SULFUR AND AMORPHOUS DITHIAZINE MEASUREMENT
20230176031 · 2023-06-08
Assignee
Inventors
Cpc classification
International classification
Abstract
The disclosure describes a method to indirectly measure the amount of elemental sulfur or amorphous dithiazine in a reservoir sample by converting them to H.sub.2S gas. The H.sub.2S is captured via caustic cyanide solution and quantified by analytical methods and correspond to the concentration of elemental sulfur or amorphous dithiazine. The method has particular applicability to determine where best to drill and avoid locations of high sulfur.
Claims
1. A method of assaying amorphous dithiazine (a-DZT) in a reservoir sample, said method comprising: a) obtaining a sample from a reservoir containing monoethanolamine (MEA) or a triazine, or MEA or a triazine being added thereto; b) analyzing said sample or portion thereof to determine an amount of a-DZT therein by treatment with a reductive solution comprising a mercaptan plus an amine plus an alcohol to convert a-DZT to H.sub.2S; c) measuring an amount of H.sub.2S produced in step b; and d) calculating an amount of a-DZT in said sample from said amount of H.sub.2S.
2. The method of claim 1, wherein said sample is a drilling mud sample obtained while drilling an oil well or a test well.
3. The method of claim 1, wherein said sample is a core sample.
4. The method of claim 1, wherein H.sub.2S is measured by reaction with caustic cyanide and determining an amount of thiocyanate or isothiocyanate produced.
5. The method of claim 4, wherein thiocyanate or isothiocyanate are determined by reaction with iron or copper plus pyridine and measuring an amount of color produced.
6. The method of claim 1, where said sample is pretreated before step b to remove any dissolved H.sub.2S in said sample.
7. A method of avoiding drilling in high H.sub.2S reservoir zones, said method comprising: a) obtaining a plurality of samples, each sample from a known location in a reservoir and containing MEA or a triazine, or MEA or a triazine being added thereto; b) optionally analyzing each of said plurality of samples or portion thereof to determine a first amount of H.sub.2S remaining unreacted with said MEA or triazine; c) analyzing each of said plurality of samples or portion thereof to determine an amount of dithiazine and correlating said amount of dithiazine to a second amount of H.sub.2S; d) analyzing each of said plurality of samples or portion thereof for an amount of amorphous dithiazine by treatment with a reductive mercaptan solution to convert a-DZT to H.sub.2S and measuring a third amount of H.sub.2S; e) calculating a total amount of H.sub.2S in a sample from a location by adding said first amount, said second amount and said third amount, thereby determining one or more highest H.sub.2S content location(s) in said reservoir; f) changing a direction of drilling of an oil well to avoid said one or more highest H.sub.2S containing location(s); and g) producing oil from said oil well, wherein said oil has less H.sub.2S than a method of producing oil from said reservoir without said changing step f.
8. The method of claim 7, wherein said plurality of samples are drilling mud samples obtained while drilling said oil well or a test well.
9. The method of claim 7, wherein said plurality of samples are core samples.
10. The method of claim 7, wherein said reductive mercaptan solution comprises a mercaptan, an amine and an alcohol.
11. The method of claim 7, wherein H.sub.2S is measured by reaction with caustic cyanide and determining an amount of thiocyanate or isothiocyanate produced.
12. The method of claim 11, wherein thiocyanate or isothiocyanate are determined by reaction with iron or copper plus pyridine and measuring an amount of color produced.
13. A method of measuring elemental sulfur S.sub.8 from a crude oil sample, the method comprising the following steps: a) centrifuging a crude oil sample to remove entrained water; b) removing dissolved H.sub.2S in said crude oil sample; c) adding a reducing agent comprising a mercaptan to said crude oil sample to convert elemental sulfur S.sub.8 to H.sub.2S; d) quantitating an amount of H.sub.2S; and e) calculating an amount of elemental sulfur S.sub.8 in said crude oil sample from said amount of H.sub.2S.
