Abstract
In scientific research drillingf the borehole may be reviewed as an endoscope into the Earth, as it happens to be the case, for example, in the international Ocean Drilling Program (ODP) and the Continental Deep Drilling Program of Germany (KTB). Development of the drilling technology in the last 15 years took place mainly in the two areas of deep and ultradeep drilling, and of horizontal drilling. The impact of big geoscientific research programs on deep drilling technology is remarkable. Scientific drilling projects need intensive and expansive R&D efforts on the one hand and produce an outstanding spin-off on the other hand.
The German Continental Deep Drilling Project (KTB) is part of the international lithosphere research. The two boreholes of the project penetrate crystalline rock from the beginning. The 4,000 m deep pilot hole was drilled from September, 1987 to April, 1989. The ultradeep hole, planned for at least 10,000 m depth, started being drilled in October, 1990. The pilot hole was drilled by applying a large diameter thin kerf wire line coring technology, which was improved to a high extent during drilling. A newly developed synthetic clay based mud has been used succesfully. For ultradeep drilling, a straight vertical wellbore trajectory is a must, to minimize drag, torque, and wear. To obtain a vertical wellbore course, active vertical drilling systems were developed and for the first time successfully utilized at the KTB. A new heavy, technologically advanced drilling rig has been constructed and is working satisfactorily.
