| 摘要 |
<p>A flow stop valve (20) is positioned in a downhole tubular (Fig.1c, 6), wherein: (A) the flow stop valve 20 is in a closed position when a pressure difference between fluid outside the downhole tubular (6) and inside the downhole tubular (6) at the flow stop valve 20 is below a threshold value, thereby preventing flow through the downhole tubular; and (B) the flow stop valve 20 is in an open position when the pressure difference between fluid outside the downhole tubular (6) and inside the downhole tubular (6) at the flow stop valve 20 is above a threshold value, thereby permitting flow through the downhole tubular (6). Alternatively the pressure differential may be measured internally to the tubular on either side of the flow stop valve 20.</p> |
