Influence of Nanofluids on Wettability Changes and Interfacial Tension Reduction
Authors: Neubauer Elisabeth , Hincapie Rafael E. , Borovina Ante , Biernat Magdalena , Clemens Torsten , Ahmad Yusra Khan 
Published: June 2020

Abstract
This work examines the potential use of two different nanoparticle solutions for EOR applications. Combining the evaluation of fluid-fluid interactions and spontaneous imbibition experiments, we present a systematic workflow. The goal of the study was to enable the generation of predictive scenarios regarding the application of Nano-EOR in OMV's assets. Therefore, influence of high and low TAN crude oil, core mineralogy, composition of the nanofluid on wettability alteration and recovery were studied. Nanomaterials used in this work employ inorganic nano-sized particles in a colloidal particle dispersion. We evaluated two types; one utilizes surface-modified silicon dioxide nanoparticles, while the other employs a synergistic blend of solvent, surfactants and surface-modified silicon-dioxide nanoparticles. IFT experiments were performed using a spinning-drop tensiometer and results were compared at ~180 min of observation. Amott-Harvey experiments enabled investigating wettability alteration considering effects of crude-oil composition and core mineralogy (~5 and ~10% clay content).
Interfacial tension reduction was observed for both nanofluids. The blend yielded slightly lower values (~0.5- 0.6 mN/m) compared to the nanoparticles-only fluid (~0.8 mN/m), which is most likely related to the surfactant contained in the formulation. Amott-Harvey spontaneous imbibition experiments depicted clear wettability alterations for both nanofluids. Cores with ~5% clay content exhibited a water-wettish behavior, and additional recoveries using the nanofluids were up to 10%. In the cores containing ~10% clay, the nanoparticle-only fluid spontaneously imbibes to the rock matrix and quickly displaces large amounts of oil (~70% independently of the oil type that was used). Contrary, the blend yields higher recovery from the 10% clay cores, with the high TAN oil than with low TAN oil (57 ± 3 vs. 45 ± 1%). However, in 5% clay cores, faster imbibition was observed when the blend was used, which can be explained by a higher capillary pressure. A special case was observed in cores with 10% clay content (Keuper), where the baseline experiments using brine exhibited a high standard deviation. We attribute this behavior to the large mineralogical heterogeneity of the Keuper cores and the heterogeneous distribution of clays and mineralogical impurities. Both the blend and the surface-modified nanoparticles managed to restore a water-wet state, and additional promising recoveries were up to 65% in the case of strong oil-wetness.
Nano-EOR is an embryonic technology; hence, literature data is scarce on how oil composition and reservoir mineralogy could influence its use to obtain additional recovery and maximize benefits. Our systematic workflow, helps understanding the parameters that require detailed evaluation in order to forecast recoveries for field tests. The experimental synergies provide a good approach to evaluate fluid-fluid and rock-fluid interaction.