Influence of borehole-eccentred tools on wireline and logging-while-drilling sonic logging measurements

Abstract

We describe a numerical study to quantify the influence of tool-eccentricity on wireline and logging-while-drilling (LWD) sonic logging measurements. Simulations are performed with a hp-adaptive Fourier Finite-Element method that delivers highly-accurate solutions of linear elasto-acoustic problems in the frequency domain. Analysis of the main propagation modes obtained from dispersion curves indicates that, for both types of logging instruments, additional high-order modes appear with increasing distance between the center of the tool and the borehole center. These new propagating modes may slightly interfere with the main modes, such as the Stoneley mode, which otherwise remain nearly insensitive to tool eccentricity.