Development and Performance Evaluation of a Temperature- and Salt-Resistant Bio-Based Profile-Control and Oil Displacement System

High-temperature and high-salinity reservoirs (typically referring here to temperatures ≥ 100 °C and salinities > 100 g/L) impose stringent requirements on chemical flooding and profile-control agents, particularly in terms of thermal stability, salt tolerance, injectivity, and environmental compatibility. In this study, a bio-based composite mobility-control and oil-displacement system was developed by combining carbonized corn-straw particles with the biopolymer scleroglucan. Corn-straw biomass particles were prepared by pyrolysis at 500 °C followed by ball milling for 2 h. Their particle-size distribution, elemental composition, and suspension stability were characterized, and the rheological behavior, thermal and salt tolerance, long-term aging stability, injectivity, plugging performance, and enhanced-oil-recovery efficiency of the composite system were evaluated systematically. The average particle size decreased from 25.6 μm for mechanically ground straw to 2.8 μm after carbonization and ball milling. The H/C atomic ratio of the carbonized particles was 0.31, indicating enhanced aromatization and structural stability. A scleroglucan concentration of 1000 ppm provided a suspension rate of 97%, balancing suspension stability and chemical dosage. The composite system maintained stable viscosity and viscoelasticity from 30 to 130 °C in deionized water, saturated NaCl solution, and saturated CaCl2 solution, with viscosity loss below 10%. After sealed anaerobic aging at 100 °C for 28 days, the viscosity retention remained above 90%. Sand-pack tests showed stable injectivity in media with permeabilities of 1235 and 2064 mD and a plugging efficiency of 95.7% in a 2846 mD model. In oil-displacement experiments, the composite system increased the final recovery factor from 46.6% for scleroglucan flooding alone to 53.3%, corresponding to an additional 6.7 percentage points. These results demonstrate that the carbonized biomass particle-scleroglucan system has promising thermal stability, salt tolerance, plugging capacity, and oil-displacement performance, providing a potential green strategy for mobility control in harsh reservoir environments.