Changes

Permeability is the measure of the ease of movement of fluid through the pore space in a rock. Where more than one fluid phase is present (e.g., oil and water), the permeability of one phase is reduced by the presence of the other phase within the pore system. In this instance, the permeability to a particular fluid is called the relative permeability.<ref name=Hawkins />

Permeability is the measure of the ease of movement of fluid through the pore space in a rock. Where more than one fluid phase is present (e.g., oil and water), the permeability of one phase is reduced by the presence of the other phase within the pore system. In this instance, the permeability to a particular fluid is called the relative permeability.<ref name=Hawkins />

For water-wet reservoirs, Craig (1971) gave some general water-oil relative permeability end points. Water will start flowing along with oil once the water saturation is greater than roughly 20–25%. This value is the irreducible water saturation; the volume of water bound and immobilized by adhesive attraction to the surface of the pores. Oil will stop flowing where the water saturation in the rock is about 70–80%. When this happens, there will not be enough oil to provide a continuous volume throughout the rock. Interfacial tension will cause the oil stream to snap off and fragment into immobilized globules and strands of residual oil.

For water-wet reservoirs, Craig<ref>Craig, F. F., 1971, The reservoir engineering aspects of waterflooding, monograph series: Richardson, Texas, Society of Petroleum Engineers, 144 p.</ref> gave some general water-oil relative permeability end points. Water will start flowing along with oil once the water saturation is greater than roughly 20–25%. This value is the irreducible water saturation; the volume of water bound and immobilized by adhesive attraction to the surface of the pores. Oil will stop flowing where the water saturation in the rock is about 70–80%. When this happens, there will not be enough oil to provide a continuous volume throughout the rock. Interfacial tension will cause the oil stream to snap off and fragment into immobilized globules and strands of residual oil.

The relative permeability end points may vary significantly between reservoirs; the quoted values can be considered as approximate. The relative permeability of water and oil as a function of water saturation is illustrated by relative permeability curves ([[:File:M91FG28.JPG|Figure 5]]).

The relative permeability end points may vary significantly between reservoirs; the quoted values can be considered as approximate. The relative permeability of water and oil as a function of water saturation is illustrated by relative permeability curves ([[:File:M91FG28.JPG|Figure 5]]).