Mitigation of Drilling Dysfunction: Data Analysis and Physical Modelling Shine a New Light on HFTO

Abstract

High frequency torsional oscillation (HFTO) is still one of the most disruptive drilling dysfunctions we encounter. Vibrations are observed with fundamental frequencies as high as 400 Hz and torque sweeps from 0 to 7000 lbf.ft. The resulting damage includes drilling collar cracking, damaged electronics, and backed-off tools. By measuring the amplitude and the fundamental frequency of this dysfunction, we present a model to characterize its drivers. This is a critical step in defining the mitigation strategies. Although there are a multitude of drilling dynamics tools deployed to record these effects, the nature of HFTO, with large amplitude harmonics on top of the fundamental modes, means that simply deploying a sensor and data acquisition tool is not sufficient to characterize the dysfunction. There are critical requirements for these recorders in terms of sampling frequency and anti-aliasing filters, without which a unique interpretation of the dynamics is impossible. We have a next-generation MWD tool that will detect HFTO. By calculating a fast fourier transform (FFT) in real time, it will also deliver a log of HFTO throughout the operation, that can be delivered to the driller in real time. With this we have developed and demonstrated a suite of mitigation strategies. These are specific to the type of HFTO detected and include increasing the collar speed or reducing the WOB (for Type 2) or reducing the rate at which the WOB is increased (for Type 1). We also show that by changing the contact points on the tool to reduce the side force (friction), the operator can mitigate the Type 2 HFTO and achieve a considerable improvement on this drilling dysfunction and its impact.