Page 163 - Reservoir Formation Damage

Paniculate Processes in Porous Media 145

The fundamental particle retention mechanisms are:

1. Surface deposition (physico-chemical)
2. Pore throat blocking (physical jamming)
3. Pore filling and internal filter cake formation (physical)
4. Screening and external filter cake formation (physical)

Forces Acting Upon Particles

Ives (1985) classified the various forces acting on particles in a flow-
ing suspension in three categories as (a) forces related to the transport
mechanisms, (b) forces related to the attachment mechanisms, and
(c) forces related to the detachment mechanisms, and characterized them
in terms of the relevant dimensionless groups.

Forces Related to the Transport Mechanisms

The important relevant quantities governing the particle behavior in a
suspension can be summarized as following: d and D are particle and
porous media grain diameters, respectively; p 5 is the density of particles;
p and \JL are the density and viscosity of the carrier liquid, respectively;
is the convective velocity; g is the gravitational acceleration coef-
v a
ficient; and T is the absolute temperature.
Inertia Force. The inertia of a particle forces it to maintain motion in
a straight line. The inertia force can be expressed by the dimensionless
group as (Ives, 1985):

(8-1)

Gravity Force. As a result of the density difference between the particle
and the carrier liquid, particles tend to move in the gravity direction
according to Stokes' law. The velocity of a spherical particle undergoing
a Stokes' motion is given by:

(8-2)

The gravity force acts upward when particles are lighter and, therefore,
buoyant. The gravity force acts downward when particles are heavier
and, therefore, tend to settle. The gravity force can be expressed by a