An Experimental Study of the Effect of Instability on Dynamic Displacement Relative Permeability Measurements

An experimental study was undertaken to investigate the effects of instability on oil and water relative permeabilities measured by the dynamic displacement method. The calculation of relative permeability from dynamic displacement data assumes a stable displacement of oil by water. This assumption is no longer valid when the displacement becomes unstable. Therefore, the computed relative permeabilities are liable to be incorrect in such a situation. Dynamic displacement experiments were carried out using unconsolidated sand packs, refined oils and distilled water. Oil and water relative permeability curves were obtained by a standard calculation technique. The degree of instability of the displacements was varied by varying a dimensionless stability number. The higher the stability number, the higher is the degree of instability. One steady state experiment also was carried out to obtain a set of control data. The results show that instability has a significant effect on both oil and water relative permeability curves, obtained from dynamic displacement data. In general, the oil relative permeabilities decreased and the water relative permeabilities increased with increasing stability number. Therefore, it is necessary to conduct dynamic displacement experiments under stable displacement conditions in order to obtain the true relative permeability curves for the fluid-rock system.