Wang Yilin, CNOOC's chairman, said the company believes it can achieve its production target for the whole year although the unit cost rose because of the Nexen deal.

Wang said that the Liwan 3-1 block, the first deepwater offshore oil field in China, will start production by the end of the year.

"The Nexen deal will be beneficial for CNOOC's structural adjustment and long-term strategy, which has the biggest significance to the company," said Wang.

Integration work after the deal has seen impressive progress and the company is working toward a Nexen listing on the Toronto Stock Exchange.

Wang added the company will keep seeking possible overseas acquisition opportunities.

"We have been looking for profitable oil fields in the overseas market following our principles of resources, risks and return," said Wang.

In the exploration sector, the company has made seven new discoveries and had 18 successful appraisal wells in offshore China.

The new discovery of the Kenli 10-4 block uncovers a new area of oil and gas exploration in the north slope of Laizhou bay.

Meanwhile, the company's average realized oil price dropped to $104.20 per barrel, down 10.9 percent year-on-year, while, because of the Nexen acquisition, its average realized natural gas price declined 3.7 percent year-on-year to $5.68 per thousand cubic feet.

Liao said current global oil prices are at a comfortable level for the market, and there's no clear sign of an oil price rebound considering China's economic slowdown and the lackluster global economy.