Innovations and applications of the thermal recovery techniques for heavy oil

Heavy oil represents a vital petroleum resource worldwide. As one of the major producers, China is facing great challenges in effective and economic production of heavy oil due to reservoir complexity. Plenty of efforts have been made to promote innovative advances in thermal recovery modes, methods, and processes for heavy oil in the country. The thermal recovery mode has been shifted from simple steam injection to a more comprehensive "thermal+" strategy, such as a novel N2-steam hybrid process and CO2-enhanced thermal recovery techniques. These advanced techniques break through the challenges of heavy oil extraction from less accessible reservoirs with thinner oil layers and greater burial depths. Regarding thermal recovery methods, China has developed the steam-assisted gravity drainage method integrating flooding and drainage (also referred to as the hybrid flooding-drainage SAGD technology) for highly heterogeneous ultra-heavy oil reservoirs and the fire flooding method for nearly depleted heavy oil reservoirs, substantially improving oil recovery. Furthermore, a range of processes have been developed for heavy oil production, including the open hole completion process using sand control screens for horizontal wells, the process of integrated injection-recovery with horizontal pump for horizontal wells, the steam dryness maintenance, measurement, and control process, efficient and environment-friendly circulating fluidized bed (CFB) boilers with high steam dryness, the recycling process of produced water, and the thermal recovery process for offshore heavy oil. Based on the advances in methodology, technology, and philosophy, a series of supporting technologies for heavy oil production have been developed, leading to the breakthrough of existing technical limit of heavy oil recovery and the expansion into new exploitation targets. For the future heavy oil production in China, it is necessary to embrace a green, low-carbon, and energy-efficient development strategy, and to expand heavy oil extraction in reservoirs with larger burial depth, more viscous oil, thinner oil layers, and lower permeability. Moreover, it is highly recommended to collaboratively maximize oil recovery and oil-to-steam ratio through technological innovations, and boost intelligentization of heavy oil production.