried out in order to evaluate the advantage of a composition according to a preferred embodiment in relation to calcium scaling in dihydrate and anhydrous forms. As calcium sulfate is the most common scaling component in a mixture Petition 870210119280, dated 12 / 21 / 2021, pages 145 / 165 27 / 39 of sulfate incrustations, it was believed to be important to evaluate the effectiveness of the known descaling agent against two preferred embodiments of the present invention. It is known that although calcium sulfate dihydrate and anhydrous calcium sulfate have very different properties, the dihydrate form is the most common and the first to be formed during deposition. It is also known that the dihydrate will convert to more stable forms after exposure to heat and pressure. The most stable form of calcium sulfate is the anhydrous form. The results of the experiments are listed in Table 6 below. Table 6 - Solubility of calcium sulfate (anhydrous) and calcium sulfate (dihydrate) Sodium Gluconate Solution (% by weight) 25-30 UP (vol%) Scale weight of scale (g) filter weight (g) filter and product weight (g) Total Solubility kg / m3 100% BSD Base 5 1 100% CaSO4 2H2O 10.0001 0.2773 3.1126 71.648 100% BSD Base 10 1 100% CaSO4 2H2O 10.0021 0.2653 2.7927 74.747 100% BSD Base \ \ 100% CaSO4 2H2O 10.0009 0.2647 3.0829 71.827 100% BSD Base 5 1 100% CaSO4 (anhydrous) 10.0027 0.2873 5.8483 44.417 100% BSD Base 10 1 100% CaSO4 (anhydrous) 10.0007 0.2774 5.4992 47.789 Petition 870210119280, dated 12 / 21 / 2021, pages 146 / 165 28 / 39 Sodium Gluconate Solution (% by weight) 25-30 UP (vol%) Scale weight of scale (g) weight of filter (g) weight of filter and product (g) Total Solubility kg / m3 100% BSD base / 100% CaSO4 (anhydrous) 10.0058 0.2774 7.9699 23.133 100% BSD base / 100% CaSO4 (anhydrous) 10.0017 0.2662 7.1513 31.166

[069] The results in Table 6 indicate that the type of calcium scale (anhydrous vs dihydrate) has a substantial and marked impact on the dissolution efficiency of the scale solvents tested.

[070] The use of sodium gluconate is an effective component in removing minor cations present in a mixed sulfate scale. Varying the amount of sodium gluconate (or similar) can have a direct impact on the effectiveness of the composition according to a preferred embodiment of the present invention, as it provides increased dissolving power of the mixed sulfate scale. Sodium gluconate is a representative compound of sugars that have the same properties, including but not limited to gluconate or similar categorization, and is quite effective in the presence of scale containing transition metal cations (such as, but not limited to, iron, manganese, zinc, tin) and post-transition metal cations (such as, but not limited to, aluminum, lead), since these cations typically have a smaller ion radius.According to a preferred embodiment, gluconate or similar substances may be present in a concentration ranging from 0.1% by weight to 20% by weight of the total weight of the composition, more preferably from 1% to 20% by weight. Petition 870210119280, dated 12 / 21 / 2021, pages 147 / 165 29 / 39 According to another preferred embodiment, gluconate or similar may be present in a concentration ranging from 1% by weight to 10% by weight of the total weight of the composition, more preferably ranging from 1% to 5% by weight, even more preferably ranging from 1% to 3% by weight.

[071] Although the presence of sodium gluconate or similar is preferable in some cases, the presence of such a compound has its limitations. For operations carried out at temperatures of 150°C or more, gluconates tend to be less stable and degradable and, therefore, would not be desirable for such applications. For this reason, their use in high-temperature applications has limitations. Therefore, in situations where the operating temperature encountered by the compositions used is 150°C or higher, a preferred composition of the present invention will not necessarily require the presence of a gluconate (or similar) compound.Thus, a preferred embodiment of the present invention to be used for the removal of mixed sulfate scale at high temperatures (i.e., above 150°C) will comprise: a chelating agent selected from the group consisting of: LisDTPA; NasDTPA; KsDTPA; CssDTPA; Na4EDTA; K4EDTA; TEAH4DTPA; and TBAH5DTPA; optionally, a scale removal enhancer; a carboxyl-containing fructan, such as carboxymethyl inulin. Thus, a preferred embodiment of the present invention to be used for the removal of barium sulfate scale will predominantly comprise: a chelating agent selected from the group consisting of: Li5DTPA; NasDTPA; KsDTPA; CssDTPA; Na4EDTA; K4EDTA; TEAH4DTPA; and TBAH5DTPA; optionally, a scale removal enhancer; a fructan containing a carboxyl group, such as carboxymethyl inulin.

