Schaef, H. Todd¹, B. Pete McGrail¹ 
(1) Pacific Northwest National Laboratory, Richland, WA

ABSTRACT: Direct Measurements of pH and Dissolved CO₂ Concentrations in H₂O-CO₂ Brine Mixtures to Supercritical Conditions

Very limited fundamental measurements of pH and aqueous speciation in water-salt-CO₂ mixtures at high pressure have been performed. The few available measurements show pH values varying as much as 1 or 2 pH units over the important range of temperature and CO₂ pressure expected in deep saline formations that are being widely considered for geologic sequestration. Stability of certain important clay and carbonate minerals is strongly affected by pH changes in this region. A high-pressure view cell equipped with a pressure-capable glass combination pH probe was used to independently measure solution pH in H₂O-CO₂ brine mixtures to beyond supercritical conditions. Raman spectra were simultaneously collected in the aqueous phase and show a linear relationship between the intensity of the main symmetrical stretching vibrational mode at 1388 cm-1 and increasing CO₂ pressure. The results are interpreted in terms of water solvation effects on dissolved CO₂.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.