QUANTIFYING THE ROLE OF PORE GEOMETRY AND MEDIUM HETEROGENEITY ON HEAVY OIL RECOVERY DURING SOLVENT/CO-SOLVENT FLOODING IN WATER-WET SYSTEMS

摘要

Porous medium characteristics (e.g., pore geometry and medium heterogeneity) as well as the chemical nature of the co-solvents crucially affect the oil displacement efficiency during solvent flooding processes. In this work, initially saturated models with heavy crude oil were used to perform a series of solvent injection experiments. Several one-quarter five-spot micromodels with pre-designed pore geometry were constructed and used. In addition, rock-look-alike flow patterns generated from thin sections of sandstone and dolomite reservoir rocks were etched onto glass plates to form micromodels mimicking the pore geometry and heterogeneity of these rocks. Four different groups of chemicals and their mixtures were used to investigate the effect of co-solvents when they were added to the main liquid hydrocarbon. High-resolution video pictures taken of the displacement process allowed microscopic analysis of the displacement mechanism at the pore level. Experimental results revealed that the displacement efficiencies of solvent mixtures greatly depend on the chemical properties of the added co-solvents. The most effective co-solvent with the greatest sweep efficiency was detected from different chemical mixtures. The experiments performed on various network patterns demonstrated that a higher coordination number along with a higher pore-throat size ratio of the flow paths improved the displacement efficiency. Media heterogeneity resulted in higher residual oil saturation by reducing the contact area, increasing the solvent bypass, and causing the oil to be trapped. The microscopic observations confirmed that the presence of connate water in strongly water-wet medium could improve the final recovery. However, the extent of this improvement greatly depends on the type of co-solvents used in the injection process.