Relative permeability curves are important for characterizing the flow behavior of multiphase fluids (such as oil and water) in porous media. These curves provide information about the fractional flow of each phase as a function of saturation.
To measure relative permeability curves, the following steps are typically involved:
- Core Sample Preparation: A representative core sample, usually cylindrical, is extracted from the subsurface reservoir. The core sample should resemble the actual rock formation in terms of porosity and permeability.
- Saturation Determination: The core sample is initially saturated with one of the fluid phases (e.g., oil). The saturation is controlled and measured to ensure that a known fraction of the pore space is filled with the desired phase.
- Steady-State Flow: A flow apparatus is set up to measure the flow rates of each fluid phase through the core sample. The apparatus typically includes pumps, pressure sensors, and flow meters. The flow is established and maintained until steady-state conditions are achieved.
- Saturation Variation: The saturation of the non-wetting phase (e.g., water in the case of oil-wet reservoirs) is systematically increased while monitoring the flow rates of both phases. The saturation can be varied by displacing the non-wetting phase through the core using the wetting phase or by adjusting the pressure and flow rates of each phase.
- Data Collection: The flow rates of each phase are recorded at different saturations. These measurements are used to calculate the relative permeabilities, which represent the fractional flow of each phase relative to the total flow capacity of the porous media.
- Curve Fitting: The collected data is analyzed and fitted to appropriate mathematical models or equations to obtain the relative permeability curves. Common models used for fitting include the Corey-Brooks model, the Leverett J-function, or other empirical or theoretical models.
The resulting relative permeability curves provide information on how the flow of each phase is affected by the presence of the other phase. They typically exhibit non-linear behavior, with relative permeabilities that depend on the saturation of each phase. These curves are essential for understanding fluid behavior in reservoirs, optimizing production strategies, and predicting the performance of enhanced oil recovery techniques.
It’s important to note that relative permeability measurements can be challenging and may require careful experimental design and specialized equipment. Advanced techniques such as centrifuge methods, magnetic resonance imaging, or microfluidic devices may also be employed to study relative permeability under more controlled and detailed conditions.