A casing packer seal arrangement includes a sliding casing packer seal assembly arranged for being set by axial compression to expand against a surrounding casing pipe, the casing packer seal assembly being compressed and sled along a cylindrical mandrel. The casing packer seal assembly includes at least one packer element ring having mutually opposite, axially outward facing radially inner and outer plane ring portions; first and second conical inner rings having an axially inward directed plane ring face abutting the packer element end rings' inner plane ring portions in their expanded state; first and second expanding rings each having a conical ramp face for climbing, thus expanding, on said conical inner rings, the first and second expanding rings each having a plane, radially outer ring face for engaging, expanding with and supporting the packer element end ring's axially outward facing plane ring portions, so that when expanded, preventing extrusion of the so expanded packer element end ring in an annulus gap between the expanding rings and the surrounding casing pipe.