On September 19, China's first deepwater oilfield secondary development project - the Liuhua 11-1/4-1 oilfield secondary development project - marked its first anniversary of production, with cumulative crude oil output surpassing 700,000 tons. The development results have exceeded expectations, marking CNOOC's successful breakthrough in tackling the world-class challenge of developing offshore reef limestone oilfields, providing strong support for ensuring national energy security and revitalizing billion-ton-class deepwater oilfields.
The Liuhua 11-1/4-1 oilfield secondary development project is located in China's Pearl River Mouth Basin, comprising the Liuhua 11-1 and Liuhua 4-1 oilfields, with an average water depth of approximately 305 meters. The project plans to put 32 production wells into operation, with main production facilities including one deepwater jacket platform "Haiji No.2", one cylindrical FPSO (Floating Production Storage and Offloading) vessel "Haikui No.1", and one subsea production system.
To date, the project has brought 27 production wells online, with daily crude oil production steadily climbing to 3,400 tons, approximately 1.25 times the designed peak daily production capacity.
According to Dai Ling, chief engineer at CNOOC Shenzhen Branch Liuhua Operating Company, the Liuhua 11-1 oilfield is China's first deepwater oilfield and remains the country's largest proven offshore reef limestone oilfield by geological reserves. Since beginning production in 1996, the oilfield has cumulatively produced over 20 million tons of crude oil, but the recovery rate stands at only 12.84%, with approximately 140 million tons of crude oil reserves still buried deep in seabed formations.
Reef limestone oilfields are recognized worldwide as one of the most challenging reservoir types to develop. Their internal reservoir structure is complex, composed of caves of varying sizes, sponge-like dense pores, and crisscrossing fractures. Massive "water cushions" often exist beneath the reservoirs, and once extraction begins, bottom water rapidly advances along paths of least resistance and flows unpredictably, causing oil wells to be quickly flooded and preventing large amounts of crude oil from being extracted. During the primary development phase of the Liuhua 11-1 oilfield, most production wells experienced water cut rates exceeding 90% within one year of production.
Water control and oil stabilization, along with enhanced oil recovery, became key to efficient oilfield development. CNOOC spent ten years conducting concentrated research on enhanced oil recovery technology for reef limestone oilfields and launched a comprehensive adjustment project for secondary oilfield development.
"Through precise control of oil column height, scientific avoidance of concealed faults, and systematic improvement of water control effectiveness, the project team achieved four technological innovations including ICD water control + light particle supersaturated filling and intelligent compartmentalization, plus two engineering innovations, forming a complete series of offshore reef limestone water control and oil stabilization technologies. This has significantly enhanced the recoverable reserves and recovery rate of the Liuhua 11-1 oilfield, extending its operational life by 30 years," Dai Ling explained.
Production data from the past year shows that currently operational production wells in the Liuhua 11-1/4-1 oilfield have daily liquid production of only 37.4% of designed values, with comprehensive water cut rates 22% lower than designed, while crude oil production exceeds expectations, proving that offshore reef limestone oilfield water control and oil stabilization technology has achieved a major breakthrough.
Jiang Junda, General Manager of CNOOC Shenzhen Branch Liuhua Operating Company, stated that the current production and operational results of the Liuhua 11-1/4-1 oilfield secondary development project fully demonstrate the stable reliability of offshore reef limestone oilfield water control and oil stabilization technology and the economic effectiveness of the "deepwater jacket platform + cylindrical FPSO" development model, contributing a "Chinese solution" for efficiently developing similar deepwater oil and gas fields.