Performance Comparison of Rolling Cutter Bits with Alternate Nozzle Configurations

Abstract

Controversy exists regarding the optimum nozzle configuration for rolling cutter bits. Frequently, this confusion is compounded by tests which compare an experimental configuration to only the standard nondirected, three nozzle design. Additionally, field data can cloud comparisons because of the lack of control and repeatability of formation and drilling conditions. The strategy of this paper is to describe the use of controlled laboratory conditions to best isolate the true benefit of various hydraulic configurations. Tests were conducted in a pressurized drilling environment using 9-7/8 tooth and insert bits in Mancos shale. Hydraulic configurations include combinations of standard and directed nozzle bits with center jets, long extended nozzles, and short extended nozzles. Results indicate that directed nozzles provide substantially better bit cleaning and rate of penetration (ROP) than the standard and short extended nozzle configurations and slightly faster rate of penetration than long extended nozzle configurations. Introduction The evolution of bit technology has shown substantial increases in durability and penetration rates. A key area of focus for improving rate of penetration has been bit hydraulics. The first advancement was to change from regular circulation bits to today's standard jet bit with three non-directed replaceable nozzles. Subsequent work by several researchers has established the importance of optimizing system hydraulics to maximize hydraulic cleaning at the bit. Adding to that success others have proposed alternate nozzle configurations to boost rate of penetration. The two basic strategies applied in alternate nozzle configurations are to place the nozzle closer to the formation and to direct nozzles so that they clean cutters and reduce balling. The alternate nozzle configurations evaluated in this work are discussed below. The authors acknowledge nozzle blanking and asymmetric nozzles as candidates for future study.

Advanced Hydraulics Analysis Optimizes Performance of Roller Cone Drill Bits

“…11 Moffitt and McGehee report that this bit drilled 31% faster than conventional bits in the laboratory. 12 Slaughter reports an increase in ROP of up to 27% over conventional nozzle bits in field tests. 10 In 1992, Moffitt et al describe tests in which a variety of nozzle targets in the neighborhood of Slaughter's original directed nozzle were evaluated.…”