NEW ORLEANS — For a spill now nearly half the size of Exxon Valdez, the oil from the Deepwater Horizon disaster is pretty hard to pin down. Satellite images show most of an estimated 4.6 million gallons of oil has pooled in a floating, shape-shifting blob off the Louisiana coast. Some has reached shore as a thin sheen, and gooey bits have washed up as far away as Alabama. But the spill is 23 days old since the Deepwater Horizon exploded April 20 and killed 11 workers, and the thickest stuff hasn’t shown up on the coast. So, where’s the oil? Where’s it going to end up? Government scientists and others tracking the spill say much of the oil is lurking just below the surface. But there seems to be no consensus on whether it will arrive in black waves, mostly dissipate into the massive Gulf or gradually settle to the ocean floor, where it could seep into the ecosystem for years. When it comes to deepwater spills, even top experts rely on some guesswork. One of their tools, a program the National Oceanic and Atmospheric Administration uses to predict how oil spills on the […]