A new 2D Forward Modeling Algorithm of Marine CSEM Data in Anisotropic Media

Abstract:

The marine Controlled Source Electromagnetic Method (CSEM) has been widely used to study the electrical conductivity distribution in the oceanic crust and the upper mantle. In recent years, the incorporation of the electrical vertical anisotropy in CSEM modeling permits the detection of very thin and shallow layers that are easily correlatable with seismic horizons and, therefore, an increasing application to hydrocarbon exploration. Nowadays, most of the marine electromagnetic surveys are made and interpreted in 3D; however, it is not uncommon to collect profile data, which are rarely modeled with 2D forward modeling algorithms that include electrical anisotropy.

We developed a 2D numerical modeling algorithm for marine CSEM data that takes electrical anisotropy into account and offers a better representation of finely layered geological units such as shale and interbedded hydrocarbon reservoirs. We solved the governing Maxwell equations that include vertical transverse anisotropy (TIV) using a finite difference (FD) scheme in the frequency domain. Our algorithm considers the field generated by a full three-dimensional Horizontal Electrical Dipolar (HED) source within a two-dimensional model with constant conductivity along the strike direction. We reduced the effective dimensionality by Fourier transforming the primary field in the strike direction and by solving for the secondary field using our 2D FD scheme in this domain.

We tested our algorithm on various homogeneous, stratified, and 2D heterogeneous models and gauged our solutions in terms of resolution for different processing parameters as compared with alternative 1D, 2D, or 3D forward modeling codes available.