US 20050039911A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2005/0039911A1 Carpenter et al. (43) Pub. Date: Feb. 24, 2005

(54) MAXIMIZING THE EFFICACY OF Publication Classification THIOCYANATE SCAVENGERS IN OLFIELD BRINES (51) Int. Cl." ...... E21B 17/00 (52) U.S. Cl...... 166/242.4 (76) Inventors: Joel F. Carpenter, Baton Rouge, LA (US); Bonnie G. McKinnie, Magnolia, (57) ABSTRACT AR (US); Techen Tsao, Baton Rouge, LA (US) A cause has been discovered for the problem of formation of corrosive Sulfur-containing decomposition products of an Correspondence Address: inorganic thiocyanate in a downhole oilfield operation in EDGAR SPIELMAN which an inorganic thiocyanate corrosion inhibitor is used in ALBEMARLE CORPORATION a concentrated brine Solution. The cause is the presence in 451 FLORIDA BLVD. the brine of methanol from several potential sources. Meth BATON ROUGE, LA 70801 (US) ods and compositions are described which enable inorganic thiocyanate to be used with concentrated brine Solutions in (21) Appl. No.: 10/646,546 downhole oilfield operations without Such decomposition taking place. These compositions are free of a thiocyanate (22) Filed: Aug. 21, 2003 decomposing amount of methanol. US 2005/0039911A1 Feb. 24, 2005

MAXIMIZING THE EFFICACY OF THIOCYANATE U.S. Pat. Nos. 4,514,374, 4,549,973; 4,753,740; 4,784,796; SCAVENGERS IN OILFIELD BRINES 4,784,797; and 5,230,879, the full disclosures of which are incorporated herein by reference. Such concentrated brine BACKGROUND Solutions can be acqueous Solutions of Such halide Salts as 0001. In recent times there has been considerable discus calcium chloride, calcium bromide, Zinc chloride, Zinc bro Sion in the oilfield technical literature Suggesting that in mide, Sodium chloride, Sodium bromide, potassium chlo oilfield brines the commonly-used inorganic thiocyanate ride, potassium bromide, or like water-Soluble Salts. Com brine corrosion inhibitors tend to decompose to hydrogen mercially-available brines of this type include a Sulfide, alkyl Sulfides, disulfides, and mercaptains. This can concentrated aqueous Solution of Sodium bromide, a con lead during downholes operations to Sulfide StreSS corrosion centrated aqueous Solution of calcium bromide, and a con cracking ("SSCC) of corrosion resistant alloys in piping, centrated aqueous Solution of a mixture Zinc and calcium casings, tubings, etc. that are present in downhole wells, bromides. In each Such Solution these specified metal bro these components being commonly referred to by those in mides are in whatever dissolved, dissociated, ionized, com the art as “OCTG’ which stands for “oil country tubular plexed, and/or Solvated form(s) in which they exist when in goods”. The severity of the problem has led at least one Solution in an aqueous medium. Typically the Sodium bro author in the field to Suggest that inorganic thiocyanates mide Solutions have contents corresponding to the range of should be avoided in brines for downhole usage. about 38 to about 47 wt % of Sodium bromide in whatever form(s) in which sodium bromide exists when in solution in 0002. In view of the existence of the foregoing problems an aqueous medium. Typically the calcium bromide Solu relating to usage of Sodium thiocyanate in concentrated tions have contents corresponding to the range of about 48 brines for downhole usage, an investigation has been made to about 57 wt % of calcium bromide in whatever form(s) in to see if a cause for Such Sodium thiocyanate decomposition which calcium bromide exists when in Solution in an aque might be found. Pursuant to this invention, a cause for Such ous medium. Typically the mixed Zinc bromide and calcium decomposition has now been discovered, and an effective bromide Solutions have contents corresponding to the range solution to the problem has been found. of about 53 to about 60 wt % of zinc bromide and corre sponding to the range of about 17 to about 22 wt % of THE INVENTION calcium bromide in whatever form(s) in which these two 0003. It has been discovered that even trace amounts of bromides exist when both are in Solution in the same methanol plays a role in decomposing Sodium thiocyanate, aqueous medium. In each case the balance to 100 wt % is a representative inorganic thiocyanate corrosion inhibitor, water. These brines may be