Experimental and theoretical determination of relative permeability together with microscopic remaining oil distribution based on pore-throat structures

In this work, experimental and theoretical techniques have been developed to examine the effects of pore-throat structure on the flow seepage behaviour and thus the oil-water relative permeability together with microscopic remaining oil distribution. Experimentally, high-pressure mercury injection (HPMI) tests have been performed to microscopically characterize the pore-throat structures in core samples under various conditions. By simulating microscopic seepage phenomenon in a flow model generated from scanning electron microscope (SEM) images, the traditional capillary bundle model is theoretically modified and generalized to incorporate the pore-throat structures together with microscopic remaining oil distribution by taking the crossflow and bypassing flow into account. Starting from the pore-scale to core-scale and then reservoir-scale, effects of pore-throat structures on the relative permeability curves and microscopic remaining oil distribution are then comprehensively examined and analyzed, while waterflooding efficiency as a function of relative permeability has been evaluated. With the newly defined cutoff throat radius, the pore-throat structure is found to impose a significant impact on exploitation efficiency in a given reservoir, depending on both relative permeability and remaining oil distribution. In an area with relatively high permeability, the crossflow and bypassing flow through large throats dictate the remaining oil saturation, most of which is mainly controlled by relatively medium throats, indicating that oil recovery can be preferably achieved by reducing the viscous force. For an area with relatively low permeability, its remaining oil is controlled by small throats due to the capillary force and viscous force. By selecting appropriate development strategies based on the microscopic remaining oil distributions, field practices show that the daily production of single wells can be increased by more than 60%, with a potential increase of more than 10% in the ultimate oil recovery. • Traditional capillary bundle model is improved by considering micro crossflow, bypassing flow and pore-throat structures. • A theoretical model is generalized for relative permeability and microscopic remaining oil distribution conditioned to lab tests. • Effects of pore-throat structures on relative permeability and displacement efficiency are examined. • Cutoff throat radius is introduced to connect microscopic remaining oil distribution and pore-throat structures. • Microscopic remaining oil distribution in different reservoirs and their production-boosting measures are differentiated.