Expandable retaining shoe

This invention relates generally to downhole tools for use in wellbores and methods of drilling such apparatus out of wellbores, and more specifically, to such tools having drillable components made at least partially of composite or non-metallic materials, such as engineering grade plastics, composites, and resins. This invention relates particularly to improvements in preventing undesired extrusion of packer seal elements between segmented non-metallic packer element shoes, alternatively referred to as back-up shoes, back-up rings, retaining shoes, packer shoes, or retaining rings, used to provide support to expandable packer elements used in drillable, essentially nonmetallic packer and bridge plug type tools. This invention is especially suitable for use with such segmented non-metallic packer element retaining shoes used in extreme temperature and differential pressure environments which tend to make expandable packer element seals more prone to extrusion, related damage, and possibly failure. An improved downhole tool apparatus for limiting the extrusion of a packer element. The apparatus includes a packer mandrel having a packer element assembly disposed in a wellbore. Packer retaining shoes are disposed about the packer mandrel at the ends of the packer element assembly. The packer retaining shoes have an inner retainer and an outer retainer. The inner retainer has a plurality of segments having gaps therebetween that expand in width when the retaining shoe is moved from an initial position in which it is disposed about the packer mandrel to an expanded position wherein it engages the wellbore to limit the extrusion of the packer element assembly. The outer retainer is likewise made up of a plurality of segments having gaps therebetween that will expand. The outer retainer engages the wellbore to limit the extrusion of the packer element assembly. The inner retainer segments cover the gaps that exist between the outer retainer segments and the outer retainer segments cover the gaps that exist between the inner retainer segments so that extrusion is limited. The packer retaining shoes also include a wedge disposed about the packer mandrel at the upper and lower ends of the packer element assembly. The retaining shoes provide enhanced high temperature and higher pressure performance in that extrusion in wells having high temperature and high pressure is severely limited if not completely prevented.