In formation evaluation and reservoir engineering, resistivity index, relative permeability, and capillary pressure are crucial parameters for estimating oil reserves and planning a production scenario. They can be determined in the laboratory using Special Core Analysis, or SCAL techniques. Since they are all functions of fluid saturation, correlations between them may exist; but the literature on their inter-relationships is lacking. In this paper, experimental relative permeabilities and relative permeabilities obtained from resistivity measurements using Li’s model (2007) are compared for different immiscible brine-oil displacements.
An experimental study on a water-wet grainstone rock was initiated in order to measure its resistivity response during different ambient water-oil flow displacements. Three different flooding techniques were performed and compared. The most popular technique is the resistivity porous plate Pc-RI method where resistivity and capillary pressure are measured at equilibrium. The steady-state flooding method was also tested; resistivity and steady-state relative permeability were measured at the equilibrium state. Finally the fastest yet least reliable method is the transient technique or unsteady-state flooding method where resistivity and unsteady-state relative permeability are measured under transient conditions.
A comparison between resistivity index obtained from the three flooding techniques showed that the unsteady-state technique cannot give reliable resistivity index curve, and so should be avoided to infer Kr from resistivity measurements. The Pc-RI method provides the most reliable resistivity index curve but relative permeability can only be derived from the capillary pressure curve. Finally, the steady-state displacement was found to be the best method to compare experimental relative permeability with relative permeability inferred from resistivity. In spite of an acceptable match between them, an improvemnent of Li’s model is proposed.
Additional investigations such as effects of wettability and rock heterogeneities on these results will be necessary to validate the generality of the overall workflow.