A method for in situ formation of a remedial annulus seal in a region of an annulus located around a pipe structure in a well, in which the method comprises the following steps: to convey a perforation device into the pipe structure to a location vis-à-vis said region of the annulus; by means of the perforation device, to make at least one hole through the pipe wall of the pipe structure at said annulus region; to heat and melt at least a part of a fusible, solid-state packer material, which is capable of entering into solid state upon cooling, and then force melted, liquid packer material through said pipe wall hole and further into the annulus region for the filling thereof, whereupon the liquid packer material, upon cooling, enters into solid state and forms said remedial annulus seal, characterized in that the method also comprises: - to use a device according to claim 12, said device comprising a packer injection module comprising at least the following components: - at least one packer chamber containing said fusible packer material; - a heating device; and - a driving device (7; 8) and a propulsion device (30; 31) therefore; - by means of a connection line, to convey the packer injection module into the pipe structure to said location vis-à-vis the annulus region; - by means of said heating device, to keep at least a part of the packer material in a melted, liquid state in the packer chamber; - to connect said packer chamber in a flow-communicating manner to said pipe wall hole; - by means of said driving device (7; 8) and propulsion device (30; 31), to force melted, liquid packer material out of the packer chamber and into the annulus region in the open hole completed portion via said pipe wall hole so as to form said remedial annulus seal upon cooling: and - to choose any one of thermoplastic elastomers and thermoplastic vulcanizates as said fusible, solid-state packer material. to convey a perforation device into the pipe structure to a location vis-à-vis said region of the annulus; by means of the perforation device, to make at least one hole through the pipe wall of the pipe structure at said annulus region; to heat and melt at least a part of a fusible, solid-state packer material, which is capable of entering into solid state upon cooling, and then force melted, liquid packer material through said pipe wall hole and further into the annulus region for the filling thereof, whereupon the liquid packer material, upon cooling, enters into solid state and forms said remedial annulus seal, characterized in that the method also comprises: - to use a device according to claim 12, said device comprising a packer injection module comprising at least the following components: - at least one packer chamber containing said fusible packer material; - a heating device; and - a driving device (7; 8) and a propulsion device (30; 31) therefore; - by means of a connection line, to convey the packer injection module into the pipe structure to said location vis-à-vis the annulus region; - by means of said heating device, to keep at least a part of the packer material in a melted, liquid state in the packer chamber; - to connect said packer chamber in a flow-communicating manner to said pipe wall hole; - by means of said driving device (7; 8) and propulsion device (30; 31), to force melted, liquid packer material out of the packer chamber and into the annulus region in the open hole completed portion via said pipe wall hole so as to form said remedial annulus seal upon cooling: and - to choose any one of thermoplastic elastomers and thermoplastic vulcanizates as said fusible, solid-state packer material. - to use a device according to claim 12, said device comprising a packer injection module comprising at least the following components: - at least one packer chamber containing said fusible packer material; - a heating device; and - a driving device (7; 8) and a propulsion device (30; 31) therefore; - at least one packer chamber containing said fusible packer material; - a heating device; and - a driving device (7; 8) and a propulsion device (30; 31) therefore; - by means of a connection line, to convey the packer injection module into the pipe structure to said location vis-à-vis the annulus region; - by means of said heating device, to keep at least a part of the packer material in a melted, liquid state in the packer chamber; - to connect said packer chamber in a flow-communicating manner to said pipe wall hole; - by means of said driving device (7; 8) and propulsion device (30; 31), to force melted, liquid packer material out of the packer chamber and into the annulus region in the open hole completed portion via said pipe wall hole so as to form said remedial annulus seal upon cooling: and - to choose any one of thermoplastic elastomers and thermoplastic vulcanizates as said fusible, solid-state packer material.