Geoelectric modelling with separation between electromagnetic and induced polarization field components

Geoelectric methods map resistivity and induced polarization in the subsurface. The differentially normalized electromagnetic method (DNME) detects geochemical alteration zones that give rise to anomalous responses. Such zones are commonly situated in sedimentary rocks some distance above hydrocarbon accumulations. Epigenetic mineral growth is stimulated by a change in pH of the pore fluid due to leakage of hydrocarbons from a non-perfect top seal. DNME uses particular geoelectric parameters derived from potential difference relaxation curves observed in the field. An electric depth model is established by 1D inversion with the Cole-Cole simulation procedure. Synthetic modelling shows that separation of the electromagnetic and induced polarization components of the total measured electric field is possible. Simulated field responses at the recording station are compared with those from two known 3D depth models. The discrepancy or misfit is less than 0.2%. The effectiveness of the workflow is demonstrated on the Severo-Guljajevskaya case study in the Barents Sea. The DNME evaluation technique reduces risks attached to drilling new hydrocarbon prospects and provides a better ranking at reasonable cost.