Novel Approach to Validation of Thermodynamic Models for the Chemistry of Oilfield Environments

Materials selection is critical in the oil and gas industry, and pH has conventionally been a key parameter in the definition of appropriate qualification test conditions (e.g., in pH-H₂S domain diagrams). Modeling of the chemistry of oilfield environments is commonly used to link pH measurements during laboratory testing to conditions in the field, but experimental validation of such models has been limited by the absence of reliable measurement techniques in these harsh environments. Here an alternative approach to model validation incorporating extraction and measurement of the total carbon content of the aqueous phase via ion exclusion chromatography is demonstrated. This method is used to validate predictions from a recently developed thermodynamic model of aqueous solution chemistry in typical oilfield environments that can be applied to diverse multi-component systems and highly concentrated solutions at various temperatures and gas pressures. Good agreement is obtained between the predicted and measured carbon contents in 0.1 M and 3.9 M sodium chloride solutions with 0.2 MPa carbon dioxide over the temperature range of 100°C to 200°C. In order to achieve more representative test programs during materials selection, it is recommended that this combined approach of modeling and solution analysis should replace conventional pH measurement in the definition of test conditions.