DRILLING HEAD FOR REBORING A STUCK VALVE

摘要

The present invention relates to a downhole drilling head (2) for mounting onto a drilling tool for reboring a stuck valve or drilling into the formation downhole, comprising a hole saw (28) having a cylindrical body with a circumferential rim (29) and a longitudinal axis going through a centre of the cylindrical body, and a drill bit (30) extending along the longitudinal axis and through the centre of the cylindrical body,wherein the circumferential rim (29) has at least one cutting edge (31) rotating for cutting a piece (37) out of the stuck valve or the formation. The drill bit has a retractable projection (34); when drilling in the valve, the projection is retracted when it is passed by the piece cut out by the cutting edge, the projection subsequently returning to its projected position, and the piece thus returning with the drilling bit when the drilling ends.