China's first 100-billion-cubic-meter gas field in the Bohai Sea — Phase I development project fully commissioned

CNOOC Tianjin Company has announced that the Phase I development project of the Bozhong 19-6 gas field, the first 100 billion cubic meter natural gas field in China's Bohai Sea, has been fully commissioned. The project currently produces over 5,200 tonnes of oil equivalent per day, and its development performance has exceeded expectations.

The Bozhong 19-6 gas field is located in the central waters of the Bohai Sea. It has proven geological reserves of over 200 billion cubic metres of natural gas and over 200 million cubic metres of proven in-place liquid petroleum. The reservoir lies at a depth exceeding 5,000 metres, with a wide but complex distribution of hydrocarbon accumulations and densely fractured buried hill formations.

According to a representative from the Engineering Technology Operations Centre of CNOOC Tianjin Company, the technical teams faced formation temperatures up to 204°C and rock hardness exceeding that of conventional carbon steel. In response, they successively broke through four key technologies, including drilling techniques for extremely hard strata and high temperature resistant drilling fluid systems, and built an independent and controllable technical system tailored to the ultra deep reservoirs in the Bohai Sea. They also successfully carried out the world’s first branch well operation in the Archean buried hill formation. In Phase I, 10 ultra deep wells deeper than 6,000 metres were drilled, setting a record for the number of ultra deep wells in a single Bohai oilfield development project, with an average well depth of over 5,500 metres.

Within the buried hill reservoir, condensate gas is mainly distributed in micron-scale fractures as fine as a human hair. Conventional depletion drive production suffers from low recovery efficiency, making it challenging to efficiently convert reserves into production. The technical team continued to tackle these difficulties, ultimately developing a development technology system for ultra-deep complex buried hill hydrocarbon reservoirs in offshore settings, and innovatively proposed a gas cycling injection development mode—re-injecting part of the produced natural gas into the formation to maintain pressure—which effectively solved the development challenges.

It is noted that China's natural gas reserves are predominantly distributed in the west, with relatively less in the east. As the largest offshore gas field in eastern China, Bozhong 19 6 has already produced over 2.8 billion cubic metres of natural gas cumulatively, making it a vital pillar for ensuring a stable natural gas supply to the Beijing Tianjin Hebei region and the surrounding Bohai Rim area.

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