Subsea Christmas tree takes root

An aerial image of the Nanhai No 7 drilling platform of the China National Offshore Oil Corp in the sea near Dongfang city, Hainan province, on May 10. ZHANG MAO/FOR CHINA DAILY

First control and monitoring system produced domestically to help hasten gas and oil exploitation

At noon on May 10, a helicopter took off from Dongfang Datian Airport in Dongfang city, Hainan province, and flew south along the coast.

About 50 minutes later, Nanhai No 7, a huge drilling platform belonging to the China National Offshore Oil Corp appeared on the horizon.

On the platform, dozens of workers were working busily under the scorching sun. Liu Shujie, one of the company's drilling experts who had arrived on the helicopter, said the men were making final checks on the first deep water subsea Christmas tree developed independently in China before it was deployed.

A subsea Christmas tree (also known as wet tree) refers to the system of valves, flow paths, piping and connectors installed on a subsea wellhead to contain and control the flow of gas or oil from the reservoir or from the surface by injection.

Liu said that the system also controls drilling speed and monitors and adjusts the process, making it a key component in underwater oil and gas extraction.

Until recently, the systems were only made by a few global manufacturers, and this resulted in a bottleneck in national oil and gas production.

"To develop the technology domestically, CNOOC worked with 16 other institutions for three years before it made a breakthrough," said Xie Yuhong, CNOOC's chief scientist.

At 5 am on May 11, eight technicians watched as their subsea tree system was finally assembled by underwater robots.

"It will be used to explore the Dongfang 1-1 gas field, which will produce an estimated 200 million cubic meters of natural gas per year," Liu said.

"It will certainly quicken the pace of oil and gas exploitation in China."

Workers on the platform wave goodbye to their colleagues who are returning to Dongfang by helicopter after a 28-day shift on the platform on May 10. 

ZHANG MAO/FOR CHINA DAILY

Liu Shujie (fourth from left) and his colleagues celebrate the launch of the subsea Christmas tree on the platform. ZHANG MAO/FOR CHINA DAILY

----The news is quoted from China Daily By QIU JIANGHUA and CHEN LIANG (www.chinadaily.com.cn)

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