Beshad Koohbor (BRGM) will give a hybrid seminar in room E001 on: Coupled simulation and experimental study of electrical resistivity evolution and multiphase flow for monitoring NAPL contamination and remediation process.
Electrical geophysical methods (e.g. time-lapse resistivity tomography, spectral induced polarization and time domain reflectometry) can be used as non-intrusive geophysical methods to monitor the NAPL (i.e. non-aqueous phase liquids) contamination and remediation process in porous media. However, due to the combined effects of porosity and saturation in the classical petrophysical relationships (e.g. Archie’s laws), the interpretation of resistivity as the sole means of explaining NAPL contamination/remediation process is deficient. Coupled multiphase flow and electrical current simulation can act as a supplementary means which gives an additional viewpoint to the process of monitoring NAPL contamination and/or remediation.
In this study, first, we present an advanced simulation of DNAPL (i.e. dense non-aqueous phase liquids) flow and complex electrical resistivity. The model was validated against existing experimental results and image measurements were carried out in a 2D tank. Two-phase flow modeling in porous media is coupled with electrical current modeling to simulate the process of DNAPL migration and the associated complex resistivity response. The simulations are developed in 3D and are performed in COMSOL Multiphysics®. The simulations using petrophysical relationships for in-phase and quadrature resistivity and the results of the experiments are generally in accordance (i.e. the accordance is better when we have lower DNAPL saturation as in the cone of depression). The present work can be regarded as a preliminary study toward further applications of coupled SIP-multiphase flow for more accurate detection and monitoring of DNAPLs.
In the second part of the study, a coupled experimental and numerical simulation methodology is performed by using Time Domain Reflectometers (TDR) and multiphase simulation of a controlled environment mimicking the water table fluctuation and its effect on the LNAPL (i.e. light non-aqueous phase liquids) residual saturation. TDR probes are installed in different locations of a flume and the bulk permittivity of the phases are measured through artificially imposed boundary conditions. The bulk permittivity is then translated into saturation of the three different phases. The translated residual saturations along with the previously measured porous media properties (e.g. porosity and saturated permeability) are then inserted into the numerical simulator (i.e. COMSOL Multiphysics® ) and the migration of the three-phase in porous media is simulated.
Though giving some valuable insights both into the physics at the Darcy scale and the choice of the simulation tool, the presented work should be regarded as a preliminary study toward further applications of coupled simulations of multiphase flow and electrical geophysical methods for more accurate detection and monitoring of NAPL contamination/remediation process in porous media. We suggest that to better understand the physics associated with electrical current and the validity of the pertophysical relationship, further studies be performed in pore-scale and the effect of contact angle and wettability of the porous media be considered. Also, for more realistic field applications of such coupled studies, the choice of simulating tool be reconsidered as COMSOL might have some shortcomings when applied to large domains.