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A drill string on a drilling rig is a column, or string, of drill pipe that transmits drilling fluid (via the mud pumps) and torque (via the kelly drive or top drive) to the drill bit. The term is loosely applied to the assembled collection of the drill pipe, drill collars, tools and drill bit. The drill string is hollow so that drilling fluid can be pumped down through it and circulated back up the annulus (the void between the drill string and the casing/open hole). == Drill string components == The drill string is typically made up of three sections: * Bottom hole assembly (BHA) * Transition pipe, which is often heavyweight drill pipe (HWDP) * Drill pipe 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Drill string」の詳細全文を読む スポンサード リンク
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