Cheling agents for barium sulfate dissolution in displacement spacer systems

Description

1 / 14 Chelating agents for dissolving barium sulfate in displacement spacer systems. CROSS-REFERENCE TO RELATED DEPOSIT REQUESTS

[0001] This application claims the benefit of U.S. Application No. 18 / 189383, filed March 24, 2023, which is incorporated herein by reference in its entirety. BACKGROUND

[0002] This disclosure relates to spacer systems and methods of using spacer systems in oil wells.

[0003] Drilling fluids (or muds) used in drilling underground oil and gas wells and other drilling applications are well known. Drilling fluids carry debris and other particles from the bottom of the drill bit, transport them through the annular space, and allow their separation at the surface, while the rotating drill bit is cooled and cleaned. A drilling fluid is also intended to reduce friction between the drill string and the sides of the hole, maintaining the stability of the uncased sections of the well. Drilling fluid is formulated to prevent unwanted influxes of formation fluids from penetrated permeable rocks. Drilling fluid can also be used to collect and interpret information available from drill fragments and cuttings, cores, and electrical logs.It will be understood that, as used in the present invention, the term drilling fluid also encompasses drill bit fluids and completion fluids.

[0004] A spacer fluid, in contrast, is a liquid used to physically separate one liquid for special purposes from another. A cement spacer fluid separates a drilling fluid from a cement slurry during cementing operations in an oil well. A cement spacer fluid can also clean the wellbore. State-of-the-art cement spacer fluids include microemulsions containing various surfactants. Although these emulsions can displace drilling muds from Petition 870250085621, dated 09 / 22 / 2025, page 13 / 91 2 / 14 wellbore, some microemulsions have certain disadvantages, for example, instability under operating conditions, especially at higher temperatures, as they may exist at the bottom of a wellbore. The ability of certain surfactants to clean the oil well may also decrease at higher oil well temperatures. Typically, these disadvantages affect the quality of the cementing operation in the drill hole, for example, by not adequately removing the drilling fluid, the performance of the settled cement slurry may be compromised in terms of its ability to bond both to the exposed rock surface in the drilled oil well and to the tubing placed in the oil well. Consequently, there remains a need in the technique for improved spacer fluids that overcome the aforementioned disadvantages.In particular, there remains a need for a cement spacer fluid that can effectively remove particulates, such as drilling mud, as well as liquid contaminants from the oil well. BRIEF DESCRIPTION

[0005] One method includes: injecting a first spacer fluid into an oil well comprising a drilling fluid, the first spacer fluid comprising barium sulfate and a first spacer fluid carrier; and injecting into the oil well a second spacer fluid comprising a chelating agent and a second spacer fluid carrier.

[0006] A spacer fluid system includes: a first spacer fluid comprising barium sulfate and a first spacer fluid carrier; and a second spacer fluid comprising from about 10% to about 30% by weight of a chelating agent based on the total weight of the second spacer fluid and a second spacer fluid carrier, wherein the first spacer fluid carrier and the second spacer fluid carrier independently comprise water or a brine; and wherein the chelating agent in the second spacer fluid comprises at least one of ethylenediaminetetraacetic acid or a salt thereof. Petition 870250085621, dated 09 / 22 / 2025, page 14 / 91 3 / 14 (N,N-dicarboxylmethylglutamic acid) or a salt thereof, aspartic acid, N,N-diacetic acid or a salt thereof, N,N-methylglycine or a salt thereof, etidronic acid or a salt thereof, diethylenetriamine pentaacetate or a salt thereof, hydroxyethylethylenediaminetriacetic acid or a salt thereof; N-(2-hydroxyethyl)iminodiacetic acid or a salt thereof, N,N'-ethylenediaminedisuccinic acid or a salt thereof, egtazic acid or a salt thereof, nitrilotriacetic acid or a salt thereof, or cyclohexanediaminetetraacetic acid or a salt thereof. DETAILED DESCRIPTION

[0007] A detailed description of one or more modalities is presented in this document by way of example and not limitation.

