Addressing BHA Whirl: The Culprit in Mobile Bay

Abstract

Summary Lateral bottomhole assembly (BHA) vibration, more particularly BHA whirl, is known to be an extremely destructive downhole phenomenon, the occurrence of which is thought to be one of the primary contributing factors to drillstring failure in Mobile Bay. Unfortunately, indications that BHA whirl is occurring while drilling are rarely evident from conventional surface measurements, especially in deeper sections of wells. Without knowledge of the existence of a problem, avoidance is almost impossible. For the first time, the potential for the surface identification of BHA whirl is thought to be possible through the measurement of drillstring vibrations. We present data from a well in Mobile Bay where surface vibration measurement and monitoring was conducted while drilling the 12¼-in. hole section. Axial and torsional data demonstrate characteristics thought to be indicative of BHA whirl, which is shown to be associated with accelerated drillstring fatigue, as demonstrated by BHA failures. Various approaches were taken to eliminate the whirl once the phenomenon was recognized, with ultimate success in that the incidence of BHA failure was reduced. Prewell planning and improved drilling practices resulted in the use of fewer bits and reduced drilling time over the same section on wells previously drilled in the area.