Page 159 - Reservoir Formation Damage
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Paniculate Processes in Porous Media 141
released by colloidal forces or mobilized by hydrodynamic shear of the
fluid flowing through porous media. Fine particles can also be generated
by deformation of rock during compression and dilatation. This is due
to variation of the net overburden stress and loss of the integrity of rock
grains. Fine particles are unleashed and liberated because of the integrity
loss of rock grains by chemical dissolution of the cementing materials
in porous rock, such as by acidizing or caustic flooding. These are the
typical internal sources of indigenous fine particles.
Paniculate matter can be produced by various chemical reactions such
as the salt formation reactions that occur when the seawater injected for
waterflooding mixes with the reservoir brine, and formation of elemental
sulfur during corrosion. Paniculate matter can also be produced by
precipitation due to the change of the thermodynamic conditions and of
the composition of the fluids by dissolution or liberation of light gases
(Amaefule et al., 1988). These are typical" mechanisms of particle pro-
duction in porous media.
Once entrained by the fluids flowing through porous media, the various
particles migrate by four primary mechanisms (Wojtanowicz et al., 1987):
1. Diffusion
2. Adsorption
3. Sedimentation
4. Hydrodynamics
The transport of the fine particles are affected by six factors (Wojtanowicz
et al., 1987):
1. Molecular forces
2. Electrokinetic interactions
3. Surface tension
4. Fluid pressure
5. Friction
6. Gravity
As the fine particles move along the tortuous flow pathways existing
in porous media, they are captured, retained, and deposited within the
porous matrix. Consequently, the texture of the matrix is adversely altered
to reduce its porosity and permeability. Frequently, this phenomena is
referred to as formation damage measured as the permeability impairment.
Particulate Processes
The various particulate processes, schematically depicted in Figure 8-1,
can be classified in two groups as the internal and external processes.