[0008] An improved method utilizes a spacer fluid system comprising a first spacer fluid comprising barium sulfate and a second spacer fluid comprising a chelating agent (collectively spacer fluids or spacers). Unlike current microemulsion-based spacers, the instant spacer fluid system can be used at higher temperatures without unpleasant odors associated with glycoside use. Furthermore, the chelating agent is effective in dissolving and removing barium sulfate and other solids left in the wellbore after a drilling operation.

[0009] The method comprises injecting a first spacer fluid into an oil well comprising a drilling fluid, the first spacer fluid comprising barium sulfate and a first spacer fluid carrier; and injecting into the oil well a second spacer fluid comprising a chelating agent and a second spacer fluid carrier.

[0010] Drilling fluid may be displaced with at least one of the first spacer fluid or the second spacer fluid. Displacement of drilling fluid includes displacement of a particulate contaminant present in the oil well. The particulate contaminant comprises at least one particulate from drilling fluid, drilling cuttings Petition 870250085621, dated 09 / 22 / 2025, p. 15 / 91 4 / 14 or a particulate reservoir rock, such as a particulate shale, particulate mudstone, particulate sandstone or particulate carbonate.

[0011] In use, at least a portion of the barium sulfate from the first spacer fluid may settle and deposit on an oil well wall, a device in the oil well, or a combination thereof. Advantageously, the deposited barium sulfate may dissolve in the second spacer fluid. Thus, the deposited barium sulfate can be removed from the wellbore along with the second spacer fluid, avoiding any potential contamination caused by the deposited barium sulfate.

[0012] As used herein, the first spacer fluid carrier and the second spacer fluid carrier are independently present in the respective first and second spacer fluids in an amount of about 10% to about 98% by weight, more preferably in an amount of about 20% to about 98% by weight, or 60% to 98% by weight based on the total weight of the respective first and second spacer fluids.

[0013] The first spacer fluid carrier and the second spacer fluid carrier can independently be fresh water or a brine.

[0014] Brine can be, for example, seawater, produced water, completion brine, or a combination comprising at least one of the aforementioned. The properties of brine can depend on the identity and components of the brine. Seawater, for example, can contain numerous constituents, including sulfate, bromine, and trace metals, in addition to the typical halide-containing salts. Produced water can be water extracted from a production reservoir (e.g., hydrocarbon reservoir) or produced from an underground reservoir source of fresh water or brackish water. Produced water may also be called reservoir brine and contain components including barium, strontium, and heavy metals. In addition to naturally occurring brines (seawater and produced water), completion brine can be Petition 870250085621, dated 09 / 22 / 2025, page 16 / 91 5 / 14 synthesized from fresh water by adding various salts such as KCl, NaCl, ZnCk, MgCb, or CaCk to increase the brine density. Completion brines typically provide optimized hydrostatic pressure to compensate for downstream reservoir pressures. The brines mentioned above can be modified to include one or more additional salts. The additional salts included in the brine can be NaCl, KCl, NaBr, MgCk, CaCb, CaBr2, ZnBr2, NH4Cl, sodium formate, cesium formate, mentioned above. The salt NaCl can be present in the brine in an amount of about 0.5 to about 25 percent by weight (% by weight), specifically from about 1 to about 15% by weight and, more specifically, from about 3 to about 10% by weight, based on the weight of the brine.

[0015] Examples of chelating agents in the second spacer fluid include, but are not limited to, ethylenediaminetetraacetic acid (EDTA) or a salt thereof, such as sodium EDTA, disodium EDTA, diammonium EDTA, or tetraammonium EDTA; (N,N-dicarboxymethyl glutamic) acid (GLDA) or a salt thereof; N,N-diacetic aspartic acid (ASDA) or a salt thereof; N,N-diacetic methylglycine acid (MGDA) or a salt thereof, such as trisodium dicarboxylinate; etidronic acid (also called 1-hydroxyethane-1,1-diphosphonic acid or HEDP) or a salt thereof; diethylenetriamine pentaacetate (DTPA) or a salt thereof, such as diethylenetriaminepentaacetate; Hydroxyethylethylenediaminetriacetic acid (HEDTA) or a salt thereof, such as trisodium N(hydroxyethyl)-ethylenediaminetriacetate; N-(2-hydroxyethyl)iminodiacetic acid (HEIDA) or a salt thereof; N,N'-ethylenediaminedisuccinic acid (EDDS) or a salt thereof; egtazine acid (EGTA) or a salt thereof; nitrilotriacetic acid (NTA) or a salt thereof;Cyclohexanediaminetetraacetic acid (CDTA) or a salt thereof; or a combination comprising at least one of the above. Preferably, the chelating agent is EDTA or a salt thereof. Petition 870250085621, dated 09 / 22 / 2025, p. 17 / 91 6 / 14

[0016] The chelating agent may be present in an amount of about 1% to about 50%, preferably about 20% to about 50%, each based on a total weight of the second spacer fluid.

