A view of Deep Sea No.1 in operation. (PHOTO: XINHUA)

By LU Zijian

The world's first 100,000-ton-level deepwater semi-submersible gas production and storage platform, Deep Sea No.1, has been operational since June 2021. To date, it has produced over 4.5 billion cubic meters of natural gas and transported over 450,000 cubic meters of gas condensate.

Deep Sea No.1 recently completed the construction and trial of its remote control system, enabling it to maintain safe and stable production even during typhoons.

Remote control made possible

The central control room of the vessel has a "normal/typhoon" mode switch. "When a typhoon or bad weather strikes, we switch to 'typhoon mode,'" said a staff member of Deep Sea No.1. The onshore control center will then take over operation from the central platform, allowing production to continue without interruption, he added.

Typhoons, which frequently occur in summer and autumn, pose the greatest challenge to the stable production of Deep Sea No.1. Although the production team strives to resume production as quickly as possible after a typhoon, they hope to eliminate such unstable factors to minimize the impact on downstream users brought by typhoon-caused shut downs.

However, there was no precedent for such a remote control system for ultra deepwater semi-submersible gas platforms.

After countless hours of calculations, modeling and debugging, the R&D team was able to determine key storm resistance indexes such as the safe range of draft. They also designed transformation and debugging solutions for over 270 sets of related equipment. The transformed equipment and specially built communication network function as a neural network, sensing the indicators of each operation, whereas the onshore control center acts as the brain.

The remote monitoring and production tests under extreme sea conditions proved that Deep Sea No.1 is capable of production via remote control, said Li Jinsong, general manager of Lingshui-Yacheng Operation Company of CNOOC's Hainan subsidiary.

According to Li, the implementation of the new system could reduce the shutdown time caused by extreme weather, potentially increasing the annual production of natural gas by 60 million cubic meters per year.

Tackling key technological problems

Deep Sea No.1 faced numerous technological challenges while extracting natural gas from a depth of 1,500 meters. However, the researchers and builders of the platform were able to overcome them. They developed three world's- first technologies, including the ability to store oil through columns of the semi-submersible platform.

Drawing inspiration from the liner of vacuum flask, the researchers built a 5,000-cubic-meter tank for gas condensate within each of the four floating columns of the platform. The tanks are equipped with specifically made protection cases to prevent oil leaking caused by collision.

The technology enables Deep Sea No.1 to integrate the production, storage and transport of gas condensate, saving approximately 800 million RMB in costs as it eliminates the need for developers to build outward transporting pipelines for gas condensate, a generally practiced design for such platforms.

There are also 13 technologies that were developed for the first time in China, some of which enable large platforms like Deep Sea No.1 to remain stable while at sea even under extreme conditions.

Sixteen anchor chains made by high-end polyester are used to keep the platform standing, with one end of the chain fastened to the corner of the platform and the other end to seabed. The breaking load of each chain exceeds 2,000 tons, which enables the platform to resist a level 16 typhoon. The technology also enables the platform to operate for a period of 30 years before requiring maintenance at the dock.

High-quality and safe platform

According to Song Jinlong, director of the Deep Sea No.1 platform, the team actively conducted adaptive reconstruction for relevant equipment, technological processes and control systems to meet the technological requirements of the normal platform function.

To ensure the safe operation of the innovative column oil storage approach, the developers installed monitoring facilities and emergency protection systems inside the tanks.

Typically, meeting the standard requirement for airtightness involves maintaining pressure within a certain range over a specific period of time, but the standard for Deep Sea No.1 is much higher.

No bubble is allowed onsite, said Lei Yafei, senior engineer at Lingshui-Yacheng Operation Company of CNOOC's Hainan subsidiary. To ensure this, he and his colleagues used various tools, such as hydraulic wrenches, chain blocks and hammers to check for bubbles.

All this hard work has resulted in Deep Sea No.1 becoming a stable and consistent gas production platform.