In deep wells, high bottom-hole pressure produces low drilling rates by increasing rock strength and by creating bottom-hole cleaning problems. New drilling bits are needed to increase rate of penetration and bit life. Both of these factors greatly influence the cost of drilling a well. This paper develops a method to compute the distribution of pressure on the cutting tooth, considering especially the effect of the nonlinearity of tooth profiles and plastic rock properties. Indentation force and deviation force on the bit-tooth are obtained integrating the non-uniform pressures between rock and tooth. Stress analysis can be applied to ensure an optimized profile of the cutter to attain fast penetration and longer life. Examples are shown and discussed for several kinds of rocks and tooth profiles, and the results compare agreeably with previous test data.
In 1973, there were 26,244 oil and gas wells drilled in the United States¹. The average depth of these wells was 5,207 feet, and the average cost was Sli7,152 per well drilled. Of those wells, 438 were drilled to depths of more than 15,000 feet, at an average cost of more than $1,096,000 per well. Approximately, in the last five years from 1972-1977, wells to below 15,000 feet accounted for only about 1.36 percent of the total drilled. But, the 3.5 billion the industry spent to drill and complete these relatively few deep wells was 14 percent of the $25 billion outlay for drilling and completing all United States wells in the period. High bottom hole pressures produce these low drilling rates by increasing rock strength and by creating bottom-hole cleaning problems. It is needed to extend and explore further the fundamental knowledge of rock/bit tooth interaction in order to design bits drilling faster and longer in ductile rock.
