| 摘要 |
In oil and gas production installations, formation sand may pass through sand screens and enter the tubing, causing damage and increasing abrasive wear. Gravel used to prevent this often leaves gaps and lets formation sand pass through. The invention eliminates such gaps by incorporating an ordinary polished bore (11) in the sand screen (4, 7) to land and seal off the wash pipe (9). Two concentric tubes (4a, 4b) are connected to each other by a collar (17) whose inside surface is a polished bore (11) and whose outer side has supports (17a, 17b) for the tubes (4a, 4b) and the upset screens.
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