Page 228 - Reservoir Formation Damage

208 Reservoir Formation Damage

Model Considering the Clayey Formation Swelling
and Indigeneous and External Particles

Civan et al. (1989) and Ohen and Civan (1991, 1993) considered the
formation damage by clayey formation swelling and migration of externally
injected and indigeneous particles. They assumed constant physical
properties of the particles and the carrier fluid in the suspension. They
also considered the effect of fluid acceleration during the narrowing of
the flow passages by formation damage. Ohen and Civan (1993) classified
the indigeneous particles that are exposed to solution in the pore space
in two groups: lump of total expansive (swelling, i.e. total authigenic clay
that is smectitic) and lump of total nonexpansive (nonswelling) particles,
because of the difference of their rates of mobilization and sweepage from
the pore surface. They considered that the particles in the flowing
suspension are made of a combination of the indigeneous particles of
porous media entrained by the flowing suspension and the external
particles introduced to the porous media via the injection of external
fluids. They considered that the particles of the flowing suspension can
be redeposited and reentrained during their migration through porous
media and the rates of mobilization of the redeposited particles should
obey a different order of magnitude than the indigeneous particles of the
porous media. Further, they assumed that the deposition of the suspended
particles over the indigeneous particles of the porous media blocks the
indigeneous particles and limits their contact and interaction with the
flowing suspension in the pore space. They considered that the swelling
clays of the porous media can absorb water and swell to reduce the
porosity until they are mobilized by the flowing suspension. They assumed
that permeability reduction is a result of the porosity reduction by net
particle deposition and formation swelling and by formation plugging by
size exclusion. The Ohen and Civan (1993) formulation is applicable for
dilute and concentrated suspensions, whereas, Gruesbeck and Collins'
(1982) model applies to dilute suspensions.
The mass balance equations for the total water (flowing plus absorbed)
in porous media and the total particles (suspended plus deposited) in
porous media are given, respectively, by:

a/a1 [(4KJ W + e w ) Pvv ] + a/a* (o wup w) = 0 (10-133)

(10-134)

Thus, adding Eqs. 10-133 and 134 yields the total mass balance equation
for the water and particles in porous media as: