THERMAL ALTERATION AND WATER DISPLACEMENT EFFICIENCY OF HEAVY OILS: LABORATORY SIMULATION AND EVALUATION OF FIELD SAMPLES

This study investigates the impact of thermal aging on heavy oil properties and displacement efficiency through laboratory simulations of steam-cycled samples from Romania’s Suplacu field. Using quartz sand-packed displacement tubes, we analyzed oil-water displacement dynamics under controlled thermal conditions (150°C) and varying steam cycle histories (1–19 cycles). Results demonstrate that increased steam exposure enhances permeability (up to 8,000 mD) and reduces pressure drops (65–160 psi), indicating improved flow efficiency. Thermal alteration also decreased residual carbon content (7.71–9.19%) while increasing total acid number (TAN) (2.38–4.41 mg KOH/g), suggesting simultaneous oil upgrading and oxidative degradation. The experiments reveal that prolonged aging (7 months) and multiple steam cycles significantly improve displacement efficiency, though diminishing returns occur beyond optimal cycle counts. These findings highlight the critical balance between thermal recovery benefits and chemical degradation in heavy oil reservoirs. The study provides actionable insights for optimizing cyclic steam stimulation (CSS) in mature fields, emphasizing the need for customized thermal EOR strategies that account for viscosity reduction, carbon residue evolution, and acidity management.