A composition for carrying solid particles

A composition for carrying solid particles, e.g. proppants used in fracturing earth formations or gravel for well screens, comprises a) a brine based fluid; a trivalent salt as a viscosifying agent; a surfactant; and an alkaline agent to initiate viscosifying. The trivalent salt used as the viscosifier may be aluminium chlorohydrate. The viscoelasticity of the composition may be broken by dilution.