2.5D FD modeling of EM directional propagation tools in high‐angle and horizontal wells

Abstract

We developed a 2.5D finite‐difference (FD) code for modeling EM tool responses for 2D formation conductivity distributions and 3D well trajectories. The code is primarily developed for well placement and for 3D formation evaluation applications to interpret responses of the new generation LWD deep directional EM tools and tensor induction tools in high angle and horizontal (HA/HZ) wells. Frequency‐domain Maxwell equations are solved using electric field formulation. The problem is discretized using a combination of staggered uniform FD grids in the tool region based on skin depth and tool orientation, optimal grids outside the tool region in the x‐z plane, and a spatial Fourier transform in the y‐direction using Zoltarov discretization. Material averaging is applied in conjunction with optimal grids, resulting in a small problem size, allowing use of a direct LUD solver. We present the directional tool responses in realistic 2D scenarios such as an unconformity structure with internal layering. In addition, we also model the coupling of faults and nearby boundaries and present how that affect the 1D real‐time inversion ignoring the fault.