Generation of methane gas hydrate equilibrium curve for the thermodynamic gas hydrate inhibitor propylene glycol

Abstract Use of thermodynamic hydrate inhibitors (THIs) for prevention of gas hydrate formation in the oil and gas field operations is a well-known and accepted process all over the world. Although glycols are reported as THIs, but only monoethylene glycol is studied in detail and applied conventionally. In this study, gas hydrate inhibition efficiency of propylene glycol is determined. The data is acquired using a stirred cryogenic PVT sapphire cell and the hydrate dissociation temperature measured at isobaric condition (constant pressure) is considered as the thermodynamic equilibrium temperature, because although dissociation temperature depends on hydrate particle size and heat flux, but, it is unlike the random nature and unpredictability of formation temperature. The key objective of this study is to establish the equilibrium condition of methane hydrate in presence of 20 wt% propylene glycol as thermodynamic inhibitor. The identification of dissociation temperature is based on visual method. The gas hydrate equilibrium curve for 20 wt% propylene glycol in methane-water system is established by determining the hydrate equilibrium dissociation temperatures for a pressure range 70–190 bar. Also performance comparison of propylene glycol with monoethylene glycol is done to gauge the inhibition efficiency of propylene glycol, the results of which have shown better inhibition efficiency of propylene glycol. Hydrate equilibrium curve of 20 wt% propylene glycol system showed an average of 10.42 °C deviation towards lower temperature compared to that of the system without the inhibitor. The fitted curve for hydrate dissociation temperatures showed co-efficient of determinants (R2) value ≥ 0.97, suggesting the reliability of the experimental observations.