Geoscience Reference
In-Depth Information
where the zeta potential is estimated. Very often, this shear
plane is considered to be between the Stern layer and the
diffuse layer.
Electroseismic effect:
Geophysical method in which a current
is injected in the ground and the ground motion is measured.
The coupling is electrokinetic in nature.
Filtration displacement:
Relative displacement between the
fluid localized in the pore space of a porous material and the
displacement of the solid phase.
First Fresnel zone:
A Fresnel zone is one of a number of concen-
tric ellipsoids defining volumes in the radiation pattern of a seis-
mic wave. The cross section of the first Fresnel zone is a circle.
Gassmann substitution formula:
The Gassmann equation
allows to connect the bulk moduli of the same porous material
saturated by two different viscous fluids. For the fluid veloci-
ties, Gassmann equations correspond essentially to the lower
frequency limit of Biot theory of poroelasticity.
Haines jump:
Haines jumps denote jumps in the position of the
meniscus between two immiscible fluids during drainage or
imbibition. These jumps happen so quickly that they generate
recordable acoustic waves that are audible.
Helmholtz decomposition:
Decomposition of a vector field as
the sum of the gradient of a scalar potential and the curl of a
vector potential.
Hooke
Markov chain Monte Carlo (MCMC) sampler:
MCMC algo-
rithms are used to sample a probability distribution based on
constructing a Markov chain that has the desired distribution
as its equilibrium distribution (e.g., Gaussian). The state of
the chain after a number of realizations is then used as a sample
of the desired probability distribution on themodel parameters.
The quality of the sampling improves as a function of the num-
ber of realizations. Therefore, after statistical convergence of the
chain, the algorithm is used to determine the posterior proba-
bility distribution on each component of the model vector.
Maxwell fluid:
A Maxwell fluid is a class of viscoelastic fluid
having the properties of both elastic and viscous materials.
Maxwell
Wagner polar-
ization occurs at the inner dielectric boundary layers of a
porous material and is related to a separation of electrical
charges. These charges are often separated over a considerable
distance relative to the distance involved in true dielectric
polarization at the molecular scale. This polarization
mechanism is due to the discontinuity of the displacement
current at the interface between different phases of a porous
material.
NAPL:
Nonaqueous phase liquids that are not easily miscible
with water.
Nonpolarizable electrode:
A nonpolarizable electrode is char-
acterized by faradic current can that freely pass (without
polarization) between the two sides of the electrical double
layer between the electrode and a porous material or an elec-
trolyte. Examples correspond to the Ag/AgCl or Pb/PbCl
2
electrodes.
Objective function:
In geophysics, an optimization problem
consists of minimizing an objective function. Optimization
includes finding optimal values of the objective function
given a set of constraints, including a variety of different terms
in the objective functions and different types of domains. For
instance the objective function is the sumof a misfit termand a
regularizer balanced by a regularization parameter.
-
Wagner polarization:
The Maxwell
-
'
s law:
Linear constitutive equations between the stress
and the strain in linear elasticity. The material property
involved in this linear constitutive law is the stiffness tensor,
which is represented by a matrix of 3 × 3 × 3 × 3 = 81 compo-
nents, and because of the symmetry of the stress and strain
tensors, only 21 elastic coefficients are independent (the stiff-
ness tensor is a fourth-order tensor).
Hydraulic fracturing:
Hydraulic fracturing (or fracking)
denotes the formation of a fracture in a rock due to the
increase of the fluid pressure. They can happen naturally, or
they can be induced from a well to increase the permeability
of a reservoir.
Imbibition:
Replacement of the nonwetting fluid by the wetting
fluid in a porous material.
Impedancemeter:
Instrument that can be used to measure the
impedance of a porous material. It can be used to determine
the complex conductivity of a porous material for a range of
frequencies.
Interface response:
Electromagnetic effect associated with the
conversion of hydromechanical to electromagnetic energy at
the interface between two porous media.
Inverse modeling:
Modeling consisting in retrieving a model
from observed data. The inverse problem is intrinsically non-
unique in geophysics. It can be solved with deterministic or
stochastic techniques.
Magnetogram:
A magnetogram is a record of the ground mag-
netic field at a measuring station as a function of time. Magne-
tograms are typically recorded in the three Cartesian axes.
Oil wet:
A porous material is oil wet if the oil has a preferential
wettability (affinity) for the solid phase. For instance, carbo-
nate reservoirs are often oil wet, while siliciclastic reservoirs
are usually water wet.
Outer Helmholtz plane:
Plane separating the Stern layer from
the diffuse layer in the electrical double layer coating the sur-
face of the mineral grains.
Perfectly matched layer (PML):
A PML is a synthetic absorb-
ing layer used in the numerical modeling of wave propagation.
It is used to simulate material with open boundaries for the
propagation of the waves (for instance, in the finite-element
method).
P-wave:
Compressional or primary elastic wave. The motion
occurs in the direction of propagation. This type of wave is
faster than the S-wave.
