High-frequency torsional oscillation (HFTO) is recognised as one of the more damaging drilling dysfunctional mechanisms. The HFTO can cause significant tool damage in addition to nonproductive time (NPT). This vibration has been shown to be more prolific in motor powered steering assembles where it is thought that the long stick-out resonates torsionally with the energy coming into the system at the bit and a reflection of torsional energy at the motor. Using data derived from a next-generation measurement-while-drilling (MWD) tool, which includes high-speed vibration and internal pressure measurements, we will show that these dynamics are more complex than generally visualized. HFTO is in fact three different families of vibration. The conventional HFTO, where the stickout below the motor is resonating, is considered to be Type 1. In the Type 2 group, energy is trapped in the lower bottomhole assembly (BHA). Typically, this vibration has a higher frequency, than the Type 1, and is independent of the tools in the upper BHA. The characteristics of this are determined by the contact points; thus, it is dominant in the curved section or where heterogeneities trigger microdoglegs. Finally, we will show that HFTO can develop when there is a steerable motor in the BHA, the Type 3 group. The torsional waves from the bit couple through the motor causing pressure perturbations; hence instabilities in the weight on bit. This new understanding of HFTO explains some of the anomalies in the performance of different mitigation strategies for HFTO. In particular, why HFTO is much more prominent in heterogeneous formations and while drilling a curved section.

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.

It is common to have measured depth exceeding 20,000 ft for unconventional oil and gas wells. To ensure the pressure pulse can be detected on the surface, many MWD tools have been designed to generate mud pressure pulse with very large amplitude. While the large pressure pulse solved the problem of sending the measured information up to the surface, it creates significant impact on drilling system energy variation and downhole drilling dynamics. This paper focuses on understanding the effects using big data and drilling system modeling. When a commonly used MWD tool generates mud pulse sequence, it chokes the flow path at designed patterns. This creates mud flow variation in the mud motor below the MWD tool. It also generates axial force variations due to pressure changes, which affect WOB. These changes cause the motor and the bit to experience significant rpm variations. The combined rpm variation and WOB variation often excite more severe axial and lateral shock and vibration. These effects are quantified by thousands of high-frequency downhole datasets and advanced numerical modeling. In the high-frequency downhole datasets, some of them are obtained from BHAs with MWD tools generating large mud pressure pulse, and some of them are obtained from BHAs with MWD tools generating smaller mud pressure pulse or transmitting the measurements using electromagnetic signal. Statistics of rpm variation and axial and lateral shock and vibrations are compared. It clearly shows that the BHAs utilizing large mud pressure pulse experience more severe torsional, axial, and lateral vibrations. When looking into specific datasets, it showed that mud pressure pulse could cause the motor to lose more than half of its rpm during the flow choking phase. Typical datasets indicate that mud pressure pulse correlates to severe high-frequency torsional oscillation (HFTO) in motorized rotary steerable BHA. An advanced transient drilling dynamics model was built to simulate the whole drilling system subjecting to mud pressure pulse incurred loading conditions. It was found that large-magnitude mud pressure pulse induced more stick/slip and axial and lateral vibrations as recorded in downhole high-frequency data. The increased rotational, axial, and lateral vibrations correspond to more loading variations in the mud motor components and PDC cutters on the drill bit. These variations could cause accelerated damage to the drill bit and downhole tools. In summary, large mud pressure pulse utilized by some MWD tools introduces significant rpm variation and shock and vibration, which is quantified by big data and further demonstrated by drilling system modeling. The information could help make decisions on BHA design and tool selection to achieve improved drilling performance and reduce the risk of premature tool failure.