14. The method of claim 13, wherein said removing dissolved H.sub.2S in said crude oil sample is by acidification, dilution and refluxing.
15. The method of claim 13, wherein H.sub.2S is quantitated by reaction with caustic cyanide to produce thiocyanate and/or isothiocyanate, and thiocyanate and/or isothiocyanate are measured.
16. The method of claim 15, wherein thiocyanate and/or isothiocyanate are measured by ion chromatography or colorimetry or spectrophotometry.
17. The method of claim 15, wherein determining an amount of elemental sulfur S.sub.8 in said crude oil sample is done by correlating thiocyanate and/or isothiocyanate to elemental sulfur S.sub.8 and calculating an amount of elemental sulfur S.sub.8 ,l m,k in said sample.
Description
BRIEF DESCRIPTION OF DRAWINGS
[0052]
[0053]
[0054]
[0055]
[0056]
[0057]
DETAILED DESCRIPTION
[0058] There are several ways to measure elemental sulfur in crude oil and other reservoir samples, and herein we use an indirect method wherein elemental sulfur is converted to H.sub.2S gas using a reductive mercaptan solution.
[0059] We also report the only indirect method for the measurement of amorphous DTZ which is a by-product of H.sub.2S scavenger reaction, thus allowing quantitation of total H.sub.2S in drilling mud samples treated with scavenger. Amorphous DTZ also reacts with reductive mercaptan solutions to release H.sub.2S gas. This evolved gas is trapped and quantified to correspond to the a-DTZ or elemental sulfur in the starting sample. See
[0060] The H.sub.2S gas produced in the above two reactions then reacts with caustic cyanide solutions to form thiocyanates and/or isothiocyanates. There are a number of analytical methods available for the quantification of thiocyanates and isothiocyanates including spectrophotometric analysis, colorimetry with iron salts, copper-pyridine method, ion chromatography and the like. The amount of thiocyanate and/or isothiocyanates calculated by one of these methods correspond to the amount of H.sub.2S gas released by the reaction of a-DTZ or elemental sulfur with reductive mercaptan solution. This method ensures accurate measurement of a-DTZ or elemental sulfur in the starting sample.
[0061] In the present disclosure, distillation over caustic cyanide solution is carried out using a micro-distillation apparatus (for example as described in U.S. Pat. No. 5,160,413) to distill elemental sulfur or a-DTZ as H.sub.2S.
[0062] In general, the distillation in the micro-distillation apparatus is carried out by adding a sample to be analyzed mixed with a reducing mercaptan solution that contains an amine and an alcohol for a-DZT and mercaptans for S.sub.8, and optionally a hydrocarbon to maintain viscosity in the lower elongated member of the column 602 (
[0063] The sample is placed in the lower elongated member of the micro-distillation column and heated to appropriate temperature controlled by the heating mantle. The heating temperature is based on a number of factors including the amount of sample used for distillation, the viscosity of the solution, the specific combination of mercaptan, amine and alcohol used, etc.
[0064] Upon reaction with the reductive mercaptan solution, the a-DTZ or the elemental sulfur in the respective samples to be tested releases H.sub.2S gas. Heating for 15-45 minutes vaporizes the H.sub.2S which passes upward from the lower elongated member through a permeable membrane (usually a Teflon tape) into the upper elongated cyanide trapping reservoir/column. This trapping column contains caustic cyanide solution which reacts with the H.sub.2S gas to produce thiocyanate and/or isothiocyanate. These are easily measured by e.g., ion chromatography or colorimetric analysis with iron salts, spectrophotometric analysis, copper-pyridine method, and the like. The amount of elemental sulfur or a-DTZ in the starting sample solution can then be back calculated.
[0065] Analysis Method amorphous DTZ: The drilling mud containing a-DTZ to be analyzed is first prepared to remove all impurities and components that may interfere with the reaction of a-DTZ with reductive mercaptan. These interferences must be removed to use H.sub.2S as a proxy for a-DTZ concentration.
