Solids Plugging. Fig. 10.9 shows that the plugging of the reservoir-rock
pore spaces can be
caused by the fine solids in the mud filtrate or solids dislodged by the filtrate within the rock
matrix. To minimize this form of damage, minimize the amount of fine
solids in the mud system
and fluid loss.
Fig. 10.9—Formation damage caused by
solids plugging.
Clay-Particle Swelling. This is an inherent problem in sandstone that contains water-sensitive
clays. When a fresh-water filtrate
invades the reservoir rock, it will cause the clay to swell and
thus reduce or totally block the throat areas.
Saturation Change. Production is predicated on the amount of saturation within the reservoir
rock. When a mud-system filtrate
enters the reservoir, it will cause some change in water
saturation and, therefore, potential reduction in production.
Fig. 10.10 shows that high fluid loss
causes
water saturation to increase, which results in a decrease of rock relative permeability. See
the chapter on transport properties in the General Engineering volume of this Handbook for
additional information.