[0017] The first spacer fluid, the second spacer fluid, or both may also include other components known for use in spacer fluids, such as, for example, a viscosifier, a viscosifier crosslinker, a pH control agent, a surfactant, a weighting agent, a lubricant, a fluid loss agent, a clay stabilizer, a biocide, an acid, a corrosion inhibitor, a friction reducer, an oxygen absorber, a formation fines controller, a foaming agent, a gel stabilizer, or a combination that includes at least one of the foregoing. These additional components are selected to prevent the transmission of unfavorable characteristics to the spacer fluids, to prevent damage to equipment in contact with the spacer fluids, and to prevent damage to the oil well or underground formation. Each additive may be present in amounts generally known to those skilled in the art.

[0018] The viscosifier may be a natural polymer, such as guar gums, guar derivatives such as hydroxypropyl guar (HPG), carboxymethyl guar (CMG) and carboxymethyl-hydroxypropyl guar (CMHPG), high molecular weight hydratable polysaccharides, xanthan gum (which may optionally be crosslinked), galactomannan gums, glucomannan gums, cellulose, cellulose derivatives such as hydroxyethylcellulose (HEC), carboxymethylcellulose (CMC), hydroxypropylcellulose (HPC) and carboxymethyl-hydroxyethylcellulose (CMHEC); synthetic polymers such as poly((meth)acrylic) acids, poly((meth)acrylamides), copolymers of (meth)acrylic acid and (meth)acrylamide and C1-8 alkyl poly(meth)acrylates; or clays such as bentonite, sepiolite and attapulgite and the like; or a combination that includes at least one of the previous viscosifiers.

[0019] A crosslinker for the viscosifier may be present, for example a borate, titanate, zirconate, aluminate crosslinker, or Petition 870250085621, dated 09 / 22 / 2025, page 18 / 91 7 / 14 chromate, or a combination comprising at least one of the crosslinking agents mentioned above.

[0020] The pH adjusting agent may be an organic or inorganic base, an organic or inorganic acid, or a buffer, which is any suitable combination of an acid and its conjugate base. Examples of inorganic bases include those represented by MOH, where M is a metal from group 1 or 2 of the periodic table, a transition metal, or a metal or metalloid from group 13, 14, or 15; a carbonate salt; a bicarbonate salt; or a combination comprising at least one of the foregoing. Examples of inorganic acids include HCl, dextromethorphan, fluoroboric acid, sulfuric acid, nitric acid, acetic acid, formic acid, methanesulfonic acid, propionic acid, chloroacetic or dichloroacetic acid, citric acid, glycolic acid, lactic acid, or a combination comprising at least one of the foregoing.Specific examples of pH control agents, particularly those used in combination with borate crosslinking agents, include hydroxides and carbonates of alkali metals and alkaline earth metals such as sodium hydroxide and sodium carbonate, metal oxides such as magnesium oxide, sodium sesquicarbonate, and amines such as hydroxyalkylamines, anilines, pyridines, pyrimidines, quinolines, and pyrrolidines, and carboxylates such as acetates and oxalates.

[0021] Surfactants can increase the compatibility of spacer fluid and drilling fluid and / or cement slurry. The surfactant can be anionic, cationic, zwitterionic, or non-ionic. Other useful surfactants include those with poly(alkylene glycol) side chains, fatty acids, or fluorinated groups such as C1-4 perfluorinated sulfonic acids grafted onto the main polymer chain. The main polymer chains include chains based on a polyester, a poly(meth)acrylate, a polystyrene, a poly(styrene-(meth)acrylate), a polycarbonate, a polyamide, a polyimide, a polyurethane, a poly(vinyl alcohol), or a copolymer comprising at least one of these main polymer chains. Petition 870250085621, dated 09 / 22 / 2025, page 19 / 91 8 / 14

[0022] Bulking agents are finely divided, high-specific-gravity solid materials used to increase density. Barium sulfate may be the sole thickening agent present in the first spacer fluid and / or the second spacer fluid. Alternatively, rare earth compounds may be used in conjunction with other bulking agents such as silica flour, fly ash, calcium carbonate, barite, hematite, ilmenite, siderite, and the like.

