Photo taken on May 12, 2021 shows the Deep Sea No.1 deep-water gas field, 150 kilometers off the city of Sanya in south China's Hainan Province. Deep Sea No.1, China's first self-operated 1,500-meter deep-water gas field, started production on Friday, according to the China National Offshore Oil Corporation (CNOOC).Photo:Xinhua

Deep Sea No 1, China's self-developed ultra-deep-water gas field, successfully completed its first-ever natural gas condensate tank cleaning and inspection operation, since commencing operations, China National Offshore Oil Corporation (CNOOC) said on Saturday. 

Cleaning and inspection of condensate tanks under deep sea is extremely hard, and completing of the task is a milestone that underscores the exceptional reliability and cutting-edge design of the pioneering platform, expert noted.

Deep Sea No 1 is equipped with four condensate storage tanks with a single capacity of 5,000 cubic meters, which are designed to safely store condensate oil separated during the process of deep-sea natural gas extraction. They are one of the three world-class innovative technologies integrated in the Deep Sea No. 1 gas field.

Condensate tanks of Deep Sea No 1 are over 48 meters deep, and they are the deepest and most intricate tanks among China's offshore oil and gas facilities. As natural gas condensate is highly volatile with a low flash point, and being insoluble in water, cleaning and inspection of the tanks are extremely dangerous, Li Zhi, a manager of Deep Sea No 1, was quoted as saying.

To ensure its safe operation, working teams at Deep Sea No 1 emptied the condensate tanks, developed an implementation plan and risk response strategy before cleaning and inspection, and built customized personnel baskets to facilitate the safe entry and exit of operators.

As China's first independently operated ultra-deep-water gas field, Deep Sea No 1 has completed multiple critical operations such as condensate tank cleaning, remote-controlled production modification and ultra-deep-water valve pigging, without any precedents to follow, said Li Li, deputy general manager of CNOOC Hainan Branch, CCTV.com reported.

During the cleaning and inspection operation, Deep Sea No. 1 maintained gas production. The station continuously supply gas to South China while improving China's independently established ultra-deep-water gas field operation and maintenance system, Li said.

Deep Sea No 1 is the world's first 100,000-ton deep-sea semi-submersible oil production and storage platform, which is independently developed and constructed by China. It was put into use on June 25, 2021. After two years of operation, the platform had produced over 5 billion cubic meters of natural gas.

The second phase of Deep Sea No 1 gas field is under construction, which is expected to increase the peak annual production by 50 percent.