Component Analysis of Electromagnetic Wave Propagation in a Layered Model for CSEM Hydrocarbon Surveying

Controlled source electromagnetic (CSEM) refers to a technique to investigate and explore possible geophysical resistive anomalies surrounded by conductive layers. This method employs an extra low frequency electromagnetic (EM) shooting and, as a result, recorded signal interpretations determine a resistivity contrast image of the strata. Therefore, CSEM is a strongly efficient technique to explore deep-water marine hydrocarbon reservoirs. However, the shallow-water unsolved limitations of EM exploration methods still exist. The main complexity of shallow-water exploration is due to airwave. Airwave is produced by the upward propagated EM signal, inside the seawater. The up-going wave travels at the interface of seawater and air, due to their large contrast of the resistivity. The airwave is then transmitted back to the seawater and will be detected by the array of receivers. In shallow-waters, air wave is the most significant recorded signal. Thus, it can mask the wanted data (called guided wave) which is due to presence of a resistive anomaly. Studying EM propagation in a layered model helps to have a clearer understanding of the physics of CSEM. Therefore, here we present a finite element based result-driven model to investigate two main EM polarized waves (i.e. transverse electric (TE) and transverse magnetic (TM) modes) in a plane layered model, consist of air, seawater, overburden, hydrocarbon and under-burden layers. TE mode refers to a polarization that electric field is perpendicular to the propagation's direction and in TM mode magnetic field is perpendicular to the direction of propagation. For a tangible comparison between TM and TE modes, a shallow-water model is assumed. The results illustrate that airwave contributes in TE mode, whereas it is quite absent in TM mode. However, the contribution of TM mode is due to presence of the thin hydrocarbon layer, as a resistive anomaly. EM component analysis and propagation behaviour study improve the interpretation techniques of CSEM hydrocarbon surveying. © 2022, Institute of Technology PETRONAS Sdn Bhd.