On March 18, China National Offshore Oil Corporation (CNOOC) announced that a billion-ton-level oil discovery was made again in the central-northern area of the Chinese Bohai Sea—Qinhuangdao 27-3 Oilfield, with proven geological reserves of 104 million tons. This is a major oil and gas discovery in the area after a decade.

Drilling operation site of Qinhuangdao 27-3 oilfield. Photo by CNOOC

Qinhuangdao 27-3 Oilfield is located in the central and northern Bohai Sea, about 200 kilometers west of Tianjin City, with an average water depth of about 25 meters. The discovery well Qinhuangdao 27-3-3 well drilled an oil layer of 48.9 meters and a completed drilling depth of 1570 meters. After testing, the daily crude oil production of a single well in this oilfield is about 110 tons, showing good exploration prospects.

"According to normal mining, Qinhuangdao 27-3 Oilfield can extract nearly 20 million tons of crude oil. After being refined into gasoline, it can meet the daily transportation needs of urban residents with a population of one million for more than 10 years. The refined asphalt can be laid for more than 100,000 kilometers of four-lane highways, equivalent to circling the earth for more than three weeks." Zhou Jiaxiong, deputy general manager of CNOOC Tianjin Branch, said.

The discovery of Qinhuangdao 27-3 Oilfield is another important practice in the exploration of shallow lithology in the Bohai Sea. The Shijiutuo bulge where it is located was one of the main battlefields for early exploration in Bohai Oilfield. Scientific researchers used the idea of structural exploration to find high parts of structural traps for well location deployment. Three large and medium-sized oil fields, including Qinhuangdao 32-6 Oilfield, were discovered in high parts. However, since 2011, the dominant areas for exploration in high locations have been completely drilled, and the laws of oil and gas enrichment in low locations are still unclear. After multiple rounds of structural exploration, the results have not been ideal.

In order to open up the exploration dilemma, CNOOC researchers learned from the successful experience of exploration and discovery of Kenli 6-1 and Kenli 1 -2 billion-ton lithologic oilfields, and gradually transformed the exploration ideas from traditional structural exploration to lithologic exploration. Based on a large number of drilled data and experiments, scientific researchers successfully proved that the low part of the bulge also has the ability to store oil and gas, changing traditional understanding. In the end, through solid basic research work such as sedimentation and geochemistry, the complex strike-slip fault zone rich in oil and gas in Shijiutuo was locked in, and major discoveries of another 100 million-ton oil fields were achieved in the old exploration areas.

Xu Changgui, deputy chief engineer of CNOOC Exploration, said that the Qinhuangdao 27-3 Oilfield is the sixth million-ton oilfield continuously discovered by Bohai Oilfield since 2019. The successful discovery of this oilfield further confirms the vast oil and gas exploration prospects of the complex strike-slip fault zone in Bohai Sea. (Cao Xiuying)

（转自《Science and Technology Daily》）