Drill Bit Considerations for Hard Rock Drilling in Newberry, Oregon

Abstract

Drilling through hard igneous formations commonly encountered in geothermal wells demands tools and parameters specifically engineered for these conditions. Generic designs optimised for sedimentary or metamorphic rocks typically result in poor drilling efficiency and reduced bit life. This paper presents the design and field performance of a 12.25” polycrystalline diamond compact (PDC) bit optimised for drilling hot, hard and abrasive volcanic tuff, andesite, and rhyolite in the vicinity of Newbury, Oregon. This bit design was also required to maintain strict directional control in aerated mud. The design methodology clearly differentiates between the roles of the primary cutting structure and the trailing support elements to enhance durability in the vibration-rich environment characteristic of igneous drilling. Field results are presented from a run in which the bit drilled 1,952 ft of volcanic rock at an average rate of penetration (ROP) of 46 ft/hr before being pulled in a repairable condition for a BHA change. Post-run analysis validates the design assumptions and identifies opportunities for further optimisation. The paper concludes with key insights and recommends best practices for PDC bit design and selection in geothermal drilling applications.