Numerical Modeling of Seismoelectric Fields through Thin-Beds

Abstract:

The seismoelectric effect might help improving our knowledge of the subsurface. This complex physical phenomenon can be described by Biot’s poroelasticity equations coupled to Maxwell’s electromagnetic equations. Besides simultaneously offering seismic resolution and electromagnetic sensitivity, the coefficient coupling these two types of fields can in principal provide us with direct information on important medium parameters like porosity and permeability.

Two types of seismoelectric coupling can be distinguished:

1) localized coupling generating an electromagnetic field that is present inside the seismic wave and travels with its velocity, referred to as the coseismic field

2) An independent electromagnetic field diffusing with electromagnetic velocity, referred to as the seismoelectric conversion, providing us with information at depth.

One of the major challenges of seismoelectrics is the very weak signal-to-noise ratio of especially the seismoelectric conversion. In order to make seismoelectrics applicable in the field, we need to find ways to improve the signal-to-noise ratio of this second order effect. Can nature help us? It is well-known that a seismic wave travelling through a package of thin-beds, can experience amplitude-tuning effects that result in anomalously high amplitudes for the seismic signal. Can similar enhancing signal effects occur for seismoelectric phenomena?

Using our analytically based, numerical modeling code ESSEMOD (ElectroSeismic and Seismoelectric Modeling), we investigate what effects thin-beds can have on the seismoelectric signal, thereby focusing especially on the seismoelectric conversion. We will highlight the factors that play a role in the possible enhancement of the seismoelectric signal-to-noise ratio by thin-beds. We show that the seismoelectric method is sensitive to changes in medium parameters on a spatial scale that is much smaller than the seismic resolution.

Acknowledgements: This research was funded as a Shell-FOM (Foundation for Fundamental Research on Matter) project within the research program ’Innovative physics for oil and gas’.