NOBLE GASES IN HYDROCARBON GAS AND OIL RESERVOIRS

In the context of playing a role in hydrocarbon exploration or field development noble gas studies are in their infancy. In principle noble gas fractionation in groundwater can provide a sensitive and quantitative tool with which to identify both natural gas 

Water associated with the sedimentary burial process ( formation water) or density driven sinking plumes from highly saline lakes have both also equilibrated with the atmosphere, contain dissolved air noble gases, and contribute to the subsurface inventory (Zaikowski et al. 1987). These latter sources remain poorly constrained. 

Podosek et al. (1980, 1981) have shown that atmosphere-derived Kr and Xe can be preferentially trapped in shales. Recently, Torgersen and Kennedy (1999) have found correlated Kr and Xe enrichments in oil-associated natural gases that are consistent with this trapped sedimentary origin of atmosphere-derived Kr and Xe. The range, type and condition of rock sequences that preferentially trap Xe and Kr, and the conditions of their release, remain poorly constrained (Table 6). 

Phase fractionation. In a simple two-phase system, the recipient phase equilibrating with the groundwater will be the sampled oil or gas. The magnitude of fractionation in the oil or gas from the original groundwater values will therefore be controlled by the equilibrium solubility law (Eqns. 20, and 22) and reflect the subsurface conditions of temperature, water salinity and gas/water or oil/water volume ratio. The most uncertainty 

Gas reservoirs that preserve the saturation CH4/ Ar ratio consistent with their 

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