Mechanistic investigation of adaptive low-initial-viscosity gel systems for targeted flow channel control and enhanced oil recovery in heterogeneous polymer-flooded oil reservoirs

Reservoir heterogeneity-induced high-conductivity thief zones critically undermine volumetric sweep efficiency in polymer-flooded reservoirs, demanding innovative conformance control strategies. This study pioneers an intelligent low-initial-viscosity gel system (ILVGS) with adaptive chemical architecture, specifically engineered to address four persistent limitations of conventional gel treatments: excessive entry viscosity (>50 mPa s), uncontrolled gelation kinetics (3–7 days), inadequate propagation in tight zones (K < 50 mD), and formation damage potential. The optimized low-initial-viscosity gel systems demonstrate ultra-low injectivity viscosity (8.7 ± 1.2 mPa s) coupled with precisely tunable gelation characteristics (10–40 days via crosslinker/polymer ratio modulation) and mechanically robust strength adjustment (2400–4100 mPa s through pH-responsive chain entanglement). Core flooding evaluations in heterogeneous sandstone analogs (4.00/2.00/0.50 μm2) under authentic reservoir conditions (45 °C, 11.3 MPa) established optimal deployment parameters of 0.1 pore volume slug volume, 1000 mg/l concentration, and 0.6 ml/min injection rate, achieving 97.3 ± 1.8% permeability contrast mitigation. Post-treatment analysis revealed transformative fluid redistribution: high-permeability layer fluid intake decreased from 70.1% to 32.1%, while combined medium/low-permeability layer absorption surged from 29.9% to 67.9%, accompanied by 75.4% thief zone velocity reduction (10.1→2.56 m/d) and establishment of new 3.87 m/d sweep pathways. Field implementation confirmed the technology's efficacy through 82.6% water cut reduction and 14.3% incremental oil recovery via strategic sealing of seven critical thief channels. By synergistically integrating shear-thinning behavior, viscoelastic memory effects, and salinity-responsive viscosity modulation, the ILVGS represents a paradigm shift in conformance control, offering a scientifically robust solution for revitalizing mature reservoirs through deep-diverted profile modification.