Geoscience Reference
In-Depth Information
CHAPTER 5
Electrical disturbances associated
with seismic sources
In this chapter, we describe the electromagnetic distur-
bances directly associated with a seismic source. We first
consider such a source in a water-saturated poroelastic
material characterized by a moment tensor. We model
the different types of electromagnetic disturbances asso-
ciated with such a source. Then, based on the presenta-
tions in Chapters 1 to 4, we show how it is possible to
observe andmodel electrical disturbances associated with
various hydromechanical disturbances in saturated or
partially saturated porous media. We present a labora-
tory experiment showing, at the scale of a cement block,
the types of electrical disturbances that can be associated
with the rupture of a seal during a hydraulic fracturing
experiment. Next, we present an example of laboratory
data generating bursts in the electrical field. These bursts
are associated with the occurrence of Haines jumps,
corresponding to jumps of the meniscus between two
immiscible fluid phases, during drainage in a sandbox.
Finally, we present a small-scale field experiment
demonstrating how a brief burst of water injection in a
small well produces a localizable transient electrical
disturbance.
(Aki & Richard, 2002; McGarr et al., 2002; Stein &
Wysession, 2003). Several methods have been developed
in the past 50 years to simultaneously compute the point
source mechanism and source time function of seismic
events (Zhao & Helmberger, 1994; Ritsema & Lay, 1995;
Sekiguchi et al., 2002). That said, in addition to the seismic
signals that are routinely recorded, there have been sev-
eral observations of direct electromagnetic disturbances
associated with seismic sources (e.g., Kuznetsov et al.,
2001; Byrdina et al., 2003). Gao and Hu (2010) demon-
strated numerically that a seismic source is directly respon-
sible for several seismoelectromagnetic signals that can
also be recorded remotely. Their study opened the door
to the possibility of extracting a seismic source location
more accurately by using both seismic and electromag-
netic signals. Moore and Glaser (2007) developed a com-
prehensive set of laboratory experiments and modeling
to explain the occurrence of electrical fields associated
with the fracturing of crystalline rocks. Wishart et al.
(2008) performed a laboratory investigation of the use
of passively recorded electrical disturbances associated
with pneumatic fracturing (see also Ushijima et al.,
1999, for a field experiment).
Our goal in this section is to show whether the joint
inversion of related seismic and electrical signals is
informative. Does the spatially distributed measurement
of the electric field during seismic data acquisition bring
useful information to the joint inversion problem? In
such a case, the electrical information may help to reduce
the uncertainty in the seismic source model parameters
5.1 Theory
5.1.1 Position of the problem
Seismic event hypocenter localization and moment
tensor solutions are integral components in the passive
seismic monitoring of the hydraulic fracturing process
