Improving stability of iron oxide nanofluids for enhanced oil recovery: Exploiting wettability modifications in carbonaceous rocks

Abstract

Superparamagnetic Iron Oxide Nanoparticles (SPION) exhibit relatively low toxicity and cost, while their chemical versatility provides an interesting class of materials for the development of nanofluids for advanced oil recovery. In this article, we present a comprehensive characterization of SPION modified with the disodium 4,5-dihydroxy-1,3-benzenedisulfonate (HBS) anionic ligand, forming a coating capable of improving the colloidal stability of the nanofluid, even in brine containing up to 22,000 ppm of sodium chloride. Fourier-transform infrared spectroscopy (FTIR) and x-ray photoelectron spectrometry (XPS) data demonstrated the chemical modification of the surface of the particles by the HBS ligand, through the linking of the catechol group, expose the sulfonate groups on the surface of the SPION-HBS. The anionic groups modify the surface charge distribution of the nanoparticles, shifting the isoelectric point of the nanoparticles from pH 6.3 (SPION) to less than pH 2 (SPION-HBS). This fact affords greater stability, supporting the drastic conditions of enhanced oil recovery (EOR) application. The interfacial properties of these particles were also investigated, revealing a slight reduction in the interfacial tension (IFT) of the nanofluid/oil, and small changes in the contact angle (CA) measured as a decane droplet on a glass surface. Despite the slight reduction in IFT and CA, spontaneous imbibition experiments showed a dramatic improvement in oil production in the nanofluid group, reaching a relative value of 2.75 times greater than in the control, at the end of the 5-month trial. The higher oil production achieved with the SPION-HBS nanofluid can be attributed to a more efficient change in wettability, reflecting the role of electrostatic interactions between the sulfonate groups at the particle surface and the porous surface of limestone rock. Since there was no surfactant in the composition of the nanofluid, the observed effects can only be attributed to the influence of the nanoparticles in the EOR process.