Production-Oriented Evaluation of a Thermo-Salinity-Responsive Modified Nanographite (MEGO) System in Deep Reservoirs: Application Performance and Profile Control Mechanisms

Summary Deep reservoirs are characterized by high temperature, high salinity, low permeability, and strong heterogeneity, conditions under which conventional profile control and water-shutoff agents often suffer from thermal degradation, salt precipitation, and structural failure. In this study, we evaluate a thermo-salinity-responsive modified nanographite (MEGO) system via multiscale experiments and molecular simulations to clarify application performance and profile control mechanisms. When mineralization is below 10,000 mg/L, the MEGO system shows stable dispersion and low viscosity, indicating good injectivity and shear resistance. Single-core tests identified optimal conditions: Injection volume = 0.4 to 0.7 PV, rate = 0.1– to 0.3 mL/min, aging = 7 to 14 days, and plug volume = 0.2 to 0.3 PV. Under these parameters, plugging rate exceeded 83% and the breakthrough pressure gradient reached 2.94 MPa·m−1. Dual-core parallel tests demonstrated improved profile control in heterogeneous reservoirs (permeability contrast 5–15), diverting flow toward low-permeability zones. 2D visualization showed that after aging, MEGO aggregates occupy dominant channels through pore filling, wall adsorption, compression-induced throat plugging, and central deposition, thereby mobilizing residual oil. Atomic force microscopy (AFM) and simulations revealed that disodium naphthalene sulfonate (DNS) adsorbs on MEGO via π-π stacking, reducing polyetheramine (PEA) and MEGO adhesion and enhancing dispersion stability. By elucidating the microscopic mechanisms governing dispersion and aggregation, this work provides a theoretical foundation for the application of responsive nanomaterials in deep and ultradeep reservoir environments.