National Geographic : 2004 Oct
GRAVES RAISED above the soggy soil are all that's left of once flood-prone Taft, Louisi ana. Nearby levees tamed the unruly Missis sippi River, transforming the region from floodplain to industrial haven ... for now. In Louisiana. I'm third generation in the oil field. We're not afraid of the industry. We just want the infrastructure to handle it." The oil industry has been good to Louisiana, providing low taxes and high-paying jobs. But such largesse hasn't come without a cost, largely exacted from coastal wetlands. The most star tling impact has only recently come to light - the effect of oil and gas withdrawal on sub sidence rates. For decades geologists believed that the petroleum deposits were too deep and the geology of the coast too complex for drill ing to have any impact on the surface. But two years ago former petroleum geologist Bob Morton, now with the U.S. Geological Survey, noticed that the highest rates of wetland loss occurred during or just after the period of peak oil and gas production in the 1970s and early 1980s. After much study, Morton concluded that the removal of millions of barrels of oil, trillions of cubic feet of natural gas, and tens of millions of barrels of saline formation water lying with the petroleum deposits caused a drop in sub surface pressure-a theory known as regional depressurization. That led nearby underground faults to slip and the land above them to slump. "When you stick a straw in a soda and suck on it, everything goes down," Morton explains. "That's very simplified, but you get the idea." The phenomenon isn't new: It was first docu mented in Texas in 1926 and has been reported in other oil-producing areas such as the North Sea and Lake Maracaibo in Venezuela. Morton won't speculate on what percentage of wetland loss can be pinned on the oil industry. "What I can tell you is that much of the loss between Bayou Lafourche and Bayou Terrebonne was caused by induced subsidence from oil and gas withdrawal. The wetlands are still there, they're just underwater." The area Morton refers to, part of the Barataria-Terrebonne estuary, has one of the highest rates of wetland loss in the state. The oil industry and its consultants dispute Morton's theory, but they've been unable to 104 NATIONAL GEOGRAPHIC * OCTOBER 2004 disprove it. The implication for restoration is profound. If production continues to taper off in coastal wetlands, Morton expects subsidence to return to its natural geologic rate, making res toration feasible in places. Currently, however, the high price of natural gas has oil companies swarming over the marshes looking for deep gas reservoirs. If such fields are tapped, Morton expects regional depressurization to continue. The upshot for the coast, he explains, is that the state will have to focus whatever restoration dollars it can muster on areas that can be saved, not waste them on places that are going to sink no matter what.