fax 01-972-952-9435. AbstractAdvances in drillbit technology have resulted in suppliers adding a seemingly endless array of features to improve bit performance. There is little standardization between bit designs, so drilling engineers and supervisors are faced with difficult choices when selecting drillbits. This paper outlines the development of a systematic method of PDC bit selection. The system is not an 'expert system', but a simple methodology that can be readily adapted by engineers to suit their conditions. A basic geological model is developed for each hole section. Formation strength and drillability are calculated from porosity, sonic travel time, matrix rock velocity, degree of compaction, abrasiveness and hole cleaning requirements. The geological model can be adapted to any area by specifying the main rock types and their percentages in the section to be drilled. If not known, typical properties can be obtained from tables included. Individual well profiles are specified by the percentages of build, drop and holding tangent, and also dogleg severity. Combining the geological model and well profile enables a set of 'ideal' bit characteristics to be generated. This ideal bit design is compared with the drillbits proposed by vendors. These are ranked by indices for design, performance and economics.[The Design Index takes into account bit characteristics such as the bit profile, number of blades and cutters, cutter size, junk slot area and backrake.] The selection is based on the bit that provides the closest match to the 'ideal' design. The methodology has been geared to fixed cutter PDC bits but is being expanded to include roller cone bits. Although the system was originally developed for extended reach and horizontal wells, it can be applied equally to any type of well.