[0023] Lubricants minimize friction and include materials such as a polyacrylamide, petroleum distillate, hydrotreated light petroleum distillate, a short-chain alcohol (e.g., methanol), or polyol (e.g., ethylene glycol or glycerol), polyisobutyl methacrylate, poly(methyl methacrylate), polyisobutylene, guar, guar derivatives, a polysaccharide such as cellulose and starch, and poly(ethylene oxide), or a combination comprising at least one of the aforementioned may be used.

[0024] Fluid loss control agents are generally water-soluble polymers such as guar gum, poly(ethyleneimine), cellulose derivatives, and poly(styrene sulfonate). In some embodiments, the same polymer functions both as a viscosifier and as a fluid loss control agent.

[0025] A biocide prevents the injection of a microbe (e.g., bacteria) into the bottom of the well by eliminating or reducing bacteria in the spacer fluid, thereby reducing the production of, for example, acid gas. Optionally, the biocide is encapsulated or coated.

[0026] The various properties of spacer fluids can be varied and adjusted according to well control and compatibility parameters of the specific drilling fluid, cement slurry, or other fluid being segregated. For example, the viscosity of the first and second spacer fluids can be varied over a wide range, such as an apparent viscosity (AV) of about 0.9 to about 200 centiPoise (cP). Petition 870250085621, dated 09 / 22 / 2025, p. 20 / 91 9 / 14

[0027] The density of the first and second spacer fluids can vary over a wide range. In one embodiment, the first spacer fluid is heavier (denser) than the previous fluid (drilling fluid) and lighter than the second spacer fluid (e.g., a 12 ppg drilling fluid, then a 14 ppg first spacer fluid, then a 16 ppg second spacer fluid, and then an 18 ppg cement slurry).

[0028] In one respect, the first spacer fluid has a density that is about 2 ppg greater than the density of the drilling fluid. The second spacer fluid has a pour point that is about 1.5 times greater than the pour point of the drilling fluid.

[0029] The first and second spacer fluids can be premixed independently or injected without mixing, for example, injected in real time, where the components are combined as the spacer fluids are injected into the bottom of the well. The order of addition can be varied and the injection time of each is the same or different.

[0030] Drilling fluid can be oil-based or water-based. In oil-based fluids, solid particles are suspended in oil, and water or brine may be emulsified with the oil. Oil is typically the continuous phase. In water-based fluids, solid particles are suspended in water or brine, and oil may be emulsified in the water. Water is typically the continuous phase.

[0031] In general, in a method of cementing an oil well, first and second spacer fluids are used to displace the drilling fluids present and, preferably, to further remove oil and solids from the wellbore and oil well surfaces. The method involves injecting, usually by pumping, into the oil well a first spacer fluid and a second spacer fluid at sufficient pressure to displace the drilling fluid. In a preferred embodiment, the drilling fluids are displaced together with solids, such as drilling fluid solids and drilling fragments and cuttings. A cement slurry is then Petition 870250085621, dated 09 / 22 / 2025, p. 21 / 91 10 / 14 injected into the well (optionally with an initial or final slurry). The cement slurry can be introduced between a penetrable / breakable bottom plug and a solid top plug. Once placed, the cement slurry is allowed to harden to form the cement plug in the oil well annular space, which prevents the flow of reservoir fluids between two or more permeable geological formations that exist with unequal reservoir pressures. As is known to those skilled in the art, there is a high degree of variability in the above description of well cementing (e.g., multiple bottom plugs, graded fluid densities, etc.) and it can be effected using the cement spacer fluid described in this document.

