| 摘要 |
In accordance with illustrative embodiments of the present invention, restriction subs (20) for use in setting cement plugs in wells include a tubular threaded adapter (35) having an internal annular recess (40), and a metal restriction sleeve (44) mounted in such recess. In one embodiment, the sleeve (44) has a corrugation (47-49) that extends into the bore of the adapter (35) to provide a deformable restriction; in another embodiment the sleeve (44) has curved resilient tabs (67, 68) whose free ends extend into such bore. The restrictions are cooperable with a displacement plug (50) having a metal expander member (53) on its nose so that a distinct pressure is required to cause the expander member (53) and plug (50) to be forced through the restriction. |
