Variation in oil recovery and residual oil saturation is mainly controlled by factors related to the relative permeability of existing and flowing fluids in the reservoir. Relative permeability is a critical parameter to evaluate the reservoir performance and considered a key in defining saturation distributions above FWL (Free Water Level). The impact of different reservoir properties such as pore geometry, wettability, fluids saturations, and reservoir temperatures on relative permeability has been investigated thoroughly. Limited studies were performed on the effect of reservoir depletion on relative permeability for carbonate reservoir samples.
In this work, relative permeability measurements were conducted under different effective stresses using different reservoir low permeable Limestone samples ranging from 0.01 – 10 mD air permeability and 5 – 20 % porosity. The relative permeability curves were generated and the irreducible water and residual oil saturations were quantified. The experimental setup composed of a triaxial hydrostatic core holder, injection pump (pore pressure system), and two accumulators to measure the two-phase oil-water relative permeability. At this stage of experimentation, the phases co-saturating the cores are crude and synthetic brine with 200K ppm salinity. Evaluation of the data showed a decrease in the effective permeability and relative permeability to oil with increase in effective stresses, a corresponding negligible decrease in water relative permeability was reported. Irreducible water and residual oil saturation had increased with effective stresses increase.
The experimental results are supposed to highlight the understanding of multiphase flow in the depletion process where the dynamic SCAL occur. In addition to that, it is expected to in light the understanding of the thick capillary transition zones formation with the stress changes due to reservoir depletion.