| 摘要 |
A flow stop valve (200, 300, 400) for placement in a downhole tubular operating in a dual fluid density system, wherein the flow stop valve is arranged such that it is in communication with a pressure difference between one of: fluid outside the downhole tubular and inside the downhole tubular at the flow stop valve; and fluid above and below the flow stop valve inside the downhole tubular, wherein the flow stop valve comprises a first valve element (226′, 326′, 424) arranged such that the pressure difference acts across at least a portion of the first valve element and that the first valve element is movable between open and closed positions under action of said pressure difference so as to selectively permit flow through the downhole tubular, wherein the first valve element comprises a first passage (212, 312, 446) arranged so as to transmit fluid from a first port (213, 313, 447) in a first side of the first valve element to a second side of the first valve element, the first port being positioned such that it is adjacent to a low pressure flow region (290) when the flow stop valve is in an open position. |
