3‐D electromagnetic anisotropy modeling using finite differences

Abstract

Electric anisotropy is considered an important property of hydrocarbon reservoirs. Its occurrence has great influence on estimation of formation water saturation and other properties derived from electromagnetic (EM) measurements. Conventional tools using coaxial coils often underestimate formation resistivity and thus overestimate water saturation. Multicomponent EM sensors provide the additional information needed for better resistivity‐based formation evaluation. We have developed a finite‐difference method to simulate multicomponent EM tools in a 3‐D anisotropic formation. The new method can model inhomogeneous media with arbitrary anisotropy. By using the coupled Maxwell’s equations, our method consumes about the same computational time to model an anisotropic formation as it would take to model an otherwise isotropic formation. We have verified the finite‐difference method using layered‐earth models that are typically encountered in hydrocarbon exploration and development. Our results show that the newly developed simulation algorithm produces accurate results for different borehole and formation conditions.