The most effective way to prevent hydrocarbon migration in wells that have been plugged and abandoned is to create a rock-to-rock, cement-to-formation bond. The Weatherford Endura dual-string section mill (DSSM) accomplishes this with the use of specially designed blades and stabilizers that enable through-casing milling of the adjacent string of casing to access the borehole quickly and efficiently. Separate milling and stabilizer blades provide two points of stabilization while creating finer, more manageable cuttings. First, the DSSM mills the inner casing to provide access to the outer casing. On the next trip, the DSSM passes through the inner string and the cutting blades expand to remove the outer casing, thereby creating a casing-exit window. The remainder of the casing is removed in a third run with the DSSM using 17-in.-long milling blades. By completely removing all casing, the DSSM exposes the formation to prepare wellbores for permanent rock-to-rock cement plugging. The resulting hydraulic seal mimics natural bedding, mitigates gas migration, and can be confirmed with a pressure test. The DSSM halves the rig-time average for most plug-and-abandonment operations and results in a stable, permanent, and verifiable seal, fulfilling some of the most stringent regulatory requirements for well abandonment.