Results From Systematic Rotary-Steerable Testing With PDC Drill-Bits Depict the Optimal Balance Between Stability, Steerability, and Borehole Quality

Abstract

Abstract There is significant discussion concerning what type of Rotary Steerable System (RSS) provides the best-quality hole, and which key characteristics of the drill bit, along with a particular RSS, will produce the optimal balance between stability and steerability in directional wells. Although some evidence can be drawn from field performance with various tools and customized drill bits, these results can often be inconclusive due to the large variance in factors involved with commercial drilling. This paper describes an extensive series of test wells drilled in a controlled and non-commercial environment, allowing single step changes in both the drill bit features and Rotary Steerable (RS) configurations. The testing is unique in that the specific RSS works in shop-configurable point-the-bit and push-the-bit modes. Between two distinct RSS operation modes, consistency in stiffness, weight, force applying capability, and control systems lead to a direct comparison of bit performance. A unique sensor system, integrated into the specific RSS, provided real-time measurement of near-bit borehole caliper and near-bit stick-slip and vibration. This feature allowed real-time evaluation of bit and BHA stability and borehole quality. After each test run, memory data was retrieved and used for more detailed assessment of bit performance. Drill bit tests were systematically structured in a controlled environment so that the relationship between gauge geometry and configuration could be examined without alteration of the cutting structure. As a result, comparison between stability, dogleg capability, torque and drag, and borehole quality was solely dependent upon gauge length and geometry. Further, the systematic testing led to the conclusion that a specific gauge design related to effective side cutting and gauge stabilization is crucial for optimized RS drilling in both point-the-bit and push-the-bit configurations. Introduction In the 90's, the introduction of the first commercial RSS revolutionized directional drilling 1. Since then, RSS technology has made remarkable improvements in reliability and has become a standard drilling tool. Today, point-the-bit and push-the-bit RSS are utilized on both directional and vertical wells worldwide. Their use is not only limited to high-cost offshore markets but is now becoming more common in lower cost land markets. The advancement of RS drilling technology goes hand in hand with the use of polycrystalline diamond compact (PDC) bits. Continual development of advanced modeling software and cutters with significantly increased abrasion resistance have led to PDC designs that can drill faster, further and with a high degree of stability. These benefits, combined with the appropriate RSS, can also deliver superior directional control, improved borehole quality, higher-quality logging and easier casing runs. This resultant improvement in economics is particularly attractive in high-cost offshore wells.