Drillstring Vibrations: Classic Ideas and Modern Approaches - Wave Propagation in Drilling, Well Logging and Reservoir Applications - page 188

indication of their presence seen at the surface. Their detailed MWD
measurements were made using a high resolution, high-data-rate wireline system
for a straight hole.
Other empirical evidence supports the foregoing observations. Vandiver,
Nicholson and Shyu (1989) likewise note that, unlike longitudinal and torsional
vibrations, those in bending are not transmitted to the surface by the drillstring.
They do suggest, optimistically, that it may be possible to see evidence of
downhole bending vibration from surface axial and torsional vibration signals;
however, the relationships are not yet understood well enough to be useful for
diagnostic purposes. The authors importantly observed from their case studies
that linear coupling of axial and bending vibrations of the bottomhole assembly
does occur, a physical mechanism developed in detail later in this chapter,
expanding on the early model of Chin (1988a,b).
Aldred and Sheppard (1992) summarized some industry-wide observations
and frustrations. They noted that once damaging transverse vibrations are
initiated, they will persist over a wide range of rotary speeds. That is, a
continuous range of dangerous frequencies exists, in contrast to simplistic
harmonic predictions that pinpoint a discrete set of modal resonant frequencies
(this is supported by our group velocity model derived later). These authors,
like others, further suggest that models based on the harmonic behavior of the
drillstring do not explain the observed response satisfactorily, possibly because
strong nonlinearities are at fault.
Interestingly, some early comments of Nicholson (1975), on the subject of
“critical rotary speeds” cautions that “critical” often implies a resonant vibration
condition - but that critical vibrations are not necessarily associated with
resonance (interestingly, our group velocity model for catastrophic breakdown
follows a mechanism other than classical resonance). But much confusion
exists. Nicholson also notes that resonance has been blamed for serious
drillpipe and hole damage, and yet, others intentionally drill “at resonance”
without success. Henneuse (1992), working from an extensive database of
results based on Elf Aquitaine' s surface vibrations monitor, agrees consistently
with Wolf, Zacksenhouse and Arian (1985) that lateral movements do not
propagate easily along the drillstring. Rewcastle and Burgess (1992) observe
that shocks due to high lateral vibrations contain the most energy, also noting
that significant mode coupling appears to be present. They conclude,
consistently with past field observations, that surface vibration measurements
are a poor indicator of the downhole environment. The destructive force behind
downhole lateral vibrations is well documented by real-time downhole
measurement. Burgess, McDaniel and Das (1987) specifically conclude that
transverse vibration is a source of downhole MWD tool failure; Cheatham and
Comeaux (1992), recognizing this industry problem, provide general guidelines
for predicting fatigue life of MWD tools.