BEIJING | (Reuters) - A subsidiary of Houston-based ConocoPhillips said on Thursday that with the approval from the China's marine authority, the company has resumed operations at some wells in China's Bohai Bay that were ordered to shut down after an oil spill.

The oil leak at the Penglai 19-3 oilfield, China's biggest offshore oil field, which started in June, has polluted 840 square kilometers of water, China's marine authorities have said.

"The company is now flowing a total of 14 production and water injection wells on platform B back into production," the company said on its website ( "Flowing these wells reduces the overall pressure in the subsurface formation, which will assure that the seeps stop and the fault which was previously activated naturally seals."

The State Oceanic Administration (SOA) has ordered ConocoPhillips to halt production at platform B and C of the Penglai 19-3 oilfield in since July 13 because of the slow process of cleaning up the leak.

The order to shut down the platform would result in a temporary reduction of about 17,000 barrels of oil per day to ConocoPhillips, the Houston-based company said.

As of Thursday, ConocoPhillips had recovered 338 cubic meters (2,126 barrels) of oil-based mud from around the Penglai 19-3 C platform and expected to finish the cleanup by the end of this month, it added.

On Wednesday, China's marine authorities expressed frustration at the failure of ConocoPhillips China to contain the two-month oil spill that has spread across the northeast coast and again urged it to halt the leak by the end of August.

ConocoPhillips has a 49 percent stake in the oilfield and acts as the operator. China's offshore oil specialist CNOOC Ltd has 51 percent.

($1 = 6.387 yuan)

Reporting by Judy Hua and Chen Aizhu