| 摘要 |
An expandable filter assembly for downhole use comprises a base pipe having an inside surface, a plurality of openings and at least one filtration layer mounted over the pipe. The filter assembly further comprises an expander (20) which is capable of multi-stage expansion of said base pipe and said filtration layer in stages up to about 30% of its original dimensions. After a first step in which an expander 20, which may be a fixed or variable diameter cone, is moved downwardly through the filter assembly, a cone latch 42 engages a larger expander or cone 22 to increase the expansion in a second step, which may be in an upward direction. |
