A method for remediating a microannulus in a cased wellbore may include conveying a downhole tool into the cased wellbore to a location of interest. The location of interest may include one or more perforations in a casing and a microannulus. The downhole tool may include a heat generation device. The method may also include activating the heat generation device to melt a fill material at the location of interest such that the fill material flows through the perforations into one or more voids, including the microannulus, in or around cement disposed between the casing and the cased wellbore. Additionally, the method may include deactivating the heat generation device to facilitate solidification of the fill material in the one or more voids and sealing of the microannulus.