WO2016061342A1

WO2016061342A1 - Methods for quantifying zinc content of fluids

Info

Publication number: WO2016061342A1
Application number: PCT/US2015/055724
Authority: WO
Inventors: Christopher J. Nalepa; Steven G. Karseboom; Ross M. VIATOR
Original assignee: Albemarle Corporation
Priority date: 2014-10-17
Filing date: 2015-10-15
Publication date: 2016-04-21

Abstract

Methods are provided for assessing whether a particular salt-based fluid that contains zinc is suitable for an intended use, in that it contains less than a specified quantity of zinc.

Description

METHODS FOR QUANTIFYING ZINC CONTENT OF FLUIDS

BACKGROUND

[0001] This invention relates to methods for quantifying zinc content of fluids, in particular, aqueous brine fluids used for oilfield drilling and production activities such as well completions.

[0002] Zinc bromide salts have historically been used as weighting agents in completion fluids used in the oil industry. However, more recently, the presence of zinc in completion fluids leads to increased reporting requirements with government agencies and more costly environmental mitigation measures and action plans. Zinc is listed as a priority pollutant by the Environmental Protection Agency. Fluids having a zinc content greater than 25 ppm are often subjected to increased scrutiny and regulatory requirements. For example, spills and leaks of such fluids must be rigorously avoided and such fluids may not be disposed of at the drill site, and instead must be transported back to land for proper disposal. So it is essential for commercial providers, and users, of such fluids to be able to quantify the zinc content of such fluids.

[0003] There are various methods available for quantifying zinc content of fluids. For example, the technique known as inductively coupled plasma (ICP) spectrometry can be used to determine the amount of zinc in a solution by comparison of the intensities of the atomic spectral lines of zinc measured in the solution compared to known standards. ICP is often a method of choice for analysis of many different elements, as most elements exhibit a unique spectral pattern that shows the presence of that particular element in a solution; the measured pattern can be compared to a known standard to determine the quantity of that element present in the solution. This test, however, requires highly-trained personnel, high-purity chemical reagents and known standards. In addition the ICP instrument itself is expensive and complex, which makes it costly to purchase and maintain.

[0004] There are also commercially available colorimetric kits and methods for quantifying zinc content of fluids. While these kits and methods are much less expensive and potentially easier to conduct than the ICP method outlined above, they do suffer from a number of issues. For example, the kits often contain reagents that are designated as hazardous, such as sodium cyanide. The kits also require use of multiple reagents to complex with the zinc content of the fluid to provide for the proper color development for the measurement. One other issue is that the test often can only determine zinc content within a narrow range, such as 0 - 10 ppm. The zinc content of the fluid, which is often unknown, must be diluted to within these ranges in order to obtain an accurate reading. Finally, the tests are subject to interference by other elements. For example, low levels (5 ppm) of several elements, e.g., Mn and Cu, are said to interfere with some of the test methods. Calcium in the form of calcium carbonate leads to a positive interference at levels of 1000 ppm or greater. This is obviously an issue for the detection of low levels of zinc in solutions of, for example, CaBr₂ fluid of 14.2 lbs/gal density which contain 53.1 wt% CaBr₂ equivalent to 10.6% (106,000 ppm) calcium content.

[0005] Further, fluids such as completion fluids, are often manufactured and stored in bulk containers, which often comprise several different batches of fluids. The bulk fluids are then typically transferred into drums, totes, trailers, etc. via hoses, pumps, etc. and moved into other bulk containers at any point of which the equipment and vessels used could contain metals and other contaminants, which likely could be introduced into the fluid. Many different parties can be part of this overall production and delivery process, such as the raw material supplier, manufacturer, distributor, end user, etc. Due to this complex supply chain, the composition of fluids can be compromised due to the introduction of impurities or cross-contamination at many points in the supply chain. Quantitative analysis of specific elements of the completion fluids can be conducted by pulling samples at various points in the supply chain. For example, when a quantity of completion fluid is transferred from a storage container to a shipping container for shipment to a user, a sample can be pulled for quantitative analysis. However, current commercially available quantitative tests are not conducive to providing results in a timely manner.

[0006] Given the foregoing, it would be commercially beneficial to have methods for quantifying zinc content of a fluid that are affordable, reliable, and provide quick results in real time.

