Step Change in Performance: Upgraded Bit Technology Improves Drilling Economics

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 103074, "Step Change in Performance: Upgraded Bit Technology Significantly Improves Drilling Economics in GOM Motor Applications," by B. Grimes, SPE, and B. Kirkpatrick, Hughes Christensen, prepared for the 2006 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, 24–27 September. Operators in the Gulf of Mexico (GOM) are constantly looking for ways to reduce the costs of drilling development wells. A new steel-tooth (ST) roller-cone bit with an advanced metal-seal bearing has achieved this goal and is having a significant effect on drilling economics. Improvements in bearing life, seal reliability, and cutting-structure durability have resulted in more time on bottom, giving the operator the confidence to use the new roller-cone bits in long directional hole sections. Introduction With large regions of the GOM rapidly becoming mature provinces, operators are looking for ways to reduce the costs of drilling development wells. Most of the wells drilled are directional, and heavy water-based drilling fluids often are required in the intermediate hole sections. Relatively high bottomhole temperatures combine with high bottomhole pressures and balling shales to present a challenging drilling environment. Operators strive to increase rate of penetration (ROP), maximize hours on bottom for each bit, reduce risk, and complete the section with fewer bits to reduce the number of trips. Improved roller-cone bits with an innovative single-energizer metal-seal (SEMS) bearing were introduced in 1998 (Fig. 1). A step change in bit life was realized, yet it took a year or two for operators in the GOM to gain sufficient confidence in the new ST bits to run them harder and leave them in the hole longer. By 2000, operators routinely were achieving runs as much as twice as long as was typical with the predecessor elastomer-sealed ST bits, particularly at higher rotary speeds (e.g., 175 to 275 rev/min). In 2000, enhanced ST cutting structures were introduced to complement the SEMS bearing (Fig. 2). The new ST cutting structure provided longer tooth life by improved tooth wear resistance and reduced tooth breakage. GOM Drilling Environment The GOM drilling environment is one of the most diverse in the world. With exploration and development programs taking wells to ever greater depths, the demands placed on ST roller-cone bits and their sealed-bearing systems become increasingly severe. The increased service life and reliability of rotary-steerable systems and top-of-the-line motor assemblies allow them to successfully drill long, complex well paths, which increases the directional challenges for roller-cone bits. Both concentric and eccentric hole-opening technologies place unique loading conditions on roller-cone bits when they are used as pilot bits.