Mechanistic Insights into Chemical-Assisted Steam Injection: Pore-Scale Evidence for More Efficient and Lower-Carbon Heavy Oil Recovery

Abstract

Steam-assisted gravity drainage (SAGD) is the primary method for in situ extraction of heavy oil and bitumen in Canada. However, it (as well as other steam injection methods) suffers from low efficiency, high water and energy consumption, and significant environmental impact. Adding chemicals to steam offers a potential solution by enhancing oil recovery while reducing carbon emissions through lower steam usage. Our previous studies have shown that deep eutectic solvents (DES) and thermally stable nonionic surfactants improve steam chamber sweep efficiency and microscopic displacement efficiency, respectively. However, their mechanisms and effects in porous media, especially at the pore scale, remain unclear. This study explores the microdisplacement mechanisms of these chemical additives. A porous medium model was created by packing glass beads between two plexiglass plates, which was then saturated with heavy oil at a slow injection rate. The research focused on steam chamber growth dynamics, physicochemical changes at the oil-steam-water-rock interface, and their impact on oil drainage. By comparing oil recovery efficiency, energy efficiency, and carbon intensity of SAGD with and without chemical additives, the effects of DES (formulated in our laboratories and named as DES 11) and Novelfroth (a commercial nonionic surfactant) on steam injection efficiency were evaluated. The results demonstrate that DES 11 and Novelfroth 190 enhance the recovery rate by 31.1% and 37%, respectively, while reducing carbon emission intensity to one-third to one-half of conventional SAGD. However, their underlying mechanisms differ. Also, the introduction of these chemical additives significantly altered the state of residual oil compared to the base case. Ultimately, the improvement in oil recovery per unit of steam injected in the chemical cases was quantified and linked to a reduction in greenhouse gas emissions during steam injection.