The Effect of Instability on Relative Permeability Curves Obtained by the Dynamic-Displacement Method

A study was undertaken to investigate how instability would affect the oil/water relative permeability curves obtained by the dynamic-displacement method. In this method, stable Buckey-Leverett displacement theory is used to calculate relative permeability curves from coreflood data. Thus, to obtain the true relative permeability curves by the dynamic-displacement method, the coreflood must be stable. However, the method frequently has been applied to unstable corefloods. The consequence of this application of the method has not been previously reported. The authors compared oil/water relative permeability curves from steady-state and dynamic-displacement experiments at several levels of instability. The results showed that the dynamic-displacement relative permeability curves deviated significantly from the steady-state curves as the degree of instability increased. This observation indicates the need to scale laboratory relative permeability measurements to account for instability. To obtain representative relative permeability curves for numerical modeling of a reservoir, laboratory displacement experiments should be conducted at the same degree of instability as that in the reservoir.