......DE......GB........NL........................RThe title of the invention has been amended (Guidelines for Examination in the EPO, A-III, 7.3).0298537EUROPEAN PATENT APPLICATIONA319890412EP88201228.919880615enenen871492119870625GB19890412198915198901111989024 4E 21B 7/28 A 4E 21B 10/32 B 4E 21B 10/60 B 4E 21B 10/46 B 4E 21B 4/02 B 4E 21B 44/00 B 4E 21B 4/18 BdeVorrichtung und Verfahren zur Herstellung einer Hinterschneidung in einem BohrlochenDevice and method for underreaming a boreholefrDispositif et procédé pour l'alésage d'un trou de forageSHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.00200440T 5510 EPCCarel van Bylandtlaan 30NL-2596 HR Den HaagNLZijsling, Djurre HansVolmerlaan 6NL-2280 AB RijswijkNLDEGBNL19890412198915

A borehole underreamer device comprises a downhole motor having a rotor part which carries by means of a pivot (2) an elongate clapper body (1) in which a series of abrasive teeth (8) are embedded. In use the device is pulled in upward direction through the borehole while the clapper body describes an orbital motion inside the borehole thereby forcing the teeth to penetrate into the surrounding side wall of the borehole so as to underream the hole.