Conventional pump-and-treat technologies have proven to be ineffective in cleaning up aquifers that are contaminated by nonaqueous phase liquids (NAPL). One possible approach for enhancing the remediation of NAPL-contaminated aquifers consists of applying seismic waves. Little is known, however, about the mechanism leading to mobilization.
We hypothesize that the mobilization of trapped NAPL blobs can be optimized by exploiting capillarity-induced resonance. We will perform experiments that visualize the response of NAPL blobs in porous media to oscillatory flow, which is one component of a seismic wave. Constant background flow in the surrounding aqueous phase will ensure that mobilized blobs are moved into a desired direction and hence simulate the combined action of pump-and-treat and seismic waves. Optical refractive index matching will allow for undisturbed view on the fluids in the flow cells. Illumination with a planar laser sheet and high speed photography will resolve the motion within an excitation cycle. Blobs will be excited (1) at their resonant frequency to enhance process understanding, and (2) in the form of appropriately parameterized frequency sweeps to account for the facts that a blob changes its resonant frequency as it moves through a pore space. A lattice-Boltzmann (LB) model will be developed that is used to guide the design of the experiments and as a simulation test bed. The importance of the formation of small, mobile droplets during excitation of the interfaces will also be measured and evaluated. Correlations for the resonant frequency of trapped blobs and intensities required to mobilize them will be inferred from physical experiments and LB simulations.
Our research could improve the efficiency of both groundwater remediation techniques for NAPL contamination and enhanced oil recovery schemes that use seismic waves. We will in general elucidate how oscillatory flows effect the distribution of immiscible fluids in porous media. The proposed research will also help understanding the effects of oscillatory flow on mass transfer (dissolution) between immiscible fluids. Furthermore, NAPL blob resonance could be exploited to monitor the shrinking of a NAPL pool during a groundwater remediation, or even to locate NAPL pools. The project will provide research opportunities for one PhD student. Moreover, the project will enrich K-12 education at Baltimore City Neighborhood Schools. The PhD student will develop a teaching module on groundwater contamination.
Conventional pump-and-treat technologies have proven to be ineffective in cleaning up aquifers that are contaminated by nonaqueous phase liquids (NAPL). This fact led to the development of various enhanced remediation approaches. One possible approach for enhancing the remediation of NAPL-contaminated aquifers consists of applying seismic waves. Despite experimental evidence, which shows that seismic waves mobilize oil, little is known about the physico-chemical mechanism leading to mobilization. We have hypothesized that the mobilization of trapped NAPL blobs can be optimized by exploiting capillarity-induced resonance. We have performed experiments in order to visualize the response of NAPL blobs in porous media to oscillatory flow, which is one component of a seismic wave. We have matched the optical refractive index of water, a NAPL, and the solid phase in order to allow for an undisturbed view onto fluid distributions in porous media. Illumination with a planar laser sheet and high speed photography has resolved the fluid motion within an excitation cycle. We have shown that NAPL blobs in capillary tubes and sphere packings indeed exhibit resonance. We have developed an analytical model in order to predict blob dynamics. With this model, we inferred theoretically the Green's function of blobs, that is, the response to unit pulse excitation, from the measured frequency response. We have also performed blob mobilization experiments in a pore doublet model, in which we applied a constant background flow of the surrounding aqueous phase in order to mimic a pump-and-treat aquifer remediation. By moving the laser light sheet used to illuminate the flow cell, we were able to obtain three-dimensional images of trapped blobs. We have shown that blob mobilization in a pore doublet can be explained through contact angle hysteresis. We still need to superimpose an oscillatory flow so that we can investigate the hypothesis that a blob can be mobilized optimally by excitation at its resonant frequency. In order to elucidate the complex dynamic behavior of the three-phase contact lines, we have investigated the effects of flow velocity on contact angle and two-fluid flow in general. We specifically derived semi-analytical and analytical solutions for flow in a capillary tube that account for a dynamic contact angle. In an upscaling effort, we have generalized the Green-Ampt model for water infiltration into soil to account for a capillary pressure that depends on the Darcy velocity. Our research could improve the efficiency of both groundwater remediation techniques for NAPL contamination and enhanced oil recovery schemes that use seismic waves. The project has elucidated how oscillatory and transient flows in general affect the distribution of immiscible fluids in porous media. The proposed research will also help understanding the effects of oscillatory flow on mass transfer (dissolution) between immiscible fluids. Furthermore, NAPL blob resonance could be exploited to monitor the shrinking of a NAPL pool during a groundwater remediation, or even to locate NAPL pools. The project has provided research opportunities for one PhD student. Moreover, the project enriches K-12 education by providing a research opportunity for a high school student from the St. Paul's School for Girls in Baltimore County.
