Hard Formation Durability Gains 14% Footage and Replaces 2.7 Bits Versus Offsets

Abstract

A specially designed diamond impregnated bit set new performance records in its initial application in a hard, abrasive Oman formation. Built for turbine drilling in the formation's sandstone-siltstones-shale, the 212.72-mm (8 3/8-in) bit drilled 588 m (1929 ft) in a single run, increasing footage drilled by 14% compared to the previous-best 8 3/8-in. run with a ROP of 2.02 m/hr (6.6 ft/hr). This performance replaced 2.7 bits through increased footage drilled and drill out capabilities. When the bit was pulled due to the BHA it was dull-graded: 3-2-WT-A-X-1-LM-BHA. The bit developed for the Oman run was a matrix body with 16 blades. Maximum durability and performance in the high-compressive strength formation was addressed with diamond-impregnated blocks on each blade and thermo/abrasion resistant PDC cutters in the bit center. Extreme drilling conditions presented by the turbine application and formation led to an optimized impregnated segment block geometry to maximize bit durability without impacting efficiency, and a change in hydraulics to maximize cooling and cleaning of the cutting faces. This paper is the first published examination of the diamond impregnated bit design process and resulting field experience in the Oman application. The study discusses the basis of the bit design and considerations in achieving operator objectives, including drilling as much footage as possible from 4190 m (13,743 ft) measured depth, while maintaining an average ROP of 2 to 2.5 m/hr (6.5 to 8.2 ft/hr). The authors examine the role of modeling and design software in optimizing durability and penetration rate in the hard formation, and they review enabling manufacturing and material advances.