Addressing BHA whirl: The culprit in Mobile Bay

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.