Laboratory Drilling Performance of the Full-Scale Rock Bit

Abstract

Abstract Laboratory drilling tests with 4 3/4-in. hard-formation rock bits were made under rock pressure and borehole fluid pressures simulating a 3,000-ft borehole. The effects of bit weight and rotary speed on drilling rate and bit rotary power were determined in a hard, impermeable dolomite. With added bit weight, the drilling rate and rotary power both increased at an increasing rate; but, with added rotary speed, the rate and power both increased at a decreasing rate. The rock volume removed per unit of energy increased as weight was raised or as rotary speed was reduced. Empiric quadratic equations for drilling rate and rotary power were obtained and bit mechanical efficiency was calculated. Introduction During the past three years, Jersey Production Research Co. has performed an extensive series of tests using roller cone, drag and diamond bits varying in size from 3 3/4 to 9 7/8 in. These tests have been made under a wide range of drilling conditions in several types of rocks at both atmospheric pressure and elevated pressures simulating depths to 3,000 ft. This paper reports the effects of bit weight and rotary speed on the penetration rate of and power consumed by a 4 3/4-in. hard-formation rock bit drilling in impermeable dolomite. The laboratory work reported here supplements and extends previously published data describing the effects of bit weight and rotary speed on drilling rate from tests made at atmospheric pressure. Similarly, the effects of pressure have been previously investigated, using 114-in. "microbits", and the effects on drilling rate of pressure and fluid environments have been reported. Several investigators have also studied certain theoretical aspects of the roller-cone rock bit performance problem. Despite this work, however, there are no published data available on the performance of field sized bits under controlled laboratory conditions which simulate the down-hole pressure environment. There also is very little information in the referenced papers on the amount of power consumed by the bit. Therefore, the purposes of this paper areto present laboratory performance data on a field-sized bit to aid in the interpretation of field test results, andto make data available on the rotary power at the bit. It is hoped that this information will stimulate industry studies of energy consumption in rotary drilling and lead to the improvement of drill-bit efficiency.