Changing Selection Concepts: True Optimization of Drill Bits with Latest Generation Rotary Steerable Systems

Abstract

Use of Rotary Steerable Systems (RSS) has steadily increased since their introduction in the mid-1990's. Improvements in durability, reliability, and operator familiarity, have moved these systems further into mainstream drilling use around the globe. However, the large majority of footage drilled with RSS is with side force (Push) tools. These tend to require some degree of sidecutting, thus utilize drill bits that have specifically engineered cutting structure, profile, and gauge design to achieve this. Due to common availability of this type of bit design, plus extensive experience with operators, they are often also utilized on the growing number of Point RSS. Due to the significant difference in operating mechanism, these bit designs can be poorly suited, resulting in sub-optimal drilling performance. This paper describes a joint engineering approach in developing specific drill bits for the latest generation of RSS that utilizes point-the-bit technology. The project has included systematic testing at a purpose-built, full-size drilling test facility. This has enabled a direct comparison of the directional response, hole quality, and drill string vibration to be made for the various combinations of drill bit and RSS configurations tested. The testing and subsequent field performance has led to development of specified characteristics of the drill bit for optimal performance. To ensure consistent and accurate matching of the bit to this specific RSS, an interactive, intranet tool was developed. This software incorporates logic regarding tool operation and assesses these against key characteristics of the bit including length, profile, gauge geometry, cutting structure, and sidecutting capability. This allows the ideal design to be rapidly identified, particularly as some characteristics are not visible within the visual geometry of the bit. Several case studies are documented that clearly demonstrate that the correct matching of drill bits to this specific Point RSS has delivered improved drilling efficiency with excellent directional control. Introduction The paper focuses on the development and testing of one of the latest generation point-the-bit RSS. The tool comprises three main elements; downhole electronic control module, mechanical bias unit and pivot stabilizer (Figure 1). The bias unit is a hydraulic/mechanical mechanism that develops power from differential rotation between the rotating drill-string and a nonrotating steering sleeve. This hydraulic power is used to deflect the drill-string (eccentrically to the borehole) in the required direction for steering. The system employs a pivot (fulcrum) stabilizer such that the driveshaft is deflected in the opposite direction to required hole deviation (Figure 2). Sprung anti-rotation guides prevent the steering sleeve from rotating, but if the sleeve begins to roll, the system automatically redirects hydraulics to maintain desired orientation. The electronic control module applies algorithms to provide closed loop control of the position of the bias unit, giving tight toolface control and proportional deflection control; enabling fine adjustment of wellbore deviation rates.

The Successful Evolution of an LWD Rotary Steerable System for Air Drilling

“…Computer-based engineering models and further full scale laboratory drilling tests resulted in refinement of BHA configurations to deliver improved dogleg capability and more predictable directional performance (Stroud, Peach & Johnston, 2004). Several further reviews of both experimental lab and field data concluded that lateral bit stability is a dominant factor in the performance of this point-the-bit RSS (Barton, Pierce & Stroud, 2009). Detailed bit selection criteria have been defined for successful deployment of the system.…”

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

“…In addition, Barton et al (2009) published results from full-scale drilling simulation testing and field testing of a point-the-bit Rotary Steerable System, providing compelling evidence that:…”