A laboratory drilling program was conducted to measure the effect of bit hydraulic horsepower on the drilling rate obtained with a polycrystalline diamond compact (PDC) bit. Drilling tests were conducted under simulated downhole conditions with an 8 1/2-in. [21.59-cm] diameter PDC bit fitted with four sets of five equal-sized nozzles. PDC bit fitted with four sets of five equal-sized nozzles. Mancos shale, Pierre shale, and Berea sandstone were drilled with both water- and oil-based drilling fluids to determine the interactions among bit hydraulics, rock characteristics, and the drilling fluid. For the range of drilling conditions and rocks examined, the results indicated that bit hydraulic horsepower had a significant influence on the drilling rate. The degree to which drilling rate was affected by bit hydraulic horsepower was dependent on the rock/drilling-fluid combination.
Proper hydraulic design for effective cleaning and Proper hydraulic design for effective cleaning and cooling of PDC bits has been recognized as a major factor in their successful application since these bits were introduced. Historically, there have been two approaches to the hydraulic design of PDC bits:
natural diamond-bit flow-distribution systems (water courses with large total flow areas) and
high-velocity jet nozzles.
Both types have been used with varying degrees of success but often for unrecognized reasons. The water-course-type hydraulic designs were characteristic of most early matrix-bodied PDC bits. Nozzled bits evolved from the steel-bodied bits with stud-mounted cutters, although matrix-bodied bits are now available with jet nozzles. An increasing number of commercial PDC bits are becoming available with interchangeable nozzles, providing the flexibility of rig-site hydraulics optimization, providing the flexibility of rig-site hydraulics optimization, With these interchangeable nozzles, the hydraulic energy (or power) of the drilling fluid that is dissipated across the bit face can be adjusted to match that portion of the rig's hydraulic power that is available for the bit after other system losses have been considered. Unfortunately, the benefit in increased drilling rate that can be expected by an optimization of bit hydraulic horsepower has yet to be adequately defined quantitatively for PDC bits. The objective of our work was to determine experimentally the effect of bit hydraulic horsepower on the drilling rate achieved with a jet-nozzled PDC bit while three rock types were drilled with both oil- and water-based drilling fluids.
PDC Bit Hydraulics-Background PDC Bit Hydraulics-
JPT
p. 2110
