Drilling in deepwater is very expensive, with rig rates in the hundreds of thousands of dollars per day and high spread costs. When coupled with drilling exploration wells in areas with unknown and "difficult" formations, the risks escalate exponentially.

An example of this is the recent drilling on the ChevronTexaco Upstream Europe discovery well in the West of Shetland province of the UKCS. On this particular wildcat exploration well the potential of encountering a volcanic/basalt sequence had been highlighted at the planning phase. Only limited offset data was available, the closest offset well being some 15 miles (24km) from the proposed well location. A general overview of the well and its objectives is given. The paper focuses on the original drilling philosophy and why it changed during the drilling of the well and the reasons which ultimately led to the use of a turbine and diamond impregnated bit. Factors in the successful drilling of the above well including lessons learnt will be explained. The trade-offs with the various BHA configurations and the impact on data acquisition is also explained.

The paper also consolidates the offset information and some of the research and development of basalt drilling at high speeds using turbines. The paper therefore outlines the equipment run in the extensive volcanic/basalt section and the establishing of new benchmarks for the drilling of this extremely challenging formation in a deepwater and high cost environment.

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