Jitendra Sangwai

In this work, a thermodynamic model is developed and used to predict the phase stability conditions for methane hydrate-ionic liquid (IL)-water system. The hydrate phase is computed from modified van der Waals-Platteeuw model. The Peng-Robinson equation of state (PR-EoS) and developed activity model as a combination of Pitzer-Mayorga-Zavitsas-hydration model is used to evaluate the fugacities of gas and liquid phases, respectively. The hydrate phase stability prediction is also computed using the liquid phase activity predicted by NRTL and Pitzer-Mayogra models, separately, and is compared with the results predicted from the developed model. The model predictions are compared with experimental results on the phase stability of methane hydrate reported in open literatures for 21 ILs. The 21 ILs chosen from various ionic groups such as tetraalkylammonium, pyrrolidinium, imidazolium cationic family with various anion group such as halides (Cl, Br, I), sulphate (HSO4, ethylsulphate), tetrafluoroborate (BF4) and dicyanamide (DCA). The absolute average relative deviation in predicted pressure (AARD-P) with developed Pitzer-Mayorga-Zavitsas-hydration-model is improved to 1.60% and non-random two liquid (NRTL), Pitzer-Mayorga model showed 2.02% and 1.77% with 120 data points in the temperature range of 272.1-291.59K and pressure range of 2.48-20.67MPa. For 120 data points of phase stability conditions of 21 ILs, 39.2% of the predicted equilibrium pressures (47 data points) were within relative absolute deviation of 0.0-1.0%, 29.2% of the equilibrium pressures (35 data points) were within absolute deviation of 1.01-2.5%, 25.8% of data (31 data points) were within 2.51-7.5% which are mainly for data with low concentrations of ILs and only 5.8% of data (7 data points) showed relative absolute deviations above 7.5% which are observed mainly for data with high concentrations of ILs. Further, the model is used to calculate the inhibition effect of selected 21 ILs on methane hydrate formation.

The need for development of better surface active agents for upstream oil and gas industry which can survive harsh condition of salinity are in great demand, particularly for the applications related to improved/enhanced oil recovery, flow assurance and oil and gas production operations keeping in mind the environmental constraints. The technical difficulties which need to be considered are those involving the surface forces such as surface tension (SFT) and interfacial tension (IFT) acting between the formation water and the low waxy crude oil. In this study, we have employed the use of eight aliphatic ionic liquids (ILs), based on di- and tri-alkyl ammonium as cations and with various anions such as [CH3COO]-, [BF4]-, [H2PO4]- and [HSO4]- for the investigation of the surface phenomenon of crude oil-water system. The synergistic effect of NaCl along with the ILs is investigated in detail. It is observed that there is a significant reduction in the surface tension of water and the interfacial tension of crude oil-water system in the presence of salt, particularly at higher concentration of NaCl (200,000ppm). Effect of temperature, time, alkyl chain length of the cationic part of the ILs, nature of anions of ILs and the concentration of ILs is also discussed. The trend in the electrical conductivity of aqueous IL solutions with various concentrations at three different temperatures 298.15-318.15K is also presented along with critical aggregation concentration. The study on the effect of ILs on the SFT/IFT of water and low waxy crude oil-water system reveal that the ILs are successful in minimizing the effect of the surface forces in the presence of salt and thereby, could pave the way for efficient enhanced oil recovery operations.

A thermodynamic model for the prediction of CO2 hydrate phase stability conditions in the presence of pure and mixed salts solutions and various ionic liquids (ILs) is developed. In the proposed model van der Waals and Platteeuw model is used to compute the hydrate phase, Peng-Robinson equation of state (PR-EoS) for the gas phase and the Pitzer-Mayorga-Zavitsas-Hydration model is employed to calculate the water activity in the liquid water phase. This model is an extension of the model developed by Tumba et al. (2011) for the prediction of methane and CO2 hydrate phase stability conditions in the presence of tributylmethylphosphonium methylsulfate IL solution. Shabani et al. (2011) mixing rule is modified by incorporating the water-inhibitor (salt/IL) interaction parameter to calculate the water activity in mixed salt solutions. The model predictions are also calculated using the Pitzer-Mayorga model separately and compared with predictions of the developed model. The model predictions are compared with experimental results on the phase stability of CO2 hydrate in the presence of ILs, pure and mixed salts as reported in literatures. The ILs are chosen from imidazolium cationic family with various anion groups such as bromide (Br), tetrafluoroborate (BF4), trifluoromethanesulfonate (TfO), and nitrate (NO3) and the common salts such as NaCl, KCl and CaCl2. Good agreement between the developed model predictions and the literature data is observed. The overall average absolute deviation (AARD%) with Pitzer-Mayorga-Zavitsas-Hydration model is observed to be within ±1.36% while Pitzer-Mayorga model accuracy were about ±1.44 %. Further, the model is extended to calculate the inhibition effect of selected inhibitors (ILs and salts) on CO2 hydrate formation.