A numerical model of coupled fluid flow and reactive geochemical transport

摘要

Experiments have shown that geochemical reactions have profound effects on the mechanics of fluid flows. Changes in hydraulic conductivity and fluid pore velocity were observed in the unsaturated flow experiments. These changes were attributed to secondary phase precipitation, which occurred under reduced saturation conditions. Clearly the depletion of water by precipitation would manifest itself if the water is not supplied via hydrologic transport. It is not difficult to see that the heterogeneous reactions including precipitation can plug pores reducing both the porosity and hydraulic conductivity, which in turn would hinder the transport of water into the affected regions. As a result, moisture content would be reduced and further precipitation would occur. The onset of further precipitation would remove water from the liquid phase. These complicated interactions between flow dynamics and geochemical reactions must be included in modelling reactive transport, especially when the degree of saturation is low. This paper communicates the development of a mechanistic-based numerical model for simulation of coupled fluid flow and reactive geochemical transport, including both fast and slow reactions, in variably saturated media. A simple example is used to illustrate the interplay and effects of advective/dispersive transport, geochemical reactions, and fluid flows. With the ability to simulate coupled fluid flow and reactive transport, an effective strategy for investigating contaminant transport and for conducting performance assessment of various waste management and remediation technologies can be developed.