Managing Drilling Vibrations Through BHA-Design Optimization

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper IPTC 13349, ’Managing Drilling Vibrations Through BHA Design Optimization,’ by J.R. Bailey, SPE, ExxonMobil Upstream Research Company, and S.M. Remmert, SPE, RasGas Company Ltd., originally prepared for the 2009 International Petroleum Technology Conference, Doha, Qatar, 7-9 December. Significant performance improvement has been achieved by managing drilling vibrations through bottomhole-assembly (BHA) redesign. This effort has resulted in increased footage per day and reduced tool damage. Previous literature has described improvements in operating practices to manage vibrations as a key component of this rate-of-penetration (ROP) management process. Dynamic modeling of the BHA has identified the key design changes leading to these improvements. The redesigned BHA has lower calculated vibration indices than the standard BHA. Introduction The appendix of a previous paper comprises a detailed mathematical description of the basics of a frequency-domain lateral-vibrations mode. The full-length paper illustrates the application of these methods to a new set of BHA-design problems in a joint study. The modeling process begins with an input panel that is populated with mechanical dimensions of the components of the BHA, usually up to the heavyweight drillpipe (HWDP), with approximately the same level of detail as a fishing diagram. It is important that the positions of the contact-point constraints be entered correctly and that the stiffness and inertial properties of the assembly be a proper representation of the subject BHA. Then, the desired operating parameters for drilling need to be provided, including the anticipated ranges of weight on bit (WOB) and rotation rate (rev/min). The linear modeling process considers a dynamic perturbation about the static state. The model uses two vibration modes to compare and contrast the response of each candidate BHA design: lateral bending and twirl. In the lateral-bending vibration mode, an identical reference bit-side-force input is applied to each design, and the magnitudes of the response at other locations along the BHA are compared. In the twirl mode, an identical mass eccentricity is applied to each model element to investigate the stability of the BHA to eccentric-mass and centrifugal-force effects. Simulation results are plotted for multiple BHA designs simultaneously in 2D or 3D displays of state vectors. Index values have been designed to summarize dynamic performance and are displayed for selected configurations to identify operating “sweet spots” immediately and to indicate which design configuration may be preferred. The indices include “BHA strain energy” and “transmitted strain energy” to represent the dynamic bending strain in the BHA and HWDP, the “stabilizer-side-force” index to quantify the dynamic wall-contact interaction forces, and the “endpoint-curvature” index to represent bending at the top of the model in response to excitation at the bit. A sensitivity analysis is completed in which multiple possible node locations are considered at the top end of the model, and the results are processed to identify average and “worst-case” conditions.