THE INVENTION

[0007] This invention meets the above-described needs by providing methods comprising (i) for a first fluid, to which a known quantity of a quaternary ammonium salt has been added, measuring total suspended solids (TSS) in the first fluid and/or measuring the Nephelometric Turbidity Units (NTU) in the first fluid, wherein the first fluid comprises a Fluid A, wherein the Fluid A comprises at least one dissolved salt, wherein the first fluid also comprises an unknown quantity of zinc, and wherein the quaternary ammonium salt and the zinc are capable of forming suspended solids in the Fluid A; and (ii) comparing the measured TSS and/or the measured NTU with a previously measured TSS and/or a previously measured NTU of a second fluid, wherein the second fluid comprises the Fluid A and a known quantity of zinc, and to which the known quantity of the quaternary ammonium salt was added, to determine whether the unknown quantity of zinc in the first fluid is greater than, equal to, or less than the known quantity of zinc in the second fluid. Also provided are such methods wherein the quaternary ammonium salt comprises a tetra(alkyl) ammonium salt;

wherein the quaternary ammonium salt comprises tetra(propyl)ammonium bromide or tetra(butyl) ammonium bromide; wherein the Fluid A comprises cations such as sodium, calcium, manganese, or zinc, and comprises anions such as chloride or bromide;

wherein the Fluid A comprises calcium bromide; and wherein the Fluid A comprises sodium bromide.

[0008] Also provided by this invention are methods comprising (i) for a first fluid, to which a known quantity of a quaternary ammonium salt has been added, making a visual determination whether the first fluid contains suspended solids or exhibits turbidity, wherein the first fluid comprises a Fluid A, wherein the Fluid A comprises at least one dissolved salt, wherein the first fluid also comprises an unknown quantity of zinc, and wherein the quaternary ammonium salt and the zinc are capable of forming suspended solids in the Fluid A; and (ii) based on the visual determination obtained in

(i), and on a previous visual determination of suspended solids content of a second fluid, wherein the second fluid comprises the Fluid A and a known quantity of zinc, and to which the known quantity of the quaternary ammonium salt was added, and on knowledge of an intended use, assessing whether the first fluid is suitable for the intended use. Also provided are such methods wherein the quaternary ammonium salt comprises a tetra(alkyl) ammonium salt; wherein the quaternary ammonium salt comprises tetra(propyl)ammonium bromide or tetra(butyl) ammonium bromide; wherein the Fluid A comprises cations such as sodium, calcium, manganese, or zinc, and comprises anions such as chloride or bromide; wherein the Fluid A comprises calcium bromide; and wherein the Fluid A comprises sodium bromide.

[0009] Also provided by this invention are methods comprising (i) for a first fluid, to which a known quantity of a quaternary ammonium salt has been added, assessing total suspended solids (TSS) and/or turbidity of the first fluid either using a visual method or an instrument-based method, wherein the first fluid comprises a Fluid A, wherein the Fluid A comprises at least one dissolved salt, wherein the first fluid also comprises an unknown quantity of zinc, and wherein the quaternary ammonium salt and the zinc are capable of forming suspended solids in the Fluid A;

(ii) comparing the assessment to a previously obtained assessment of TSS and/or turbidity of a second fluid using either the visual method or the instrument-based method, wherein the second fluid comprises the Fluid A and a known quantity of zinc, and to which the known quantity of the quaternary ammonium salt was added; and

(iii) based on the comparison obtained in (ii) and on knowledge of an intended use, assessing whether the first fluid is suitable for the intended use. Also provided are such methods wherein the quaternary ammonium salt comprises a tetra(alkyl) ammonium salt; wherein the quaternary ammonium salt comprises tetra(propyl)ammonium bromide or tetra(butyl) ammonium bromide; wherein the Fluid A comprises cations such as sodium, calcium, manganese, or zinc, and comprises anions such as chloride or bromide; wherein the Fluid A comprises calcium bromide; and wherein the Fluid A comprises sodium bromide.

[0010] Methods according to this invention provide simple, on-site methods based on inexpensive test equipment, e.g., a turbidimeter. The tests requires no specialized training to conduct and utilize a relatively non-hazardous quaternary ammonium salt as the test reagent. Quaternary ammonium compounds as a class find their way into many everyday consumer products such as antimicrobial wipes and are generally recognized as safe.