[0032] The use of spacer fluids offers several benefits. The fluids are stable at high wellbore temperatures, for example, up to about 350°F. In some embodiments, the fluids are stable at about 150 to about 350°F, or about 150 to about 250°F. Spacer fluids are compatible with both drilling fluid and cement slurries with which they are used in conjunction. In addition, spacer fluids can more effectively remove drilling mud and contaminant particles from oil wells, for example, drilling fluid particulates, fragments and drilling cuttings, and reservoir rock particles released in the oil well drilled from weak formations, for example, shale particulate, mud particulate, sandstone particulate, carbonate particulate and the like.Spacer fluids can further suppress the mixing of drilling fluids and cement slurries when compared to turbulent flow spacer fluids.

[0033] The methods and compositions also have the advantages of improved cementation, reducing the amount of drilling fluids, contaminant particles and other debris before introducing the cement slurry.

[0034] The following specific embodiments are additionally included in this disclosure, which do not necessarily limit the claims. Petition 870250085621, dated 09 / 22 / 2025, p. 22 / 91 11 / 14

[0035] Aspect 1. Method, comprising: injecting a first spacer fluid into an oil well comprising a drilling fluid, the first spacer fluid comprising barium sulfate and a first spacer fluid carrier; and injecting into the oil well a second spacer fluid comprising a chelating agent and a second spacer fluid carrier.

[0036] Aspect 2. The method, as in any previous aspect, further comprising displacing the drilling fluid with at least one of the first spacer fluid or the second spacer fluid.

[0037] Aspect 3. The method, as in any previous aspect, in which moving the drilling fluid also involves moving a particulate contaminant present in the oil well.

[0038] Aspect 4. The method of Aspect 3, wherein the contaminant particulate comprises at least one particulate from drilling fluid, drilling cuttings or a particulate from reservoir rock.

[0039] Aspect 5. The method, according to any previous aspect, in which at least a portion of the barium sulfate of the first spacer fluid is deposited on an oil well wall, an apparatus in the oil well, or a combination thereof by contact with the first spacer fluid.

[0040] Aspect 6. The method of aspect 5, further comprising dissolving and removing the deposited barium sulfate with the second spacer fluid.

[0041] Aspect 7. The method, as in any preceding aspect, wherein the first spacer fluid carrier and the second spacer fluid carrier independently comprise water or a brine.

[0042] Aspect 8. The method, according to any previous aspect, wherein the first spacer fluid, the second spacer fluid or both further comprise independently at least one of a viscosifier, a viscosifier crosslinker, a pH control agent, a surfactant, a thickening agent, a lubricant, a fluid loss agent, a clay stabilizer, a biocide, an acid, a corrosion inhibitor, Petition 870250085621, dated 09 / 22 / 2025, p. 23 / 91 12 / 14 a friction reducer, an oxygen scavenger, a fines formation controller, a foaming agent or a gel stabilizer.

[0043] Aspect 9. The method, in accordance with any previous aspect, in which the first spacer fluid has a density that is about 2 ppg greater than the density of the drilling fluid.

[0044] Aspect 10. The method, as in any previous aspect, where the second spacer fluid has a pour point that is about 1.5 times greater than the pour point of the drilling fluid.

[0045] Aspect 11.0 method, according to any previous aspect, wherein the chelating agent in the second spacer fluid comprises at least one of ethylenediaminetetraacetic acid or a salt thereof, (N,N-dicarboxymethyl glutamic) acid or a salt thereof, aspartic acid, N,N-diacetic acid or a salt thereof, N,N-methylglycine diacetic acid or a salt thereof, etidronic acid or a salt thereof, diethylenetriamine pentaacetate or a salt thereof, hydroxyethylethylenediaminetriacetic acid or a salt thereof; N-(2-hydroxyethyl)iminodiacetic acid or a salt thereof, N,N'-ethylenediaminedisuccinic acid or a salt thereof, egtazic acid or a salt thereof, nitrilotriacetic acid or a salt thereof, or cyclohexanediaminetetraacetic acid or a salt thereof.

[0046] Aspect 12. The method, according to any previous aspect, wherein the chelating agent in the second spacer fluid comprises at least one of sodium ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetic acid, diammonium ethylenediaminetetraacetic acid, or tetraammonium ethylenediaminetetraacetic acid, trisodium dicarboxymethyl alaninate, pentasodium diethylenetriaminepentaacetate; or trisodium N(hydroxyethyl)-ethylenediaminetriacetate.

