| 摘要 |
<p>The present invention generally provides a system and method for selectively sealing a drill string (14) or other tubular member. In one aspect, a sealing member, such as a valve (50), allows a certain level of flow of drilling fluids and/or other fluids through one or more flow channels (76) when the valve is open. To close the valve, the flow rate is increased so that a backpressure develops and urges the valve to a closed position. The valve can remain in position in the drill string and alternately open (right-hand half of the figure) and close (left-hand half of the figure) depending on the flow rate and/or the pressure drop through the valve. The valve also comprises a removable plug (90) disposed in the valve to provide access with, for example, wireline tools to a region below the valve in a wellbore.</p> |
