When the oil saturation becomes the residual oil saturation, what is the value of the effective oil permeability ko?

When the oil saturation becomes the residual oil saturation, what is the value of the effective oil permeability ko?

• A. One
• B. Undefined
• C. Zero
• D. Infinite

Answer: (C)

The key idea is that effective permeability to a phase depends on a continuous path for that phase through the pore space. When oil saturation reaches the residual level, all the oil becomes trapped in isolated ganglia and there is no connected pathway for oil to flow. In reservoir terms, the relative permeability to oil, kr_o, goes to zero at residual oil saturation, and ko = kr_o × k (where k is the absolute permeability). With kr_o approaching zero, ko also becomes zero, meaning there is no ability for the oil to flow despite oil still being present. So the value is zero because at residual oil saturation there is no continuous oil pathway to support flow.

The key idea is that effective permeability to a phase depends on a continuous path for that phase through the pore space. When oil saturation reaches the residual level, all the oil becomes trapped in isolated ganglia and there is no connected pathway for oil to flow. In reservoir terms, the relative permeability to oil, kr_o, goes to zero at residual oil saturation, and ko = kr_o × k (where k is the absolute permeability). With kr_o approaching zero, ko also becomes zero, meaning there is no ability for the oil to flow despite oil still being present.

So the value is zero because at residual oil saturation there is no continuous oil pathway to support flow.