Clay migration and entrapment in synthetic porous media

Abstract Water-sensitivity in sandstones is commonly ascribed to mobilization, transport and recapture of clays in downstream pore throats. This is based mainly on knowledge of the clay mineral content and its electrochemistry. This paper describes a method for directly observing water-sensitivity mechanisms under the microscope using pore networks etched in glass, with clays introduced into the networks. This allows direct identification of colloidal and transport factors, which is not possible in sandstone cores. The migration behaviour has been investigated with variations in flow rate, acceleration forces and salinity. Migration was observed to occur in two distinct modes: (1) as flocs, especially in concentrated brines and at high flow rates, (2) as deflocculated individual particles, especially in distilled water. Recapture of clays occurs by the formation of ‘particle briges’. The upstream pressure indicates that particle recapture is related to decreasing permeability.