[0047] Aspect 13. The method, according to any previous aspect, wherein the second spacer fluid comprises about 10% to about 30% of the chelating agent based on the total weight of the second spacer fluid.

[0048] Aspect 14. The method, as in any previous aspect, also includes the displacement of the second spacer fluid with a cement paste. Petition 870250085621, dated 09 / 22 / 2025, page 24 / 91 13 / 14

[0049] Aspect 15. The method as in any previous aspect, where the well has a bottom oil temperature of about 150°F to about 350°F.

[0050] Aspect 16. Spacer fluid system comprising: a first spacer fluid comprising barium sulfate and a first spacer fluid carrier; and a second spacer fluid comprising from about 10% to about 30% by weight of a chelating agent based on the total weight of the second spacer fluid and a second spacer fluid carrier, wherein the first spacer fluid carrier and the second spacer fluid carrier independently comprise water or a brine; and wherein the chelating agent in the second spacer fluid comprises at least one of ethylenediaminetetraacetic acid or a salt thereof, (N,N-dicarboxylmethylglutamic) acid or a salt thereof, aspartic acid, N,N-diacetic acid or a salt thereof, N,N-methylglycine diacetic acid or a salt thereof, etidronic acid or a salt thereof, diethylenetriamine pentaacetate or a salt thereof, hydroxyethylethylenediaminetriacetic acid or a salt thereof;N-(2-hydroxyethyl)iminodiacetic acid or a salt thereof, N,N'-ethylenediamine disuccinic acid or a salt thereof, egtazic acid or a salt thereof, nitrilotriacetic acid or a salt thereof, or cyclohexanediaminetetraacetic acid or a salt thereof.

[0051] Aspect 17. The spacer fluid, according to any previous aspect, wherein the first spacer fluid, the second spacer fluid or both further comprise independently at least one of a viscosifier, a viscosifier crosslinker, a pH control agent, a surfactant, a bulking agent, a lubricant, a fluid loss agent, a clay stabilizer, a biocide, an acid, a corrosion inhibitor, a friction reducer, an oxygen scavenger, a fines formation controller, a foaming agent or a gel stabilizer.

[0052] All tracks disclosed in the present invention are inclusive of the endpoints, and the endpoints are independently Petition 870250085621, dated 09 / 22 / 2025, page 25 / 91 14 / 14 combinable with each other. As used in the present invention, the term combination is inclusive of blends, mixtures, alloys, reaction products and the like.

[0053] The use of the terms a, an, and similar references in the context of describing the invention (especially in the context of the following claims) should be interpreted as encompassing both the singular and the plural, except where otherwise indicated in the present invention or clearly contradicted by the context. Additionally, it should be considered that the terms first, second, and similar in the present invention do not denote any order, quantity, or importance, but are instead used to distinguish one element from another. The terms approximately, substantially, and generally are intended to include the degree of error associated with measuring the specific quantity based on the equipment available at the time of filing. For example, approximately and / or substantially and / or generally may include a range of ±8% or 5% or 2% of a given value.

[0054] Unless otherwise defined, the technical and scientific terms used in this document have the same meanings commonly understood by those skilled in the art to which the present invention relates.

[0055] All references cited in this invention are incorporated by reference in their entirety. Although typical embodiments have been presented for illustrative purposes, the foregoing descriptions should not be considered a limitation on the scope of the present invention. Consequently, various modifications, adaptations, and alternatives may occur to those skilled in the art without departing from the spirit and scope of the present invention. Petition 870250085621, dated 09 / 22 / 2025, p. 26 / 91

Claims

1 / 3 CLAIMS 1. A method for conducting an oil well operation, characterized by: injecting a first spacer fluid into an oil well comprising a drilling fluid, the first spacer fluid comprising barium sulfate and a first spacer fluid carrier; and injecting into the oil well a second spacer fluid comprising a chelating agent and a second spacer fluid carrier.

2. A method according to claim 1, characterized by further displacing the drilling fluid with at least one of the first spacer fluid or the second spacer fluid.

