Exploration of the Interaction Between Drill Bit Gauge Profile and Point-The-Bit Rotary Steerable Systems

Abstract

Abstract This paper describes an investigation of bit passive gauge profiles for a latest generation point-the-bit Rotary Steerable System (RSS) shown in Figure 1. Using theoretical analyses, a methodology has been developed for exploiting lateral stability afforded by extended passive gauge, without limiting steerability or creating stick-slip or high torque. Results of laboratory testing and field studies are presented, showing a step-change improvement in drilling performance and efficiency. Full scale laboratory testing and field studies explore the impact of extended passive gauge in maintaining lateral stability. Results show that typically much longer passive gauge length than is common can be applied without adversely affecting steerability or stick-slip. These practical results are fully explained by theoretical analyses that predict critical gauge lengths. The optimum gauge profile is shown to be dependent on hole size and formation type. For some time; short gauge drill bits have been the fashion, dominating the industry. More recently the importance of extended passive gauge to lateral bit stability has been recognised, but concerns over steerability and torque generation has limited adoption. These misconceptions are likely a consequence of early point-the-bit RSS testing in which incremental increases in gauge length unwittingly produced assemblies close to the critical length/diameter ratio for ‘cock and lock’. Until now, solutions applied have either reduced gauge length or tapered the gauge at the steering system tilt angle -solving the problem at the expense of much of the lateral stability, leaving the drilling assembly vulnerable to undesirable dynamic conditions.