Downhole milling tool

A method of removing burrs or debris from an internal surface of a pipeline, casing or tubular, comprising the steps of:

• providing a downhole milling tool, comprising:
• a hollow tool body mountable on a drill string;
• an annular element mountable about an outside surface of the tool body, wherein the annular element houses a portion of at least one elongate milling blade, the annular element including at least one opening through which the at least one milling blade projects;
• wherein the at least one milling blade is radially biased to project outwards and projects outwardly beyond an outside surface of the annular element;
• each milling blade includes an elongate cutting face;
• wherein the annular element is configured to be rotatably coupled to and rotationally dependent on the tool body in an active configuration and rotatably decoupled and rotationally independent from the tool body in an inactive configuration;
• wherein the tool body comprises an inner tubular member and a drive system, wherein the drive system comprises a drive member extending radially from the inner tubular member, wherein the drive member rotationally engages the annular element and rotatably couples the annular element to the tool body when in the active configuration and wherein the drive member rotationally disengages from the annular element in the inactive configuration;
• wherein the cutting faces are each configured to remove unwanted debris only when the annular element and the tool body are rotationally dependent, such that, in use, rotation of the tool body effects operation of the milling blades to remove unwanted debris;
• and
• wherein the cutting faces are inoperable to remove unwanted debris when the annular element and the tool body are rotationally independent;
• lowering the downhole milling tool without rotation into a pipeline, casing or tubular to a desired depth;
• rotating and reciprocating the tool across a required depth such that the cutting faces are operable to remove unwanted debris from the internal surface of the pipeline, casing or tubular in which the tool is deployed;
• decoupling the annular member and the tool body such that the annular element and the tool body are rotationally independent and the cutting faces are inoperable to remove unwanted debris.