Measurement of three-phase relative permeability during gravity drainage using CT scanning

This thesis presents a study of three-phase gravity drainage experiments to find relative permeability. The investigation begins with the analysis of a dynamic displacement experiment where three-phase relative permeabilities had been measured. Saturation paths and recovery for this experiment were calculated analytically using the method of characteristics. The predicted paths compared well with the experimental measurements, and with one-dimensional numerical solutions. The saturation paths and recoveries were greatly influenced by the three-phase relative permeability, a parameter still not well understood. To better understand this, we measured three-phase relative permeabilities for gravity drainage using a dual-energy medical CT scanner modified to scan vertical cores. Independent measurements of two saturations as a function of time and distance along the length of the core were made from which relative permeabilities were found. Three-phase (air/oil/water) gravity drainage experiments were performed on systems with different spreading coefficients and at different initial conditions. Experiments were run on both consolidated and unconsolidated porous media. The results were compared to measurements of three-phase flow in capillary tubes, micromodels and to predictions from network modeling. We found that at low oil saturation, the oil relative permeability is proportional to approximately the square of its own saturation, for hexane and octane as the oil phase. This functional form of relative permeability was consistent with the drainage of oil layers, wedged between the water and gas in crevices of the pore space. For decane, which is non-spreading, the layer drainage regime was not observed. At higher oil saturations the oil relative permeability is proportional to approximately the fourth power of its own saturation, for spreading and non-spreading systems. Within the scatter of the experimental data, oil and water relative permeability were functions only of their own saturations and independent of initial conditions.