石油污染物在地下环境系统中运移的多相流数值模型

Numerical modeling with multiphase flow model of petroleum pollutant transport in subsurface environment

在综合考虑有石油污染物在地下环境体系中扩散、吸附解吸、界面间分配以及微生物降解等作用下, 建立了有机污染物在多孔介质迁移转化的多相流动力学模型, 并采用特征有限差分方法和隐式压力显式饱和度方法对耦合模型进行数值离散, 编制了相应的计算程序; 利用该程序对石油污染物在地下环境系统中运移机制进行定量化研究. 研究结果表明: 石油污染物在地表泄漏以后, 将在重力和毛细力的作用下, 产生水平位移和垂直位移. 当污染物迁移到地下毛细管区后, 其向下的运动将整体受到毛细张力的阻碍, 污染物要想进入毛细饱和带必须克服油水界面的进气压力, 这时污染物在毛细饱和带顶部聚集以期获取压力, 同时将产生以水平方向为主的迁移, 最终随着污染物的压力超过其进气压力, 导致污染物进入毛细饱和带, 在地下水水位上形成一个透镜体. 数值模拟曲线与实验测试曲线吻合较好, 验证了模型的可靠性. 这为定量化研究石油污染物在地下环境系统中分配与归宿及污染预测、预报提供了理论依据.

A coupled multiphase flow model was established to predict transient flow and petroleum pollutant transport in subsurface environment. The model accounted for the complex process of dispersion, absorption/desorption, distribution between liquid-solid interfaces and microbiological degradation under the assumption of local chemical equilibrium. Solutions of the coupled equations were accomplished by the characteristic finite difference method and implicit pressure explicit saturation method. The code was developed for simulating petroleum pollutant transport and migration mechanism in porous media. Numerical results showed petroleum pollutant leaking into subsurface environment, with vertical and horizontal displacement under gravity and capillary pressure. As pollutant migrated into the capillary zone, capillary tension restricted the vertical movement. The pollutant must overcome the entrapment pressure of oil-water interface before entering the capillary zone, and pollutant accumulated on the top of the capillary zone to become pressurized. The pore pressure of pollutant exceeded the entrapment pressure of oil-water interface, and pollutant entered the capillary zone and formed a lens above the groundwater level. The model simulations were compared with experiential measurements of petroleum pollutant mass distribution in soil, and there was reasonable agreement between model simulation and measured data. It provides theoretical evidence for studying distribution and destination of organic pollutant transport in subsurface environment.