Geoscience Reference
In-Depth Information
for a variety of situations such as determining the source
or direction of the water, fouling or failure of water
uptake or injection systems, and other issues related to
well integrity.
greater than the drainage pore pressures. Consequently,
if one or many of the other pore throat capillary meniscus
forces connected to the newly filled pore are smaller than
the initial throat holding the interface, these throats and
subsequent pores spontaneously fill with the nonwetting
phase also. Therefore, once the interface at a particular
throat becomes unstable, it causes an avalanche of pore
and throat fillings with the nonwetting phase that only
stops at throats with capillary meniscus forces greater
than the previous drainage pore pressures. This jump
of the position of the meniscus is called a Haines jump
(Haines, 1930; Aker et al., 2000; Crandall et al., 2009).
Imbibition is also characterized by Haines jumps.
However, because imbibition is a collective process and
because water is a mineral wetting fluid, capillary forces
will hold up the invading water at the larger pores. Once
a certain pore fills, all of the throats connected to that
pore fill as they are smaller in size. However, during
imbibition, even if a small pore lies behind a large pore,
the small pore may not spontaneously fill after the filling
of the large pore. This limits the size of the potential
avalanches on imbibition when compared to drainage.
Another process called
5.4 Haines jump laboratory
experiment
5.4.1 Position of the problem
The dual and multiphase fluid and gas flow through
porous media is a very common phenomenon that occurs
in multiple types of settings such as industrial processes,
aquifer drainage and recharge, oil extraction, and surf
action on beaches as well as in many other types of set-
tings. This phenomenon is so common that it is often
ignored with respect to the information that can be
extracted from the physical processes that occur with this
type of fluid flow. In the following sections, a very simple
experiment will be described and discussed. This experi-
ment is simply the draining and imbibing of an aquarium
filled with sand that starts with 100% tap water satura-
tion. This simple experiment has substantial similarity
to several common yet important processes, as described
earlier, as well as everyday experiences at the beach. This
experiment focused only on the two-phase flow phe-
nomena associated with general fluid flow in an uncon-
solidated porous medium. This was the process under
investigation, and therefore, we describe here the discov-
ery of an electrical phenomenon that is directly and
uniquely associated with this type of fluid flow.
Drainage of a porous mediumwith an invading immis-
cible nonwetting phase like air, which is initially satu-
rated by a wetting phase like water, takes place under
a process called invasion percolation (Aker et al., 2000;
Crandall et al., 2009). In a granular material like a sand,
large pores are connected by smaller throats. The invad-
ing nonwetting fluid (air) will get held up at the throats
between the pores where the capillary forces are greatest.
As the wetting phase (water in the experiments reported
in the following text) is continuously removed from
below, the air/water interface at the throat with the lar-
gest radius will become unstable. Finally, when the cap-
illary entry pressure of the throat is exceeded, the throat
spontaneously fills with air. All the larger pores con-
nected to it fill with the air along with it in an avalanche
process. The wetting/nonwetting interface then restabi-
lizes at pore throats that have capillary meniscus forces
is also acting during
imbibition to decrease the size of the avalanches. Water
layers move along the edges of the pore space, allowing
small throats ahead of the wetting front to fill spontane-
ously (Tuller & Or, 2001). These filling events would con-
sist of a single throat and may therefore not emit enough
energy to be detectable.
Because fluid is moving with respect to mineral grain
surfaces, it is reasonable to expect that Haines jumps
would generate bursts of electrical currents. Indeed, in
a porous material, all minerals in contact with water
develop a surface charge through chemical reactions.
Part of this charge is neutralized by the sorption of coun-
terions in the so-called Stern layer. Neutrality is achieved
by the presence of an excess of charge in the vicinity of
the mineral surface through coulombic interaction
with the charge attached to the mineral framework,
known as the electrical double layer (see description in
Chapter 1). This coulombic interaction implies that the
pore water carries a net amount of charge, which is
generally positive (Leroy et al., 2007). The displacement
of this positive charge by the flow of pore water is
equivalent to a source of electrical current density
(chargemoving per unit surface area per unit time) called
the streaming current. The associated electrical field is
called the streaming potential and is generated from
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