Geoscience Reference
In-Depth Information
Glossary: The Seismoelectric Method
(imaginary) component describes the ability of the porous
material to store reversibly electrical charges.
Coseismic effect: The coseismic effect describes the electrical
and magnetic fields associated with the passage of a seismic
wave through an electromagnetic receiver. This type of elec-
tromagnetic disturbances travels with the seismic wave itself.
Diffuse layer: External part of the electrical double layer
coating the surface of the minerals in contact with water. If
the surface of the mineral is negatively charged, the diffuse
layer carries an excess of cations and has a deficiency of anions
to counterbalance the charge of the mineral surface and the
Stern layer. The thickness of the diffuse layer is given by twice
the Debye length.
Double layer: Generic term describing the disturbances in the
ionic concentrations in the vicinity of the mineral surface in
contact with water. The electrical double layer comprises the
Stern layer of sorbed ions and the diffuse layer.
Drained: A drained mechanical behavior describes the behavior
of a porous material when the fluid is free to flow through the
connected porosity. In this case, the fluid does not resist to the
deformation of the elastic skeleton (frame) of the porous
material.
Drainage: Replacement of the wetting fluid by the nonwetting
fluid in a porous material.
Electrical resistivity tomography: Geophysical imaging tech-
nique using the injection of electrical current in the ground
and the measurements of the electrical field on another set
of electrodes. Through inversion, an image of the electrical
resistivity distribution can be obtained.
Electroencephalography: Medical technique based on the
passive measurement of the electrical field on the scalp and
the localization of the causative source of electrical current
in the brain of a patient.
Electrogram: An electrogram is a record of the ground electrical
field at a measuring station as a function of time. Electrograms
are typically recorded in two Cartesian axes along the ground
surface (the vertical component is usually zero).
Electrokinetic coupling: Electrokinetic coupling mechanism
denotes a set of phenomena involving the relative displace-
ment between a charged solid and the pore water including
a fraction of the electrical diffuse layer. The plane of zero
velocity is called the shear plane and characterizes the position
Acoustic emission: Acoustic emissions describe the generation
of elastic waves in a porous material, for instance, associated
with a change in the stress state (and the formation of
microcracks or the reactivation of existing cracks) or with
the rapid movement of the meniscus between two immiscible
fluids in the pore space of a porous material.
Adaptive Metropolis algorithm (AMA): AMA describes a
specific choice of a proposal distribution for Markov chain
Monte Carlo (McMC) sampling methods. This distribution is
crucial factor for the convergence of the stochastic algorithm.
AMA uses a Gaussian proposal distribution, which is updated
along the sampling process using the full information cumu-
lated so far. Due to the adaptive nature of the process, AMA
is non-Markovian in nature.
Bayesian approach: In geophysics, the Bayesian inference
approach is a method of inference in which Bayes
rule is used
to update the probability density estimate for a model vector as
additional information (e.g., geophysical data) is acquired.
Beamforming: Geophysical method allowing to focus seismic
energy at a desired location in space and at a known time.
It requires some knowledge or assumptions regarding the
seismic velocity model.
Capillary pressure curve: The capillary pressure denotes the
difference in pressure across the interface between two
immiscible fluid phases in a porous material, the nonwetting
phase and the wetting phase (e.g., oil and water in a siliciclastic
material). It is caused by interfacial tension between the two
phases that must be overcome to initiate flow. The capillary
pressure curve denotes the evolution, with respect to the
saturation of the wetting phase, of the capillary pressure when
the nonwetting phase replaces the wetting phase (drainage)
or when the wetting phase replaces the nonwetting phase
(imbibition).
Cation exchange capacity (CEC): Amount of exchangeable
cations in a porous material reported per unit mass of grains
(solid). Very often, the CEC is reported in equivalent charge
per unit mass of solid.
Complex conductivity: Electrical conductivity of a porous
material written as a complex number to account for the phase
lag between the current and the electrical field. The inphase
(real) component characterizes the ability of the porous
material to conduct electrical current, while the quadrature
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