Downhole fluid control processes

The invention provides a downhole process for the reduction of the permeability to water of a microporous subterranean formation which has average permeability of not greater than 10 Darcy, the process comprising applying to the formation a dispersion in non-aqueous liquid of water swellable, reverse-phase polymerized, substantially spherical particles of absorbent polymer of which at least 90% by weight have a diameter less than 10 mu m whereby the dispersion of the substantially spherical particles of which at least 90% by weight have a size below 10 mu m is injected into the micropores of the subterranean formation and the particles are allowed to swell on contact with water and cause the reduction in permeability.