Project Title

Imaging the Earth Interior using Virtual Seismic Electrodes

PI

Paul Sava

Email

psava@mines.edu

Department

Geophysics

Project summary

Surface geophysics provides information about subsurface physical

properties and their distribution. Geophysical observations depend on

the interaction of a man-made perturbation with the heterogeneous

subsurface. A seismic wave propagating through a porous rock generates

electromagnetic signals that depend on the fluid saturation in rock

pores (oil, water, etc), and that can be observed remotely. This

seismoelectric effect allows us to determine fluid saturation and rock

permeability, which cannot be observed with seismic waves

alone. However, seismoelectric exploration is difficult because the

observed signals are weak, and because seismoelectric conversions are

distributed in the medium to places where seismic waves interact with

solid/fluid contacts. Therefore, we cannot associate an observed

change in electric potential with a specific seismoelectric conversion

in the subsurface. The goal is to observe this effect for a strong

seismic wave localized at a point in space, at a given moment in

time. This would allow us to scan the subsurface and make direct

measurements of the fluid content, which would have a huge impact on

oil and gas exploration, and on groundwater management.

Our solution to the localization problem is to use multiple sources of

seismic energy synchronized in space and time in order to focus the

seismic waves at a target point. Focusing not only reduces the

ambiguity of the seismoelectric conversion origin, but also insures

strong conversions since all the energy induced into the medium

concentrates at a single point, instead of being distributed

throughout the medium. The localized electric source produced by

seismic focusing acts as a virtual electrode with an arbitrary but

known position and trigger time.

Commercial software

N/A

Open Source software

All codes come from the Madagascar software package.

Our CSM group is among the top developers of this open-source package.