It took patience, ingenuity and untold millions of dollars to heal the wounds Hurricane Katrina inflicted on Royal Dutch Shell's Mars platform, the most prolific oil-producing platform in the Gulf of Mexico. But nearly a year and a half after the storm pummeled the 36,500-ton structure with 175-mph winds and 80-foot waves that left dead fish and crumpled steel on its decks, the platform has surpassed its pre-Katrina oil production levels. The biggest step left to restore Mars to its pre-Katrina strength is the return of its drilling rig. Due in April, it will have a new 250-foot derrick atop a repaired 1,000-ton substructure that the storm ripped from its clamps and then slammed back onto the platform. And how.