Expandable milling head for gas well drilling

摘要: A tool head is separably attached to the end of a hollow well drilling string for cutting operations within and detachment from without removing well. The by ball clutch structure having pressure responsive release mechanism an actuating on cuttiong string, upwardly open passage downward flow permitting check valve passing fluid through head. Release effected dropping sealing member down drill close increase in above mechanism. includes part which retain balls prevent head, that being anchored int its retaining position shear pins are fracturable increased position. invention relates method use or milling off inner ends plugs casings provide gas passages casing wall.