Haiji-1, Asia's first 300-meter deepwater jacket designed and built independently by China National Offshore Oil Corp, was successfully installed offshore in the South China Sea, marking a breakthrough in the country's design, construction and installation technology of ultra-large offshore oil and gas platform jackets, said its operator CNOOC on Monday.

The installation will further guarantee the country's energy security by boosting offshore oil and gas production and is expected to create a new mode for the country's medium and deep-sea oil and gas resources development, said CNOOC, the country's top offshore oil and gas producer.

The installation of the jacket is a major breakthrough as it is the first time China has installed a fixed jacket some 300 meters underwater. It is also a milestone in the construction of super large offshore oil and gas platforms in China, the company added.

An analyst said that when put into operation in September, the jacket will further improve the country's energy supply and help guarantee the country's energy security.

China has been stepping up domestic oil and gas production with significant offshore results, said Li Ziyue, an analyst with BloombergNEF.

China's offshore oil and gas production, with great upside potential, is expected to continue rising over the next few years, Li said.

Deepwater jackets serve as foundations for offshore oil and gas platforms. Used to support the massive weight of an offshore platform, they are the most widely used offshore oil and gas engineering modality globally. Construction on the jacket was completed in Zhuhai, Guangdong province, on March 1 and the finished product was successfully hauled onto a barge on March 15.

Liu Yiyong, deputy manager of the construction department of Offshore Oil Engineering Co Ltd, a CNOOC unit, said the company has overcome numerous challenges including water injection under pressure, underwater grouting and sand slopes on the seabed, to ensure the jacket is precisely installed.

As Asia's first 300 meter-plus deepwater jacket-with a total actual height of 302 meters, a weight up to 30,000 tons and a working water depth of up to 284 meters-Haiji-1 will serve the Lufeng Platform 15-1 of Lufeng Oilfield Complex located in the eastern part of the South China Sea.

With a peak annual oil production capacity of 1.85 million tons, the Lufeng oilfield clusters will inject new momentum into the Guangdong-Hong Kong-Macao Greater Bay Area while further lifting the country's energy self-sufficiency capacity, said the company.