INFLUENCE OF BRINE-HYDROCARBON INTERACTIONS ON FT-IR MICROSPECTROSCOPIC ANALYSES OF INTRACRYSTALLINE LIQUID INCLUSIONS

Hydrocarbon droplets surrounded by an aqueous phase and trapped in a host crystal (i.e., fluid inclusions) are windows to the migrating hydrocarbon-water emulsions in petroleum reservoirs. Using synthetic hydrocarbon inclusions, Fourier transform infrared microspectrometric analysis shows that the interactions at the two liquid (hydrocarbon-aqueous solution) phase interface can be determined on a 20-mu-m scale. Spectral deformation, observed for the CH stretching bands, disappears when the alkali salt concentration decreases, when the organic solvent (CCL4 or C6H6) concentration increases, and when the mu-FT-IR analysis point moves off the interface. This deformation is due to the cation effect on the interaction of the OH/CH dipoles. The Na+, K+ cations break the water structure and induce modifications to the OH dipole at the interface, which then modifies the CH dipole moment and the CH stretching band intensity. Knowledge of the salinity of the aqueous phase is essential for complete understanding of infrared microanalysis of hydrocarbon fluid inclusions.