New, Stable PDC Technology Significantly Reduces Hard Rock Cost Per Foot

Abstract

Abstract Historically, the hardest and most abrasive rock formations, such as the Travis Peak, Hosston, and Bossier Sands areas of East Texas and North Louisiana, were drilled almost exclusively by roller-cone insert bits. With some exceptions, the only polycrystalline diamond compact (PDC) runs were small-diameter holes where the formation was predominantly comprised of shale and limestone. Significant advances in design and cutter technology in PDC bits during the past 5–10 years have made it possible for PDC to be used more frequently on the fringes of these hard rock intervals. Combining advanced PDC bit designs with state-of-the-art cutter technology has opened up many new applications for PDC bits that were once only appropriate for IADC Series 6, 7, and 8 insert drill bits. Because of this new technology, PDC has become a practical alternative for drilling hard rock, providing a significant reduction in cost per foot. Combining new, highly abrasion-resistant PDC cutters with competent stable bit designs that provide both low torque and dynamically stable characteristics was the key to this development. Several case histories of hard rock drilling using PDC bits will be discussed in this paper, illustrating the reduction in costs. These case histories demonstrate, through descriptions of trial and error, the problems associated with these new PDC applications and how they were overcome.