A packer and pressure differential drilling tool and method of controlled pressure balanced drilling in Big Hole well bores and shafts, characterized by a large diameter packer slideably engaged with the well bore over a drill bit and through which a dual drill pipe operates and isolates drilling fluid...http://www.google.es/patents/US4534426?utm_source=gb-gplus-sharePatente US4534426 - Packer weighted and pressure differential method and apparatus for Big Hole drilling
Packer weighted and pressure differential method and apparatus for Big Hole ...
