Rolling Cone Bits with Novel Gauge Cutting Structure Drill Faster, More Efficiently

Abstract

Roller cone bit design practices that focus on improving gauge durability have resulted in heavily reinforced and rugged, but highly inefficient, cutting structures. This dilemma prompted an in-depth study of the cutting mechanics in the corner of the borehole. The study consisted of a review of gauge cutting structure design and kinematics, laboratory testing with individual cutting elements to determine cutting forces and full-scale simulator and field tests. The work not only confirmed the original supposition, but led to the development of a novel, patented gauge cutting structure that is more aggressive, faster, and at least as durable and wear resistant as conventional designs. Introduction The overriding concern for the gauge-holding ability of roller cone rock bits has produced designs in which the maximum number of highly wear resistant tungsten carbide heel and gauge inserts are brought into conformal contact with the borehole wall to reduce contact stress and wear rate. Polycrystalline diamond enhanced inserts are used to further enhance wear resistance. A fundamental design assumption holds that in harder and more abrasive formations the back surfaces of rock bit cones simply slide along the borehole wall to smooth out the rough surfaces on the periphery that are generated by the crushing action of the inserts on the face of the bit. While this assumption may be true in brittle formations under atmospheric pressure where an insert generates a crater many times its own volume, it does not hold true under downhole pressure or in tougher, more plastically behaving materials. Under these conditions, the volume generated by an insert indentation is at most equal to the volume of the insert at the level of greatest penetration. Substantial amounts of uncut material remain between craters, of which only a small amount is removed by the gauge inserts. Most of the remaining formation has to be ground up and crushed in a highly inefficient manner by the steel cone shell. P. 241

Unique Gauge Structure and Other Bit Modifications Improve Drilling Efficiency of Baram, Baronia Fields

“…After resolving the former, the partners achieved the latter by modifying the hydraulic configuration and introducing a roller cone bit that employed a unique gauge cutting structure, 4 The insight gained in improving both gauge wear and ROP in the 12 l/4-in, sections of the Baram and Baronia fields was subsequently implemented in the 17 l/2-in, sections. Previous drilling rates in the 17 l/2-in, angle building section had been satisfactory, but the understanding acquired in the 12 l/4-in.…”