Recently, the application of low salinity water (LSW), nanoparticles (NPs), and surfactants (collectively abbreviated as LNS) in carbonate formations for enhanced oil recovery (EOR) purposes has been under investigation, but relatively few studies have been performed for their implementation in fractured carbonate reservoirs (FCRs). The objective of this study is to apply the recently proposed method of alternatively injecting LNS in cycles into FCRs using silica and zirconia NPs. The cumulative oil recovered from the two coreflooding experiments performed at 3000 psi overburden pressure and 70 °C temperature is reported in this study in addition to spontaneous imbibition (SI) experiments. The experimental design is structured to depict the best industrial practice for the injected fluids in FCRs. Furthermore, this work investigates the effect of zirconia NPs on the interfacial tension (IFT) between the injected fluids and crude oil under the previously stated experimental conditions. The outcome of these experiments divulges that the alternating injection of LNS employing silica and zirconia NPs is effective and well suited for EOR applications in FCRs owing to a cumulative oil recovery of approximately 8 and 7% of the original oil in place (OOIP), respectively. This study validates the implementation of the recently proposed alternating injection of the LNS technique for FCRs and shows its performance utilizing newly acquired zirconia NPs, which is relevant for industrial application at a large scale.

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Several studies have reported that the viscosity profile of nanofluids has a similar trend to electrolytes. This behavior is attributed to the complex interactions of the ions of nanoparticles (NPs) with the ions of aqueous solutions. Recently, laboratory experiments have shown that nanofluids are suitable candidates for enhanced oil recovery in different reservoirs. The improvement in oil recovery during nanofluid injection is attributed to the wettability alteration, interfacial tension reduction, and viscosity modification. Low salinity water and surfactants are used to stabilize and prevent the aggregation of NPs, which are injected into the reservoir. However, the interactions between the reservoir/injected fluids with NPs alter the properties of the fluid. The complex interactions among the ions present in the solutions of NPs, surfactants, and electrolytes (NSE) that result in the viscosity modification are not completely understood. Therefore, this work presents a detailed study on the complex interactions existing between the ions of NPs and other ions of aqueous solution present in the reservoir fluid using the dynamic light scattering, transmission electron microscopy, and Fourier transform infrared spectroscopy techniques to understand the viscosity behavior of NSE solutions. The viscosity profile of NSE solutions with increasing concentration of NPs has the same trend as aqueous solutions, while that with increasing concentration of the sodium dodecyl sulfate surfactant behaves like spherical particles. The explained mechanisms behind the viscosity behavior of NSE solutions in this study can improve the optimization design for nanofluid injection into the reservoir.

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