Method for sealing cavities in or adjacent to a cured cement sheath surrounding a well casing

Abstract

A method for sealing cavities in or adjacent to a cured cement sheath (4) surrounding a well casing (3) of an underground wellbore comprises:- providing an expansion device (1) with edged expansion segments (2) that is configured to be moved with the expansion segments (2) in an unexpanded configuration up and down through the well casing (3);- moving the unexpanded expansion device (1) to a selected depth in the well casing (3); and- expanding the edged expansion segments (2) at the selected depth, thereby plastically expanding a selected casing section and pressing the expanded casing section into the surrounding cement sheath thereby sealing the cavities