Figures

[0011] The invention will be better understood by reference to the Figures in which:

[0012] Fig. 1 provides plots of total suspended solids ("TSS") measurements in mg/L determined by Hach Method 630 using a Hach DR 3900 Spectrometer and using 15 mL of sample with 1 .0 mL of 15% tetra(n-propyl)ammonium bromide ("TPAB") solution added, each measurement taken 3 minutes after addition of the TPAB solution, for samples of a sodium bromide-based clear completion fluid (12.5 lb/gal) (the "NaBr

Fluid"), each sample having a different, but known, zinc content, and for samples of a calcium bromide-based clear completion fluid (14.2 lb/gal) (the "CaBr₂ Fluid"), each sample having a different, but known, zinc content. It is known in that art that tetra(n-propyl)ammonium bromide is often generically referred to as

tetrapropylammonium bromide and that the tetra(n-alkyl)ammonium bromides as a class are often referred to simply in a generic sense as tetraalkylammonium bromides. The raw data is shown below in Table A1 .

Table A1

[0013] Fig. 2 provides plots of turbidity measurements in Nephelometric Turbidity Units ("NTUs") determined by Hach Turbidimeter Model 2100Q and using 15 mL of sample with 1 .0 mL of 15% tetra(n-propyl)ammonium bromide ("TPAB") solution added, each measurement taken 3 minutes after addition of the TPAB solution, for samples of the NaBr Fluid, each sample having a different, but known, zinc content, and for samples of the CaBr₂ Fluid, each sample having a different, but known, zinc content. The raw data is shown below in Table A2. Table A2

Detailed Description

[0014] In a method according to this invention, for example, a person interested in a calcium bromide-based completion fluid known as Fluid Z, and knowing of an intended use for Fluid Z in which Fluid Z must contain a known minimum of zinc, 25 ppm or less, could develop, or have developed for her, data similar to that shown in Tables A1 and A2. Furthermore, if desired, charts similar to those shown in Fig. 1 and in Fig. 2 based on analysis of Fluid Z, using a quaternary ammonium salt that is capable of forming suspended solids with the zinc in Fluid Z, selected based on knowledge of one skilled in the art having the teachings provided herein, the selected quaternary ammonium salt being referred to herein as Quat Z, and in accordance with the following procedures: (i) measure TSS in mg/L by Hach Method 630 using a Hach DR 3900 Spectrometer or equivalent and using 15 ml_ of sample Fluid Z with 1 .0 ml_ of Quat Z solution added, each measurement taken 3 minutes after addition of the Quat Z solution, for various samples of Fluid Z, each sample having a different, but known, quantity of zinc, preferably, some having more than 25 ppm zinc and some having 25 ppm zinc or less

(the "TSS Procedure for Z"), and (ii) measure turbidity in NTUs by Hach Turbidimeter

Model 2100Q or equivalent and using 15 mL of sample Fluid Z with 1 .0 mL of Quat Z solution added, each measurement taken 3 minutes after addition of the TPAB solution, for various samples of Fluid Z, each sample having a different, but known, quantity of zinc, preferably, some having more than 25 ppm zinc and some having 25 ppm zinc or less (the "Turbidity Procedure for Z"). Then, given a sample of a commercial Fluid Z containing an unknown quantity of zinc, and knowing that to be suitable for its intended use the commercial Fluid Z must contain 25 ppm or less zinc, this person could (i) add a known quantity of Quat Z to the sample of commercial Fluid Z; and (ii) measure TSS of the sample of commercial Fluid Z using the TSS Procedure for Z and/or measure the turbidity of the sample of commercial Fluid Z using the Turbidity Procedure for Z. Then this person could (i) compare the measured TSS of the sample of commercial Fluid Z and/or the measured NTU of the sample of commercial Fluid Z with the previously measured TSS and/or a previously measured NTU values for the Fluid Z with known quantities of zinc to determine whether the unknown quantity of zinc in the Fluid Z is greater than, equal to, or less than the known quantity of zinc in the various samples of

Fluid Z, and therefore, whether the quantity of zinc in the commercial Fluid Z is 25 ppm or less. While 25 ppm zinc was used in the foregoing example, this invention is not limited by that value and is flexible enough to select any zinc value of interest.

