Chinese state-controlled monopoly offshore producer China National Offshore Oil Corp has confirmed its Penglai 9-1 discovery, made in Bohai Bay in 2010, as a "large oil field," after it produced at around 700 b/d during testing, the company said in a statement Tuesday.

The PL9-1 field is located in the Miaoxibei uplift in the eastern part of Bohai, in an average water depth of 25 meters. The crude oil was produced during testing at one of the field's appraisal wells, PL9-1-5, which encountered oil pay zones with total thickness of more than 200 meters.

"PL9-1 is the largest oil field among the recent years' discoveries by scale in Bohai," CNOOC said.

It is about 40 km (25 miles) northeast of Penglai 19-3, China's largest offshore oilfield which was shut-in last year following oil seeps into the seabed at two production platforms.

"The successful appraisal on PL9-1 will open up a new prospect for exploration and development in eastern Bohai waters as well as make great contribution to maintain steady production in Bohai region," said CNOOC CEO Li Fanrong.

In the course of appraising the area, CNOOC also made a discovery at the PL15-2 structure, located 8 km (5 miles) south of PL9-1. The PL15-2-1 discovery well encountered oil pay zones with total thickness of 83 meters, and tested at an average indicated rate of more than 1,200 b/d, the company said.

In a note Tuesday, Bernstein Research said the discovery opened up a new deeper play "buried hill" formation, which could potentially lead to new exploration and discoveries.

Bernstein said it sees the PL15-2 structure as a medium-sized discovery. Bernstein expected full production to be restored at Peng Lai 19-3 imminently. It restarted last month under an "approved interim reservoir management plan" and gross production is at 40,000 b/d, operator ConocoPhillips said on April 5. It was producing 122,000 b/d before the shutdown in September last year.

Bernstein said on March 15 it did not believe the oil spill would have any impact on the project's reserves recovery and the field will ultimately be able to resume production levels within 10% to 20% of the pre-spill rate. ConocoPhillips has a 49% stake the field while CNOOC has 51%.