Abstract: The water permeability of a subterranean formation is selectively reduced by introducing a non-aqueous treatment agent into the formation. The treatment agent comprises a hydrogel polymer and a non-aqueous fluid carrier. The treatment agent preferably further comprises an alkali metal carbonate when calcium-rich aqueous brines are resident in the formation. The treatment agent is maintained within the formation for a time sufficient to permit the hydrogel polymer to absorb water from the formation. As it contacts water, the hydrogel polymer swells and thereby blocks further water flow through formation pores. Treatment of formations in accordance with this method permits enhanced recovery of minerals, such as hydrocarbons, by selective reduction of water flow into producing wells or shafts.