blended with one another in any whereby methyl mercaptan, dimethyl sulfide, and dimethyl proportions. Also these brines may be mixed with another disulfide are produced. These Substances are highly corro halide Salt whether Such Salt is in the Solid State or as a brine Sive and will readily attack corrosion resistant alloys. On the solution to afford a mixture with the desired density for the other hand, it has been found that under the same conditions, operation in which the resultant mixed solution will be used. ethanol does not cause formation of corrosive components For example, a composite brine with a density of 13.3 lbs/gal that will attack corrosion resistant alloys. at 70° F (ca. 1.6 kgs/liter at 21 C.) can be formulated using 0004 Thus per this invention, in an oilfield brine solution 0.4155 bbl of an 11.6 lbs/gal calcium chloride brine with in which an inorganic thiocyanate corrosion inhibitor Such 0.4826 bbl of a 14.2 lbs/gal calcium bromide brine and 77.9 as Sodium thiocyanate is used, the brine is improved by lbs of 80% calcium chloride Solid salt. providing and/or using a brine in which there is an absence 0008 Pursuant to this invention, when employing a thio of a thiocyanate-decomposing amount of methanol. cyanate corrosion inhibitor in a concentrated brine Solution for downhole usage, one should ensure that there is no 0005 Various methods and compositions constituting thiocyanate-decomposing amount of methanol in the brine. embodiments of this invention will be still further apparent Among analytical procedures that can be used are gas from the ensuing description and appended claims. chromatography, maSS Spectroscopy, and nuclear magnetic 0006 Oilfield downhole operations in which concen resonance spectroScopy. The following NMR procedure is trated aqueous brine Solution can be used include drilling, illustrative and recommended: completion, packer, and gravel packing. Such methods are well known to those of ordinary skill in the art, and are 0009. In general, deuterium oxide is added to a sample described in the literature. See for example A Primer of under test. The proton NMR spectrum for samples in water Oilwell Drilling, 5th Edition, Revised by Ron Baker, Austin, is obtained under water Suppression conditions when nec Tex., 1996; and Completion and Workover Fluids, Mono essary to observe very low levels of methanol. The methanol graph, Volume 19 SPE, by Kenneth L. Bridges, Richardson, content is identified and the concentration estimated. The Tex., 2000. The disclosures of each of these reference works methanol impurity is quantitated using a weighed internal to the extent they relate to downhole operations in which a Standard and the weight percent of methanol is calculated concentrated aqueous brine Solution is or can be used are from the weights and integrals. incorporated herein by reference. 0010) A high-field NMR instrument capable of low 0007 One potential source of methanol is in the brine power water Suppression is used. High proton NMR Sensi itself inasmuch as methanol can be used as component, often tivity is required and a 400 MHz or higher field instrument as a bromine Scavenger, in the manufacture of concentrated is preferred. The chemicals employed in the procedure are aqueous brine Solutions for use in downhole operations, or deuterium oxide, 99.9 isotope 96 deuterium (Cambridge can be used in the manufacture of, or as a Solvent for, Isotopes DLM-4 or equivalent), and dimethylsulfoxide, additives for use in Such brine Solutions. See for example reagent grade. US 2005/0039911A1 Feb. 24, 2005

0011. In conducting the procedure, the sample is diluted 0025 The following Examples are presented for the 1:2 or 1:3 in D.O. Proton NMR spectra of the brines are purpose of illustration. They are not intended to limit the obtained with Suppression of the water resonance, as needed. generic Scope of the invention to the only the Subject matter The observed frequency is set on the water resonance. The described minimum presaturation power is used to effectively SuppreSS the water peak. This is typically a gamma H. of <50 Hz with EXAMPLES a preSaturation time of 2 S. Some adjustment of the power, 0026. As a demonstration of the efficacy of this invention, irradiation frequency and other parameters as necessary to an experimental program was conducted for measuring maximize water Suppression while minimizing attenuation thiocyanate decomposition as effected by the copresence of of any nearby peaks is employed. PreSaturation power levels alcoholic additives. In three high pressure bombs were of 0.05-0.25% of maximum power are typical. Peaks within placed the following components, respectively: the 3.8-5.8 ppm chemical shift window (water peak at 8 4.8 ppm) can be expected to lose Some intensity under these 0027 Bomb 1) Aqueous calcium bromide brine (53 wit conditions. %) and 0.2 wt % sodium thiocyanate.) 