| 摘要 |
A downhole hammer is provided comprising a casing having a top sub at one end and a drill bit and support at the other end. A central tube is extended therethrough to define an annular space between the casing and the tube. A reciprocating piston is accommodated within the annular space and is operated by injecting a pressurized fluid from the surface into the annular space via a plurality of ports in the casing. The pressurized fluid is exhausted into the central tube and toward the surface via a plurality of passageways therethrough without contacting the borehole.
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