Membrane-filtration processes capable of filtering dissolved inorganic salts from water have been well documented in the laboratory and in industrial applications (desalination). Application of such processes to earth (sedimentary-basin) models, however, is inadequately documented and subject to several difficulties. These difficulties include the facts that (1) natural pressure gradients adequate to overcome the osmotic pressures required to separate salt from water do not appear to be available or reported in sediment-sedimentary rock environments, and (2) salt exclusion properties of membranes correlate inversely with permeability. To achieve geologically significant enrichment of salts in subsurface fluids requires that large volumes of fluids pass across what would n rmally be regarded as aquicludes and nonreservoir rocks under relatively leak-free conditions. No proof of such massive movements has been offered. In fact, the consequences of such movements, consistently applied to sedimentary basins, would negate much of the existing principles and practice of petroleum geology and petroleum engineering.

Recent pore-fluid studies from ocean drilling operations show no evidence of membrane filtration in deep-ocean sediments or in geosynclinal sediments from the Gulf of Mexico. These factors contribute to the conclusion that membrane filtration concepts as presently formulated have little importance in enriching subsurface waters in salt, and probably have only minor influence on the ionic composition of subsurface fluids.

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