Superparamagnetic nanoparticles are potentially useful for reservoir imaging and reservoir flow monitoring. Under an imposed magnetic field, magnetomotive motion of the nanoparticles at oil-water interfaces generates acoustic waves that indicate the location of oil in the reservoir. Nanoparticles have been designed with long-term dispersion stability in brine and minimal retention in reservoir rock and with preferential adsorption at oil-water interfaces.  The sensitivity of interfacial movements depends on several parameters including nanoparticle size and geometry, and saturation magnetization of the nanoparticles.  Under the given magnetic field, larger magnetic nanostructures experience stronger magnetic force and thus produce a larger acoustic signal.  Large magnetic iron-oxide nanoparticles are, however, ferromagnetic and the magnetic interactions between particles cause colloidal aggregation.  We have designed nanoclusters that not only exhibit superparamagnetism but also have long-term dispersion stability. When superparamagnetic nanoparticles are adsorbed at oil-water interface in reservoir rock pores, and exposed to external magnetic field, the resultant particle movements displace the interface. The measurements of interfacial motion by phase-sensitive optical coherence tomography (PS-OCT) indicate greater interfacial displacement with an increase in interfacial adsorption and saturation magnetization. The larger size of the nanoclusters made of superparamagnetic primary nanoparticles increases the magnetic coupling force. The ability to detect interfaces with the nanoparticles is an important step for the development of a magnetic field-based method to image the distribution of multiphase fluids in reservoir rock.

Magnetic nanoparticles for imaging in downhole applications

242nd National Meeting (2011)

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