The trading of technologies is nothing new for the upstream oil and gas and medical communities. The connection makes sense, particularly since both disciplines rely heavily on applied math for diagnoses. It should come as no surprise, then, that a popular paper at the 2021 Virtual SPE/IADC International Drilling Conference proposed a medically inspired approach to prevent catastrophic drilling system failures brought on by downhole shocks (SPE/IADC 204098). The paper describes a “drilling electrocardiogram” that diagnoses “arrhythmic drilling” similarly to how medical electrocardiograms diagnose dangerous vibration anomalies in heart patients.
The approach classifies shock wave-forms acquired at 31,250 hertz (Hz) downhole. The shock signals are treated as drilling electrocardiograms (D-ECG) that are processed using clustering algorithms and merged with drilling incidents to identify in real time an arrhythmic signature pattern that can lead to catastrophic failures.
Justo Matheus, senior control engineer for Schlumberger and lead author of the paper, said that in studying field incidents in which rotary steerable system (RSS) bottomhole assemblies (BHA) had been severely damaged by shocks, the signature patterns reminded him of ECGs (Fig. 1).
This led him to medical libraries, which in turn led to a revelation—that throughout the 3 decades that downhole vibration measurements while drilling (MWD) have been studied, only the analysis of the amplitude and root mean square (rms) values of shocks had been the focus. No one had considered frequency for diagnosing downhole shocks. It was this revelation that drove the concept of the D-ECG based on shock waveforms acquired at high frequency in real time to prevent failures of the BHA.
Drilling-generated shocks and vibrations affect rate of penetration, directional control, and wellbore quality, making them among the main causes of failures in drilling.
“Shocks are present almost all the time,” said Matheus. “The challenge is in knowing which are normal and which are not.”
RSS are equipped with measurement devices such as magnetometers, accelerometers, and shock and vibration sensors that obtain statistical information from which whirl, bit bounce, and stick/slip severity are inferred. Often, however, the derived statistics are not sufficient to distinguish between normal drilling vs. abnormal drilling for a location in the wellbore. Recent electronic advances enabled the development of high-resolution drilling dynamic data recorders, extending the sampling frequency from traditional 100 Hz to 1,600 Hz. However, most of these devices are for data recording only. There is no real-time communication with surface and no capability to inform about drilling conditions downhole.