Measurment and prediction of salt formation in the presence of hydrate organic inhibitors

Organic inhibitors (e.g. methanol, ethanol, ethylene glycol, triethylene glycol) are generally used to reduce the risk of gas hydrate formation in drilling and production operations. The addition of organic inhibitors has a significant adverse effect on the solubility of salts, increasing the risk of salt deposition. A better understanding of salting-out problems is necessary for effective design and implementation of flow assurance strategies in such complex systems. In this communication we present an experimental investigation on the effect of methanol, ethanol and ethylene glycol on the solubility of several salts, including halite, sylvite and antarcticite. The results show that ethylene glycol has a much lesser adverse impact on salt deposition than methanol and ethanol. The details of an experimental set-up used for measuring salt solubility and salting out are described. The set-up could also provide valuable information on the effectiveness of various inhibitors used for preventing salt deposition in the presence or absence of gas hydrate organic inhibitors. In addition, a novel predictive numerical approach is proposed to model salt formation in brine solutions with or without hydrate organic inhibitors. The model is based on the equality of the fugacity of salt in the solid phase and aqueous phase, which are calculated by an equation of state. The validity of the new developed model is demonstrated over a wide temperature range (i.e., -20 to 125°C), salt concentration up to saturation point and hydrate inhibitor concentration up to 50 mass%.