SEGJ Technical Conference

Analysis of negative apparent conductivity anomalies in loop-loop electromagnetic surveys: a 3D forward modeling approach

Abstract Under certain geological conditions, low induction number electromagnetic (LIN-EM) instruments are known to produce negative apparent electrical conductivity response. This is particularly the case when surveying over lateral heterogeneities in the ground. In this work we describe the use of a 3D integral equation forward modeling technique to analyze negative apparent electrical conductivity responses and the nature of the causative subsurface structures. We present numerical calculations of LIN-EM response across a synthetic block conductor immersed in a homogenous half space. As a result, negative apparent electrical conductivity responses were observed for the vertical magnetic dipole array directly over the conductor. However, the horizontal magnetic dipole response produced a central minima over the conductive block but remained positive throughout the profile.