Evaluation of Hammerdrill-Potential for KTB

Abstract

The technique of drilling at great depths with large diameters is established worldwide in the field of oil and gas exploration. The rotary drilling and the downhole mud motor system, in combination with roller-cone and diamond bits, is the most efficient way of drilling in sedimentary rock. Problems arise during rotary drilling in hard and ultra-hard formations because the roller-cone bits lose much of their drilling efficiency, while the diamond bits have a short life caused by wear, especially in formations with a high quartz content. In order to improve the efficiency of the drilling process in hard crystalline rock with large hole diameters in the super-deep well in the continental crust drilling program of the FRG, alternative drilling methods have to be developed to overcome the weak points of conventional rotary drilling. Special preference is given to an effective hydraulic downhole hammer that can be operated with the nonsolid, light-weight drilling fluid consisting of water, polymers and lubricants used at the KTB well. In hard formations and large hole diamters of up to 17–1/2 in., the diamond bits generally have a very low performance and the roller-cone bits make excessive bit weights (WOB) necessary so that the bearings may be overstressed and the deviation of the borehole axis cannot be controlled.