SOLUBILITY MEASUREMENTS OF METHANE AND ETHANE IN WATER AT AND NEAR HYDRATE CONDITIONS

The isobaric solubility of pure methane and ethane gases in liquid wat er was measured under different conditions, including hydrate formatio n points, using a ramping method in which measurements are made throug h the entire and continuous hydrate formation/decomposition cycle. The work was conducted for methane at 3.45 MPa (500 psia) and temperature s ranging from 17.0 to 0.0 degrees C (290.2 to 273.2 K), and for ethan e at 0.66 MPa (95 psia) and a temperature range of 17.0 to 0.0 degrees C (290.2 to 273.2 K). The isobaric solubilities obtained show a signi ficant divergence from (normal) Henry's law solubility as the temperat ure is lowered, The increase in the solubility is presumably the resul t of the onset of a sorption process that traps the gas molecules in t he water structure. Several sub-processes were observed as the hydrate formation was taking place: (1) the dissolution of the gas in the liq uid water, or interstitial solubility, (2) the onset of the sorption s ub-process and build-up of the hydrate precursors, (3) the catastrophi c formation and the existence of the solid phase with its slushy chara cteristics, and (4) the solidification of the hydrates, therefore caus ing the total plugging of the experimental cell.