NEW ORLEANS — A 42-foot crewboat struck a sealed wellhead late Tuesday, releasing oily water into the shallow water of a bay off Plaquemines Parish, the Coast Guard said.

Well control operations would begin Thursday morning, Coast Guard Capt. Peter Gautier, captain of the port for the New Orleans sector, said in a news release Wednesday. The statement said less than 840 gallons of oil a day are coming from the well owned by Swift Energy Co. of Houston.

Crews began surrounding the wellhead with containment boom Tuesday night, after it was hit, Swift Energy President Bruce Vincent said. By Wednesday morning, he said, it was intermittently burping oily water, probably from a damaged valve.

He said containment boom was set out along marshland about a mile from the wellhead, and two skimmer boats were at work.

The Coast Guard said the accident occurred about 8 p.m. in Lake Grande Ecaille Bay, 9 miles southwest of Port Sulphur.

As a result of the accident, the Departments of Health and Hospitals and Wildlife and Fisheries shut oyster harvest Area 11, west of the Mississippi River, effective at sunset Wednesday.

The area will remain closed indefinitely until oysters from the area are determined safe to eat.

The well was shut in about five years ago as a weak producer and the company planned to plug it this year, Vincent said. Enough natural gas pressure had built up over five years to push out water mixed with a small amount of oil, he said.

“It flows for a while, then stops flowing until it builds up some pressure and flows again,” he said.

Nobody was injured on the crewboat Sea Raider, also owned by Swift, Vincent said.

Coast Guard Petty Officer Carlos Vega said the accident happened about 8 p.m.

A statement from Swift said the well in January 2008 was shut. Its last production test, shortly before that, showed 18 barrels — 756 gallons — of oil, 3 barrels of water and 59 thousand cubic feet of natural gas per day, the company said.

The site is about 50 miles west of where the BP-leased drilling rig Deepwater Horizon was drilling at the Macondo well when it exploded in April 2010, killing 11 workers on the rig and setting off the nation’s worst offshore oil disaster.

Capping the BP well was hampered by the force of oil and gas pushing out of the well — an estimated 200 million gallons of oil eventually escaped — and because the well was about a mile under the Gulf surface. It took months for engineers to stop oil from flowing into the Gulf.

A trial to determine responsibility for the BP spill is going on in U.S. District Court New Orleans, about 70 miles north of the Swift wellhead.