Drillpipe-Dynamics Measurements - Insight Into Drillstring Dysfunctions

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 145910, ’Drillpipe-Dynamics Measurements Provide Valuable Insight Into Drillstring Dysfunctions,’ by Constantijn Raap, SPE, Andrew D. Craig, SPE, and Ryan Graham, SPE, NOV, prepared for the 2011 SPE Annual Technical Conference and Exhibition, Denver, 30 October-2 November. The paper has not been peer reviewed. The drilling industry has become increasingly interested in drilling dynamics and in vibration as a cause of reduced drilling performance and downhole-tool and drillstring failures. Vibration data have been captured with measurement-while-drilling (MWD) tools in the lower bottomhole assembly (BHA). However, this approach is not always sufficient to understand the drillstring dynamics of more-complex applications. High-frequency vibration data were recorded at several strategic points within the drillstring by use of downhole dynamics recorders (DDRs). These data provided new insights into the dynamic behavior of drillstrings in high-angle wells. Introduction Drillstring vibration is a limiting factor when drilling horizontal and extended-reach wells. While rotating, long sections of drillstring are positioned on the low side of the hole. If sufficient friction exists in the wellbore while being rotated at constant speed from surface, the string will decelerate angularly, followed by a rapid increase in rotational speed. This torsional vibration, often referred to as stick/slip, generally increases with a combination of lower rotary speeds and higher surface weights. Typical consequences of torsional vibration may include overtorqued connections, torsional fatigue, and high wear of downhole-tool components, and it has been identified as the leading cause of damage to polycrystalline-diamond-compact bits. Rotating the string faster than a system specific threshold or at increased compressive load causes the string to move up and down the wellbore. This snaking motion is characterized by movement in the lateral plane, which causes lateral shocks each time the BHA or pipe contacts the wellbore. Field experience indicates that higher rotary speeds generally lead to increased levels of lateral vibration. Severe lateral vibration, such as whirl, can have detrimental consequences, such as downhole-tool failure, impact damage to drill bits, and drillstring twistoffs. Both torsional and lateral vibration lead to reduced penetration rates and numerous unwanted BHA or bit trips. Another limiting factor encountered when drilling high-angle wells is the torque required to rotate the drillstring. High drillstring torque can limit the well stepout if the maximum available top-drive- or drillpipe-torque limit is exceed-ed. It is common that both high torque and vibration occur simultaneously.