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Non-Ideal Gases and Solutions Complexes and Ion Pairs in Corrosion

The design of corrosion tests and computer corrosion rate simulations that do not incorporate the concepts of non-ideal chemistry can introduce very significant errors to the results.

Product Number: 51317--8835-SG
ISBN: 8835 2017 CP
Author: Stephen Smith
Publication Date: 2017
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$20.00
$20.00

Ideal and non-ideal gases are a well recognized concept in the oil and gas industry with corrections for non-ideal behavior frequently made in the design and operation of hydrocarbon processing facilities. Application of the concepts of non-ideal gas and aqueous solution chemistry to corrosion testing and modeling for oilfield application has been limited until quite recently. However with the advent of HPHT production with supercritical gas conditions and heavy brines require the consideration of non-ideality of the field applications are to be simulated accurately. When designing tests or evaluating production conditions that include supercritical fluids or gas/liquid phases that are near critical conditions failure to use the fugacity of a gas rather than partial pressure can cause errors that exceed X%. For aqueous solutions when dealing with brines that are more concentrated than 3 to 5% assuming that reactions occur based upon the ionic concentration of a species rather than true activity can produce errors in excess of Y%. The chemistry of field brines is also much more complicated than that of a simple NaCl brine. The presence of divalent cations such as Fe2+ Ca2+ and Mg2+ and non-halide anions introduces the potential for the formation of ionic complexes and dissolved molecular species (ion pairs) such as CaSO4. Failure to consider the presence of these dissolved species in heavy brines can lead to simulations that do not reflect field production conditions. Among the properties that are most sensitive to solution nonideality and ion pair formation pH and solubility of scale and protective film-forming solids such as FeCO3 and FeS are of particular importance in corrosion. A methodology will be presented for maximizing the accuracy of predicting these properties.

Key words: Thermodynamics, electrolyte solutions, fugacity, corrosion testing, speciation, solubility

Ideal and non-ideal gases are a well recognized concept in the oil and gas industry with corrections for non-ideal behavior frequently made in the design and operation of hydrocarbon processing facilities. Application of the concepts of non-ideal gas and aqueous solution chemistry to corrosion testing and modeling for oilfield application has been limited until quite recently. However with the advent of HPHT production with supercritical gas conditions and heavy brines require the consideration of non-ideality of the field applications are to be simulated accurately. When designing tests or evaluating production conditions that include supercritical fluids or gas/liquid phases that are near critical conditions failure to use the fugacity of a gas rather than partial pressure can cause errors that exceed X%. For aqueous solutions when dealing with brines that are more concentrated than 3 to 5% assuming that reactions occur based upon the ionic concentration of a species rather than true activity can produce errors in excess of Y%. The chemistry of field brines is also much more complicated than that of a simple NaCl brine. The presence of divalent cations such as Fe2+ Ca2+ and Mg2+ and non-halide anions introduces the potential for the formation of ionic complexes and dissolved molecular species (ion pairs) such as CaSO4. Failure to consider the presence of these dissolved species in heavy brines can lead to simulations that do not reflect field production conditions. Among the properties that are most sensitive to solution nonideality and ion pair formation pH and solubility of scale and protective film-forming solids such as FeCO3 and FeS are of particular importance in corrosion. A methodology will be presented for maximizing the accuracy of predicting these properties.

Key words: Thermodynamics, electrolyte solutions, fugacity, corrosion testing, speciation, solubility

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