[072] In addition, the compositions according to the modalities Petition 870210119280, dated 12 / 21 / 2021, pp. 148 / 165 30 / 39 preferred embodiments of the present invention are environmentally safer than many other solvents. This represents a major advantage over any known chemical-based methods of mixed sulfate fouling. Another advantage of the compositions according to the preferred embodiments of the present invention includes the dissolution rate, which is considerably faster than any known commercial compositions. Another advantage of the preferred compositions according to the present invention is that they can be employed in wells according to a one-step process and are therefore highly desirable for operators dealing with mixed sulfate fouling problems on a regular basis, such as in the North Sea.

[073] According to another aspect of the present invention, a method is provided for solubilizing barium sulfate into particles smaller than 1 micron in size, said method comprising: - To provide a surface contaminated with a fouling containing barium sulfate; - to provide a liquid composition comprising: or a chelating agent selected from the group consisting of: L5DTPA; Na5DTPA; K5DTPA; Cs5DTPA; Na4EDTA; K4EDTA; TEAH4DTPA; and TBAH5DTPA; or optionally, a scale removal enhancer; a fructan containing a carboxyl group, such as carboxymethyl inulin; and a compound selected from the group consisting of: sodium gluconate; gluconic acid; glucono-delta-lactone; sodium gluconate; calcium gluconate; potassium gluconate; - expose the aforementioned surface contaminated with said barium sulfate encrustation to the liquid composition; Petition 870210119280, dated 12 / 21 / 2021, pages 149 / 165 31 / 39 - allow sufficient exposure time to remove barium sulfate scale particles from the contaminated surface; wherein said barium sulfate particles are complexed with carboxymethyl inulin and have a particle size smaller than 1 micron; - allowing the pH of the solution to drop from a pH ranging from 10 to 11 to a pH ranging from 7 to 8, thus causing a reprecipitation of the solubilized barium sulfate to a particle size smaller than 1 micron (due to the low solubility product of barium sulfate at low pH (7 to 8)).

[074] The interaction of CMI with dissolved barium sulfate is not completely clear, but it appears that CMI interacts / interferes with the surface of the barium sulfate crystal in order to prevent / minimize / inhibit crystal growth and thus maintain the barium sulfate at a particle size smaller than 1 micron. The hypothesis is that the CMI-barium sulfate complex creates a kind of nanoparticle that, due to its small size, is capable of undergoing Brownian motion and therefore never fully fixes (i.e., does not reprecipitate, at least during the duration period (up to 7 days) that the tests in the present invention seem to support). According to a preferred embodiment, the carboxyl-containing fructan may be present in a concentration ranging from 0.01% by weight to 15% by weight of the composition, more preferably from 0.5% by weight to 15% by weight.According to another more preferred embodiment, the carboxyl-containing fructan may be present in a concentration ranging from 0.01% by weight to 1% by weight. According to a more preferred embodiment, the carboxyl-containing fructan may be present in a concentration ranging from 0.1% by weight to 0.5% by weight. According to yet another preferred embodiment, the carboxyl-containing fructan may be present in... Petition 870210119280, dated 12 / 21 / 2021, pages 150 / 165 32 / 39 a concentration ranging from 0.01% by weight to 0.4% by weight, more preferably from 0.1% by weight to 0.35% by weight, even more preferably from 0.25% by weight to 0.32% by weight.

