Study on the Oil - Water Relative Permeability Regulation Effect of Pinning Group - Type Black Nanocard in Low - Permeability Heterogeneous Reservoirs

Abstract Medium- and low-permeability reservoirs present significant challenges for conventional water shutoff and profile modification techniques, as well as polymer-based relative permeability modifiers (RPMs), which often hinder oil-phase permeability. In this study, we present the development and evaluation of a novel nanomaterial system, "PinNano," designed to anchor to rock surfaces and achieve long-lasting control over oil–water flow by modulating surface hydrophobicity. PinNano was synthesized by coupling the hydrothermal growth of MoS2 nanosheets (~20 nm) with pulsed laser fragmentation, producing additional sub-10 nm quantum dots that enhance pore compatibility. Sequential surface grafting with polydopamine (PDA) and polypropylene oxides (PPO) endowed the nanosheets with strong interfacial adsorption ("pinning") and hydrophobic functionality. The resulting MoS2@PDA-g-PPO material was comprehensively characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and Fourier-transform infrared (FTIR) spectroscopy, confirming successful PDA and PPO modifications. The stability and dispersibility of PinNano suspensions (0.2–1.0 wt%) were evaluated using Turbiscan measurements, revealing optimal stability at 0.2–0.6 wt% (TSI < 1.0). Interfacial tension (IFT) and contact angle tests demonstrated substantial wettability alteration: at 0.6 wt%, IFT with crude oil decreased from approximately 30 mN/m to 2.03 mN/m, and static contact angles reached 146.3°, maintaining capillary resistance in hydrophobic pores and improving residual oil mobilization. Laboratory-on-a-chip and coreflooding experiments further validated PinNano’s efficacy. Chase waterflooding with 0.6 wt% PinNano enhanced sweep efficiency by 61.6% and increased oil recovery by 19.7% compared to primary waterflooding, outperforming amphiphilic MoS2 fluid. Offline nuclear magnetic resonance (NMR) confirmed increased oil displacement in low-permeability zones. Relative permeability measurements indicated that PinNano reduced Krw* by 0.077 at residual-oil saturation and increased Kro* by 0.12 at connate-water saturation, while shape-factor adjustments delayed water breakthrough and enhanced oil mobility. Overall, PinNano offers an innovative, durable RPM strategy for waterflood management in high-water-cut reservoirs. Future work will focus on field pilot trials to translate these laboratory successes into improved oilfield performance and economic returns.