China's first undersea carbon dioxide (CO2) re-injection well, developed by the China National Offshore Oil Corporation (CNOOC), started drilling in the Pearl River mouth basin, the South China Sea, on Sunday, filling in a void in the country's offshore CO2 storage technology.

CO2 re-injection refers to the technology that injects the captured CO2 into the land at a depth of 800 meters to 3,500 meters underground or the sea salt water layer.

It is an internationally-recognized measure to promote carbon emission reduction.

The drilling work was undertaken by CNOOC's Enping 15-1 oil platform, which is part of the Enping 15-1 oilfield complex that deployed the country's first offshore carbon capture, utilization and storage project.

Read more: China launches Enping 15-1, Asia's largest offshore oil platform

After the well's operation, the Enping 15-1 platform will collect the CO2 during the oil and gas exploitation process and then inject and store it undersea.

It is expected to store 300,000 tonnes of CO2 per year at its peak, and more than 1.5 million tonnes accumulatively, equivalent to planting nearly 14 million trees or taking nearly 1 million cars off the road, according to the CNOOC.

Enping 15-1 oilfield contains high CO2 content in the South China Sea. Based on geological and technological research, the CNOOC finally decided to sequester CO2 in a "dome-like" geological structure about 3 kilometers away from the Enping 15-1 platform.

"The geological structure is like an upside-down 'giant bowl' underground, forming a strong natural seal that can trap CO2 steadily for a long time," Deng Chenghui, manager of well drilling and completion at the project team of the Enping 15-1 oilfield complex development, told Xinhua.

The well will also help to store the CO2 produced by some high-emission enterprises in the coastal areas, thus facilitating the Guangdong-Hong Kong-Macao Greater Bay Area to achieve green and low-carbon development, the China Media Group reported.