烟道气辅助SAGD蒸汽腔扩展机理

Mechanisms on expansion of SAGD steam chamber assisted by flue gas

通过研究烟道气对蒸汽冷凝传热的影响,借助可视化物理模型实验,观察了烟道气辅助SAGD蒸汽腔扩展特征。蒸汽冷凝实验结果表明,常规注蒸汽过程中,蒸汽会在冷却壁面迅速冷凝并聚成大液滴,248 ms后大液滴在重力作用下快速脱落。蒸汽内加入烟道气后,1 217 ms后才观察到少量液滴脱落现象,气体增加了蒸汽分子扩散的阻力,大量的液滴在冷凝壁面形成隔热膜,降低了蒸汽与冷却壁面的冷凝传热系数。可视化物理模型实验结果表明,低物性储层阻碍了SAGD蒸汽腔向上发育。随着烟道气和蒸汽的共同注入,烟道气可以促进SAGD蒸汽腔突破低物性储层,蒸汽腔波及系数提高6.6%,采出程度提高9.6%。这是由于烟道气辅助SAGD开发中,烟道气通过降低蒸汽与油藏岩石之间的冷凝传热系数,蒸汽腔遇到低物性储层后没有迅速冷凝变为热水,而是保持蒸汽腔状态突破低物性储层,从而增加了蒸汽腔的扩展范围,提高了储层的动用程度和采油速度。

The influence of flue gas on steam condensation heat transfer was studied firstly in this work, and then the expansion characteristics of steam chamber in flue gas assisted SAGD(steam assisted gravity drainage)was observed through visualization of physical model experiments. The steam condensation heat transfer experiment shows that the steam condensed rapidly on the condensation wall and formed large droplets during the conventional steam injection process, and then the droplets fell off quickly under the action of gravity after 248 ms. While when adding flue gas in steam, few droplets fell off until 1 217 ms. The reason for this phenomenon is the gas increased the resistance of steam molecular diffusion, a large number of droplets formed a heat-insulating film on the condensation wall and then reduced the condensation heat transfer coefficient between the steam and the condensation wall. The visualization physical simulation experiments show that the reservoirs with poor properties impeded the upward growth of steam chamber in SAGD process. With the co-injection of flue gas and steam, flue gas can strengthen SAGD steam chamber to break through the reservoirs with poor properties, and the sweep efficiency of steam chamber and the recovery increased by 6.6% and 9.6% respectively. The reason is the flue gas reduced the condensation heat transfer coefficient between steam and reservoir rock in flue gas assisted SAGD development. When the steam chamber met reservoirs with poor properties, it did not condense quickly into hot water, but kept the state of steam chamber to break through the reservoirs with poor properties, thus increased the expansion range of steam chamber.