Theoretical and experimental investigation of the motion of multiphase fluids containing paramagnetic nanoparticles in porous media

Abstract Paramagnetic nanoparticles are potentially useful for monitoring of immiscible fluids distribution in subsurface, as they can be induced to move by an imposed magnetic field. The nanoparticles can be designed to be preferentially adsorbed at oil–water interface, as well as to have the long-term dispersion stability with minimal retention in the porous medium to be monitored. When exposed to magnetic field, they generate sufficient interfacial movements for external detection. When paramagnetic nanoparticles are either adsorbed at oil–water or air–water interface or dispersed in one of two fluid phases co-existing in pores, and exposed to external magnetic field, the resultant particle movements displace the interface. Interfacial tension acts as a restoring force, leading to interfacial fluctuation and a pressure (sound) wave. Our previous work (Prodanovic et al., 2010) provided a theoretical explanation for the motion of the interface between a suspension of paramagnetic nanorods and a non-magnetized fluid in a cylindrical dish, as measured by phase-sensitive optical coherence tomography (PS-OCT). Here we report on additional experiments carried out with a range of in-house synthesized and surface-modified iron-oxide nanoparticles. We also improved numerical method to be volume conserving for more quantitative matching. The measurements of interfacial motion by PS-OCT reported confirm theoretical predictions of the frequency doubling and the importance of material properties, such as magnetic susceptibility, for the interface displacement. The results are encouraging: this laboratory and modeling study is thus an important step to develop a magnetic field-based method for an accurate, non-invasive determination of multiphase fluids distribution in reservoir rock. With the combined experimental and modeling work, strategies for improved nanoparticle design will be developed so that the interfacial, thereby acoustic, response can be magnified.