Study On Two-phase Flow In Porous Media By Light Transmission And Electrical Resistivity Tomography Method

In recent years, as with the organic contaminant of dense non-aqueous phase liquids(DNAPL) in soil and groundwater has become more and more serious, study on the migration of DNAPL and its remediation in aquifer has also become a hot problem at home and abroad. In order to remove the DNAPL contaminant effectively, the most important is to characterize the scope of DNAPL and quantify the amount of DNAPL, and to get the saturation of DNAPL in the media is crucial to quantify DNAPL. Many researchers focus on the migration of DNAPL and saturation of DNAPL now.A light transmission visualization (LTV) and electrical resistivity tomography (ERT) methods are used to monitor the migration of DNAPL and quantify DNAPL saturation in the homogeneous and heterogeneous media in a two-dimensional (2-D) sand box with two fluid phase systems of water and DNAPL.Infiltration experiment of DANPL is conducted in the2-D sand box. Meanwhile, Charged Coupled Digital (CCD) camera and LCR Digital Bridge are used to monitor the movement of DNAPL. The LTV model was applied to calculate the saturation of DNAPL in this study. To get the spatial distribution of DNAPL saturation in ERT method, one needs to transform the resistance to resistivity, and then uses the empirical formula "Archie Formula". A new method was proposed to calculate the value of β, which was the only parameter in "Archie Formula". The amounts of DNAPL infiltration are calculated based on the spatial distribution of DNAPL saturation at different time, and compared with the observations. The main conclusions are as follows:(1) The shape and scope of the DNAPL(TCE) infiltration monitored by LTV methods was consistent with the actual situation. It shows that it is feasible to monitor migration of DNAPL real-time in saturated porous media by LTV method.(2) The shape and scope of the DNAPL(TCE) infiltration monitored by electrical resistivity tomography(ERT) method was consistent with the results of the LTV method and actual situation. The conclusions are similar to LTV method, but the resolution is not as good as it, especially in heterogonous media. But it still able to reflect the migration of DNAPL infiltration overall. It indicates that it is feasible to monitor migration of DNAPL real-time in saturated porous media by ERT method.(3) The predicted results of DNAPL infiltration under the condition of homogeneous saturated porous media compared with the measured data. It shows that the preliminary results are larger and the latter results are smaller than the measured data, and there were larger absolute of the relative errors at the beginning of DNAPL infiltration experiment. The root mean square error(RMSE) of the estimated results and the measured data was3.22ml, RMSE%was6.78%corresponding to the total volume of DNAPL infiltration47.5ml. Although only the total DNAPL infiltration was estimated in the non-homogeneous media, and the result was46.9ml, which was close to the actual total volume50ml, the absolute of the relative error was6.2%. Overall, the estimated results fitted well with the measured data either in homogeneous media or in non-homogeneous media. It means that it is feasible to quantify the saturation of DNAPL in saturated porous media by LTV method.(4) A new method combined with LTV method was proposed to calculate the value of β, which was the only parameter in "Archie Formula".On the one hand, the spatial distribution of DNAPL saturation at different time estimated by LTV method, on the other hand the resistance in different location at different time measured by ERT method. According to the corresponding resistance and water saturation at some observation points could fit the parameter β by Archie formula. The new method is much more simple and convenient in comparison with the traditional ways. The fitting results in homogenous and non-homogenous is2.17,1.91, respectively, and the correlation was reached0.96,0.98, respectively.(5) The amount of DNAPL infiltration was estimated by ERT method after obtained the value of β. It showed that the results had the same trend with the LTV method in homogenous saturated porous media. RMSE was4.69ml, RMSE%was9.9%corresponding to the total volume of DNAPL infiltration47.5ml. Under the condition of non-homogenous, RMSE is4.64ml, RMSE%was9.28%corresponding to the total volume of DNAPL infiltration50.0ml. In general, the estimated results fitted well with the measured data either in homogeneous media or in non-homogeneous media. It means that it is feasible to quantify the saturation of DNAPL in saturated porous media by ETV method, and the new method to obtain the value of β is applicable.