Continuous Borehole-Curvature Estimates Based on Downhole Bending-Moment Measurements

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 90794, "Continuous Borehole-Curvature Estimates While Drilling Based on Downhole Bending-Moment Measurements," by G. Heisig, SPE, Baker Hughes Inteq; G. Cavallaro, Eni SpA Div. E&P; and P. Jogi, SPE, J. Hood, SPE, and I. Forstner, SPE, Baker Hughes Inteq, prepared for the 2004 SPE Annual Technical Conference and Exhibition, Houston, 26-29 September. A downhole bending-moment measurement combined with a simple mathematical model can provide a good estimate of well-bore curvature, matching results obtained from survey-data analysis well. The bending-moment measurement delivers well-bore-curvature information at a much higher resolution than the standard minimum-curvature method that assumes a constant curvature between survey stations. Introduction Any drilling bottomhole assembly (BHA) in a directional wellbore is subjected to bending moments caused by side forces acting on the BHA. These side forces may be caused by gravity, by dynamic effects, or by wall contacts of the BHA in curved wellbore sections. Mathematical models have been developed to predict the side forces, bending moments, and stresses that are introduced into a BHA by a given borehole-curvature profile, usually derived from measured survey data. The full-length paper discusses application of mathematical models to predict the borehole curvature from measured bending-moment data. The bending-moment data were acquired with a recently introduced drilling-dynamics tool in a variety of different applications and tool configurations including rotary-steerable systems (RSSs) and steerable-motor BHAs. The bending-moment data can be both transmitted to the surface while drilling and recorded in on-board memory for post-run processing and detailed analysis.