0012 Quantitation of methanol is accomplished as fol 0028 Bomb 2) Aqueous calcium bromide brine (53 wit lows. Accurately weigh 2-6 grams of sample with 0.01-0.02 %), 0.2 wt % sodiumthiocyanate, and 0.1 wt % metha grams of reagent grade dimethylsulfoxide. Dissolve the nol.) sample in deuterium oxide. Obtain the proton NMR spec trum with 64K real data points and recycle time of 20-30s. 0029 Bomb 3) Aqueous calcium bromide brine (53 wit Obtain the appropriate peak integrals for the methanol %), 0.2 wt % sodiumthiocyanate, and 0.1 wt % ethanol. species (83.3 ppm) and for the DMSO standard. Positive 0030) The sealed bombs were held at 175° C. and atmo identification can be made Via Spiking with the authentic spheric pressure for 10 days. Then GC-MS analyses were compounds. conducted on the contents of the respective head Spaces of these bombs. The Table Summarizes the results of these 0013 The calculations employed are as follows: analyses. 0014 Wt % of methanol species=A TABLE 0015) Area of species=B Bomb 0016 Area of standard=C No. GC-MS Results 1. No HS, mercaptan, sulfide or disulfide were found. 0017 Wt of standard=D 2 No HS, Found: MeSSMe 15.7%, MeS 65.1%, and MeSH 0.1%. The balance to 100% was air. 0018) Wt of sample=E 3 No H.S, mercaptan, sulfide or disulfide were found. 0019 Using dimethylsulfoxide for Standard: A=(82.15)(BxD)/(CxE) 0031. Without desiring to be bound by theory, one may 0020 Report no more than two significant figures for the explain the above results by Suggesting that methanol reacts impurity concentrations. with thiocyanate by a Second order nucleophilic Substitution to afford methyl thiocyanate which is subsequently hydro 0021 For determination or estimation of solid metal lyzed to afford methyl mercaptan. By Simple oxidation, halide Salts see below. Some of this is then converted to dimethyl sulfide. On the 0022 Quantitation of known impurities is accomplished other hand, these results indicate that ethanol does not as follows. Accurately weigh 1-4 grams of Sample with undergo these reactions, at least under the conditions used. 0.01-0.02 grams of reagent grade dimethylsulfoxide. Dis 0032. It can be seen from the above that not only has a Solve the sample in deuterium oxide. Obtain the proton cause been discovered for the downhole corrosion problem NMR spectrum with 64K real data points and recycle time due to the decomposition of an inorganic thiocyanate caused of 20-30 S. Obtain the appropriate peak integrals for the by the copresence of methanol in a concentrated brine methanol species (8-3.3 ppm) and for the DMSO standard. Solution but additionally, approaches to Solving this problem 0023 Preferably, the analytical procedure used is have been found. One involves methods and compositions in employed prior to addition of an inorganic thiocyanate which the presence of methanol is avoided. A Second corrosion inhibitor to the Solution. involves the equally Surprising discovery that ethanol can be Substituted for methanol wherever methanol is used. For 0024 Typical inorganic thiocyanates that, as a result of example ethanol can be Substituted for methanol (a) in the this invention, can be more efficiently used in concentrated manufacture of a concentrated brine Solution at a production aqueous oilfield brine Solutions and in downhole operations facility, or (b) as a raw material or component in a produc there with include Sodium thiocyanate, potassium thiocyan tion process for making an additive to be incorporated into ate, ammonium thiocyanate, or a combination of any two or the concentrated brine Solution before it is used in a down more of these. Typically they will be used in amounts in the hole operation, or (c) as a Solvent or diluent in the formu range of about 0.05 to about 1 wt %, and preferably in lation of a formulated additive to be incorporated into the amounts of about 0.1 to about 0.2 wt % based on the total concentrated brine Solution before it is used in a downhole weight of the solution including additives. Other additives operation. that can be used in the compositions of this invention include hydrate inhibitors, Scale inhibitors, thickeners, Viscosifiers, 0033 Components referred to herein by chemical name and/or biocides. or formula, whether referred to in the Singular or plural, are US 2005/0039911A1 Feb. 24, 2005