[0015] In another method according to this invention, for example, a person interested in a sodium bromide-based completion fluid known as Fluid X, and knowing of an intended use for Fluid X in which Fluid X must contain 25 ppm or less zinc, could select an appropriate quaternary ammonium salt that is capable of forming suspended solids with the zinc in Fluid X, selected based on knowledge of one skilled in the art having the teachings provided herein, the selected quaternary ammonium salt being referred to herein as Quat X, and add 1 .0 mL of a Quat X solution to a 15 mL sample of

Fluid X containing 25 ppm zinc, and observe the Fluid X about 3 minutes after addition of the Quat X solution, and make a visual determination whether the Fluid X contains suspended solids or exhibits turbidity; then this person could add 1 .0 mL of a Quat X solution to a 15 mL sample of commercial Fluid X containing an unknown quantity of zinc, and observe the Fluid X about 3 minutes after addition of the Quat X solution to make a visual comparison of any suspended solids or turbidity in the sample of commercial Fluid X to her previous visual determination regarding the sample of Fluid X containing 25 ppm zinc, to assess whether the commercial Fluid X is suitable for the intended use.

[0016] A test for zinc content in an aqueous fluid can be run as follows, for example. A sample of clear fluid is placed into a test vial. Then an aqueous solution of quaternary ammonium compound, e.g., tetra(n-propyl)ammonium bromide, is introduced into the fluid with agitation. In the presence of certain levels of zinc - typically in a range of 10 to 20 ppm (depending on concentration of reagents and other factors) - a fine white suspended solid will result. This fine white solid can serve as an indication of zinc level in the fluid and can indicate whether the zinc content of the fluid is suitable for its intended use, e.g. as a heavy fluid for oilfield drilling and production operations.

[0017] In methods according to this invention, where a quaternary ammonium salt is introduced into a zinc-containing salt-based fluid, to assist in making a determination of the amount of zinc in such fluid, various quaternary ammonium salts may be used. Generally any quaternary compound that forms an insoluble quat-zinc complex under the particular properties of the fluid to be tested and the conditions of the test - salt concentration, zinc content, quat concentration and development time, for example - can potentially be used in this work. For example, a wide range of quaternary compounds are available in containing a range of alkyl groups of various sizes and properties as well as a range of counter ions such as chloride, bromide, iodide, borate, carbonate, hydroxide, etc., as disclosed in US Patent Publication 20070255074 (November 1 , 2007). In practice, some quaternary compounds have been found to be particularly useful for this test. Some example quaternary ammonium salts that may be used are tetra(propyl)ammonium bromide and tetra(butyl)ammonium bromide. These compounds provide a good balance in terms of turbidity development without issues with foaming or residue on glassware. Further, given the teachings provided herein, those skilled in the art may select other quaternary ammonium salts that would be useful for the particular salt-based fluid being analyzed for zinc content.

[0018] In methods according to this invention, fluid of interest that comprises dissolved salt, such as a clear completion fluid, can comprise cations such as sodium, calcium, manganese, zinc, and the like, as will be familiar to those skilled in the art, and can also comprise anions such as chloride or bromide or the like, as will also be familiar to those skilled in the art. [0019] Development of turbidity or suspended solids due to formation of this quat-zinc complex can thus provide insight into the levels of zinc in these fluids. This test, due to its ease and simplicity can also serve as a convenient, in-field method to determine whether fluids are suitable for intended use, for example, as completion fluids in support of offshore drilling activities in the Gulf of Mexico and other land-based and water-based arenas of oil exploration and recovery.

EXAMPLES

[0020] The following examples are illustrative of the principles of this invention. It is understood that this invention is not limited to any one specific embodiment exemplified herein, whether in the examples or the remainder of this patent application.

Examples 1 and 2

[0021] Examples 1 and 2 illustrate the utility of this invention for use in the field, e.g., by a technician at a storage facility, via a relatively quick and easy test, for analyzing a fluid for determining whether the zinc content exceeds, or is close to, a set amount. In Examples 1 and 2, the set amount was 25 ppm zinc. The fluids analyzed were the NaBr Fluid and the CaBr₂ Fluid, each of the fluids analyzed containing a different, but known, quantity of zinc. Results were compared to the data of Fig. 1 and Fig. 2, to confirm that, had the amounts of zinc in each of the fluids been unknown, the TSS and/or NTU measurements could be used for a timely decision on whether the fluid was suitable for a use requiring a fluid containing 25 ppm or less zinc. A visual review of Fig. 1 shows that for a CaBr₂ Fluid containing 25 ppm zinc, the TSS reading is about 340 mg/L, and that for a NaBr Fluid containing 25 ppm zinc, the TSS reading is about 410 mg/L. A visual review of Fig. 2 shows that for a CaBr₂ Fluid containing 25 ppm zinc, the turbidity reading is about 250 NTUs, and that for a NaBr Fluid containing 25 ppm zinc, the turbidity reading is about 290 NTUs.

