We developed a numerical method for accurate simulation of triaxial induction measurements in the presence of borehole-eccentered logging instruments. This 3D simulation method combines a Fourier series expansion in a new system of coordinates with a 2D, goal-oriented, high-order, and self-adaptive hp finite-element refinement strategy. The resulting numerical scheme provides accurate and reliable simulations of triaxial induction measurements while reducing the computational complexity of conventional 3D problems. We employed this method to quantify effects of borehole-eccentered triaxial tools fabricated with conductive and resistive mandrels. Numerical experiments indicate that a conductive mandrel can mitigate borehole-eccentered effects on horizontal magnetic field measurements to a level below 25%, which contrast those observed in the presence of resistive mandrels, in which measurements can differ by more than 100% depending solely upon the borehole-eccentered distance. When the mandrel and borehole were conductive, measurements experienced significant (up to 100%) tool-eccentered effects across layers whose electrical conductivity was different from that of the borehole.