Stratigraphic analysis of sparse seismic data in 1981 indicated the presence of a carbonate bank complex over the western part of the Dongsha Massif, 220 kilometers southeast of Hong Kong. Two Lower Miocene shelf edge trends were recognized and a large carbonate bank closure mapped on the axis of the massif. The study also predicted the presence of a widespread, thick basal sandstone below the carbonate complex that could serve as a conduit for long distance migration of hydrocarbons. Although the prospect was a high risk play in deep water 38 kilometers south of the most probable Paleogene source basin, it was intriguing because of its size and similarity to the giant Bombay High Field offshore India.

After drilling by other companies demonstrated that oil had migrated well out of the source basin (Huizhou Sag), Amoco negotiated for Contract Area 29/04 and was awarded the area in November 1985. The first well, Liuhua 11-1- 1A, tested 2,240 BOPD of 21 degree API oil from a 76 meter pay section in a carbonate bank sequence topped at 1197 meters. A 400 meter lower carbonate section and a 150 meter sandstone sequence resting on basement were water bearing. Additional drilling has confirmed a giant in place accumulation, but commerciality is yet to be determined. The carbonate complex consists of a leached limestone bank with a reefal margin, and has excellent porosity and permeability. The oil is less waxy and heavier than other Huizhou Sag sourced oils because of biodegradation after migration.

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