A comparison has been made of the results obtained with a new soft formation PDC bit (the Security STRAT-X Bit) and those obtained in a wide range of formations with the various types of PDC bits currently available. The results indicate that, at present, PDC bits are special products for special situations. The clearly superior results have been obtained in homogeneous soft formations when the bit hydraulics and application practices have been appropriate for the particular bit design involved. Very high penetration rates and significant reductions in cost/foot have been achieved when bit design, hydraulics, mud and application practices have been matched well with the bit characteristics. However, even the newest and most productive PDC bits cannot compete when the formation is unsuitable for the particular bit design in combination with the drilling fluid and the hydraulics available. A review of several specific examples in South Texas, the North Sea, and the Rocky Mountains illustrate what can be done with currently available PDC bits, and how to identify those circumstances under which PDC bits should not be run. The results also indicate how to identify when a formation change requires that a PDC bit be pulled or when one can drill through hard streaks and retain the high productivity of the PDC bit for the softer portions of the formation. Maintaining a full gage hole under these conditions is shown to depend critically on bit design and control of weight and rpm.

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