ABSTRACT
What used to be considered a novel drilling technique, the use of synthetic diamond cutters in a drag bit configuration, has now emerged in the drilling industry as a time and cost efficient drilling tool. These bits, utilizing polycrystalline diamond compact cutters for drilling soft or plastic formations have been proven successful through a systematic development. First, the main problem associated with drilling soft or plastic formations was identified as bit cleaning. Second, laboratory tests of a single compact cutting plastic shale under confining pressure with a load dynamometer and high speed photography were studied. The results demonstrated that a compact incorporating side rake angle and ample chip clearance space can provide efficient mechanical cleaning action. Finally, new style drill and core bits, built with side rake orientation along with previous style drill and core bits without side rake features, were field tested and observed in the same drill hole or in the same formation. The drill or core bits with side rake features always drilled or cored faster in the soft or plastic formations than those bits without side rake under the same operating parameters (hydraulic, bit weight and rpm). It was concluded that bits with side rake features can enhance the bit cleaning by mechanical cleaning action and, therefore, improve the bit performance in soft or plastic formations.
