China’s first offshore carbon injection platform completes main construction

According to China National Offshore Oil Corporation, the main structure of the new central platform for the Dongfang 1-1 gas field, China’s first demonstration project of offshore carbon injection for gas enhancement, finished construction on 4 October and has entered a full commissioning phase. Once operational, the facility will store more than one million tonnes of carbon dioxide in subsea formations each year.

The Dongfang 1-1 gas field, China’s first self-operated offshore gas field, has produced over 50 billion cubic metres of gas since it came into service in 2003. The newly built central platform weighs nearly 17,000 tonnes and rises higher than a 28-storey building, with a deck area exceeding 10,000 square metres. 

It hosts a complete closed-loop system covering offshore carbon dioxide capture, purification, storage and gas displacement. 

The platform adopts an innovative natural gas decarbonisation process combining low-temperature rectification and membrane separation, with all core equipment domestically manufactured. 

The process cuts energy consumption by 20 per cent against conventional decarbonisation methods and lifts gas recovery rates by more than 12 per cent, capable of purifying 1.75 million cubic metres of carbon dioxide each day.

The project’s jacket structure has also been installed offshore. The 77.2-metre jacket features an eight-leg and twelve-skirt pile design, with an installation weight close to 8,000 tonnes. Dense existing platforms and subsea pipelines occupy the operation zone. 

The project team adjusted plans for onshore slip launching and wet towing according to local water depth and subsea layout. 

Upending operations were moved to open waters, and three-dimensional simulation plus continuous monitoring allowed the jacket to be positioned accurately in a single installation run.