| 摘要 |
<p>A reverse circulation drill string including two or more multi-walled drill pipe sections coupled together in series. Each drill pipe section includes at least three concentrically arranged annular sections generally coaxially aligned with a drilling axis. The annular sections include an outer pipe, an intermediate tube enclosed within the outer pipe, the outer pipe and intermediate tube having a first axial conduit there between, and an inner tube arranged within the intermediate tube. The intermediate tube and the inner tube have a second axial conduit there between, the interior of the inner tube providing a third axial conduit therein. The second axial conduit is arranged for the passage of pressurised fluid to a drilling head of the drill string, the third axial conduit is configured as a cuttings passage through which cuttings from the drill head can travel, and the first axial conduit is arranged for communication with the environment external of the drill string.</p> |