Example 1 :

[0022] Laboratory samples of the NaBr Fluid having known zinc contents were prepared. These same samples were analyzed according to the following procedure, to show the usefulness of this invention for determining suitability of a fluid for offshore drilling or production operations (Zn content = 25 ppm maximum). The samples (15 ml_s each) were treated with a 1 5% solution of TPAB (1 .0 ml_). TSS in mg/L of the samples was determined 3 minutes after addition of the TPAB solution using a Hach 3900 UV-Vis Spectrometer and Hach Method 630. Turbidity of the sample in NTUs was determined 3 minutes after addition of the TPAB solution using a Hach

Turbidimeter, Model 2100Q. Results are shown in Table E1 . TSS readings for sample IDs 1 , 2, 3, and 4 were 1 mg/L, 1 mg/L, 91 mg/L, and 406 mg/L, respectively.

Comparing to the data of Fig. 1 , each of sample ID'S 1 , 2, 3, and 4 has a zinc content of about 25 ppm or less, as each of these readings is less than 410 mg/L. TSS readings for sample IDs 5, 6, and 7 were 590 mg/L, 930 mg/L, and 905 mg/L, respectively.

Comparing to the data of Fig. 1 , each of sample ID'S 5, 6, and 7 has a zinc content of more than 25 ppm, as each of these readings is more than 410 mg/L. Turbidity readings for sample IDs 1 , 2, 3, and 4 were 0.069 NTUs, 0.94 NTUs, 26.6 NTUs, and 287 NTUs, respectively. This data confirms that each of the sample ID'S 1 , 2, 3, and 4 contains about 25 ppm zinc or less, as each of these readings is less than 290 NTUs. Turbidity readings for sample IDs 5, 6, and 7 were 543 NTUs, 710 NTUs, and Off Scale, respectively. A reading higher than 750 NTUs is considered "Off Scale" as it exceeds the capabilities of the instrument. This data confirms that each of the sample ID'S 5, 6, and 7 contains more than 25 ppm zinc, as each of these readings is greater than 290 NTUs. All of this data confirmed that fluids having sample IDs 1 , 2, 3, and 4 were suitable for offshore drilling and production operations as each contained 25 ppm or less of zinc, whereas fluids having sample IDs 5, 6, and 7 were not suitable for offshore drilling and production operations as each contained more than 25 ppm zinc. This test is considered suitable for situations as discussed herein when fluid analysis and decision are desired in a timely manner. An analyzer of the data might also subject a tested sample to additional testing for zinc content, perhaps by the ICP method discussed above.

Table E1

Example 2:

[0023] Laboratory samples of the CaBr₂ Fluid having known zinc contents were prepared. These same samples were analyzed according to the following procedure, to show the usefulness of this invention for determining suitability of a fluid for offshore drilling or production operations (Zn content = 25 ppm maximum). The samples (15 ml_s each) were treated with a 1 5% solution of TPAB (1 .0 ml_). TSS in mg/L of the samples was determined 3 minutes after addition of the TPAB solution using a Hach 3900 UV-Vis Spectrometer and Hach Method 630. Turbidity of the sample in NTUs was determined 3 minutes after addition of the TPAB solution using a Hach

Turbidimeter, Model 2100Q. Results are shown in Table E2. TSS readings for sample IDs 1 , 2, 3, 4, and 5 were 6 mg/L, 16 mg/L, 21 mg/L, 67 mg/L, and 326 mg/L, respectively. Comparing to the data of Fig. 1 , each of sample ID'S 1 , 2, 3, 4, and 5 has a zinc content of less than 25 ppm, as each of these readings is less than 340 mg/L. TSS readings for sample IDs 6 and 7 were 726 mg/L and 946 mg/L, respectively.

