| 摘要 |
A well drilling bit having a bit body attachable to a tubular drill string, which bit body is internally provided with a passageway providing fluid communication, when the drill string is attached to the bit body, between the interior of the drill string and the exterior of the bit body; a closure element for selectively closing the passageway; and one or more chip-making elements, wherein the chip-making elements has one or more roller-cones, wherein the closure element is releasably connectable to the bit body, and outwardly movable from a closing position to an opening position, and wherein the closure element includes at least one of the roller-cones. |
