Characterizing Residual Oil Distribution in Heavy Oil Reservoirs after Multiple Hot Water Huff and Puff: A Comprehensive Analysis

Abstract

In the development of China's Shengli deep heavy oil reservoirs, steam injection is the primary method. However, the effectiveness and efficiency of this method decline as the number of injection rounds increases. This study investigates the impact of different huff and puff rounds on the recovery rate of porous media by conducting hot water huff and puff tests on rock samples and using nuclear magnetic resonance (NMR) experiments to quantitatively determine the residual oil distribution at different injection rounds. A novel relationship has also been discovered to link oil saturation with the NMR conversion factor (C), which differs significantly from the traditional model, where C is considered a constant. Additionally, the research reveals migration patterns during the heavy oil huff and puff process. The results show that the maximum potential oil recovery achievable through huff and puff is only 45.4%, significantly lower than the oil recovery of 52.69% achieved through displacement methods. When the oil saturation exceeds 63.8%, the C value decreases exponentially. Under saturated oil conditions, the oil primarily exists as droplets larger than 10 μm. During each huff and puff process, oil is redistributed. As the number of huff and puff rounds increases, residual oil recovery is prioritized at the injection end. The local maximum oil saturation shifts progressively toward the far end. This research sheds light on the distribution patterns of residual oil in pore structures, providing support for the selection and assessment of enhanced recovery rate technologies.