Roller reamers improve drilling performance in wells limited by bit and bottomhole assembly vibrations
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Stick-slip and whirl are vibrational problems that commonly limit drilling performance in hard formations and extended reach wells. The introduction of roller reamers has resulted in significant performance improvement in a number of the operator's drill teams with chronic stick-slip or whirl-induced borehole features. Whirl is a dysfunction characterized by lateral vibration that may occur both at the bit and in the bottomhole assembly (BHA). When whirl becomes severe, lateral vibrations cause significant side forces in stabilizers. Frictional drag resulting from these side forces causes high levels of torque to be generated at stabilizers and can result in stick-slip (a condition characterized by fluctuations in the rotational speed of the BHA). The operator refers to this as "coupled stick-slip" because the condition is caused by whirl in stabilizers. When these conditions exist, the replacement of stabilizers with roller reamers significantly reduces the potential for torque-generation at the contact points. Consequently, more torque becomes available to the bit and the driller may raise weight on bit (WOB). This results in reduced levels of bit whirl and improved rate of penetration (ROP). The reduction of bit whirl and elimination of stick-slip prevent damage to bit and BHA components. Roller reamers are also seen to serve the historical purpose of conditioning the borehole. The operator's field experience indicates that the need for conditioning is often due to whirl-induced features in the borehole. These features include spiraling and ledges. The use of roller reamers greatly reduces the prevalence and impact of whirl features. This paper details the conditions where roller reamers provide benefits allowing improved performance. A conceptual model for coupled stick-slip is provided as well as a summary of whirl-induced borehole features which may be mitigated with roller reamers. Representative examples are provided that show drilling performance improvements using roller reamers to mitigate these conditions. Copyright 2009, SPE/IADC Drilling Conference and Exhibition.
