Abstract
Background: High water cut increases operating costs and reduces oil recovery. Gravity-driven redistribution of oil and water during well shut-in periods has been proposed for reducing water cut; however, laboratory methodologies for investigating this phenomenon in core samples remain limited. Aim: To develop a laboratory methodology for evaluating gravity segregation in oil–water saturated cores under controlled conditions. Materials and methods: The methodology is based on epoxy-sealed cores fixed inside a sleeve, providing a practical and cost-effective core holder capable of accommodating pressure ports. Two experimental scenarios are considered: early water breakthrough caused by an unfavorable mobility ratio, and breakthrough induced by a high-permeability channel. After water breakthrough, flooding is suspended, the core is aged in a vertical position, and water injection is subsequently resumed. Effluent analysis is performed using a gravimetric oil–water separation technique based on the adhesion of oil to polyethylene. The methodology enables qualitative and quantitative assessment of fluid redistribution caused by gravity. Results: Fractional flow analysis demonstrates that, when viscous oils are used, a significant fraction of mobile oil remains in the core after water breakthrough, whereas artificial high-permeability channels can be used to preserve low-viscosity mobile oil within the matrix for subsequent redistribution by gravity segregation. Conclusion: The developed methodology provides a reliable and inexpensive platform for investigating gravity segregation in cores and may support the development of field technologies aimed at reducing water cut and improving oil recovery.