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Reducing sulfide in production fluids during oil recovery

a production fluid and sulfide technology, applied in the field of oil recovery, can solve the problems of reducing the value of recovered crude oil, competition for nutrients, health and environmental hazards,

Inactive Publication Date: 2013-06-27
EI DU PONT DE NEMOURS & CO
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The invention is about a method for reducing sulfide in oil production fluid from an oil reservoir. This is achieved by adding an aqueous solution containing an inorganic oxidizing agent to the well casing, where it flows down the well casing and contacts the production fluid in the well bore below the production pipe. This process results in a reduction in sulfide concentration in the production fluid compared to a control group without the step of adding the oxidizing agent. The aqueous solution can contain nitrate ions, nitrite ions, or a mixture of both, or other suitable oxidizing agents such as permanganates, persulfates, inorganic peracids, chromates, bromates, iodates, chlorates, perchlorates, chlorites, hypochlorites, inorganic peroxides, or oxides.

Problems solved by technology

The metabolism of these SRB converts sulfate that is typically present in injection water to sulfide, which results in souring of a reservoir and the oil produced, thereby reducing the value of the recovered crude oil.
In addition sulfide in production water causes corrosion of equipment used to recover oil including storage reservoirs, surface facilities, and pipelines, and it can cause plugging by the formation of iron sulfide, as well as causing health and environmental hazards.
When both are present, there may be competition for nutrients between SRB and nitrate-reducing bacteria (NRB).
Biodegradation of light oil components is undesirable because this causes increased oil viscosity and the higher viscosity causes increased resistance to oil flow.

Method used

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  • Reducing sulfide in production fluids during oil recovery

Examples

Experimental program
Comparison scheme
Effect test

example 1

NO2− Reactivity with Sulfide

[0061]A sodium nitrite solution was used to oxidize a sodium sulfide solution at room temperature in a closed system in order to look at the kinetics of the reaction and to prevent the volatilization of sulfide. Based on a balanced redox reaction, 1 mole of nitrite should be able to oxidize at least 0.5 mole of hydrogen sulfide. The nitrite and sulfide solutions used in the experiment were made up in artificial brine, which mimics the moderately high salinity of many oil reservoirs. The brine had the following composition: CaCl2.2H2O, 6.75 g, NaCl, 26.1 g, Na2SO4, 0.015 g, MgCl2.6H2O g, 4.45, KCl, 0.7 g plus enough water to make a total of 500 ml of brine solution. The sulfide solution in brine was approximately 15 ppm S2−. The nitrite solutions were approximately 50 ppm and 725 ppm NO2−. Two different treatments were run. In treatment 1 (Table 1) the nitrite:sulfide molar ratio was 29:1, which resulted in reaction conditions where nitrite was approximate...

example 2

NO2− Reactivity with Sulfide: Titration of Molar Ratios Needed for a Rapid Reaction

[0063]A range of nitrite:sulfide ratios were tested to determine the molar ratio needed to cause a rapid oxidation of sulfide. The nitrite and sulfide solutions used in the experiments were made up in artificial brine as described in Example 1. Experiments were performed as described in Example 1 using eight different treatments. The nitrite / sulfide molar ratios used were 2, 5, 10, 15, 20, 25, 30, and 35. Results given in Table 2 showed that the reaction rate remained slow at a ratio of 2, as seen in the previous Example, but at a ratio of 5:1 or higher the reaction occurred rapidly with sulfide becoming undetectable in 10 minutes or less. The ability to rapidly remove sulfide at lower nitrite:sulfide ratios makes the process more economical

TABLE 2Changes in sulfide concentrations with time following the additionof nitrite at NO2−:S2− ratios from 2:1 to 35:1.ppm S2−Observed ppmNO2−:S2− molarReactionad...

example 3

Prophetic

Production Well Treatment Using Continuous Addition of Nitrate / Nitrite Solution in Well Casing to Mitigate Sulfide Present in Production Fluid of Soured Wells

[0064]In this example, a producer well is continuously treated to mitigate sulfide present in the production water using a nitrate / nitrite mixture. Sulfide in the production fluids often results from well souring, following the start of water injection for secondary oil recovery. Rather than treating the injected water and all reaches of the subterranean oil reservoir, as is the normal practice to mitigate souring by sulfide formation, a process is used that treats the smaller produced water volume, making it more economical, while still sweetening the produced fluids by removing sulfide.

[0065]A nitrate / nitrite solution is produced by dissolving any inexpensive nitrate and nitrite salts, such as NaNO2 or NaNO3, in water. This solution is continuously pumped into the well casing of a production well. The production flui...

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PUM

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Abstract

Methods are provided for treating production fluid in a production well in an oil reservoir to reduce the amount of sulfide in the production fluid. The production fluid is treated with nitrate and / or nitrite ions or inorganic oxidizing agent in an aqueous solution that is added to the well casing.

Description

[0001]This application claims the benefit of U.S. National application Ser. No. 13 / 226,717, filed Sep. 7, 2011, which is incorporated by reference in its entirety.FIELD OF THE INVENTION[0002]This disclosure relates to the field of oil recovery. More specifically, it relates to reducing sulfide in production fluids recovered from oil reservoirs.BACKGROUND OF THE INVENTION[0003]Hydrogen sulfide (H2S) is commonly found in oil reservoirs due to its production by sulfate-reducing bacteria (SRB), which may be indigenous to an oil reservoir and / or introduced such as during water injection in water flooding secondary oil recovery methods. The metabolism of these SRB converts sulfate that is typically present in injection water to sulfide, which results in souring of a reservoir and the oil produced, thereby reducing the value of the recovered crude oil. In addition sulfide in production water causes corrosion of equipment used to recover oil including storage reservoirs, surface facilities,...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): E21B43/16
CPCC09K8/532E21B43/16E21B21/062
Inventor ALSOP, ALBERT W.FALLON, ROBERT D.JACKSON, SCOTT CHRISTOPHER
Owner EI DU PONT DE NEMOURS & CO
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