A wellbore casing formed by extruding a tubular liner off of a mandrel. The tubular liner and mandrel are positioned within a new section of a wellbore with the tubular liner in an overlapping relationship with an existing casing. A hardenable fluidic material is injected into the new section of the wellbore below the level of the mandrel and into the annular region between the tubular liner and the new section of the wellbore. The inner and outer regions of the tubular liner are then fluidicly isolated. A non hardenable fluidic material is then injected into a portion of an interior region of the tubular liner to pressurize the portion of the interior region of the tubular liner below the mandrel. The tubular liner is then extruded off of the mandrel.