The field of the invention is seal assemblies for borehole packers or bridge plugs and more particularly assemblies that use a structural insert separating seal segments that flexes when the packer or bridge plug is set.
Conformability, stability and element extrusion are main factors that affect packer sealing performance. Conformability is the ability of the seal to conform to the surface irregularity and imperfection on the casing inside diameter and mandrel outside diameter. Stability is the structural soundness of the seal assembly during set and the pressure above or below thereafter. Any sudden movement of the element during set and after set is considered structural instability, which negatively impacts seal performance. Element extrusion indicates that polymeric sealing material is acting like fluid during set and subsequent pressure above or below, which causes the sealing element to escape any available space or gaps.
Various seal designs are illustrated in U.S. Pat. No. 6,666,276; U.S. Pat. No. 8,490,979; U.S. Pat. No. 7,363,975 US2005/0230100; W02010135644; US 2003/0080515; US2011/0147015 and U.S. Pat. No. 8,905,149. Lacking in these designs and addressed by the present invention are features such as radially stacked segments separated with a reinforcing member shaped to fold on itself as the seal is axially compressed when set. Seal rings that bookend the sealing element have outwardly facing ramps to guide out anti-extrusion rings with a conforming tapered surface for axial extrusion control. The stacked elements and the reinforcing member that separates them create a gap volume near the mandrel that enables fluid to escape rather than becoming trapped, which could undermine the sealing ability of the sealing assembly. These and other aspects of the present invention will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while appreciating that the full scope of the invention is to be determined from the appended claims.
A seal assembly features radially stacked sealing elements separated by a ring shaped structural member with the structural member configured to fold on itself as the inner and outer sealing elements are axially compressed during the setting process. The structural member remains embedded in the outer sealing element when the assembly is set. Seal rings flank the inner and outer sealing element and feature an outwardly facing bevel to contact a conforming bevel shape on extrusion ring assemblies. During axial compression the extrusion rings are pushed out with the seal rings and then the inner and outer sealing elements are axially compressed as the structural member's ends come together and its middle folds. The structural member creates gaps to allow fluid to escape during setting.
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Those skilled in the art will appreciate that radially stacking an inner and outer sealing element while separating them with a stiffener that folds and stores potential energy allows the assembly in the set position to better resist pressure differentials and to conform to surface irregularities in the surrounding tubular or the mandrel without leaking. The stiffener helps the assembly perform better than a single component sleeve sealing element as the material is also more resistant to axial extrusion. The seal ring design is not only beveled to extend the beveled extrusion barrier but allows the seal rings themselves to act as extrusion barriers. The nesting of the stacked sealing elements with the seal rings and the extending members off the seal rings keep the components in proper alignment as the set position is assumed and maintained. The extending segments being forced against the mandrel in the set position also minimizes any extrusion path along the mandrel. The deliberate gaps present when running in are formulated to allow fluid to escape during the setting to avoid fluid locking which would undermine the sealing capability of the assembly. The stiffener pushes the outer sealing member against the borehole but does not itself contact the borehole. The stiffener bends elastically to store potential energy and provide a continuing sealing force of the seal assembly 18 against the casing 12 or the borehole wall in an open hole. The stiffener preferably does not contact the casing 12 or the borehole wall in an open hole.
The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below: