Effects of Monoethylene Glycol on Carbonate Equilibrium and Calcite Solubility in Gas/Monoethylene Glycol/Water/Salt Mixed Systems

摘要

Monoethylene Glycol (MEG), HOCH2CH2OH, is an important raw material with numerous industry applications, which include polyester synthesis, automobile antifreeze, coolant, and aircraft anti-icer. In oil and gas industry, MEG is commonly used as a gas hydrate inhibitor, which can prevent the formation of gas hydrate during the production of oil and gas in oil wells. However, MEG has the adverse effects on the solubility of minerals. The lowering solubility of minerals will result in the precipitation of mineral scales, which is another serious problem in the production of oil and gas and also causes scaling problems during glycol regeneration. Despite the importance of scale problems with MEG in oil production, there are few investigations on the solubility of mineral salt in the co-solvent of MEG and brine solutions due to the complexities of this mixed-solvent system. In this research, experiments have been conducted on the carbonate equilibrium and the solubility of calcite at 2°C- 70°C, 0-6.5 m ionic strengths, and 0-100% MEG. MEG activity coefficients with respect to dissolved CO2, bicarbonate, carbonate, and calcium are determined as a function of temperature, ionic strength, and mole fraction MEG in mixed solvent. A self-consistent activity model is proposed based on the data obtained from this study. Pitzer theory was used to calculate the effect of salt and a Born type equation was applied to analyze the effects of MEG. This model can predict mineral scales solubility in the presence of MEG and brine solutions, provide a better understand of effects of MEG on solubility of scales, and gain an insight into the scale inhibitor studies.