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Understanding steel corrosion in oilfield Brines

Understanding steel corrosion in oilfield Brines
Understanding steel corrosion in oilfield Brines

During the recovery of oil and gas, an aqueous brine saturated with carbon dioxide is one component of a multiphase flow through carbon steel pipes. In many oilfields, including Wytch Farm in Southern England and Trinidad, enhanced rates of steel corrosion are thought to result from the presence of the brine of the anions of weak acids, particularly acetate ions. This thesis examines the premise that the enhanced rate of corrosion results from the presence in the brine of acetic acid and this proton donor reduces alongside the free proton in the cathodic reaction leading to corrosion.

Experiments have used both simulated brines (3 % NaCl + sodium acetate (NaOAc), saturated with CO2) and brine samples from the oilfields. The programme requires a detailed understanding of the speciation within the brines. This has been examined using a computer package (PHREEQC 2.2) available on the World Wide Web and physical constants from the literature. It is shown that deviations from ideal solution behaviour must be taken into account. The influence of other species in the brine, particularly bicarbonate has also been considered. The conclusions of the speciation calculation have been tested by examining the voltammetry of the solutions at a Pt rotating disc electrode (RDE) and a good fit between the predicted and experimental limiting current densities has been demonstrated. The voltammetry shows that NaCl/NaOAc/CO2 solutions behave identically to NaCl/NaOAc/HOAc solutions of the same pH. It is also confirmed that the thermodynamics of hydrogen evolution depend only on the solution pH but the rate of hydrogen evolution depends on the concentrations of both free proton (pH) and undissociated acetic acid because of the rapid dissociation of the acetic acid. Moreover, in the conditions of interest, the concentration of acetic acid is far higher than that of free proton and acetic acid reduction is the major cathodic process.

University of Southampton
Garsany, Yannick
699dc832-7052-4820-80f4-ade41a7180d0
Garsany, Yannick
699dc832-7052-4820-80f4-ade41a7180d0

Garsany, Yannick (2002) Understanding steel corrosion in oilfield Brines. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

During the recovery of oil and gas, an aqueous brine saturated with carbon dioxide is one component of a multiphase flow through carbon steel pipes. In many oilfields, including Wytch Farm in Southern England and Trinidad, enhanced rates of steel corrosion are thought to result from the presence of the brine of the anions of weak acids, particularly acetate ions. This thesis examines the premise that the enhanced rate of corrosion results from the presence in the brine of acetic acid and this proton donor reduces alongside the free proton in the cathodic reaction leading to corrosion.

Experiments have used both simulated brines (3 % NaCl + sodium acetate (NaOAc), saturated with CO2) and brine samples from the oilfields. The programme requires a detailed understanding of the speciation within the brines. This has been examined using a computer package (PHREEQC 2.2) available on the World Wide Web and physical constants from the literature. It is shown that deviations from ideal solution behaviour must be taken into account. The influence of other species in the brine, particularly bicarbonate has also been considered. The conclusions of the speciation calculation have been tested by examining the voltammetry of the solutions at a Pt rotating disc electrode (RDE) and a good fit between the predicted and experimental limiting current densities has been demonstrated. The voltammetry shows that NaCl/NaOAc/CO2 solutions behave identically to NaCl/NaOAc/HOAc solutions of the same pH. It is also confirmed that the thermodynamics of hydrogen evolution depend only on the solution pH but the rate of hydrogen evolution depends on the concentrations of both free proton (pH) and undissociated acetic acid because of the rapid dissociation of the acetic acid. Moreover, in the conditions of interest, the concentration of acetic acid is far higher than that of free proton and acetic acid reduction is the major cathodic process.

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Published date: 2002

Identifiers

Local EPrints ID: 464813
URI: http://eprints.soton.ac.uk/id/eprint/464813
PURE UUID: 6415be12-0e89-4e69-a5a7-4ad562d30d04

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Date deposited: 05 Jul 2022 00:03
Last modified: 05 Jul 2022 03:14

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Author: Yannick Garsany

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