Noble gas solubility in water and oil

Early laboratory determinations of noble gas solubility were neither comprehensive nor over large temperature ranges. Benson and Krause (1976) produced the first complete data set for noble gas solubilities in pure water for the temperature range 0-50°C, but as only helium reaches a minimum in this range no extrapolation from this data is possible to higher temperatures. Potter and Clyne (1978) increased the data set by investigating solubilities up to the critical point of water. However, this work was subject to some error, as shown by the subsequent work of Crovetto et al. (1982) and confirmed by Smith (1985) both of whom have fitted their solubility data to curves with a third order power series between 298K and the critical temperature of water. The fit from Crovetto et al. 

Although it is usual to express the Henry s constant in units of pressure (Eqn. 1), to enable comparison between oil (in which the mole fraction is difficult to calculate) and water systems, we use here the molality convention where  

The solubility constant of the noble gases in oil is dependent on oil density. Coefficients taken from Kharaka and Specht (1987) for two oils fit the equation Log(K ) = A + BT where the solubility constant K follows the molality convention and is in units of atm Kg mof . T is temperature in °C. The vahd temperature range for the determination is 25-100 °C. 

calculated from Table 4 following the molality convention, plotted as a funchon of temperature. Noble gas solubility constants in more dense oil are higher (Table 4). The valid temperature range of the experimental determination is 298-373 K, although with no apparent minima, extrapo-lahon to higher temperatures is probably reasonable. 

The molality convention is followed because crude oil consists of various mixtures of different molecules that make the determination of the gas mole fraction almost impossible to determine. Unlike the studies of noble gas solubilities in water, there is no comprehensive study that has investigated the noble gas solubility in oil as a function of oil density and temperature. While a linear relationship between solubility based on the two oils measured can be assumed (e.g., Ballentine et al. 1996) and to a first order is supported by the empirical approximations (Zanker 1977 ASTM 1985), this remains a limiting factor in the application of noble gas solubility studies involving an oil phase. 

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