Feasibility of Deepwater Drilling In South China Sea By Applying ABS Unit

COSL (China oilfield Services Ltd.), the biggest offshore drilling company in China, owns three semi-submersible rigs which can operate in water depth up to 470 meters. COSL is constructing a deepwater drilling rig recently, and it will be completed in 4–5 years. COSL needs to find out a way to modify semi submersibles to explore oilfield in water of 1,500 m during these years. COSL noticed the Artificial Buoyancy Seabed (ABS) unit, which may be matched to semisubmersible platform to perform drilling operation in deepwater up to 1500 m. The main principle of concept is to set a tank of buoyancy (the ABS unit) under 300m below sea surface, which is as a base of the semi-submersible rig. The ABS unit could utilize its buoyancy force to support the weight of BOP and other facilities such as risers, and the BOP will be set in a short distance from the sea surface. Since June 2004, COSL has carried out a series of tests to prove the feasibility of the new concept to deepwater drilling, and acquired a lot of data on the limited conditions for ABS unit. These data are, for example, the maximum loading forces, the maximum currents to resistance and the window of time to operation and so on. The tests were taken from both the pool of the lab and the lake in the main land of China, except for a model test in a pool. COSL had researched the test results for ABS unit, including a test of ABS unit in the sea near a city of Norway in 2002, and thought ABS unit is an accepted concept to do in the deepwater drilling. The paper describes not only the base structure, the procedure of testing about the feasibility by COSL, and showed some preliminary conclusions about this new concept.