包气带裂隙中轻非水相液体(LNAPL)迁移及滞留是一个复杂的多相渗流过程,涉及到LNAPL、水、气三相流体的相互作用.采用透明裂隙模型开展了干燥/存水状态下LNAPL迁移试验,并结合图像采集与处理技术获取了LNAPL动态迁移过程与滞留特征,揭示了裂隙存水对LNAPL迁移及滞留行为的影响.结果表明:LNAPL在干燥裂隙(两相渗流)中表现为指进流形态,而在存水裂隙(三相渗流)中则以膜状流形态沿水滴边缘流动.与指进流相比,膜状流模式下LNAPL的流动通道更曲折、扩展范围更广,导致裂隙中的滞留量更大.膜状流影响的强弱依赖于裂隙存水量及其分布特征,与裂隙倾斜角度密切相关;当裂隙趋于水平时LNAPL迁移范围最广、滞留量最大,而趋于垂直时这种影响则最弱.此外,发现干燥/存水裂隙中LNAPL滞留区的裂隙隙宽均服从正态分布特征,但存水状态下LNAPL滞留的裂隙隙宽大于干燥状态,主要集中在0.3~0.4mm.
Abstract
The migration and retention of light non-aqueous phase liquid (LNAPL) in fractured vadose zone is a complex multiphase seepage process, involving interactions among LNAPL, water, and air. To reveal the influence of entrapped water on LNAPL migration in fractures, comparative experiments on LNAPL migration in dry and water-entrapped fractures were conducted using a transparent fracture model. By combining image acquisition and processing techniques, the migration processes and retention characteristics of LNAPL in the experiments were obtained. The results showed that in dry fractures (under two-phase seepage conditions), LNAPL moved in the form of finger flow; however, in water-entrapped fractures (under three-phase seepage conditions), LNAPL moved in the form of film flow along the edges of water droplets. Compared with finger flow, the flow channel of film flow was more tortuous and the expansion range was wider, resulting in a larger retention volume of LNAPL in the fracture. The influence strength of film flow depended on the amount and distribution characteristics of water entrapped in the fracture, which were related to the fracture inclination angle. When the fracture tended to be horizontal, the migration range of LNAPL was the largest, and the residual amount was the greatest, whereas this effect was the weakest when the fracture tended to be vertical. Additionally, it was found that the fracture apertures of LNAPL residual zones in both dry and water-entrapped fractures followed a normal distribution. However, under water-entrapped conditions, the fracture aperture corresponding to the maximum LNAPL residual amount was larger than that under dry conditions, and it was mainly concentrated in the range of 0.3~0.4mm.
关键词
裂隙介质 /
轻非水相液体 /
可视化试验 /
多相渗流 /
流动模式 /
滞留结构
Key words
fractured media /
light non-aqueous phase liquid /
visualization test /
multiphase flow /
flow pattern /
entrapment configuration
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基金
国家自然科学基金资助项目(52209135,42177079);湖北省自然科学基金资助项目(2024AFB813)
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