[075] Once a composition according to a preferred embodiment of the present invention is exposed to a surface contaminated with sulfate fouling, the fouling is removed over a period of time, but the dissolved fouling is at risk of reprecipitating after exposure to formation water. Since the fouling solvent has a pH that preferably ranges from 11 to 11.5, barium sulfate and other fouling will dissolve, but as the dissolved fouling is increasingly exposed to formation water, which typically has a pH of about 6 to 7, the pH of the water surrounding the dissolved fouling will decrease. Reprecipitation of barium sulfate around pH -8 is inevitable, as the Ksp of barium sulfate is very low at that pH.This is one of the main reasons why the aforementioned preferred composition is desirable, as it will prevent the reprecipitation of barium sulfate and thus allow fluids to flow after scale removal. Comparative test of a preferred scale remover of the present invention

[076] In order to evaluate the efficiency of a preferred scale remover of the present invention, it was compared with three other commercially available barium sulfate scale removers at 50°C and 90°C. The test results are found in Tables 7 and 8 below. Compositions A, B, and C are commercially available barium sulfate scale removers. Composition D is a preferred scale remover of the present invention comprising a BSD base + 10% by weight sodium gluconate and 1% by volume CMI (approximately 30 to 32% by weight). Petition 870210119280, dated 12 / 21 / 2021, pages 151 / 165 33 / 39 Table 7 - Amount of barium sulfate scale dissolved after 24 hours at a temperature of 50°C Composition of dissolved barium sulfate scale (in % by weight) A 57 B 16 C 72 D 84 Table 8 - Amount of barium sulfate scale dissolved after hours at a temperature of 90°C Composition of dissolved barium sulfate scale (in % by weight) A 77 B 22 C 79 D 87

[077] In both experiments, the composition according to a preferred embodiment of the present invention (Composition D) performed better than all three commercially available barium sulfate scale removers. Another not insignificant observation is that all three commercially available barium sulfate scale removers (A, B, and C) have a pH above 12 (some close to 13), while Composition D has a pH ranging between 11 and 11.5. This pH difference is significant for operators and anyone handling this type of caustic product, and therefore it is highly desirable to have a product with a pH as close to neutral as possible. Comparative test with other sulfate scale inhibitors Petition 870210119280, dated 12 / 21 / 2021, pages 152 / 165 34 / 39

[078] In another round of tests, several commercially available barium sulfate scale dissolvers (compositions A, B, D, E, F, I, J, K, L, N and P) were tested for mixed sulfate scale dissolution efficiency (at 60°C) compared with a composition according to a preferred embodiment of the present invention (Composition Q comprising BSD base + CMI (1% vol. to approximately 30-32% by weight)) + sodium gluconate (10% by weight)).

[079] Composition Q outperformed all commercially available mixed sulfate scale solvents. The scale composition was (main elements only): barium (44% by weight); calcium (4.4%); strontium (8.4% by weight), with the remaining scale composition consisting mainly of anions and organic compounds. Scale dissolution for each composition was measured 2 hours, 4 hours, 8 hours, and 24 hours after the start of treatment. Figure 1 is a graphical representation of the performance of each composition over a 24-hour period at 60°C. The time axis (x-axis) is not plotted to scale because the large number of compositions tested would not be easily distinguishable in the first three measurements (2, 4, and 8 hours), and the graphical representation provided in Figure 1 allows for a better assessment of the efficiency of each composition over time.The composition according to a preferred embodiment of the present invention was by far the most effective scale dissolver in terms of total scale dissolution (measured in ppm). Similarly, unlike Compositions A and B, which began to reprecipitate after 8 hours, Composition Q maintained the scale dissolution and managed to dissolve even more scale after the 8-hour measurement. Laboratory Tests for Barium Sulfate Reprecipitation

[080] Several experiments were conducted to evaluate the ability of Petition 870210119280, dated 12 / 21 / 2021, pages 153 / 165 35 / 39 certain compositions (BSD base, BSD base + CMI (1% vol. (in approximately 30 to 32% by weight)) and BSD base + sodium gluconate (10% by weight)) to keep the barium sulfate dissolved in solution. Reprecipitation experiment #1