Comparing to the data of Fig. 1 , each of sample ID'S 6 and 7 has a zinc content of more than 25 ppm, as each of these readings is more than 340 mg/L. Turbidity readings for sample IDs 1 , 2, 3, 4, and 5 were 6.4 NTUs, 20.8 NTUs, 1 3.4 NTUs, 41 .1 NTUs, and 234 NTUs, respectively. This data confirms that each of the sample ID'S 1 , 2, 3, 4, and 5 contains less than 25 ppm zinc, as each of these readings is less than 250 NTUs. Turbidity readings for sample IDs 6 and 7 were 710 NTUs and Off Scale, respectively. A reading higher than 750 NTUs is considered "Off Scale" as it exceeds the capabilities of the instrument. This data confirms that each of the sample ID'S 6 and 7 contains more than 25 ppm zinc, as each of these readings is greater than 250 NTUs. All of this data confirmed that fluids having sample IDs 1 , 2, 3, 4, and 5 were suitable for offshore drilling and production operations as each contained less than 25 ppm zinc, whereas fluids having sample IDs 6 and 7 were not suitable for offshore drilling and production operations as each contained more than 25 ppm zinc. This test is considered suitable for situations as discussed herein when fluid analysis and decision are desired in a timely manner. An analyzer of the data might also subject a tested sample to additional testing for zinc content, perhaps by the ICP method discussed above.

Table E2

Example 3:

[0024] A total of 50 commercial samples of the NaBr Fluid and of the CaBr₂ Fluid were tested for suitability of use in terms of zinc content. These samples had already been analyzed for zinc by the ICP technique. Of the 50 samples, 3 samples (Sample Set 1 ) had zinc values by ICP of 38.4, 59.1 , and 59.3 ppm. Of the remaining 47 samples (Sample Set 2) zinc values by ICP ranged from 0.5 to 19.3 ppm. These samples were tested for suitability for offshore drilling and production operations (Zn content = 25 ppm maximum) using the turbidity test as follows. Samples (15 ml_s each) were treated with a 1 5% solution of TPAB (1 .0 ml_). Turbidity of the sample in NTUs was determined 3 minutes after addition of the TPAB solution using a Hach

Turbidimeter, Model 2100Q. Turbidity readings for the three samples from Sample Set 1 were 462, Off Scale and Off Scale, respectively. The turbidity data thus confirmed that these fluids were not suitable for offshore drilling and production operations as the NTU readings exceeded 250 NTUs. The data for the 47 samples representing Sample Set 2 ranged from 0.2 to 100 NTU units, thus confirming that these fluids were suitable for use in terms of zinc content (< 25 ppm).

[0025] Many variations of this test are possible and of course one skilled in the art could apply this test to other fluids of interest, Also one could use quaternary compounds of different structure than tetra(n-propyl)ammonium bromide ("TPAB") and apply the quat at different concentrations than that outlined above. One could also develop calibration curves and, using suitable dilution techniques, develop the test into a more quantitative tool for zinc analysis.

[0026] Unless otherwise specified, this invention is not limited to any specific embodiment(s) exemplified herein, whether in lists of suitable components or otherwise.

[0027] It is to be understood that the reactants and components referred to by chemical name or formula anywhere in the specification or claims hereof, whether referred to in the singular or plural, are identified as they exist prior to being combined with or coming into contact with another substance referred to by chemical name or chemical type (e.g., another reactant, a solvent, or etc.). It matters not what chemical changes, transformations and/or reactions, if any, take place in the resulting

combination or solution or reaction medium as such changes, transformations and/or reactions are the natural result of bringing the specified reactants and/or components together under the conditions called for pursuant to this disclosure. Thus the reactants and components are identified as ingredients to be brought together in connection with performing a desired chemical reaction or in forming a combination to be used in conducting a desired reaction. Accordingly, even though the claims hereinafter may refer to substances, components and/or ingredients in the present tense ("comprises",

"is", etc.), the reference is to the substance, component or ingredient as it existed at the time just before it was first contacted, combined, blended or mixed with one or more other substances, components and/or ingredients in accordance with the present disclosure. Whatever transformations, if any, which occur in situ as a reaction is conducted is what the claim is intended to cover. Thus the fact that a substance, component or ingredient may have lost its original identity through a chemical reaction or transformation during the course of contacting, combining, blending or mixing operations, if conducted in accordance with this disclosure and with the application of common sense and the ordinary skill of a chemist, is thus wholly immaterial for an accurate understanding and appreciation of the true meaning and substance of this disclosure and the claims thereof. As will be familiar to those skilled in the art, the terms "combined", "combining", and the like as used herein mean that the components that are "combined" or that one is "combining" are put into a container, e.g., a combustion chamber, a pipe, etc. with each other. Likewise a "combination" of components means the components having been put together in such a container.

