DOWNHOLE APPARATUS

摘要

A downhole drilling assembly (10) comprises a body (11) for mounting on a drillstring, the body defining a fluid conduit. A drilling fluid driven motor (12) is mounted in the body (11) and is coupled to a flow restricting device (14) axially movably mounted to the body (11). The device is coupled to a drill bit (16). In use, the flow restricting device (14) is driven by the motor (12) to vary the flow of drilling fluid through the body and produce a varying fluid pressure force to induce axial movement of the device (14) relative to the body (11), and thus provide a percussive or hammer drilling effect. The flow restricting device (14) may be coupled to the drill bit (16) by a mandrel (46) splined or otherwise coupled to the body. Alternatively, the flow restricting device (68) may be coupled to the drill bit (72) by a rotatable shaft (70), such that the motor (64) may also rotate the drill bit (72).