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Nanoparticles (NPs) have recently gained great attention as effective agents for enhanced oil recovery (EOR) applications, especially at ambient temperatures. Nevertheless, harsh conditions are needed to synthesize them and many tend to lack stability, exhibiting strong limitations in EOR application. As a solution, many researchers have used silica nanomaterials and grafted them with various agents to enhance their stability and alter their functionality. However, altering their overall functionality via coating could limit their stability in an aqueous media. Thus, partially coated nanoparticles should be used, such that the functionalizing agent is bonded to certain active groups on the nanoparticle surface. Herein, environmentally safe and tunable silicate-based nanoparticles, nanopyroxene, were synthesized under mild conditions. Nanopyroxene consists of two forms of binding sites on the surface made of the structural iron framework imparting a negative charge on the surface, which is compensated by sodium ions and the hydroxyl groups present on the surface of the silicate framework, which is responsible for its hydrophilicity. In this study, we partially altered the functionality of the nanopyroxene by anchoring a hydrophobic functionalizing agent of triethoxy(octyl)silane to the hydroxylated binding sites, generating half and totally hydroxyl functionalized nanopyroxene, such as hydrophobic pyroxenes (HPNPs) and Janus pyroxenes (JPNPs), respectively. Characterization techniques, such as scanning electron microscopy, Fourier transform infrared, X-ray diffraction, thermal gravimetric analysis, dynamic light scattering, and ζ-potential were conducted for the produced NPs to confirm their surface identity, functionality, stability, and morphology. After that, in comparison with brine, three different nanofluids were generated from the synthesized NPs to test their performance toward EOR in sandstone cores. The EOR performance was investigated by interfacial tension, contact angle, spontaneous imbibition, and displacement tests. The results showed that the HPNPs have the best stability and functionality compared with the other nanoparticle types. Contact angles in the presence of NPNP, JPNP, and HPNP nanofluids were measured to be 44 ± 2, 50 ± 2, and 55 ± 2°, respectively, confirming wettability alteration from oil-wet to water-wet. Interfacial tension was also noticeably reduced with the produced nanofluids at all temperatures, showing their great potential of oil displacement and to prove that a core flooding test was performed, confirming the capability of the stable nanoparticles as effective EOR agents in hydrocarbon reservoirs by recovering an additional 10.57% after brine flooding.

Recently, the application of nanoparticles for enhancing oil recovery (EOR) in carbonate reservoirs has received great attention from various researchers across the oil and gas industry. In contrast to sandstone reservoirs, carbonates are naturally neutral wet or preferentially oil wet and, therefore, the recovery of oil from these reservoirs by waterflooding techniques is relatively low and inefficient. Hence, the addition of chemical agents can modify rock wettability and increase the efficiency of the waterflooding process. The role of nanoparticles and their implementations in the field of oil recovery has been highlighted by many researchers in the past, due to their attractive features and characteristics. However, choosing the appropriate nanoparticles is not the only limiting factor to guarantee better performance in EOR but also depends on their stability and dispersion under aqueous conditions. Accordingly, many metal oxides or silicate-based nanomaterials have been subjected to surface modifications, following some complex and costly ineffective functionalization steps before their application. In this study, novel and stable nanomaterials of faujasite were synthesized at mild conditions without following any surface modification steps to alter the wettability of Austin Chalk carbonate rocks from oil wet to strongly water wet in the presence of low-salinity water (LSW). The synthesized nanoparticles were well characterized by scanning electron microscopy (SEM), transfer electron microscopy (TEM), X-ray diffraction (XRD), dynamic light scattering (DLS), and ζ potential to confirm their surface identity, functionality, morphology, and stability. The prepared nanofluids from the synthesized nanoparticles were tested in comparison to brine for their EOR efficiency in carbonate cores. The EOR performance was investigated by interfacial tension (IFT), contact angle, spontaneous imbibition, and displacement tests. The results showed that, compared to formation brine and LSW, the formulated nanofluid could notably alter the rock wettability from strong oil wet to strong water wet. To confirm this, a core-flooding test was performed, which further reiterated the capability of these nanofluids as effective EOR agents in hydrocarbon carbonate reservoirs by recovering an additional 9.6% of OOIP. Consequently, on the basis of the obtained findings, these faujasite-based nanofluids provide a prospect of being applied in EOR in carbonate formations.

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