关键词: 蒸汽-氮气混合物, 流体流动, 井筒换热, 气液相平衡, 氮气辅助蒸气注入技术

Abstract:

Aimed at the issues of steam overlap, channeling flow and heat loss in the process of heavy oil development with steam injection, the nitrogen-assisted steam injection technique was researched. The mathematical models for steam-nitrogen mixture flow and heat exchange in wellbore were established on the basis of heat transfer principle and flow theory．The flow features and heat exchange rules of the mixture in wellbore were analyzed. The effects of the nitrogen flow rate and steam quality at well head on the pressure, temperature and steam quality of the mixture flow were discussed. The results showed that the mixture pressure, steam partial pressure and the mixture temperature increased as the mixture was injected into wellbore, but the steam quality and gas dryness descended. The heat loss of formation was provided by the latent heat of steam vapor condensation. Increasing nitrogen flow rate at well head is helpful to improve the steam quality and gas dryness fraction at well bottom and decrease the shaft heat loss. Field application showed that the steam-nitrogen mixture injection could improve the utilization rate of heat energy and increase oil-gas ratio.

Key words: steam-nitrogen mixture, fluid flow, heat exchange in wellbore, gas-liquid equilibrium, nitrogen-assisted steam injection technique