The drilling efficiency of any operation is directly related to borehole stability and optimized drilling parameters. Borehole stability is directly related to reactions with the drilling fluid being used. Penetration rate, although directly related to the strength of the formation, can also be affected by the drilling fluid.

Many active drilling areas around the world have seen the advent of new drilling fluid systems along with new types of drilling bits. A study was initiated to correlate the similarities of these two aspects into the improved penetration rates being realized. Primary interest has been with the use of the PCD (polycrystalline) bits and the use of oil muds, especially the low toxicity oil muds for offshore use. The oil mud drilling fluid has prevented many of the wellbore instability problems that can occur with the use of water base muds. With the use of oil muds and the PCD bits, considerable savings in drilling costs have been realized.

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