Patent ID: 7703542

Claim:
An expandable casing for a wellbore, the expandable casing comprising: a radially expandable body having an outer wall surface; an extrudable sealing element comprising an inner surface and an outer surface, the inner surface of the extrudable sealing element being disposed on the outer wall surface of the radially expandable body; and a plurality of retainer rings disposed on the outer surface of the extrudable sealing element, wherein radial expansion of expandable casing causes the extrudable sealing element to be compressed and extruded through at least one gap disposed between at least two of the plurality of retainer rings, wherein the plurality of retaining rings comprise a first retainer ring having an upper end and a lower end, and a second retainer ring having an upper end and a lower end, wherein the first retainer ring is disposed above the second retainer ring, and wherein the gap is disposed between the lower end of the first retainer ring and the upper end of the second retainer ring, and wherein the first retainer ring is disposed over a first portion of the extrudable sealing element and the second retainer ring is disposed over a second portion of the extrudable sealing element, wherein the extrudable sealing element is disposed relative to the first and second retainer rings such that extrusion of the extrudable sealing element causes the extrudable sealing element to protrude outwardly through the gap between first and second retainer rings, above the upper end of the first retainer ring, and below the lower end of the second retainer ring, to engage a wall of a wellbore in at least three locations.