Formation damage effects have been reported in a number of oil
reservoirs in secondary and enhanced recovery stages of production.
The loss in permeability has been widely attributed to the swelling or
pore-plugging action of colloidal clay minerals which are present in
varying quantities in the pore spaces of reservoir rocks. This
research has been aimed at predicting the action of non-swelling clay
particles such as those commonly found in North Sea reservoir
The literature from the areas of formation damage, colloidal
suspensions, and deep bed filtration has been examined with particular
attention being given to the subject of clay mineralogy. An
experimental test rig was designed, comprising a cylindrical packed
sand bed used as a model reservoir to study the permeability changes
associated with the action of clay fines under various flooding
regimes. The pH, salinity and valency of ionic species present in the
flooding fluids were found to be the controlling factors for clay
mobilisation. Fines dispersal coincided with spontaneous decrease. in
permeability when sandpacks treated with monovalent brine were
subjected to fresh water flow. Analysis showed that'the fines released
from the bed were primarily kaolinite in the size range 1-5 micron. A
minimum critical+ salinity of flooding water was shown to exist, above
which particle dispersal is prevented. Further, experimental work
provided a measure of the ion exchange capacity of the clay fines in
the sandpack as well as of pure clay materials.
The close-range interaction of kaolinite particles with silica
surfaces was measured in a continuous flow glass apparatus which
allowed in-situ observation and measurement by optical microscopy.
Particle deposition in this system was found to be very sensitive to
the method of cleaning of the silica surface. Deposition was also a
function of the suspension flowrate. Clay mobilisation behaviour, as
observed in the sandpack experiments, was confirmed with suspension
pH, salinity and flowrate to a lesser extent, governing the particle
The research has identified the conditions under which clay
mobilisation is initiated. It is proposed that any model of
permeability reduction should be adapted to include the effects of
specific ion-exchange processes between clays and flooding liquids.
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.