[081] Three mixtures containing the composition of BSD Base (BSD Base, BSD Base + CMI and BSD Base + sodium gluconate) were prepared with added barium sulfate and were observed as reprecipitation occurred in each pH range from 11 to 7 with the addition of 1 N hydrochloric acid. 61.66% of the barium sulfate precipitate was filtered from the BSD Base + sodium gluconate solution and 12.94% of the barium sulfate precipitate was filtered from the BSD Base + CMI solution, with the remainder suspended in the solution. Procedure:

[082] To observe the reprecipitation of barium sulfate, 2.0000 g of barium sulfate were dissolved in 100 mL of each BSD Base composition (BSD Base, BSD Base + CMI, and BSD Base + sodium gluconate) at 60°C for 4 hours on a stirrer plate heated to 190 rpm. The solutions were then cooled to room temperature, transferred to new beakers, and then placed on stirrer plates with stir bars. A pH probe was placed in the solution to monitor the pH of the solution as 1 N hydrochloric acid (HCl) was added dropwise, with a photo taken at each pH interval.

[083] After 3 days, the reprecipitated solutions were filtered through P8 filter paper and then P2, and then re-examined after 7 days. Results and Observations:

[084] Using P8 and P2 filter papers, 61.66% of the barium sulfate precipitate was filtered from the BSD base + sodium gluconate solution. For the BSD base + CMI solution, 12.94% of the barium sulfate precipitate was filtered. Petition 870210119280, dated 12 / 21 / 2021, pages 154 / 165 36 / 39 while the remaining barium sulfate remained suspended in the solution for a period of at least 7 days. Laboratory Tests of Barium Sulfate Reprecipitation - Experiment #2

[085] BSD + CMI base test solutions were heat-treated in a Teflon-lined high-pressure / high-temperature cell at 150°C (302°F), 400 psi (2,758 MPa), for 6 hours and 24 hours to simulate bottom-hole conditions. Barium sulfate was then dissolved in the heat-treated BSD + CMI base to ensure unaltered functionality. Subsequently, the pH was gradually reduced to 7 with the addition of 1 N hydrochloric acid. This was performed to determine the pH at which reprecipitation occurs and whether the specific additive in the BSD + CMI base is still functional after heat treatment to suppress precipitation formation at a lower pH, and whether the size of the formed barium sulfate crystal is still altered to smaller particle sizes by the BSD + CMI base. The different solutions with reprecipitation were filtered through filters with different pore sizes.It was determined that a minimum of 94% by weight of the reprecipitated barium sulfate from both BSD + CMI Base test solutions (6 hours and 24 hours at 150°C) is less than 1 μm. The remaining crystalline material remains suspended in the solution for an extended period (7 days) without further sedimentation. Procedure: BSD + CMI base solutions were prepared and subjected to heat treatment in Teflon-lined high-pressure / high-temperature cells at 150°C, 400 psi (2,758 MPa), for 6 hours and 24 hours. After heat treatment, each cell was depressurized and the solution was allowed to cool to room temperature. No visual decomposition of the additive package was observed in the BSD + CMI base. Petition 870210119280, dated 12 / 21 / 2021, pages 155 / 165 37 / 39

[086] To determine the functionality of the thermally treated BSD + CMI Base, 2.0 g of barium sulfate were dissolved in 100 mL of the two BSD + CMI Base mixtures (thermally treated for 6 hours at 150°C and 24 hours at 150°C) at 60°C for 4 hours on a stirrer plate heated to 190 rpm. The solubility capacity was not altered compared to the non-thermally treated BSD + CMI Base. The solutions were then cooled to room temperature. The solutions were transferred to a beaker with a stirring bar and placed on a stirrer plate. A pH probe was placed in the solution to monitor the pH of the solution as 1 N hydrochloric acid (HCl) was added (drop by drop). A photo was taken at each pH interval. The first slight reprecipitation of barium sulfate occurs at a pH of 8. Complete reprecipitation occurred at a pH of 7. The test solutions were stored at room temperature for 3 days.

[087] After 3 days, the reprecipitated barium sulfate from the BSD Base + CMI solutions was filtered through P8 and then through P2 filter paper and left to stand for an additional 7 days. Results:

[088] Using filter paper P8 and P2, 97.4% by weight of the barium sulfate reprecipitate passed through both filters from the BSD Base + CMI solution (24 hours at 150°C) and 94.3% by weight of the barium sulfate reprecipitate passed through both filters from the BSD Base + CMI solution (6 hours at 150°C). The remaining material remained suspended in the solution. Based on these results and observations, it is assumed that most of the crystalline material formed is smaller than 1 pm. This is a direct effect of the additive package used in the BSD Base + CMI. Laboratory Tests of Barium Sulfate Reprecipitation - Experiment #3 Petition 870210119280, dated 12 / 21 / 2021, pages 156 / 165 38 / 39

[089] To observe the reprecipitation of barium sulfate, laboratory tests were carried out to compare three compositions (BSD base, BSD base + CMI and BSD base + sodium gluconate) were prepared with barium sulfate to observe how reprecipitation occurs in each pH range from 11 to 7 with the addition of 1 N hydrochloric acid. Procedure: To observe the reprecipitation of barium sulfate, 2.0000 g of barium sulfate were dissolved in 100 mL of the three BSD compositions tested (BSD base, BSD base + CMI, and BSD base + sodium gluconate) at 60 °C for 4 hours on a stirrer plate heated to 190 rpm. The solutions were then cooled to room temperature. The solutions were transferred to a beaker with a stir bar and placed on a stirrer plate. A pH probe was placed in the solution to monitor the pH of the solution as 1 N hydrochloric acid (HCl) was added (drop by drop). A photograph was taken at each pH interval.

[090] After 3 days, the reprecipitated solutions were filtered through P8 filter paper and then through P2 filter paper and left to stand for 7 days for further observation. Fischer Scientific P8 filter papers have a porosity such that particles larger than 20 microns are filtered out. P2 filter paper (from Fischer Scientific) has a porosity such that particles as small as 1 micron are filtered out of the solution. Observations: The barium sulfate precipitate was filtered from the solution containing only BSD Base; however, the precipitate in the solutions containing BSD Base + 1% by volume of CMI and BSD Base + sodium gluconate could not be filtered and remained suspended in the solution even after 7 days.

[091] Although the prior invention has been described in some detail for the sake of clarity and understanding, it will be appreciated by those skilled in the art in the relevant techniques once they have become familiar with this invention, Petition 870210119280, dated 12 / 21 / 2021, pp. 157 / 165 39 / 39 that various changes in form and details can be made without departing from the true scope of the invention in the appended claims.

Claims

CLAIMS 1. Method for removing mixed sulfate scale, characterized in that it comprises: - providing a liquid composition comprising: a chelating agent selected from the group consisting of: pentalithium salt of diethylenetriaminepentaacetic acid (LÍ5DTPA); pentasodium salt of diethylenetriaminepentaacetic acid (Na5DTPA); pentapotassium salt of diethylenetriaminepentaacetic acid (K5DTPA); pentacetic salt of diethylenetriaminepentaacetic acid (Cs5DTPA); tetrasodium salt of ethylenediaminetetraacetic acid (Na4EDTA); tetrapotassium diethylenetriaminepentacetate (K4EDTA); tetraethylammonium hydrogen diethylenetriaminepentacetate (TEAH4DTPA); and tetrabutylammonium hydrogen diethylenetriaminepentacetate (TBAH5DTPA); a scale removal enhancer selected from the group consisting of: potassium carbonate; potassium formate; cesium formate; cesium carbonate; and combinations thereof;a fructan containing a carboxyl group, such as carboxymethyl inulin; and a compound selected from the group consisting of: sodium gluconate; gluconic acid; glucono-delta-lactone; calcium gluconate; potassium gluconate; - exposing a surface contaminated with said mixed sulfate fouling to the liquid composition; - allowing sufficient exposure time to remove said mixed sulfate fouling from the contaminated surface; wherein the chelating agent and the counter-ion are present in the composition in an amount ranging from 5 to 40% by weight of the composition.

