Abstract: A plug (1) for plugging wells, and in particular oil and gas wells, is provided. The plug (1) has a plug body formed from an outer metal tube (2) of a reduced thickness. The plug also has reinforcement means (4), attached to an inner surface of the outer tube (2), that give the plug a cross-sectional structural strength that is at least equivalent to that of a thicker metal tube. The plug has a central heater receiving void located along the axis of the plug to enable a plug deployment heater to be received therein. Also provided is a plug assembly (10) with a variable cross-sectional area in a plane perpendicular to the plane in which the assembly is deployed during the plugging of underground conduits.

Abstract: Apparatus, in the form of a eutectic alloy plug (1) and a deployment heater (10) are provided. The plug (1) and the deployment heated (10) are provided with means (5, 13) for releasably retaining the deployment heater (10) within a cavity (4) in the plug (1). The nature of the retaining means is such that once the plug (1) is secured in a well the heater (10) can be recovered without the plug (1). An extraction heater (20), which is also receivable within the cavity (4) of the plug (1), is provided to re-melt the eutectic alloy and thus enable the extraction of the plug from a well. Various method of plugging abandoned wells are made possible by the control that the provided apparatus gives.