On January 4, China National Offshore Oil Corporation (CNOOC) announced that China’s largest offshore gas field, Deep Sea No.1, has recently completed its 100th shipment of crude oil since coming on stream. In 2025, the field’s total oil and gas output exceeded 4.5 million tonnes of oil equivalent, comparable to the production scale of a medium-sized onshore oilfield, marking China’s deepwater gas field production and operation technologies as having reached a world-advanced level.

Deep Sea No.1 is China’s most challenging offshore gas field independently developed to date, featuring the deepest operating water depth, the highest formation temperature and pressure, the greatest exploration and development difficulty, and the largest natural gas production capacity. The maximum operating water depth exceeds 1,500 meters, with formation temperatures reaching up to 138°C. Proven geological natural gas reserves exceed 150 billion cubic meters, and the field has been developed in two phases.

Phase I adopted a development model combining a subsea production system, a semi-submersible production platform, and subsea pipelines. Phase II employs a model integrating a subsea production system, a shallow-water jacket platform, subsea pipelines, and remote-controlled semi-submersible production platforms. The two core facilities—the Deep Sea No.1 energy station and the “Four Stars in a Row” platform cluster—are both equipped with deepwater oil and gas processing capabilities, enabling on-site offshore separation and export of natural gas and condensate.

At present, Deep Sea No.1 produces 15 million cubic meters of natural gas per day and more than 1,600 tonnes of condensate. Part of the condensate is stored in oil tanks located within the four columns of the platform and, once sufficient volume is accumulated, is exported via shuttle tankers. This storage-and-export solution represents one of the three world-first technologies deployed at the Deep Sea No.1 energy station.

Since production began in 2021, CNOOC’s offshore operations team has continuously upgraded production facilities, applying nearly 30 years of offshore gas field production management experience to optimize process flows. By exploring optimal combinations of operating parameters, the team has maximized deepwater gas field production potential and ensured safe and stable operations. In 2025, annual natural gas output from the field reached 5 billion cubic meters for the first time, exceeding the project’s designed peak capacity.

In 2025, offshore gas fields around Hainan Island, including Deep Sea No.1, collectively produced over 10 million tonnes of oil equivalent, doubling output compared with the end of the 13th Five-Year Plan period. Deepwater oil and gas emerged as a key growth driver, contributing more than 90% of the region’s incremental oil and gas production.