3. A method according to claim 2, characterized in that the displacement of the drilling fluid further comprises displacing a particulate contaminant present in the oil well.

4. Method according to claim 3, characterized in that the contaminant particulate comprises at least one of a drilling fluid particulate, a drilling cutting particulate or a reservoir rock particulate.

5. A method according to claim 1, characterized in that at least a portion of the barium sulfate of the first spacer fluid is deposited on a wellbore wall, an apparatus in the wellbore, or a combination thereof by contact with the first spacer fluid.

6. Method according to claim 5, further characterized by the dissolution and removal of the deposited barium sulfate with the second spacer fluid.

7. Method according to claim 1, characterized in that the first spacer fluid, the second spacer fluid or both further comprise, independently, at least one of a viscosifier, a viscosifying crosslinker, a pH control agent, a surfactant, a weight-increasing agent, a lubricant, a fluid loss agent, a clay stabilizer, a biocide, an acid, a corrosion inhibitor, a friction reducer, an oxygen scavenger, a fines formation controller, a foaming agent or a gel stabilizer.

8. Method according to claim 1, characterized in that the first spacer fluid has a density that is about 2 ppg greater than the density of drilling fluid.

9. Method according to claim 1, characterized in that the second spacer fluid has a pour point that is about 1.5 times greater than the pour point of the drilling fluid.

10. Method according to claim 1, characterized in that the chelating agent comprises at least one of ethylenediaminetetraacetic acid or a salt thereof, (N,N-dicarboxylmethylglutamic) acid or a salt thereof, aspartic acid, N,N-diacetic acid or a salt thereof, N,N-methylglycine diacetic acid or a salt thereof, etidronic acid or a salt thereof, diethylenetriamine pentacetate or a salt thereof, hydroxyethylethylenediaminetriacetic acid or a salt thereof; N(2-hydroxyethyl)iminodiacetic acid or a salt thereof, N,N'-ethylenediaminedisuccinic acid or a salt thereof, egtazic acid or a salt thereof, nitrilotriacetic acid or a salt thereof, or cyclohexanediaminetetraacetic acid or a salt thereof.

11. A method according to any one of claims 1 to 10, characterized in that the second spacer fluid comprises about 10% to about 30% of the chelating agent based on the total weight of the second spacer fluid.

12. Method, according to any one of claims 1 to 10, characterized by displacing the second spacer fluid with a cement paste. Petition 870250085621, dated 22 / 09 / 2025, p. 28 / 91 3 / 3 13. Method, according to any one of claims 1 to 10, characterized in that the oil well has a bottomhole temperature of about 150°F to about 350°F.

14. Spacer fluid system characterized by: a first spacer fluid comprising barium sulfate and a first spacer fluid carrier; and a second spacer fluid comprising about 10% to about 30% by weight of a chelating agent based on the total weight of the second spacer fluid and a second spacer fluid carrier, wherein the first spacer fluid carrier and the second spacer fluid carrier independently comprise water or a brine; and wherein the chelating agent in the second spacer fluid comprises at least one of ethylenediaminetetraacetic acid or a salt thereof, (N,N-dicarboxylmethylglutamic) acid or a salt thereof, aspartic acid, N,N-diacetic acid or a salt thereof, N,N-methylglycine diacetic acid or a salt thereof, etidronic acid or a salt thereof, diethylenetriamine pentaacetate or a salt thereof, hydroxyethylethylenediaminetriacetic acid or a salt thereof;N-(2-hydroxyethyl)iminodiacetic acid or a salt thereof, N,N'-ethylenediaminediuccinic acid or a salt thereof, egtazic acid or a salt thereof, nitrilotriacetic acid or a salt thereof, or cyclohexanediaminetetraacetic acid or a salt thereof.

15. Spacer fluid, according to claim 14, characterized in that the first spacer fluid, the second spacer fluid, or both further comprise, independently, at least one of a viscosifier, a viscosifier crosslinker, a pH control agent, a surfactant, a thickening agent, a lubricant, a fluid loss agent, a clay stabilizer, a biocide, an acid, a corrosion inhibitor, a friction reducer, an oxygen scavenger, a fines formation controller, a foaming agent, or a gel stabilizer. Petition 870250085621, dated 22 / 09 / 2025, p. 29 / 91