Do offshore wells fight natural pollution?

Environmental organizations have tarred the oil industry for its history of fouling the atmosphere and oceans, but a new study suggests some oil and gas wells may have helped clean up natural pollutants leaking from the seafloor off the coast of Santa Barbara, Calif.

Records of these seeps go back to the early Spanish explorers who sailed the Santa Barbara Channel and noticed oil slicks in the water. As the oil ages, it transforms into a goopy tar that washes up on shore. Natural gas leaks end up in the atmosphere. Area residents have long suspected that the dozens of wells offshore exacerbated the problem over the past 3 decades.

In the November GEOLOGY, however, Bruce P. Luyendyk of the University of California, Santa Barbara and his colleagues report that pumping oil and gas has actually decreased the amount of hydrocarbons leaking out of the seafloor. Evidence of this trend comes from two 30-meter-wide steel tents that oil companies set up on the seafloor to capture escaping gas and oil. Through the 1980s, the enclosures collected about 45,000 cubic meters of gas per day. Since 1990, however, the emission rate has dropped to about half its peak level.

Sonar snapshots of rising gas bubbles at another site back up this finding. Surveys made in 1973 and 1995 show that the area of seepage decreased by half, most dramatically near a production platform.

"The main point is if you suck the oil out of the ground, the seepage rate is going to drop off," says Luyendyk. Removal of oil and gas over the years has decreased pressure in the subsea hydrocarbon formation, thereby reducing the amount of material oozing up to the seafloor, propose the researchers.

This pattern should hold at other wells, they say, unless fluids and gas are injected into the rock to drive up pressure--a common technique to boost production.

Keith A. Kvenvolden of the U.S. Geological Survey in Menlo Park, Calif., says that the hypothesis suggested by Luyendyk's team makes sense. "These guys have gone a long way toward proving it," he says.

If the new findings are correct, then the petroleum industry may be cleaning Santa Barbara's air, which occasionally fails to meet smog standards. In the Sept. 15 JOURNAL OF GEOPHYSICAL RESEARCH, Luyendyk and his colleagues report that the quantity of smog-forming reactive hydrocarbons coming from the seeps is twice the amount produced by automobiles in Santa Barbara County. The study also suggests that the county has greatly underestimated the volume of escaping gas.

Oil and gas companies could even be reaping global rewards. Concentrations of methane--a greenhouse gas--have been rising in the atmosphere, but the rate of increase has flagged in the last decade. The Santa Barbara scientists suggest that hydrocarbon production companies could take part of the credit for reducing methane seepage.

The new study, however, does not convince officials who monitor local air pollution near the seeps. Tom M. Murphy of Santa Barbara County Air Pollution Control District questions whether sonar data can offer a good measurement of the leaking gas. "We have always voiced concerns about the methodology," he says.

Luyendyk's team has demonstrated that the vigorous seep sites under the tents have decreased their output over the years, Murphy says, but these covered spots haven't had an impact on air quality for decades. Whether other sites have also declined remains unclear, he says.

What's more, marine hydrocarbons may not contribute significantly to ozone pollution because the gases emitted by automobiles are more reactive in the atmosphere, he says.