identified as they exist prior to coming into contact with 10. The improvement of claim 8 wherein the brine solu another Substance referred to by chemical name or chemical tion that is utilized therein is an aqueous calcium bromide type (e.g., another component or a Solvent). Also, even Solution containing in whatever form(s) in which calcium though the claims hereinafter may refer to Substances, bromide becomes and/or exists while in Solution in Said components and/or ingredients in the present tense (e.g., aqueous Solution, an amount thereof in the range that “comprises” or “is”), the reference is to the substance, corresponds to about 48 to about 57 wt % of anhydrous component or ingredient as it existed at the time just before calcium bromide. it was first contacted, blended or mixed with one or more 11. The improvement of claim 8 wherein the brine solu other Substances, components and/or ingredients in accor tion that is utilized therein is an aqueous Zinc bromide and dance with the present disclosure. calcium bromide Solution containing in whatever form(s) these two bromides become and/or exist while both are in 0034. This invention is susceptible to considerable varia Solution in Said aqueous Solution, an amount thereof in the tion within the Spirit and Scope of the appended claims. range that corresponds to about 53 to about 60 wt % of That which is claimed is: anhydrous Zinc bromide and in the range that corresponds to 1. A method which comprises reducing formation of about 17 to about 22 wt % of anhydrous calcium bromide. corrosive Sulfur-containing decomposition products of an 12. A method of formulating a concentrated brine Solution inorganic thiocyanate in a downhole oilfield operation in for downhole operations wherein an inorganic thiocyanate which an inorganic thiocyanate corrosion inhibitor is used in corrosion inhibitor is used as an ingredient of the Solution, a concentrated aqueous brine Solution by providing as the which method comprises ensuring that the brine Solution concentrated acqueous brine Solution in Said operation a does not contain a thiocyanate-decomposing amount of concentrated aqueous brine Solution in which there is an methanol. absence of a thiocyanate-decomposing amount of methanol. 13. A method as in claim 12 wherein a portion the 2. A method as in claim 1 wherein the brine Solution that concentrated brine Solution is Subjected to analysis to ensure is provided is an aqueous Sodium bromide Solution contain that the brine Solution does not contain a thiocyanate ing in whatever form(s) in which sodium bromide becomes decomposing amount of methanol. and/or exists while in Solution in Said aqueous Solution, an 14. A method as in claim 13 wherein a portion the amount thereof in the range that corresponds to about 38 to concentrated brine Solution is Subjected to the analysis prior about 47 wt % of anhydrous sodium bromide. to addition of an inorganic thiocyanate corrosion inhibitor to 3. A method as in claim 1 wherein the brine Solution that the Solution. is provided is an aqueous calcium bromide Solution con 15. A concentrated aqueous brine Solution adapted for use taining in whatever form(s) in which calcium bromide in downhole operations and which does not form of corro becomes and/or exists while in Solution in Said aqueous Sive Sulfur-containing decomposition products from an inor Solution, an amount thereof in the range that corresponds to ganic thiocyanate corrosion inhibitor despite the presence about 48 to about 57 wt % of anhydrous calcium bromide. therein of an inorganic thiocyanate corrosion inhibitor, Said 4. A method as in claim 1 wherein the brine Solution that Solution comprising water containing in Solution therein: is provided is an aqueous Zinc bromide and calcium bromide Solution containing in whatever form(s) these two bromides a) in the range of about 38 to about 47 wt % of sodium become and/or exist while both are in Solution in said bromide in whatever form(s) in which sodium bromide aqueous Solution, an amount thereof in the range that becomes and/or exists wherein Solution in Said Solu corresponds to about 53 to about 60 wt % of anhydrous Zinc tion; or bromide and in the range that corresponds to about 17 to b) in the range of about 48 to about 57 wt % of calcium about 22 wt % of anhydrous calcium bromide. bromide in whatever form(s) in which calcium bromide 5. A method as in claim 1 wherein Said aqueous brine becomes and/or exists when in Solution in Said Solution; Solution is an aqueous metal halide brine Solution. O 6. A method as in claim 5 wherein said metal halide brine Solution is a metal halide brine Solution formed from at least c) a mixture in the range of about 53 to about 60 wt % of one metal bromide and at least one metal chloride. Zinc bromide and in the range of about 17 to about 22 7. A method as in claim 5 wherein said metal halide brine wt % of calcium bromide in whatever form(s) or Solution is a metal halide brine Solution formed from at least composition(s) these two bromide Salts become and/or two different metal bromides. exist when they both are in Solution in Said Solution, 8. In an oilfield operation in which an inorganic thiocy and anate corrosion inhibitor is used in a concentrated aqueous d) in the range of about 0.2 to about 5 wt % of at least one brine Solution, the improvement which comprises reducing water-Soluble inorganic isocyanate corrosion inhibitor formation of corrosive Sulfur-containing decomposition in whatever form(s) in which said at least one corrosion products of an inorganic thiocyanate in Said operation by inhibitor becomes and/or exists when in Solution in Said utilizing as the concentrated brine Solution a concentrated brine Solution in which there is an absence of a thiocyanate Solution; and wherein: decomposing amount of methanol. e) the percentages specified in a), b), and c) are based on 9. The improvement of claim 8 wherein the brine solution the weight of the specified metal bromide(s) and water that is utilized therein is an aqueous Sodium bromide Solu only, and the percentages specified in d) are based on tion containing in whatever form(s) in which Sodium bro the total weight of the concentrated acqueous brine mide becomes and/or exists while in Solution in Said aque Solution of a), b), or c), and including the weight of any ous Solution, an amount thereof in the range that corresponds and all additive(s) in the concentrated aqueous brine to about 38 to about 47 wt % of anhydrous sodium bromide. Solution; and US 2005/0039911A1 Feb. 24, 2005

f) Said concentrated aqueous brine Solution is devoid of a 20. The improvement as many of claims 8-11 wherein the thiocyanate-decomposing amount of methanol inorganic thiocyanate in Said operation consists essentially whereby the formation of corrosive Sulfur-containing of Sodium thiocyanate, potassium thiocyanate, ammonium decomposition products due to interaction between thiocyanate, or a mixture of any two or all three of them. methanol and Said inorganic thiocyanate corrosion 21. A method as in any of claims 12-14 wherein said inhibitor cannot occur. inorganic thiocyanate consists essentially of Sodium thiocy 16. A concentrated acqueous brine Solution as in claim 15 wherein said Solution contains a) rather than b) or c). anate, potassium thiocyanate, ammonium thiocyanate, or a 17. A concentrated acqueous brine Solution as in claim 15 mixture of any two or all three of them. wherein said Solution contains b) rather than a) or c). 22. A concentrated acqueous brine Solution as in any of 18. A concentrated acqueous brine Solution as in claim 15 claims 15-18 wherein d) consists essentially of sodium wherein said Solution contains c) rather than a) or b). thiocyanate, potassium thiocyanate, ammonium thiocyanate, 19. A method as in any of claims 1-7 wherein said or a mixture of any two or all three of them. inorganic thiocyanate consists essentially of Sodium thiocy anate, potassium thiocyanate, ammonium thiocyanate, or a mixture of any two or all three of them.