Experimental Design for Surface-to-Borehole Hydrocarbon Applications

We discuss in a simplified surface-to-borehole example the resolution of the coefficient of anisotropy A for an anisotropic layer sandwiched in an isotropic half-space as a function of transmitter-receiver configuration and magnetic field components. Our analysis supposes that the horizontal resistivity of the anisotropic bed has been established by previous logging, and that only horizontal magnetic fields will be used to determine the vertical resistivity. The resolution analysis shows that for the model studied the coefficient of anisotropy λ can be resolved within 10% for a broad range of transmitter-receiver configurations if ∂Bz/∂t and ∂By/∂t are used jointly in the interpretation. Using only ∂Bx/∂t or ∂By/∂t individually, A can only be resolved for a limited range of transmitter-receiver configurations. A joint interpretation of both horizontal magnetic field components facilitates a better resolution of the coefficient of anisotropy compared to a single interpretation.