China's first domestically-built, semi-submersible deep-water oil production unit has been completed after 21 months of construction.

The platform is now ready to set off to the country's first deep-water gas field in the South China Sea.

The gas field, called Lingshui 17-2, is 150 kilometers off the city of Sanya in south China's Hainan Province and lies at a depth of 1,500 meters. Both these facts pose new challenges and uncertainties.

The general director of the project, You Xuegang from China National Offshore Oil Corporation (CNOOC), said special designs have been used to help the platform better adapt to the environment.

This platform weighs in at an impressive 50,000 tonnes, and its deck is as large as two standard football pitches. With a tank at the bottom and four pillars, the main body weighs 110,000 tonnes, which is equal to three medium-sized aircraft carriers, making it the heaviest of its kind in China.

There are two parts sitting above water. The upper module is used for work and it's also a living area. And the four pillars are used to store oil.

"The four pillars are used for oil storage. This is the first of its kind in the world. It can store a maximum of 20,000 cubic meters of oil for 10 days, allowing extra time for delivery vessels to carry the oil back on land 150 kilometers away," said You.

The platform is also designed to resist oxidation and the toughest typhoon, and should be able to work in the field for at least 30 years without needing to return to dry dock.

Building such a huge platform was obviously no easy task, especially given the challenges such as a severe cold snap, limited time and the impact of the COVID-19 pandemic. But managers say none of those were allowed to get in the way of completing the project and meeting all important quality standards.

"The China Classification Society (CCS) carried out a strict quality checking process for the project. Take the weld for example. It is a full 60 kilometers in length, and we checked all of it centimeter by centimeter and it's all very well done. Only in this way can we achieve smooth operation of the project," said Li Jun, CCS project manager.

The platform was assembled in Yantai, east China's Shandong Province, but it can't possibly travel all by itself.

Three vessels will be used to tow the platform, dragging it along the waterway like three horses and a carriage. There will also be another vessel at its rear, pushing it along the way.      

It'll take a month-long voyage for the platform to arrive in Hainan. Organizers say the trip is environmentally friendly with zero emissions reached.

It's expected to begin operation in June, providing 3 billion cubic meters of gas for households in Hainan Province and the Guangdong-Hong Kong-Macao Greater Bay Area every year.

"The project is a test for our design level, our shipbuilding level, as well as deep-water project management," said You.

He added despite difficulties and challenges ahead, there is no doubt that China has taken a solid first step towards deep-water oil exploration.