[0066] This is achieved by a rigorous washing program including washes with weak acids, hydrocarbon, alcohols, and water. The cleaned solids are then added to the lower elongated column of the micro-distillation apparatus followed by the addition of mercaptan, amine and alcohol solution. Optionally a hydrocarbon is also added to this column to maintain the viscosity of the solution so as to allow for uniform heating of the solution. Immediately after the reduction solution is added, the trapping column is attached, and the lower distillation column is heated.
[0067] The assembled apparatus is heated for 15-45 minutes to allow all evolved H.sub.2S diffuse across the Teflon tape barrier and react with the caustic cyanide solution resulting in production of thiocyanate or isothiocyanate as shown in Eq. 3. This thiocyanate and/or isothiocyanate is measured by one of the various analytical methods and back calculated to determine the amount of a-DTZ in the original solution. This number can then be added to the number obtained by separately measuring dithiazine and/or H.sub.2S in the samples, providing a more accurate total H.sub.2S reading.
[0068] Copper-pyridine thiocyanate analysis method can be used whereby the thiocyanate stoichiometrically reacts with copper(II) salts in the presence of pyridine to form a bright green complex that precipitates and is easily quantified, shown in Eq. 4. A more common method of reaction with iron(III) salts can be carried out that forms bright red iron-thiocyanate complex, shown in Eq 5., which can be analyzed using a spectrophotometer.
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[0069] One particular process for the analysis of a-DTZ will involve taking 3.0 g of drilling mud in a 50 mL separation flask followed by the addition of 15 mL n-hexane. Mixing the content of the flask thoroughly and decanting the n-hexane. This n-hexane wash will be carried out 2-3X. Acid wash will be carried out with 2-3X 15 mL wash with dilute hydrochloric acid solution. Water wash with 2-3X 15 mL distilled water will then carried out and the solution centrifuged for 20 minutes to remove water soluble impurities. The resulting drilling mud sample will be air dried at room temperature and weighed and placed in a lower elongated column of the micro-distillation apparatus.
[0070] In a measuring flask, 5 mL dithiothreitol or 2-mercaptoethanol, 5 mL N,N-dimethyl-N-(2-hydroxypropyl) amine and 5 mL butanol will be added and mixed with the drilling mud sample. This solution will be slowly poured over the lower elongated column of the micro-distillation apparatus. The H.sub.2S trapping column will be immediately attached to the lower elongated column and the set-up will be placed on a heating mantle. This solution will be heated at 45° C. for 25 minutes. H.sub.2S gas will evolve which will diffuse across the Teflon tape barrier into the trapping column containing known amount of caustic cyanide solution.
[0071] After the completion of the reaction, the set-up will be allowed to cool and the trapping column will be removed and treated with standardized solution of ferric ammonium sulfate solution and analyzed by spectrophotometer. The amount of H.sub.2S evolved in the micro-distillation apparatus will be calculated. The amount of a-DTZ in the starting material will be back calculated by knowing this H.sub.2S amount.
[0072] Analysis Method Elemental Sulfur: Quantitative analysis of crude oil samples to determine elemental sulfur is carried out by first removing any trapped H.sub.2S gas, entrained water, inorganic sulfides and polysulfides. These chemicals would give a positive bias to the quantification described herein and must be removed, although as above may be separately quantified and contribute to total sulfur levels if desired.
[0073] Entrained water can be eliminated by centrifugation. Dissolved H.sub.2S can be removed by sample acidification, dilution, and refluxing. The acidification/dilution solution will reduce sample viscosity and maintain a single-phase solution as the analysis progresses.
[0074] The purged, diluted sample is cooled before adding the reduction solution. The reduction solution would contain a reducing agent solution comprising of a mercaptan, an amine, an alcohol and optionally a hydrocarbon. This solution would induce the conversion of elemental sulfur to H.sub.2S and maintain a single phase in the distillation column.
