Method and apparatus for isolating tubing with a swellable seal

An apparatus for isolating at least a portion of a tubular for use in a wellbore comprising a first, inner tubular in the form of carrier tube and a second, outer tubular in the form of protective shroud, coupled to the carrier tube. One or more aperture is provided in a wall of the carrier tube for permitting fluid transfer through the tube and one or more aperture is provided to permit fluid transfer through the shroud. A sealing layer is disposed on a surface of the shroud, the sealing layer defining a first configuration permitting fluid flow through the apertures and, on exposure to a selected reactant, adopting a second configuration to restrict fluid flow through the apertures, the sealing layer adapted to return from the second configuration to the first configuration where concentration of the selected reactant falls below a selected threshold.