A method to manipulate a well, comprising running an apparatus (60a) having a container (68a) with a volume of gas at a higher pressure than a surrounding portion of the well. The well is isolated, and a wireless control signal, such as an electromagnetic or acoustic signal, is sent to operate a valve assembly (62a) to selectively allow or resist fluid exit from a portion of the container (68a), via a port (61a). Some of the pressurised gas may itself be expelled in to the surrounding portion of the well, or it may be used to drive a fluid out of the container, such as an acid.