2.5D Resistivity Inversion in Anisotropic Media: Numerical Experiments

Abstract

We present a set of 2.5D synthetic inversion experiments for a model comprising an isotropic block embedded within an anisotropic background. We examine and compare the image reconstructions obtained using the correct anisotropic code and those obtained using code based on the inappropriate but widely adopted isotropic assumption. Superior reconstruction in terms of reduced data misfit, true anomaly shape and position, and anisotropic background parameters were obtained when the correct anisotropic code was employed for media characterized by moderate to high coefficients of anisotropy. However, for low coefficient values, the isotropic inversion produced slightly better results because there are fewer parameters to determine. When an erroneous isotropic inversion is performed on medium to high level anisotropic data, the images are dominated by patterns of banded artefacts and high data misfits. TheoryIn its most general form, electrical anisotropy is described by a symmetric, second rank conductivity tensor with 6 independent components . In this paper we consider a more specific but prevalent class of anisotropy, that of a 2D tilted transversely isotropic (TTI) medium involving just 3 independent components of the tensor. In a TTI model (Figure 1) resistivity is constant for all directions within a specified plane, termed the plane of isotropy (e.g., plane of stratification or foliation) but different in all other directions outside that plane. SAGEEP 2014 111Downloaded 09/29/15 to 128.111.121.42. Redistribution subject to SEG license or copyright; see Terms of Use at http://library.seg.org/