Mandrel assemblies for a plug and associated methods

A plug for sealing a wellbore, comprising:

• a mandrel assembly comprising an outer rod comprising an inner surface and an inner surface feature positioned on the inner surface, and an inner rod that is distinct from the outer rod and comprises a different material than the outer rod, wherein the inner rod comprises an outer surface and an outer surface feature positioned on the outer surface that is in interlocking engagement with the inner surface feature of the outer rod;
• and
• a packer disposed about the mandrel assembly, the packer configured to seal the wellbore in response to the plug being actuated from a first position to a second position, wherein the mandrel assembly is configured to apply a compressive force to the packer as the plug is actuated from the first position to the second position;
• wherein the interlocking engagement between the inner rod and the outer rod overlaps the packer along a longitudinal axis of the plug such that the inner rod and the outer rod jointly resist axial loads applied to the uphole end of the outer rod.

A method for fracturing an earthen subterranean formation, the method comprising:

• (a) deploying a tool string into a wellbore extending through the subterranean formation, the tool string comprising a perforating gun and a bridge plug including a mandrel assembly that comprises an inner rod that is solid across a central axis of the inner rod, and an outer rod that is distinct from the inner rod such that the outer rod overlies the inner rod, and further wherein the outer rod comprises a different material than the inner rod and the inner rod and the outer rod cooperate to restrict fluid communication across the mandrel assembly in both a first axial direction and an opposed second axial direction;
• (b) actuating the bridge plug from a first position to a second position whereby a packer of the bridge plug disposed about the mandrel assembly seals the wellbore, wherein the mandrel assembly applies a compressive force to the packer as the bridge plug is actuated from the first position to the second position;
• (c) actuating the perforating gun to form a plurality of perforations in a casing string lining the wellbore thereby establishing fluid communication between the wellbore and the subterranean formation;
• (d) pumping a fracturing fluid through the wellbore and into the subterranean formation through the plurality of perforations formed in the casing string;
• and
• (e) drilling out the mandrel assembly of the bridge plug by an external tool to release the compressive force applied by the mandrel assembly to the packer of the bridge plug.