| 摘要 |
A wellbore system comprising a borehole (5, 7, 9) formed in the earth formation, the borehole being provided with a valve (60, 26, 62) having a passage for a stream of fluid flowing from an upstream side of the valve to a downstream side of the valve, a closure member (44) exposed to a drag force exerted by the stream and movable relative to the passage (40) between an open position in which the closure member allows fluid to flow through the passage and a closed position in which the closure member closes the passage, said drag force biasing the closure member to the open position thereof, and a spring (48) exerting a spring force to the closure member biasing the closure member to the closed position, wherein the spring force when the closure member is in the closed position exceeds a selected lower limit of the drag force. |
