China National Offshore Oil Corporation (CNOOC) and Taiwanese government-owned CPC Corporation have completed a drilling campaign in the deep water of the Taiwan Straits, the first such exploration attempt in these waters.

The Shantou 18-6-1 well was drilled in water depths of 1300 metres to a depth of 1000 metres at the Taichao block in the middle of the Taiwan Straits, using the deep-water semi-submersible drilling rig COSL Prospector operated by China Oilfield Service Ltd (COSL).

No results have been made public on the well. Subject to the analysis of well data, Tainan-Chaoshan Petroleum Operating Company, which is a 50:50 joint venture of CNOOC and CPC, may drill an additional well next year though no plan has yet been firmed up for such a probe.

Tainan-Chaoshan drilled the first deep-water well after CNOOC and CPC decided to extend their agreement to explore the block for a fourth time last year by expanding the size of the block to cover the deep-water area.

The current extension will expire by the end of next year.

Taiwan's regulatory body normally rules that no drilling facilities and service vessels are allowed to operate in Taiwan waters, but they gave an exception to COSL Prospector because the block sits in the middle of the Taiwan Straits between Taiwan and mainland China.

Earlier this year, the company completed a 3D seismic survey covering 2000 square kilometres in the central part of the 15,400 square kilometre block.

The block includes 7800 square kilometres on the western side of the Taiwan Strait contributed by CNOOC, while CPC contributed a licensed area of 7600 square kilometres on the eastern side.

Tainan-Chaoshan drilled two shallow-water wells, respectively in 2003 and 2009 on the block in the north and south, but they were not commercial.

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CNOOC and CPC complete Taiwan Strait drilling campaign