Reliable Steady-State Relative Permeability Measurement for Carbonate Rocks from a Middle Eastern Offshore Reservoir with an In-Situ Saturation Monitoring by X-Ray Ct Scanner

Abstract

Abstract The results of special core analyses using carbonate rocks from a Middle Eastern offshore reservoir are presented based on laboratory and simulation studies. The study aims to obtain reliable relative permeability in an oil-water system under steady-state conditions, and confirm the resulting relative permeability through a simulation study by comparing water saturation distributions along the core at various injection ratios of water to oil. The difficulties in steady-state relative permeability measurements are to determine water saturations and steady-state conditions as only the effluents are measured. To obtain accurate water saturations, we adopted an X-ray CT (Computed Tomography) scanner that allows us to precisely measure porosity and fluid saturation distributions inside cores under reservoir conditions, especially for reservoir wettability. In addition, not only the ratios of water to oil in effluents but also water saturation distributions derived from CT measurements inside the core were used as a measure of steady-state conditions. Core flood experiments were conducted with periodic measurements at various injection ratios of water to oil. As a result, we obtained eleven relative permeability points with respect to water saturation calculated from CT numbers. Next, a simulation study was conducted to confirm the relative permeability curves using a core model where CT derived porosity and absolute permeability were assigned based on the core flooding experiments. Results of the core flood simulations with the resulting relative permeability curves show that the simulated water saturation distributions are in excellent agreement with those of the core flood experiments, especially low injection ratios of water to oil. Through laboratory and simulation work, it is confirmed that reliable relative permeability measurements were made by carefully determining water saturations and steady-state conditions with simultaneously measuring the effluents from the core and monitoring the inside core by X-ray CT scanner.