Impact of high-cycle huff and puff on residual oil distribution in heavy oil reservoirs

Steam huff and puff plays a crucial role in exploiting deep heavy oil reservoirs, where effectiveness and recovery rates decrease with increasing cycles. Understanding the pore-level distribution of residual oil post high-cycle is essential. This study investigates the impact of repeated huff and puff cycles on oil recovery in porous media. Experiments mimicked field conditions with hot water huff and puff, substituting for steam, which remains liquid due to significant heat loss. CT scans of rock samples assessed residual oil distribution, and digital rock core data were calibrated with mercury intrusion porosimetry to improve accuracy, achieving 87 % precision. Results showed the high-cycle huff and puff process occurs in two phases: initially, oil in larger pores (radii >150 μm) is preferentially removed, with minimal mobilization in smaller pores (radii 0–50 μm). In subsequent phases, oil from medium and small pores gradually migrates to and replenishes the previously depleted larger pores. As cycles increase, oil migrates from smaller to larger pores, decreasing overall core saturation. Smaller pores thus require more cycles for effective oil mobilization. Although relative permeability of oil in cores initially drops sharply, it stabilizes after several cycles. This study advances understanding of pore-level oil distribution dynamics, providing important insights into oil recovery behavior in deep heavy oil reservoirs.