Setting a New Standard: PDC Bits Equipped with Compact Vibration Recorders Monitor Entire Run and Reveal Stick-Slip Mitigation System Dysfunction and Downhole Motor Under Performance

Abstract

Downhole vibration measurements are used real-time and post-run to monitor drilling dynamics. Real-time monitoring tools are applied to facilitate immediate corrective actions but their deployment adds operational constraints and costs. This paper describes a new high-capability vibration recorder embedded in the drill bit as a standard component. The analysis of two case studies in the Middle East shows how memory devices available at a reduced cost and on every run are a valuable option for many appraisal or development wells. Developing a fleet of reliable downhole recording tools typically takes years and involves teams of experts in various fields. The paper describes the strategy followed by a drill bit manufacturer to develop and deploy a compact, high capability and cost-effective vibration recorder to provide continuous readings of accelerations, rotation speed (RPM) and temperature at 100Hz and over 250 hours. Sensors and batteries have been packaged to fit into the drill bit shank or elsewhere in the bottom hole assembly (BHA). The recording starts automatically and thus removes the need for onsite personnel. The paper also presents proprietary data analytics software used to retrieve, process and synchronize the recorded data with other available data (mud logs, Measurement/Logging While Drilling logs) and to present critical drilling events. In the first application, the 8 ½-in. bit drilled a 20,000 ft horizontal drain. More than 250 hr of data were recorded showing intense levels of stick-slip. During the entire run, the drilling team deployed several strategies to mitigate stick-slip, including the use of two surface-based stick-slip mitigation systems. The analysis shows that these systems are sometimes unsuccessful in mitigating stick-slip and are difficult to calibrate. It is demonstrated how the vibration recorder may contribute to fine tuning these mitigation efforts through optimization of their settings. In the second application, the vibration recorder was mounted on a 12 1/4-in. bit used to drill 5,000 ft through cement and formation. The analysis shows the motor was subjected to erratic RPM cycles, leading to frequent stalls and acceleration peaks during the run. It is shown how motor performance then decreased consistently during the last hundreds of feet of the section and how this affected rate of penetration (ROP). Deployment of a vibration recorder over the entire drill bit manufacturer's fleet allows continuous monitoring of critical drilling issues and malfunctions related to a variety of drilling equipment that enables the operator to improve drilling performance. The bit-sensor package makes high frequency data systematically available at a reduced cost for every drilling application.