Lateral bottomhole assembly (BHA) vibration, more particularly BHA whirl, i
s known to be an extremely destructive downhole phenomenon, the occurrence
of which is thought to be one of the primary contributing factors to drills
tring failure in Mobile Bay. Unfortunately, indications that BHA whirl is o
ccurring while drilling are rarely evident from conventional surface measur
ements, especially in deeper sections of wells. Without knowledge of the ex
istence of a problem, avoidance is almost impossible.
For the first time, the potential for the surface identification of BHA whi
rl is thought to be possible through the measurement of drillstring vibrati
ons. We present data from a well in Mobile Bay where surface vibration meas
urement and monitoring was conducted while drilling the 121/4-in. hole sect
ion.
Axial and torsional data demonstrate characteristics thought to be indicati
ve of BHA whirl, which is shown to be associated with accelerated drillstri
ng fatigue, as demonstrated by BHA failures. Various approaches were taken
to eliminate the whirl once the phenomenon was recognized, with ultimate su
ccess in that the incidence of BHA failure was reduced. Prewell planning an
d improved drilling practices resulted in the use of fewer bits and reduced
drilling time over the same section on wells previously drilled in the are
a.