China achieves breakthrough as million-tonne offshore carbon storage project begins operations

SHENZHEN -- Amid the vast expanse of the South China Sea, the Enping 15-1 oil platform rises above the water. A distinct green pipe stands out from the network of lines piercing the sea floor from the platform, injecting hundreds of tonnes of liquid carbon dioxide (CO2) into the deep sea.

On Thursday, China's first offshore million-tonne carbon storage project was put into operation in the South China Sea. It serves the Enping 15-1 oil platform 200 km southwest of Shenzhen, capturing and processing CO2 from oilfields and then injecting it into a domed geological structure at an approximate depth of 800 meters below the seabed and about 3 km from the platform.

"The geological structure resembles a massive bowl, containing the CO2 securely and acting as an immense seabed 'carbon can,'" said Deng Changhong, vice general manager of the Shenzhen branch of the China National Offshore Oil Corporation (CNOOC).

Experts have revealed that viable subsurface CO2 storage options include deep saline aquifers and a depleted oil and gas layer. Take the deep saline aquifers with a domed geological structure as an example. Most of these structures resemble large bowls and have diameters exceeding 10 km.

When CO2 is injected into these aquifers, it rises to the top of the bowl structure as its density is lower than the saltwater present underground. The thick, impermeable or low-permeability cap layer at the top of the bowl prevents the CO2 from leaking out, ensuring it is effectively sealed and contained.

The project is designed to store a total of more than 1.5 million tonnes of CO2, which is equivalent to planting nearly 14 million trees.

Its operations signify China's achievement in acquiring a complete set of technologies and equipment to capture, process, inject, store and monitor CO2 at sea.

It is the first oilfield in the South China Sea with a high CO2 concentration, according to Wan Nianhui, general manager of the CNOOC Enping oilfield.

The China Geological Survey, conducted by the Ministry of Natural Resources, reveals that China's sea areas possess significant potential for CO2 geological sequestration. The sequestration capacity in these areas is projected to reach 2.58 trillion tonnes.

"The Enping project has not only marked a significant breakthrough in CO2 storage, but has also paved the way for future endeavors in this field," Deng said.

On the basis of this project, the CNOOC has initiated China's first 10-million-tonne carbon capture and storage cluster project in Huizhou, south China's Guangdong Province. It will capture CO2 emitted in Daya Bay and ship it to the Pearl River Mouth Basin sea area for storage.

"The CNOOC remains committed to enhancing scientific research to provide valuable insights for the future development of oil and gas fields and for the large-scale emissions reduction efforts of coastal enterprises," said Qi Meisheng, general manager of the CNOOC Shenzhen branch.