Influence of pore structure heterogeneity on channeling channels during hot water flooding in heavy oil reservoir based on CT scanning

Abstract

Hot water flooding is an effective way to develop heavy oil reservoirs. However, local channeling channels may form, possibly leading to a low thermal utilization efficiency and high water cut in the reservoir. The pore structure heterogeneity is an important factor in forming these channels. This study proposes a method that mixes quartz sand with different particle sizes to prepare weakly heterogeneous and strongly heterogeneous models through which hot water flooding experiments are conducted. During the experiments, computer tomography (CT) scanning identifies the pore structure and micro remaining oil saturation distribution to analyze the influence of the pore structure heterogeneity on the channeling channels. The oil saturation reduction and average pore size are divided into three levels to quantitatively describe the relationship between the channeling channel distribution and pore structure heterogeneity. The zone where oil saturation reduction exceeds 20% is defined as a channeling channel. The scanning area is divided into 180 equally sized zones based on the CT scanning images, and three-dimensional (3D) distributions of the channeling channels are developed. Four micro remaining oil distribution patterns are proposed, and the morphology characteristics of micro remaining oil inside and outside the channeling channels are analyzed. The results show that hot water flooding is more balanced in the weakly heterogeneous model, and the oil saturation decreases by more than 20% in most zones without narrow channeling channels forming. In the strongly heterogeneous model, hot water flooding is unbalanced, and three narrow channeling channels of different lengths form. In the weakly heterogeneous model, the oil saturation reduction is greater in zones with larger pores. The distribution range of the average pore size is larger in the strongly heterogeneous model. The network remaining oil inside the channeling channels is less than outside the channeling channels, and the hot water converts the network remaining oil into cluster, film, and droplet remaining oil.