2. Method according to claim 1, characterized in that Petition 870260046012, dated 05 / 14 / 2026, page 14 / 20 2 / 7 the carboxyl-containing fructan is a derivative of inulin or another fructan containing 0.3 to 3 carboxyl groups per anhydrofructose unit.

3. Method according to claim 2, characterized in that the inulin derivative or other fructan containing 0.3 to 3 carboxyl groups per anhydrofructose unit contains at least 0.8 carboxyl groups per anhydrofructose unit.

4. Method according to claim 2, characterized in that the carboxyl-containing fructan is carboxymethyl inulin (CMI).

5. Aqueous composition for use in the method of removing mixed sulfate scale defined in claim 1, from a surface contaminated therewith, characterized in that it comprises: - a chelating agent and a counter-ion component selected from the group consisting of: pentalithium salt of diethylenetriaminepentaacetic acid (LisDTPA); pentasodium salt of diethylenetriaminepentaacetic acid (NasDTPA); pentapotassium salt of diethylenetriaminepentaacetic acid (KsDTPA); pentacetic salt of diethylenetriaminepentaacetic acid (Cs5DTPA); tetrasodium salt of ethylenediaminetetraacetic acid (Na4EDTA); tetrapotassium diethylenetriaminepentacetate (K4EDTA); tetraethylammonium hydrogen diethylenetriaminepentacetate (TEAH4DTPA); and tetrabutylammonium hydrogen diethylenetriaminepentacetate (TBAHsDTPA); - a scale removal enhancer selected from the group consisting of: potassium carbonate; potassium formate; cesium formate; cesium carbonate;and combinations thereof; - carboxyl-containing fructan, such as carboxymethyl inulin; and - a compound selected from the group consisting of: sodium gluconate; gluconic acid; glucono-delta-lactone; calcium gluconate; potassium gluconate; Petition 870260046012, dated 05 / 14 / 2026, page 15 / 20 3 / 7 in which the chelating agent and the counter-ion are present in the composition in an amount ranging from 5 to 40% by weight of the composition.

6. Aqueous composition according to claim 5, characterized in that the scale removal enhancer is present in the composition in an amount ranging from 5 to 20% by weight of the composition.

7. Aqueous composition according to claim 5 or 6, characterized in that the scale removal enhancer is present in the composition in an amount ranging from 10 to 15% by weight of the composition.

8. Aqueous composition according to any one of claims 5 to 7, characterized in that the scale removal enhancer is present in the composition in an amount of 10% by weight of the composition.

9. Aqueous composition according to any one of claims 5 to 8, characterized in that the chelating agent and the counter-ion are present in the composition in an amount ranging from 10 to 30% by weight of the composition.

10. Aqueous composition according to any one of claims 5 to 9, characterized in that the chelating agent and the counter-ion are present in the composition in an amount ranging from 10 to 20% by weight of the composition.

11. Aqueous composition according to claim 5 or 6, characterized in that the pH of the composition varies from 10 to 11.

12. Aqueous composition according to claim 5 or 6, characterized in that carboxymethyl inulin is present in the composition in an amount ranging from 0.5 to 15% by weight of the composition.

13. Aqueous composition according to claim 5 or 6, characterized in that sodium gluconate is present in the composition in an amount ranging from 1% to 20% by weight of the composition.

14. Method for removing anhydrous calcium sulfate scale from a contaminated surface, characterized in that it comprises: - providing a liquid composition comprising: a chelating agent and a counter-ion component selected from the group consisting of: pentalithium salt of diethylenetriaminepentaacetic acid (LÍ5DTPA); pentasodium salt of diethylenetriaminepentaacetic acid (Na5DTPA); pentapotassium salt of diethylenetriaminepentaacetic acid (K5DTPA); pentacetic salt of diethylenetriaminepentaacetic acid (Cs5DTPA); tetrasodium salt of ethylenediaminetetraacetic acid (Na4EDTA); tetrapotassium diethylenetriaminepentacetate (K4EDTA); tetraethylammonium hydrogen diethylenetriaminepentacetate (TEAH4DTPA); and tetrabutylammonium hydrogen diethylenetriaminepentacetate (TBAH5DTPA); a scale removal enhancer selected from the group consisting of: potassium carbonate; potassium formate; cesium formate; cesium carbonate;and combinations thereof; carboxymethyl inulin; and a compound selected from the group consisting of: sodium gluconate; gluconic acid; glucono-delta-lactone; calcium gluconate; potassium gluconate; wherein the chelating agent and the counter-ion are present in the composition in an amount ranging from 5 to 40% by weight of the composition; - expose said surface contaminated with said mixed sulfate fouling to the liquid composition; - allow sufficient exposure time to remove said anhydrate calcium sulfate fouling from the contaminated surface.

