Pathway to zero-carbon emission of energy recovery processes from heavy oil reservoirs

In recent years, declining production of conventional light oil, together with steadily increasing global energy demand, has elevated the strategic importance of heavy oil resources. However, the intrinsically high viscosity of heavy oil severely limits the effectiveness of conventional recovery methods, with typical recovery factors generally below 15%. Thermal recovery technologies enhance oil mobility by injecting heat carriers into the reservoir, thereby substantially improving recovery efficiency. Nevertheless, the generation of thermal agents relies on large-scale fuel combustion and is associated with considerable CO 2 emissions, rendering traditional thermal processes increasingly incompatible with current goals of green and low-carbon oilfield development. Against this background, low-carbon development technologies for heavy oil reservoirs have emerged as major research and application frontiers. Representative approaches include expanding-solvent SAGD (ES-SAGD), non-condensable gas-assisted SAGD (NCG-SAGD), in-situ reflux (ISR), vapor extraction (VAPEX), cyclic solvent injection (CSI) and in-situ hydrogen generation (ISHG). Despite growing research efforts, a comprehensive understanding of their underlying mechanisms, field performance, and carbon emission reduction potential in enhancing oil recovery (EOR) remains limited, which constrains objective assessments of engineering applicability and rational technology selection. To address this gap, this study provides an integrated review of representative mentioned six low-to zero-carbon emission heavy oil EOR technologies, focusing on their fundamental mechanisms, carbon emission reduction potential, technical advantages and limitations, and future development trends. These findings provide scientifically grounded screening criteria and practical references for the low-to zero-carbon development of heavy oil reservoirs, thereby supporting the green and sustainable development of heavy oil reservoirs worldwide.