Wave field simulation and analysis with FEM for acoustic LWD in horizontal and deviated wells

Abstract

We developed a finite element method (FEM) in conjunction with a Complex-Frequency-Shifted Perfectly Matched Layer (CFS-PML) boundary to effectively study the wave field radiated by acoustic multi-pole LWD tool in horizontal and highly deviated wells surrounded by slow formations. We found that under the condition of tool eccentricity in these wells, some non-monopole modes would appear in monopole measurements and Stoneley (St.) mode would appear in dipole measurements; the flexural collar wave would appear and become increasingly stronger with the increase of tool eccentricity; and there would be St. mode as the later arrival event, especially in the case of severely eccentric quadrupole tool. Based on these studies, we introduce a method to quantify the degree and the angle of the tool eccentricity with the phase difference in the eccentric dipole measurements. These parameters are very useful for geo-steering.