After the Obama administration gave Royal Dutch Shell conditional approval to explore oil drilling off the coast of Alaska this May, protesters dangled from a bridge in Portland, Ore. They kayaked in the path of a 380-foot icebreaker vessel, budging only on the orders of police. And they parked their string instruments in front of Shell’s London headquarters for a melancholy performance of the “Requiem for Arctic Ice.”

In the face of those detractors, Shell plowed forward. With citations from the U.S. Coast Guard, the protesters left the bridge. Shell’s drilling vessel recovered from the hull damage that had stranded it in Portland in the first place, and the hulking mass called the Fennica cleared the bridge with little delay.

It seemed the explorations could not be stopped, even after Alaska’s Bureau of Ocean Energy Management recognized in an environmental impact statement that development activities had a 75 percent chance of causing large oil spills.

But a serendipitous moment arrived for environmentalists early Monday, when Shell announced that it will abandon its drilling venture in the Arctic waters off Alaska’s coast for the “foreseeable future.”

“Shell has found indications of oil and gas in the Burger J well,” said a company statement referring to its exploration in the Chukchi Sea, “but these are not sufficient to warrant further exploration in the Burger prospect. The well will be sealed and abandoned in accordance with U.S. regulations.”

“Shell continues to see important exploration potential in the basin, and the area is likely to ultimately be of strategic importance to Alaska and the U.S.,” Marvin Odum, director of Shell Upstream America, said in the news release. “However, this is a clearly disappointing exploration outcome for this part of the basin.”

“Shell will now cease further exploration activity in offshore Alaska for the foreseeable future,” the company said. “This decision reflects both the Burger J well result, the high costs associated with the project, and the challenging and unpredictable federal regulatory environment in offshore Alaska.”

Studies in the region have suggested that it could hold as much as 30 billion barrels of oil, The Post reported in May, noting that industry experts believe 30 percent of the world’s undiscovered natural gas is contained in offshore Arctic fields.

The conservation community responded with elation.

“That’s incredible. That’s huge,” the Anchorage World Wildlife Fund’s Margaret Williams told the AP. “All along the conservation community has been pointing to the challenging and unpredictable environmental conditions. We always thought the risk was tremendously great.”

According to The Guardian, Shell has expressed privately that protests against drilling were a serious threat to its reputation. The company’s chief executive, Ben van Beurden, may also be concerned that Arctic drilling would undermine his position in the climate change debate.

Greenpeace U.K. Executive Director John Sauven told Bloomberg in an e-mail, “Big oil has sustained an unmitigated defeat.”