[0028] While the present invention has been described in terms of one or more preferred embodiments, it is to be understood that other modifications may be made without departing from the scope of the invention, which is set forth in the claims below.

Claims

CLAIMS What is claimed is:

1 . A method comprising:

(i) for a first fluid, to which a known quantity of a quaternary ammonium salt has been added, measuring total suspended solids (TSS) in the first fluid and/or measuring the Nephelometric Turbidity Units (NTU) in the first fluid, wherein the first fluid comprises a Fluid A, wherein the Fluid A comprises at least one dissolved salt, wherein the first fluid also comprises an unknown quantity of zinc, and wherein the quaternary ammonium salt and the zinc are capable of forming suspended solids in the Fluid A; and

(ii) comparing the measured TSS and/or the measured NTU with a previously measured TSS and/or a previously measured NTU of a second fluid, wherein the second fluid comprises the Fluid A and a known quantity of zinc, and to which the known quantity of the quaternary ammonium salt was added, to determine whether the unknown quantity of zinc in the first fluid is greater than, equal to, or less than the known quantity of zinc in the second fluid.

2. A method according to claim 1 wherein the quaternary ammonium salt comprises a tetra(alkyl) ammonium salt.

3. A method according to claim 1 wherein the quaternary ammonium salt comprises tetra(propyl)ammonium bromide or tetra(butyl) ammonium bromide.

4. A method according to claim 1 wherein the Fluid A comprises cations such as sodium, calcium, manganese, or zinc, and comprises anions such as chloride or bromide.

5. A method according to claim 1 wherein the Fluid A comprises calcium bromide.

6. A method according to claim 1 wherein the Fluid A comprises sodium bromide.

7. A method comprising;

(i) for a first fluid, to which a known quantity of a quaternary ammonium salt has been added, making a visual determination whether the first fluid contains suspended solids or exhibits turbidity, wherein the first fluid comprises a Fluid A, wherein the Fluid A comprises at least one dissolved salt, wherein the first fluid also comprises an unknown quantity of zinc, and wherein the quaternary ammonium salt and the zinc are capable of forming suspended solids in the Fluid A; and

(ii) based on the visual determination obtained in (i), and on a previous visual determination of suspended solids content of a second fluid, wherein the second fluid comprises the Fluid A and a known quantity of zinc, and to which the known quantity of the quaternary ammonium salt was added, and on knowledge of an intended use, assessing whether the first fluid is suitable for the intended use.

8. A method according to claim 7 wherein the quaternary ammonium salt comprises a tetra(alkyl) ammonium salt.

9. A method according to claim 7 wherein the quaternary ammonium salt comprises tetra(propyl)ammonium bromide or tetra(butyl) ammonium bromide.

10. A method according to claim 7 wherein the Fluid A comprises cations such as sodium, calcium, manganese, or zinc, and comprises anions such as chloride or bromide.

1 1 . A method according to claim 7 wherein the Fluid A comprises calcium bromide.

12. A method according to claim 7 wherein the Fluid A comprises sodium bromide.

13. A method comprising:

(i) for a first fluid, to which a known quantity of a quaternary ammonium salt has been added, assessing total suspended solids (TSS) and/or turbidity of the first fluid either using a visual method or an instrument-based method, wherein the first fluid comprises a Fluid A, wherein the Fluid A comprises at least one dissolved salt, wherein the first fluid also comprises an unknown quantity of zinc, and wherein the quaternary ammonium salt and the zinc are capable of forming suspended solids in the Fluid A; (ii) comparing the assessment to a previously obtained assessment of TSS and/or turbidity of a second fluid using either the visual method or the instrument-based method, wherein the second fluid comprises the Fluid A and a known quantity of zinc, and to which the known quantity of the quaternary ammonium salt was added; and

(iii) based on the comparison obtained in (ii) and on knowledge of an intended use, assessing whether the first fluid is suitable for the intended use.

14. A method according to claim 13 wherein the quaternary ammonium salt comprises a tetra(alkyl) ammonium salt.

15. A method according to claim 13 wherein the quaternary ammonium salt comprises tetra(propyl)ammonium bromide or tetra(butyl) ammonium bromide.

16. A method according to claim 13 wherein the Fluid A comprises cations such as sodium, calcium, manganese, or zinc, and comprises anions such as chloride or bromide.

17. A method according to claim 13 wherein the Fluid A comprises calcium bromide.

18. A method according to claim 13 wherein the Fluid A comprises sodium bromide.