Adaptation thresholds and mechanistic insights into dispersed particle gel strengthened alkali for enhanced oil recovery in heterogeneous reservoirs

Abstract

After developing dispersed particle gel strengthened alkali (DPGSA) as a heterogeneous combination flooding, the research focused on adaptation thresholds and mechanisms of action of DPGSA. The adaptation thresholds of DPGSA have been verified, including temperatures (25–100 °C), salinities (0–200,000 mg/L for NaCl and up to 0–2200 mg/L for CaCl₂), oil viscosities (10–200 mPa s), acid value (0.04–0.44), and permeabilities (0.25–1.89 μm²). The study investigated the mechanism of DPGSA on the oil-water interface. The interfacial tension (IFT) of 0.7 wt% DPG + 1.6 wt% Na₂CO₃ is initially 0.071 mN/m, decreasing to 0.045 mN/m after 60 days of aging. Na₂CO₃ is conducive to low IFT and stable the interfacial membrane. The interfacial membrane strength was reduced by 6.64 %–7.49 % with an increase in DPG concentration, and by 27.01 %–27.98 % with an increase in aging time. At 0.03–0.1 Hz, the elastic modulus (21–35 mN/m) > viscous modulus (13–17 mN/m), enhancing the dynamic stability of the interfacial membrane. The normalized breakthrough time are 0.39 for DPG and 0.65 for Na₂CO₃, facilitating Na₂CO₃ entry into low-permeability zones. The recovery rate in low-porosity layers (0.01–1 μm) increased from 6.91 % to 54.59 % with the application of DPGSA. The coalescence of residual oil, stripping oil film, and oil emulsification are due to the low IFT and high-strength interfacial membrane of DPGSA. This study elucidated DPGSA's adaptability and mechanism, facilitating its widespread use in oilfield.