Аннотация
Abstract The main objective of this study was to theoretically and experimentally evaluate the performance of nanocapsules composed of a surfactant core and resin shell, designed for the targeted delivery of surfactant molecules at the oil–water interface. The primary purpose of surfactant encapsulation is to achieve an effective reduction in interfacial tension (IFT) while inhibiting surfactant adsorption in porous media. This study included a tuning process to determine the optimal nanocapsule (Ncap) dosage that maximized IFT reduction and minimized surfactant adsorption, thereby enhancing oil recovery. Molecular dynamics (MD) simulations were performed to elucidate the primary mechanisms of surfactant release, based on solubility analysis. The nanocapsules were synthesized via a nanoprecipitation method, encapsulating a commercial anionic surfactant, previously employed in a field trial, as the core, and resins extracted from the vacuum residue as the shell. Ncap characterization included Fourier-transformed infrared spectroscopy, transmission electron microscopy, and dynamic light scattering to determine its hydrodynamic diameter. Nanofluids were prepared by varying the ratio of encapsulated to free surfactants in the aqueous phase. The Ncap performance was evaluated using IFT measurements, wettability changes assessed by contact angle analysis, and coreflooding tests. The potential of Ncaps lies in their ability to reduce surfactant adsorption, as indicated by capillary number calculations and confirmed through coreflooding experiments. A 10:90 ratio (encapsulated surfactant:free surfactant) yielded favorable results in coreflooding tests, demonstrating a reduction in the pore volume required to achieve the same oil recovery as the free surfactant. This outcome is consistent with the expected decrease in adsorption resulting from the inclusion of Ncaps in the adsorbent formulation. Additionally, at the same 10:90 ratio, higher oil recovery values were obtained by replacing 100 each mixed with nanocapsules at concentrations ranging from 10 to 10,000 mg·L–1 of surfactant with 100 each mixed with nanocapsules at concentrations ranging from 10 to 10,000 mg·L–1 of Ncap, resulting in an increase of up to 3.1% in the additional oil recovery. The MD results confirmed the effectiveness of the encapsulation approach and that the release behavior was governed by solubility differences. Furthermore, Hansen Solubility Parameter (HSP) analysis provided insights into the solubility behavior of Ncaps by highlighting variations in their dispersive, polar, and hydrogen-bonding contributions.