[0075] Immediately after the reduction solution is added, the trapping column is attached to capture any evolved H.sub.2S. The assembled apparatus would be heated for 15-45 minutes to allow all evolved H.sub.2S diffuse across the Teflon tape barrier and react with the caustic cyanide solution resulting in production of thiocyanate or isothiocyanate. This thiocyanate and/or isothiocyanate would then be measured by one of the various analytical methods discussed above and back calculated to determine the amount of elemental sulfur in the original solution.
[0076] Although the systems and processes described herein have been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from the spirit and scope of the invention as defined by the following claims. Those skilled in the art may be able to study the preferred embodiments and identify other ways to practice the invention that are not exactly as described herein. It is the intent of the inventors that variations and equivalents of the invention are within the scope of the claims while the description and abstract are not to be used to limit the scope of the invention. The invention is specifically intended to be as broad as the claims below and their equivalents.
Element Sulfur Analysis
[0077] A proposed experiment to prove proof of concept is described next:
[0078] A. Centrifuge a sample of Ss-containing hydrocarbon to settle entrained water;
[0079] B. Transfer 1-5 mL centrifuged hydrocarbon in the 602 section of the micro-distillation apparatus;
[0080] C. Pipet 1 mL of a 2%-48%-50% valeric acid, isopropanol, toluene solution into section 602;
[0081] D. Cover with Teflon membrane and heat to 100-110° C. for 15-45 minutes to remove free H.sub.2S from fluids;
[0082] E. Remove section 602 from the heater and cool to below boiling point, then pipet 1 mL of a 1.25%-28.75%-35%-35% triethylamine, 2-mercaptoethanol, isopropanol, toluene solution thereinto;
[0083] F. Cap with section 610 and reflux for 15-45 minutes; and
[0084] G. Remove caustic cyanide solution and analyze via preferred analytical method for thiocyanate and/or isothiocyanate.
A-Dtz in Drilling Mud Analysis
[0085] A proposed experiment to prove proof of concept is described next:
[0086] A. Isolate drilling solids using centrifugation or filtering apparatus;
[0087] B. Wash solids with hot xylenes 3X to remove hydrocarbons and elemental sulfur from the solids;
[0088] C. Wash solids 3X with methanol and 3X with water to remove remaining dissolvable material;
[0089] D. Dry remaining solid in vacuum overnight;
[0090] E. Transfer 100-1000 mg dried solids to section 602;
[0091] F. Pipet 1 mL of a 2%-48%-50% valeric acid, isopropanol, toluene solution into section 602;
[0092] G. Cover with Teflon membrane and heat to 100-110° C. for 15-45 minutes to remove free H.sub.2S from fluids;
[0093] H. Remove section 602 from heater and cool below boiling point, then pipet 1 mL of a 1.25%-28.75%-35%-35% triethylamine, 2-mercaptoethanol, isopropanol, toluene solution;
[0094] I. Cap with section 610 and reflux for 15-45 minutes; and
[0095] J. Remove caustic cyanide solution and analyze via preferred analytical method for thiocyanate and/or isothiocyanate.
[0096] The following references are incorporated by reference in their entirety. [0097] U.S. Pat. No. 5,160,413 Micro-distillation process for cyanide. [0098] US2012247515 Methods for dissolution of amorphous dithiazine. [0099] US2013149788 Assay for quantifying elemental sulfur levels in a sample. [0100] Ser. No. 17/494,673 (US20220112443) Method for dissolution of amorphous dithiazines. [0101] Ser. No. 17/494,470 (US20220112433) Elemental sulfur dissolution and solvation. [0102] Grahame T. N.; Matherly, R. “Use of Portable Analytical Methods to Determine the Stoichiometry of Reaction for Hexahydrotriazine-Based Hydrogen Sulfide Scavenger Operations.” Anal. Chem. 86(10): 4879-4882 (2014). [0103] Saleh, T. A. “Characterization, determination and elimination technologies for sulfur from petroleum: Toward cleaner fuel and a safe environment.” Trends in Environmental Anal. Chem., 25: e00080 (2020). [0104] Long, J. H. “A textbook of elementary analytical chemistry qualitative and volumetric.” (1910)