Downhole drilling motors: technical review. Final report

Abstract

Dyna-Drills and turbodrills are used primarily for directional drilling where it is critical that the drillpipe not be rotated. These tools are not widely used for straight-hole drilling because of problems with bearing failures, low power outputs, low bit pressures, and high rotary speeds. The high rotary speeds produce bit bearing failures in 10 to 15 h, compared to 100 to 200 h life at lower rotary speeds. The technology now exists to develop reliable high-torque motors which will operate roller bits at speeds of 150 to 250 RPM and diamond bits at speeds of 400 to 800 RPM for periods of 100 to 200 hours. Sealed bearing assemblies which allow the bearings to operate in lubricant are being developed. These improved bearings allow bits to operate at the high bit weights needed for optimum drilling. Improved drilling motors can reduce drilling costs to significantly increase the number of wells drilled per drilling rig per year. Now, this is increasingly important because of the drilling rig shortage developing in this country. At least ten companies are working on the development of improved drilling motors and it is likely that several of these new motors will become commercially available within themore » next 2 to 3 years. Several companies are working on the development of improved high speed roller bits for use on drilling motors. The development of these high speed bits should significantly increase the use of drilling motors since bit bearing failures are a major problem when drilling with motors. The development of reliable, high-speed STRATAPAX bits should also increase motor useage since these bits drilling most effectively at rotary speeds of 300 to 500 RPM.« less