| 摘要 |
In drilling wells tubular members are added to or removed from the drill string whilst the circulation of mud continues and there is a blind preventer (6) positioned between lower slips and grips (8) engaging a downhole drill string and an upper slips and grips (5) engaging a tubular to be added to the drill string and the tubular is positioned on the blind preventer, the blind preventer opened and the upper slips and grips passed through the blind preventer and the tubular connected to the drill string.
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