Mud Hammer Drilling in Hard Formations: Bit Design Improvement Leads To Increased Rate of Penetration

Abstract

Percussion drilling system, combining a mud hammer with drill bits, has been developed to increase drilling performances in hard formations. This system is based on a high-power down-the-hole hammer (Power output of 30 kW), capable of delivering high-energy impacts at high frequency (35 Hz) used with mud pressure as the power source. The drill bit is a key performance element because it is the one that is in contact with the rock and destroys it. It must be designed to optimize the cutting process. Numerous elementary tests of the insert-rock contact and the development of a model of the performances have been performed. It makes it possible to show the importance of the bit design parameters and the need to adapt the design to the drilling conditions. A new generation of bits optimized for performance has thus been developed and manufactured. The 6” mud hammer and the new drill bit have been then tested on a full scale drilling test bench. The performances comparison with roller cone bit showed an improvement of 100 to 300% of Rate of Penetration (ROP). The set was ultimately used in field drilling operations and validated the large improvement in ROP of 300%.