15. Method according to claim 14, characterized in that the composition comprises: a chelating agent and a counter-ion component selected from the group consisting of: pentalithium salt of diethylenetriaminepentaacetic acid (LisDTPA); pentasodium salt of diethylenetriaminepentaacetic acid (NasDTPA); pentapotassium salt of diethylenetriaminepentaacetic acid (KsDTPA); pentacetic salt of diethylenetriaminepentaacetic acid (CssDTPA); tetrasodium salt of ethylenediaminetetraacetic acid (Na4EDTA); tetrapotassium diethylenetriaminepentacetate (K4EDTA); tetraethylammonium hydrogen diethylenetriaminepentacetate (TEAH4DTPA); and tetrabutylammonium hydrogen diethylenetriaminepentacetate (TBAHsDTPA); a scale removal enhancer selected from the group consisting of: potassium carbonate; potassium formate; Cesium formate; cesium carbonate; and combinations thereof; carboxymethyl inulin; and sodium gluconate.

16. Method for solubilizing barium sulfate in particles smaller than 1 micron, characterized in that it comprises: - providing a contaminated surface with a fouling containing barium sulfate; - providing a liquid composition comprising: a chelating agent and a counter-ion component selected from the group consisting of: pentalithium salt of diethylenetriaminepentaacetic acid (LisDTPA); pentasodium salt of diethylenetriaminepentaacetic acid (NasDTPA); Petition 870260046012, dated 05 / 14 / 2026, page 18 / 20 6 / 7 pentapotassium salt of diethylenetriaminepentaacetic acid (K5DTPA); pentacetic salt of diethylenetriaminepentaacetic acid (Cs5DTPA); tetrasodium salt of ethylenediaminetetraacetic acid (Na4EDTA); tetrapotassium diethylenetriaminepentacetate (K4EDTA); tetraethylammonium hydrogen diethylenetriaminepentacetate (TEAH4DTPA); and tetrabutylammonium hydrogen diethylenetriaminepentacetate (TBAH5DTPA);a scale removal enhancer selected from the group consisting of: potassium carbonate; potassium formate; cesium formate; cesium carbonate; and combinations thereof; or a carboxyl-containing fructan, such as carboxymethyl inulin; wherein the chelating agent and the counter-ion are present in the composition in an amount ranging from 5 to 40% by weight of the composition; and - exposing said surface contaminated with said barium sulfate scale to the liquid composition; - allowing sufficient exposure time to remove barium sulfate scale particles from the contaminated surface; wherein said barium sulfate particles have complexed with carboxymethyl inulin and have a particle size smaller than 1 micron;- Allow the pH of the solution to drop from a pH ranging from 10 to 11 to a pH ranging from 7 to 8, thus causing a reprecipitation of the solubilized barium sulfate to a particle size smaller than 1 micron.

17. Method according to claim 16, characterized in that the carboxyl-containing fructan is a derivative of inulin or another fructan containing 0.3 to 3 carboxyl groups per anhydrofructose unit.

18. Method according to claim 17, characterized in that the inulin derivative or other fructan containing 0.3 to 3 carboxyl groups per unit of anhydrofructose contains at least 0.8 carboxyl groups per unit of anhydrofructose.

19. Method according to any one of claims 16 to 18, characterized in that the carboxyl-containing fructan is carboxymethyl inulin (CMI).

20. A method according to any one of claims 16 to 19, characterized in that the composition further comprises a compound selected from the group consisting of: sodium gluconate; gluconic acid; glucono-delta-lactone; calcium gluconate; potassium gluconate; and combinations thereof.

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