Over the years, drilling technology in the Dutch sector of the North Sea has evolved in an attempt to overcome many drilling challenges. Gaz de France’s 12-1/4" hole section, in the K12 field, has been a very active arena for technological advancement and new product development. Many new drilling systems and new drill bit designs have been tested and developed through this complex drilling interval. However, even with all of the advanced technology utilized in drilling this section, many operational difficulties remain, due to the variety of formations, the directional requirements, and the length of this interval. Until recently, this section was drilled using a variety of different products, including roller cone and PDC drill bits, on both downhole motors and rotary drive systems.
In an effort to improve the performance through this interval, another new technology was introduced to this drilling program, the geared Turbodrill. This new downhole drive system is capable of producing very high mechanical power at the bit, both high torque and relatively high RPM. The high power of this new tool, in conjunction with aggressive PDC drill bits, has proven to provide excellent performance in this challenging environment. This paper will detail the development and characteristics of this new geared Turbodrill, and also analyze recent North Sea case histories that included the 12-1/4" hole section through the upper Cretaceous chalk down to the upper Permian Zechstein formation.