Assessment of bit life under conditions of rotary-vibratory drilling

This study addresses the topic of the life of the rock bit under conditions of rotary-vibratory drilling as compared to conventional rotary drilling. Conventional rotary drilling systems were analyzed to determine the causes of large dynamic bit loads currently experienced in the drilling industry. Power delivery to the rock due to the large dynamic bit forces was calculated for representative conventional rotary drilling systems. For an idealized rotary-vibratory system, power delivery to the rock was calculated at dynamic force levels comparable to those found in conventional rotary drilling systems. Comparison of values of power delivery to the rock for the two systems indicate the rotary-vibratory system has the potential to increase the instantaneous penetration rate up to 4.14 times the rate of conventional rotary drilling systems, at comparable dynamic force levels. Experimental data was analyzed to assess the relative penetration depth per bit between the rotary and rotary-vibratory system. Results indicate that the bit life, in terms of total depth of penetration per bit, is potentially greater for the rotary-vibratory system.