UPDATE 1-Oil catcher dome hits snag near leak site -BP exec

* BP says will take 48 hours to assess new solution

* Hydrates a danger, but also a possible energy source

* Relief well could take two-three months to drill

By Erwin Seba

ROBERT, La., May 8 (Reuters) - London-based BP Plc's plan to lower a giant containment dome to trap oil from a blown-out Gulf of Mexico oil well on the sea floor hit a technical obstacle on Saturday in the form of methane hydrates, or flammable ice, a BP (BP.L) executive said on Saturday.

BP officials are scrambling for a solution after methane hydrates stopped up the 98-ton containment dome as they were maneuvering it into place, Doug Suttles, BP's chief operating officer, told reporters at a briefing in Robert.

"As we were placing the dome over the leak source a large volume of hydrates formed inside the top of the dome, requiring us to move the dome to the side of the leak point," Suttles said. "I wouldn't say it's failed yet."

The four-story structure, BP's only short-term hope of controlling the leak, is supposed to redirect the unchecked flow of crude from nearly one mile (1.6 km) below the water and, once connected, pump it to a surface tanker.

If the dome plan fails, BP faces the prospect of drilling a relief well to cut off the leaky oil well, which could take two to three months. A giant oil slick from the gush of oil threatens to create an environmental disaster for four Gulf Coast states.

Methane hydrates -- a slush of frozen hydrocarbons and water that form in the deep, cold conditions at the leak site -- began clogging up the opening in the dome, forcing them to set the structure aside, Suttles said.

The dome is now resting on the ocean floor about 200 metres (660 ft) from the leak source, and it could take 48 hours or more to find a workaround, Suttles said.

Those could include using hot water to heat up the hydrates at the ocean floor, or using hydrocarbons like methanol to thin them out, Suttles said.

Suttles said BP is mulling two other short-term fixes, including installing a new blow-out preventer on the leak site and trying to clog up the existing failed blow-out preventer with an injection of rubber and other solids, known as a "junk shot."

Hydrates are highly flammable and present a danger to BP workers on ships above the leak. If they dethaw in an uncontrolled manner, they could send a flood of natural gas to the top of the ocean surface and potentially ignite.

Ironically, methane hydrates are a promising future energy source in themselves, but researchers are still searching for ways to safely harness them.

A recent study by the Minerals Management Service pegged methane hydrate resources in the Gulf of Mexico at 21,000 trillion cubic feet of natural gas -- 100 times the country's current proven supply.

(Reporting by Erwin Seba, Writing by Chris Baltimore, Editing by Eric Walsh)