Experimental Study of the Effect of HCO₃^– and Cl^– Ions on Natural Gas Hydrate Formation in a Porous Medium

A differential thermal analysis study was carried out on the formation and decomposition of hydrates in systems containing natural gas, sand, and 5 mass % aqueous NaHCO₃ as well as natural gas, sand, and 5 mass % aqueous NaCl with initial gas pressures from 3 to 9 MPa. Equilibrium conditions, enthalpy of dissociation, and the kinetic parameters of hydrate formation were determined. Hydrate formation in the system containing aqueous sodium bicarbonate proceeds at higher temperatures and lower pressures and has higher kinetic parameters than in the system with aqueous sodium chloride of the same concentration. Composition of the solutions is one of the factors affecting hydrate formation in the studied systems. The HCO₃^– ion is found to have a greater structure-making effect than the Cl^– ion, which leads to differences in the thermodynamic conditions and kinetic parameters of natural gas hydrate formation in a porous medium.