ABSTRACT

Formation waters from clastic reservoirs offshore Norway are saturated or supersaturated with respect to albite deeper than 2.5 km, and support the view of Saigal et al. (1988) that albitization of K-feldspar is presently active in these sandstones. Thermodynamic and mass constraints show that the albitization process is more sensitive to potassium removal than sodium supply. The temperature of albitization commencement coincides more or less with the estimated onset temperature of illitization of smectite (70-80°C). Interbedded shales seem to be the major potassium sink and source of sodium. Kinetic considerations indicate that at temperatures below 145°C the dissolution of K-feldspar is always faster than albite growth. Combined with replacement constraints, the kinetic data also explain the observed coarsening of growing albite crystals with increasing burial temperature.